Optimisation of Q.Clear (BSREM) Reconstruction Parameters for ¹²³I and ¹⁷⁷Lu Imaging with a 360° CZT Detector

Accurate quantitative SPECT depends strongly on the reconstruction protocol, particularly for penalised-likelihood reconstruction algorithms, such as Q.Clear (BSREM). This study aimed to optimise Q.Clear reconstruction parameters for ¹²³I and ¹⁷⁷Lu imaging. SPECT images of a NEMA IEC PET Body phantom filled with ¹²³I and ¹⁷⁷Lu were acquired on a ring-shaped CZT camera and on a conventional Anger camera. The images were reconstructed using Q.Clear and OSEM and evaluated using quantitative image-quality metrics. Q.Clear was optimised for each radionuclide. The ¹²³I dataset was reconstructed using different combinations of the regularisation parameters β and γ. The ¹⁷⁷Lu dataset was reconstructed using literature-reported parameters, and the best-performing reconstruction was fine-tuned. The best-performing Q.Clear reconstructions were compared with corresponding OSEM reconstructions. Overall, increasing β reduced the recovery coefficients, background variability, and contrast recovery coefficients while increasing the signal-to-noise ratio. γ had no appreciable influence on the metrics within the investigated range. The candidate optimised StarGuide/Q.Clear reconstructions outperformed the standard Symbia/OSEM reconstructions in terms of activity recovery, whereas Symbia/OSEM produced lower image noise for most of the analysed VOIs. This study identified settings associated with improved quantitative metrics within the evaluated parameter space, with potential implications for quantitative imaging requiring clinical validation. Nevertheless, multiple reconstruction parameter combinations remain unexplored.