CA1107407A - Device for computer tomography - Google Patents
Device for computer tomographyInfo
- Publication number
- CA1107407A CA1107407A CA303,633A CA303633A CA1107407A CA 1107407 A CA1107407 A CA 1107407A CA 303633 A CA303633 A CA 303633A CA 1107407 A CA1107407 A CA 1107407A
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- ray source
- ray
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- ray detector
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/42—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment with arrangements for detecting radiation specially adapted for radiation diagnosis
- A61B6/4275—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment with arrangements for detecting radiation specially adapted for radiation diagnosis using a detector unit almost surrounding the patient, e.g. more than 180°
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/02—Devices for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
- A61B6/03—Computerised tomographs
- A61B6/032—Transmission computed tomography [CT]
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/06—Diaphragms
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- Engineering & Computer Science (AREA)
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- Surgery (AREA)
- Animal Behavior & Ethology (AREA)
- General Health & Medical Sciences (AREA)
- Pulmonology (AREA)
- Theoretical Computer Science (AREA)
- Apparatus For Radiation Diagnosis (AREA)
- Analysing Materials By The Use Of Radiation (AREA)
Abstract
30.1.78 ABSTRACT:
A device for computer tomography in which a pa-tient to be examined is irradiated in different directions by a flat, fan-shaped beam of X-rays which is generated by an X-ray source having a comparatively small emissive surface area. The locally transmitted radiation is measur-ed by means of an X-ray detector comprising a series of de-tection elements which are arranged on an arc of a circle and which have a comparatively small radiation entrance surface area. A computer is used to calculate the density distribution of the irradiated part of the patient on the basis of the measuring data. During an examination, the X-ray source and the X-ray detector rotate in opposite direc-tions about a common axis of rotation which extends trans-versely of the plane of the fan-shaped beam. The distance between the radiation entrance surfaces of the detection elements and the axis of rotation equals the distance be-tween the emissive surface of the X-ray source and the axis of rotation. Because the X ray source and the X-ray detector rotate in opposite directions, the patient to be examined is scanned by the X-ray source and a detection element in mutually substantially parallel, consecutive paths. Differences in the sensitivity of detection ele-ments do not become manifest as annular interference pat-terns in the calculated density distribution.
A device for computer tomography in which a pa-tient to be examined is irradiated in different directions by a flat, fan-shaped beam of X-rays which is generated by an X-ray source having a comparatively small emissive surface area. The locally transmitted radiation is measur-ed by means of an X-ray detector comprising a series of de-tection elements which are arranged on an arc of a circle and which have a comparatively small radiation entrance surface area. A computer is used to calculate the density distribution of the irradiated part of the patient on the basis of the measuring data. During an examination, the X-ray source and the X-ray detector rotate in opposite direc-tions about a common axis of rotation which extends trans-versely of the plane of the fan-shaped beam. The distance between the radiation entrance surfaces of the detection elements and the axis of rotation equals the distance be-tween the emissive surface of the X-ray source and the axis of rotation. Because the X ray source and the X-ray detector rotate in opposite directions, the patient to be examined is scanned by the X-ray source and a detection element in mutually substantially parallel, consecutive paths. Differences in the sensitivity of detection ele-ments do not become manifest as annular interference pat-terns in the calculated density distribution.
Description
PHN. 3803.
The invention relates to a device for comput r tomography, comprising an X-ray source for generatin~ a flat, fan-shaped beam of X-rays, and an X-ray detector comprising a series of detection elements which are arranged on an arc of a circle, said X-ray source and X-ray detector being rotatable about a common axis of rotation which is directed transversely of the plane of the fan-shaped beam.
; A device of this kind is particularly suitable for X-ray diagnosis. During such an examination, a part of the body of a patient is irradiated by the flat, fan-shaped beam from different directions. Locally trans-mitted radiation is measured and, using the measuring data thus obtained, a computer calculates the density distribution of the part of the body of the patient in the irradiated plane, the result being displayed, for example, on a television monitor.
A device of the described kind is known from Netherlands Patent Application No. 7,503,520 by EMI
; 20 Limited which was filed on March 24, 1975 and laid open to public inspection on September 25, 1975. This spec-ification describes a device in which use is made of a flat, fan-shaped beam of X-rays which completely encloses the part of the body to be examined in at least one direction. In order to obtain an adequate number of measuring data, the X-.` '~' ~' ' ` P~ 8803 30.1.78 ray source and the X-ray detector rotate together about the patient which is arranged in the vicinity of a common axis of rotation, The device comprises means to compensate for the effect exerted on the measuring signals by dif-ferences in the sensitivity of the various detection elements.
The X-ray ~ource and the X-ray detector of the kno~n device rotate together around the axis of rotation at a uniform speed during examination. The output signals of the detection elements are integrated over a short period of time in order to obtain reliable measurements, the X-ray source and the X-ray detector rotating through a small angle of, for example 1 during said period of time. Subsequently, the logarithms of the intensity measurements are determined. During examination, each detection element thus supplies a set of logarithms of the intensities of X radiation transmitted by the patient in different directions. During the examination, these data are stored in a first electronic memory and, after completion of exannination, they are sorted according to sets of logarithms, originating from different detection elements, of the intensities of X-radiation transrnitted in parallel directions. The sorted sets are stored in a second electronic memory. Subsequently, the density of each picture point in the irradia-ted plane of the part of the body examined is calculated by means of a recon-struction techni~ue, which means that the data of the ~7~Q~
30.1.78 sorted sets which cover the relevant picture point are summed.
In the known device, the occurrence of disturb~
ing ring-like interference patterns in the display of the calculated density distribution, referred to as ring artefacts, is suppressed by compensation of the dif-ferences in sensitivity of the detection elements. To ~ this end, a fast movement of the X-ray source is sepa-; rately superposed on the uniform, common rotary movement of X-ray source and X-ray detector, so that each measure-ment by each detection element is repeated by a neigh-bouring detection element during examin~tion. On the basis of the measurements thus obtained, the detection elements are compared with each other and differences in sensiti-vity are compensated Ior; for this purpose, an addi-tional electrollic processing network is included.
The present invention has for its object to provide a device for computer to-nography in which on ths ; one hand differences in the sensitivity of detection elements do not become manifest in the occurrence of ring artefacts, whereas on the other hand each detec-tion element provides, d-uring the examination, a set ; of measurements of the intensity of the X-radiation transmitted in parallel directions, so that the sort- ¦
ing of the measurements af`ter termination of the exami~
nation can be dispensed wi-th. To this end, the de-~ice for computer tomography in accordance with the inven-.
~' I
-; - 4 PI~N 8803 30.1.78 tion is characterized in that the X~ray source has a com-paratively small emissive surface area, the detection elements having a comparatively small radiation entrance surface area, the distan.ce betl~een the radiation entrance surf`ace of the detection elements and the axis of rota-tion being substantially equal to the distance bet~een the emissive surface of the X-ray source and the axis of ro-tation, the X-ray source and the X-ray detector being . rotatable about the axis of rotation with a substantial-.: 10 ly equal angular velocity, but in an opposite sense.
During operation, the output signals of th.e detection elements are integrated over a shor-t period O r time in order to achieve adecluate measuring accuracy, the X ray source and the X-ray detector being rotated through. a small angle of, for example, 1 during said period o~
time. Because the X-ray source and the X-ray detec-tor move in opposite directions, the part of the bocly to be examined is scanned by the X-ray source and a detection elemellt in mutually substantially parallel, consecutive 20 . paths. This means that each calculation of the density in each picture point of the irradiated plane includes - a measurement by each detection element. ~s a result, interference patterns in the display of the calculated density distribution, caused by differences in the sen~
sitivity of the detection elements, cannot occur. The said ring artefacts are thus avoided.
~. preferred enlbodiment of the device for com-, :` :
30.l.78 .
':
puter tomography in accordance with the inventio-n is characterized in that the X-ray detector consists of a closed circle array of detection elements. As a result, sets of measurements of the intensity of the X-radiation transmitted in parallel directions can be determined for all directions in the plane of examination~
One embodiment in accordance with the in~rention will be described in detail hereinafter, by way of exam-ple, with reference to the accompanying diagrammatic drawing.
Fig. 1 is a diagrammatic longitudinal sectional ; view of a device for computer tomography in accordance with the invention;
; Fig. 2 is a diagrammatic cross-sect:Lonal view of the device shown in Fig. 1, taken along the line II - II;
i~ Fig. 3 shows a circuit diagram o~ a device for ':' ' comp~lter tomography in accordance with the invention;
Fig. 4 diagrammatically S~lOWS the position of the X-ray source and a detection element with respect to each other at successive instants;
Fig. 5 diagrammatically shows an Y-ray detec-tor which is particularly suitable for use as a detector element, and Fig. 6 illustra-tes Ihe scanning possibilities offerad ~y the device shos~ll in the Figs. 1 and 2.
Fi gs, 1 and 2 are a di.agramrnE~ t L c l ongi ta di nal ; - 6 .
30.1.78 sectional view and a diagrammatic cross-sectional view, respectively, of the same device for computer tomography in which a patient 1, resting on patient table 2, is ir-radiated by a flat, fan-shaped beam of X-rays 3. The beaM
' 5 of X-rays 3 has an angle of aperture, referred to herein-- after as fan angle ~ , of, for example, 30 in the plane of the drawing of` Fig. 2, and is comparatively flat in " the direction perpendicularly thereto, its thickness be-' ing approximately 10 mm. The fan angle is so large that the beam 3 encloses the entire patient 1 in the fan direc-tion. The X-ray beam is generated by an X~ray tube 4, comprising a rotary anode (not shown)~, Because the emis-sive surface of th,e rotary anode (the actual X-ray source) is comparatively small, its length and its width being approximately 2 mm, the X-ray source may be considered to be point-shaped ~rom a radiation-technical point of view. The radiation transmitted by the patient is measur-ed by an X-ray detector 5 which comprises a series of, '~ for example, 400 detection elements 6 which are arrang-ed on a circle. The detection elements 6, to be describ-ed hereina~ter and to be considered to be point-shaped -- f`rom a radi,ation-technical point of view consiclering the comparatively smal.l dimensiorls, comprise, for example, a scintil,]ation crystal and a light detector. The X-ray tube 4 is mounted on a ring 7 which is journalled on wheels 10 which are secured to the housing 9 alld which is rotatable, by means o~ a drive motor 12, abcut an axis 7~ ~7 PHN 8803 30.1.78 ' :
14 whieh extends transversely of the plane of the fan-shaped beam 3, The aetual X-ray source - the emissive surface of the rotary anode - rotates in a circular path 15. The X-ray deteetor 5 is connected to a ring 8 which is journalled on wheels 11 connected to the housing 9 and which is rotatable about the axis 14 by means of a drive motor 13. The ring 7 and the ring 8 rotate in op-posite directions during an examination. The detection elements 6 rotate in a oircular path~ the radius of which is substantially equal to the radius of the cir-eular path 15 in which the actual X-ray source xotates;
the radii are, for example, 90 cm and 85 cm, respective-ly. The processing of the measuring data will be describ-ed in detail herinaftel with reference to F:ig. 3.
~; l5 Fig. 3 diagrammatically shows a device of the ;::
described kind, with a patient 20, an X-ray source 21 and an X-ray detector 22 wbich comprises a series of cle-tection elements ~3 which are arranged on a circle The X-ray source 21 and the detection elements 23 rotate in opposite directions during an examination, in the same circular path 24 in a first approximation. ~ll detec-tion e]ements are connected, even thougll this is shown for only three elements, to an integration circuit 2~
in which the measuring signals of the detection elements 23 are integrated over a short period of tine of, for example, 10 ms in order to ach:ieve adecluate measurillg accuracy. Because the X-ray source 21 and the X-ray de-P~IN 8803 30.1.78 tector 22 move in opposite direetions, the part of the body 20 to be examined is scar~led in mutually suhstan-tially parallel, consecutive paths as shown in Fig. 4~
: in which the posi.tion Or the X-ray source 21 and one de-tection element 23 is indi.cated with respect to each other a1 consecutive instants ta, tb, t , ... th. The X-ray source 21 and the X-ray detector 23 in first ap-proximation follow the same circular path 24 during the examination, so that the distance between the X~ray source and a detection element ch.anges during the examin.ation, with the result that the intensities measured by the de-tection elements change during the examination, indepen-dent of the local. absorption of the patient. These changes are eorrected in the circuits 26. ~fter correc-tion., the logari.thms of` the measuri.ng signals of the detection ele-ments are determi.ned in logarithrnic ampl.ifie:rs 27 and the signals thus treated are stored in a memory 28. Thus, dur-ing examination each detecti.on el.ement 23 produces a set of logarithms of the intensities of X-radiation trans--mitted i.n substantia].ly parallel directions th.rougll the pati.ent. ~fte:r completion. Or -the examination, th.e com-puter 29 calculates, by way of a reconstruct:ion techn:ique, the c1ensity distributio:n of -the irradiatecl part of the body 20; th.is :is disp1.a~ed~ for exarnple, o n a te]e~-isi.on monitor 30.
Fi.g~ 5 diagramlllatical]y S110WS a:n X-~ay deiec-; tor 31 whi.ch is particular]y sui-tabLe for use as a de-. 9 ~0 7 ~ ~ P~ 8803 . 30.1.7~
tection element in the described device for computer tomography. The detector 31 comprises a cylindrical scin-tillator 32, having a diameter of, for example, 5 mm and a length of, for example, 20 mm, and a light detector 33 which is axially coupled thereto. The two bea.ms of` ~-rays 34 and 3~, diagrammatically shown and inciden-t on the de tector from dif`ferent directions, are detected in the same manner due to the cylinder-s-ymmetry thereof. Thi.s property renders the detector particularly su:itab.~e for said application, because the direction of the X-rad:i.a-tion incident on a d.etecti.on element continuously changes during the examinatic)n. This change i.s independent of the .. local absorption of thc patient and, therefore, i.t should not influence the measuri.n.g signal 1~ Subsequently, the scannlng possibiliti.es of the described devi.ce will be elaborated wi.th reference to Fig. 6. Therein, the circle ~l1 denotes the path to be followed by a poi.nt-shaped X~ray source 42 and an X-ray detector 43 comprising a series of detection elements 4-4~ The position of the X-ray source /12 is shown at three instants, i.e~ a.t the beginning of the examinati.on t = 0, at the end OL the examilla1ion t = T, and at an :instant i therebetween. The posi-ti.on of the detector 43 is shown ; at -t = 0. During the exami.Ilt.ltion~ the source moves a-t an
The invention relates to a device for comput r tomography, comprising an X-ray source for generatin~ a flat, fan-shaped beam of X-rays, and an X-ray detector comprising a series of detection elements which are arranged on an arc of a circle, said X-ray source and X-ray detector being rotatable about a common axis of rotation which is directed transversely of the plane of the fan-shaped beam.
; A device of this kind is particularly suitable for X-ray diagnosis. During such an examination, a part of the body of a patient is irradiated by the flat, fan-shaped beam from different directions. Locally trans-mitted radiation is measured and, using the measuring data thus obtained, a computer calculates the density distribution of the part of the body of the patient in the irradiated plane, the result being displayed, for example, on a television monitor.
A device of the described kind is known from Netherlands Patent Application No. 7,503,520 by EMI
; 20 Limited which was filed on March 24, 1975 and laid open to public inspection on September 25, 1975. This spec-ification describes a device in which use is made of a flat, fan-shaped beam of X-rays which completely encloses the part of the body to be examined in at least one direction. In order to obtain an adequate number of measuring data, the X-.` '~' ~' ' ` P~ 8803 30.1.78 ray source and the X-ray detector rotate together about the patient which is arranged in the vicinity of a common axis of rotation, The device comprises means to compensate for the effect exerted on the measuring signals by dif-ferences in the sensitivity of the various detection elements.
The X-ray ~ource and the X-ray detector of the kno~n device rotate together around the axis of rotation at a uniform speed during examination. The output signals of the detection elements are integrated over a short period of time in order to obtain reliable measurements, the X-ray source and the X-ray detector rotating through a small angle of, for example 1 during said period of time. Subsequently, the logarithms of the intensity measurements are determined. During examination, each detection element thus supplies a set of logarithms of the intensities of X radiation transmitted by the patient in different directions. During the examination, these data are stored in a first electronic memory and, after completion of exannination, they are sorted according to sets of logarithms, originating from different detection elements, of the intensities of X-radiation transrnitted in parallel directions. The sorted sets are stored in a second electronic memory. Subsequently, the density of each picture point in the irradia-ted plane of the part of the body examined is calculated by means of a recon-struction techni~ue, which means that the data of the ~7~Q~
30.1.78 sorted sets which cover the relevant picture point are summed.
In the known device, the occurrence of disturb~
ing ring-like interference patterns in the display of the calculated density distribution, referred to as ring artefacts, is suppressed by compensation of the dif-ferences in sensitivity of the detection elements. To ~ this end, a fast movement of the X-ray source is sepa-; rately superposed on the uniform, common rotary movement of X-ray source and X-ray detector, so that each measure-ment by each detection element is repeated by a neigh-bouring detection element during examin~tion. On the basis of the measurements thus obtained, the detection elements are compared with each other and differences in sensiti-vity are compensated Ior; for this purpose, an addi-tional electrollic processing network is included.
The present invention has for its object to provide a device for computer to-nography in which on ths ; one hand differences in the sensitivity of detection elements do not become manifest in the occurrence of ring artefacts, whereas on the other hand each detec-tion element provides, d-uring the examination, a set ; of measurements of the intensity of the X-radiation transmitted in parallel directions, so that the sort- ¦
ing of the measurements af`ter termination of the exami~
nation can be dispensed wi-th. To this end, the de-~ice for computer tomography in accordance with the inven-.
~' I
-; - 4 PI~N 8803 30.1.78 tion is characterized in that the X~ray source has a com-paratively small emissive surface area, the detection elements having a comparatively small radiation entrance surface area, the distan.ce betl~een the radiation entrance surf`ace of the detection elements and the axis of rota-tion being substantially equal to the distance bet~een the emissive surface of the X-ray source and the axis of ro-tation, the X-ray source and the X-ray detector being . rotatable about the axis of rotation with a substantial-.: 10 ly equal angular velocity, but in an opposite sense.
During operation, the output signals of th.e detection elements are integrated over a shor-t period O r time in order to achieve adecluate measuring accuracy, the X ray source and the X-ray detector being rotated through. a small angle of, for example, 1 during said period o~
time. Because the X-ray source and the X-ray detec-tor move in opposite directions, the part of the bocly to be examined is scanned by the X-ray source and a detection elemellt in mutually substantially parallel, consecutive 20 . paths. This means that each calculation of the density in each picture point of the irradiated plane includes - a measurement by each detection element. ~s a result, interference patterns in the display of the calculated density distribution, caused by differences in the sen~
sitivity of the detection elements, cannot occur. The said ring artefacts are thus avoided.
~. preferred enlbodiment of the device for com-, :` :
30.l.78 .
':
puter tomography in accordance with the inventio-n is characterized in that the X-ray detector consists of a closed circle array of detection elements. As a result, sets of measurements of the intensity of the X-radiation transmitted in parallel directions can be determined for all directions in the plane of examination~
One embodiment in accordance with the in~rention will be described in detail hereinafter, by way of exam-ple, with reference to the accompanying diagrammatic drawing.
Fig. 1 is a diagrammatic longitudinal sectional ; view of a device for computer tomography in accordance with the invention;
; Fig. 2 is a diagrammatic cross-sect:Lonal view of the device shown in Fig. 1, taken along the line II - II;
i~ Fig. 3 shows a circuit diagram o~ a device for ':' ' comp~lter tomography in accordance with the invention;
Fig. 4 diagrammatically S~lOWS the position of the X-ray source and a detection element with respect to each other at successive instants;
Fig. 5 diagrammatically shows an Y-ray detec-tor which is particularly suitable for use as a detector element, and Fig. 6 illustra-tes Ihe scanning possibilities offerad ~y the device shos~ll in the Figs. 1 and 2.
Fi gs, 1 and 2 are a di.agramrnE~ t L c l ongi ta di nal ; - 6 .
30.1.78 sectional view and a diagrammatic cross-sectional view, respectively, of the same device for computer tomography in which a patient 1, resting on patient table 2, is ir-radiated by a flat, fan-shaped beam of X-rays 3. The beaM
' 5 of X-rays 3 has an angle of aperture, referred to herein-- after as fan angle ~ , of, for example, 30 in the plane of the drawing of` Fig. 2, and is comparatively flat in " the direction perpendicularly thereto, its thickness be-' ing approximately 10 mm. The fan angle is so large that the beam 3 encloses the entire patient 1 in the fan direc-tion. The X-ray beam is generated by an X~ray tube 4, comprising a rotary anode (not shown)~, Because the emis-sive surface of th,e rotary anode (the actual X-ray source) is comparatively small, its length and its width being approximately 2 mm, the X-ray source may be considered to be point-shaped ~rom a radiation-technical point of view. The radiation transmitted by the patient is measur-ed by an X-ray detector 5 which comprises a series of, '~ for example, 400 detection elements 6 which are arrang-ed on a circle. The detection elements 6, to be describ-ed hereina~ter and to be considered to be point-shaped -- f`rom a radi,ation-technical point of view consiclering the comparatively smal.l dimensiorls, comprise, for example, a scintil,]ation crystal and a light detector. The X-ray tube 4 is mounted on a ring 7 which is journalled on wheels 10 which are secured to the housing 9 alld which is rotatable, by means o~ a drive motor 12, abcut an axis 7~ ~7 PHN 8803 30.1.78 ' :
14 whieh extends transversely of the plane of the fan-shaped beam 3, The aetual X-ray source - the emissive surface of the rotary anode - rotates in a circular path 15. The X-ray deteetor 5 is connected to a ring 8 which is journalled on wheels 11 connected to the housing 9 and which is rotatable about the axis 14 by means of a drive motor 13. The ring 7 and the ring 8 rotate in op-posite directions during an examination. The detection elements 6 rotate in a oircular path~ the radius of which is substantially equal to the radius of the cir-eular path 15 in which the actual X-ray source xotates;
the radii are, for example, 90 cm and 85 cm, respective-ly. The processing of the measuring data will be describ-ed in detail herinaftel with reference to F:ig. 3.
~; l5 Fig. 3 diagrammatically shows a device of the ;::
described kind, with a patient 20, an X-ray source 21 and an X-ray detector 22 wbich comprises a series of cle-tection elements ~3 which are arranged on a circle The X-ray source 21 and the detection elements 23 rotate in opposite directions during an examination, in the same circular path 24 in a first approximation. ~ll detec-tion e]ements are connected, even thougll this is shown for only three elements, to an integration circuit 2~
in which the measuring signals of the detection elements 23 are integrated over a short period of tine of, for example, 10 ms in order to ach:ieve adecluate measurillg accuracy. Because the X-ray source 21 and the X-ray de-P~IN 8803 30.1.78 tector 22 move in opposite direetions, the part of the body 20 to be examined is scar~led in mutually suhstan-tially parallel, consecutive paths as shown in Fig. 4~
: in which the posi.tion Or the X-ray source 21 and one de-tection element 23 is indi.cated with respect to each other a1 consecutive instants ta, tb, t , ... th. The X-ray source 21 and the X-ray detector 23 in first ap-proximation follow the same circular path 24 during the examination, so that the distance between the X~ray source and a detection element ch.anges during the examin.ation, with the result that the intensities measured by the de-tection elements change during the examination, indepen-dent of the local. absorption of the patient. These changes are eorrected in the circuits 26. ~fter correc-tion., the logari.thms of` the measuri.ng signals of the detection ele-ments are determi.ned in logarithrnic ampl.ifie:rs 27 and the signals thus treated are stored in a memory 28. Thus, dur-ing examination each detecti.on el.ement 23 produces a set of logarithms of the intensities of X-radiation trans--mitted i.n substantia].ly parallel directions th.rougll the pati.ent. ~fte:r completion. Or -the examination, th.e com-puter 29 calculates, by way of a reconstruct:ion techn:ique, the c1ensity distributio:n of -the irradiatecl part of the body 20; th.is :is disp1.a~ed~ for exarnple, o n a te]e~-isi.on monitor 30.
Fi.g~ 5 diagramlllatical]y S110WS a:n X-~ay deiec-; tor 31 whi.ch is particular]y sui-tabLe for use as a de-. 9 ~0 7 ~ ~ P~ 8803 . 30.1.7~
tection element in the described device for computer tomography. The detector 31 comprises a cylindrical scin-tillator 32, having a diameter of, for example, 5 mm and a length of, for example, 20 mm, and a light detector 33 which is axially coupled thereto. The two bea.ms of` ~-rays 34 and 3~, diagrammatically shown and inciden-t on the de tector from dif`ferent directions, are detected in the same manner due to the cylinder-s-ymmetry thereof. Thi.s property renders the detector particularly su:itab.~e for said application, because the direction of the X-rad:i.a-tion incident on a d.etecti.on element continuously changes during the examinatic)n. This change i.s independent of the .. local absorption of thc patient and, therefore, i.t should not influence the measuri.n.g signal 1~ Subsequently, the scannlng possibiliti.es of the described devi.ce will be elaborated wi.th reference to Fig. 6. Therein, the circle ~l1 denotes the path to be followed by a poi.nt-shaped X~ray source 42 and an X-ray detector 43 comprising a series of detection elements 4-4~ The position of the X-ray source /12 is shown at three instants, i.e~ a.t the beginning of the examinati.on t = 0, at the end OL the examilla1ion t = T, and at an :instant i therebetween. The posi-ti.on of the detector 43 is shown ; at -t = 0. During the exami.Ilt.ltion~ the source moves a-t an
2~ uniform angular ~eloci.ty ~, so the tOt~l]. anglllar dis-p].acement of the source and the detector is ~'.T. The fan angle GC of the X-ray beam is determined by a di.a-~1~740~7 3 0 . 1 . 7 8 , grammati.cally shown collimator 45 which moves wi.th the source so that the centre of the beam of X-rays is always directed OlltO t'he centre M of the circle ~l1. During the exarrlination, the detection elements produce sets o~
measurements o~ the intensity of X-radiation transmitted by the patient in mutually parallel directions, the direc-tiOIl bei.ng s~ uated be-tween the diagrammatically shown.
X-rays 46 a.d 47. These two rays enclose the examination angle 0. In the tri.angle determined by the source posi-tions a-t the instants t = 0 and t = T and the intersec-tion o~ the rays 46 and 1l7, it carl be simply seen that ~/ T = C~ + ~. Because radi.at:ion is rneasured only in '; Inutually parallel dlrecti.ons s:i.tuated between the ex-trelne rays 46 and 47, thc X-ray bea1n is shielded, ex-cept f`or the ray 46 at the instant t = 0, and except for the ray 47 at -the instant t. = T, by the aperture 48 whicl moves wi.th the source. ~s a resu.1.t, the radiat:ioIl dose whereto the patient is exposed i.s substantia].ly reduc--ed. The ape:rture performs only a trarlsl.atory rnovement~
~rom left to right in ]?igure 6, so that the aperture angle ~ is equal to ~, as can be readily seen. Durillg th.e examination, the detcctor 43 follows -the ci.rcular path /11 in the indicated di.recti.on at an ang~lar vel.o c:ity ~ . OuriIlg the time T, the de-tection elelrlent wllich measures the ray 47 a-t the :i.nstant t = T completes the angl.e ~,~ T In order to enable t}~e exa.min.ation, a de--tector is reqllired who.se detectio:rl angle ~ equals 30.1.78 ~J ,T + a, for which ~ = 360 - ~. T - 2(1~0- C~
~ = W .T - 2 ~ (as can be seen i.n Figo 6), so that - ~ = 2 ( ~.T ~ ~ ) = 2 ~. .
The foregoing illustrates that, in order to perform an examination througll ~ = 180 at a fan angle = 60 , the X-ray source and the detector must be rotat-', ed through an angle ~.T = 240 in opposite directions, a detector having a detection angle ~ = 360 -th.el~ being re-quired. A moving aperture 38 then preferably has an aper-ture angle ~ = 180 . It is to be noted that, i.f the cle-tection angle ~ = 3~0, the examination an6rle i.s i,ncreas-ed to ~ = 360 by using each detection elelrlent l,L3 twice, ~) .T then being 420.
' For.~ exami.nation angles ~ of 180 and more, the X-ray tube 4 and the X-ray detector 5 of Figs. 1 and 2 cannot move i.n the same circular path in practice, but they can move in circular paths whosc radi.i differ by a few centimeters. During an examination, each detect:ion element then supplies - at the same angular velocity of source and detec-tor - a set o* measurements,oI` the in-tensity oI` the radiation -transmitted by the patient in a number of directions w]-lich. are not exactly m-u-tuall.y paral.l.el. This non-para]leli,ty is so smal:L for a I`an angle of approxilnately 30 and a length of the radii of the circulax pat:lls of approximately 100 cm, -tl)at the effect thereof on the calculation of tlle dells:ities in the irradi.ated plane is negligibl.y srnall.. Correctioll, ,:,. ' ~ 12 -~
30.1~78 if desired, is possible by rnaking the X-ray source, mov-in the smallest circular path, rotate slightly faster than the X~ray detector.
For a fan angle ~ = 30, on]y an angle of 60 ; 5 of the detection elernents 44 of Fig. 6 is being used at any instant, so that the examinatio~ can be accelerated by using, ~or example, three or five X-ray sources which are arranged on the circle 41 accordillg to a regular triangular or pentagon.
. , .
measurements o~ the intensity of X-radiation transmitted by the patient in mutually parallel directions, the direc-tiOIl bei.ng s~ uated be-tween the diagrammatically shown.
X-rays 46 a.d 47. These two rays enclose the examination angle 0. In the tri.angle determined by the source posi-tions a-t the instants t = 0 and t = T and the intersec-tion o~ the rays 46 and 1l7, it carl be simply seen that ~/ T = C~ + ~. Because radi.at:ion is rneasured only in '; Inutually parallel dlrecti.ons s:i.tuated between the ex-trelne rays 46 and 47, thc X-ray bea1n is shielded, ex-cept f`or the ray 46 at the instant t = 0, and except for the ray 47 at -the instant t. = T, by the aperture 48 whicl moves wi.th the source. ~s a resu.1.t, the radiat:ioIl dose whereto the patient is exposed i.s substantia].ly reduc--ed. The ape:rture performs only a trarlsl.atory rnovement~
~rom left to right in ]?igure 6, so that the aperture angle ~ is equal to ~, as can be readily seen. Durillg th.e examination, the detcctor 43 follows -the ci.rcular path /11 in the indicated di.recti.on at an ang~lar vel.o c:ity ~ . OuriIlg the time T, the de-tection elelrlent wllich measures the ray 47 a-t the :i.nstant t = T completes the angl.e ~,~ T In order to enable t}~e exa.min.ation, a de--tector is reqllired who.se detectio:rl angle ~ equals 30.1.78 ~J ,T + a, for which ~ = 360 - ~. T - 2(1~0- C~
~ = W .T - 2 ~ (as can be seen i.n Figo 6), so that - ~ = 2 ( ~.T ~ ~ ) = 2 ~. .
The foregoing illustrates that, in order to perform an examination througll ~ = 180 at a fan angle = 60 , the X-ray source and the detector must be rotat-', ed through an angle ~.T = 240 in opposite directions, a detector having a detection angle ~ = 360 -th.el~ being re-quired. A moving aperture 38 then preferably has an aper-ture angle ~ = 180 . It is to be noted that, i.f the cle-tection angle ~ = 3~0, the examination an6rle i.s i,ncreas-ed to ~ = 360 by using each detection elelrlent l,L3 twice, ~) .T then being 420.
' For.~ exami.nation angles ~ of 180 and more, the X-ray tube 4 and the X-ray detector 5 of Figs. 1 and 2 cannot move i.n the same circular path in practice, but they can move in circular paths whosc radi.i differ by a few centimeters. During an examination, each detect:ion element then supplies - at the same angular velocity of source and detec-tor - a set o* measurements,oI` the in-tensity oI` the radiation -transmitted by the patient in a number of directions w]-lich. are not exactly m-u-tuall.y paral.l.el. This non-para]leli,ty is so smal:L for a I`an angle of approxilnately 30 and a length of the radii of the circulax pat:lls of approximately 100 cm, -tl)at the effect thereof on the calculation of tlle dells:ities in the irradi.ated plane is negligibl.y srnall.. Correctioll, ,:,. ' ~ 12 -~
30.1~78 if desired, is possible by rnaking the X-ray source, mov-in the smallest circular path, rotate slightly faster than the X~ray detector.
For a fan angle ~ = 30, on]y an angle of 60 ; 5 of the detection elernents 44 of Fig. 6 is being used at any instant, so that the examinatio~ can be accelerated by using, ~or example, three or five X-ray sources which are arranged on the circle 41 accordillg to a regular triangular or pentagon.
. , .
Claims (4)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A device for computer tomography, comprising an X-ray source for generating a flat, fan shaped beam of X-rays, and an X-ray detector comprising a series of detec-tion elements which are arranged on an arc of a circle, said X-ray source and X-ray detector being rotatable about a common axis of rotation which is directed transversely of the plane of the fan-shaped beam, characterized in that the X-ray source has a comparatively small emissive surface area, the detection elements having a comparatively small radiation entrance surface area, the distance between the radiation entrance surface of the detection elements and the axis of rotation being substantially equal to the distance between the emissive surface of the X-ray source and the axis of rotation, the X-ray source and the X-ray detector being rotatable about the axis of rotation with substantially the same angular velocity, but in an oppo-site sense.
2. A device for computer tomography as claimed in Claim 1, characterized in that the X-ray detector consists of a closed circle array of detection elements.
3. A device for computer tomography as claimed in Claim 1 or 2, characterized in that the device comprises a number of X-ray sources which are arranged on an arc of a circle.
PHN. 8803.
PHN. 8803.
4. A device for computer tomography as claimed in Claim 1, characterized in that the device comprises an electronic circuit for correcting variations of measur-ing signals of a detection element by variation of the distance between the detection element and the X-ray source during the rotation about the axis of rotation.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL7705788A NL7705788A (en) | 1977-05-26 | 1977-05-26 | DEVICE FOR COMPUTER TOMOGRAPHY. |
| NL7705788 | 1977-05-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1107407A true CA1107407A (en) | 1981-08-18 |
Family
ID=19828617
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA303,633A Expired CA1107407A (en) | 1977-05-26 | 1978-05-18 | Device for computer tomography |
Country Status (11)
| Country | Link |
|---|---|
| JP (1) | JPS53147493A (en) |
| BE (1) | BE867413A (en) |
| BR (1) | BR7803296A (en) |
| CA (1) | CA1107407A (en) |
| DE (1) | DE2822089A1 (en) |
| ES (1) | ES470148A1 (en) |
| FR (1) | FR2391698A1 (en) |
| GB (1) | GB1603593A (en) |
| IT (1) | IT1095910B (en) |
| NL (1) | NL7705788A (en) |
| SE (1) | SE7805837L (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103860190A (en) * | 2013-04-15 | 2014-06-18 | 上海杰瑞高新技术有限公司 | X ray detection and 3D (three-dimensional) imaging device |
| CN116919432A (en) * | 2023-09-18 | 2023-10-24 | 四川大学华西第二医院 | Medical imaging equipment based on mobile DR |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2921820C2 (en) * | 1979-05-29 | 1983-12-29 | Siemens AG, 1000 Berlin und 8000 München | Layering device for the production of transverse layer images |
| JPS5738023A (en) * | 1980-08-20 | 1982-03-02 | Tokyo Electric Power Co Inc:The | Level detecting method of phase pulse signal |
| FR2578643B1 (en) * | 1985-03-07 | 1990-03-09 | Siderurgie Fse Inst Rech | CROSS-SECTION THICKNESS PROFILE MEASUREMENT ASSEMBLY |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5444597B2 (en) * | 1974-03-23 | 1979-12-26 |
-
1977
- 1977-05-26 NL NL7705788A patent/NL7705788A/en not_active Application Discontinuation
-
1978
- 1978-05-18 CA CA303,633A patent/CA1107407A/en not_active Expired
- 1978-05-20 DE DE19782822089 patent/DE2822089A1/en not_active Withdrawn
- 1978-05-23 IT IT23714/78A patent/IT1095910B/en active
- 1978-05-23 GB GB21386/78A patent/GB1603593A/en not_active Expired
- 1978-05-23 BR BR7803296A patent/BR7803296A/en unknown
- 1978-05-23 SE SE7805837A patent/SE7805837L/en unknown
- 1978-05-23 JP JP6154578A patent/JPS53147493A/en active Granted
- 1978-05-24 ES ES470148A patent/ES470148A1/en not_active Expired
- 1978-05-24 BE BE187984A patent/BE867413A/en unknown
- 1978-05-25 FR FR7815571A patent/FR2391698A1/en active Granted
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103860190A (en) * | 2013-04-15 | 2014-06-18 | 上海杰瑞高新技术有限公司 | X ray detection and 3D (three-dimensional) imaging device |
| CN116919432A (en) * | 2023-09-18 | 2023-10-24 | 四川大学华西第二医院 | Medical imaging equipment based on mobile DR |
| CN116919432B (en) * | 2023-09-18 | 2023-12-05 | 四川大学华西第二医院 | Medical imaging equipment based on mobile DR |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS53147493A (en) | 1978-12-22 |
| NL7705788A (en) | 1978-11-28 |
| IT7823714A0 (en) | 1978-05-23 |
| BE867413A (en) | 1978-11-24 |
| JPS6251622B2 (en) | 1987-10-30 |
| IT1095910B (en) | 1985-08-17 |
| BR7803296A (en) | 1979-01-23 |
| ES470148A1 (en) | 1979-02-01 |
| SE7805837L (en) | 1978-11-27 |
| FR2391698A1 (en) | 1978-12-22 |
| FR2391698B1 (en) | 1983-07-08 |
| DE2822089A1 (en) | 1978-12-14 |
| GB1603593A (en) | 1981-11-25 |
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