CA2464827A1 - Method and system of determining depth of interaction in a scintillation camera - Google Patents
Method and system of determining depth of interaction in a scintillation camera Download PDFInfo
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- CA2464827A1 CA2464827A1 CA 2464827 CA2464827A CA2464827A1 CA 2464827 A1 CA2464827 A1 CA 2464827A1 CA 2464827 CA2464827 CA 2464827 CA 2464827 A CA2464827 A CA 2464827A CA 2464827 A1 CA2464827 A1 CA 2464827A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/16—Measuring radiation intensity
- G01T1/161—Applications in the field of nuclear medicine, e.g. in vivo counting
- G01T1/164—Scintigraphy
- G01T1/1641—Static instruments for imaging the distribution of radioactivity in one or two dimensions using one or several scintillating elements; Radio-isotope cameras
- G01T1/1644—Static instruments for imaging the distribution of radioactivity in one or two dimensions using one or several scintillating elements; Radio-isotope cameras using an array of optically separate scintillation elements permitting direct location of scintillations
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/16—Measuring radiation intensity
- G01T1/20—Measuring radiation intensity with scintillation detectors
- G01T1/208—Circuits specially adapted for scintillation detectors, e.g. for the photo-multiplier section
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Abstract
An apparatus for measuring a depth-of-interaction of a scintillation event in a scintillation camera having a scintillation crystal and an array of photomultiplier tubes is disclosed. The apparatus comprises (a) a collimator coupled to and along the lateral surface of the scintillation crystal for receiving scintillation photons traveling parallel to the plane of the scintillation crystal when a scintillation event occurs, (b) a light deflector optically coupled to and along the lateral surface of the scintillation crystal with the collimator sandwiched between the scintillation crystal and the light deflector for deflecting the direction of the scintillation photons received through the collimator to a certain angle, and (c) a position sensitive photomultiplier tube for detecting the deflected scintillation photons and determining the depth of the scintillation event within the scintillation crystal.
Description
METHOD AND SYSTEM OF DETERMINING DEPTH OF
Field of the Invention The invention relates generally to a scintillation camera, and more specifically an apparatus and method for determining a depth of interaction associated with a scintillation event in a scintillation camera.
Background of the Invention Scintillation cameras are well known in the art of nuclear medicine, and are used for medical diagnostics. A
patient ingests, inhales~or is injected with a small quantity of-a radioactive isotope. The radioactive isotope emits radiations that are detected by a scintillation medium in the scintillation camera. The scintillation medium is commonly a sodium iodide crystal, BGO or other.
The scintillation medium emits a small flash or scintillation of light, in response to stimulating radiation, such as from a patient. Th.e intensity of the scintillation of light is proportional to the energy of the stimulating radiation, such as a gamma ray.
A conventional scintillation camera (or a gamma camera) includes a detector, which converts into electrical signals gamma rays emitted from a patient after radioisotope has been administered to the patient: The detector includes a scintillation crystal and an array of photomultiplier tubes. The gamma rays are directed to the scintillation crystal, which absorbs the gamma rays and produces, in response, a very small flash of light (scintillation photons). The array of photomultiplier tubes, which are placed in optical communication with the scintillation crystal,, convert these flashes into electrical signals which are subsequently processed. The signal processing enables the camera to.produce an image of the distribution of the radioisotope within the patient.
When a gamma ray is absorbed in the scintillation crystal, a fraction of the deposited energy is emitted as scintillation photons which have wavelengths within the visible spectrum.TBecause the scintillation photons are emitted isotropically from the point of absorption, only a small amount of the emitted photons reach the photomultiplier tubes. The fraction of the total amount of photons reaching the photomultiplier tubes that produces an electrical signal in any one of photomultiplier tubes is' dependent on the position of that photamultiplier tube relative to the location of the scintillation event, local variations. in physical properties of the crystal, reflective surfaces, other transparent media such as light guides, and the interfaces between all of these materials.
The photomultiplier tubes and their associated electronic circuits determine the coordinate position of each scintillation event relative to the plane of the scintillation crystal and each scintillation intensity or energy. Generally, a glass light guide is coupled between the tubes and the scintillation crystal to help spread the light between tubes to improve positioning. As the thickness of the scintillation crystal increases, the degree of uncertainty as to the exact location of the scintillation event, i.e., the depth within the crystal, increases. In general, the photomultiplier tubes respond to each scintillation with a two-dimensional generally bell-shaped curve where the apex corresponds to the coordinate location of the scintillation event and the area under the curve denotes the energy. It has been found that when the scintillation event occurs on the radiation receiving face, i.e., the face furthest from the photomultiplier tubes, the curve is relatively shallow and wide; whereas, when the scintillation event occurs on the rear face of the scintillation crystal closest to the photomultiplier tube plane, the curve is more sharply pealed and narrower.. The __ ._. _ _ . ._ _._ _ ___ _widtl~ _~r _dif-fus-ivi.t-y-.øf-_the _respons_e_provide~__arL indication.
of the depth within the scintillation crystal at which the scintillation event occurred. This depth-of-interaction (DOI) information can be used in various data correction techniques to improve the resultant images.
Specifically, the measurement of the spatial location of a gamma ray absorption event (scintillation event) in the scintillation crystal has been limited to a two-dimensional point in the X, Y plane of the crystal.
However, because the number of scintillation photons reaching each PMT is dependent on the sol~.d.angle subtended by the area of that PMT to the point of the gamma ray absorption within the crystal, the amount of scintillation photons received by each PMT is also a function of the depth of interaction (DOI) of the incident gamma ray within the crystal, i.e., along the Z axis of the crystal. The DOT
is an important parameter when applied to imaging detector geometries in which the directions from which incident gamma rays impinge upon the crystal are not all substantially normal to the crystal surface. If incident gamma rays intersect the crystal from directions not normal to the crystal, the unknown depth of interaction of those gamma rays within the crystal will result in an additional uncertainty in the measured position of the interaction because of the parallax effect, if only a two dimensional (i.e., X, Y) spatial location is calculated for such an absorption event.
Therefore, there exists a need for a scintillation (gamma) camera, which is capable of measuring not only the spatial location of scintillation events in a scintillation crystal in terms of X, Y coordinates, but which is also capable of measuring the depth of interaction of the event within the crystal in the Z axis direction, so.as to improve the accuracy and performance of the imaging function.
Summarv of the Invention According to one aspect of the present invention, there is provided an apparatus for measuring a depth-of-interaction of a scintillation event in a scintillation camera having a scintillation crystal. and an array of photomultiplier tubes. The apparatus comprises (a) a collimator coupled to and along the 7.ateral surface of the scintillation crystal for receiving scintillation photons traveling parallel to the surface of the scintillation crystal when a scintillation event occurs, (b) a light deflector optically coupled to and a7.ong the lateral surface of the scintillation crystal with the collimator sandwiched between the scintillation crystal and the light deflector for deflecting the direction of the scintillation photons received through the collimator to a certain angle, and (c) a position sensitive photomuZ.tiplier tube for detecting the deflected scintillation photons and determining the depth of the scintillation event within the scintillation crystal.
The light deflector includes a light-deflecting mirror, or a right angle prism. The position sensitive photomultiplier tube includes a plurality of photodetectors, each responding to photons incident from its corresponding depth of interaction within the 5 scintillation crystal.
According to another aspect of the invention, there is provided a method for measuring a depth-of-interaction of a scintillation event in a scintillation camera having a scintillation crystal and an array of photomultiplier q0 tubes. The method comprises steps of (a) detecting scintillation phatons travelling parallel to the plane of the scintillation crystal when a scintillation event occurs; and (b) determining the depth of interaction within the scintillation crystal by using a position sensitive photodetector.
The method can further comprise a step of deflecting the scintillation photons to a certain degree for facilitating the detection of the photons.
Other aspects and advantages of the invention, as well as the structure and operation of various embodiments of the invention, will become apparent too those ordinarily skilled in the art upon review of the following description of the invention in conjunction. with the accompanying drawings.
Brief Description of the Drawings Embodiments of the invention will be described with reference to the accompanying drawings, wherein:
Fig.l is a perspective view of a horizontal cross-section of a scintillation camera combined with an apparatus according to the invention;
Field of the Invention The invention relates generally to a scintillation camera, and more specifically an apparatus and method for determining a depth of interaction associated with a scintillation event in a scintillation camera.
Background of the Invention Scintillation cameras are well known in the art of nuclear medicine, and are used for medical diagnostics. A
patient ingests, inhales~or is injected with a small quantity of-a radioactive isotope. The radioactive isotope emits radiations that are detected by a scintillation medium in the scintillation camera. The scintillation medium is commonly a sodium iodide crystal, BGO or other.
The scintillation medium emits a small flash or scintillation of light, in response to stimulating radiation, such as from a patient. Th.e intensity of the scintillation of light is proportional to the energy of the stimulating radiation, such as a gamma ray.
A conventional scintillation camera (or a gamma camera) includes a detector, which converts into electrical signals gamma rays emitted from a patient after radioisotope has been administered to the patient: The detector includes a scintillation crystal and an array of photomultiplier tubes. The gamma rays are directed to the scintillation crystal, which absorbs the gamma rays and produces, in response, a very small flash of light (scintillation photons). The array of photomultiplier tubes, which are placed in optical communication with the scintillation crystal,, convert these flashes into electrical signals which are subsequently processed. The signal processing enables the camera to.produce an image of the distribution of the radioisotope within the patient.
When a gamma ray is absorbed in the scintillation crystal, a fraction of the deposited energy is emitted as scintillation photons which have wavelengths within the visible spectrum.TBecause the scintillation photons are emitted isotropically from the point of absorption, only a small amount of the emitted photons reach the photomultiplier tubes. The fraction of the total amount of photons reaching the photomultiplier tubes that produces an electrical signal in any one of photomultiplier tubes is' dependent on the position of that photamultiplier tube relative to the location of the scintillation event, local variations. in physical properties of the crystal, reflective surfaces, other transparent media such as light guides, and the interfaces between all of these materials.
The photomultiplier tubes and their associated electronic circuits determine the coordinate position of each scintillation event relative to the plane of the scintillation crystal and each scintillation intensity or energy. Generally, a glass light guide is coupled between the tubes and the scintillation crystal to help spread the light between tubes to improve positioning. As the thickness of the scintillation crystal increases, the degree of uncertainty as to the exact location of the scintillation event, i.e., the depth within the crystal, increases. In general, the photomultiplier tubes respond to each scintillation with a two-dimensional generally bell-shaped curve where the apex corresponds to the coordinate location of the scintillation event and the area under the curve denotes the energy. It has been found that when the scintillation event occurs on the radiation receiving face, i.e., the face furthest from the photomultiplier tubes, the curve is relatively shallow and wide; whereas, when the scintillation event occurs on the rear face of the scintillation crystal closest to the photomultiplier tube plane, the curve is more sharply pealed and narrower.. The __ ._. _ _ . ._ _._ _ ___ _widtl~ _~r _dif-fus-ivi.t-y-.øf-_the _respons_e_provide~__arL indication.
of the depth within the scintillation crystal at which the scintillation event occurred. This depth-of-interaction (DOI) information can be used in various data correction techniques to improve the resultant images.
Specifically, the measurement of the spatial location of a gamma ray absorption event (scintillation event) in the scintillation crystal has been limited to a two-dimensional point in the X, Y plane of the crystal.
However, because the number of scintillation photons reaching each PMT is dependent on the sol~.d.angle subtended by the area of that PMT to the point of the gamma ray absorption within the crystal, the amount of scintillation photons received by each PMT is also a function of the depth of interaction (DOI) of the incident gamma ray within the crystal, i.e., along the Z axis of the crystal. The DOT
is an important parameter when applied to imaging detector geometries in which the directions from which incident gamma rays impinge upon the crystal are not all substantially normal to the crystal surface. If incident gamma rays intersect the crystal from directions not normal to the crystal, the unknown depth of interaction of those gamma rays within the crystal will result in an additional uncertainty in the measured position of the interaction because of the parallax effect, if only a two dimensional (i.e., X, Y) spatial location is calculated for such an absorption event.
Therefore, there exists a need for a scintillation (gamma) camera, which is capable of measuring not only the spatial location of scintillation events in a scintillation crystal in terms of X, Y coordinates, but which is also capable of measuring the depth of interaction of the event within the crystal in the Z axis direction, so.as to improve the accuracy and performance of the imaging function.
Summarv of the Invention According to one aspect of the present invention, there is provided an apparatus for measuring a depth-of-interaction of a scintillation event in a scintillation camera having a scintillation crystal. and an array of photomultiplier tubes. The apparatus comprises (a) a collimator coupled to and along the 7.ateral surface of the scintillation crystal for receiving scintillation photons traveling parallel to the surface of the scintillation crystal when a scintillation event occurs, (b) a light deflector optically coupled to and a7.ong the lateral surface of the scintillation crystal with the collimator sandwiched between the scintillation crystal and the light deflector for deflecting the direction of the scintillation photons received through the collimator to a certain angle, and (c) a position sensitive photomuZ.tiplier tube for detecting the deflected scintillation photons and determining the depth of the scintillation event within the scintillation crystal.
The light deflector includes a light-deflecting mirror, or a right angle prism. The position sensitive photomultiplier tube includes a plurality of photodetectors, each responding to photons incident from its corresponding depth of interaction within the 5 scintillation crystal.
According to another aspect of the invention, there is provided a method for measuring a depth-of-interaction of a scintillation event in a scintillation camera having a scintillation crystal and an array of photomultiplier q0 tubes. The method comprises steps of (a) detecting scintillation phatons travelling parallel to the plane of the scintillation crystal when a scintillation event occurs; and (b) determining the depth of interaction within the scintillation crystal by using a position sensitive photodetector.
The method can further comprise a step of deflecting the scintillation photons to a certain degree for facilitating the detection of the photons.
Other aspects and advantages of the invention, as well as the structure and operation of various embodiments of the invention, will become apparent too those ordinarily skilled in the art upon review of the following description of the invention in conjunction. with the accompanying drawings.
Brief Description of the Drawings Embodiments of the invention will be described with reference to the accompanying drawings, wherein:
Fig.l is a perspective view of a horizontal cross-section of a scintillation camera combined with an apparatus according to the invention;
Fig. 2 is.a part of vertical cross-sectional view of Fig. 1; and Fig. 3 is~a part of vertical cross-sectional view showing an operation of the apparatus of the invention.
Figures 4-7 are diagrams showing one embodiment of a scintillation camera system.
Figures 4-7 are diagrams showing one embodiment of a scintillation camera system.
Detailed Description of the Preferred Embodiments?
The present invention pertains to amapparatus and method for determining a depth-of-interaction of a scintillation event in scintillation cameras. The invention will be described below, in. conjunction with a scintillation camera, in which the present invention is principally utilized, but not exclusively.
Fig. 1 schematically shows a horizontal cross-section of an embodiment of the invention applied to a conventional scintillation camera having a scintillation crystal and a plurality of photomultiplier tubes, whose structures and operation are well known to those skilled in the field of nuclear medicine. Figs. 2 and 3 illustrate part of vertical cross section of Fig. 1, including an edge portion of the camera.
Referring to Figs. 1 to 3, an embodiment of the present invention will be detailed below.
As shown in the figures, the apparatus comprises. a scintillation crystal, a plurality of position sensitive photmultiplier tubes disposed along the edge of the scintillation crystal, a light deflector attached to and along the lateral surface of the scintillation crystal, and a collimator sandwiched between the lateral surface of the scintillation crystal and the light deflector. The position sensitive photomultiplier tubes are optically coupled to the scintillation crystal via the lateral surface of the crystal, the collimator and the light deflector. For the convenience of the description, other components necessary for inherent operation of the scintillation camera will not be detailed in this application.
As sY~own in Figs. 2 and 3, a scintillation event can occur at the various locations, for example points A, B, C, and D within the thickness of the scintillation crystal, i.e. every scintillation event has a different depth of interaction. When a certain scintillation event occurs, the emitted scintillation lights (photons) spread out within all the direction inside the crystal.
The collimator attached to and along the lateral surface of the scintillation crystal is adapted to receive those of the scintillation photons that travel parallel to the plane of the scintillation crystal. Thus, as shown in Fig. 2, with respect to every scintillation event, the photons including information on the depth of interaction transmit through the collimator. In other words, the collimator between the scintillation crystal and the light deflector allows horizontally travelling light (photons) to enter the.light deflector, so that the entered photons contains information on the depth of interaction of the scintillation event, which isclearly illustrated in Fig.
The light deflector serves to deflect the transmitted photon through the collimator toward the position sensitive photomultiplier tubes or photodetector, as shown in Figs. 2 and 3. In this embodiment, the light deflect is adapted to deflect the received photons to 90 degrees. The light deflector can be a long right-angle prism attached to and along the lateral surface of the scintillation crystal, or a light-reflecting mirror disposed to be able to deflect the photons to a desired direction, or any other light-deflecting means, which can deflect the scintillation light toward the position sensitive photomultiplier tube.
The position sensitive photodetector is adapted to convert the light photons deflected by the light deflector into an electrical signal containing DOI (Depth-of-Interaction) information, which is sent to a DOI
determination module or electronic circuitry. In this embodiment, each of the position sensitive photomultiplier tubes includes a plurality of photo- detectors or photo-sensors, for example photo-sensors P7., P2, P3, P4, and P5 of Fig. 2. Each of the photo-sensors P1 to P5 converts light or photons into an electrical signal, and each photo-sensor is also optically connected correspondingly to various depth of interaction within the scintillation crystal, for example the points A, B, C, and D
respectively. In response of each scintillation events they produce electrical signals, for example signal a, b, c, and d, as clearly illustrated in Fig. 2.
As illustrated in Figs. 2 and 3, some of the photo-sensors can be used for measuring an X, Y coordinat a position of a scintillation event relative the plane of the scintillation crystal.
Referring Fig. 3, an exemplary operation of this embodiment will be described below. When a scintillation event occurs at the point C within the scintillation crystal, scintillation photons travelling parallel to the plane of the crystal via the collimator and the light deflector reach and activate the position-sensitive s photomultiplier tube, especially most intensively activate the photo-sensor P3 among the plurality o~ photo-sensor so that the signal C from the sensor P3 has the highest intensity, indicating the depth-of-interaction corresponding to the scintillation event at the point C. As shown in Fig. 3, all the signals a to a are provided to a DOT determination module or circuitry to determine the depth-of-interaction of every scintillation event. Also, since all the signals a to a present part of energy or 1p scintillation photons produced by the scintillation event at the point C, all the signals can be summed and provided to a coordinate positioning module or circuitry to correct the X, Y coordinate position of the corresponding scintillation event. This implies a wider solid angle clase to 180 degrees.
Figures 4-7 show schematic diagrams showing one embodiment of a scintillation camera system 10. Figure 5 shows a schematic diagram showing a horizontal cross-section view of the gamma camera detector 12 of Figure 4.
5 A scintillation crystal 14, a collimator 16 and a light deflector 18 are provided to the gamma camera detector 12 of the scintillation camera system 10. The gamma-camera-detector 12 has a plural-:ity-of-position sensitive photomultiplier tubes (PMTs) 20 and 22. The PMTs 10 are disposed along the plane 2 of the scintillation crystal 14. PMTS are optically coupled to the scintillation crystal 14 The light deflector 18 is attached to and along the lateral surface 4 of the scintillation crystal 1.4. The collimator 16 is sandwiched between the lateral surface 4 of the scintillation crystal 14 and the light deflector 18.
PMTs 20 are arranged so as to cross the lateral surface 4 of the scintillation crystal 14, the collimator 16 and the light deflector 18. The PMTS 20 are optically coupled to the scintillation crystal 14 and the light deflector 18.
The scintillation camera system 10 further includes a data processor for processing data output from the gamma camera detector 12. The data processor includes a DOI
determination module 30, a summer 32 and a positioning module 34. The DOI determination module 30 processes the output of the PMT 20 to determine the depth of the interaction (DOI) of a scintillation event. In Figure 4 the DOI determination module 30 is provided to each PMT 20.
However, the DOI determination module 30 may process the outputs of a plurality of the PMTS 20..
The summer 32 is provided to each PMT. However, the summer may process the outputs of a plurality of PMTs.
The positioning module 34 determines the position of the scintillation event based on the outputs of the summer modules 34.
For the convenience of the description, other components necessary for inherent operation of the scintillation camera will not be detailed in this application.
Figures 6 and 7 are schematic diagrams showing part of vertical cross section of Figure 4, including an edge _ . _ _ _ - portion of --t-he-- camera e-_ _ - - _ The gamma rays, which strike the scintillation crystal 14, cause scintillation events. In Figure 4, 42A, 42B, 42C, and 42D are shown as the points of the scintillation events in the scintillation crystal 14. In Figure 6, each scintillation event has a different depth of interaction.
When a certain scintillation event occurs, the emitted scintillation lights (hereinafter referred to as photons) spread out in the scintillation crystal 14. The photons include information on the depth of interaction.
The collimator 16 is adapted to receive those of the scintillation photons that travel parallel to the plane 2 of the scintillation crystal 14. As shown in Figure 6, the photons are transmitted to the light deflector 18 through the collimator 16. In other words, the collimator 16 between the scintillation crystal 14 and the light deflector 18 allows horizontally travelling photons to enter the light deflector 16, so that the entered photon contains information on the depth of interaction of the scintillation event.
The light deflector 18 deflects the photons transmitted through the collimator 16 toward the PMT 20.
In this embodiment, the light deflecter 18 may be adapted to deflect the photons perpendicularly to the incident angle of the photons.
The light deflector 18 may be a long right-angle prism attached to and along the lateral surface 4 of the scintillation crystal 14. The light deflector 18 may be a light-reflecting mirror disposed to be able to deflect the photons to a desired direction. The light deflector 18 may be any other light-deflecting means, which may deflect the scintillation light toward the PMT 20.
The PMTS 20 and 22 include a plurality of photo-sensors to convert photons into electrical signals. In Figures 2 and 3, the photo-sensors Pl-P10 of the PMT 20 are -~ shown. The PMTS 20 and 22 may include a plurality of photo-detectors to detect photons.
The photons deflected by the light deflector 18 may reach the photo-sensors P1-P5. The photo-sensors P1-P5 convert the photons deflected by the light deflector 18 into electrical signals 44A-44E. The signals 44A-44E
contain DOI (Depth-of-Interaction) information, which is sent to the DOI determination module 30. In Figure 6, the photons at the positions 42A-42D are reached to the photo-sensors P1-P4, respectively.
P1-P5 and P6-P10 are elements in a position sensitive PMT and have all the same characteristic elements. P6-P10 2Q are used and summed as a conventional PMT to define the edge of the field of view.
As illustrated in Figs. 6 and 7, some of the photo-sensors can be used for measuring an X, Y coordinate position of a scintillation event relative the plane 2 of the scintillation crystal.
Referring Figure 3, an exemplary operation of this embodiment will be described below. When a scintillation event occurs at the point 42C, scintillation photons travelling parallel to the plane 2 of the scintillation crystal 14 via the collimator 16 and the light deflector 18 reach and activate the photo-sensor P3 of the PMT 20 among the plurality of photo-sensors P1-P10. The signal 44C from the sensor P3 has the highest intensity among the outputs from the photo-sensors P1-P5, which indicates the depth-of-interaction corresponding to the scintillation event at the point 42C.
The signals 44A-44E are provided to the DOI
determination module 30 to determine the depth-of-interaction of every scintillation event. Based on the intensity of the signals 44A-44E, the depth-of=interaction is determined.
---- -- - - - - - - ~lso~- -since the -signal-s-outpzzt -from-th-a photo=sensors P1-P10 present part of energy or scintillation photons produced by the scintillation event at,for example, the point 44C, the output signals P1-P10 may be summed and provided to the coordinate positioning module 34 to correct the X, Y coordinate position of the corresponding scintillation event. This implies a wider solid angle close to 180 degrees, as light from a input gamma photon is normally reflected and diffused when striking the edge of the crystal, loosing its positional information.
The DOT determination module 30 sums the outputs of the P1 to P5 position sensitive element of the Position Sensitive PMT (PS PMT). All the P5 signals (44E) from all the PS PMT's 20, that are above a threshold. Similarly all the P4 signals from all the PS PMT's are summed and so on.
The summed signal which is the largest indicates at which depth the scintillation occurred. By using weighting and ratios of signals the DOI can be resolved at greater than the number of elements.
The summer 32 sums all the Pl-P10 signals and uses these signals in the same way as the "edge packing" PMT's.
While the invention has been described according to what are presently considered to be the most practical and preferred embodiments, it must be understood that the invention is not limited to the disclosed embodiments.
Those ordinarily skilled in the art will understand that various modifications and equivalent structures and 14 , functions may be made without departing from the scope of the invention as defined in the claims.
The present invention pertains to amapparatus and method for determining a depth-of-interaction of a scintillation event in scintillation cameras. The invention will be described below, in. conjunction with a scintillation camera, in which the present invention is principally utilized, but not exclusively.
Fig. 1 schematically shows a horizontal cross-section of an embodiment of the invention applied to a conventional scintillation camera having a scintillation crystal and a plurality of photomultiplier tubes, whose structures and operation are well known to those skilled in the field of nuclear medicine. Figs. 2 and 3 illustrate part of vertical cross section of Fig. 1, including an edge portion of the camera.
Referring to Figs. 1 to 3, an embodiment of the present invention will be detailed below.
As shown in the figures, the apparatus comprises. a scintillation crystal, a plurality of position sensitive photmultiplier tubes disposed along the edge of the scintillation crystal, a light deflector attached to and along the lateral surface of the scintillation crystal, and a collimator sandwiched between the lateral surface of the scintillation crystal and the light deflector. The position sensitive photomultiplier tubes are optically coupled to the scintillation crystal via the lateral surface of the crystal, the collimator and the light deflector. For the convenience of the description, other components necessary for inherent operation of the scintillation camera will not be detailed in this application.
As sY~own in Figs. 2 and 3, a scintillation event can occur at the various locations, for example points A, B, C, and D within the thickness of the scintillation crystal, i.e. every scintillation event has a different depth of interaction. When a certain scintillation event occurs, the emitted scintillation lights (photons) spread out within all the direction inside the crystal.
The collimator attached to and along the lateral surface of the scintillation crystal is adapted to receive those of the scintillation photons that travel parallel to the plane of the scintillation crystal. Thus, as shown in Fig. 2, with respect to every scintillation event, the photons including information on the depth of interaction transmit through the collimator. In other words, the collimator between the scintillation crystal and the light deflector allows horizontally travelling light (photons) to enter the.light deflector, so that the entered photons contains information on the depth of interaction of the scintillation event, which isclearly illustrated in Fig.
The light deflector serves to deflect the transmitted photon through the collimator toward the position sensitive photomultiplier tubes or photodetector, as shown in Figs. 2 and 3. In this embodiment, the light deflect is adapted to deflect the received photons to 90 degrees. The light deflector can be a long right-angle prism attached to and along the lateral surface of the scintillation crystal, or a light-reflecting mirror disposed to be able to deflect the photons to a desired direction, or any other light-deflecting means, which can deflect the scintillation light toward the position sensitive photomultiplier tube.
The position sensitive photodetector is adapted to convert the light photons deflected by the light deflector into an electrical signal containing DOI (Depth-of-Interaction) information, which is sent to a DOI
determination module or electronic circuitry. In this embodiment, each of the position sensitive photomultiplier tubes includes a plurality of photo- detectors or photo-sensors, for example photo-sensors P7., P2, P3, P4, and P5 of Fig. 2. Each of the photo-sensors P1 to P5 converts light or photons into an electrical signal, and each photo-sensor is also optically connected correspondingly to various depth of interaction within the scintillation crystal, for example the points A, B, C, and D
respectively. In response of each scintillation events they produce electrical signals, for example signal a, b, c, and d, as clearly illustrated in Fig. 2.
As illustrated in Figs. 2 and 3, some of the photo-sensors can be used for measuring an X, Y coordinat a position of a scintillation event relative the plane of the scintillation crystal.
Referring Fig. 3, an exemplary operation of this embodiment will be described below. When a scintillation event occurs at the point C within the scintillation crystal, scintillation photons travelling parallel to the plane of the crystal via the collimator and the light deflector reach and activate the position-sensitive s photomultiplier tube, especially most intensively activate the photo-sensor P3 among the plurality o~ photo-sensor so that the signal C from the sensor P3 has the highest intensity, indicating the depth-of-interaction corresponding to the scintillation event at the point C. As shown in Fig. 3, all the signals a to a are provided to a DOT determination module or circuitry to determine the depth-of-interaction of every scintillation event. Also, since all the signals a to a present part of energy or 1p scintillation photons produced by the scintillation event at the point C, all the signals can be summed and provided to a coordinate positioning module or circuitry to correct the X, Y coordinate position of the corresponding scintillation event. This implies a wider solid angle clase to 180 degrees.
Figures 4-7 show schematic diagrams showing one embodiment of a scintillation camera system 10. Figure 5 shows a schematic diagram showing a horizontal cross-section view of the gamma camera detector 12 of Figure 4.
5 A scintillation crystal 14, a collimator 16 and a light deflector 18 are provided to the gamma camera detector 12 of the scintillation camera system 10. The gamma-camera-detector 12 has a plural-:ity-of-position sensitive photomultiplier tubes (PMTs) 20 and 22. The PMTs 10 are disposed along the plane 2 of the scintillation crystal 14. PMTS are optically coupled to the scintillation crystal 14 The light deflector 18 is attached to and along the lateral surface 4 of the scintillation crystal 1.4. The collimator 16 is sandwiched between the lateral surface 4 of the scintillation crystal 14 and the light deflector 18.
PMTs 20 are arranged so as to cross the lateral surface 4 of the scintillation crystal 14, the collimator 16 and the light deflector 18. The PMTS 20 are optically coupled to the scintillation crystal 14 and the light deflector 18.
The scintillation camera system 10 further includes a data processor for processing data output from the gamma camera detector 12. The data processor includes a DOI
determination module 30, a summer 32 and a positioning module 34. The DOI determination module 30 processes the output of the PMT 20 to determine the depth of the interaction (DOI) of a scintillation event. In Figure 4 the DOI determination module 30 is provided to each PMT 20.
However, the DOI determination module 30 may process the outputs of a plurality of the PMTS 20..
The summer 32 is provided to each PMT. However, the summer may process the outputs of a plurality of PMTs.
The positioning module 34 determines the position of the scintillation event based on the outputs of the summer modules 34.
For the convenience of the description, other components necessary for inherent operation of the scintillation camera will not be detailed in this application.
Figures 6 and 7 are schematic diagrams showing part of vertical cross section of Figure 4, including an edge _ . _ _ _ - portion of --t-he-- camera e-_ _ - - _ The gamma rays, which strike the scintillation crystal 14, cause scintillation events. In Figure 4, 42A, 42B, 42C, and 42D are shown as the points of the scintillation events in the scintillation crystal 14. In Figure 6, each scintillation event has a different depth of interaction.
When a certain scintillation event occurs, the emitted scintillation lights (hereinafter referred to as photons) spread out in the scintillation crystal 14. The photons include information on the depth of interaction.
The collimator 16 is adapted to receive those of the scintillation photons that travel parallel to the plane 2 of the scintillation crystal 14. As shown in Figure 6, the photons are transmitted to the light deflector 18 through the collimator 16. In other words, the collimator 16 between the scintillation crystal 14 and the light deflector 18 allows horizontally travelling photons to enter the light deflector 16, so that the entered photon contains information on the depth of interaction of the scintillation event.
The light deflector 18 deflects the photons transmitted through the collimator 16 toward the PMT 20.
In this embodiment, the light deflecter 18 may be adapted to deflect the photons perpendicularly to the incident angle of the photons.
The light deflector 18 may be a long right-angle prism attached to and along the lateral surface 4 of the scintillation crystal 14. The light deflector 18 may be a light-reflecting mirror disposed to be able to deflect the photons to a desired direction. The light deflector 18 may be any other light-deflecting means, which may deflect the scintillation light toward the PMT 20.
The PMTS 20 and 22 include a plurality of photo-sensors to convert photons into electrical signals. In Figures 2 and 3, the photo-sensors Pl-P10 of the PMT 20 are -~ shown. The PMTS 20 and 22 may include a plurality of photo-detectors to detect photons.
The photons deflected by the light deflector 18 may reach the photo-sensors P1-P5. The photo-sensors P1-P5 convert the photons deflected by the light deflector 18 into electrical signals 44A-44E. The signals 44A-44E
contain DOI (Depth-of-Interaction) information, which is sent to the DOI determination module 30. In Figure 6, the photons at the positions 42A-42D are reached to the photo-sensors P1-P4, respectively.
P1-P5 and P6-P10 are elements in a position sensitive PMT and have all the same characteristic elements. P6-P10 2Q are used and summed as a conventional PMT to define the edge of the field of view.
As illustrated in Figs. 6 and 7, some of the photo-sensors can be used for measuring an X, Y coordinate position of a scintillation event relative the plane 2 of the scintillation crystal.
Referring Figure 3, an exemplary operation of this embodiment will be described below. When a scintillation event occurs at the point 42C, scintillation photons travelling parallel to the plane 2 of the scintillation crystal 14 via the collimator 16 and the light deflector 18 reach and activate the photo-sensor P3 of the PMT 20 among the plurality of photo-sensors P1-P10. The signal 44C from the sensor P3 has the highest intensity among the outputs from the photo-sensors P1-P5, which indicates the depth-of-interaction corresponding to the scintillation event at the point 42C.
The signals 44A-44E are provided to the DOI
determination module 30 to determine the depth-of-interaction of every scintillation event. Based on the intensity of the signals 44A-44E, the depth-of=interaction is determined.
---- -- - - - - - - ~lso~- -since the -signal-s-outpzzt -from-th-a photo=sensors P1-P10 present part of energy or scintillation photons produced by the scintillation event at,for example, the point 44C, the output signals P1-P10 may be summed and provided to the coordinate positioning module 34 to correct the X, Y coordinate position of the corresponding scintillation event. This implies a wider solid angle close to 180 degrees, as light from a input gamma photon is normally reflected and diffused when striking the edge of the crystal, loosing its positional information.
The DOT determination module 30 sums the outputs of the P1 to P5 position sensitive element of the Position Sensitive PMT (PS PMT). All the P5 signals (44E) from all the PS PMT's 20, that are above a threshold. Similarly all the P4 signals from all the PS PMT's are summed and so on.
The summed signal which is the largest indicates at which depth the scintillation occurred. By using weighting and ratios of signals the DOI can be resolved at greater than the number of elements.
The summer 32 sums all the Pl-P10 signals and uses these signals in the same way as the "edge packing" PMT's.
While the invention has been described according to what are presently considered to be the most practical and preferred embodiments, it must be understood that the invention is not limited to the disclosed embodiments.
Those ordinarily skilled in the art will understand that various modifications and equivalent structures and 14 , functions may be made without departing from the scope of the invention as defined in the claims.
Claims (6)
1. An apparatus for measuring a depth-of-interaction of a scintillation event in a scintillation camera having a scintillation crystal and an array of photomultiplier tubes, the apparatus comprising:
(a) a collimator coupled to and along the lateral surface of the scintillation crystal for receiving scintillation photons traveling parallel to the plane of the scintillation crystal when a scintillation event occurs;
(b) a light deflector optically coupled to and along the lateral surface of the scintillation crystal with the collimator sandwiched between the scintillation crystal and the light deflector for deflecting the direction of the scintillation photons received through the collimator to a certain angle; and (c) a position sensitive photomultiplier tube for detecting the deflected scintillation photons and determining the depth of the scintillation event within the scintillation crystal.
(a) a collimator coupled to and along the lateral surface of the scintillation crystal for receiving scintillation photons traveling parallel to the plane of the scintillation crystal when a scintillation event occurs;
(b) a light deflector optically coupled to and along the lateral surface of the scintillation crystal with the collimator sandwiched between the scintillation crystal and the light deflector for deflecting the direction of the scintillation photons received through the collimator to a certain angle; and (c) a position sensitive photomultiplier tube for detecting the deflected scintillation photons and determining the depth of the scintillation event within the scintillation crystal.
2. An apparatus according to claim 1, wherein said light deflector includes a light-deflecting mirror.
3. An apparatus according to claim 1, wherein said light deflector includes a right angle prism.
4. An apparatus according to claim 1, wherein said position sensitive photomultiplier tube includes a plurality of photodetectors, each responding to photons incident from its corresponding depth of interaction within the scintillation crystal.
5. A method for measuring a depth-of-interaction of a scintillation event in a scintillation camera having a scintillation crystal and an array of photomultiplier tubes, the method comprising steps of:
(a) detecting scintillation photons travelling parallel to the plane of the scintillation crystal when a scintillation event occurs; and (b) determining the depth of interaction within the scintillation crystal by using a position sensitive photodetector.
(a) detecting scintillation photons travelling parallel to the plane of the scintillation crystal when a scintillation event occurs; and (b) determining the depth of interaction within the scintillation crystal by using a position sensitive photodetector.
6. A method according to claim 5, further comprising a step of deflecting the scintillation photons to a certain degree for facilitating the detection of the photons.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2464827 CA2464827A1 (en) | 2004-04-22 | 2004-04-22 | Method and system of determining depth of interaction in a scintillation camera |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2464827 CA2464827A1 (en) | 2004-04-22 | 2004-04-22 | Method and system of determining depth of interaction in a scintillation camera |
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| Publication Number | Publication Date |
|---|---|
| CA2464827A1 true CA2464827A1 (en) | 2005-10-22 |
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ID=35276866
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2464827 Abandoned CA2464827A1 (en) | 2004-04-22 | 2004-04-22 | Method and system of determining depth of interaction in a scintillation camera |
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| CA (1) | CA2464827A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2012034220A1 (en) * | 2010-09-14 | 2012-03-22 | Abdelmounaime Faouzi Zerrouk | Depth-of-interaction scintillation detectors |
| CN106872505A (en) * | 2015-12-10 | 2017-06-20 | 中国科学院深圳先进技术研究院 | A kind of experiment porch for measuring crystal resolution ratio |
-
2004
- 2004-04-22 CA CA 2464827 patent/CA2464827A1/en not_active Abandoned
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2012034220A1 (en) * | 2010-09-14 | 2012-03-22 | Abdelmounaime Faouzi Zerrouk | Depth-of-interaction scintillation detectors |
| US9442199B2 (en) | 2010-09-14 | 2016-09-13 | Zecotek Imaging Systems Pte. Ltd. | Depth-of-interaction scintillation detectors |
| CN106872505A (en) * | 2015-12-10 | 2017-06-20 | 中国科学院深圳先进技术研究院 | A kind of experiment porch for measuring crystal resolution ratio |
| CN106872505B (en) * | 2015-12-10 | 2020-04-14 | 中国科学院深圳先进技术研究院 | Experiment platform for measuring crystal resolution |
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