IN VIVO T2, T1R, AND SODIUM IMAGING OF ARTICULAR CARTILAGE AT 30T

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Detection of matrix changes of articular cartilage in early osteoarthritis is important for drug discovery. We studied the fesability of comparing T2, T1r, and sodium imaging in healthy volunteers and one subject with knee pain at 3.0T. T2 mapping was done with a T2-prepared spiral method. T1r imaging was performed using a continious spin-lock pulse at several locking frequencies. Sodium imaging was done with a custom surface coil and a short echo-time 3D cones trajectory. Our results indicate it is feasible to compare these methods in vivo at 3.0T for early cartilage matrix changes.Introduction: Early detection of proteoglycan depletion in cartilage is important in development of treatments for osteoarthritis. T1r imaging, or relaxation of spins under the influence of a radio-frequency field, has been shown to be sensitive to changes in the cartilage matrix . T2 mapping is thought to reflect changes in the collagen matrix of cartilage. Sodium imaging has also been used to measure proteoglycan content in cartilage. We studied the feasibility of using these techniques in vivo at 3.0T. Methods: Four volunteers (ages 34-43) were imaged in the axial plane at 3.0T on a GE Signa MRI (GE Healthcare, Milwaukee, WI) using 3-inch coil. One volunteer had a history of anterior knee pain. Measurements of T1r were made with a continuous RF spin locking pulse at the same anatomic locations with spin lock frequencies of 300, 500, 700 and 1000 Hz. The maximum spin-lock frequency in the continuous RF sequence was limited by RF power deposition limits. T2 relaxation time at the same location was measured using a T2-prepared spiral sequence. The T1r and CPMG T2 sequences had identical imaging parameters: TR of 2000 ms, 14 spiral arms, 4096 points, and bandwidth +125 kHz. In-plane resolution was 0.7 mm with a 16 cm FOV, 4 mm slice thickness. A single slice through the patella cartilage was acquired in 5 minutes with two signal averages. The T1r sequences acquired 4 spin lock times (TSL) of 3, 15, 35, and 80 ms. The CPMG T2 sequence acquired 6 echoes at approximately 6, 17, 28, 49, 71 and 92 ms. Sodium imaging was performed with a custom 3-inch surfaces coil and a short echo time "cones" trajectory . Sodium acquisitions were obtained at a voxel size of 1.25x1.25x4 mm. Parameters for the scan were: TR/TE = 50/0.6 ms, FOV = 16x16x12.8cm, matrix = 128x128x32, readout time = 8 ms, alpha = 70 deg, and 16 averages for a total scan time of 17 min 8 s. T1p and T2 relaxation times for each subject were measured in 10 cartilage locations on the medial and lateral patella facets. Sodium SNR was also measured in 10 locations on the medial and lateral facets, and in an area of increased relaxation times in the subject with knee pain. Relaxation measurements and maps were created using Osirix software .