T1p relaxation mapping in human osteoarthritis (OA) cartilage:: Comparison of T1p with T2

Purpose: To quantify the spin-lattice relaxation time in the rotating frame (T-1p) in various clinical grades Of human osteoarthritis (OA) cartilage specimens obtained from total knee replacement Surgery, and to correlate the Tip with CA disease progression and compare it with the transverse relaxation time (T-2). 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. T-2- and T-1p-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 T-1p ) compared to healthy cartilage tissue. In various grades of CA specimens, the Tip relaxation dines varied from 62 5 msec to 1.00 +/- 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 Tip in various clinical grades of OA specimens were similar to 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 Tip relaxation mapping is a sensitive noninvasive marker for quantitatively predicting and monitoring the status of macromolecules in early OA. Furthermore, T-1p has a higher dynamic range (> 100%) for detecting early pathology compared to T-2. This bigher dynamic range can be exploited to measure even smallmacromolecular changes with greater accuracy compared to T-2. Because of these advantages. Tip relaxation mapping may be useful for evaluating early OA therapy.