... Peter Olcott and Craig S Levin are in the Department of Radiology and the Molecular Imaging P... more ... Peter Olcott and Craig S Levin are in the Department of Radiology and the Molecular Imaging Program at Stanford University, Palo Alto, CA, USA (email: fhabte@stanford. edu, cslevin@stanford.edu and pdo@stanford.edu respectively). ...
We are developing a novel, portable dual-panel positron emission tomography (PET) camera dedicate... more We are developing a novel, portable dual-panel positron emission tomography (PET) camera dedicated to breast cancer imaging. With a sensitive area of ∼ 150 cm2, this camera is based on arrays of lutetium oxyorthosilicate (LSO) crystals (1×1×3 mm3) coupled to 11×11-mm2 position-sensitive avalanche photodiodes (PSAPD). GATE open source software was used to perform Monte Carlo simulations to optimize the parameters for the camera design. The noise equivalent counting (NEC) rate, together with the true, scatter, and random counting rates were simulated at different time and energy windows. Focal plane tomography (FPT) was used for visualizing the tumors at different depths between the two detector panels. Attenuation and uniformity corrections were applied to images.
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2004
Recently, there has been great interest in developing finely pixellated position-sensitive scinti... more Recently, there has been great interest in developing finely pixellated position-sensitive scintillation detectors for ultra-high-resolution Positron Emission Tomography (PET) systems designed for breast cancer detection, diagnosis, and staging and for imaging small laboratory animals. We are developing a different high-resolution PET detector design that promotes nearly complete scintillation light collection in ⩽1 mm wide, >10 mm thick lutetium oxyorthosilicate (LSO) crystals. The design requires the use of semiconductor photodetector arrays in novel configurations that significantly improve the light collection aspect ratio for minute crystals. To reduce design complexity and dead area we are investigating the use of 1 mm thick sheets of LSO in addition to discrete crystal rods, and the use of position-sensitive avalanche photodiodes (PSAPDs) which require only four readout channels per device, in addition to pixellated APD arrays. Using a 1 mm thick scintillation crystal sheet coupled to a finely pixellated APD array results in a pseudo-discrete response to flood irradiation: due to a very narrow light spread function in the thin sheet we observe sharp (<1 mm wide) peaks in sensitivity centered at the APD pixel locations in a very linear fashion all the way out to the crystal edge. We measured an energy resolution of 13.7% FWHM at 511 keV for a 1 mm LSO crystal coupled to two APD pixels. Using a 1 mm thick crystal sheet coupled to a PSAPD the response to flood and edge-on irradiation with a 22Na point source shows a compressed dynamic range compared to that observed with discrete crystals or direct X-ray irradiation. With a discrete LSO crystal array the flood response is peaked at the crystal location where light is focused onto one spot on the PSAPD. We observed strong pin-cushioning effects in all PSAPD measurements. All LSO-PSAPD configurations studied had high aspect ratio for light collection and achieved energy resolutions ⩽12% FWHM at 511 keV.
We are developing cadmium zinc telluride detectors with three-dimensional positioning capabilitie... more We are developing cadmium zinc telluride detectors with three-dimensional positioning capabilities for high-resolution PET imaging. These detectors exhibit high spatial resolution (1 mm), energy resolution (2.5% full width at half maximum for 511 keV photons), and the ability to identify the 3-D coordinates of individual Compton and photoelectric interactions within the detector. These detectors can operate in conventional PET mode measuring photons in coincidence and as a Compton camera for single photon events. In this work, we show how the capabilities of this detector can be used to reconstruct tissue-scatter coincidence events. We present a scatter projector function for positioning tissue-scatter coincidence events in the field of view. Using Monte Carlo simulated data generated by GATE (Geant4), we showed that this new approach might be used to increase the number of usable counts in PET.
We have developed a method using polynomial correction derived from a finite element model (FEM) ... more We have developed a method using polynomial correction derived from a finite element model (FEM) to correct spatial linearity of scintillation detectors that use position sensitive avalanche photodiodes (PSAPD). A PSAPD is a planar avalanche photodiode with a resistive coating that allows continuous, but non-linear, positioning of scintillation light pulses over the entire active area. The spatial response of a scintillation crystal array coupled to a PSAPD shows a characteristic pincushion distortion when using a linear center of mass positioning calculation. A finite element simulation was used to derive the spatial response function for the PSAPD detector, and then used to calculate a polynomial linearity correction. We performed spatial linearity correction of several flood histograms from a 22Na point source on discrete, scored and continuous crystal arrays of lutetium orthosilicate (LSO). For discrete arrays, spatial linearity correction improves crystal segmentation by correcting the pincushion distorted peaks in the 2-D crystal positioning histogram. For continuous sheets, spatial linearity correction allows for linear positioning over the central part of the crystal array without the use of time consuming spatial calibration measurements
We studied the performance of a dual-plate positron emission tomography (PET) camera dedicated to... more We studied the performance of a dual-plate positron emission tomography (PET) camera dedicated to breast cancer imaging using Monte Carlo simulation based on GATE open code software. The PET camera under development has two 10times15 cm2 plates that are constructed from arrays of 1times1times3 mm3 LSO crystals coupled to novel silicon-based ultra-thin (<300 mum) position-sensitive avalanche photodiodes (PSAPD). With the photodetector configured "edge-on", incoming photons see effectively 2-cm-thick of LSO with directly measured 3-mm photon depth-of-interaction. Simulations predict that this camera will have >10% sensitivity, and detector measurements show ~1 mm3 intrinsic spatial resolution, <12% energy resolution, and ~2 ns coincidence time resolution. With a breast phantom including breast, heart and torso activity (concentration ratio of 1:10:1, respectively), count performance was studied under varying time and energy windows. We also studied visualization of hot spheres within the breast for 1times1times3 mm3, 2times2times10 mm3, 3times3times30 mm3 and 4times4times20 mm3 crystal resolutions at different plate separations. Images were reconstructed by focal plane tomography and 3D OS-EM with attenuation and solid angle corrections applied. With an activity concentration ratio of tumor:breast:heart:torso of 10:1:10:1, only the dual-plate PET camera comprising 1times1times3 mm3 crystals can resolve 2.5-mm tumor spheres with an average peak-to-valley ratio of 1.3 in only 30 seconds of acquisition time
PET at the highest level is an inverse problem: reconstruct the location of the emission (which l... more PET at the highest level is an inverse problem: reconstruct the location of the emission (which localize biological function) from detected photons. Ideally, one would like to directly measure an annihilation photon's incident direction on the detector. In the developed algorithm, Bayesian Estimation for Angle Recovery (BEAR), we utilized the increased information gathered from localizing photon interactions in the detector and developed a Bayesian estimator for a photon's incident direction. Probability distribution functions (PDFs) were filled using an interaction energy weighted mean or center of mass (COM) reference space, which had the following computational advantages: (1) a significant reduction in the size of the data in measurement space, making further manipulation and searches faster (2) the construction of COM space does not depend on measurement location, it takes advantage of measurement symmetries, and data can be added to the training set without knowledge and recalculation of prior training data, (3) calculation of posterior probability map is fully parallelizable, it can scale to any number of processors. These PDFs were used to estimate the point spread function (PSF) in incident angle space for (i) algorithm assessment and (ii) to provide probability selection criteria for classification. The algorithm calculates both the incident θ and φ angle, with ~16 degrees RMS in both angles, limiting the incoming direction to a narrow cone. Feature size did not improve using the BEAR algorithm as an angle filter, but the contrast ratio improved 40% on average.
The number of lines of response (LOR) in a system with small crystals and depth of interaction (D... more The number of lines of response (LOR) in a system with small crystals and depth of interaction (DOI) measurement capability can require prohibitive amounts of memory and computational resources. The number of independent LORs in the small animal imaging system evaluated in this study is ∼2 × 109. We propose a method to adapt the component-based normalization model to include (1) DOI and (2) large field of view (FOV) to system inner bore volume percentage (near 100%) or percentage of view (POV) considerations without an order of magnitude increase in computational resources. This method can also compensate for bin location errors made during the LOR calculation. Included in the study were radial, axial and interference geometric efficiency and crystal absorption factors. We have observed a large effect on sensitivity from axial geometric factors, distance between positioned coincident photon interactions, and amount of crystal surrounding any particular crystal in our system. Assessing direct plane sinograms of direct normalization data (infinitely thin cylindrical annulus), we have observed that there are LORs that received zero counts due to inter-module gaps. Component based normalization pre-correction weights significantly improved the coefficient of variation for the reconstructed 1.5 mm and 1.75 mm spheres in the row nearest the center line in the axial image slices by 17%, 32%, and 51% in the z = 0 cm, z = 1.5 cm, and z = 3.0 cm axial planes, respectively.
... Peter Olcott and Craig S Levin are in the Department of Radiology and the Molecular Imaging P... more ... Peter Olcott and Craig S Levin are in the Department of Radiology and the Molecular Imaging Program at Stanford University, Palo Alto, CA, USA (email: fhabte@stanford. edu, cslevin@stanford.edu and pdo@stanford.edu respectively). ...
We are developing a novel, portable dual-panel positron emission tomography (PET) camera dedicate... more We are developing a novel, portable dual-panel positron emission tomography (PET) camera dedicated to breast cancer imaging. With a sensitive area of ∼ 150 cm2, this camera is based on arrays of lutetium oxyorthosilicate (LSO) crystals (1×1×3 mm3) coupled to 11×11-mm2 position-sensitive avalanche photodiodes (PSAPD). GATE open source software was used to perform Monte Carlo simulations to optimize the parameters for the camera design. The noise equivalent counting (NEC) rate, together with the true, scatter, and random counting rates were simulated at different time and energy windows. Focal plane tomography (FPT) was used for visualizing the tumors at different depths between the two detector panels. Attenuation and uniformity corrections were applied to images.
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2004
Recently, there has been great interest in developing finely pixellated position-sensitive scinti... more Recently, there has been great interest in developing finely pixellated position-sensitive scintillation detectors for ultra-high-resolution Positron Emission Tomography (PET) systems designed for breast cancer detection, diagnosis, and staging and for imaging small laboratory animals. We are developing a different high-resolution PET detector design that promotes nearly complete scintillation light collection in ⩽1 mm wide, >10 mm thick lutetium oxyorthosilicate (LSO) crystals. The design requires the use of semiconductor photodetector arrays in novel configurations that significantly improve the light collection aspect ratio for minute crystals. To reduce design complexity and dead area we are investigating the use of 1 mm thick sheets of LSO in addition to discrete crystal rods, and the use of position-sensitive avalanche photodiodes (PSAPDs) which require only four readout channels per device, in addition to pixellated APD arrays. Using a 1 mm thick scintillation crystal sheet coupled to a finely pixellated APD array results in a pseudo-discrete response to flood irradiation: due to a very narrow light spread function in the thin sheet we observe sharp (<1 mm wide) peaks in sensitivity centered at the APD pixel locations in a very linear fashion all the way out to the crystal edge. We measured an energy resolution of 13.7% FWHM at 511 keV for a 1 mm LSO crystal coupled to two APD pixels. Using a 1 mm thick crystal sheet coupled to a PSAPD the response to flood and edge-on irradiation with a 22Na point source shows a compressed dynamic range compared to that observed with discrete crystals or direct X-ray irradiation. With a discrete LSO crystal array the flood response is peaked at the crystal location where light is focused onto one spot on the PSAPD. We observed strong pin-cushioning effects in all PSAPD measurements. All LSO-PSAPD configurations studied had high aspect ratio for light collection and achieved energy resolutions ⩽12% FWHM at 511 keV.
We are developing cadmium zinc telluride detectors with three-dimensional positioning capabilitie... more We are developing cadmium zinc telluride detectors with three-dimensional positioning capabilities for high-resolution PET imaging. These detectors exhibit high spatial resolution (1 mm), energy resolution (2.5% full width at half maximum for 511 keV photons), and the ability to identify the 3-D coordinates of individual Compton and photoelectric interactions within the detector. These detectors can operate in conventional PET mode measuring photons in coincidence and as a Compton camera for single photon events. In this work, we show how the capabilities of this detector can be used to reconstruct tissue-scatter coincidence events. We present a scatter projector function for positioning tissue-scatter coincidence events in the field of view. Using Monte Carlo simulated data generated by GATE (Geant4), we showed that this new approach might be used to increase the number of usable counts in PET.
We have developed a method using polynomial correction derived from a finite element model (FEM) ... more We have developed a method using polynomial correction derived from a finite element model (FEM) to correct spatial linearity of scintillation detectors that use position sensitive avalanche photodiodes (PSAPD). A PSAPD is a planar avalanche photodiode with a resistive coating that allows continuous, but non-linear, positioning of scintillation light pulses over the entire active area. The spatial response of a scintillation crystal array coupled to a PSAPD shows a characteristic pincushion distortion when using a linear center of mass positioning calculation. A finite element simulation was used to derive the spatial response function for the PSAPD detector, and then used to calculate a polynomial linearity correction. We performed spatial linearity correction of several flood histograms from a 22Na point source on discrete, scored and continuous crystal arrays of lutetium orthosilicate (LSO). For discrete arrays, spatial linearity correction improves crystal segmentation by correcting the pincushion distorted peaks in the 2-D crystal positioning histogram. For continuous sheets, spatial linearity correction allows for linear positioning over the central part of the crystal array without the use of time consuming spatial calibration measurements
We studied the performance of a dual-plate positron emission tomography (PET) camera dedicated to... more We studied the performance of a dual-plate positron emission tomography (PET) camera dedicated to breast cancer imaging using Monte Carlo simulation based on GATE open code software. The PET camera under development has two 10times15 cm2 plates that are constructed from arrays of 1times1times3 mm3 LSO crystals coupled to novel silicon-based ultra-thin (<300 mum) position-sensitive avalanche photodiodes (PSAPD). With the photodetector configured "edge-on", incoming photons see effectively 2-cm-thick of LSO with directly measured 3-mm photon depth-of-interaction. Simulations predict that this camera will have >10% sensitivity, and detector measurements show ~1 mm3 intrinsic spatial resolution, <12% energy resolution, and ~2 ns coincidence time resolution. With a breast phantom including breast, heart and torso activity (concentration ratio of 1:10:1, respectively), count performance was studied under varying time and energy windows. We also studied visualization of hot spheres within the breast for 1times1times3 mm3, 2times2times10 mm3, 3times3times30 mm3 and 4times4times20 mm3 crystal resolutions at different plate separations. Images were reconstructed by focal plane tomography and 3D OS-EM with attenuation and solid angle corrections applied. With an activity concentration ratio of tumor:breast:heart:torso of 10:1:10:1, only the dual-plate PET camera comprising 1times1times3 mm3 crystals can resolve 2.5-mm tumor spheres with an average peak-to-valley ratio of 1.3 in only 30 seconds of acquisition time
PET at the highest level is an inverse problem: reconstruct the location of the emission (which l... more PET at the highest level is an inverse problem: reconstruct the location of the emission (which localize biological function) from detected photons. Ideally, one would like to directly measure an annihilation photon's incident direction on the detector. In the developed algorithm, Bayesian Estimation for Angle Recovery (BEAR), we utilized the increased information gathered from localizing photon interactions in the detector and developed a Bayesian estimator for a photon's incident direction. Probability distribution functions (PDFs) were filled using an interaction energy weighted mean or center of mass (COM) reference space, which had the following computational advantages: (1) a significant reduction in the size of the data in measurement space, making further manipulation and searches faster (2) the construction of COM space does not depend on measurement location, it takes advantage of measurement symmetries, and data can be added to the training set without knowledge and recalculation of prior training data, (3) calculation of posterior probability map is fully parallelizable, it can scale to any number of processors. These PDFs were used to estimate the point spread function (PSF) in incident angle space for (i) algorithm assessment and (ii) to provide probability selection criteria for classification. The algorithm calculates both the incident θ and φ angle, with ~16 degrees RMS in both angles, limiting the incoming direction to a narrow cone. Feature size did not improve using the BEAR algorithm as an angle filter, but the contrast ratio improved 40% on average.
The number of lines of response (LOR) in a system with small crystals and depth of interaction (D... more The number of lines of response (LOR) in a system with small crystals and depth of interaction (DOI) measurement capability can require prohibitive amounts of memory and computational resources. The number of independent LORs in the small animal imaging system evaluated in this study is ∼2 × 109. We propose a method to adapt the component-based normalization model to include (1) DOI and (2) large field of view (FOV) to system inner bore volume percentage (near 100%) or percentage of view (POV) considerations without an order of magnitude increase in computational resources. This method can also compensate for bin location errors made during the LOR calculation. Included in the study were radial, axial and interference geometric efficiency and crystal absorption factors. We have observed a large effect on sensitivity from axial geometric factors, distance between positioned coincident photon interactions, and amount of crystal surrounding any particular crystal in our system. Assessing direct plane sinograms of direct normalization data (infinitely thin cylindrical annulus), we have observed that there are LORs that received zero counts due to inter-module gaps. Component based normalization pre-correction weights significantly improved the coefficient of variation for the reconstructed 1.5 mm and 1.75 mm spheres in the row nearest the center line in the axial image slices by 17%, 32%, and 51% in the z = 0 cm, z = 1.5 cm, and z = 3.0 cm axial planes, respectively.
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Papers by Angela Foudray