Assessment of Osteoarthritis in the Human Hip with Delayed Gadolinium Enhanced Magnetic Resonance Imaging (dGEMRIC) and T₂ Mapping of Hip Cartilage

Principal Investigator: Robert T. Trousdale, M.D.
Project Coordinator: Matthew F. Koff, Ph.D. — koff.matthew@mayo.edu

Figure 1: Unconfined compression testing apparatus. Load cell measures resistance force, LVDT measures displacement.

The purpose of this study is to use the novel MRI techniques of delayed gadolinium-enhanced MRI of cartilage (dGEMRIC, T₁^Gd) and T₂ mapping to quantitate osteoarthritis (OA) in the human hip across all stages of hip OA. This study will provide a complete clinical, biochemical and biomechanical assessment of the dGEMRIC (T1 ^Gd) and T₂ mapping procedures.

The study will be accomplished by comparing in-vivo MRI measures of cartilage during OA (T₁^Gd and T₂ values) with in-vitro measures of cartilage during OA (water content, collagen content, proteoglycan content, mechanical properties) across different stages of OA. The different OA grading scales used in the study are based on radiographic and MRI images of the joint, direct visualization of the articular surface and histological examination of articular cartilage samples.

Figure 2: A T2 map of patellar cartilage through the depth of the tissue. Higher T2 values indicate collagen disruption in the articular cartilage.

The MR techniques used in this study are the newest in-vivo approaches to studying OA of diarthrodial joints. We believe our experiment maximizes the potential of using dGEMRIC (T₁^Gd) and T₂ mapping in a clinical setting. The current study will provide an accurate baseline for the MR parameters of T₁^Gd and T₂ for each stage of hip OA. The results of this study may be useful in selecting the proper surgical procedure to treat various disorders of the hip. We anticipate these new MR techniques will become standard clinical diagnostic procedures.

Tools needed for data acquisition and data analysis have been developed in the past year. First, a custom-designed unconfined compression chamber was constructed. A schematic drawing of the device is shown in Figure 1. This testing apparatus will be used to calculate the material properties of cartilage samples extracted from femoral heads. Second, custom-written software has been created to calculate T₂ values of cartilage from MRI images. This program has already been used in Dr. K.R. Kaufman's project investigating aerobic exercise intervention for knee OA. A representative T₂ map of patellar cartilage is shown in Figure 2. A T₂ map across the articular surface of the patella is shown in Figure 3. Finally, a collaboration has been established been the Biomechanics/Motion Analysis Laboratory and the Cartilage and Connective Tissue Laboratory to perform the biochemical and histological analyses of cartilage samples.

Figure 3: A 3-D T2 map across the articular surface of a patella. Higher T2 values indicate collagen disruption in the articular cartilage.