WO2004081606A1 - Improved gamma-ray camera system - Google Patents
Improved gamma-ray camera system Download PDFInfo
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- WO2004081606A1 WO2004081606A1 PCT/GB2004/000982 GB2004000982W WO2004081606A1 WO 2004081606 A1 WO2004081606 A1 WO 2004081606A1 GB 2004000982 W GB2004000982 W GB 2004000982W WO 2004081606 A1 WO2004081606 A1 WO 2004081606A1
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- gamma
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- ray
- detector response
- ray camera
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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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- 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
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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
- G01T1/1642—Static instruments for imaging the distribution of radioactivity in one or two dimensions using one or several scintillating elements; Radio-isotope cameras using a scintillation crystal and position sensing photodetector arrays, e.g. ANGER cameras
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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
-
- 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
- A61B6/4208—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment with arrangements for detecting radiation specially adapted for radiation diagnosis characterised by using a particular type of detector
- A61B6/4258—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment with arrangements for detecting radiation specially adapted for radiation diagnosis characterised by using a particular type of detector for detecting non x-ray radiation, e.g. gamma radiation
Definitions
- the invention relates to gamma-ray camera systems, in particular to spectral processing of data in gamma-ray camera systems.
- Figure 1 schematically shows in vertical cross-section a gamma-ray camera system 2 viewing a sample 4.
- the sample comprises a point-like gamma- ray source 6 embedded within an extended body 8.
- the gamma-ray camera system comprises a gamma-ray camera 10 and an energy spectra accumulating component 12.
- the gamma-ray camera 10 is an Anger-type camera [1]. This is a type widely used as a diagnostic tool in nuclear medicine.
- the gamma-ray camera 10 includes a gamma-ray imager 14 coupled to a detector read-out component 16.
- the energy spectra accumulating component includes an energy spectra accumulator 18 and a data storage component 20.
- the gamma-ray imager 14 includes a parallel collimator 22, a scintillator crystal 24, a light guide element 26 and a plurality of photo-multiplier tubes 28.
- the scintillator crystal is, for example, a large single crystal of Thallium doped Sodium Iodide (Nal(Tl)).
- the scintillator crystal is shielded from gamma-ray photons not incident through the parallel collimator by a shield 30.
- the gamma-ray imager provides a 50cm square image plane.
- the parallel collimator comprises an array of apertures with a characteristic cell size of 2mm. Each cell provides a f ⁇ eld-of-view of around 3°.
- the photo-multiplier tubes form a close packed hexagonal array of 61 tubes arranged to collectively view much of the 50cm square scintillator crystal 24 forming the image plane.
- photons are emitted by the gamma-ray source in all directions.
- the photons will be emitted by radio-labelled pharmaceuticals in a patient's body (i.e. pharmaceuticals labelled with a radioactive tracer).
- the gamma-ray source is Cobalt-57.
- Cobalt- 57 primarily emits gamma-ray photons with an energy of around 122 keV.
- Photons A-F Six such photons, labelled A-F, are emitted in the plane of the figure as schematically shown in Figure 1.
- Photons A, B and C exit the sample 4 in the directions indicated in the figure and are not seen by the gamma-ra ⁇ camera.
- Photon D is emitted towards the gamma-ray camera, but is not sufficiently parallel to the axis of the parallel collimator 22 to pass through it. As can be seen from the figure, Photon D it is absorbed in a wall of the parallel collimator, and as such is not detected by the scintillator crystal 24.
- Photon E does reach the scintillator crystal 24 since its path is within the parallel collimator's field-of-view.
- the energy of photon E is deposited in the scintillator crystal 24 in a scintillation event.
- a detection of this kind where the gamma-ray photon travels directly between the gamma-ray source and the scintillator crystal, is known as a direct detection event.
- the detection event generates a pulse of optical radiation which illuminates several of the photo-multiplier tubes 28 via the light guide element 26.
- the light guide element assists in coupling the pulse of optical radiation from the scintillator crystal, which typically has a relatively high refractive index at visible wavelengths. In a typical scintillation event, the resulting pulse of optical radiation will be detected by up to seven of the of the photo-multiplier tubes.
- the signals from the photo-multiplier tubes are supplied to the detector readout component.
- the detector read-out component determines the X- and Y- coordinates of the scintillation event from the relative intensities of the signals seen by each of the photo-multiplier tubes.
- the detector read-out component also calculates the total energy deposited in the scintillation event from a summation of the signal amplitudes seen by the photo-multiplier tubes.
- Read-out components for Anger-type gamma-ray cameras are well known [1]. One mode of operation is known as list-mode operation.
- the detector read-out component outputs a signal in response to each scintillation event, the output signal including the calculated energy deposited in the scintillator crystal and the X- and Y-coordinates of the scintillation event.
- the output signals from the detector read-out component are coupled to the energy spectra accumulating component 12.
- the functionality of the energy spectra accumulating component 12 in this example is provided by a suitably programmed general purpose computer.
- the computer includes an appropriate interface to receive and decode the output signals from the detector read-out component 16.
- the energy spectra accumulator 18 within the energy spectra accumulating component 12 operates to generate a three- dimensional observed data array I(X,Y,E).
- This array comprises a count of the number of scintillation events occurring within an exposure period as a function of their X, Y position within the detector, and the energy deposited in the scintillator crystal.
- a bin-size used in generating I(X,Y,E) is typically 5 mm for each spatial coordinates (i.e.
- the scintillator crystal 24 is a large single crystal, the 5 mm spatial binning used in generating I(X,Y,E) defines effective detector pixels, and these have a size of around 5 mm square. However, because of Compton scattering within the sample 4, the resolution in a resulting image is worse than this.
- the observed data array I(X,Y,E) is normalized to the exposure time and stored in the data storage component 20 of the energy spectra accumulating component for later analysis.
- I(X,Y,E) will typically be used in generating two-dimensional diagnostic images representing gamma-ray emission intensity from the source 4 as seen within selected gamma-ray energy ranges.
- FIG. 2 shows a typical energy spectrum which might be seen in one of the detector pixels of a gamma-ray camera system similar to that shown in Figure 1.
- the full width at half maximum (FWHM I NT) of the peak corresponding to gamma-ray emission from the Cobalt-57 source is approximately 25 keV. Accordingly, at an energy of 122 keV the gamma- ray camera has an intrinsic energy resolution of around 20%. This relatively poor energy resolution is significantly worse than that predicted by photon-statistics alone and is due to several factors.
- One effect is the variance in the scintillation efficiency of the crystal itself, this is energy dependent and cannot be corrected for simply.
- Another effect is the non-uniformity of the response of the photo-multiplier tubes.
- the intensity of gamma-ray emission seen by the gamma-ray camera can be represented by a summation over the full width of the peak around 122 keV, for example between 100 keV and 150 keV. Because the poor energy resolution does not directly effect the imaging capabilities of the camera in such cases, a summation over this wide energy range provides the best signal-to-noise ratio possible by making use of all detected events, without unduly compromising image quality.
- the energy of gamma-rays emitted by radioactive sources used to label commonly-used pharmaceuticals in nuclear medicine is typically on the order of 10 keV.
- Technetium-99 emitting at 140 keV is commonly used.
- This energy is chosen to be sufficiently energetic to allow emitted gamma-ray photons to escape from the surrounding body in which the gamma-ray source is embedded, yet without being so energetic as to make collimation and detection difficult.
- One disadvantage of this choice of energy is that the gamma-ray photons have a relatively high probability of scattering within the surrounding body before being viewed by the gamma-ray camera. An example of such a scattering event is shown by the photon labelled F in Figure 1.
- photon F is initially emitted by the gamma-ray source 6 in a direction away from the gamma-ray camera system 2.
- Photon F should not normally contribute to the observed data array I(X,Y,E).
- photon F undergoes a Compton scattering event in the surrounding body 8 which scatters it towards the gamma-ray camera.
- the scattered photon passes through the parallel collimator 22 and is detected by the scintillator crystal 24.
- Photon F is scattered off an electron marked e " in Figure 1. The electron carries away some of the energy of Photon F.
- the gamma-ray camera system records a scintillation event occurring at a position not commensurate with the position of gamma-ray photons arriving directly from the source 6, and at an energy slightly lower than of the gamma-ray photons arriving directly from the source 6. While for simplicity a point source of gamma-ray photons is shown in Figure 1, in general there will be an extended gamma-ray source within the surrounding body.
- Figure 3 shows a typical energy spectrum which would be seen in one of the detector pixels of a gamma-ray camera system similar to that shown in Figure 1.
- data are obtained with the gamma-ray source positioned behind a 5 cm thick body of water, as opposed to in isolation.
- the body of water corresponds to the surrounding body 8 shown in Figure 1, and it is in this body of water that Compton scattering can occur leading to Compton scattered detection events being detected.
- an appropriate energy-width known as an energy window, over which to sum the count rate n(E).
- the energy window must be chosen to obtain a summed count rate reflecting as many direct detection events as possible, while rejecting as much of the contribution from Compton scattered detection events as possible. Determining the most appropriate width of energy window will generally be a matter of compromise. For example, if an energy window such as that marked Wi in Figure 3 were to be used, most of the direct detection events would be included in the image generation as desired. However, with this wide energy window a significant fraction of Compton scattered detection events will also be included.
- Figure 4A schematically shows in negative an idealized diagnostic image of an example extended gamma-ray source distribution obtained using an idealized gamma-ray camera system.
- the example source distribution is in the form of a cross with a bright spot at the centre, and the source distribution is directly reflected in the resulting image.
- Figures 4B and 4C schematically show how the same example gamma-ray source distribution imaged in Figure 4A would appear when imaged with a gamma- ray camera system of the kind discussed and using different width energy windows.
- Figure 4B shows the result of using a wide energy window, such as the one marked Wi in Figure 3.
- Figure 4C shows the result of using a narrow energy window such as the one marked W 2 in Figure 3.
- US 5903008 describes the use of dual energy-windows for diagnostic image formation [6].
- This dual energy- window technique measures the relative number of counts recorded in two energy channels; one centred on the photo-peak energy and the second, some 10-15% below that energy. This ratio is measured initially when there is no scattering present. Thereafter, the photo-peak values are modified according to the value of the number of counts in the lower window. This value is dominated by the presence of scattered events.
- US 5530248 describes a scheme for theoretical modelling of the contribution of Compton scattered detection events to the energy spectra [7]. This technique generates a trial function from the energy spectrum recorded in each pixel when no scattering material is present. This is achieved by taking the first differential of the spectrum to emphasise the photo-peak. This modified function is then fitted to the energy spectra seen when a scattering medium is present in order to distinguish between 'wanted' and 'unwanted' photons.
- US 5633499 describes a scheme based on calculating a correction table to be applied to an image acquired using a conventional method of selecting only those events that fall within an energy window spanning + 10% of the photo-peak [8]. The correction value is derived from the measurement of the centroid of the spectrum recorded in a particular detector pixel. The data are used to estimate the scatter contribution.
- a gamma-ray camera system comprising: a gamma-ray imager including detector pixels formed from a scintillator material; a detector read-out component for determining positions and energies of scintillation events occurring within the scintillator material; an energy spectra accumulating component for compiling observed energy spectra of scintillation events in the detector pixels; and a spectra processing component operable to deconvolve a pixel specific detector response function from the observed energy spectra.
- the detector response functions are selected from a store of detector response functions which include detector response functions specific to individual detector pixels. By providing a separate detector response function for each individual detector pixel, the most accurate mapping of the detector response to detector pixel can be obtained.
- the detector response functions may be selected from a store of detector response functions which comprises a family, and for the pixels in the gamma-ray image a detector response function is selected from the family.
- the invention is equally applicable to a range of gamma-ray camera systems employing different detection planes.
- an Anger-type gamma-ray imager in which the scintillator material comprises a single scintillator crystal optically coupled to a plurality of photo-detectors may be used.
- other types of gamma-ray imager may be employed, for example, gamma-ray imagers in which the scintillator material comprises an array of discrete scintillator crystal elements optically coupled to a corresponding array of discrete photo-detectors.
- a method of processing energy spectra recorded in detector pixels of a gamma-ray scintillation camera comprising: providing observed energy spectra recorded in the detector pixels; and deconvolving a pixel specific detector response function from the observed energy spectra.
- This method provides much higher energy resolution than previous methods of processing data from gamma-ray camera systems and correspondingly provides similar benefits to those of the first aspect of the invention described above.
- the method of processing energy spectra may include selecting detector response functions from a store of detector response functions which include a detector response function specific to individual detector pixels.
- the method may include selecting detector response functions from a store of detector response functions which comprises a family, and for the detector pixels a detector response function is selected from the family.
- a computer program product bearing machine readable instructions for implementing the method is also provided.
- a method of generating pixel-specific detector response functions for a gamma-ray imager including detector pixels formed from a scintillator material comprising: obtaining a theoretical component to the detector response as a function of position by performing a simulation; obtaining an empirical component to the detector response as a function of position by observing the response of the gamma-ray imager to a calibration source; and combining the theoretical and empirical components to provide detector response functions for the detector pixels.
- a computer program product bearing machine readable instructions for implementing the method and a data storage medium bearing detector response functions calculated according to the method are also provided.
- Figure 1 schematically shows in vertical cross-section a prior art gamma-ray camera system viewing a sample containing a gamma-ray source
- Figure 2 schematically shows an example energy spectrum seen in one of the detector pixels of the gamma-ray camera system shown in Figure 1 when viewing an isolated gamma-ray source;
- Figure 3 schematically shows an example energy spectrum seen in one of the detector pixels of the gamma-ray camera system shown in Figure 1 when viewing a gamma-ray source surrounded by a body in which Compton scattering occurs;
- Figure 4A schematically shows an example diagnostic image of a gamma-ray source which would be obtained with an idealized gamma-ray camera system
- Figure 4B schematically shows an example diagnostic image of the same gamma-ray source obtained using the gamma-ray camera system shown in Figure 1 formed using a broad energy window;
- Figure 4C schematically shows an example diagnostic image of the same gamma-ray source obtained using the gamma-ray camera system shown in Figure 1 formed using a narrow energy window;
- Figure 5 schematically shows in vertical cross-section a gamma-ray camera system according to a first embodiment of the invention viewing a sample containing a gamma-ray source
- Figure 6 schematically shows an example energy spectrum which might be seen in one of the detector pixels of the gamma-ray camera system shown in Figure 5 when viewing an isolated gamma-ray source;
- Figure 7 schematically shows an example diagnostic image of the same gamma-ray source as imaged in Figures 4A-C obtained using the gamma-ray camera system shown in Figure 5 and formed using a narrow energy window;
- Figure 8 shows a flow chart which schematically details some of the operational steps performed within a spectra processing component in the gamma-ray camera system shown in Figure 5;
- Figure 9 shows a flow chart which schematically details some of the operational steps performed within a spectra processing component in a gamma-ray camera system according to a second embodiment of the invention.
- Figure 10 schematically shows in vertical cross-section a gamma-ray camera system according to a third embodiment of the invention.
- Figure 5 schematically shows in vertical cross-section a gamma-ray camera system 32 according to a first embodiment of the invention.
- the gamma-ray camera system 32 additionally includes a spectra processing component 34.
- the spectra processing component includes a store of detector response functions 36, a spectra processor 38 and a data storage component 40.
- the functionality of the spectra processing component in this example is provided by a suitably configured general purpose computer.
- an application specific integrated circuit (ASIC), a field programmable gate array (FGPA) or a digital signal processor (DSP) may also be employed.
- ASIC application specific integrated circuit
- FGPA field programmable gate array
- DSP digital signal processor
- the spectra processing component 34 is arranged to read the observed data array I(X,Y,E) from the data storage component 20 in the energy spectra accumulating component 12.
- the observed data array is read by the spectra processor 38 in the spectra processing component 34.
- the spectra processor is operable to deconvolve a detector response function from the individual spectra associated with each pixel in the observed data array I(X,Y,E), the specific detector response function employed in the deconvolution is selected from a store of detector response functions 36. The choice of detector response function is based on which detector pixel the spectrum currently being processed is associated with.
- the refined data array is of the same form as I(X,Y,E) and may be used in the same way to generate diagnostic images.
- n(E) j(R X ⁇ (E, E') ⁇ A(E') + ⁇ (E)) ⁇ dE'
- R x ⁇ (E, E') describes the detector response function for the detector pixel at position X 0 ,Yo and e(E) is the noise contribution.
- This integral can be discretised as:
- R TM ⁇ describes the probability that a detected gamma-ray photon which generates a scintillation event in pixel Xo,Yo, and having an incident energy falling into energy bin , will be actually detected as having an energy falling within bin m.
- Figure 6 shows a typical energy spectrum which would be seen in one of the detector pixels of a gamma-ray camera system similar to that shown in Figure 5.
- an isolated (i.e. not embedded in a body) gamma-ray point source is viewed to show the intrinsic energy resolution of a gamma-ray camera system including deconvolution. This allows the performance of the gamma-ray camera system shown in Figure 5 to be directly compared with that shown in Figure 1.
- count rate n(E) is plotted as a function of energy E for a detector pixel at position o, YQ.
- n(E) S(X 0 ,Yo,E), i.e. it is a deconvolved energy spectrum which is plotted and not the observed energy spectrum.
- the detector response function employed in the deconvolution is deteraiined as detailed further below.
- the deconvolved full width at half maximum (FWHMD E C) of the peak corresponding to gamma-ray emission from the Cobalt-57 source is approximately 6 keV. Accordingly, at an energy of 122 keV the gamma-ray camera system shown in Figure 5 has an energy resolution of around 5%. This is a significant improvement on the energy resolution of around 20% seen with previous gamma-ray camera systems such as shown in Figure 1.
- the much improved resolution makes it easier to distinguish Compton scattered detection events from direct detection events when forming diagnostic images from the refined data array S(X,Y,E).
- a narrower energy widow around the peak energy may be used when generating diagnostic images so as to discard much of the Compton scattered detection events, while maintaining most of the direct detection events.
- the width of the narrow energy window W 2 shown in Figure 3 is also marked on Figure 6. While in Figure 3 this window excluded a significant fraction of the direct detection events, it can be seen from Figure 6 that after appropriate deconvolution, most of the direct detection events are included within the window.
- the broad energy distribution of the Compton scattered detection events is inherent in their contribution to the incident gamma-ray spectrum A(E).
- the light collection efficiency will depend on detector pixel both due to differences in transfer function from different scintillation sites to the photo-multiplier tubes, and also to non- uniformities in the response of the photo-multiplier tubes. Further variations in the detector response function for different detector pixels are introduced as a consequence of non-linearities in the response of the scintillation crystal as a function of energy deposited in a scintillation event..
- a Monte Carlo technique it is possible to predict the way that the scintillator material responds to incident gamma-ray photons at energies within an energy range of interest, for instance between 50 keV and 500 keV. Other modelling methods could also be used.
- the calibration data may be acquired, for example, by observing a number of monochromatic radioactive sources emitting within the energy range of interest.
- the positional dependence of the detector response function can be determined.
- data can be obtained for each pixel simply by removing the collimator and placing the source at a distance of say 50cm from the scintillator crystal, or by mounting the calibration source on a translation stage such that it can be scanned across the field-of-view of the camera. It is most appropriate to determine how the detector response function varies with position at a spatial resolution comparable with that of the gamma-ray imager.
- the determined detector response functions are specific to an individual gamma-ray camera.
- Monte Carlo or similar simulation provides a base model which is modified according to empirically determined calibration data
- the simulation may be dispensed with.
- purely empirical pixel specific detector response functions can be obtained from observations of the response of the gamma-ray imager to point calibration source.
- deconvolution can be performed on a detector pixel by detector pixel basis using the techniques noted above [10]. Accordingly, following an exposure, when energy spectra for each detector pixel have been recorded in an observed data array I(X,Y,E) as described above, the gamma-ray spectrum incident on each detector pixel can be recovered using the position-sensitive detector response functions in a standard deconvolution algorithm.
- Figure 7 schematically show how the same gamma-ray source leading to the idealized image shown in Figure 4 A would appear when obtained with a gamma-ray camera system shown in Figure 5.
- the energy window shown in Figure 6 and marked W is used in generating the diagnostic image. Since the narrow energy window excludes a high fraction of the Compton scattered detection events, there is no Compton scattered halo surrounding the image as seen with a wide energy window, for example as shown in Figure 4B.
- the improved spectral resolution provided by the spectra processing component also ensures that the narrow energy window includes almost all of the direct detection events. This leads to a higher signal-to-noise ratio than that seen in the image shown in Figure 4C. Accordingly, the gamma-ray camera system shown in Figure 5 is able to provide diagnostic images which are much more closely matched to the idealized image shown in Figure 4 A than prior art gamma-ray camera systems.
- Figure 8 is a flow chart which schematically details some of the operational steps performed within the spectra processing component 34.
- the gamma-ray camera imager provides a square array of X ⁇ o ⁇ by Y ⁇ o ⁇ detector pixels.
- an observed data array I(X,Y,E) obtained during an observation of interest is read from the data storage element 20 shown in Figure 5.
- iteration parameters X and Y are set to zero.
- the iteration parameters X and Y are respectively incremented by one.
- S5 the spectrum corresponding to the detector pixel X, Y is copied into a one-dimensional data array O(E).
- a detector response function R(E,Eo) is retrieved from the detector response function store 36.
- the selected detector response function is selected based on the values of X and Y.
- the selected detector response function is deconvolved from O(E) to provide a one dimensional data array A(E).
- A(E) accordingly represents a calculation of the incident gamma-ray spectrum falling on detector pixel X, Y.
- the array A(E) is copied to the elements of a refined data array S(X,Y,E) which correspond to the detector pixel currently being processed.
- the value of Y is tested to determine whether it is equal to Y ⁇ o ⁇ - If Y s less than Y ⁇ o ⁇ , the process flow returns to S4.
- Steps S4-S8 are repeated, with Y being incremented at S4 in each iteration, until Y is equal to Y ⁇ o ⁇ - hi S10, the value of X is tested to determine whether it is equal to X ⁇ o ⁇ - If X s less than X ⁇ o ⁇ > the process flow returns to S3.
- Steps S3-S9 are repeated, with X being incremented at S3 in each iteration, until X is equal to X ⁇ o ⁇ - hi Sll, the spectra processing is completed and the refined data array S(X,Y,E) is written to the data storage component 40.
- S(X,Y,E) is then available for further use from the data storage component in the spectra processing component in the same way that the observed data array I(X,Y,E) is available in prior art gamma- ray camera systems. Because there are more than 2000 detector pixels present in the gamma-ray camera system, the process shown in Figure 8 can be very time consuming. If faster processing is required, a fast parallel-processor may be used to accelerate the process such that diagnostic images can be made available within a time period which is comparable with the exposure time required to acquire the observed data array.
- the functionality of the processing component 34 can be achieved by using a suitably configured general purpose computer with parallel processing capability, or an application specific integrated circuit.
- Figure 9 is a flow chart which schematically details some of the operational steps performed within a spectra processing component employed in a gamma-ray camera system according to second embodiment of the invention.
- the gamma-ray camera imager provides a square array of X ⁇ o ⁇ by Y ⁇ o ⁇ detector pixels.
- the observed data array I(X,Y,E) orresponding to a prior observation is read from the data storage element 20 shown in Figure 5.
- the spectra processing component is configured to process the spectra associated with each detector pixel in parallel. A separate process thread operates for each individual detector pixel, this removes the need to iterate seen Figure 8, and provides for significantly faster processing.
- a detector response function R(E,Eo) is retrieved from a detector response function store similar to that described above for the gamma-ray camera system shown in Figure 5.
- the selected detector response function is chosen based on the values of X and Y corresponding to the thread being processed, in this case, 1 and 2 respectively.
- the detector response function is deconvolved from O(E) to provide a one dimensional data array A(E).
- each process thread is finished, and a completed refined data array S(X,Y,E) is obtained.
- the spectra processing is complete and the refined data array S(X,Y,E) is written to a data storage component similar to the one described above for the gamma-ray camera system shown in Figure 5.
- S(X,Y,E) is then available for further use in the same way that the observed data array I(X,Y,E) is made available in prior art gamma-ray camera systems.
- an observed data array I(X,Y,E) including energy spectra for a total of 2000 pixels might be processed using twenty parallel processor channels, with each process channel sequentially processing 100 energy spectra. This would allow, for example, faster processing of the observed data array than would be seen using the method shown in Figure 8, but would not require the same level of computing power necessary for the method shown in Figure 9.
- detector response functions are determined and stored for each detector pixel, it will be appreciated that in some circumstances the variation of detector response on spatial scales comparable to the detector pixel size will be small. In such cases, it may be unnecessary to store a detector response function for each pixel. For instance, in a gamma-ray camera system with a 50 cm square scintillator crystal detector and an imaging resolution of 5 mm, detector response functions may be determined with a spatial resolution of, for example, 1 cm. In this way a family of detector response functions are calculated corresponding to an array of 1 cm square elements spanning the scintillator crystal. When selecting a suitable detector response function to deconvolve form the observed data array corresponding to detector pixel at X, Y, the detector response function corresponding to the 1 cm square element which includes detector pixel X, Y is chosen.
- Figure 10 schematically shows in vertical cross-section a gamma-ray camera system 58 according to a further embodiment of the invention. Many of the features of the gamma-ray camera system 58 shown in Figure 10 are similar to and will be understood from the correspondingly numbered features shown in Figure 5 and described above. However, in the example shown in Figure 10 a modified gamma-ray camera 60 is used. In this example, a discrete detector element gamma-ray camera imager 50 replaces the gamma-ray camera imager 14 shown in Figure 5.
- a detection plane comprising discrete scintillator crystal elements 52 coupled by discrete light guide elements 54 to individual photo-detectors 56 are used.
- This is type of gamma-ray imager is similar to the Digirad "2020tc Imager" camera discussed above.
- the photo-detector signals are coupled to a read-out component 62 which is configured to provide a list mode output to the spectra accumulating component 12 similar to that described above.
- the spectra accumulating component 12 and spectra processing component 34 function as described above.
- the detector response functions associated with the different detector pixels in a gamma-ray camera system are specific to each particular gamma- ray camera system. Accordingly, appropriately calculated detector response functions may be provided along with a gamma-ray camera system at first supply to an end user.
- the calculated detector response functions and software operable to configure the general purpose computer may be supplied together or separately on a computer program product, for instance a CD-ROM or other data-storage medium.
- the functionality of the spectra processing component is to be provided in firmware or hardware, for example by an ASIC, a FPGA or a DSP
- the calculated detector response functions can, for example, be stored in ROM on an integrated chip along with the firmware.
- spectra processing components similar to those described above can be coupled to existing gamma-ray camera systems as an 'after-market' add-on for improving energy resolution.
- an existing user of a gamma-ray camera system may provide a third party with access to the camera system, such that the third party can fully calculate the detector response functions using the techniques described above.
- the existing user might supply the third party with appropriate calibration data from the gamma-ray camera from which the third party calculates the appropriate detector response functions to be supplied to the existing user.
- the detector response functions may be supplied alone, for example on a data-storage medium, or along with a computer program product bearing machine readable instructions for implementing the functionality of a spectra processing component.
- a hardware add-on may be supplied to an existing user.
- the hardware add-on including, for example, an appropriately configured interface for interfacing with the detector read-out component of the existing gamma-ray camera system, firmware or hardware, for example an ASIC, a FPGA or a DSP, for providing the functionality of a spectra processing component, and a memory, for example ROM or a replaceable datastorage medium, for storing appropriate detector response functions.
- detector response functions are calculated for individual gamma-ray camera systems, improvements in spectral resolution may also be achieved by deconvolving more generic pixel dependent detector response functions. For example, for commonly used configurations of gamma-ray camera system, detector response functions may be calculated for each detector pixel in a manner dependent only on properties of the scintillator material and the geometric configuration of the gamma-ray camera imager.
- Another way to obtain more generic detector response functions for a particular gamma-ray camera imager configuration would be to determine the average of a number of previously determined detector response functions seen in examples of the imager configuration of interest.
Abstract
Description
Claims
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US10/548,985 US7504635B2 (en) | 2003-03-11 | 2004-03-09 | Gamma-ray camera system |
EP04718683A EP1601992A1 (en) | 2003-03-11 | 2004-03-09 | Improved gamma-ray camera system |
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GB0305555A GB2401766B (en) | 2003-03-11 | 2003-03-11 | Improved gamma-ray camera system |
GB0305555.5 | 2003-03-11 |
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WO2004081606A1 true WO2004081606A1 (en) | 2004-09-23 |
WO2004081606A8 WO2004081606A8 (en) | 2005-01-13 |
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PCT/GB2004/000982 WO2004081606A1 (en) | 2003-03-11 | 2004-03-09 | Improved gamma-ray camera system |
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US (1) | US7504635B2 (en) |
EP (1) | EP1601992A1 (en) |
GB (1) | GB2401766B (en) |
WO (1) | WO2004081606A1 (en) |
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WO2008062360A2 (en) * | 2006-11-21 | 2008-05-29 | Koninklijke Philips Electronics N.V. | Apparatus and method for determining a detector energy weighting function of a detection unit |
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RU2472179C2 (en) * | 2007-06-19 | 2013-01-10 | Конинклейке Филипс Электроникс Н.В. | Digital pulse processing in multispectral photon counting circuits |
US10156647B2 (en) | 2012-11-23 | 2018-12-18 | Kromek Limited | Method of spectral data detection and manipulation |
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Also Published As
Publication number | Publication date |
---|---|
GB0305555D0 (en) | 2003-04-16 |
GB2401766B (en) | 2006-03-15 |
EP1601992A1 (en) | 2005-12-07 |
WO2004081606A8 (en) | 2005-01-13 |
US20060180767A1 (en) | 2006-08-17 |
GB2401766A (en) | 2004-11-17 |
US7504635B2 (en) | 2009-03-17 |
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