Abstract
PurposeThe DMI PET/CT is a modular silicon photomultiplier–based scanner with an axial field-of-view (FOV) between 15 and 25 cm depending on ring configuration (3, 4, or 5 rings). A new generation of the system includes a reengineered detector module, featuring improved electronics and an additional 6th ring, extending the axial FOV to 30 cm. We report on the performance evaluation of the 6-ring upgraded Generation 2 (Gen2) system while values are also reported for the 5-ring configuration of the very same system prior to the upgrade.MethodsPET performance was evaluated using the NEMA NU 2–2018 standard for spatial resolution, sensitivity, image quality, count rate performance, timing resolution, and image co-registration accuracy. Patient images were used to assess image quality.ResultsThe average system sensitivity was measured at 32.76 cps/kBq (~ 47% increase to 5 rings at 22.29 cps/kBq) while noise equivalent count rate peaked at 434.3 kcps corresponding to 23.6 kBq/mL (~ 60% increase to Generation 1 (Gen1) and 39% to Gen2 5 rings). Contrast recovery ranged between 54.5 and 85.8% similar to 5 rings, while the 6 rings provided lower background variability (2.3–8.5% for 5 rings vs 1.9–6.8% for 6 rings) and lower lung error (4.0% for the 5 rings and 3.16% for the 6 rings). Transverse/axial full width at half-maximum (FWHM) at 1 cm (3.79/4.26 mm) and 10 cm (4.29/4.55 mm), scatter fraction (40.2%), energy resolution (9.63%), and time-of-flight (TOF) resolution (389.6 ps at 0 kBq/mL) were in line to previously reported values measured across different system configurations. Improved patient image quality is obtained with the 6 rings compared to the 5 rings, while image quality is retained even at reduced scan times, enabling WB dynamic acquisitions.ConclusionsThe higher sensitivity of the 6-ring DMI compared to the 5-ring configuration may lead to improved image quality of clinical images at reduced scan time. Additionally, it could equally be used to allow improved temporal sampling and/or reduced overall scan time in dynamic acquisitions. Conversely, temporal sampling and scan time could be traded per application to further drive injected dose at lower levels.
Highlights
Hybrid positron emission tomography/computed tomography (PET/CT) imaging has been the spearhead of the nuclear medicine since its introduction in the early 2000s
With respect to count rate performance, the peak noise equivalent count rates (NECRs) on the 6-ring system was measured at 434.3 kcps at 23.6 kBq/mL while in comparison the 5-ring NECR peaked at 312.9 kcps at 22.5 kBq/mL (Fig. 1)
Maximum absolute error and mean error below peak NECR was measured at 3.95% and 2.77% for the 6-ring and 4.61% and 2.31% for the 5-ring Generation 2 (Gen2) respectively and with a linear response for a wide range of DMI system (a, b) and 5-ring configuration of the same system (c, d)
Summary
Hybrid positron emission tomography/computed tomography (PET/CT) imaging has been the spearhead of the nuclear medicine since its introduction in the early 2000s. Additional modifications to the dmod-integrated circuits for faster coincidence event processing allow for improved count rate performance on all pre-existing and new extended axial FOV detector configurations. Incorporation of an additional ring coupled with improved dmod photon-counting electronics is expected to substantially improve the intrinsic sensitivity as well as count rate capability of such extended axial FOV system. Such a change in detector specifications and corresponding performance is expected to impact upon image quality, scan time, and injected dose in static and dynamic acquisitions performed.
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