Effects of system geometry and other physical factors on photon sensitivity of high-resolution positron emission tomography

Habte, Frezghi; Foudray, A.M.K.; Olcott, Peter D.; Levin, Craig S.

doi:10.1088/0031-9155/52/13/007

Cited by 58 publications

(71 citation statements)

References 54 publications

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“…To provide sufficient DoI information and increase intrinsic spatial resolution, successive generations of PET scanners have tended to reduce the size of the scintillation crystals-or, in the extreme case, may eliminate the scintillator altogether, instead using direct gamma photon detection in pixellated semiconductor detector arrays (typically fabricated from relatively thick silicon or CZT) (Domenico et al 2007, Habte et al 2007, Park et al 2007, Li et al 2013. This geometry results in a very large number of potential LoRs, especially for 3D scanners with a multi-ring geometry.…”

Section: Introductionmentioning

confidence: 99%

A new virtual ring-based system matrix generator for iterative image reconstruction in high resolution small volume PET systems

Safavi-Naeini

Franklin

et al. 2015

Phys. Med. Biol.

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A common approach to improving the spatial resolution of small animal PET scanners is to reduce the size of scintillation crystals and/or employ high resolution pixellated semiconductor detectors. The large number of detector elements results in the system matrix-an essential part of statistical iterative reconstruction algorithms-becoming impractically large. In this paper, we propose a methodology for system matrix modelling which utilises a virtual single-layer detector ring to greatly reduce the size of the system matrix without sacrificing precision. Two methods for populating the system matrix are compared; the first utilises a geometrically-derived system matrix based on Siddon's ray tracer method with the addition of an accurate detector response function, while the second uses Monte Carlo simulation to populate the system matrix. The effectiveness of both variations of the proposed technique is demonstrated via simulations of PETiPIX, an ultra high spatial resolution small animal PET scanner featuring high-resolution DoI capabilities, which has previously been simulated and characterised using classical image reconstruction methods. Compression factors of × 5 10 7 and × 2.5 10 7 are achieved using this methodology for the system matrices produced using the Institute of Physics and Engineering in MedicineContent from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. geometric and Monte Carlo-based approaches, respectively, requiring a total of 0.5-1.2 GB of memory-resident storage. Images reconstructed from Monte Carlo simulations of various point source and phantom models, produced using system matrices generated via both geometric and simulation methods, are used to evaluate the quality of the resulting system matrix in terms of achievable spatial resolution and the CRC, CoV and CW-SSIM index image quality metrics. The Monte Carlo-based system matrix is shown to provide the best image quality at the cost of substantial one-off computational effort and a lower (but still practical) compression factor. Finally, a straightforward extension of the virtual ring method to a three dimensional virtual cylinder is demonstrated using a 3D DoI PET scanner.

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Section: Introductionmentioning

confidence: 99%

A new virtual ring-based system matrix generator for iterative image reconstruction in high resolution small volume PET systems

Safavi-Naeini

Franklin

et al. 2015

Phys. Med. Biol.

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“…The detector modules can be tightly stacked to maximize packing fraction, and their ability to position the 3-D coordinates of individual photon interactions enables uniform spatial resolution throughout the system's 8 cm x 8 cm x 8 cm field of view [1,4]. The modules are arranged such that annihilation photons enter the CZT crystal edge-on to traverse a minimum of 4 cm of CZT material, yielding >86% intrinsic detection efficiency for single 511 keY photons (>73% for coincident pairs) [2,3]. MIlL's prior studies of CZT focused on the performance of singular CZT crystals.…”

Section: Introductionmentioning

confidence: 99%

Characterization of inter-detector effects in a 3-D position-sensitive dual-CZT detector modules for PET

Levin

2012

2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC)

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This study presents results from two 3-D position sensitive dual-CZT photon detector modules designed for a high resolution small animal PET system. Each module comprises a stack of two 40 mm x 40 mm x 5 mm monolithic CZT crystals metalized with a cross-strip electrode pattern that achieves better than 1 mm resolution. In contrast to our prior work focusing on single-crystal CZT performance, this study investigated the impact of detector packaging and module construction on detector performance. This study measured five module-level characteristics; the corresponding findings are as follows. First, the study measured the fraction of event triggers potentially induced by intra-module cross-talk, i.e. occurrence of simultaneous triggers on anode or cathode strips of one detector and the corresponding electrode strips on another detector across the thin flex circuit. This was measured to be 1.51±0.34% for anode channels and 6.40±1.21 % for cathode channelssufficiently low not to be of specific concern for PET imaging.Second, detector photon sensitivity is maintained at detector detector boundaries, with the edge anode strip detecting approximately equal number of events as other anode strips.Third, the anode energy resolution in dual-module configuration was measured to be 6.18±0.87% and 4.38±0.67% -slightly degraded from previous studies of an individual detector crystal due to either increased anode stray capacitance or crystal variances, or both. Fourth, stray capacitance on cathode channels was seen to increase the readout noise level by a factor of -2.8 for a free-standing dual-detector module, and by a factor of -4.8 for two stacked dual-detector modules. This revealed the need to increase the cathode-cathode separation across flex circuits and the use of a lower dielectric constant flex substrate.Finally, a survey of noisy, intermittent or disconnected electrode channels highlighted the need for tight control of the module assembly process.

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“…Techniques for determining DoI include placing photodetectors on opposite sides of a single scintillator slab and using the relative pulse heights to determine DoI (phoswitch detector), using a non-uniform optical coupling between adjacent pairs of scintillator crystals, in which DoI is determined from the relationship between the energies measured in the adjacent crystals, and segmenting (optically isolating) the scintillator and detectors in the radial direction [2], [3], [4]. Simulation based studies have also suggested alternative system geometries such as box-like formation (as apposed to cylendrical) to optimise photon sensitivity [5].…”

Section: Introductionmentioning

confidence: 99%

SiPM based detector module and digital data acquisition system for PET: Initial results

Safavi-Naeini

Franklin

Petasecca

et al. 2009

2009 IEEE Nuclear Science Symposium Conference Record (NSS/MIC)

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Abstract-A novel detector module configuration based on silicon photomultiplier (SiPM) detectors with LYSO scintillators, a multichannel mixed analog/digital ASIC and an FPGA-based digital data acquisition system has been developed for preclinical positron emission tomography (PET). The SCEPTER ASIC, originally developed for soft X-ray detection at Brookhaven National Laboratory, has a unique architecture incorporating multiple peak detectors and time-to-amplitude converters, and offers an extremely low dead time, making it ideal for coincidence detection. A representative pair of channels in the prototype system has been characterised. Measured energy and timing resolutions are reported for coincidences between a singlepixel SiPM detector and a conventional PMT. A timing resolution of 11.7 ns was achieved during a 48 hour run. Energy resolution for the SiPM device and data acquisition system was found to be 17%.

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Effects of system geometry and other physical factors on photon sensitivity of high-resolution positron emission tomography

Cited by 58 publications

References 54 publications

A new virtual ring-based system matrix generator for iterative image reconstruction in high resolution small volume PET systems

A new virtual ring-based system matrix generator for iterative image reconstruction in high resolution small volume PET systems

Characterization of inter-detector effects in a 3-D position-sensitive dual-CZT detector modules for PET

SiPM based detector module and digital data acquisition system for PET: Initial results

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