Radiofrequency (RF) coil impacts the value and reproducibility of cartilage spin–spin (T2) relaxation time measurements

Abstract

T2 (spin-spin) relaxation time is frequently used for compositional assessment of articular cartilage. However little is known about the influence of magnetic resonance (MR) system components on these measurements. The reproducibility and range of cartilage T2 values were evaluated using different extremity radiofrequency (RF) coils with potential differences in flip angle uniformity and signal-to-noise ratio (SNR). Ten knees underwent 3T MR exams using RF coils with different SNR: quadrature transmit/receive (QTR); quadrature transmit/eight-channel phased-array receive (QT8PAR). Each knee was scanned twice per coil (four exams total). T2 values were calculated for the central medial and lateral femoral (cMF, cLF) and medial and lateral tibial (MT, LT) cartilage. The flip angle varied across a central 40mm diameter region-of-interest of each coil by <1.5%. However SNR was significantly higher using QT8PAR than QTR (P<0.001). T2 values for cMF (50.7msec/45.9msec) and MT (48.2msec/41.6msec) were significantly longer with QT8PAR than QTR (P<0.05). T2reproducibility was improved using QT8PAR for cMF and cLF (4.8%/5.8% and 4.1%/6.5%; P<0.001), similar for LT (3.8%/3.6%; P=1.0), and worse for MT (3.7%/3.3%; P<0.001). T2 varied spatially, with cLF having the longest (52.0msec) and the LT having the shortest (40.6msec) values. All deep cartilage had significantly longer, and less variable, T2 values using QT8PAR (higher SNR; P<0.03). SNR varied spatially (significant) depending upon coil, but refocusing flip angle only slightly. With higher SNR, significantly longer T2 values were measured for deep (all plates) and global (MT, cMF) cartilage. T2 values varied by depth and plate, in agreement with prior studies.