Influence of knee positions on T2, T*2, and dGEMRIC mapping in porcine knee cartilage

We examined the influence of flexed knee positions on cartilage MR assessments. Sagittal T₂, T*₂, and delayed gadolinium‐enhanced MRI of cartilage (dGEMRIC) maps of the femoral cartilage were obtained in eight 6‐month‐old porcine femorotibial joints in the extended knee position (position A: flexion 0° and femoral shaft in parallel with the amplitude of static field), flexed knee position (position B: flexion 40° and femoral shaft oriented at 40° to the amplitude of static field), and oblique‐placed knee‐extended position (position C: flexion 0° and femoral shaft oriented at 40° to the amplitude of static field). Comparison of the MR parameters between positions A and C showed isolated influence of the magic‐angle effect, and comparison between positions A and B showed effects of knee flexion. Proteoglycan and hydroxyproline content in cartilage specimen at each region of interest had no significant correlation with T₂, T*₂, and dGEMRIC values. At the central zone, located on a weight‐bearing area and parallel to the amplitude of static field, T₂/T*₂/dGEMRIC values increased by 6.8/11/0.8% at position C and by 24/44/31% at position B compared with position A. There was a significant increase in T₂ and T*₂ values at position B compared with those at position A. The substantial changes in T₂, T*₂, and dGEMRIC were shown in response to knee flexion, presumably due to the compounding influence of the magic‐angle effect and change in the intra‐articular biomechanical condition. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.