Investigating the relationship between quantitative-based ultrasound and MRI estimations of rotator cuff fatty infiltration.

INTRODUCTION: Fatty infiltration (FI) of the rotator cuff has important clinical implications. Quantitatively estimating FI using ultrasound (US) has considerable benefits for assessing FI in a non-invasive, accessible manner. This research investigated whether FI of the supraspinatus (SS) and infraspinatus (IS), estimated using US was related to intramuscular fat fractions measured from magnetic resonance images (MRI). METHODS: Data from 12 healthy young adult participants were used for analysis. US images of the SS and IS were captured using multiple transducer placement techniques from which echogenicity of the muscle region was quantified. Shoulder MRI were captured from which SS and IS were manually segmented and intramuscular fat fractions calculated. Six upper limb strength exertions were performed, resisted by a hand dynamometer. RESULTS: IS and SS echogenicity explained a significant amount of variance in MRI fat fractions for certain body positions and transducer techniques. Echogenicity agreement was higher for IS than SS. Significant relationships were identified between strength exertions and both echogenicity and MRI muscle volume, but not MRI fat fraction. CONCLUSIONS: This research provides preliminary evidence showing that quantitative-based US methods can be used to estimate MRI calculated fat fractions for the rotator cuff.

Investigating the reliability and validity of subacromial space measurements using ultrasound and MRI.

BACKGROUND: While ultrasound (US) measures of the subacromial space (SAS) have demonstrated excellent reliability, measurements are typically captured by experts with extensive ultrasound experience. Further, the agreement between US measured SAS width and other imaging modalities has not been explored. This research evaluated the agreement between SAS measures captured by novice and expert raters and between US and magnetic resonance imaging (MRI). This study also evaluated the effect of US transducer tilt on measured SAS. METHODS: Nine men and nine women participated in this study. US images were captured by a novice and expert with the participant in both seated and supine positions. An inclinometer was fixed to the US probe to measure transducer tilt. SAS width was measured in real time from freeze framed images. MRI images were captured, and the humerus and acromion manually segmented. The SAS width was measured using a custom algorithm. RESULTS: Intraclass correlation coefficients (ICCs) between novice and expert raters were 0.74 and 0.63 for seated and supine positions, respectively. Intra-rater agreement was high for both novice (ICC = 0.83-0.84) and expert (ICC ≥ 0.94) raters. Agreement between US and MRI was poor (ICC = 0.21-0.49) but linearly related. CONCLUSIONS: Moderate agreement between novice and expert raters was demonstrated, while the agreement between US and MRI was poor. High intra-rater reliability within each rater suggests that US measures of the SAS may be completed by a novice with introductory training.