Grants and Contributions:

Grant or Award spanning more than one fiscal year. (2017-2018 to 2022-2023)

The progress made in developing a new generation of gradient-free magnetic resonance imagers (MRIs) will continue. Progress made includes the design of a wrist-sized MRI for the International Space Station (ISS), for the Canadian Space Agency (CSA), and the construction and testing of two wrist-sized gradient-free MRIs.

At the heart of gradient-free MRI is a novel radio frequency (RF) transmitting coil. The RF field design of the coil allows for direct spatial encoding with no need for magnetic field gradients - gradient-free MRI. When combined with a low field (500 gauss), a very portable MRI results. The magnet mass of both wrist MRIs constructed to date is less than 5 kg. The spatial variation of both RF magnitude and RF phase can be used for image encoding. One of my existing wrist MRIs combines a varying RF field with motorized motion of the RF coils. My other existing MRI uses spatially varying RF phase to achieve spatial encoding. The two MRI designs will be developed further, along with other designs.

The research will be done by HQP trainees following the very successful approach, to date, of doing mathematically based research projects coupled with investigations using the wrist-size MRIs. Modification of the existing MRIs and construction of one more wrist-sized MRI is anticipated. A start-up company has been planned to build helmet-size gradient-free MRIs for use in existing remote-presence enabled clinics in the Canadian north. But our focus for the NSERC sponsored research will be wrist-sized MRIs because our purpose is to develop the MRI engineering and not to study anatomy or physiology. This approach also keeps the hardware costs down.

The ISS-MRI design uses a highly homogeneous magnetic field and a linearly varying transmitted RF phase profile. The proposed work uses non-linearly varying transmitted RF phase profiles. A non-linearly varying phase profile means that the Fourier transform cannot be used directly to reconstruct the image from the received RF signal, except in a very small field of view near the center of the RF transmit coil. Novel spin echo pulse sequences, using composite pulses, are also required. Our wrist-size MRIs also do not use homogeneous magnetic fields so that isomagnetic surfaces in the object are excited to give non-planar slices. These new approaches require mathematical transformations that go beyond the standard Fourier transformation for image reconstruction. Mathematical reconstruction algorithms will be the focus of some of the research projects. Other research projects will involve RF coil design, RF pulse sequence design and magnetic field design. LT Imaging and MRI Tech will provide the MRI hardware needed for the projects.

Portable gradient-free MRI has the potential to displace both x-ray and ultrasound as medical imaging modalities. The proposed research will move MRI technology toward those future roles to deliver accessible medical diagnostics.