Impact of projection quantity on SPECT/CT image quality assessed with a NEMA body phantom

Single-photon emission computed tomography (SPECT), combined with CT in hybrid SPECT/CT systems, enables tomographic visualization of the in vivo distribution of gamma-emitting radiopharmaceuticals. During acquisition, the system records angular projection data at uniformly spaced increments to ensure complete and accurate datasets for tomographic reconstruction. The aim of this study was to evaluate the impact of the number of angular projections on SPECT/CT image quality using a NEMA body phantom.

A NEMA body phantom containing six spheres of different sizes and sphere-to-background activity ratios (2:1-9:1) was scanned using 32 and 64 projections on a Siemens Symbia T2 SPECT/CT system. Images were reconstructed using OSEM and Flash 3D algorithms. Quantitative analysis included image contrast and contrast-to-noise ratio (CNR), while visual assessment of sphere detectability was performed by three independent reviewers. Statistical significance was evaluated using the Mann-Whitney U test, and interobserver agreement was assessed with the kappa coefficient.

Visual evaluation of Flash 3D reconstructions demonstrated no differences in sphere detectability between 32 and 64 projection acquisitions, with 34 spheres identified in both protocols. For OSEM reconstruction, 33 spheres were detected with 64 projections and 32 spheres with 32 projections (κ = 0.97). Contrast analysis revealed no statistically significant differences (OSEM: p = 0.51; Flash 3D: p = 0.61). However, CNR values were significantly higher for the 64-projection protocol (OSEM: p = 0.04; Flash 3D: p = 0.02).

SPECT acquisitions using 32 projections, particularly when combined with iterative reconstruction and attenuation correction, provide image quality comparable to the standard 64-projection protocol. Reduced acquisition time may help minimize motion artifacts and improve clinical workflow efficiency PLAIN LANGUAGE SUMMARY: SPECT scans are a type of imaging that show how substances move inside the body, and image quality can depend on how the scan is performed. This study compared scans done with fewer and more image angles using a test model to check image quality. This study found that fewer angles gave similar image quality, even though more angles slightly improved clarity. This matters because shorter scans can reduce movement, save time, and improve patient comfort while keeping results reliable.