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Improved Imaging of Osteoarthritis using Fluctuating Equilibrium Magnetic Resonance Imaging
Gary Gold, MD; S. Vasanawala, MD, PhD; D. Nishimura, PhD; J. Pauly, PhD; Gary S. Beaupré, PhD Objectives: The overall purpose of our program is to develop new methods for imaging articular cartilage and studying cartilage biomechanics. Osteoarthritis is a disease of cartilage degeneration, and is extremely common in aging veterans. Magnetic resonance imaging (MRI) is a promising non-invasive tool for evaluation of cartilage. The purpose of this study is to evaluate the use of Fluctuating Equilibrium MR (FEMR) to image cartilage. Methods: Current MRI methods lack sufficient spatial resolution and contrast for detailed evaluation of cartilage. Three-dimensional spoiled gradient recalled echo (3D-SPGR) offers high resolution, but has relatively long scan times and suboptimal cartilage/fluid contrast. T2-weighted Fast Spin Echo (FSE) produces bright synovial fluid, but has limited resolution and low cartilage signal. Proton density FSE provides good contrast, but blurring limits detail. ![]() Proton Density and FEMR images of a patient with cartilage damage. Note the sharp detail in the area of damage (arrow) using FEMR. We have developed a rapid 3D fat/water separating technique called fluctuating equilibrium magnetic resonance (FEMR). The sequence refocuses magnetization over a repetition time (TR), and uses a TR of 6.6 ms for fat/water separation at 1.5 T. FEMR shows excellent synovial fluid/cartilage contrast and cartilage signal. The knee joints of ten healthy volunteers and one patient were imaged on a GE Signa 1.5 T scanner with CV/i gradients (150 T/m/s), using an extremity coil. The FEMR sequence was followed by a 3D-SPGR (50 ms TR), T2-weighted FSE (3.2 s TR) and a proton density FSE (4 s TR), all with fat saturation. Scans were preceded by a field shimming sequence. Results: Contrast-to-noise measurements for cartilage using FEMR were superior to T2W-FSE. Proton density FSE images showed bright synovial fluid with limited cartilage detail. 3D-SPGR had comparable resolution to FEMR, but suboptimal cartilage/fluid contrast and longer scan times (8 minutes versus 2 minutes). Cartilage surface detail, outlined by bright synovial fluid, was best seen on the FEMR images. Conclusion: FEMR obtains high-resolution 3D images of the entire knee in two minutes with excellent cartilage/fluid contrast. FEMR is sensitive to field inhomogeneity and requires shimming. Surface defects are outlined by bright synovial fluid, and cartilage has higher contrast-to-noise compared with T2W-FSE. Funding Acknowledgment: This study was funded by the VA Rehabilitation Research and Development Service, Research Career Development Grant #B2376V. |