Abstract
We report on the development of the PennPET Explorer whole-body imager. Methods: The PennPET Explorer is a multiring system designed with a long axial field of view. The imager is scalable and comprises multiple 22.9-cm-long ring segments, each with 18 detector modules based on a commercial digital silicon photomultiplier. A prototype 3-segment imager has been completed and tested with an active 64-cm axial field of view. Results: The instrument design is described, and its physical performance measurements are presented. These include sensitivity of 55 kcps/MBq, spatial resolution of 4.0 mm, energy resolution of 12%, timing resolution of 256 ps, and a noise-equivalent count rate above 1,000 kcps beyond 30 kBq/mL. After an evaluation of lesion torso phantoms to characterize quantitative accuracy, human studies were performed on healthy volunteers. Conclusion: The physical performance measurements validated the system design and led to high-quality human studies.
Highlights
In the last 2 decades, commercial PET scanner performance has improved dramatically with CT-based attenuation correction [1], the use of lutetium oxyorthosilicate or lutetium-yttrium oxyorthosilicate scintillators [2,3], time-of-flight reconstruction [4,5,6,7], and, most recently, silicon photomultiplier (SiPM)–based time-of-flight detectors [4,8]
The EXPLORER Consortium supported the development of our system, which we describe as a whole-body imager, since it neither requires multiposition scanning nor covers the total body, as with the United Imaging Healthcare instrument
This may not yield an absolute measure of spatial resolution for a point source in air, the results provide insight into the dependence of spatial resolution on the axial acceptance angle as it increases toward the mid-axial field of view (AFOV)
Summary
In the last 2 decades, commercial PET scanner performance has improved dramatically with CT-based attenuation correction [1], the use of lutetium oxyorthosilicate or lutetium-yttrium oxyorthosilicate scintillators [2,3], time-of-flight reconstruction [4,5,6,7], and, most recently, silicon photomultiplier (SiPM)–based time-of-flight detectors [4,8]. The axial field of view (AFOV) has not grown; it remains 16–26 cm for the newest commercial SiPM-based scanners [9,10,11] This choice is due mainly to scintillator and SiPM photosensor costs and the prevalence of clinical 18F-FDG scanning focused on measuring lesion SUV, typically at 60 min after injection, when the uptake is assumed to be at steady state. The motivation for a long-AFOV PET system is to use its high sensitivity to enhance clinical performance and to enable research applications requiring simultaneous measurement of multiple organ systems [12]. It is unknown whether such a system would primarily be used clinically to take advantage of high throughput or low-dose imaging or for research with new radiotracers. We present measurements quantifying the physical system performance, along with phantom and initial human images demonstrating its imaging performance
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