Quantification of SPECT concentric ring artifacts by radiomics and radial features

Background: Conspicuous concentric ring artifacts in phantom reconstructions triggers retuning SPECT systems. These evaluations are visual, not quantitative. Our study was undertaken to determine the degree to which observers agree about SPECT concentric ring artifacts, and to test whether quantitative texture analysis metrics correspond to significant artifacts.Methods: Test data were acquired as part of quarterly quality assurance using standardized SPECT phantoms containing solid spheres, solid rods and volumes of uniform activity concentration loaded with 99mTc. Forty SPECT studies were identified as having concentric ring artifacts or were acquired to assess whether artifacts were resolved following camera retuning after obtaining an unacceptably non-uniform result. Transaxial reconstructions were reviewed independently by two medical physicists who graded severity of artifacts on a 5-point scale. Counts were tabulated in volumes of interest created in uniform phantom sections, from which were computed 72 radiomics image texture analysis metrics. Radial contrast (RContrast) derived from the radial profile of summed slices transformed into polar coordinates and radial noise-to-signal (RNSR) also calculated.Results: Artifacts were considered sufficiently severe to require camera retuning in 10 rods sections, 17 sphere sections, and 16 uniform sections. In uniform sections, there was “good agreement” for inter-observer and intra-rater assessments (κ = 0.66, Fisher exact p < 0.0001 and κ = 0.61, Fisher exact p = 0.001, respectively). While 3 radiomics image analysis features agreed significantly (p = 0.001) with visual detection of significant artifacts in uniform sections, the parameters most strongly associated with severe artifacts were RContrast > 4.75% and RNSR > 2.7%, for which ROC AUC accuracy = 88%±5%, sensitivity = 83%, specificity = 83%, p < 0.0001. Accuracy was 76%-78% for the 3 radiomics features, with significantly lower specificity (48%-61%, p < 0.05) than RContrast and RNSR. Increasing magnitude of RContrast and RNSR correlated significantly with increasingly severe artifact scores (ρ = 0.71-0.72, p < 0.0001).Conclusion: There was good agreement among physicists as to the presence of circular ring artifacts in uniform sections of SPECT quality assurance scans, with artifacts accurately detected by radial contrast and noise-to-signal ratio measurements.