EP1067870A1 - Densitometre ultrasonore muni de membranes de couplage hydraulique prealablement gonflees - Google Patents

Densitometre ultrasonore muni de membranes de couplage hydraulique prealablement gonflees

Info

Publication number
EP1067870A1
EP1067870A1 EP99914223A EP99914223A EP1067870A1 EP 1067870 A1 EP1067870 A1 EP 1067870A1 EP 99914223 A EP99914223 A EP 99914223A EP 99914223 A EP99914223 A EP 99914223A EP 1067870 A1 EP1067870 A1 EP 1067870A1
Authority
EP
European Patent Office
Prior art keywords
ultrasonic
densitometer
bladder
transducer
ultrasonic transducer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP99914223A
Other languages
German (de)
English (en)
Inventor
Richard F. Morris
Steven Morris
David R. Strait
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
GE Lunar Corp
Original Assignee
Lunar Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Lunar Corp filed Critical Lunar Corp
Publication of EP1067870A1 publication Critical patent/EP1067870A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/44—Constructional features of the ultrasonic, sonic or infrasonic diagnostic device
    • A61B8/4483—Constructional features of the ultrasonic, sonic or infrasonic diagnostic device characterised by features of the ultrasound transducer
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/08—Clinical applications
    • A61B8/0875—Clinical applications for diagnosis of bone

Definitions

  • the present invention relates to ultrasonic densitometer equipment using ultrasonic sound waves to measure bone integrity, and in particular, to an ultrasonic densitometer in which the ultrasound is conducted to a human heel through liquid filled bladders.
  • Non-invasive density measuring devices can be used to determine cumulative internal damage caused by micro-crushing and micro-fracturing occurring in the bones of humans or animals such as race horses. Additionally, osteoporosis, or loss of bone mineralization, detection in humans and its cure or prevention are increasingly becoming areas of intense medical and biological interest. As the average age of the human population increases, a greater number of patients are developing complications due to rapid trabecular bone loss.
  • Early Work U.S. Patent No. 3,847,141 to Hoop discloses a device for measuring the density of a bone structure, such as a finger bone or heel bone, to monitor the calcium content thereof.
  • the device includes a pair of opposed spaced ultrasonic transducers which are held within a clamping device clamped on the bone being analyzed.
  • a pulse generator is coupled to one of the transducers to generate an ultrasonic sound wave which is directed through the bone to the other transducer.
  • An electric circuit couples the signals from the receive transducer back to the pulse generator for retriggering the pulse generator in response to those signals.
  • the pulses therefore are produced at a frequency proportional to the transit time that the ultrasonic wave takes to travel through the bone structure which is directly proportional to the speed of the sound through the bone.
  • the speed of sound through a bone has been found to be proportional to the density of the bone.
  • the frequency at which the pulse generator is retriggered is proportional to the density of the bone.
  • a common site for the ultrasonic measurement is the os calcis of the human heel.
  • opposed ultrasonic transducers are placed on opposite sides of a receptacle sized to hold the human foot.
  • the receptacle is filled with water of a controlled temperature which serves to couple the ultrasonic energy from a first transducer, through the gap between that transducer and the human heel, and from an exit point of the human heel back through a corresponding gap between the exit point and the receiving transducer.
  • water approximates the acoustic impedance of the soft tissue surrounding the heel
  • While a water filled receptacle provides a simple mechanism for coupling ultrasonic energy to the heel, it may be desired to contain the water behind a flexible membrane or the like so as to reduce the possibility of spilling or contaminating the water. It is known to contain water within flexible bladders and to mount those bladders on an adjusting mechanism so that the bladders may be moved to compress the heel between them. This movement of the bladder supports may be augmented with limited inflation of the bladders and/or movement of the transducers. Such compressive type bladder systems create a risk of air entrapment between the bladders and the heel such as may affect the quality of the measurements.
  • the present invention provides a contained- water ultrasonic densitometer using stationary pre-inflated bladders.
  • the bladders are arranged to form a cavity between them slightly smaller than the heel and the heel is slid in between the bladders. The sliding provides a wiping action that helps eliminate air trapped between the bladders and the foot.
  • the densitometer provides pre-inflated bladders opposed along an ultrasonic propagation axis.
  • a coupling material is contained within the bladders and ultrasonic transducers are positioned within the bladders to direct ultrasonic signals through the coupling material along an ultrasonic propagation axis between the transducers.
  • the bladders are compliant so as to permit them to move apart to allow insertion of a human heel.
  • the shape and composition of the bladder surfaces allow the bladders to slide over and conform with the heel while remaining substantially in alignment with the propagation axis.
  • the sliding action of the foot against the compliant membranes tends to reduce and eliminate entrapped air.
  • the first ultrasonic transducer may be held in opposition to a second ultrasonic transducer both with fixed separation and the first and second bladder surfaces may be mounted to a fixed support.
  • the bladder surfaces may be comprised of an elastomeric membrane having a surface coding of ultrasonic coupling gel.
  • Fig. 2 is a perspective view of an acoustic coupler, two of which are shown in Fig. 1;
  • Fig. 3 is a front view of a transducer face from which acoustic signals are transmitted or by which acoustic signals are received, the face of the other transducer being the mirror image thereof;
  • Fig. 4 is a schematic block diagram view of the circuitry of the ultrasound densitometer device constructed in accordance with the present invention.
  • Fig. 6 is a schematic block diagram view of the circuitry of an alternative embodiment of an ultrasound densitometer constructed in accordance with the present invention.
  • Fig. 8 is a sample plot of relative ultrasound pulse intensity over frequency range
  • Fig. 9 is a graph in frequency domain illustrating the shift in attenuation versus frequency characteristic of a measured object as compared to a reference
  • Fig. 10 is a perspective view of an alternative embodiment of the present invention showing a basin for receiving a patient's foot and having integral opposed ultrasonic transducers;
  • Fig. 12 is a cross-sectional detail of the foot plate of Fig. 11 showing the method of attaching the sliding toe peg of the foot plate;
  • Fig. 13 is a block diagram of a system for transporting the acoustic coupling liquid used in the embodiment of Fig. 10;
  • Fig. 14 is a schematic block diagram view of the circuitry of the embodiment of
  • Fig. 10; Fig. 15 is an exploded view of the underside of the foot basin of Fig. 10 showing a c-clamp for holding the opposed ultrasonic transducers in precise alignment and separation;
  • Fig. 16 is a perspective detailed view of the shank of the c-clamp of Fig. 15 showing a lever for moving the separation of the transducers between an open and precisely separated closed position;
  • Fig. 17 is a cross-section of a human heel and ultrasonic transducers of the basin of Fig. 10 showing flexible liquid filled bladders surrounding the transducers and providing a coupling path between the transducers and the heel;
  • Fig. 18 is a plot of the inverse of time of flight (TOF) for two bone conditions and broadband ultrasonic attenuation (BUA) as a function of heel width showing their opposite functional dependencies;
  • TOF time of flight
  • BOA broadband ultrasonic attenuation
  • Fig. 19 is a plot of bone quality versus bone width as might be obtained from empirical measurement of multiple bone phantoms and as may be used to eliminate bone width effects in the ultrasonic assessment of bone quality;
  • Fig. 20 is an exploded view of the elements of an ultrasonic detector array showing a driving mechanism for improving the resolution of the acquired data and the location of a piezoelectric film detector array above a spatially offset connector;
  • Fig. 22a is a detailed perspective fragmentary view of the piezoelectric film detector with electrodes on its surface as communicating with connector terminals via acoustically transparent conductors;
  • Fig. 22b is a detailed fragmentary view of the piezoelectric film of Fig. 22a showing a method of assembling the acoustically transparent conductors;
  • Fig. 23 is a detailed view of the face of the detector showing its displacement by the driving mechanism of Fig. 20;
  • Fig. 24 is a figure similar to that of Fig. 17 showing use of the detector array to provide focused reception at a point within a patient's heel;
  • Fig. 25 is a perspective view in phantom of a patient's heel showing a raster scan pattern of a reception point within the heel to measure volumetric bone density variations within a inner and outer portion of the os calcis;
  • Fig. 26 is a schematic representation of a data cube collected in the scanning shown in Fig. 25 with isodensity lines used to locate a measurement region of interest
  • Fig. 27 is a flow chart of the operation of the present invention in locating a region of interest uniformly over several patient visits;
  • Fig. 29 is a partial cross-sectional view of an alternative embodiment to Fig. 17 using overlapping inflatable bladders;
  • Fig. 32 is a perspective exploded view and partial cutaway of an outer bladder element adapted for disposable use
  • Fig. 33 is a flowchart describing a program executed with a microprocessor 38 of Fig. 4 using the bladder configuration of Fig. 29;
  • Fig. 34 is a graph representing variations in value of attenuation, speed of sound and a combined stiffness quantity as a function of time.
  • Fig. 36 is geometric diagram showing representational stretching of membranes with cross axis patient movement for membranes of two different aspects
  • Fig. 37 is a cross sectional view of a closed system for distending two membranes using a rolling diaphragm pump element;
  • Fig. 38 is a perspective view of a contained-water ultrasonic densitometer system of the present invention showing a receptacle for receiving a human foot holding opposed pre-inflated bladder surfaces;
  • Fig. 1 shows a portable ultrasound densitometer 10 for measuring the physical properties and integrity of a member, such as a bone, in vivo.
  • the densitometer 10 as shown in Fig. 1 includes a handle 11 with actuator button 12. Extending linearly from the handle 11 is a connection rod 13.
  • the densitometer 10 also includes a fixed arm 15 and an adjustable arm 16.
  • the fixed arm 15 preferably is formed continuously with the connection rod 13, and therefore is connected to an end 17 of the connection rod 13.
  • the adjustable arm 16 is slidably mounted on the connection rod 13 between the handle 11 and a digital display 18 mounted on the rod 13.
  • the knob 19 may be turned so as to be locked or unlocked to allow the adjustable arm 16 to be slid along the connection rod 13 so that the distance between the arms 15 and 16 may be adjusted.
  • a first (left) transducer 21 Connected at the end of the fixed arm 15 is a first (left) transducer 21 and at the end of the adjustable arm 16 is a second (right) transducer 21.
  • each of the transducers 21 has mounted on it a respective compliant acoustic coupler 23 to acoustically couple the transducer to the object being tested.
  • the acoustic coupler 23 includes a plastic ring 24 and attached pad 26 formed of urethane or other compliant material.
  • This object 32 represents a member, such as a bone, or some material with known acoustic properties such as distilled water or a neoprene reference block.
  • the leftmost transducer 21 is a transmit transducer and the rightmost transducer 21 a receive transducer. In fact though, either or both of the transducers 21 may be a transmit and/or receive transducer.
  • the transmit and receive transducers 21 of the circuit of Fig. 4 are connected by element select signals 36 and 37 to a microprocessor 38.
  • the microprocessor 38 is programmed to determine which one of the respective pairs of transducer elements a through / are to be transmitting and receiving at any one time.
  • the microprocessor 38 is also connected by a data and address bus 40 to the digital display 18, a digital signal processor 41, a sampling analog to digital converter 42, and a set of external timers 43.
  • the microprocessor 38 has "on board” electrically programmable non-volatile random access memory (NVRAM) and, perhaps as well, conventional RAM memory, and controls the operations of the densitometer 10.
  • the digital signal processor 41 has “on board” read-only memory (ROM) and performs many of the mathematical functions carried out by the densitometer 10 under the control of the microprocessor 38.
  • the transmit transducer 21 converts the amplified pulse into an acoustic signal which is transmitted through the object or material 32 to be received by the receive transducer 21 which converts the acoustic signal back to an electrical signal.
  • the electrical signal is directed through output signal 57 to a receiver amplifier 59 which amplifies the electrical signal.
  • the excitation amplifier circuit 55 is preferably a digitally controllable circuit designed to create a pulsed output.
  • the amplification of the pulse can be digitally controlled in steps from one to ninety-nine. In this way, the pulse can be repetitively increased in amplitude under digital control until a received pulse of appropriate amplitude is received at the receiver/amplifier circuit 59, where the gain is also digitally adjustable.
  • a digitally controllable automatic gain control circuit which optimizes the sensitivity of the receive transducer 21 and the amplifier circuit 59 to received acoustic signals.
  • the microprocessor 38 is connected to the amplifier circuit and automatic gain control 59 through signal line 60 to regulate the amplification of the amplifier circuit and gain control 59.
  • the amplified electric signals are directed through lead 61 to the A D converter 42 which samples those signals at timed intervals.
  • the A D converter 42 therefore in effect samples the received acoustic signals.
  • the A D converter 42 progressively samples an incremental portion of each successive signal waveform.
  • the microprocessor 38 is programmed so that those portions are combined to form a digital composite waveform which is nearly identical to a single waveform.
  • This digitized waveform may be displayed on the digital display 18, or processed for numerical analysis by the digital signal processor 41.
  • the densitometer constructed in accordance with Figs. 1-4 can be operated in one or more of several distinct methods to measure the physical properties of the member, such as integrity or density. The different methods, as described in further detail below,
  • the densitometer is intended to be placed at some point in the process on the member whose properties are being measured. This is done by placing the transducers 21 on the opposite sides of the member. To accomplish this, the knob 19 is loosened to allow the adjustable arm 16 to be moved so that the transducers 21 can be placed on opposite sides of the member, such as the heel of a human patient. The outside surfaces of the pads 26 can be placed against the heel of the subject with an ultrasound gel 35 or other coupling material placed between the pads 26 and subject 32 to allow for improved transmission of the acoustic signals between the member 32 and transducers 21.
  • the knob 19 may be tightened to hold the adjustable arm 16 in place, with the transducers 21 in spaced relation to each other with the member 32 therebetween.
  • the actuator button 12 may then be pressed so that acoustic signals will be transmitted through the member 32 to be received by the receive transducer 21.
  • the electronic circuit of Fig. 4 receives the electrical signals from the receive transducer 21, and samples and processes these signals to obtain information on the physical properties and integrity of the member 32 in vivo.
  • the microprocessor 38 is programmed to indicate on the digital display 18 when this information gathering process is complete. Alternatively, the information may be displayed on the digital display 18 when the information gathering process is completed. For example, the transit time of the acoustic signals through the member 32 could simply be displayed on the digital display 18.
  • the circuitry is designed to create an ultrasonic pulse which travels from transmit transducer 21 through the subject 32 and is then received by the receive transducer 21.
  • the circuitry is designed to both determine the transit time of the pulse through the
  • the circuitry of Fig. 4 operates under the control of the microprocessor 38.
  • the microprocessor 38 selectively selects, through the element select signal lines 36, a corresponding pair or a group of the elements a through / on the face of each of the transducers 21. The corresponding elements on each transducer are selected simultaneously while the remaining elements on the face of each transducer are inactive.
  • the microprocessor then causes the external timer 43 to emit a pulse on signal line 53 to the excitation amplifier circuit 55.
  • the output of the excitation amplifier 55 travels along signal line 56 to element a of the transmit transducer 21, which thereupon emits the ultrasonic pulse.
  • the corresponding element a on the receive transducer 21 receives the pulse and presents its output on the signal line 57 to the amplifier circuit 59.
  • What is desired as an output of the A D converter 42 is a digital representation of the analog waveform which is the output of the single transducer element which has been selected. Unfortunately, "real time" sampling A D converters which can operate rapidly enough to sample a waveform at ultrasonic frequencies are relatively expensive.
  • the A/D converter 42 be an "equivalent time” sampling A/D converter.
  • “equivalent time” sampling it is meant that the A D converter 42 samples the output of the transducer during a narrow time period after any given ultrasonic pulse.
  • the general concept is illustrated in Fig. 5.
  • the typical waveform of a single pulse received by the receive transducer 21 and imposed on the signal line 57 is indicated by a function "f '.
  • the same pulse is repetitively received as an excitation pulse and is repetitively launched.
  • the received pulse is sampled at a sequence of time periods labeled t ⁇ -t, ⁇ .
  • the signal is sampled during individual fixed time periods t ⁇ -t, 0 after the transmit pulse is imposed, the analog value during each time period is converted to a digital function, and that data is stored.
  • the total analog waveform response can be recreated from the individual digital values created during each time period t, with the overall fidelity of the recreation
  • the sampling is not accomplished during a single real time pulse from the receive transducer 21. Instead, a series of pulses are emitted from the transmit transducer 21.
  • the external timer is constructed to provide signals to the sampling A/D converter 42 along signal lines 51 and 52 such that the analog value sampled at time period t ⁇ when the first pulse is applied to a given transducer element, then at time during the second pulse, time t ⁇ during the third pulse, etc. until all the time periods are sampled. Only after the complete waveform has been sampled for each element is the next element, i.e. element b, selected.
  • the output from the A/D converter 42 is provided both to the microprocessor 38 and to the signal processor 41.
  • the digital output values representing the complex waveform f of Fig. 5 can be processed by the signal processor 41 after they are compiled for each transducer element.
  • the waveform can then be analyzed for time delay or attenuation for any given frequency component with respect to the characteristic of the transmitted ultrasonic pulse.
  • the process is then repeated for the other elements until all elements have been utilized to transmit a series of pulses sufficient to create digital data representing the waveform which was received at the receive transducer array 21. It is this data which may then be utilized in a variety of methods for determining the physical properties of the member.
  • the appropriate output can be provided from either the microprocessor 38 or the signal processor 41 through the digital display 18.
  • the process of creating a sampled ultrasonic received pulse can optionally be repeated several times to reduce noise by signal averaging. If this option is to be implemented, the process of repetitively launching ultrasonic pulses and sampling the received waveform as illustrated in Fig. 5 is repeated one or more times for each element in the array before proceeding to the next element. Then the sampled waveforms thus produced can be digitally averaged to produce a composite waveform that will have a lesser random noise component than any single sampled waveform. The number of repetitions necessary to sufficiently reduce noise can be determined by testing in a fashion known to one skilled in the art.
  • the first method of use involves measuring transit time of an ultrasonic pulse through a subject and comparing that time to the time an ultrasonic pulse requires to travel an equal distance in a substance of known acoustic properties such as water.
  • the adjustable arm 16 is adjusted until the member of the subject, such as the heel, is clamped between the transducers 21. Then the knob 19 is tightened to fix the adjustable arm in place. The actuator button 12 is then pressed to initiate a pulse and measurement.
  • the densitometer may determine the physical properties and integrity of the member 32 by both or either of two forms of analysis.
  • the densitometer may compare the transit time of the acoustic signals through the member with the transmit time of the acoustic signals through the material of known acoustic properties, and/or the device 10 may compare the attenuation as a function of frequency of the broadband acoustic signals through the member 32 with the attenuation of corresponding specific frequency components of the acoustic signals through the material of known acoustic properties.
  • the "attenuation" of an acoustic signal through a substance is the diminution of the ultrasonic waveform from the propagation through either the subject or the standard. The theory and experiments using both of these methods are presented and
  • the microprocessor 38 may therefore be programmed so that the device determines the physical properties and integrity of the member by comparing either relative transit times and/or relative broadband ultrasonic attenuation through the member and a material of known acoustic properties.
  • the microprocessor 38 may be programmed most simply so that the electronics, having received the acoustic signals after they have been transmitted through the member, determines the "member" transit time of those acoustic signals through the member, and after the acoustic signals have been transmitted through the material of known acoustic properties, determines the "material" transit time of the acoustic signals through the material.
  • time periods may be measured most simply by counting the number of clock pulses of known frequency emitted by the timer 43 between the time of launching the pulse and the sensing of the received pulse at the A/D converter 42.
  • the microprocessor 38 then makes a mathematical "time" comparison of the member transit time to the material transit time and then relates that mathematical time comparison to the physical properties and integrity of the member.
  • the mathematical time comparison may be made by either determining a difference between the member transit time and the material transit time, or by determining a ratio between the member transit time and the material transit time.
  • it may also determine the physical properties and integrity of the member 32 by determining and comparing the attenuation of the broadband frequency components of the acoustic signals through the member
  • the transmit transducer 21 transmits an acoustic signal which has a broad range of frequency components, such as a simple ultrasonic pulse. In any case, the acoustic signal should have at least one specific frequency component.
  • the microprocessor 38 is programmed so that after the receive transducer 21 receives the acoustic signals transmitted through the bone member 32, it determines the absolute attenuation through the member 32 of the frequency component spectrum of the acoustic signals. It is to facilitate the measurement of attenuation that the excitation amplifier circuit 55 and the receiver amplifier 59 have amplification levels which may be digitally controlled. By successively varying the gain of the amplifiers 55 and 59 on successive pulses, the circuit of Fig. 4 can determine what level of gain is necessary to place the peak of the received waveform at a proper voltage level. This gain is, of course, a function of the level of attenuation of the acoustic pulse during transit through the member 32.
  • microprocessor 38 in conjunction with the signal processor 41 determines the absolute attenuation of individual specific frequency components of the received acoustic signal transmitted through the material.
  • the digital signal processor 41 makes mathematical "attenuation" comparisons of the corresponding individual specific frequency components through the member. A set of mathematical attenuation comparisons between corresponding frequency components may be thereby obtained, one comparison for each frequency component compared. The manner in which the attenuation functions with respect to frequency can thus be derived.
  • the microprocessor 38 and digital signal processor 41 then relate that function to the physical properties and integrity of the member.
  • Fig. 7 Shown in Fig. 7 is a sample broadband ultrasonic pulse and a typical received waveform.
  • an electronic pulse such as indicated at 70 is applied to the selected ultrasonic transducer in the transmit array 21 which then resonates with a broadband ultrasonic emission.
  • the received signal such as indicated at 72 in Fig. 7 in a time domain signal plot, is then processed by discrete Fourier transform analysis so that it
  • the actual value calculated, broadband ultrasonic attenuation is calculated by first comparing the received signal against the reference signal, then performing the discrete Fourier transform to convert to frequency domain, then performing a linear regression of the difference in attenuation slope to derive broadband ultrasonic attenuation.
  • the discrete Fourier transform is such that another parameter related to bone member density may be calculated in addition to, or in substitution for, broadband attenuation (sometimes referred to as “attenuation” or “BUA” below).
  • the solution for each point includes a real member component and an imaginary member component.
  • the values graphed in Figs. 8 and 9 are the amplitude of the received pulse as determined from this discrete Fourier transform by taking the square root of the sum of the squares of the real component and the imaginary component.
  • the phase angle of the change in phase of the ultrasonic pulse as it passed through the member can be calculated by taking the arctangent of the ratio of the imaginary to the real components. This phase angle value is also calculated to bone member density.
  • the microprocessor 38 may be programmed so that the densitometer 10 operates in a mode whereby the need for calculating either the relative transit time or the attenuation of the acoustic signals through a material of known acoustic properties is eliminated.
  • the microprocessor 38 would include a database of normal absolute transit times which are based upon such factors as the age, height, weight, race or the sex of the individual being tested as well as the distance between the transducers or the thickness or size of the member. This database of normal transit times can be stored in the non- volatile memory or could be stored in other media.
  • the relevant factors for the individual are placed into the microprocessor 38 to select the pertinent normal transit time based on those factors.
  • the transducers 21 are placed on the bone member being tested as described above.
  • the actuator button 12 is pressed, the acoustic signals are transmitted through the member 32.
  • the receive transducer 21 receives those signals after they have been transmitted through the member, and the electronics 31 then determine the "member" transit time of the acoustic signals through the member.
  • the microprocessor 38 and digital signal processor 41 then make a mathematical comparison of the measured member transit time to the selected database normal transit time, and relate the mathematical time comparison to the physical properties and integrity, or density of the member, which is displayed.
  • the digital display 18 could also include a display corresponding to the pattern of the array of elements on the face of the transducer 21 as seen in Fig. 3. This display could then display, for each element a through /, a gray scale image proportional to the parameter, i.e. transit time or attenuation, being measured. This image may provide a visual indication to an experienced clinician as to the physical properties of the member present in the patient.
  • Fig. 6 Shown in Fig. 6 is a circuit schematic for an alternative embodiment of an ultrasonic densitometer constructed in accordance with the present invention.
  • parts having similar structure and function to their corresponding parts in Fig. 4 are indicated with similar reference numerals.
  • Fig. 6 The embodiment of Fig. 6 is intended to function with only a single transducer array 21 which functions both as the transmit and the receive transducer array.
  • a digitally controlled multiple pole switch 66 preferably an electronic switch rather than a mechanical one, connects the input to and output from the elements of the transducer array 21 selectively either to the excitation amplifier 55 or to the controllable gain receiver/amplifier circuit 59.
  • the switch 66 is connected by a switch control line 68 to an output of the microprocessor 38.
  • the microprocessor 38 causes a signal to appear on the switch control line 68 to cause the switch 66 to connect the output of the excitation amplifier 55 to the selected element in the transducer array 21.
  • the microprocessor 38 changes the signal on the switch control line 68 to operate the switch 66 to connect the selected element or elements as an input to the amplifier 59. Meanwhile, the pulse propagates through the member 32.
  • Fig. 6 can thus be used to analyze the physical properties and integrity of a member using only one transducer 21. All of the methods described above for such measurements may be used equally effectively with this version of the device.
  • the transit time of the pulse through the member can be measured simply by measuring the time period until receipt of the reflected pulse, and then simply dividing by two.
  • This time period can be compared to the transit time, over a similar distance, through a standard medium such as water.
  • the time period for receipt of the reflected pulse could also be simply compared to standard values for age, sex, etc.
  • Attenuation measurements to detect differential frequency measurement can be directly made on the reflected pulse. If no reflecting surface 64 is used, and it is desired to determine absolute transit time, the thickness of the member or sample can be measured.
  • 1-9 is conveniently used by measuring the density of the os calcis as measured through the heel of a human patient.
  • a region of interest in the os calcis can be located reliably and repeatedly based on the comparisons of broadband ultrasonic attenuation at the points in the array.
  • the region of interest in the os calcis is identified as a local or relative minimum in broadband ultrasonic attenuation and/or velocity closely adjacent the region of highest attenuation values in the body member.
  • This technique of using a multiple element array to avoid position criticality is applicable to other techniques other than the determination of broadband ultrasonic attenuation as described here.
  • the concept of using an array and comparing the array of results to determine measurement locus would be equally applicable to measurements taken of member-density based on speed of sound transit time, other measurements of attenuation or on the calculation of phase angle discussed above. The use of such a
  • multiple-element array with automated selection of one element in the region of interest, can also be applied to other measurement techniques useful for generating parameters related to bone member density, such as measuring speed changes in the transmitted pulse such as suggested in U.S. Patent 4,361,154 to Pratt, or measuring the frequency of a "sing-around" self-triggering pulse as suggested in U.S. Patent 3,847,141 to Hoop.
  • the concept which permits the position independence feature is that of an array of measurements generating an array of data points from which a region of interest is selected by a reproducible criterion or several criteria.
  • the number of elements in the array also clearly can be varied with a larger number of elements resulting in a greater accuracy in identifying the same region of interest.
  • Basin Embodiment Shown in Fig. 10 is another variation on an ultrasonic densitometer constructed in accordance with the present invention.
  • the densitometer 100 of Fig. 10 there are two ultrasonic transducer arrays 121, which are generally similar to the ultrasonic transducer arrays 21 of the embodiment of Fig. 1, except that the transducer arrays 21 are fixed in position rather than movable.
  • the densitometer 100 includes a generally box-shaped mounting case 101 with sloping upper face 102 in which is formed a basin 103.
  • the basin 103 is sized to receive a human foot and is generally trigonous along a vertical plane aligned with the length of the foot so that when the foot is placed within the basin 103, the toes of the foot are slightly elevated with respect to the heel of the foot.
  • the transducer arrays 121 are positioned in the case 101 so that they extend into the basin 103 to be on opposite sides of the heel of the foot placed in the basin 103.
  • the sole of the foot may rest directly on a bottom 104 of the basin 103 with the heel of the foot received within a curved pocket
  • the slot 112 cants inward toward a medial axis 114 of the foot, defined along the foot's length, as one moves along the slot 112 towards the portion of the foot plate 108 near the heel of the foot. This canting reflects the general relation between foot length and width and allows simple adjustment for both dimensions at once.
  • the toe peg 110 is sized to fit loosely between the toes of the foot without discomfort and does not completely prevent voluntary movement of the foot. Nevertheless, it has been found that the tactile feedback to the patient provided by the toe peg 110 significantly reduces foot movement during operation of the densitometer 100.
  • Two different foot plates 108 being mirror images of each other, are used for the left and right foot.
  • the toe peg 110 is held to the slot 112 by a fastener 111 having a threaded portion which engages corresponding threads in the toe peg 110.
  • the head of the threaded fastener 111 engages the slot 112 so as to resist rotation.
  • the toe peg 110 may be fixed at any position along the length of the slot 112 by simply turning the toe peg 110 slightly about its axis to tighten the threaded fastener 111 against the foot plate 108.
  • the basin 103 of the densitometer 110 is flanked, on the upper face 102 of the enclosure 101, by two foot rest areas 116 and 118 on the left and right side respectively.
  • the patient's left foot may rest on foot rest area 118 while the patient's right foot may be placed within basin
  • foot rest area 116 For examination of the patient's left foot, the left foot of the patient is placed within basin 103 and the patient's right foot may rest on foot rest area 116.
  • the foot rest areas have a slope conforming to that of the upper face 102 and approximately that of bottom 104.
  • the flanking foot rest areas 116 and 118 allow the densitometer 100 to be used in comfort by a seated patient.
  • the basin area 103 is covered with a generally planar cover 120 hinged along the lower edge of the basin 103 to move between a closed position substantially within the plane of the upper face 102 and covering the basin 103, and an open position with the plane of the cover 120 forming an angle ⁇ with the bottom 104 of the basin 103 as held by hinge stops 122.
  • the angle ⁇ is approximately 90° and selected so as to comfortably support the calf of the patient when the patient's foot is in place within basin 103.
  • the upper surface of the cover 120 when the cover 120 is in the open position, forms a curved trough to receive a typical calf.
  • the support of the patient's calf provided by the cover 120 has been found to reduce foot motion during operation of the densitometer 100.
  • a coupling liquid is provided in the basin 103 to provide a low loss path for acoustic energy between the transducers 121 and the patient's foot regardless of the dimensions of the latter.
  • the coupling liquid is preferably water plus a surfactant, the latter which has been found to improve the signal quality and consistency of the reading of the densitometer.
  • the surfactant may be, for example, a commercially available detergent.
  • Coupled liquid should be considered to embrace materials having a viscosity higher than that of water such as, for example, water based slurries and thixotropic gels.
  • the liquid in the basin 103 should be changed in between each use of the densitometer 103. Changing this liquid is time consuming and ordinarily would require convenient access to a sink or the like, access which is not always available. Failure to change the liquid may have no immediate visible effect, and hence changing the liquid is easy to forget or delay. For this reason, the present embodiment employs an automated
  • premixed water and surfactant for filling the basin 103 are contained in a removable polypropylene supply tank 124, whereas exhausted water and surfactant from the basin 103 are received by a similar drain tank 126.
  • Each tank 124 and 126 contains a manual valve 128 which is opened when the tanks are installed in the densitometer 100 and closed for transporting the tanks to a remote water supply or drain.
  • the supply tank 124 and the drain tank 126 have vents 150, at their upper edges as they are normally positioned, to allow air to be drawn into or expelled from the interior of the tanks 124 and 126 when they are in their normal position within the densitometer 100 and valves 128 are open.
  • the tanks 124 and 126 hold sufficient water for approximately a day's use of the densitometer 100 and thus eliminate the need for convenient access to plumbing.
  • the valve 128 of the supply tank 124 connects the tank through flexible tubing to a pump 130 which may pump liquid from the supply tank 124 to a heating chamber 132.
  • the heating chamber 132 incorporates a resistive heating element 164 which is supplied with electrical current through a thermal protection module in thermal contact with the coupling liquid in the heating chamber 132.
  • the thermal protection module 166 includes a thermostat and a thermal fuse, as will be described below.
  • a thermistor 168 also in thermal communication with the liquid in the heating chamber, provides a measure of the liquid's temperature during operation of the densitometer 100.
  • the heater chamber 132 additionally incorporates an optical level sensor 172.
  • the level sensor 172 detects the level of liquid in the heating chamber 132 by monitoring changes in the optical properties of a prism system when the prism is immersed in liquid as opposed to being surrounded by air. The operation of the thermistor 168 and the level sensor 172 will be described further below.
  • the heating chamber 132 communicates through an overflow port 134 and flexible tubing to an overflow drain outlet 136.
  • the overflow outlet 136 is positioned at the bottom of the densitometer 100 removed from its internal electronics.
  • the overflow port 134 is positioned above the normal fill height of the heating chamber 132 as will be described in detail below.
  • the heating chamber 132 also communicates, through its lowermost point, with an electrically actuated fill valve 138 which provides a path, through flexible tubing, to a fill port 140 positioned in the wall of basin 103.
  • a drain 146 in the bottom 104 of the basin 103, provides a path to an electronically actuated drain valve 148.
  • the drain valve 148 operates to allow liquid in the basin 103 to flow through the drain 146 to the T-connector 144 and into the drain tank 126.
  • the overflow port 142 and drain 146 incorporate screens 152 to prevent debris from clogging the tubing or the drain valve 148 communicating with the drain tank 126.
  • the supply tank 124 and the drain tank 126 are positioned within the case 101 of the densitometer 100 and located at a height with respect to the basin 103 so that liquid will drain from the basin 103 into the drain tank 126 solely under the influence of gravity and so that gravity alone is not sufficient to fill the basin 103 from supply tank 124 when fill valve 138 is open.
  • the heating chamber 132 is positioned above the basin 103 so that once the heating chamber 132 is filled with liquid by pump 130, the filling of the basin 103 from the heating chamber 132 may be done solely by the influence of gravity. Accordingly, the operation of the densitometer in filling and emptying the basin 103 is simple and extremely quiet.
  • the liquid contacting surfaces of the basin 103, the heating chamber 132, the valves 138 and 148, and the connecting tubing are susceptible to bacterial colonization and to encrustation by minerals.
  • the coatings of colonization or encrustation are potentially unhygienic and unattractive. Sufficient buildup of minerals or bacteria may also adversely affect the operation of the densitometer 100
  • FIG. 14 the general arrangement of the electrical components of Fig. 4 is unchanged in the ultrasonic densitometer 100 of Fig. 10 except for the addition of I/O circuitry and circuitry to control the pump 130, valves 138 and 148, and heating chamber 132 of the liquid handling system.
  • microprocessor 38 now communicates through bus 40 with an I/O module 174, a pump/valve control circuit 160 and a heater control circuit 162.
  • I/O module 174 provides the ability to connect a standard video display terminal or personal computer to the densitometer 100 for display of information to the user or for subsequent post processing of the data acquired by the densitometer and thus allows an alternative to microprocessor 38 and display 18 for processing and displaying the acquired ultrasound propagation data.
  • the pump/valve control circuit 160 provides electrical signals to the fill valve 138 and the drain valve 148 for opening or closing each valve under the control of the microprocessor 38.
  • the pump/valve control circuit 160 also provides an electrical signal to the pump 130 to cause the pump to begin pumping water and surfactant from the supply tank 124 under the control of microprocessor 38, and receives the signal from the
  • the heater control circuit 162 controls the current received by the resistive heating element 164 and also receives the signal from a thermistor 168 in thermal contact with the heating chamber 132.
  • a second thermistor 170 positioned in basin 103 to be thermal contact with the liquid in that basin 103, is also received by the heater control circuit 162.
  • the pump/valve control circuit 160 Under control of microprocessor 38, the pump/valve control circuit 160 provides current to the pump 130 which pumps water and surfactant upward into heating chamber 132 until a signal is received from level sensor 172. When the heating chamber 132 is filled to the proper level as indicated by level sensor 172, the signal from level sensor 172 to pump/valve control circuit 160 causes the pump 130 to be turned off. At this time, a predetermined volume of liquid is contained in heating chamber 132 which translates to the proper volume needed to fill basin 103 for measurement. Under command of microprocessor 38, the heater control circuit 162 provides a current through thermal protection module 166 to resistive heating element 164. The temperature of the liquid in the heating chamber 132 is monitored by thermistor 168 and heating continues until the liquid is brought to a temperature of approximately 39° C.
  • the thermistor and a thermal fuse (not shown) of the thermal protection module 166 provide additional protection against overheating of the liquid.
  • the thermistor opens at
  • the thermal fuse 50° C and resets automatically as it cools and the thermal fuse opens at 66° C but does not reset and must be replaced.
  • the opening of either the thermistor or the thermal fuse interrupts current to the resistive heating element 164.
  • fill valve 138 is opened by microprocessor 38, through pump/valve control circuit 160, and liquid flows under the influence of gravity into the basin 103 at the proper temperature.
  • the control of the temperature of the liquid serves to insure the comfort of
  • the fill valve 138 is closed and the pump 130 is reactivated to refill the heating chamber 132.
  • fresh liquid for the next measurement may be heated during the present measurement to eliminate any waiting between subsequent measurements.
  • the measurement of the os calcis by the densitometer 100 may begin.
  • the operation of the ultrasonic densitometer of Fig. 10 is similar to that of the embodiment of Fig. 1 except that the order of pulsing and measurement can be varied.
  • the measurement pulse through the member was generally performed before the reference pulse through homogenous standard, i.e. water.
  • the reference pulse through the homogenous standard material which is simply the liquid in basin 103, may be conducted before or after a measurement pulse through a live member is performed.
  • the standard transmit time measurement can be made once for the instrument and thereafter only measurement pulses need be transmitted.
  • the standard transit time measurement is stored as a number in the memory of microprocessor 38 during the initial calibration of the unit at the place of manufacture or during subsequent recalibrations.
  • the signal from the thermistor 170 is used to produce a transit time corrected for the temperature of the liquid according to well known functional relations linking the speed of sound in water to water temperature. It is this corrected transit time that is stored in the memory associated with microprocessor 38 as a stored standard reference.
  • the transit time of the measurement pulses is compared to the stored standard reference transit times through the coupling liquid to give an indication of the integrity of the member just measured. Thus, one may dispense with the reference pulse entirely.
  • Empirical tests have determined that by proper selection of a standard reference value stored in the memory of microprocessor 38 and by holding the liquid in the basin within a
  • BUA is broadband ultrasonic attenuation, as described in greater detail above.
  • the constants A, B, C, and D offset and scale the influence of the BUA measurement relative to the SOS measurement to provide a more effective predictor of bone density.
  • These constants may be determined empirically and may be selected for the particular machine to provide numbers compatible with dual photon absorptiometry devices, such as an estimated bone mineral density (BMD) value, and to reduce bone width effects. Since this method utilizing ultrasonic measurement of the heel is quick and free from radiation, it offers a promising alternative for evaluation of bone integrity. It will be understood that multiple SOS and BUA values may be obtained, averaged, then combined per the above formula, or that each SOS and BUA value may be combined to produce a bone integrity value and the multiple bone integrity values then averaged.
  • the drain valve 148 is opened by microprocessor 38 through pump/valve control circuitry 160, and the liquid in the basin 103 is drained through "T" 144 to the drain tank 126.
  • the drain valve 148 is closed and liquid is again transferred from the heating chamber 132 as has been described.
  • the densitometer may be stored.
  • the microprocessor 38 instructs the pump/valve control circuit 160 to open both the fill valve 138 and the drain valve 148 and to run the pump 130.
  • the drain valve 138 is opened slightly before the pump 130 is actuated to prevent the rush of air from causing liquid to flow out of the overflow port 134.
  • the transducers 121 are inserted into the basin 103 through tubular sleeves 180 extending outward from the walls of the basin 103 at the curved pocket along an axes 212 of the opposed transducers 121.
  • the tubular sleeves 180 define a circular bore in which the transducers 121 may be positioned.
  • Each transducer 121 seals the sleeve 180 by compression of o-ring 182 positioned on the inner surface of the sleeve 180.
  • the transducers 121 fit tightly within the sleeves 180, their separation and alignment are determined not by the sleeves 180 but by an independent C-brace 184 comprising a first and second opposed arm 186 separated by a shank 188.
  • the arms 186 are generally rectangular blocks transversely bored to receive the cylindrically shaped transducers 121 at one end and to hold them along axis 212.
  • the other ends of the arms 186 provide planar faces for abutting the opposite ends of the block like shank 188, the abutting serving to hold the arms 186 opposed and parallel to each other.
  • the dowel tubes 190 are received by threaded holes in the shank 188 to hold the arm 186 firmly attached to the shank 188.
  • the dowel tubes 190 and surfaces between the arms 186 and shank 188 serve to provide extremely precise alignment and angulation of the transducers 121, and yet a joint that may be separated to permit removal of the transducers 121 from the densitometer 10 for replacement or repair.
  • Transducers 121 are matched and fitted to the arms 186 in a controlled factory environment to provide the necessary acoustic signal strength and reception.
  • the shank 188 may be separated from one or both arms 186 by loosening of the cap screws 194 so as to allow the transducers 121 extending inward from the arms 186 to be fit within the sleeves 180.
  • Proper alignment and angulation of the transducers is then assured by reattaching the arm or arms 186 removed from the shank 188 to the shank 188 to be tightened thereto by the cap screws 194.
  • the alignment of the transducers is not dependent on the alignment of the sleeves 180 which may be molded of plastic and thus be of relatively low precision. Nor must alignment be tested while the transducers are in the sleeves 180 attached to the basin 103 but may be checked in a central controlled environment.
  • the bladders 202 serve to contain the gel about the face of the transducers 121 and conform to the left and right sides of a patient's heel 207, respectively, to provide a path between the transducers 121 and the soft tissue and bone of the heel 207 without intervening air.
  • the bladder 202 further prevents the coupling material from direct contact with the heel to permit selection of the coupling material 204 from a broader range of materials.
  • each dowel pin 210 is press fit within bores in the shank 188' parallel to the axis 212 of the opposed transducers in portion 206.
  • the other ends of the dowel pins 210 slide within larger bores in portion 208 so that portions 208 and 206 may slide toward and away from each other parallel to the axis 212. With such motion, the attached arms 186 move towards and away from each other adjusting the separation of the transducers 121 between an open position for insertion of the heel 207 and a closed position of known separation and orientation where portions 208 and 206 abut. Control of the separation is provided by means of cam pins 214 protruding from portions 206 and 208 on the side away from the extension of the arms 186 and generally perpendicular to the axis 212. These pins 214 are received by spiral shaped slots in a cam disk 217 fitting over the cam pins 214. The disk includes radially extending lever 218 whose motion rotates the disk causing the cam pins 214 within the slots 215 to be moved together or apart depending on motion of lever 218.
  • the transducers 121 may be moved apart together with the bladders 202 for insertion of the heel 207 into the basin 103. Once the heel is in place, motion of the lever
  • the collars 200 may provide a conduit for electrical wiring (not shown) including wiring attached to a temperature sensor for monitoring the temperature of the contained coupling material 204 and heater elements for heating the temperature of the contained coupling material to a predetermined temperature. As has been described above, the controlled heating provides both for comfort to the patient and for reproducibility of the measurements which may be influenced by the temperature of the contained coupling material 204.
  • BUA broadband ultrasonic attenuation
  • the time of flight (TOF) of an acoustic pulse between the transducers 121 will be proportional to the time of flight of the acoustic pulse through regions A of Fig. 17 comprising the path length through coupling gel 204, regions B comprising the path length through soft tissue of the heel 207 surrounding the calcaneus 216, and region C comprising the path length through the heel bone or calcaneus 216.
  • TOF time of flight
  • V ⁇ , Vg, and Vc are the average speed of sound through the coupling gel, soft tissue and bone respectively and A, B, C are the path lengths through these same
  • a combined bone quality figure may be obtained by combining BUA and 1/TOF measurements (1/TOF because BUA increases but TOF decreases with denser bone). Further, if (1) the conditions of ultrasonic propagation are adjusted so that the slope of 1/TOF with heel width is opposite in sign to the slope of BUA with heel width (i.e., V ⁇ >
  • BUA and TOF are functionally related to both bone quality and bone width. It should be possible, therefore, to solve the equations governing these relationships for bone quality alone and thus to eliminate the effect of the common variable of heel width. With such an approach, the variable of heel width is eliminated not just for a portion but through the entire range of bone measurement provided that the coupling medium is different from the bone being measured so that there will be a width effect in both BUA and TOF measurements. Approximations of the algebraic relationships describing the functional dependence of BUA and TOF on bone quality and bone width, can be obtained through the construction of a set of bone phantoms of different widths and bone qualities when using a particular coupling gel.
  • the data will describe a curve 222 linking that value with different combinations of bone quality and bone width.
  • This data may be placed in a look-up table in the memory of the microprocessor of the densitometer as has been previously described.
  • the data of the look-up table (comprising many bone quality and bone width pairs for each of the determined BUA and TOF values) are scanned to find a bone quality and width data pair for the BUA value matching a bone quality and width data pair for the TOF value. This is equivalent to finding the intersection of the two curves 222 associated with the measured BUA and TOF values.
  • the matching bone quality values of the data base will give a bone quality having little or no bone width influence. This value may be displayed to the clinician. It is noted that the previously described technique of summing weighted values of BUA and 1/TOF is but a specialized form of this process of algebraic solution.
  • the piezoelectric sheet 302 may be constructed of polyvinylidene fluoride and has a front face 306 covered with a grid of interconnected square electrodes 308 deposited on the front face by vacuum metallization. These square electrodes 308 are arranged at the interstices of a rectangular grid to fall in rectilinear rows and columns. Referring also to Fig. 23, each square electrode 308 is spaced from its neighboring electrodes 308 by
  • These square electrodes 308 are connected together by metallized traces (not shown) and to a common voltage reference by means of a lead 310.
  • the polyvinylidene sheet 302 is polarized to create its piezoelectric properties by heating and cooling the sheet in the presence of a polarizing electrical field according to methods generally understood in the art.
  • this polarizing field is applied only to the area under the square electrodes 308 so that only this material is piezoelectric and the material between square electrodes 308 has reduced or no piezoelectric properties.
  • this selective polarization of the piezoelectric sheet 302 provides improved spatial selectivity in distinguishing between acoustic signals received at different areas on the piezoelectric sheet.
  • Each conductive pin 320 is connected directly to a preamplifer and then by means of printed circuit traces to a multiplexer 325 to a reduced number of control and data lines 324 which may be connected to the microprocessor 38 of the densitometer through an A to D converter 42 described previously with respect to Fig. 1 and as is well understood in the art.
  • the preamplifers allow grounding of those electrodes 312 not active during scanning to reduce cross-talk between electrodes 312.
  • each plated finger 314 on the front of the Mylar strip 316 is then connected to an electrode 312 by a second layer of anisotropically conductive adhesive film 317.
  • the Mylar strip 316 flexes to allows the pins 320 to be spaced away from the electrode 312 to reduce reflections off the pins 320 such as may cause spurious signals at the piezoelectric sheet 302.
  • the Mylar strip 316 and conductive fingers 314 are essentially transparent to the acoustic wave.
  • a second layer of the anisotropically conductive adhesive film 315 is placed on the rear surfaces of the overlapping Mylar strips 316 and the conductive pins 320 pressed down on this film 315, aligned with the other ends of the conductive fingers 314 to attach to their respective fingers 314.
  • the conductive pins 320 are then raised and fixed in spaced apart relationship with the piezoelectric sheet 302, the Mylar strips 316 flexing to accommodate this displacement.
  • the ultrasonic wave 410 passing through portions of the piezoelectric sheet 302 between electrodes 308 and 312 may thereby be measured at a number of points over the surface of the piezoelectric sheet by the electric signals generated and collected by
  • Electrodes 308 and 312 according to multiplexing methods well known in the art. Each electrode pair 308 and 312 provides an independent signal of the acoustic energy passing through the area of the piezoelectric sheet 302 embraced by the electrode pair.
  • a protective frame 325 encloses the piezoelectric sheet 302 and connector board 318 protecting them from direct contact with water of the basin 103 shown in Figs. 10 and 15 into which the receiving transducer array 300 may be placed.
  • the frame 325 holds on its front face an acoustically transparent and flexible material 326 such as a Teflon film so that the ultrasonic wave 410 may pass into the frame to reach the piezoelectric sheet 302.
  • the above described array may be used either to receive or transmit acoustic waves and is not limited to use in the medical area but may provide an inexpensive and rugged industrial acoustic array useful for a variety of purposes including industrial ultrasonic imaging and the construction of high frequency synthetic aperture microphones.
  • an electric motor 328 driving a central gear 330 about an axis aligned with transmission axis 304 and approximately centered within the frame 325.
  • the central gear 330 in turn engages two diagonally opposed planet gears 332 also turning about axes aligned with the transmission axis.
  • Each planet gear 332 has a rod 334 extending forwardly from a front face of the planet gear 332 but offset from the planet gear's axis to move in an orbit 336 thereabout.
  • the orbit 336 has a diameter approximately equal to the spacing between electrodes 308.
  • a sampling of the signals from the detector elements 400 may be made at four points 342 in the orbit 336 at which each electrode 308 is first at a starting position, and then is moved half the inter-electrode spacing upward, leftward, or upward and leftward.
  • the effect of this motion of the detector elements 400 is to double the spatial resolution of the received acoustic signals without increasing the amount of wiring or the number of detector elements 400.
  • the sampling of acoustic energy at each of the points 342 is stored in the memory of the microprocessor and can be independently processed to derive attenuation, BUA or time of flight measurements or a combination of
  • a transmitting ultrasonic transducer 408 is positioned opposite the receiving transducer array 300 from the heel 207 and produces a generally planar ultrasonic wave 410 passing into the heel. Generally, the acoustic signal received by each transducer element 400 will have arrived from many points of the heel.
  • two acoustic signals 405 and 406 from focus voxel 404 both crest at the location of a transducer element 400' as a result of the equidistance of each transducer element 400' from focus voxel 404.
  • the signals from transducer elements 400' are summed, the signal from focus voxel 404 will increase.
  • acoustic signals from other voxels not equidistant to transducer elements 400' will tend to cancel each other when summed and thus decrease.
  • the present invention does not curve the transducer elements 400 into a hemisphere but accomplishes the same effect while retaining the transducer element 400 in a planar array by delaying the signals received by the transducer elements 400 as one moves toward the centermost transducer element 400" so as to produce an effective hemispherical array.
  • the center-most transducer elements 400 appear to receive the acoustic wave a little later than the transducer elements 400 at the edge of the receiving transducer array 300.
  • the position of the focus voxel 404 at which the receiving array 300 is focused may be scanned electrically as will be described.
  • the signals from each of the transducer elements 400 are received by the A/D converter 42
  • Phase shifting as described simply involves shifting the point at which one starts reading the stored signals.
  • Adjusting the phase of the acoustic signals received by each of the transducer elements 400 allows the location of the focus voxel 404 from which data is obtained to be scanned through the heel.
  • the phase is simply adjusted so that the effective arrival time of an acoustic signal originating at the desired location is the same for each of the transducer elements 400.
  • the location of focus voxel 404 may be moved in a first and second raster scan pattern 412 and 414 (as readings are taken over many ultrasonic pulses) to obtain separated planes of data normal to the transmission axis 304.
  • the first plane of data 412 may, for example, be positioned near the outer edge of the os calcis 216 to measure the cortical bone quality while the second plane 414 may be placed in a centered position in the trabecular bone to obtain a somewhat different reading, both readings providing distinct data about the bone. It will be understood that this same approach of scanning in different planes may be used to obtain a volume of data within the heel 207, in this case, the focus voxel 404 being moved to points on a three dimensional grid.
  • the transmitting ultrasonic transducer may be an array and the phases of the ultrasonic signals transmitted by each of the elements of the array may be phased so as to focus on a particular voxel within the heel.
  • the receiving array may be a single broad area detector or may also be an array focused on the same voxel for increased selectivity.
  • the focus point of the transmitting and receiving arrays may also be shifted with respect to each other to investigate local sound transfer phenomenon.
  • the focal points of either array may be steered electrically by the microprocessor through a shifting of the phases of the transmitted and received signals.
  • each element of the transmit array may be energized individually while all receive elements of the receive array are read. This may be continued until each of the elements of the transmit array have been energized.
  • the receiving array 300 may be actually formed so that its elements follow along the hemisphere 402 so as to have a fixed focus on focus voxel 404. Additional circuitry to effect the phase adjustment needed to focus the array is not needed in this case.
  • the receiving array 300 is attached to an X-Y-Z table 600
  • the transmitting array 408 may be held stationary or may be moved with the scanning of the receiving array 300 and may be focused as well.
  • such a data volume 415 may include a plurality of data voxels 416 each providing a measured member parameter for the bone or tissue at that point in the heel.
  • a point of minimum bone density 418 may be found within this data volume 415 and used to identify a region of interest 420 which will serve as a standard region for measuring the bone density of the heel.
  • This region may be automatically found after collection of the data volume 415 and only those voxels 416 within the region of interest 420 may be used for a displayed measurement. This automatic location of a region of interest 420 provides a much more precise bone characterization.
  • Acquiring a data volume 415 also provides the opportunity to use the extra data outside the region of interest 420 to ensure that the same region of interest 420 is measured in the patient's heel over a series of measurements made at different times.
  • the data volume 415 may be stored in memory as a template that may be matched to subsequently acquired data volumes.
  • the region of interest 420 spatially located with respect to the first template may then be used as the region of interest for the subsequent data volumes aligned with that template to provide more repeatability in the measurement.
  • a collection of a data volume 415 within the heel is obtained.
  • a region of interest 420 is identified at process block 504 from this data, as a predetermined volume centered about a point of minimum bone density 418 as described with respect to Fig. 26.
  • the data volume is stored as a template along with the region of interest defined with respect to the data of the template.
  • the program may proceed to process block 508 and the template previously established may be correlated to a new data volume 415 collected at process block 500.
  • the correlation process involves shifting the relative locations of the two data volumes to
  • the region of interest 420 associated with the template is then transferred to the new data volume as it has been shifted into alignment with the template so that the identical region of interest may be measured in a patient even if the patient's foot has taken a different alignment with respect to the transducer array 300 and 408. This use of the template's region of interest 420 is indicated by process block 510.
  • an index is calculated at the region of interest 420 for the new data volume 415 being typically an average value of a bone parameter such as BUA or time of flight for the voxels 416 within the region of interest 420.
  • This data is then displayed to the clinician at process block 520 as has been described.
  • a heat exchanger 532 couples to the delivery pipe 528 to ensure that the coupling liquid 534 is at a constant predetermined temperature to which the device has been previously calibrated.
  • the heat exchanger 532 may make use of a circulating exchanger liquid preheated to a constant temperature by means of a combination thermostat and electric heater (not shown) well known in the art.
  • a pressure transducer 536 communicating with the delivery pipe 528 measures the pressure of the
  • Second coupling liquid 542 differs from coupling liquid 534 by having either significantly different ultrasonic attenuation characteristics or a significantly different sound speed characteristics for reasons as will be describe below.
  • the annular collar 538 holding the second bladder 540 is also pierced by an orifice 544 connecting to a delivery pipe 546, which like delivery pipe 528, passes through a heat exchanger 550 supplied with the same liquid at the same temperature as heat exchanger 532.
  • Delivery pipe 546 also communicates with pressure transducer 536 through a coupler 552 which prevents intermingling of the liquids in delivery pipe 528 and 546.
  • Delivery pipe 546 includes a branch connection 554, which like branch connection 530, provides a comparable liquid at a comparable temperature to the opposed transducer not shown in Fig. 29.
  • a separate pump 130A delivers the coupling liquid 542 from a distinct reservoir from that connected to pump 130B.
  • the bladders 522 and 540 for both transducers are sufficiently flexible and have ample size so that either bladder 522 or 540 through inflation to a pressure less than the predetermined pressure controlled by pressure transducer 536 will bridge any gap between the transducer array 300 and the heel 207, thus allowing the transducer arrays 300 to be fixed in separation. This both simplifies mechanical construction and eliminates errors resulting from uncertainty about the separation distance of the transducer arrays 300 as is inherent in any movable system.
  • annular collar 538 outside of annular collar 538 is yet another annular locking collar 556 mounted along with the other annular collars 538 and 524 against one wall of the basin 103 about the transducer arrays 300.
  • Locking collar 556 includes radially outward extending tabs 558 which engage notches 560 in a stretcher ring 562 which may be installed against and removed from locking collar 556 by passing the
  • the stretcher ring is covered with a third flexible bladder 566 which envelopes both bladders 522 and 540 and yet which is easily removed and may be disposed of to provide for hygienic reuse of bladder 540 and 522. Because the third flexible bladder 566 is not required to retain a liquid and is disposable, it may be made from a lighter and less resilient material.
  • series of pulse measurements are made but with an alternating of the transmitting transducer between the left and right side of the heel 207 with the opposed transducer serving as the receiving transducer. Pairs of such measurements may be averaged together to reduce the variation in heel measurement, however, it will also be understood that other statistical techniques may be applied to the left-going and right- going pulses to detect, for example, abnormal situations indicated by the deviation between these pulses being too great.
  • the deviation between successive measurements at process block 570 may be compared until the deviations drop below a predetermined amount indicating that an asymptote in the measurements has been reached.
  • the successive ultrasonic measurements may be fit to a decaying exponential or other similar curve until the deviation between that projected curve and the actual curve drops below a predetermined
  • the asymptote for the projected curve may be used as a final value.
  • attenuation and speed of sound measurements may be made at process block 570 and combined to reduce the asymptotic variation in the successive measurements. These combined measurements may also be fit to a curve as previously described.
  • the present inventors have recognized that in apparatus of this type, the measured values of sound speed 574 tend to decline with time whereas measured values of broad band ultrasonic attenuation (BUA) 576 tend to rise with time.
  • a combination of these values reflected in a stiffness measurement 578 such as may be an empirically weighted sum of BUA and SOS converges more quickly to the asymptote value 580.
  • the process may conclude.
  • the coupling liquid A from bladder 522 is withdrawn and bladder 540 is inflated with coupling liquid B having a different sound speed as shown in Fig. 31 by process block 582.
  • the pressure and temperature of the coupling liquid B are controlled to be the same as coupling liquid A.
  • process block 570 interleaved left to right, right to left ultrasonic measurements are then taken as indicated by process block 584..
  • decision block 586 an asymptote value is again derived, as has been described, and the program proceeds to process block 588 where width of the heel is calculated by the following means:
  • the shape of the flexible membrane 626 in the foregoing examples is controlled in shape so as to provide a maximum resistance to movement of the patient member 207 across the axis 212 when the member 207 is in contact with the membrane 626.
  • membrane 626a was attached about transducer 300 at a periphery 654a conforming closely to the active front surface 656 of the transducer 300.
  • the membrane 626a extends a distance D along axis 212 by an amount intended to bridge the gap between the transducers 300 and a patient member (not shown in Fig. 35) for different sized patient members while providing ample clearance for insertion and removing of the patient member.
  • the present invention recognizes that superior patient immobilization is obtained by expanding the point of peripheral attachment of the membrane 626b to an outer periphery 654b substantially greater than the ultimate extension distance D and preferably greater than twice D.
  • the surface of the membrane 626 extending the distance D while retaining a generally hemispherical shape such as is believed to provide greatest resistance to cross axis motion.
  • the diameter of the periphery as used herein will refer to the diameter of a circle circumscribed within the periphery 654b.
  • the advantage of the expanded periphery 654b may be seen by imagining the displacement of a point 658a on the membrane 626 to a new location 658b displaced across axis 212 such as might be caused by motion of the patient member.
  • Such motion would require a substantially greater stretching of the membrane 626(b) with respect to the periphery 654b as shown by displacement distance 660 than it would require of the membrane 626(a) with respect to the periphery 654a as shown by displacement 662.
  • a greater displacement from these points corresponds to a greater stretching of the curved membrane 626(b), thus a greater restoring force provided by the membrane 626(b) in preventing that movement.
  • Motion of the patient member along axis 212 may be controlled by controlling the pressure within the membrane 626 to provide the desired degree of immobilization.
  • a closed environment for the acoustic coupling fluid 640 may also be obtained in an inflation-type system wherein cylindrical chambers 664 having open ends facing each other along axis 212 with front opposed surfaces enclosed by membranes 626 and rear surfaces connected by means of hydraulic tubing 666 to pump chamber 668.
  • the chambers 664 are fixed in separation and with respect to the transducers contained therein.
  • the transducers may be any combination of arrays 300 and/or individual transducers 121 as have been previously described.
  • Valves 641 communicating with the interior of the chambers 664 may allow removal of coupling fluid 640 or the bleeding out of entrapped air.
  • An open face of the pump chamber 668 may be closed by a rolling diaphragm 670 being essentially a flexible membrane attached at its edges to close the chamber 558 and attached at its center to a piston 672. Displacement of the piston 672 in toward the chamber 668 creates a predefined reduction in volume of the chamber 668 causing, through hydraulic equalization, a distention of membranes 626 outward toward the patient member contained between them.
  • the rolling diaphragm 670 requires no sliding seals, as are found in conventional piston pumps, nor creates the possibility of backwash as can occur with peristaltic-type pumps. Further, the flow rate provided to the chambers 664 need not be measured in order to determine the amount of distention of the membranes 626 as there will be a fixed and easily calculated relationship between movement of the piston 672 and distention of the membranes 626.
  • the transducer chambers 664, interconnecting hydraulic tubing, and 666 pump chamber 668 all may be partially formed from or incorporated into a thermally conductive matrix such as an aluminum block to form an effective a single heating chamber whose temperature may be controlled by activation of resistance heating elements 164 also in thermal communication with the heating chamber 132 and monitored by thermistor 168 as previously disclosed. This arrangement eliminates the need for separate thermal regulation circuitry for each of these elements and provides good uniformity of temperature of the various elements.
  • the chamber 558 may be in communication with a pressure sensor and the piston 672 further controlled to monitor the pressure in the chamber 558 to substantially 1 PSIG.
  • this same mechanism may be used to pre-inflate the membranes 626 prior to insertion of the patient's foot.
  • the pressure sensor may be used to monitor the pressure as a function of volume of liquid in the chambers 664, and hence inflation of the membranes 626, to determine that the patient's foot is not in place during the inflation process. Presence of the patient's foot would increase the pressure sensed by the pressure sensor for a given inflation volume and thus may also be used to confirm that the patient's foot has been inserted.
  • an ultrasonic densitometer 710 includes a housing 712 having an aperture 714 and its upper surface exposing a receptacle 718 sized to receive a human heel therein when the housing 712 placed on the floor in front of a seated patient.
  • Attached to left and right walls 716 of a receptacle 718 and positioned below the aperture 714 are left and right bladders 720 presenting opposed convex bladder surfaces 722 formed of distended membranes. It will be recognized that a similar system may be used with a single bladder in a reflection mode where one of the bladders 720 is replaced simply by a soft material providing support for the side of the heel. Further, the bladders
  • 49 720 may be used not with single transducers but with transducer arrays or a combination of single transducers or single elements of array transducers and arrays may be used.
  • the bladders 720 prior to insertion of the patient's heel 724, the bladders 720 are pre-inflated so that surfaces 722 define therebetween a cavity sized to be smaller than a standard human heel 724.
  • the bladders 720 are pre-inflated with a coupling liquid, typically water 726, to distend a sheet of silicone rubber to a nearly hemispherical configuration as described above. While the bladders 720 are pre-inflated before the heel 724 is inserted, they are initially inflated by a pump system such as described above and may be deflated for storage or shipping. The act of inflation is, of course, intrinsic to any inflated bladder.
  • each bladder surface 722 and a corresponding backer plate 728 is attached to the membrane of the bladder 720 at its circular periphery.
  • an ultrasonic transducer 730 Positioned within the cavity defined by the backer plate 728 and the bladder surface 722 is an ultrasonic transducer 730 as described above.
  • the transducers 730 and backer plates 728 are held by structure 721 in fixed separation and essentially fixed with respect to the foot plate 738 as will be described.
  • the ultrasonic transducers 730 are aligned along an ultrasonic propagation axis 732 extending therebetween and intersecting the center of the bladder surfaces 722.
  • a thin coating of ultrasonic coupling gel 734 is placed on the outer surface of the membrane forming the bladder surface 722 to provide lubrication and coupling for the later insertion of a heel 724.
  • the heel 724 may be inserted in a downward direction 736 across (i.e., perpendicular) to the ultrasonic propagation axis 732 so as to slide pass past the bladder surfaces 722 deforming them inward, the heel 724 to abut a heel plate 738 stopping further downward motion of the heel 724.
  • the elastic nature of the membranes of bladder surfaces 722 causes the surfaces 722 to deform as they slide along the outer surfaces of the heel 724 in a wiping action reducing entrapment of air between the bladder surfaces 722 and the heel 724.
  • their longitudinal extension or conical shape may collapse or fold over with the insertion of a the heel.
  • the load cell 746 may measure downward pressure 747 of the heel 724 on the plate 738 and backward pressure 749 of the heel 724 on the surface 742 so as to insure proper seating of the heel 724 against the plate 738 and proper location of the ultrasonic propagation axis 732 in the desired region of the os calcis 748.
  • the downward force 747 (FI) and backward force 749 (F2) may be monitored by the microprocessor 38 (described above) so as to ensure that the forces (FI and F2) of a given measurement lie within a desired range 750 indicating proper seating of the foot against the plate 738 without undue force thereon and indicating further that the calf of a patient's leg abutting a calf support 120 (shown in Fig. 38 in phantom) is not holding the back of the heel 724 away from surface 742.
  • the bladders 720 may be pre-inflated so as to touch and in this way provide an acoustic path directly from one ultrasonic transducer 730 to the other without air gap or intervening heel 724. This provides a separation distance of zero.
  • This configuration may be used to provide a pre-measurement standard pulse between ultrasonic transducers 734 as has been previously described, and/or to provide a positive indication (by measurement of the ultrasonic propagation) as to whether the patient's heel 724 has been inserted between the bladders or not.
  • the shape and composition of the bladders 720 is such as to allow the foot to slide between the bladders 720 even when there is initially no appreciable gap between the bladders 724. It will be within the understanding of one of ordinary skill in the art, that the features of the various embodiments described herein may be interchanged with other embodiments to effect the purposes described herein and therefore that the inventor contemplates the construction of commercial devices including either combinations of

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Abstract

On décrit un densitomètre ultrasonore hydraulique qui met en oeuvre des vessies préalablement gonflées contenant un fluide de couplage autour de transducteurs ultrasonores. A l'état relaxé, les vessies délimitent une cavité plus petite que le talon d'un être humain, si bien que, lorsque le talon est inséré, les vessies en épousent la forme dans un mouvement glissant qui chasse l'air occlus.
EP99914223A 1998-03-31 1999-03-26 Densitometre ultrasonore muni de membranes de couplage hydraulique prealablement gonflees Withdrawn EP1067870A1 (fr)

Applications Claiming Priority (3)

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US8015898P 1998-03-31 1998-03-31
US80158P 1998-03-31
PCT/US1999/006739 WO1999049789A1 (fr) 1998-03-31 1999-03-26 Densitometre ultrasonore muni de membranes de couplage hydraulique prealablement gonflees

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EP1067870A1 true EP1067870A1 (fr) 2001-01-17

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CN104622510A (zh) * 2015-01-20 2015-05-20 中国科学院合肥物质科学研究院 一种用于超声骨密度测量的足部的定位装置及方法
CN110448331B (zh) * 2019-09-12 2024-08-23 深圳市索诺瑞科技有限公司 一种空气填充的超声换能器
US12364456B2 (en) * 2019-12-19 2025-07-22 GE Precision Healthcare LLC Air filled chamber in an ultrasound probe
CN112540637B (zh) * 2020-11-27 2022-01-21 株洲时代电子技术有限公司 一种耦合液智能控制系统
CN112540638B (zh) * 2020-11-27 2022-01-21 株洲时代电子技术有限公司 一种耦合液智能控制方法
CN117214310B (zh) * 2023-08-22 2025-09-30 四川大学 一种管道超声检测耦合装置及检测方法

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US5603325A (en) * 1988-05-11 1997-02-18 Lunar Corporation Ultrasonic densitometer with width compensation
US5134999A (en) * 1991-05-22 1992-08-04 Walker Magnetics Group, Inc. Ultrasonic transducer assembly
GB9414909D0 (en) * 1994-07-25 1994-09-14 Ritchie Roy Osteoporosis apparatus
US5895357A (en) * 1996-01-29 1999-04-20 Aloka Co., Ltd. Bone assessment apparatus

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See references of WO9949789A1 *

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WO1999049789A1 (fr) 1999-10-07

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