Quantitative MRI of the vastus medialis using T1 mapping and fat analysis calculation technique for evaluating early-stage knee osteoarthritis

Conventional diagnosis and radiographic grading of early-stage knee osteoarthritis (EKOA) rely on visual assessment, which is subjective and limited in monitoring disease progression. More sensitive imaging techniques capable of reflecting microstructural alterations in EKOA are needed to support quantitative assessment. This study aimed to evaluate the diagnostic and grading value of T1 mapping and fat analysis calculation technique (FACT)-derived parameters of vastus medialis combined with clinical indicators in EKOA, and to examine their relationships with Kellgren–Lawrence (KL) grade, pain severity, lower-limb alignment, and muscle strength. This retrospective study included healthy volunteers and patients with EKOA. Patients with EKOA were categorised into KL grades 0, I, and II groups based on weight-bearing radiographs. Vastus medialis T1 values and fat fraction (FF) were quantified. Pain intensity was evaluated using the visual analogue scale (VAS) score, muscle strength was graded by manual muscle testing (MMT), and lower-limb alignment was measured with the varus angle. For the discrimination between KL grade 0 and controls, FF alone yielded the highest single‑parameter AUC (0.776), and the combined parameter (T1 + FF) further improved the AUC to 0.845. For separating KL grade I from KL grade 0, VAS score alone gave an AUC of 0.737, and the combined parameter (T1 + FF + VAS score) achieved the highest AUC (0.814). For differentiating KL grade II from KL grade I, FF alone produced an AUC of 0.720, and the combined parameter (FF + MMT + varus angle) reached an AUC of 0.765. T1 and FF showed moderate-to-strong correlations with KL grade ( r s = 0.395; r s = 0.554) and VAS score ( r s = 0.428; r s = 0.581), weakly-to-moderately with varus angle ( r s = 0.192; r s = 0.488), and only FF showed a weak negative correlation with MMT grade ( r s = − 0.173). Quantitative parameters derived from T1 mapping and FACT suggest efficacy for the early diagnosis and grading of EKOA and are correlated with KL grade, VAS score, MMT grade and varus angle.