Ultrashort echo time quantitative magnetization transfer MRI detects non-enzymatic crosslinking of collagen in ex vivo rat bones

Increased bone fragility despite preserved or elevated BMD in type 2 diabetes mellitus (T2DM) is linked to nonenzymatic collagen crosslinking via advanced glycation end-products (AGEs). However, there is no noninvasive method clinically available to probe these collagen alterations in the bone. We examined the potential of ultrashort echo time quantitative magnetization transfer (UTE-qMT) MRI for detecting AGE-induced collagen crosslinking in bones. Rat tibial bones were subject to ribosylation ex vivo to induce AGE accumulation. UTE-qMT MRI was performed to quantify the magnetization exchange rate (k_ba) and macromolecular fraction (MMF), which were compared to mechanical properties from 3-point bending tests and AGE concentrations from fluorometric assays. Ribosylation significantly increased AGE crosslinking, confirmed by a 3-fold rise in AGE fluorescence intensity. UTE-qMT MRI revealed a significantly higher k_ba and MMF in ribosylated bones, whereas BMD did not show significant differences. A 3-point bending test showed that ribosylation reduced post-yield displacement, fracture displacement, and work-to-fracture from load-displacement curves, indicating reduced bone ductility and toughness. Importantly, k_ba and MMF correlated significantly with these mechanical properties, whereas BMD showed no significant correlations. These findings demonstrate that UTE-qMT MRI is a novel noninvasive tool sensitive to AGE-mediated collagen crosslinking and its critical role in predicting bone fragility.