Rapid 3D isotropic cartilage assessment with VIPR MRI

While current MRI technology is adequate for imaging severe cartilage degeneration, significant increases in resolution are necessary to image early changes and defects in cartilage. Though MRI advocates often tout its 3D capabilities, most clinical scans consist of a series of 2D thick slices with gaps in between. Partial volume artifact can cause several low grade lesions to be missed or incompletely characterized. Robust fat suppression is also necessary to provide high contrast between bone and cartilage. Commonly available clinical 3D techniques are largely based on sequences which spend considerable amounts of scan time suppressing fat instead of imaging. We present a method that provides a comprehensive 3D evaluation of cartilage in the knee with isotropic resolution and bright fluid through T2-like contrast. Termed VIPR-SSFP, the method separates fat and water and thus spends the entire exam imaging cartilage and relevant joint tissues. A single VIPR-SSFP scan may be reformatted into multiple orthogonal or oblique reformats where the variable thickness of the reformat allows a trade-off between SNR and partial volume artifact. The radial trajectory in VIPR-SSFP is ideally suited to exploit larger coil arrays using the parallel imaging strategy known as PILS. Relative to our previous work, we have reduced voxel volume by 100%, demonstrating 0.56 mm isotropic resolution at 1.5T and 0.33 mm at 3.0T in a five minute scan, using a new eight channel coil. Improved cartilage assessment is demonstrated in a study of nearly 100 patients through reduction in partial volume artifact.