Tapered LSO arrays for small animal PET

Yang, Yongfeng; James, Sara St.; Wu, Yue; Du, Heng; Qi, Jinyi; Farrell, R.; Dokhale, Purushottam; Shah, K.S.; Vaigneur, Keith; Cherry, Simon R.

doi:10.1088/0031-9155/56/1/009

Cited by 51 publications

(51 citation statements)

References 32 publications

(53 reference statements)

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“…29 There is a growing trend of going toward finer crystal pixelation to improve spatial resolution, specifically in preclinical or dedicated brain PET systems. 5,[30][31][32][33] Using radially long scintillation crystals to maximize the detection sensitivity of the PET camera increases the parallax error 34,35 and degrades the system's spatial resolution, 28 especially at trans-axial distances far from the center field of view (FOV). Additionally, by accepting bigger ring differences for coincident events along the axial FOV, the parallax error causes distortions in the reconstructed image.…”

Section: Introductionmentioning

confidence: 99%

Development of a novel depth of interaction PET detector using highly multiplexed G‐APD cross‐strip encoding

Kolb¹,

Parl²,

Mantlik³

et al. 2014

Medical Physics

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Purpose: The aim of this study was to develop a prototype PET detector module for a combined small animal positron emission tomography and magnetic resonance imaging (PET/MRI) system. The most important factor for small animal imaging applications is the detection sensitivity of the PET camera, which can be optimized by utilizing longer scintillation crystals. At the same time, small animal PET systems must yield a high spatial resolution. The measured object is very close to the PET detector because the bore diameter of a high field animal MR scanner is limited. When used in combination with long scintillation crystals, these small-bore PET systems generate parallax errors that ultimately lead to a decreased spatial resolution. Thus, we developed a depth of interaction (DoI) encoding PET detector module that has a uniform spatial resolution across the whole field of view (FOV), high detection sensitivity, compactness, and insensitivity to magnetic fields. Methods: The approach was based on Geiger mode avalanche photodiode (G-APD) detectors with cross-strip encoding. The number of readout channels was reduced by a factor of 36 for the chosen block elements. Two 12 × 2 G-APD strip arrays (25 μm cells) were placed perpendicular on each face of a 12 × 12 lutetium oxyorthosilicate crystal block with a crystal size of 1.55 × 1.55 × 20 mm. The strip arrays were multiplexed into two channels and used to calculate the x, y coordinates for each array and the deposited energy. The DoI was measured in step sizes of 1.8 mm by a collimated 18 F source. The coincident resolved time (CRT) was analyzed at all DoI positions by acquiring the waveform for each event and applying a digital leading edge discriminator. Results: All 144 crystals were well resolved in the crystal flood map. The average full width half maximum (FWHM) energy resolution of the detector was 12.8% ± 1.5% with a FWHM CRT of 1.14 ± 0.02 ns. The average FWHM DoI resolution over 12 crystals was 2.90 ± 0.15 mm. Conclusions: The novel DoI PET detector, which is based on strip G-APD arrays, yielded a DoI resolution of 2.9 mm and excellent timing and energy resolution. Its high multiplexing factor reduces the number of electronic channels. Thus, this cross-strip approach enables low-cost, high-performance PET detectors for dedicated small animal PET and PET/MRI and potentially clinical PET/MRI systems.

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Section: Introductionmentioning

confidence: 99%

Development of a novel depth of interaction PET detector using highly multiplexed G‐APD cross‐strip encoding

Kolb¹,

Parl²,

Mantlik³

et al. 2014

Medical Physics

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“…The computational cost using the LORI method can be significantly reduced without compromising image quality; furthermore, it provides good insights into collimated PET. Finally, the collimated PET method can mitigate the technical difficulties of manufacturing extremely small crystals with extremely high cost (Yang et al 2011), and it may open a new dimension to improve spatial resolution in small-animal and human PET imaging applications.…”

Section: Discussionmentioning

confidence: 99%

“…The most direct method is to reduce the crystal size (i.e. increase the number of crystals per unit area) by scintillator manufacturing techniques (Cherry et al 1997, Miyaoka et al 2001, Yang et al 2011). The reduction in crystal size can effectively improve the spatial resolution; however, it may not be cost effective with current manufacturing processes and it leads to increased inter-crystal scatter.…”

Section: Introductionmentioning

confidence: 99%

LOR-interleaving image reconstruction for PET imaging with fractional-crystal collimation

Li¹,

Matej²,

Karp³

et al. 2015

Phys. Med. Biol.

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Positron emission tomography (PET) has become an important modality in medical and molecular imaging. However, in most PET applications, the resolution is still mainly limited by the physical crystal sizes or the detector’s intrinsic spatial resolution. To achieve images with better spatial resolution in a central region of interest (ROI), we have previously proposed using collimation in PET scanner. The collimator is designed to partially mask detector crystals to detect lines of response (LORs) within fractional crystals. A sequence of collimator-encoded LORs is measured with different collimation configurations. This novel collimated scanner geometry makes the reconstruction problem challenging, as both detector and collimator effects need to be modeled to reconstruct high-resolution images from collimated LORs. In this paper, we present an LOR-interleaving (LORI) algorithm, which incorporates these effects and has the advantage of reusing existing reconstruction software, to reconstruct high-resolution images for PET with fractional-crystal collimation. We also develop a 3-D ray-tracing model incorporating both the collimator and crystal penetration for simulations and reconstructions of the collimated PET. By registering the collimator-encoded LORs with the collimator configurations, high-resolution LORs are restored based on the modeled transfer matrices using the nonnegative least-squares method and EM algorithm. The resolution-enhanced images are then reconstructed from the high-resolution LORs using the MLEM or OSEM algorithm. For validation, we applied the LORI method to a small-animal PET scanner, A-PET, with a specially designed collimator. We demonstrate through simulated reconstructions with a hot-rod phantom and MOBY phantom that the LORI reconstructions can substantially improve spatial resolution and quantification compared to the uncollimated reconstructions. The LORI algorithm is crucial to improve overall image quality of collimated PET, which can have significant implication in preclinical and clinical ROI imaging applications.

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“…In many other studies, it has been shown that a diffuse reflector generally provides superior DOI resolution. 22,23 Second, mispositioned events will introduce greater DCI uncertainty as each crystal displays a unique DCI vs DOI relationship. Finally, beam broadening and intercrystal scatter with side-on measurements will introduce blurring of DOI metrics.…”

Section: Head-on (%)mentioning

confidence: 99%

A combined time‐of‐flight and depth‐of‐interaction detector for total‐body positron emission tomography

et al. 2016

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Purpose: In support of a project to build a total-body PET scanner with an axial field-of-view of 2 m, the authors are developing simple, cost-effective block detectors with combined time-of-flight (TOF) and depth-of-interaction (DOI) capabilities. Methods: This work focuses on investigating the potential of phosphor-coated crystals with conventional PMT-based block detector readout to provide DOI information while preserving timing resolution. The authors explored a variety of phosphor-coating configurations with single crystals and crystal arrays. Several pulse shape discrimination techniques were investigated, including decay time, delayed charge integration (DCI), and average signal shapes. Results: Pulse shape discrimination based on DCI provided the lowest DOI positioning error: 2 mm DOI positioning error was obtained with single phosphor-coated crystals while 3-3.5 mm DOI error was measured with the block detector module. Minimal timing resolution degradation was observed with single phosphor-coated crystals compared to uncoated crystals, and a timing resolution of 442 ps was obtained with phosphor-coated crystals in the block detector compared to 404 ps without phosphor coating. Flood maps showed a slight degradation in crystal resolvability with phosphor-coated crystals; however, all crystals could be resolved. Energy resolution was degraded by 3%-7% with phosphor-coated crystals compared to uncoated crystals.Conclusions: These results demonstrate the feasibility of obtaining TOF-DOI capabilities with simple block detector readout using phosphor-coated crystals. C 2016 American Association of Physicists in Medicine. [http://dx

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Tapered LSO arrays for small animal PET

Cited by 51 publications

References 32 publications

Development of a novel depth of interaction PET detector using highly multiplexed G‐APD cross‐strip encoding

Development of a novel depth of interaction PET detector using highly multiplexed G‐APD cross‐strip encoding

LOR-interleaving image reconstruction for PET imaging with fractional-crystal collimation

A combined time‐of‐flight and depth‐of‐interaction detector for total‐body positron emission tomography

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