Magnetic resonance imaging (MRI) is a key diagnostic imaging modality, used for diagnosis and treatment monitoring, with over 150 million scans performed annually. However, MRI is a highly expensive modality, with its use compared to ultrasound and X-ray, for example, limited by several factors including:
(i) purchase costs in the millions of euros,
(ii) annual maintenance costs in the hundreds of thousands of euros,
(iii) highly stringent siting requirements, typically needing a large electromagnetically-shielded room to house the system, access to high power and high fidelity electricity lines, chilled water for cooling different components, and a humidity/temperature controlled environment,
(iv) extensive training for experienced personnel
All of these considerations mean that MRI facilities are confined to centrally-located medical centres in large towns and cities. Globally over 70% of the world’s population has absolutely no access to MRI, and clinical conditions such as hydrocephalus, stroke, pneumonia, head trauma and many manifestations of viral diseases, which could benefit from even very simple scans, cannot be fully treated.
A potential solution to increasing the availability and accessibility of MRI in both the developed and developing worlds is to design new low-field systems based on permanent magnet arrays. In the developed world these could be used as screening devices, or via new geometrical designs to open up areas, such as surgical interventions, in which MRI is not used. In the developing world, these types of systems could significant increase the accessibility of MRI, particularly if they can be made portable, as well as sustainable in terms of maintenance and repair.
Advantages:
(i) The most obvious practical advantage of low field MRI is the significantly lower financial burden (system costs, maintenance costs, running costs and siting costs),
(ii) The physical size of the magnet can be small and the geometry open, which means that patient comfort is much higher In addition the acoustic noise (the most complained-about aspect of MRI) from the gradient coils is extremely low,
(iii) The power required to run the gradient and RF amplifiers can be provided by conventional mains supplies, and can even be supplied by rechargeable batteries, greatly increasing the number of potential sites for such systems, as well as portability between sites, and
(iv) Contra-indications due to medical implants are dramatically reduced: forces on any metal implant, heating around implants, and any image artifacts close to the implants are orders of magnitude lower than for conventional clinical field strengths.
Major challenges (addressed in this proposal):
(i) The major technical challenge is that lower magnetic fields result in severely reduced MR signal intensity, with for example a 50 mT system having ~400 lower signal-to-noise ratio (SNR) than a conventional 1.5 T scanner, and
(ii) to be truly operational in the field (for example rural settings or in an ambulance) issues of changes in temperature causing small changes in the system’s magnetic field, and cancellation of environmental/man-made electromagnetic noise need be addressed.
