Comparison of SZ-HRX and LEHR collimators for reduced-duration 123I-ioflupane brain SPECT/CT: a phantom study

¹²³I-ioflupane Single Photon Emission Computed Tomography with Computed Tomography (SPECT-CT) imaging is widely used to assess dopaminergic denervation in parkinsonian syndromes, such as Parkinson's disease and atypical variants. Standard imaging generally uses low-energy high-resolution (LEHR) parallel-hole collimators, which require long acquisition times and minimal source-to-detector distance to optimize spatial resolution. Recently, the Smart-Zoom High-Resolution and eXtended magnification volume (SZ-HRX) solution was designed specifically for neurological applications. It incorporates multifocal collimators and a dedicated reconstruction algorithm, promising a reduction in acquisition duration, and an improvement in patient comfort by allowing detectors to be positioned further away from the head. The aim of this study is to investigate the performance of SZ-HRX system compared to LEHR collimators.

A striatal phantom with 5 compartments (putamens, caudates, and background) was filled with different concentrations of ¹²³I-ioflupane to simulate various clinical situations. Tomographic acquisitions were performed on each LEHR and SZ-HRX system. The summation of dynamically acquired projections allowed testing different acquisition durations with the SZ-HRX collimator. Sensitivity and Spatial resolution were assessed and compared. The data were reconstructed according to EANM recommendations. Contrast-to-noise ratio (CNR), striatum-to-background ratio (SBR), coefficient of variation (CV), and normalized asymmetry index (NAI) were calculated for both systems and compared to the LEHR acquisition. To estimate the shortest SZ-HRX acquisition duration, a linear regression of all quantitative results were calculated between the two systems.

SZ-HRX collimation had superior performance characteristics than LEHR, with relative changes in CNR, CV, and SBR of + 99%, -28% and + 42% respectively, without any decrease in spatial resolution or change in asymmetry index. SZ-HRX system seems to be at least as good as LEHR system, up to 40% of scan time reduction.

SZ-HRX collimation showed superior performance characteristics to LEHR collimation in the study of ¹²³I-ioflupane filled striatal phantom, enabling shorter acquisitions.