Isotropic morphometry and multicomponent T₁ ρ 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.