Fatty infiltration of rotator cuff muscles has been reported to affect the outcome of rotator cuff repair. Until now, quantitative evaluation of fatty infiltration of rotator cuff muscles has not been reported. T2 mapping is a quantitative magnetic resonance (MR) imaging technique that potentially evaluates the concentration of fat in muscles. The purpose of this study was to evaluate fatty infiltration of rotator cuff muscles using T2 mapping. Forty-seven shoulders of 46 patients with shoulder pain were studied. The subjects consisted of 27 males (27 shoulders) and 19 females (20 shoulders) with an average age of 58 years old (range, 16-84). Twenty-four shoulders had no rotator cuff tear (group A), and 23 shoulders had rotator cuff tear: 7 incomplete (group B), 10 small to medium (group C) and 6 large to massive tears (group D). T2 mapping was performed at a proximal muscular slice in oblique sagittal images with a 1.5-tesla imager. T2 of the supraspinatus (SSP) and infraspinatus (ISP) muscles were measured and compared among groups. The relationship between T2 and Goutallier's staging was also examined. The average T2 of SSP in groups A, B, C and D were 34.6 ± 3.0, 39.1 ± 2.8, 41.4 ± 7.2 and 49.0 ± 11.5 msec, respectively. The average T2 of ISP in groups A, B, C and D were 34.3 ± 3.4, 34.0 ± 2.6, 40.0 ± 11.3 and 44.5 ± 3.5 msec, respectively. Although no significant difference was observed in T2 of ISP between groups A and B, T2 increased with extension of tear in both muscles. However, T2 varied in larger tears. The higher stage in Goutallier's staging demonstrated a longer T2. However, the T2 varied in higher stage. T2 of rotator cuff muscles increased in accordance with extension of tear but varied in larger tears. T2 mapping was a useful quantitative evaluation method of fatty infiltration.
