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

Berg, Eric; Roncali, Emilie; Kapusta, M.; Du, Junwei; Cherry, Simon R.

doi:10.1118/1.4940355

Cited by 42 publications

(34 citation statements)

References 32 publications

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“…This relatively small increase in scatter fraction for larger acceptance angles may appear somewhat counterintuitive since oblique sinograms contain higher numbers of scatter events (35); however, the number of additional sinograms diminishes with increasing acceptance angle and so the overall scatter fraction is minimally affected by increasing acceptance angle, as demonstrated previously in simulations (10,35). Lastly, we measured the effect of the acceptance angle on spatial resolution by imaging a point source in a warm background, as it has been suggested that parallax error from depthof-interaction effects and blurring from photon noncollinearity may increase in a scanner with a wide acceptance angle, leading to degraded axial spatial resolution (7,36). However, there was only minor degradation in axial spatial resolution (0.5 mm in full width at half maximum) at a 46°acceptance angle, compared with a 14°a cceptance angle, in agreement with the simulation results shown by Schmall et al (7).…”

Section: Discussionmentioning

confidence: 64%

Development and Evaluation of mini-EXPLORER: A Long Axial Field-of-View PET Scanner for Nonhuman Primate Imaging

et al. 2018

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We describe a long axial field-of-view (FOV) PET scanner for high-sensitivity and total-body imaging of nonhuman primates and present the physical performance and first phantom and animal imaging results. The mini-EXPLORER PET scanner was built using the components of a clinical scanner reconfigured with a detector ring diameter of 43.5 cm and an axial length of 45.7 cm. National Electrical Manufacturers Association (NEMA) NU-2 and NU-4 phantoms were used to measure sensitivity and count rate performance. Reconstructed spatial resolution was investigated by imaging a radially stepped point source and a Derenzo phantom. The effect of the wide acceptance angle was investigated by comparing performance with maximum acceptance angles of 14°-46°. Lastly, an initial assessment of the in vivo performance of the mini-EXPLORER was undertaken with a dynamicF-FDG nonhuman primate (rhesus monkey) imaging study. The NU-2 total sensitivity was 5.0%, and the peak noise-equivalent count rate measured with the NU-4 monkey scatter phantom was 1,741 kcps, both obtained using the maximum acceptance angle (46°). The NU-4 scatter fraction was 16.5%, less than 1% higher than with a 14° acceptance angle. The reconstructed spatial resolution was approximately 3.0 mm at the center of the FOV, with a minor loss in axial spatial resolution (0.5 mm) when the acceptance angle increased from 14° to 46°. The rhesus monkeyF-FDG study demonstrated the benefit of the high sensitivity of the mini-EXPLORER, including fast imaging (1-s early frames), excellent image quality (30-s and 5-min frames), and late-time-point imaging (18 h after injection), all obtained at a single bed position that captured the major organs of the rhesus monkey. This study demonstrated the physical performance and imaging capabilities of a long axial FOV PET scanner designed for high-sensitivity imaging of nonhuman primates. Further, the results of this study suggest that a wide acceptance angle can be used with a long axial FOV scanner to maximize sensitivity while introducing only minor trade-offs such as a small increase in scatter fraction and slightly degraded axial spatial resolution.

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Section: Discussionmentioning

confidence: 64%

Development and Evaluation of mini-EXPLORER: A Long Axial Field-of-View PET Scanner for Nonhuman Primate Imaging

et al. 2018

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“…To fully exploit the sensitivity gains of extended axial length, and greater solid angle coverage, the axial acceptance angle will be large and cause a parallax error in the axial direction (a fully-3D 2 m long scanner with a 85 cm diameter will have an axial acceptance angle ±67°). This parallax error will be most pronounced in the center of the axial and transverse imaging FOV, and in addition to an inherent radial parallax error associated with the ring geometry, it has been suggested that PET scanner designs with long-axial FOVs may have worse spatial resolution compared to more traditional scanner designs having a shorter axial FOV (Berg et al 2016, Zhang et al 2016). …”

Section: Introductionmentioning

confidence: 99%

Parallax error in long-axial field-of-view PET scanners—a simulation study

et al. 2016

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There is a growing interest in the design and construction of a PET scanner with a very long axial extent. One critical design challenge is the impact of the long axial extent on the scanner spatial resolution properties. In this work, we characterize the effect of parallax error in PET system designs having an axial FOV of 198 cm (total-body PET scanner) using fully-3D Monte Carlo simulations. Two different scintillation materials were studied: LSO and LaBr3. The crystal size in both cases was 4×4×20 mm3. Several different depth-of-interaction (DOI) encoding techniques were investigated to characterize the improvement in spatial resolution when using a DOI capable detector. To measure spatial resolution we simulated point sources in a warm background in the center of the imaging FOV, where the effects of axial parallax are largest, and at several positions radially offset from the center. Using a line-of-response based OSEM reconstruction algorithm we found that the axial resolution in an LSO scanner degrades from 4.8 mm to 5.7 mm (FWHM) at the center of the imaging FOV when extending the axial acceptance angle (α) from ±12° (corresponding to an axial FOV of 18 cm) to the maximum of ±67°—a similar result was obtained with LaBr3, in which the axial resolution degraded from 5.3 mm to 6.1 mm. For comparison we also measured the degradation due to radial parallax error in the transverse imaging FOV; the transverse resolution, averaging radial and tangential directions, of an LSO scanner was degraded from 4.9 mm to 7.7 mm, for a measurement at the center of the scanner compared to a measurement with a radial offset of 23 cm. Simulations of a DOI detector design improved the spatial resolution in all dimensions. The axial resolution in the LSO-based scanner, with α = ±67°, was improved from 5.7 mm to 5.0 mm by incorporating a two-layer DOI detector. These results characterize the maximum axial blurring for a fully open 2 m long PET scanner and demonstrate that large sensitivity gains are possible with a modest reduction in resolution when using current clinical detector technology with no DOI capability.

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“…Better configurations for TOF applications have been studied by several groups using a LaBr 3 /CeBr 3 pair (Schmall et al 2015) or an L 0.95 GSO-fast (0.025 mol% Ce)/L 0.95 GSO-slow (0.75 mol% Ce) pair (Yamamoto et al 2016). Another possible approach is the use of a phosphor-coated single layer crystal to make the depth-dependent decay time different (Berg et al 2016). Future work should therefore include a DOI detector using the fast and bright scintillator pair to construct the DOI-TOF block.…”

Section: Discussionmentioning

confidence: 99%

Single transmission-line readout method for silicon photomultiplier based time-of-flight and depth-of-interaction PET

Lee

2017

Phys. Med. Biol.

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We propose a novel single transmission-line readout method for whole-body time-of-flight positron emission tomography applications, without compromising on performance. The basic idea of the proposed multiplexing method is the addition of a specially prepared tag signal ahead of the scintillation pulse. The tag signal is a square pulse that encodes photon arrival time and channel information. The 2D position of a silicon photomultiplier (SiPM) array is encoded by the specific width and height of the tag signal. A summing amplifier merges the tag and scintillation signals of each channel, and the final output signal can be acquired with a one-channel digitizer. The feasibility and performance of the proposed method were evaluated using a 1:1 coupled detector consisting of 4 × 4 array of LGSO crystals and 16 channel SiPM. The sixteen 3 mm LGSO crystals were clearly separated in the crystal-positioning map with high reliability. The average energy resolution and coincidence resolving time were 11.31 ± 0.55% and 264.7 ± 10.7 ps, respectively. We also proved that the proposed method does not degrade timing performance with increasing multiplexing ratio. The two types of LGSO crystals (LGSO and LGSO) in phoswich detector were also clearly identified with the high-reliability using pulse shape discrimination, thanks to the well-preserved pulse shape information. In conclusion, the proposed multiplexing method allows decoding of the 3D interaction position of gamma rays in the scintillation detector with single-line readout.

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

Cited by 42 publications

References 32 publications

Development and Evaluation of mini-EXPLORER: A Long Axial Field-of-View PET Scanner for Nonhuman Primate Imaging

Development and Evaluation of mini-EXPLORER: A Long Axial Field-of-View PET Scanner for Nonhuman Primate Imaging

Parallax error in long-axial field-of-view PET scanners—a simulation study

Single transmission-line readout method for silicon photomultiplier based time-of-flight and depth-of-interaction PET

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