Impact of CT parameter reduction on quantitative SPECT/CT assessment in 99mTc imaging: A phantom study.

INTRODUCTION: Quantitative SPECT/CT provides objective assessment of radiotracer distribution but may be influenced by CT acquisition parameters used for attenuation correction and by object related factors such as the partial volume effect. Optimization of CT protocols is therefore important to reduce radiation exposure while maintaining quantitative reliability. METHODS: A study evaluated the effect of CT acquisition parameters on quantitative SPECT/CT measurements. A NEMA IEC Body phantom containing six spheres (10-37 mm) with a target to background activity ratio of 10:1 was scanned using six CT protocols combining 80, 110, and 130 kV with 35 and 70 mAs. Quantitative measurements were analysed using Shapiro-Wilk test, multiple regression, multiple linear regression, and Levene's test. RESULTS: Measurements showed normal distribution for CNR on CT to the Shapiro-Wilk test (p > 0.05), whereas SUVmean, SUVmax, and CNR on SPECT showed non-normal distribution (p < 0.05). Sphere diameter demonstrated a strong positive correlation with quantitative values (r ≈ 0.99, p < 0.001), whereas CT acquisition parameters showed no significant effect. Regression analysis identified sphere diameter as the main determinant of measurement variability. Levene's test confirmed homogeneous variance between acquisition protocols (p > 0.05). CONCLUSION: Quantitative SPECT/CT measurements remained stable across the investigated CT protocols. Object size was the main factor influencing quantitative accuracy, likely due to partial volume effects. IMPLICATION FOR PRACTICE: The findings support the use of optimized low dose CT protocols in SPECT/CT without compromising quantitative reliability, helping radiographers and nuclear medicine technologist balance radiation protection with diagnostic requirements.