A direct correlation between T(1ρ), T(2) and quantified proteoglycan and collagen contents in human osteoarthritic cartilage has yet to be documented. We aimed to investigate the orientation effect on T(1ρ) and T(2) values in human osteoarthritic cartilage and to quantify the correlation between T(1ρ), T(2) vs. biochemical composition and histology in human osteoarthritic cartilage.
Thirty-three cartilage specimens were collected from patients who underwent total knee arthroplasty due to severe osteoarthritis and scanned with a 3T MR scanner for T(1ρ) and T(2) quantification. Nine specimens were scanned at three different orientations with respect to the B(0): 0°, 90° and 54.7°. Core punches were taken after MRI. Collagen and proteoglycan contents were quantified using biochemical assays. Histology sections were graded using Mankin scores. The correlation between imaging parameters, biochemical contents and histological scores were studied.
Both mean T(1ρ) and T(2) at 54.7° were significantly higher than those measured at 90° and 0°, with T(1ρ) showing less increase compared to T(2). R(1ρ) (1/T(1ρ)) values had a significant but moderate correlation with proteoglycan contents (R=.45, P=.002), while R(2) (1/T(2)) was not correlated with proteoglycan. No significant correlation was found between relaxation times (T(1ρ) or T(2)) and collagen contents. The T(1ρ) values of specimen sections with high Mankin scores were significantly higher than those with low Mankin scores (P<.05).
Quantitative MRI has a great potential to provide noninvasive imaging biomarkers for cartilage degeneration in osteoarthritis.