Cerebral SPECT imaging with different acquisition schemes using varying levels of multiplexing versus sensitivity in an adaptive multi-pinhole brain-dedicated scanner

Abstract

Application of multi-pinhole collimator in pinhole-based SPECT increases detection sensitivity. The presence of multiplexing in projection images due to the usage of multiple pinholes can further improve the sensitivity at the cost of adding data ambiguity. We are developing a next-generation adaptive brain-dedicated SPECT system -AdaptiSPECT-C. The AdaptiSPECT-C can adapt the multiplexing level and system sensitivity using adaptable pinhole modules. In this study, we investigated the performance of 4 data acquisition schemes with different multiplexing levels and sensitivities on cerebral SPECT imaging. Schemes #1, #2, and #3 have <1%, 67%, and 31% overall multiplexing, respectively, while the 4th scheme without multiplexing is considered as ground truth. The ground-truth and schemes #1-3 have 1.0, 1.7, 5.1, and 4.0 times higher sensitivity, respectively, compared to a dual-headed parallel-hole SPECT system at matched spatial resolution. A customized XCAT brain perfusion digital phantom emulating the distribution of I-123 N-isopropyl iodoamphetamine (IMP) in a 99th percentile size male was used for simulations. Data acquisition for each scheme was performed at two count levels (low-count and high-count relative to the recommended clinical count level). The normalized root-mean-square error (NRMSE) for schemes #1, #2, and #3 with the low-count (high-count) scenario showed 11%, 4%, and 5% (10%, 5%, and 6%) deviation, respectively, from that of the multiplex-free ground truth. For both the low-count and high-count scenarios, scheme #1 resulted in the least accurate activity ratio (AR) for almost all the analyzed graymatter brain regions. Further schemes #2 or #3 led to the most accurate AR values with both lowcount and high-count scenarios for all the analyzed gray-matter regions. It was thus observed that even with this large head size which leads to significant multiplexing levels, the higher sensitivity from multiplexing could to some extent mitigate the data ambiguity and be translated into reconstructed images of higher quality. RECEIVED

Mesh modeling of system geometry and anatomy phantoms for realistic GATE simulations and their inclusion in SPECT reconstruction

“…Each module of AdaptiSPECT-C can be irradiated by up to 5 pinholes, the status (i.e. closed or opened) and size of which can be adapted to the imaging task for highperformance imaging (Momsen et al 2018, Zeraatkar et al 2021b. For the purposes of this study, each of the 23 modules was associated to a single knife-edge pinhole, 4 mm in diameter, with an 80.5°opening angle (Auer et al 2021).…”

“…We are constructing a multi-pinhole, stationary, adaptable SPECT system dedicated to clinical brain imaging and capable of dynamic imaging, which we named AdaptiSPECT-C (Zeraatkar et al 2020, Auer et al 2021, Zeraatkar et al 2021aZeraatkar et al , 2021b. Some research groups have described the usage of SPECT simulation employing mesh modeling of a few system components, such as the collimator, but the limited number of detector modules arranged in a simple configuration remains modeled via primitive objects and replicate tools for which projections can be generated automatically via the built-in tools currently available in GATE (Nguyen et al 2019).…”