FR2488995A1 - EXAMINATION DEVICE USING DISPERSE RADIATION FOR DETERMINING INTERNAL STRUCTURES OF A BODY - Google Patents

Abstract

THE INVENTION RELATES TO A DEVICE FOR EXAMINATION BY MEANS OF A DISPERSED RADIATION SERVING TO DETERMINE THE INTERNAL STRUCTURE OF A BODY 5. THIS BODY IS, AS A COMPARISON BODY THAT CORRESPONDS TO IT, CROSSED BY A BEAM OF RAYS. LOW SECTION 3 PRIMARY WITH AT LEAST THREE DIFFERENT RADIATION ENERGIES IN ORDER TO STORE IN MEMORY PARASITE SIGNALS AND RESPECTIVE PARASITE COMPARISON SIGNALS. FOR EACH RADIATION ENERGY, THE PARASITIC SIGNALS AND THE PARASITIC COMPARISON SIGNALS ARE COMPARED WITH ONE TO THE OTHERS SO THAT WE OBTAIN A SYSTEM OF FORMULAS SHAPED AT LEAST THREE FORMULAS FOR THE QUOTIENT OF THE PARASITIC SIGNALS AND THE PARASITIC COMPARISON SIGNALS FROM WHICH WE CAN DETERMINE THE DISTRIBUTION OF BODY DENSITIES.

Description

"Device for examining by means of scattered radiation for

  the determination of internal structures of a body.

  The present invention relates to an examination device for determining internal structures of a body, comprising at least one source of radiation for producing a primary beam of rays of small cross section passing through the body and having at least three energies of

  separate radiation, at least one pre-slit diaphragm

  senses outside the path of the primary ray beam and having a slit-like opening which extends in a direction approximately transverse to the primary ray beam, a detector device extending transversely

  at the length of the slot and comprising separate detectors

  res for detecting stray radiation produced by the primary beam in the body and passing through the opening

  slot-shaped and an electronic device for processing

  and reproduction of detector signals.

  Such a device is described in the published German patent application OS 27 13 581. The device of this patent

  however, only produces representations that

  direct litatives, for example of layer images of a

  three-dimensional body without additional corrective measures

  shut up. If, for example, the attenuation of the radiation along the path taken by the primary beam or by the stray radiation must also be taken into account, the measurement values obtained by means of the device must be corrected according to the correction methods also described in the published German patent application OS 27 13

  581, which makes it necessary to use a caliper machine

digital culer.

  To correct a measurement of the surface area of the body, one begins for example by analyzing in this surface area the

  body a line whose stray radiation reaches the

  positive detector without being weakened or attenuated by an intermediate tissue. The parasitic radiation emitted by the first cell of this line is not yet subject to attenuation and can therefore be used directly as

  density measurement in this cell. A primary influence

  mayor reaching the second cell of this line is di-

  minuted of the energy converted into stray radiation in the first cell and, since this part is known by the measurement of the first cell, it is possible to take this into account by a corresponding increase in an output signal from the detector associated with the second cell, relative to the detector output signal associated with the first cell. For a third cell in this row,

  due account must be taken of the fact that

  blinding by the first two cells, etc. For a

  first cell of a following line, the primary radiation

  re is certainly not weakened either but the radiation

  rasitis from this cell is weakened by those

  cells of the previous line arranged between the slot and this cell. Since the weakening of the radiation by these cells is however already determined in the measurement

  previous, the measurement value associated with the first cell-

  the of the second line can be corrected according to

  this previous measurement. For the detector output signal

  tor which measures the parasitic radiation produced in the second cell of the second line must take into account on the one hand a weakening of the primary beam by the

  first cell of this line and on the other hand of the busi-

  stray radiation from neighboring cells. Using this correction method, internal regions of layers of the body can therefore only be reproduced fully corrected when the external regions of the layer of the body to be reproduced are also crossed by radiation. In addition, when using this correction method, only the stray radiation produced

  by the primary beam in the body and extending practi-

  that in the plane of the layer to be reproduced should be

  measured because the attenuation coefficients correspond

  weighting for image points separated from the layer image

  are not disturbed by regions with high absorption

  tion (bones, gas occlusions, etc.) possibly found

  outside the body layer to reproduce.

  The object of the invention is to provide a scattered radiation device for determining the internal structure of a body by means of which, without using such a correction method, it is possible to form images of layers.

  improved in a simplified way.

  - According to the invention, this object is achieved by the fact that each detector supplies detector output signals dependent on the energy of the incident radiation and is connected

  to an electronic circuit to form detection signals

  parasite from the separate primary radiation energies and the device is also equipped with a memory

  electronics for storage of parallel comparison signals

  sites which are recorded by the same examination device and in the same way using a known comparison body, the electronic memory being connected to the

  electronic processing which is equipped to compare if-

  parasitic signals and parasitic comparison signals for different radiation energies and for determining the internal structure of the body from parasitic signals and parasitic comparison signals thus compared

with each other.

  The parasitic signals (S) or the parasitic comparison signals (V) (radiation intensities) measured for radiation energy for a region of the body through which the primary beam passes, are, as already mentioned above, dependent on the density of the electrons in the region of the body,

  the weakening of the primary radiation in the body until

  that this region of the body and the weakening of the ray-

  parasitic in the body. These three quantities represent

  strangers. If the spurious signals are now compared

  res to the parasitic comparison signals which have been obtained beforehand from a known comparison body, for example by forming the quotient of the parasitic signal and the parasitic comparison signal and its logarithm (ln (S / V)), the three unknowns can be determined if this occurs for a point on the body each time for at least three different radiation energies. The corresponding quantities for the comparison body are then known. The comparison

  sound of a spurious signal with a spurious comparison signal

  you must however each time be carried out for the same radiation energy. In this way, a determination

  simple for example of the distribution of the density of the elect

  sections in the region of the body crossed by the primary beam and thus a reproduction for example of layered images of the body are possible when this is done for

  a large number of radiation paths, for example paral-

  lèles, located in the plane of the layer.

  These layer images no longer need to be corrected

  for the weakening of primary or parasitic radiation.

  In particular, a reproduction of qualitative layer images

  tatively good located inside a plane of the body is possible, that is to say that it is no longer necessary to measure the entire cutting plane of the body. Naturally, layer images of a body that are not located in

  a plan can also be produced.

  It is also advantageous that for example quantities

  like the sensitivity of the detectors, the dependence of the

  energy of multiple dispersion in the body etc. no longer have any influence on the quality of the reconstructed layer or body structure. When comparing spurious signals and spurious comparison signals,

  they cancel each other out if the body and the body

  parison are recorded in the same way with the same scattered radiation examination device, that is to say if they are crossed by the same primary radiation. The body and the comparison body should then as much as possible

look alike.

  According to an advantageous embodiment of the invention

  tion, the radiation source is made from an X-ray source or at least three gamma rays from

  different energy-emitting substances.

  This way, we can have a simple way

  of radiation comprising at least three ray energies-

different.

  In another embodiment of the invention, the

  detector device each time comprises several detectors

  teurs in a line passing through a detector and parallel to the main direction of extension of the shaped opening

slot.

  The stray radiation measured each time by a detector

  line detector (row of detectors) is then used for the determination of the internal structure of the body, for example the density of the electrons of the substance of the body

  on the corresponding region of the body emitting the ray-

  parasitic. The average of the electron densities thus obtained is then calculated. Strongly absorbent body structures, for example, can then be located between the activated region of the body and the detectors and

  can take this into account for example, when calculating the mo-

  yenne, by weighting the electron densities associated with the

  corresponding detector in the correct manner. Such a provision

  detector detector increases the accuracy of the

  truction. The image quality is further improved by measuring more of the stray photons emitted by the scattering center. By the fact that the linear detector as described in the German patent 2 713 581 has no local resolving power in the linear direction, no highly absorbent structure (bones, air occlusions)

  located between the activated body region and the device

  cannot be reconstructed and cannot be taken into account so that the density of electrons in the region

  activated body is not well reproduced here.

  Exemplary embodiments of the invention will be described

  below with reference to the accompanying drawings, in which:

  - Figure 1 is a cross-sectional view of the dis-

  positive test according to the invention;

  - Figure 2 is a block diagram for the processing-

  detector output signals each time for a detector; Figure 3 is a perspective view of the examination device, and - Figure 4 illustrates a device forming a source of

  radiation which has three sources of radiation

  different radiation energies.

  Figure 1 is a sectional view of an examination device

  men according to the invention. This device includes for example

  ple a source 1 of X-rays whose polychromic radiation

  tick is diaphragmed by means of a diaphragm 2 up to a

  primary beam 3 of thin cross section passing through

  pours a body 5 lying on a table 4. The primary beam 3 then follows a path of primary radiation which it defines itself. The parasitic radiation 6, 6 'produced in the

  region of the body 5 through which the primary beam 3 reaches

  each generate a respective detector device 9, 9 'through

  towards slot diaphragms 7, 7 ′ disposed respectively on either side of the primary beam 3, the openings in

  slot form 8, 8 'of these diaphragms which may preferably

  rence be moved in the direction of their width extending perpendicular to the primary beam 3. The detector devices 9, 9 'are formed by separate detectors 10, 10'

  which are located next to each other on a straight line

  te parallel to the primary beam 3. The detectors 10, 10 'can for example be arranged in strips and be arranged

  in such a way that their main extension direction-

  it is parallel to the slots 8, 8 '.

  For the analysis of various regions of the body, the body 5 and

  the examination device can be moved one by one

port to another.

  Each detector of the devices 9, 9 ′ provides information

  detector output signals I (E) dependent on energy E

  stray radiation hitting it. The energy E of the ray-

  parasite is then determined for a determinate energy

  mined E of primary radiation and for a dispersion angle

  6- determined that the stray radiation forms with the

  primary skin 3 according to the known Compton formula

  general. The position of the slit diaphragms 7, 7 ′ determines

  ne thus, for each point located on the primary beam 3,

  the angles 6 at which the stray radiation is measured.

  The extent to which stray radiation depends on energy is therefore only determined by the measurement in

  which primary radiation depends on energy.

  Figure 2 is a block diagram for processing detector output signals. A detector, for example

  the detector 10 is each time connected to an electric circuit

  Tronic 11 which, among the parasitic photons of different energies

  ferent arriving on the detector 10, which are produced from polychromatic X-rays, records parasitic photons for only three different energies, namely

  I (El), I (E2) and I (E3). From the output signals of the

  tectors associated each time with one of these ray energies-

  parasitic El, E2 and E3, we then form signals pa-

  rasites S (E1), S (E2), S (E3). The electronic circuit 11 can for this purpose comprise for example three circuits 12 forming an energy window which produce an output signal only when the input signal (detector output signal) is in a range of determined magnitude which corresponds

  to a predetermined energy range of the stray radiation.

  The output signals of the circuits 12 each time belonging to the same energy domain are then added for the production of parasitic signals S (E1), S (E2), S (E3) which

  can also take place in the electronic circuit 11.

  A spurious signal which is picked up by means of a detector can each time be represented in the following form S (El) N (El) dn El) 7k Eexp- p (El, ll) dl.lj r exP-jJu (El , 12) dl2 (1) This formula 1 is valid for all the energies El, E2, E3, etc. In this case, as already mentioned above, S (El) is the intensity of the radiation dispersed with the energy El, N (El) and the intensity of primary radiation outside

  of body 5 with the energy El, d ((El) / d flest the effective section

  differential space for the dispersion of primary radiation

  re Y k is the density of the electrons of the body 5 in the point

  P considered (see Fig. 1), the fourth term is

  blinding of the primary beam 3 between the ray source-

  ment 1 and the point P considered (path 11) and the fifth term is the weakening of the scattered radiation between the point P of the body and the detector measuring the radiation

parasite (path 12).

  For energies higher than 100 KeV, in the case of a biological matter, it is mainly the dispersion according to the coefficient of weakening y (see formula 1),

  which constitutes a contribution, which can be written in the manner

next re:

12 (E, 1) = 6 (E). <(1) (2)

  In this case 6- (E) is the cross section of total Klein-Nishina dispersion and f (1) is the density of the electrons

  which depends on the location.

  After using formula 2 in formula 1, the parasitic signals S (E1), S (E2), S (E3) are brought to an electronic calculating machine 13 to which the circuit

  electronic 11 is electrically connected and which is part of

  tie of the electronic processing device 14. To the electronic calculating machine 13 is simultaneously connected a

  electronic memory 15 in which are stored

  parasitic comparison signals V (El), V (E2), V (E3) which

  respond to parasitic signals S (E1), S (E2), S (E3) and which

  are registered under the same conditions as these,

  i.e. with the same radiation energies El, E2, E3, on

  a known comparison body corresponding to the body to be examined

  mine using the same examination device. The body of com-

  parison (not shown) can for example be a "hydro-

ghost".

  The comparison between parasitic signals and parasitic comparison signals in the calculating machine 13 is carried out in such a way that for each energy El, E2,

  E3, we form the quotient S (El) / V (El2) etc. from if

  parasitic general and a parasitic comparison signal and we take the logarithm. We therefore obtain a set of three formulas with three unknowns. The formula for scattered radiation at energy El is as follows: nk (El) nk _ (l) f- r '(11) - Y, (11) j dll- 6 (El) lnS V (El) = in útk (12) - Y, (12) 3 d12 (3)

  For E2 and E3, corresponding formulas are valid.

  The subscript k thus designates the body 5 to be examined while

  the index v denotes the comparison body.

  We can therefore determine from the system of formulas 3 (formulas for El, E2, E3) the density of the electrons Y'k each time for a point of the body P crossed by the primary beam 3. The densities of electrons' t ( 11) or Y (12) of the comparison body on the path il of the primary radiation or on the path 12 of the stray radiation are known and the same is true of the Klein-Nishina dispersion cross sections dO (El), e ( E1) (and correspondingly for the energies E2, E3). The energy of the scattered radiation El can, as mentioned above, be calculated using

  of the Compton formula from the energy El of the rayon-

  primary. Naturally, photons can also be

  detected for more than three radiation energies. The cir-

  electronic baking it should for this purpose simply be-

  ter other circuits 12 (or additional channels of a multiple channel). The system of formulas thus obtained would be

  then then minimized in the correct way.

  A detector 10, 10 ', etc. is therefore each time connected to an electronic circuit 11 of which only one is shown in FIG. 2, these circuits all being connected to the calculating machine 13. The memory 15 also contains the parasitic comparison signals for all the points located

  3.5 on the primary beam 3 passing through the comparator body

  his. The densities of Yek electrons determined by the calculating machine 13 or the quantities which are derived therefrom can then be reproduced on a monitor 16 or be stored in a mass memory 17 (magnetic tape, disk of

memory or equivalent).

  Figure 3 is a perspective view of the device

  with scattered radiation according to the invention. The diaphragm

  me in slot 7 has in this case a long opening in the form of slot 8 so that a scattered beam of rays 6 starting from the point P of the body and activated by the primary beam of rays 3 is produced by a very large angle of aperture ". This scattered ray beam 6 reaches a line of detectors which is formed of separate detectors 10a, b, etc. which are situated on a parallel to the opening in

  slot shape 8 perpendicular to the primary beam 3.

  The whole detector device 9 or the slit diaphragm

  7 can in an extreme case however also surround complete-

  The primary beam, for example in the form of a cylinder, the primary beam 3 then following the axis of the cylinder. Each detector separates from the detector device

  9 (in the form of a cylinder or a detector matrix

  two-dimensional sensors) is then connected to an electrical circuit

  clean cone 11 (not shown) via connections a to d etc. A quantity characterizing the internal structure of the body 5, for example the density of the electrons CPk ′ can then be derived each time by means

  a detector of the detector device. Election densities

  sections of the same line of detectors relate each time to the same point P in the body. From these densities, we can determine an improved electron density on the point P of the body for example by calculating a value

weighted average.

  It goes without saying that the detectors 10a, b etc. of a li-

  One of the detectors can also be replaced by one

  bar shaped detector which has a power of

  local solution in the direction of the line, so that the in-

  The intensity of the scattered radiation can be measured for different line sections (see Fig. 2). For this purpose, one can use for example scintillators in the form of bars comprising photomultipliers placed on the ends of the bar, whose output signals are processed according to the principle of Anger's camera. The length of the bar must then be parallel to the slot-shaped opening 8 or perpendicular to the primary beam 3. Another source of radiation 1 ′ for the emission of primary radiation having at least three different radiation energies is shown in Figure 4. The

  radiation source 1 'has three sources of radiation

  separated 18a-c emitting Y rays, for example each

  once 137Cs <0.66 MeV), 203 Hg (0.28 MeV) and 57Co (0.12 MeV). The three separate radiation sources 18a to c are for example inside a rotating disc 19 which has a radial channel 20 towards the outlet

  of radiation for each separate radiation source.

  The disc 19 rotates at a correct angular speed around an axis 21 so that the separate radiation sources 18a to c come one after the other in front

  an outlet opening 22 of a protective housing

  tre the radiation 23. The primary ray beam 24 passing each time through the outlet opening 22 is then collimated again by means of a diaphragm 25. The circuit

  electronics 11 in this case has three circuits 12 for-

  mant energy windows for example pulse height analyzers which are tuned on the energies of

  radiation from separate radiation sources 18a-c.

  Naturally, the separate radiation sources 18a to c can also be arranged in another way.

  correct compared to a spoke exit opening

  or can be moved, for example loosely

  born. As other sources of radiation, it is however also possible to use a mixture of the three aforementioned radiation emitting substances which is placed, for example, in the rotating disc 19 at the location of one of the sources of radiation.

radiation 18a to c.

Claims (8)

  1.- Examination device for the determination of struc-   internal tures of a body (5) comprising at least one radiation source (1,1 ') for producing a primary beam of rays of small cross section passing through the body   and having at least three distinct radiation energies   tes, at least one slit diaphragm (7) present outside the path of the primary beam of rays and having a   slot-shaped opening (8) which extends in one direction   roughly transverse to the primary beam (3), a detector device (9) extending transversely to the length of the slit and comprising separate detectors (10) for detecting stray radiation produced   by the primary beam in the body and crossing the opening   slot-like structure and an electronic device (14) for processing and reproducing detector signals, characterized in that each detector supplies detector output signals dependent on the energy of the incident radiation and is connected to a circuit electronics (11) to form parasitic detector signals S (El), S (E2), S (E3)) from the separate primary radiation energies (I (El), I (E2), I (E3)) and the device is further equipped with an electronic memory (15) for storing signals   comparison parasites (V (El), V (E2), V (E3)) which are recorded   managed by the same examination device and in the same way   re using a known comparison body, the elec- tric memory   tronic being connected to the electro- processing device   pic (14) which is equipped to compare parasitic signals   tes and the parasitic comparison signals (S (El), V (El);   S (E2), V (E2); S (E3), - V (E3)) for ray energies-   different and to determine the internal structure of the   body from spurious signals and com-   Parasitic parison thus compared to each other.   2.- Device according to claim 1, characterized in that the radiation source (1) is a source of X-rays.   3.- Device according to claim 1, characterized in that the radiation source comprises at least three   Y-ray emitting substances of different energies.   4.- Device according to claim 3, characterized in that three substances emitting Y-rays are arranged separate from each other and can be brought   one after the other in front of a collima-   tor (22, 25) to diaphragm a beam of primary rays re.   5.- Device according to claim 3 or 4, character-   laughed at in that the Y-ray emitting substances are   137Cs (0.66 MeV), 203Hg (0.28 MeV) and 57Co (0.12 MeV).   6.- Device according to claim 1, characterized in that the detector device (9) each time comprises several detectors (lOa, lOb) in a line passing through   a detector and parallel to the main extension direction   blade of the slot-shaped opening (8).   7.- Device according to claim 1, characterized in that the detectors comprise scintillators in the form of bars comprising photomultipliers placed on the ends of the bar and the length of the bar is   parallel to the main extension direction of the opening slit-shaped structure (8).   8.- Device according to any one of the claims   1 to 7, characterized in that the slit diaphragm (7)   and the detector device (9) surround in a cylindrical   that the primary beam of rays (3) which extends along of the cylinder axis.