Ultra-Homogeneous B0 field for High-Field
Body Magnetic Resonance Imaging with Unified Shim-RF Coils
Abstract High-field magnetic resonance imaging (MRI, 3.0T and above) offers numerous advantages for imaging the human body over lower-field strengths. However, it suffers from unwanted fast spatially-varying main (B0 ) fields caused by the susceptibility mismatch at the tissue interfaces. When this is combined with the anatomical complexity of the human body, undesirable image artifacts can become damaging as they can compromise potential image contrasts, limit the use of accelerated imaging, and interfere with clinical interpretation. Consequently, these limitations restrict the effective utilization of high-field body MRI and emphasize the need for a major improvement in B0 field homogeneity to take full advantage of the ever increased B0 field. Here we introduce a Unified shim-RF Coil (UNIC) to overcome this existing bottleneck by transcending the conventional low-efficiency, distantly located B0 shim coils. UNIC allows a shim array to be freely allotted and seamlessly integrated into a standard surface RF coil, thus maximizing both the performance of RF receive sensitivity and effective B0 shimming. We demonstrate the capacity of the UNIC approach through detailed characterization of the coil design, prototyping a body coil integrating the UNIC features, and conducting in-vivo imaging of deep organs adjacent to the lung. Our studies provide evidence that UNIC enables homogeneous B0 fields in the liver and the heart, where strong image artifacts are known to occur, and hence facilitate the acquisition of unprecedented image quality in a clinical 3.0T scanner. Further, UNIC’s design is practical as it overcomes one of the most, if not the most, critical limitations of the state-of-the-art high-field MRI with minimal changes to the current MRI hardware architecture. Accordingly, the proposed technique offers opportunities for major advancements in noninvasive imaging of deep organs with high-field imaging in a way it has not been possible thus far.
