Classifications

• • 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
  • A61B8/0858—Clinical applications involving measuring tissue layers, e.g. skin, interfaces
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/20—Measuring for diagnostic purposes; Identification of persons for measuring urological functions restricted to the evaluation of the urinary system
  • A61B5/202—Assessing bladder functions, e.g. incontinence assessment
  • A61B5/204—Determining bladder volume

Definitions

• This invention generally concerns non-in ⁇ vasive ultrasonic medical apparatus, and more specific* ally concerns such an apparatus which is used to deter ⁇ mine the volume of urine in the bladder.
• bladder dysfunction is associated with a number of clinical conditions requir ⁇ ing treatment. It has been estimated that as many as twelve million urinary conditions requiring treatment occur each year in the United States. In many of these cases, it is important that the volume of urine in the bladder be accurately determined, sometimes on a fre ⁇ quent, if not substantially continuous, basis. This is especially true in cases involving spinal cord injuries which require bladder retraining and in those cases, such as post-operative recovery, where there is a tem ⁇ porary loss of bladder sensation and/or a loss of the normal voiding mechanism. Knowing the volume of urine in the bladder in such situations helps both bladder management and aids in the prevention of bladder over- distension.
• catheteriza* tion The most common and reliable current tech ⁇ nique of bladder volume determination is catheteriza* tion. Catheterization is used both as a diagnostic tool, and to actually empty the bladder when necessary. Typically, catheterization with respect to bladder volume is accurate to within approximately ten percent, and is currently the standard against which other meth ⁇ ods are judged.
• Non-invasive procedures for bladder volume estimation are known, but are either unreliable or expensive or have some other significant disadvantage. Palpation and ascultatory percussion are known to be unreliable, while radiography and dye-excretion tech ⁇ niques are known to be similarly inaccurate and are now regarded to be obsolete at this point. Radio-isotopic procedures have also been used, and while accurate, are complicated and relatively expensive, as well as not being suitable for routine and/or continuous measure ⁇ ment.
• the non-invasive al ⁇ ternatives to catheterization all have significant disadvantages, so that catheterization remains the most commonly used procedure for determining bladder volume. As outlined above, however, it is invasive, traumatic to the patient, and is accompanied by a risk of infec ⁇ tion.
• the present invention is an apparatus for measuring the volume of urine in a human bladder, including means for transmitting an ultrasound signal into the bladder, means for receiving the re- turning ultrasound signal, means for determining from the received signal the distance between selected por ⁇ tions of the border of the bladder, and means for de ⁇ termining the volume of urine in the bladder from said distance.
• Figure 1 is a simplified cross-sectional view showing the location of the bladder in human tissue and the relationship thereto of the ultrasound beam.
• Figure 2 is a diagram showing the returned ultrasound beam from the patient.
• Figure 3 is a diagram showing the signal of Figure 2 following processing thereof by the present invention.
• Figure 4 is a functional block diagram of the apparatus of the present invention.
• Figure 5 is a cross-sectional view showing a linear array embodiment of the transducer portion of the apparatus of Figure 4.
• Figure 6 is a flow chart of the signal proc ⁇ essing software portion of the present invention.
• the present invention uses ultra- sound to determine bladder volume, it is unlike a tra ⁇ ditional ultrasound apparatus which produces a two dimensional visual image of a target or portion of a target, which image is then interpreted by an operator.
• the currently used but still experimental techniques using conventional ultrasound apparatus produce two dimensional images of the bladder. The diameter of the bladder is then actually measured by the operator off the image on the screen, and the bladder volume is then calculated using that measurement information.
• the present invention is substan ⁇ tially different in concept, in that it uses an ultra ⁇ sound signal to automatically determine selected portions of the border of the bladder, i.e. the loca ⁇ tion of the front and back walls of the bladder, rather than to produce a two-dimensional image.
• the inventors utilized the known fact that a returning ultrasound signal from a tissue region of the human body has a relatively high signal level, while the returning signal from a fluid-filled region, such as a bladder, has a very low level, almost zero, because a fluid filled region is anechoic.
• the returning signal after processing, provides a clear representation of the selected portions of the border of the bladder, from which the diameter of the bladder is then deter ⁇ mined by the processing circuitry.
• the volume of the bladder is then calculated automatically by the appa ⁇ ratus and the result displayed as a number, instead of a two-dimensional image.
• the apparatus of the present invention includes a scanhead element 10.
• the scanhead 10 is placed against the abdomen of the patient and transmits and receives the ultrasound signals.
• the scanhead is a transducer which may comprise one or more transducing elements.
• the scanhead comprises a single focused transducer which is mounted at the end of a pen-like handle. Such an element is commercially available.
• a transmission gel is applied to the surface of the transducer and it is placed directly on the patient's abdomen.
• a single focused transducer is mounted in a gimbaled structure, which permits freedom of movement along two orthogonal axes.
• a pair of stepper motors move the transducer through a predetermined path, under computer control.
• microprocessor 12 and the accompanying control software 14 would perform the control function for the stepper motors.
• the front of the transducer in such an embodiment is covered with a convex neoprene dome, which in use is coated with transmission gel and then placed on the patient's abdomen.
• the bladder to be measured has a substantially spherical configuration.
• a plurality of focused transducers 16-16 are potted on a substrate 18.
• the individual trans ⁇ ducers 16 are mounted at predetermined angles and with predetermined spacing relative to each other such that when the individual transducers are activated in a particular known sequence, accurate volume measurements of any bladder shape are obtained.
• a flexible neoprene facing sheet 20 forms the front surface of the transducer, with an acoustic fluid 21 filling the re ⁇ gion between facing sheet 20 and substrate 18.
• the transducers 16-16 may also be positioned in a single plane, in which case the transducers are activated sequentially, under computer control, so as to pro ⁇ vide coverage over a relatively large region.
• the transceiver 24 is a conventional combined transmitter and receiver, which is switched between its two operational modes at selected times by micropro- cessor 12.
• the signal produced by the transceiver in its transmit mode is a typical ultrasound signal, for example 2.25 megahertz pulses in groups or bursts at a pulse repetition frequency of 0.5 kilohertz.
• transceiver in the receive mode should have sufficient dynamic range to capture the desired border informa ⁇ tion. In the present case, a dynamic range of 50db will likely be sufficient.
• the receiver section in- eludes a variable gain amplifier which can be adjusted to compensate for tissue attenuation of the returning signal.
• the received signal is applied to an analog signal processor 26, which detects, rectifies and amp- lifies it.
• the analog signal processor 26 includes a detector circuit, low and high pass filters and an am ⁇ plifier.
• Figure 2 shows a typical signal output of the analog signal processor. The maximum amplitude of the signal for the embodiment shown is approximately 2.5 volts.
• the signal contains information about the bor ⁇ ders of the bladder, specified as FW (front wall) and B (back wall) , and the distance therebetween. The remaining portion of the signal is the returning sig ⁇ nal from the surrounding tissue.
• the output of the analog signal processor is applied to a standard digitizer circuit 28 and a dis ⁇ play circuit module 30, such as a liquid crystal dis ⁇ play or a CRT.
• Digitizer 28 is a conventional analog-to-digital converter which in the embodiment shown comprises two high speed six-bit units in cascade to provide a capability of 12 bits of resolution, al ⁇ though only 7 bits of resolution are actually used in the embodiment shown, i.e. each line of data comprises 256 individual bits of data. It is also possible that the digitizer will include only one six bit unit should such an arrangement provide acceptable results.
• the resulting digital signal is stored in a buffer memory 32 and from there is transferred to the microprocessor's main memory.
• the data is oper ⁇ ated on by the signal processing software 34.
• the signal processing software is responsible for the most significant portion of the processing of the received ultrasound signals.
• the control software 14 is responsible for the timing of the transceiver modes as well as the sequencing of the various functions of the microprocessor and related modules.
• the control software is conventional, but the signal processing software is unique in concept.
• the scanhead 10 is placed on the abdomen of a patient, with the patient typically being in a su ⁇ pine position.
• the transducer is moved around on the patient's abdomen until the the visual display is similar to that shown in Figure 2, which indicates that the transducer is generally over the area of the blad- der 13. This is the initial positioning step for the apparatus.
• the transducer is then rocked gently by the operator about its initial position, so that the ultrasound signals proceed through the bladder, at various angles from this point.
• the ultrasound sig- nals which are substantially straight lines, thus are directed through a substantial portion of the cross- sectional area of the bladder 11.
• each line of data is digi ⁇ tized and individually processed in microprocessor 12 by the signal processing system of the present inven ⁇ tion.
• the signal processing system comprises a series of key operations which are performed on the data.
• the first operation is a threshold determinati ⁇ on. In this step, the level of noise present in the returning signal is estimated.
• the overall noise level is first estimated by computing the standard deviation of the entire A-line data. Each A-line corresponds to a single transmission burst. This initial noise esti ⁇ mate is then used as a rough threshold. A refined noise level estimate is then ob ⁇ tained by calculating the standard deviation for that segment of the signal with amplitudes equal to or below that of the crude threshold. This refined threshold value then represents an estimate of the noise which accompanies the signal returning from the bladder re ⁇ gion and is used as the final threshold value for the border detection process.
• the next operation is noise cleaning or fil ⁇ tering.
• noise cleaning or fil ⁇ tering Before performing the actual thresholding op- eration, it is necessary to filter out as much of the noise in the returning signal as possible.
• a more conventional linear smooth- ing filter With low pass characteristics, would remove valuable information.
• a non-linear median fil ⁇ ter is used.
• Median filters are characterized by their ability to remove "spikey" noise, while leaving border information intact.
• the length of the median filter is chosen such that noise spikes with a base of less than 0.5 centimeter in width are removed.
• each ele ⁇ ment of the filtered signal vector is compared with the refined threshold value established earlier and des ⁇ cribed above.
• Each element with original amplitudes which are greater than or equal to the threshold value are set to a preset constant value, while the ampli- tudes of the other elements are set to zero.
• the A-line data is now transformed to a binary signal, with the zero amplitude elements representing the fluid filled bladder region.
• the front to back wall separation is estimated.
• the front wall is determined by locating the first element of the thresholded A-line with an amplitude value of zero.
• the back wall is determined by locating the first of a set of at least five consecutive non-zero values. The criterion for detecting the actual location of the back wall was developed experimentally to avoid inaccuracies due to reverberation.
• Block 40 represents the beginning or initializing of the border detection process.
• Block 41 represents the next operation in the process, the se ⁇ lection of the memory bank containing the data set associated with the ith line of data, or more conven- iently, the ith A line.
• the mean value mean( i ) of this data is computed as well as the standard deviation
• the ith A line is processed to determine a minimum amplitude value A m i n( i ) for the ith line of data.
• the line of data encompasses the distance from the pa ⁇ tient's abdomen to the back wall of the patient's blad ⁇ der.
• a rough threshold value T cruc j e ( i j is computed by adding
• the standard deviation is the square root of the mean of the squares of the differences of the individual data points relative to the mean value B ⁇ an ⁇ ) .
• a re * fined threshold value Trefnd(i) is then computed by adding Bmin ( i ) to Bsdev ( i ) .
• the refined threshold value is also shown in Figure 2 for that line of data.
• the next step, as shown in block 50, is to filter the data, to remove as much noise as possible without harming the signal itself.
• a conventional low pass filter is not used, since such a filter would remove valuable information from the signal.
• the median filter leaves the true signal information, such as the borders in Figure 2, intact.
• the operation of a median filter is discussed in detail in a book titled Digital Imaging Processing by W. Pratt, which is hereby incorporated by reference. Basically, a three point median filter proc- esses three consecutive bits of data at a time, begin ⁇ ning at the start of a data string. There is thus a filter window of three data elements.
• the value of the middle data point is replaced by the median value of the three data points.
• the filter window is then moved one data element along the data string, so that substantially each data point in the data string is processed three times by the filter. At the end of the filtering process, the noise spikes have been removed, leaving the border information in- tact.
• each data point in the A-line data set from the median filter is compared against the refined threshold value ⁇ refn d( i ) * *f tne amplitude of a particular data point is greater than the threshold value that data point is set to a predetermined high value, A const « ⁇ f fc h e amplitude of the data point is below the threshold value, the bit is set to zero.
• the first data point which is below the threshold re f n( 3 ( i ) (which is hence set to zero) indicates the presence of the front wall of the bladder. There will then be a string of zero data points which represents the bladder region.
• the next operation in the processing .of the i tn line of data is shown in block 54.
• the inter-wall distance between the front and back wall of the bladder is computed. This distance is stored in a second bank in the microprocessor memory with an associated software pointer to indicate which A-line this distance corresponds to.
• the above de ⁇ scribed process is then repeated for the next A-line data. The process is further repeated until all the A-lines have been processed.
• the information is then used with an appropriate geometric model and the estimated volume is computed.
• an ellipsoid of rotation is used as the geometric model.
• the resulting volumetric meas ⁇ urement is then displayed as a numerical amount on the front of the apparatus.

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• 1986
  • 1986-05-02 EP EP86903755A patent/EP0221994A1/de not_active Withdrawn
  • 1986-05-02 WO PCT/US1986/000969 patent/WO1986006606A1/en not_active Ceased

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