T1rho relaxation mapping in human osteoarthritis (OA) cartilage: comparison of T1rho with T2.

TLDR: To quantify the spin‐lattice relaxation time in the rotating frame (T1ρ) in various clinical grades of human osteoarthritis cartilage specimens obtained from total knee replacement surgery, and to correlate the T1ρ with OA disease progression and compare it with the transverse relaxation time (T2).

Abstract: Purpose To quantify the spin-lattice relaxation time in the rotating frame (T1ρ) in various clinical grades of human osteoarthritis (OA) cartilage specimens obtained from total knee replacement surgery, and to correlate the T1ρ with OA disease progression and compare it with the transverse relaxation time (T2). Materials and Methods Human cartilage specimens were obtained from consenting patients (N = 8) who underwent total replacement of the knee joint at the Pennsylvania Hospital, Philadelphia, PA, USA. T2- and T1ρ-weighted images were obtained on a 4.0 Tesla whole-body GE Signa scanner (GEMS, Milwaukee, WI, USA). A 7-cm diameter transmit/receive quadrature birdcage coil tuned to 170 MHz was employed. Results All of the surgical knee replacement OA cartilage specimens showed elevated relaxation times (T2 and T1ρ) compared to healthy cartilage tissue. In various grades of OA specimens, the T1ρ relaxation times varied from 62 ± 5 msec to 100 ± 8 msec (mean ± SEM) depending on the degree of cartilage degeneration. However, T2 relaxation times varied only from 32 ± 2 msec to 45 ± 4 msec (mean ± SEM) on the same cartilage specimens. The increase in T2 and T1ρ in various clinical grades of OA specimens were ∼5–50% and 30–120%, respectively, compared to healthy specimens. The degenerative status of the cartilage specimens was also confirmed by histological evaluation. Conclusion Preliminary results from a limited number of knee specimens (N = 8) suggest that T1ρ relaxation mapping is a sensitive noninvasive marker for quantitatively predicting and monitoring the status of macromolecules in early OA. Furthermore, T1ρ has a higher dynamic range (>100%) for detecting early pathology compared to T2. This higher dynamic range can be exploited to measure even small macromolecular changes with greater accuracy compared to T2. Because of these advantages, T1ρ relaxation mapping may be useful for evaluating early OA therapy. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc.