EP0001729A2 - Verfahren und Einrichtung zur Verbesserung des radiologischen Auflösungsvermögens eines röntgendiagnostischen Systems - Google Patents

Verfahren und Einrichtung zur Verbesserung des radiologischen Auflösungsvermögens eines röntgendiagnostischen Systems Download PDF

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Publication number
EP0001729A2
EP0001729A2 EP78400121A EP78400121A EP0001729A2 EP 0001729 A2 EP0001729 A2 EP 0001729A2 EP 78400121 A EP78400121 A EP 78400121A EP 78400121 A EP78400121 A EP 78400121A EP 0001729 A2 EP0001729 A2 EP 0001729A2
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EP
European Patent Office
Prior art keywords
voltage
bias voltage
cathode
value
tube
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.)
Granted
Application number
EP78400121A
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English (en)
French (fr)
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EP0001729B1 (de
EP0001729A3 (en
Inventor
Dang Tran Quang
Jacques Leguen
Jacques Delair
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.)
Compagnie Generale de Radiologie SA
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Compagnie Generale de Radiologie SA
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Publication date
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Publication of EP0001729A2 publication Critical patent/EP0001729A2/de
Publication of EP0001729A3 publication Critical patent/EP0001729A3/xx
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Publication of EP0001729B1 publication Critical patent/EP0001729B1/de
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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05G—X-RAY TECHNIQUE
    • H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
    • H05G1/08—Electrical details
    • H05G1/26—Measuring, controlling or protecting
    • H05G1/30—Controlling
    • H05G1/52—Target size or shape; Direction of electron beam, e.g. in tubes with one anode and more than one cathode
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J35/00—X-ray tubes
    • H01J35/02—Details
    • H01J35/14—Arrangements for concentrating, focusing, or directing the cathode ray
    • H01J35/147—Spot size control

Definitions

  • the present invention relates to a method and a device for improving radiological quality. or definition of the foci of X-ray tubes.
  • the quality of the image in radiology is linked, among other things, to the dimensions of the focal point of the X-ray tube.
  • the geometrical blur is all the lower the smaller the focal point.
  • the effective dimensions of the focal points can be determined by the pinhole method or by the modulation transfer function (FTM) method of test patterns.
  • FTM modulation transfer function
  • This second method has the advantage of also giving the electronic distribution at the focal surface.
  • the radiological quality of a focus of given nominal dimensions is also linked to the uniformity of this distribution.
  • a microdensitometric section of these radio-images shows on a densitogram two or more peaks and one or more very pronounced valleys, as shown in Figure 1 which represents diagrams of the distribution of incident electrons (N, number of electrons) in a cross section of the focus (X, distance from the focal point axis).
  • the dimensions measured by the pinhole method are always smaller than those determined by the FTM of the test patterns.
  • this last method is often applied by radiologists for the quality control of the hearths of X tubes.
  • manufacturers are obliged to sort the hearths or to replace the tubes until '' to customer satisfaction, resulting in a loss of time, money and reputation for the manufacturer's brand, despite the dimensional compliance of homes with most of the standards in force based on the pinhole method.
  • the dimensions of the foci can be reduced by applying a voltage to the concentrating part of the electron beam emitted by the filament constituted by a cup-shaped electrode surrounding the latter on the side opposite that opposite the target (anticathode). of negative polarization Vp.
  • Vp negative polarization
  • Figure 1 attached gives the width 1 and the electrical distribution tronic of the hearths of the same tube for several values V.
  • a fixed target X-ray tube having a cathode of substantially circular shape, indirectly heated and of large dimension (diameter) emitting towards the target, which is of comparable size, a large diameter electron beam.
  • the tube is surrounded by a focusing coil which acts on the concentration of the election beam in response to the current flowing through it. The periodic variation of this current causes a contraction and a periodic spreading of the flow of electrons striking the target so as to compensate for irregularities in the beam.
  • the X-ray tube also comprises an additional electrode, called a grid, of cylindrical or annular shape, placed approximately halfway between the cathode and the target, and surrounding the electron beam so as to act simultaneously on the concentration of the electron flow and on its intensity. Pulsed modulation of the grid bias voltage therefore acts on the current and the size of the hearth in the opposite direction.
  • a set of conventional deflection coils generating orthogonal magnetic fields also makes it possible to scan the target with the electron beam.
  • the cathode and the grid. are then equivalent to a rectifier diode, because the anode-cathode voltage is then negative and there is no anode current.
  • the grid bias voltage becomes all the more negative as the potential of the anode becomes positive, thus generating a relative stabilization of the current and of the dimensions of the focal point.
  • the object of the invention is to remedy the drawbacks of the constant polarization of the 3rd concentration part in a linear filament tube. end constituting the cathode. It allows, while keeping constant the overall dimensions, read in pinhole, to modify the electronic distribution of the focus so that the dimensions determined by the function of the transfer of modulation of test patterns can be adjusted to equal values, smaller or much smaller (up to 50%) than the dimensions determined by the pinhole method.
  • the method according to the invention is mainly characterized in that the biasing voltage of the concentrating part is periodically varied between a minimum negative value cu zero and a maximum negative value, with a frequency such that each operating time of the X-ray tube has a large number of periods of variation of the bias voltage.
  • the electron beams give rise to bars which can scan the entire focal surface, in order to ensure a substantially uniform electronic distribution to the focus.
  • the modulation frequency of the bias voltage is between 20 and 60 kilohertz.
  • the invention also relates to a device for implementing the method defined above.
  • FIGS. 1 (a) to 1 (e) the densitometric distribution curves of the electrons are shown respectively in the transverse direction of a linear focus, for several values of the DC bias voltage V p of the concentrating part. . It can be seen there that the width l at mid-height of the focal point and the spacing and the number of peaks (bars) vary appreciably as a function of the absolute value of the negative bias voltage.
  • Figure 1 (a) gives for a pulp tension V, a width l of 1.45 mm with four peaks (three minima) whose extremes have significant amplitudes.
  • Figure 1 (b) gives, for a voltage V p of - 100 V, a width of 1.09 mm with three peaks (two minima) of substantially equal heights.
  • Figure 1 (c) has been taken at a polarization voltage V p of - 200 V and it gives a width l of 0.91 mm with three peaks of lesser amplitude.
  • Figure 1 (d) gives, for a voltage V p of - 300 V, a width l of 0.78 mm with substantially two peaks of even lower amplitude
  • Figure 1 (e) gives, for a voltage V of - 400 V, a width l of 0.65mm with two peaks (maximum) delimiting a median trough (minimum), of reduced amplitudes.
  • the method of the invention consists in varying or modulating the bias voltage of the concentrator, negative with respect to the cathode, with a voltage waveform whose frequency is greater than 10 KHz and, preferably between 20 and 60 kHz.
  • a voltage waveform whose frequency is greater than 10 KHz and, preferably between 20 and 60 kHz.
  • the bias voltage will therefore vary between a minimum or zero negative value and a maximum negative value chosen experimentally.
  • FIG. 2 shows a method of producing a device for modulating the bias voltage of the concentrator for implementing the method according to the invention. It includes an amplifier 1, one input of which is supplied by the output of a signal generator 2, the amplitude, waveform and frequency of which can be varied, as required.
  • the other input of amplifier 1 receiving a continuous supply voltage, variable from a voltage source 13, makes it possible to vary the gain of amplifier 1 in order to adjust the peak-to-peak amplitude from there negative bias voltage of the concentrator.
  • the output of the amplifier 1 supplies the primary winding 31 of an isolation transformer 3 which isolates the amplifier 1 from the high-voltage part of the circuit while transmitting to it the AC component of its output signal.
  • the secondary winding 32 of the transformer 3 supplies a series circuit composed of a capacitor 4 and a diode 5, the anode of which is joined to one of the capacitor terminals 4 and the cathode of which is connected to one of the terminals of the secondary winding, the other terminal of the capacitor 4 being joined to the other terminal of this winding 32.
  • This series arrangement is equivalent to a half-wave peak rectifier which generates across the capacitor 4 a DC voltage substantially equal to the peak value of the AC voltage, with the positive pole at the junction of the capacitor 4 with the winding 32 and the negative pole at its junction with the anode of diode 5.
  • the cathode of diode 5 is therefore galvanically connected to the positive pole and its anode to the negative pole.
  • This rectified DC voltage is superimposed on the alternating voltage from the amplifier 1, which is transmitted by the capacitor 4 and appears substantially entirely at the terminals A and B of the diode 5.
  • the diode 5 also plays the role of a setting diode (known as "clamping" in Anglo-American literature) by making the positive peaks of the waveform coincide with the potential of the positive pole of the capacitor 4, because it only conducts when its anode is positive with respect to at his cathode.
  • a setting diode known as "clamping” in Anglo-American literature
  • the positive pole B of the variable or modulated negative polarization device is connected to the cathode of the X-ray tube 12, more precisely to the junction C of two filaments 7 and 8 because FIG. 2 shows a tube 12 with two foci.
  • the negative pole A of this device is then connected to the conventional concentrating part 6, in the form of a cup which surrounds the filaments 7, 8 on the sides opposite to that opposite the target.
  • the concentrating part 6 will then be subjected to a negative bias voltage with respect to the cathode C of the tube which will vary between a zero value and a maximum negative value - V pmax which is equal to the peak-to-peak value of the voltage waveform supplied by the secondary winding, the DC component of this bias voltage then being equal to the average value of the voltage between poles A and B.
  • V p of the concentrator may be desirable to vary the bias voltage V p of the concentrator between a minimum negative value - V pmin less than zero and a maximum negative value - V p max .
  • This can be obtained by inserting between terminals C (junction of filaments 7 and 8) and B (positive pole of the polarization device) a fixed DC voltage source (not shown) of low internal resistance, joined with its positive pole to the terminal C and with its negative pole at terminal B.
  • the peak-to-peak value of the voltage waveform at the bemes of winding 32 must then be equal to (V pmax - V pmin ).
  • the filaments 7, 8 are supplied in a conventional manner by a supply 10 which may include an isolation transformer and the adaptation and the anode and the cathode C of the tube 12 are respectively joined to the two poles of a very high supply -variable and controllable voltage with regard to the duration of its operation, called radiological generator.
  • a supply 10 which may include an isolation transformer and the adaptation and the anode and the cathode C of the tube 12 are respectively joined to the two poles of a very high supply -variable and controllable voltage with regard to the duration of its operation, called radiological generator.
  • the invention is in no way limited to the embodiments described and / or shown.
  • the modulation circuit described can be replaced by any other device making it possible to obtain the same output voltage.

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  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • X-Ray Techniques (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
EP78400121A 1977-10-21 1978-09-29 Verfahren und Einrichtung zur Verbesserung des radiologischen Auflösungsvermögens eines röntgendiagnostischen Systems Expired EP0001729B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR7731743 1977-10-21
FR7731743A FR2406890A1 (fr) 1977-10-21 1977-10-21 Procede et dispositif pour ameliorer la definition radiologique des foyers des tubes a rayons x

Publications (3)

Publication Number Publication Date
EP0001729A2 true EP0001729A2 (de) 1979-05-02
EP0001729A3 EP0001729A3 (en) 1979-08-08
EP0001729B1 EP0001729B1 (de) 1981-03-25

Family

ID=9196804

Family Applications (1)

Application Number Title Priority Date Filing Date
EP78400121A Expired EP0001729B1 (de) 1977-10-21 1978-09-29 Verfahren und Einrichtung zur Verbesserung des radiologischen Auflösungsvermögens eines röntgendiagnostischen Systems

Country Status (7)

Country Link
US (1) US4213048A (de)
EP (1) EP0001729B1 (de)
JP (1) JPS5484988A (de)
CA (1) CA1118115A (de)
DE (1) DE2860563D1 (de)
FR (1) FR2406890A1 (de)
IT (1) IT1159940B (de)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2129233A (en) * 1982-10-08 1984-05-10 Yokogawa Electric Works Ltd X-ray computerized tomograph
FR2687505A1 (fr) * 1992-02-13 1993-08-20 Gen Electric Cgr Circuit de chauffage de filaments de cathode d'un tube a rayons x.

Families Citing this family (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4685118A (en) * 1983-11-10 1987-08-04 Picker International, Inc. X-ray tube electron beam switching and biasing method and apparatus
US4764947A (en) * 1985-12-04 1988-08-16 The Machlett Laboratories, Incorporated Cathode focusing arrangement
US5007074A (en) * 1989-07-25 1991-04-09 Picker International, Inc. X-ray tube anode focusing by low voltage bias
US5535254A (en) * 1995-05-17 1996-07-09 Carlson; Todd R. X-ray tube with self-biasing deck
DE20218138U1 (de) 2002-11-21 2004-04-08 Heuft Systemtechnik Gmbh Röntgenanlage zur Erzeugung von kurzen Röntgenstrahlenimpulsen und mit einer solchen Röntgenanlage arbeitende Inspektionsvorrichtung
US8401151B2 (en) * 2009-12-16 2013-03-19 General Electric Company X-ray tube for microsecond X-ray intensity switching
US9224572B2 (en) 2012-12-18 2015-12-29 General Electric Company X-ray tube with adjustable electron beam
US9484179B2 (en) 2012-12-18 2016-11-01 General Electric Company X-ray tube with adjustable intensity profile

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2862107A (en) * 1951-04-06 1958-11-25 Gen Electric Means for and method of controlling the generation of x-rays
US3691417A (en) * 1969-09-02 1972-09-12 Watkins Johnson Co X-ray generating assembly and system
US3743836A (en) * 1972-02-22 1973-07-03 Machlett Lab Inc X-ray focal spot control system
US3992633A (en) * 1973-09-04 1976-11-16 The Machlett Laboratories, Incorporated Broad aperture X-ray generator

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2129233A (en) * 1982-10-08 1984-05-10 Yokogawa Electric Works Ltd X-ray computerized tomograph
FR2687505A1 (fr) * 1992-02-13 1993-08-20 Gen Electric Cgr Circuit de chauffage de filaments de cathode d'un tube a rayons x.

Also Published As

Publication number Publication date
EP0001729B1 (de) 1981-03-25
DE2860563D1 (en) 1981-04-16
FR2406890A1 (fr) 1979-05-18
EP0001729A3 (en) 1979-08-08
JPS5484988A (en) 1979-07-06
IT1159940B (it) 1987-03-04
CA1118115A (fr) 1982-02-09
IT7828853A0 (it) 1978-10-18
FR2406890B1 (de) 1980-09-12
US4213048A (en) 1980-07-15

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