Isotropic morphometry and multicomponent T1ρ mapping of human knee articular cartilage in vivo at 3T

Background The progressive loss of hyaline articular cartilage due to osteoarthritis (OA) changes the functional and biochemical properties of cartilage. Measuring the T1 ρ along with the morphological assessment can potentially be used as noninvasive biomarkers in detecting early-stage OA. To correlate the biochemical and morphological data, submillimeter isotropic resolution for both studies is required. Purpose To implement a high spatial resolution 3D-isotropic-MRI sequence for simultaneous assessment of morphological and biexponential T1 ρ relaxometry of human knee cartilage in vivo. Study type Prospective. Population Ten healthy volunteers with no known inflammation, trauma, or pain in the knee. Field strength/sequence Standard FLASH sequence and customized Turbo-FLASH sequence to acquire 3D-isotropic-T1 ρ-weighted images on a 3T MRI scanner. Assessment The mean volume and thickness along with mono- and biexponential T1 ρ relaxations were assessed in the articular cartilage of 10 healthy volunteers. Statistical tests Nonparametric rank-sum tests. Bland-Altman analysis and coefficient of variation. Results The mean monoexponential T1 ρ relaxation was 40.7 ± 4.8 msec, while the long and short components were 58.2 ± 3.9 msec and 6.5 ± 0.6 msec, respectively. The mean fractions of long and short T1 ρ relaxation components were 63.7 ± 5.9% and 36.3 ± 5.9%, respectively. Statistically significant (P ≤ 0.03) differences were observed in the monoexponential and long components between some of the regions of interest (ROIs). No gender differences between biexponential components were observed (P > 0.05). Mean cartilage volume and thickness were 25.9 ± 6.4 cm3 and 2.2 ± 0.7 mm, respectively. Cartilage volume (P = 0.01) and thickness (P = 0.03) were significantly higher in male than female participants across all ROIs. Bland-Altman analysis showed agreement between two morphological methods with limits of agreement between -1000 mm3 and +1100 mm3 for volume, and -0.78 mm and +0.46 mm for thickness, respectively. Data conclusion Simultaneous assessment of morphological and multicomponent T1 ρ relaxation of knee joint with 0.7 × 0.7 × 0.7 mm isotropic spatial resolution is demonstrated in vivo. Comparison with a standard method showed that the proposed technique is suitable for assessing the volume and thickness of articular cartilage. Level of evidence 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;48:1707-1716.