Development of a versatile image quality test phantom for single photon emission computed tomography system

Single photon emission computed tomography (SPECT) is a vital imaging tool for visualizing functional and physiological processes of human body. Periodic quality assurance (QA) ensures imaging accuracy, but high-cost commercial phantoms limit accessibility in resource-constrained settings. To address this, a cost-effective and modular SPECT phantom was developed to evaluate imaging parameters in a single scan. The phantom, made from PMMA, features interchangeable modules designed to assess tomographic resolution, tomographic uniformity, tomographic contrast, and slice thickness. Its cylindrical structure accommodates radionuclide solutions to simulate imaging conditions. Validation was conducted using^99mTc and a dual-head SPECT/CT scanner (Discovery 670 DR, GE Healthcare, Chicago, USA) equipped with low-energy high-resolution (LEHR) collimators. Imaging data were analysed for pixel size accuracy, tomographic resolution, tomographic uniformity, slice thickness and tomographic contrast. The measured pixel size was 1.11 mm (x-axis) and 1.12 mm (y-axis), aligning closely with the system-calculated size of 1.10 mm. The tomographic resolution in air, assessed with the OSEM algorithm (2 iterations, 10 subsets) with post-reconstruction filtering using Butterworth filter (cutoff frequency: 0.48; order: 10), achieved a horizontal FWHM of 13.12 mm, superior to results from filtered back-projection (FBP). Tomographic uniformity assessments showed contrast variations within 3.6%, meeting IAEA standards. Cold rod and sphere contrast tests detected rods as small as 6.5 mm and spheres down to 9 mm diameter, while hot rod contrast test identified rods as small as 9 mm. Measurement results of our phantom was also found comparable with the measurements results of Jaszczak phantom. The test results indicate that our image quality test phantom is suitable for comprehensive QA of SPECT system. Its modular design offers additional advantage to add new test sections or modify currently available test sections without changing the core design of the phantom. Hence, it is a versatile cost-effective solution for the periodic QA in nuclear medicine.