Biexponential T_1ρ relaxation mapping of human knee menisci

Background: Measuring T_1ρ in the knee menisci can potentially be used as noninvasive biomarkers in detecting early-stage osteoarthritis (OA).

Purpose: To demonstrate the feasibility of biexponential T_1ρ relaxation mapping of human knee menisci.

Study type: Prospective.

Population: Eight healthy volunteers with no known inflammation, trauma, or pain in the knee and three symptomatic subjects with early knee OA.

Field strength/sequence: Customized Turbo-FLASH sequence to acquire 3D-T_1ρ -weighted images on a 3 T MRI scanner.

Assessment: T_1ρ relaxation values were assessed in 11 meniscal regions of interest (ROIs) using monoexponential and biexponential models.

Statistical tests: Nonparametric rank-sum tests, Kruskal-Wallis test, and coefficient of variation.

Results: The mean monoexponential T_1ρ relaxation in the lateral menisci were 28.05 ± 4.2 msec and 37.06 ± 10.64 msec for healthy subjects and early knee OA patients, respectively, while the short and long components were 8.07 ± 0.5 msec and 72.35 ± 3.2 msec for healthy subjects and 2.63 ± 2.99 msec and 55.27 ± 24.76 msec for early knee OA patients, respectively. The mean monoexponential T_1ρ relaxation in the medial menisci were 34.30 ± 3.8 msec and 37.26 ± 11.38 msec for healthy and OA patients, respectively, while the short and long components were 7.76 ± 0.7 msec and 72.19 ± 4.2 msec for healthy subjects and 3.06 ± 3.24 msec and 55.27 ± 24.59 msec for OA patients, respectively. Statistically significant (P ≤ 0.05) differences were observed in the monoexponential relaxation between some of the ROIs. The T_1ρ,short was significantly lower (P = 0.02) in the patients than controls. The rmsCV% ranges were 1.51-16.6%, 3.59-14.3%, and 4.91-15.6% for T_1ρ -mono, T_1ρ -short, and T_1ρ -long, respectively.

Data conclusion: Our results showed that in all ROIs, T_1ρ relaxation times of outer zones (red zones) were less than inner zones (white zones). Monoexponential T_1ρ was increased in medial, lateral, and body menisci of early OA while the biexponential numbers were decreased in early OA patients.

Level of evidence: 2 Technical Efficacy Stage: 1 J. Magn. Reson. Imaging 2019. J. Magn. Reson. Imaging 2019;50:824-835.