Clinical Assessment of Musculoskeletal Spatial Resolution Degradation with Distance from Isocenter In EID CT
Abstract
Purpose
Accurate musculoskeletal (MSK) CT assessment relies on high spatial resolution, which can be compromised when extremities are positioned away from the scanner isocenter. The purpose of this study is to evaluate the effect of off-center positioning on spatial resolution degradation in energy-integrating detector (EID) CT of the elbow.
Methods
This retrospective study included 57 elbow EID CT examinations acquired at varying distances from the isocenter. Three radiologists independently evaluated spatial resolution and diagnostic utility using a 5-point Likert scale (5 = much better than standard of care; 1 = much worse than standard of care). Interrater agreement was quantified using intraclass correlation coefficients (ICC). Ordinal logistic regression was applied to assess the association between distance from the isocenter and image quality scores, with analyses performed separately for two patient cohorts, (1) patients with a cast, splint or splinted elbow positioned over the chest or (2) patients without those in the field, to account for and rule out the influence of confounding factors such as casts, splints, or beam attenuation from the chest on the Likert score.
Results
Interrater agreement was excellent for both spatial resolution (ICC = 0.975) and diagnostic utility (ICC = 0.973). Increasing distance from the isocenter was significantly associated with lower image quality, with approximately a 2% reduction in the odds of achieving a higher Likert score per 1-mm increase in distance (p < 0.05). A probability greater than 0.8 for diagnostic utility scores ≥4 was observed when the elbow was positioned within 226 mm in cohort 1 and within 240 mm in cohort 2. For spatial resolution, this probability threshold was maintained within 247 mm and 225 mm, respectively.
Conclusion
Elbow should be within 225 mm of isocenter for patients, regardless of cast/splint presence to preserve high spatial resolution and diagnostic utility of the images.