Investigation of Image Quality for Cuboid and Tapered Array microPET Systems

Purpose

Small animals are integral to medical research as they provide insights into human diseases. Mice, particularly suitable as human models, share gene functions, making them vital for biomedical research. Positron emission tomography (PET) has emerged as a key tool for non-invasive imaging of mouse models, providing molecular-level insights with remarkable sensitivity. Achieving optimal spatial resolution is crucial for capturing detailed images of small animal organs, and enhancing sensitivity is imperative for microPET scanner efficiency.

Methods

This study investigates the performance of microPET scanners using cuboidal and tapered arrays, simulated by the GATE Monte Carlo package. To this end, it focuses on detector materials, crystal geometry, and reconstruction methods. Finally, critical parameters such as sensitivity, NECR, and FWHM of Gaussian fit of image intensity profiles are assessed.

Results

Simulation outputs reveal that tapered arrays outperform their cuboid counterparts by 44% in sensitivity and NECR, along with a 22% improvement in spatial resolution. The relative FWHM difference for crystals compared to LSO remains below 5%. Crystal material significantly affects sensitivity and NECR, with BGO demonstrating 25% greater values than LSO. Meanwhile, GSO and LYSO showed 32% and 60% lower values, respectively. BGO crystal demonstrated a higher profile amplitude, indicating higher counts. This difference could be attributed more to heightened noise than an increase in signal, as BGO crystals exhibit a higher scatter fraction than other crystals. Furthermore, COSEM and ACOSEM algorithms achieve the minimum FWHM of 0.7 mm, suggesting 10% better spatial resolution than the OSEM algorithm. In contrast, RAMLA and MRAMLA algorithms showed 14% and 4% worse spatial resolution than the OSEM algorithm, respectively.

Conclusion

Tapered arrays, especially when paired with BGO crystals, demonstrate superior sensitivity, NECR, and lower FWHM suggesting better spatial resolution than cuboid arrays. Crystal material choice minimally affects FWHM for a low-activity point source but significantly influences sensitivity and NECR, with BGO outperforming other crystals. COSEM and ACOSEM reconstruction algorithms yielded better image quality with lower FWHM and noise, demonstrating their effectiveness in microPET applications.