Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
  • G21K1/00—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating
  • G21K1/02—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators
  • G21K1/04—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators using variable diaphragms, shutters, choppers
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
  • G21K1/00—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating
  • G21K1/02—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators
  • G21K1/04—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators using variable diaphragms, shutters, choppers
  • G21K1/043—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators using variable diaphragms, shutters, choppers changing time structure of beams by mechanical means, e.g. choppers, spinning filter wheels
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
  • G21K1/00—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating
  • G21K1/10—Scattering devices; Absorbing devices; Ionising radiation filters
• • 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
  • H05G1/36—Temperature of anode; Brightness of image power
• • 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
  • H05G1/60—Circuit arrangements for obtaining a series of X-ray photographs or for X-ray cinematography

Definitions

• the invention relates to a method for contrast equalization of X-ray photographs of a body having a locally varying transmission for X-ray radiation, made with an apparatus for slit radiography which is provided with a slit diaphragm, by means of which a body is scanned with a flat fan-shaped X-ray beam, and with at least one controllable absorption apparatus which interacts with the slit diaphragm and with which the fanshaped X-ray beam is influenced per sector, which absorption apparatus is controlled as a function of the quantity of radiation instantaneously transmitted per sector through the body in a manner such that the quantity of radiation transmitted in a particular sector through the absorption apparatus is reduced with an increasing value of the transmission of the body occurring instantaneously in said sector from a first threshold value upwards, and also an apparatus for slit radiography equipped for taking equalized X-ray photographs.
• a general problem in taking X-ray photographs is that the dynamic range of the radiation incident on the X-ray detector is larger than the dynamic range of the available image-forming means, in particular of X-ray film.
• X-ray photographs are necessary to be able to carry out a good investigation of the various parts of the thorax. If a photograph is taken which is such that the lungs are shown with a good contrast reproduction, it is usually almost impossible to distinguish the abdominal region any longer. If the photograph is taken, however, in a mannersuch that both the lungs and the abdominal region are clearly visible, the contrast reproduction is then unsatisfactory. All of this is also related to the choice of film, the method of development, and the setting of the X-ray tube.
• Dutch Patent Application 8401411 describes an apparatus for slit radiography, by means of which the thorax of a patient, or another part of the body or object to be examined, is scanned with a flat fan-shaped X-ray beam, transmitted by a slit diaphragm, in a direction which is transverse to the longitudinal direction of the slit of the slit diaphragm.
• an absorption apparatus which interacts with the slit diaphragm and which has absorption elements which, while the X-ray photograph is being taken, are instantaneously controlled under the influence of electrical signals generated by detection means which detect the quantity of radiation transmitted by the patient at every instant in every sector in order to match the quantity of radiation, which reaches the patient or the object, locally to the patient transmission at that point.
• the absorption elements are controlled in such a manner that, above a certain value of the quantity of X-ray radiation transmitted locally through the patient or the specimen, the associated absorption element(s) is (are) always brought to a state which corresponds to the exposure of the image-forming means associated with said particular value.
• the object of the invention is to meet said need and, in general, to provide a reliable and expedient method for contrast equalization of an X-ray image.
• a method of the type described is characterized in that, above the threshold value, a higher transmission value results to a predetermined extent in an essentially higher quantity of radiation transmitted through the body, at least in region of relevance for the X-ray photograph.
• An apparatus for slit radiography equipped for taking equalized X-ray photographs and comprising a combin tion of an X-ray source and a slit diaphragm for forming a flat fan-shaped X-ray beam by means of which a body can be scanned, an X-ray detector for collecting the radiation transmitted through the body, at least one absorption apparatus which is situated near the slit diaphragm and which can influence the quantity of X-ray radiation transmitted through the slit diaphragm instantaneously per sector of the fan-shaped beam under the influence of suitable regulating signals, detection means which detect the quantity of X-ray radiation instantaneously transmitted through the body per sector of the fan-shaped beam and deliver an input signal to a regulating apparatus which forms output signals acting as regulating signals for the absorption apparatus, which regulating apparatus is equipped to form, starting from a first threshold value of the quantity of radiation transmitted through the body in a particular sector, a regulating signal which controls the absorption apparatus in a manner such that the quantity of radiation
• Figure 1 shows diagrammatically an apparatus for slit radiography in side view
• Figure 2 shows an example of a suitable control circuit for controlling according to the invention absorption elements shown in Figure 1;
• Figure 3 shows a graph of the relationship between screen dosage and patient transmission, or film blackening, to illustrate the invention;
• Figures 4 and 5 show details of a modification of an apparatus according to the invention.
• Figure 1 shows diagrammatically an apparatus for slit radiography in side view.
• the apparatus shown comprises an X-ray source 1 with an X-ray focal point F.
• Placed in front of the X-ray source is a slit diaphram 2 by means of which a fairly flat, fan-shaped X-ray beam 3 which is directed at an X-ray detector 4 is formed.
• the X-ray beam 3 is somewhat wedge-shaped in side view, the height at the position of the X-ray detector is small, for example 3 cm, while the width of the beam perpendicular to the plane of the drawing may be, for example, 40 cm, so that, in general, reference is made to a flat X-ray beam.
• the X-ray source and the slit diaphragm are able to move together in a manner such that the X-ray beam performs a scanning movement transversely to the width direction of the beam, that is to say, vertically in the plane of the drawing, as indicated by a double arrow 5.
• a scanning movement can be achieved in a simplemanner by causing the combination of X-ray source and slit diaphragm to swivel about an axis extending transversely to the plane of the drawing through the X-ray focal point F as indicated by an arrow 6.
• a flat fan-shaped beam which performs a scanning movement can, however, also be obtained in another manner, such as, for example, specified in the Dutch Patent Application 8401411.
• the X-ray detector 4 is a conventional large-image cassette which is exposed stripwise in the vertical direction during the scanning movement of the X-ray beam. Instead of such a stationary large-image . cassette, it will also be possible to use a strip-type
• X-ray detector which converts the incident X-ray radiation into a strip-type light image which is used in turn to expose a photographic film.
• An example of such an application of a strip-type X-ray detector is shown in the Dutch Patent Application 8401411.
• X-ray detector is also regulated, an absorption apparatus 8 is placed near the slit diaphragm 2 in the X-ray beam.
• the absorption apparatus is equipped in a manner such that the quantity of radiation transmitted per sector of the X-ray beam and at every instant can be regulated under the influence of suitable regulating signals.
• an absorption apparatus comprising a number of tongues 9 placed next to each other, one of which can be seen, is shown in Figure 1.
• the tongues have free ends which, under the influence of regulating signals can be introduced into the X-ray beam to a greater or lesser extent in order to absorb part of the X-ray radiation.
• the regulating signals for the absorption apparatus are provided by a regulating circuit 10.
• the regulating circuit 10 receives input signals from a detection apparatus 11 which instantaneously detects the amount of X-ray radiation transmitted through the patient or the specimen 7 per sector of the fan-shaped X-ray beam and delivers corresponding electrical output signals.
• the detection apparatus may be situated between the patient or the object and the X-ray detector 4, as shown in Figure 1 but in principle it can also be situated behind the X-ray detector 4. In both cases the detection apparatus may respond either directly to incident X-ray radiation or to light radiation generated by the X-ray detector in response to incident X-ray radiation.
• the detection apparatus is situated between the patient or the specimen 7 and the X-ray detector 4, the detection apparatus should be as' transparent as possible for X-ray radiation so that the final X-ray image is influenced as little as possible by the detection apparatus.
• Suitable detection apparatuses are, for example, described in the Dutch Patent Application 8503152 and the Dutch Patent Application 8503153.
• FIG. 2 shows an example of a suitable regulating circuit 10 for application of the invention.
• the regulating circuit 10 forms a connection between the detection apparatus and the absorption apparatus and comprises in principle an associated sub—circuit for each set of corresponding sections of the detection apparatus and the absorption apparatus.
• said sub-circuits only one is shown and this will be termed regulating circuit below for the sake of simplicity. Attention is drawn to the fact that in practice some parts of the regulating circuit can be used jointly for all the sub-circuits by means of multiplex techniques.
• the regulating circuit shown in Figure 2 is essentially identical to the regulating circuit shown in the Dutch Patent Application 8401411.
• the regulating circuit 10 receives, on the one hand, input signals from a section of the detection apparatus via the conductor 20 and provides, on the other hand, output signals to a corresponding section of the absorption apparatus via a conductor 21.
• the regulating circuit comprises a comparator circuit, which in this example comprises a reference amplifier 23.
• a signal proportional to the input signal of the regulating circuit is fed to one input of the reference amplifier via a conductor 24 and a reference signal which is provided in the example shown by a potentiometer 25, is fed to the other input.
• the output signal of the amplifier 25 corresponds at least in polarity to the difference between the signals supplied to the two inputs.
• the output of the amplifier 23 is connected to the input of an amplifier 26 which may be a voltage amplifier or a current amplifier depending on the type of absorption apparatus used and which forms a suitable output signal for the control of the appropriate section of the absorption apparatus.
• This output signal controls the absorption apparatus in a manner such that the difference between the input signals of the reference amplifier is reduced to zero.
• the regulating circuit 10 furthermore comprises in addition an input amplifier 27, the output signal of which is supplied to the reference amplifier 23.
• the regulating circuit described hitherto corresponds to the circuit shown and described in the Dutch Patent Application 8401411.
• Figure 3 shows in the right-hand part the relationship between the patient transmission (or specimen transmission) T for X-ray radiation plotted along the horizontal axis and the screen dosage S plotted along the vertical axis.
• the screen dosage is the quantity of Xray r a d i a t i o n which reaches the X-ray detector.
• the left-hand part of Figure 3 shows the relationship between the screen dosage and the picture halftone resulting therefrom (optical density D) of an image on an X-ray film.
• the graph shown relates to a so-called reversal film which forms a faint image for a low exposure (after the film is developed) and which forms a dark image for a high exposure, and consequently for a high X-ray dosage.
• the invention is, however, equally applicable for the use of other types of film or other imageforming means.
• a thorax is furthermore also depicted diagrammatically for the purpose of illustration.
• the lung region is indicated by I and the abdominal region is specified by II.
• the lungs are the most transparent for X-ray radiation and the abdomen is the least transparent.
• the associated patient transmission ranges or the optical density ranges are also indicated by I and II in the graphs.
• the right-hand part of Figure 3 shows a number of characteristic curves 30, 31, 32 and 33.
• the characteristic curve 30 indicates the relationship between the patient transmission and the screen dosage if any form of influencing of the scanning X-ray beam is absent while a photograph is taken.
• the characteristic curve 30 is therefore essentially a straight line. It can be seen that the patient transmission in the abdominal region (hatched region II) corresponds to a screen dosage S 1 which in turn corresponds to a density range D 1 of the film used. Although the range D 1 does not fall completely within the optimum working range, indicated by W, of the film in which the film characteristic curve 34 shown is essentially linear, it is clear that the range S 1 corresponds to a relatively wide range D 1 so that the contrast reproduction in this range is good.
• the patient transmission in the lung region (hatched region I) is, on the other hand, much greater for the same setting of the X-ray source and corresponds to a screen dosage range S 2 which in turn corresponds to a density range D 2 .
• the screen dosage range S 2 is situated, however, far outside the optimum working range of the film so that, with a screen dosage in this range, overexposure of the film occurs. The result thereof is a very dark photograph with a very poor contrast reproduction in addition, as should be evident from the relatively small width of the range D 2 .
• Dutch Patent Application 8401411 is represented by the curve 31 which consists of a section 31a which approximately coincides with the straight line 30 and a section 31b which is situated beyond a point of inflection 31c and which essentially extends horizontally.
• the section 31a corresponds to a range of low patient transmission in which the absorption apparatus is not, or virtually not, in operation. Beyond the point of inflection 31c, however, the regulating loop formed by the detection apparatus, the regulating circuit, the absorption apparatus and the X-ray beam aims at an averaged picture halftone determined by the setting of the reference signal generator 25 ( Figure 2). If the sections of the absorption apparatus (and the sections of the detection apparatus) were to be infinitely small, such a regulation would result in a uniformly grey image. The sections of the absorption apparatus, however, each influence at any instant a region on the X-ray detector of dimensions which are not negligible, for example 4 x 4 cm. As a result thereof, contrast differences within such regions remain clearly visible in the final image.
• a regulation curve such as is shown at 32, the section of which beyond a point of inflection, which may again be the point of inflection 31c, has a slope which is between that of the straight line 30 and the horizontal part 31b of the curve 31. If such a regulation curve is used, the natural character of the final X-ray photograph is maintained because a larger patient transmission results in a greater film darkening, while no overexposure can nevertheless occur.
• the patient transmission range corresponding to the lung region I therefore corresponds in the case of curve 32 to a screen dosage range S 3 which falls within the working range W of the film and results in a film blackening in the density range D 3 .
• Such a regulation curve is obtained by not regulating the difference between the input signals of the reference amplifier completely to zero in the regulating circuit of Figure 2. All this can be achieved in practice by constructing the amplifier 26 with a gain control device 28.
• the set gain determines the slope of the regulation curve 32 beyond the point of inflection. More generally, the slope of the regulation curve 32 may be adjusted by a suitable adjustment of the loop gain in the circuit formed by the X-ray beam, the detection apparatus, the regulating circuit and the absorption apparatus.
• the X-ray source should obviously be adjusted in such a manner that even in the least transparent part of the patient or of the specimen a screen dosage still occurs which is such that this part and the contrast occurring therein can still be satisfactorily reproduced by the film.
• the regulating method described can also be modified in a manner such that the patient transmission range corresponding to the lung region I of a patient is reproduced within the working range W of the film with a better contrast reproduction than is the case for the regulation curve 32.
• the absorption apparatus can be constructed in a manner such that the absorption elements are able to influence the slit of the slit diaphragm only over a predetermined partof the height of the slit.
• This can be achieved, for example, by using a mechanical stop for the absorption elements which prevents the absorption elements completely shutting off the slit diaphragm.
• a similar effect can also be achieved in an electronic manner or by suit- able programming of a microprocessor controlling the absorption element.
• a suitable mechanical stop can be constructed in many ways depending on the type of absorption elements used. If pivoting tongue-like absorption elements or sliding elements are used, use may be made of a cord or the like which is connected to an absorption element and limits the deflection thereof. All this is shown in Figure 4. The cord is indicated by 40 in the stretched state and by 40' in the rest state. In Figure 4 it can be seen that the slit S of the slit diaphragm 2 always remains clear over a part "a" of the total height.
• a similar effect can be obtained by means of a stop 50, as shown in Figure 5. Since the stop is situated in front of the slit S, the stop has to be transparent to X-ray radiation.
• the stop may be constructed, for example, from perspex.
• a regulation curve of the type indicated at 33 in Figure 3 is produced.
• This curve comprises a first section 31a which coincides with that of the curve 31 in which the absorption apparatus is still not, or almost not, in operation and in which the screen dosage increases in proportion to the patient transmission.
• a sloping section 33a in which the absorption apparatus is in operation.
• the angle of slope of the section 33a can be adjusted in the manner already described.
• Figure 3 is suitably chosen, that is to say with a value of the patient transmission which is lower than the patient transmission in the lung region I, the screen dosage increases in proportion to the patient transmission in the entire lung region.
• the X-ray photograph has therefore a natural character both for the patient transmission values encountered in the abdominal region II and for the patient transmission vaIues encountered in the lung region I, at least if the X-ray film used is able to process the associated screen dosage values satisfactorily.
• the screen dosage range S 1 has already been discussed earlier and the screen dosage range S 3 ' which corresponds to the point of intersection of the curve 33 with the range of patient transmission values associated with the lung region I essentially falls within the working range W of the film. A good contrast reproduction is therefore ensured.
• the position of the range S 3 ' can be adjusted by the choice of the point of inflection 31c by adjusting the angle of slope of the curve 33 beyond the point of inflection 31c and by the choice of the stop point 31b (adjustment of the stop 40 or 50). It is pointed out, furthermore, that the angle of slope of the section 33a could be adjusted in a manner such that the section 33a coincides with the section 31b of the curve 31. In fact a system of the type described in the Dutch Patent Application 8401411 is then produced, a stop point for the absorption elements being provided electrically or mechanically.
• the section 33c of the curve 33 is drawn parallel to the straight line 30. Theoretically it is possible to give the section 33c a different angle of slope. A less steep gradient can be obtained by effecting a certain increase in the operation of the absorption apparatus beyond the stop point 33b. If a mechanical stop device is used, this could be achieved by dividing the mechanical stop device into sections which correspond to different absorption elements and by setting up the stop sections in a sprung manner so that displacement is possible under the influence of a force exerted by an absorption element. All this can be achieved in the configuration shown in Figure 4 by including a (tension) spring in the connection 40. In a similar manner, for example, a (compression) spring 51 can be used in the configuration of Figure 5.
• a steeper gradient of the part 33c can be obtained by causing the influence of the absorption apparatus, which is a maximum at the point 33b, to decrease again for screen dosage values which are higher than those associated with the stop point 33b.
• This effect can be achieved, for example, by means of a suitably programmed microprocessor or in an electronic manner.
• a microprocessor for regulating the absorption apparatus, it is possible to achieve a regulating curve which has more than one point of inflection and stop point.
• a similar effect can be obtained by using one or more additional absorption apparatuses which are controlled with separate regulating signals.
• a second absorption apparatus could be placed, for example, at the other side of the slit S and could have a point of inflection situated beyond the stop point 33b. Past such a point of inflection, a stop point could then also be created again. Such modifications are considered to fall within the scope of the invention.

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• Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Health & Medical Sciences (AREA)
• General Health & Medical Sciences (AREA)
• Toxicology (AREA)
• Apparatus For Radiation Diagnosis (AREA)
• X-Ray Techniques (AREA)

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Citations (7)

• 1987
  • 1987-04-02 NL NL8700781A patent/NL8700781A/nl not_active Application Discontinuation
• 1988
  • 1988-03-28 WO PCT/EP1988/000274 patent/WO1988007807A1/en active IP Right Grant
  • 1988-03-28 DE DE8888903228T patent/DE3877749T2/de not_active Expired - Fee Related
  • 1988-03-28 EP EP88903228A patent/EP0348433B1/en not_active Expired - Lifetime
  • 1988-03-28 JP JP63503038A patent/JP2651229B2/ja not_active Expired - Lifetime
  • 1988-03-29 IN IN259/CAL/88A patent/IN169731B/en unknown
  • 1988-04-01 IL IL85959A patent/IL85959A/xx not_active IP Right Cessation
  • 1988-04-02 CN CN88101717.5A patent/CN1032234C/zh not_active Expired - Fee Related

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