Instrumentation and Methods for Magnetic Resonance Imaging

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This research program will improve magnetic resonance imaging (MRI) technology and enhance not only the imaging performance (e.g., signal-to-noise ratio (SNR), resolution, speed) but also safety and patient experience. These goals depend greatly on the radio frequency (RF) signal detectors or "coils", which are placed around the patient and used for signal excitation and for signal reception. The first core goal of this research program is to improve MRI in the torso and abdomen by taking advantage of better imaging performance that is possible with MRI magnetic field strengths (measured in tesla or T) that are higher than those used clinically (1.5 and 3.0 T). While lower than the 7 T available at some research centres, the 4.7 T at the University of Alberta offers the unique opportunity to do body imaging (never done before) at this intermediate field strength which we believe is the "sweet spot". Higher fields cause patchy bright and dark regions in the images because of the short RF wavelength. Despite the high SNR achievable in the bright regions, the patchiness compromises image quality and precludes clinical use because the dark regions could conceal disease invisible to a radiologist. At 7 T, patchiness is very prominent and impossible to eliminate over a large enough field of view without the most advanced methods, which are technically challenging and require expert supervision to work reliably. Indeed, the US FDA has cleared 7 T for clinical use only on the head and limbs. We will build the coils needed for body imaging at 4.7 T and compare image quality with that at 3 and 7 T. The second core goal of this research program is to develop enabling innovations and advanced instrumentation, beginning with a reliable detector for specific absorption rate (SAR) calibration. Signal excitation uses RF pulses which inevitably heat the patient's body. Therefore MRI scanners need real-time SAR monitoring to ensure the heating does not cause injury. Devices that emit ionizing radiation (e.g., x-ray machines) are calibrated using standardized procedures, but the SAR monitoring system is calibrated by each manufacturer using proprietary methods. We will develop a robust "SAR detector" and method to calibrate the SAR monitor, to allow a standardized comparison of SAR levels from different scanners. We will also develop technology to enable truly ergonomic "wearable" coils, instead of the bulky, intimidating cages currently in use. One component needed to achieve this is a better RF switch to make sensitive receive-only coils immune to the transmit pulses. The two types of switch in current use have problems such as generating heat or low reliability, and they both require control wires that complicate the cabling. We will realise a switch without these limitations. Finally, we will adapt the lightweight coils we designed for linac-MR radiation therapy machines to PET-MR scanners which also require coils that are essentially transparent to x-rays.