Ultrashort echo time (UTE) imaging reveals a shift in bound water that is sensitive to sub-clinical tendinopathy in older adults

Use ultrashort echo time (UTE) magnetic resonance imaging to quantify bound water components of asymptomatic older Achilles tendons and investigate the relationship between UTE findings and imaging assessment of sub-clinical tendinopathy. Thirteen young (age 25 ± 4.8) and thirteen older (age 67 ± 4.7) adults were tested. A UTE sequence was used to quantify the transverse relaxation times of bound (T${}^{\text{â}}\text{ˆ}{\text{—}}_{2,s}$) and free (T${}^{\text{â}}\text{ˆ}{\text{—}}_{2,l}$) water and the bound water fraction (F${}_s$) in the Achilles tendon. Anatomical images were collected and graded by a musculoskeletal radiologist to identify signs of sub-clinical tendinopathy. Two-sample t tests were used to compare T${}^{\text{â}}\text{ˆ}{\text{—}}_{2,s}$, T${}^{\text{â}}\text{ˆ}{\text{—}}_{2,l}$, and F${}_s$ between age groups and between adults with and without sub-clinical tendinopathy. Older tendons exhibited a 60% longer T${}^{\text{â}}\text{ˆ}{\text{—}}_{2,s}$ (p = 0.004), similar T${}^{\text{â}}\text{ˆ}{\text{—}}_{2,l}$ (p = 0.86), and 5% smaller F${}_s$ (p = 0.048) than young tendons. Seven older adult tendons exhibited tendon thickening and increased signal intensity indicative of sub-clinical tendinopathy. This subset of tendons exhibited a 7% smaller bound water fraction (p = 0.02) and significantly longer T${}^{\text{â}}\text{ˆ}{\text{—}}_{2,s}$ (p < 0.001) than the normal tendons from young and older adults. Older adult tendons exhibited unique UTE signatures that are consistent with disruption of the collagen fiber network and changes in macromolecular content. UTE imaging metrics were sensitive to early indicators of tissue degeneration identified on anatomical images and hence could provide a quantitative biomarker by which to track changes in tissue health resulting from injury, disease, and treatment.