An Unmatched Radio Frequency Chain for Low-Field Magnetic Resonance Imaging.

Joshua R Harper,Jorge Molina,Ivan Muhumuza,Johnes Obungoloch,Steven J Schiff,Federico Krauch,Cristhian Zárate

doi:10.3389/fphy.2021.727536

Abstract

Magnetic Resonance Imaging (MRI) is a safe and versatile diagnostic tool for intracranial imaging, however it is also one of the most expensive and specialized making it scarce in low- to middle-income countries (LMIC). The affordability and portability of low-field MRI offers the potential for increased access to brain imaging for diseases like Hydrocephalus in LMIC. In this tutorial style work, we show the design of a low powered and low cost radio frequency chain of electronics to be paired with a previously reported prepolarized low-field MRI for childhood hydrocephalus imaging in sub-Saharan Africa where the incidence of this condition is high. Since the Larmor frequency for this system is as low as 180 kHz, we are able to minimize the impedance of the transmit coil to 5 ohms rather than match to 50 ohms as is traditionally the case. This reduces transmit power consumption by a factor of 10. We also show the use of inexpensive and commonly available animal enclosure fencing (“chicken wire”) as a shield material at this frequency and compare to more traditional shield designs. These preliminary results show that highly portable and affordable low-field MRI systems could provide image resolution and signal-to-noise sufficient for planning hydrocephalus treatment in areas of the world with substantial resource limitations. Employment of these technologies in sub-Saharan Africa offers a cost-effective, sustainable approach to neurological diagnosis and treatment planning in this disease burdened region.

Highlights

Magnetic Resonance Imaging (MRI) is one of the safest and most versatile biomedical imaging methods available
The unequal distribution of MRI and other medical technologies throughout the world has been well documented [3]. Even when technology such as MRI is introduced into low-to-middle income countries (LMIC) through donation or purchase, more than half typically falls into disrepair and more than a quarter may never even be operational [4]
RF chain design is an important aspect of an MRI system, especially at low magnetic field where SNR is typically low

Summary

Introduction

Magnetic Resonance Imaging (MRI) is one of the safest and most versatile biomedical imaging methods available. The unequal distribution of MRI and other medical technologies throughout the world has been well documented [3] Even when technology such as MRI is introduced into LMIC through donation or purchase, more than half typically falls into disrepair and more than a quarter may never even be operational [4]. This is due to the lack of spare parts, Unmatched Radio Frequency Chain consumables, trained technical staff, or reliable power in addition to the high initial cost of acquisition [5]. A sustainable solution is necessary if diagnostic imaging is to be a useful tool for clinical practice in LMIC

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