3D-T 1ρ-relaxation mapping of articular cartilage : In vivo assessment of early degenerative changes in symptomatic osteoarthritic subjects 1

Abstract

Rationale and objectives To determine the in vivo feasibility of quantifying early degenerative changes in patellofemoral joint of symptomatic human knee using spin-lattice relaxation time in the rotating frame (T 1ρ) magnetic resonance imaging (MRI). Materials and methods All the MRI experiments were performed on a 1.5 T whole-body GE Signa clinical scanner using a custom built 15-cm diameter transmit-receive quadrature birdcage radiofrequency coil. The T 1ρ-prepared magnetization was imaged with a three-dimensional gradient-echo pulse sequence pre-encoded with a three-pulse cluster consisting of two hard 90° pulses and a low power spin-lock pulse. Quantitative T 1ρ relaxation maps of asymptomatic (n = 8 males), and six symptomatic human volunteers (four men, two women) were computed using a appropriate signal expression. Results All six symptomatic volunteers showed elevation in T 1ρ relaxation times when compared with asymptomatic subjects. In symptomatic population, the T 1ρ relaxation times varied from 63 ± 4 ms to 95 ± 12 ms (mean ± standard deviation) depending on the degree of cartilage degeneration. The increase in T 1ρ of symptomatic population was statistically significant (n = 6, P < .002) when compared with corresponding asymptomatic population. However, in asymptomatic population the relaxation times varied only from approximately 45 to 55 ms (n = 8, age range 22–45 years). Conclusion Preliminary results demonstrated the in vivo feasibility of quantifying early biochemical changes in symptomatic osteoarthritis subjects employing T 1ρ-weighted MRI on a 1.5 T clinical scanner. This study on limited number of symptomatic population shows that T 1ρ-weighted MRI provides a noninvasive marker for quantitation of early degenerative changes of cartilage in vivo. However, further studies are needed to correlate early osteoarthritis determined from arthroscopy with T 1ρ in a large symptomatic population.