Assessment of CZT Dual Panel PET as total-body imaging in small animal with high spatial resolution and multi-sample capability

Introduction: Positron Emission Tomography (PET) scanners represent a pivotal advancement in nuclear medicine, providing unparalleled insights into metabolic processes and molecular function within the human body. The clinical advantages of PET scanners have catalyzed the development of small animal PET scanners, expanding their applications such as treatment efficiency evaluation, drug delivery, and system design [1]. Given the diminutive size of subjects such as mice and rats, the spatial resolution of the scanner plays a crucial role in the accuracy of studies. While the majority of conventional small animal PET scanners provide a spatial resolution above one millimeter, there is a growing demand for tomographs capable of sub-millimeter precision.

Another challenge in preclinical PET imaging is the time-intensive scanning process, stemming from limitations in the number of samples that can be scanned simultaneously. This constraint, a result of the tomograph's small imaging volume, restricts the total number of animals per study, potentially impacting the reliability of the obtained results.

The dual-panel head and neck PET scanner, developed at UCSC with a CZT detector, boasts exceptional performance features, including high spatial resolution, a modular configuration, and an adjustable diameter [2-5].

The primary objective of this study is to assess the efficacy of the CZT dual-panel detector in facilitating multi-sample preclinical imaging studies as a total body grade PET scanner.

Methods: This study zeroes in on the key characteristics of the CZT dual-panel PET scanner, evaluating its suitability for multi-sample imaging. The system has been modelled using the GATE toolkit, featuring two flat panels each measuring 15 x 20 cm². These panels comprise CZT crystals, each sized at 40 x 40 x 5 mm³. We assessed the scanner's sensitivity, scatter fraction, and spatial resolution in accordance with NEMA NU4 2008 standards. For scatter fraction evaluation, we employed mouse and rat size phantoms as recommended by NEMA. The distance between the two panels of this scanner is adaptable based on the imaging requirements. For the current study, distances of 8 cm and 10 cm were selected for the mouse and rat, respectively.

Results: The spatial resolution of the scanner was meticulously evaluated at the positions recommended by the NEMA NU4 2008 standards. We employed the Maximum Likelihood Expectation Maximization (MLEM) algorithm with a voxel size of 0.25 mm for image reconstruction. This approach yielded an average full width at half maximum of approximately 0.5 mm within the scanner's imaging volume. To calculate scatter fractions, we used the single-slice rebinning (SSRB) method, resulting in scatter fraction values of 0.42% for mice and 4.97% for rats. Correspondingly, the sensitivities achieved were 9.5% for mouse imaging and 7.8% for rat imaging.

Conclusions: The main aim of this study was to assess the performance of the CZT dual-panel PET scanner for preclinical applications, particularly its ability for simultaneous multi-object imaging. The high spatial resolution of the CZT dual-panel PET scanner (~0.5 mm), capable of sub-millimeter precision, marks a significant advancement in highly accurate preclinical studies, including brain function and metabolic imaging. Its large imaging volume enables the scanning of multiple mice or rats at once, offering a speed enhancement of up to three times compared to the largest and nine times faster than conventional small animal PET scanners. Figure 1 shows the volumetric resolution of the total body grade small animal PET scanners as the function of their sensitivity [1]. CZT dual panel PET scanner with very good sensitivity and spatial resolution has outstanding performance compared to the other conventional tomographs.

Along with the unique performance of CZT dual panel PET, its modular configuration and adjustable diameter make it versatile for custom scans of larger animals, such as monkeys.

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