Quantitative Evaluation of Reconstruction Methods for 180° Vs. 360° Acquisition Protocols In 99mTc-Sestamibi SPECT of Renal Tumors
Abstract
Purpose
Quantitative 99mTc-sestamibi SPECT/CT is routinely used to distinguish benign kidney tumors from renal cell carcinoma. Standard clinical acquisitions typically use 360° orbits. However, a 180° posterior orbit can reduce scan time and patient discomfort. This study evaluates whether a 180° acquisition preserves linear quantitative relationships and quantitative consistency relative to 360° acquisitions across tumors and multiple organs.
Methods
A clinical dataset of 50 patients imaged with 99mTc-sestamibi SPECT/CT was retrospectively analyzed. Original projection data were acquired over 360° with 120 views, and a 180° posterior acquisition dataset was generated by extracting 60 posterior views. Images were reconstructed using 8 iterations of ordered-subsets expectation-maximization (OS-EM) with compensation for attenuation (A), scatter (S), and collimator-detector response (D), or no compensation (N). Tumors were manually segmented while kidneys and abdominal organs were segmented using AI-based methods. Relative uptake (RU) ratios were computed for tumors and organs (liver, spleen, stomach, pancreas, and duodenum) using kidney mean activity as the reference. Quantitative agreement between 180° and 360° acquisitions was assessed using linear regression and Bland-Altman analysis.
Results
With compensations applied, 180° and 360° RU ratios demonstrated strong linear agreement across organs, including the tumor-to-kidney RU, specifically for organs located posteriorly. Uncompensated reconstructions showed substantially poorer agreement and increased dispersion. Bland-Altman analysis with normalized difference demonstrated differences centered near zero for compensated methods with wider spread for low-uptake organs and uncompensated reconstructions.
Conclusion
A 180° posterior acquisition preserves quantitative agreement with 360° acquisitions across multiple organ-to-kidney uptake ratios when appropriate compensations are applied during reconstruction. These findings support reduced-angle quantitative renal and abdominal SPECT/CT as a feasible protocol for improving imaging efficiency while maintaining quantitative consistency.