Sustainable low-field cardiovascular magnetic resonance in changing healthcare systems

Abstract

Cardiovascular disease continues to be a major burden facing healthcare systems worldwide. In the developed world, cardiovascular magnetic resonance (CMR) is a well-established non-invasive imaging modality in the diagnosis of cardiovascular disease. However, there is significant global inequality in availability and access to CMR due to its high cost, technical demands as well as existing disparities in healthcare and technical infrastructures across high-income and low-income countries. Recent renewed interest in low-field CMR has been spurred by the clinical need to provide sustainable imaging technology capable of yielding diagnosticquality images whilst also being tailored to the local populations and healthcare ecosystems. This review aims to evaluate the technical, practical and cost considerations of low field CMR whilst also exploring the key barriers to implementing sustainable MRI in both the developing and developed world.

Keywords: Global Health; Low field; MRI; Sustainable; Technology.

Figure 1

Bar chart displaying the MRI units per million population, as recorded by the Organization for Economic Co-operation and Development (OECD). The data are organized by density, with Japan having the highest density at 55.21 units per million population.

Figure 2

The proportion of low-, mid-, and high-field MRI scanners of selected countries. From left to right: (A) the distribution in North America as of 2017, (B) the distribution in China as of 2019, (C) the distribution in Japan as of 2011, and (D) the distribution in West Africa as of 2018.

Figure 3

From left to right, top row – (A) hyperfine 0.064 T (image courtesy of Hyperfine), designed to deliver point of care brain imaging. In this instance, the scanner would need to be optimized for use in a cardiac setting. (B) The Siemens Free.Max 0.55 T scanner (image courtesy of Siemens). These illustrate the size of the 80 cm bore, which is optimized to provide more comfort to patients when undergoing MRI treatment, or for those who cannot tolerate typical bore sizes. Bottom row—(C) Esaote C-Scan from Esaote, which scans at 0.2 T and is optimized for musculoskeletal injuries. (D) Aperto Lucent Plus 0.4 T from FUJIFILM, which has the advantage of being an open bore scanner for more comfort for patients.

Figure 4

ECG traces obtained at B₀ = 0.3 T, B₀ = 1.0 T, and B₀ = 7.0 T using three-lead vector ECG. ECG, an inherently electrical measurement, is prone to interferences with electromagnetic fields and magnetohydrodynamic (MHD) effects. The MHD effect scales with the magnetic flux density, flow orientation with respect to the magnetic field lines, and velocity of an electrical charge carrier such as blood. The MHD effect creates electric potential, which is superimposed onto the ECG potential. At B₀ = 0.3 T, the ECG trace is mainly free of distortions. At B₀ = 1.0 T, adverse signal elevation is found in the ECG for cardiac phases where typically the T-wave occurs. These artefacts are pronounced at B₀ = 7.0 T. MHD induced artefacts in the ECG trace, and T-wave elevation might be misinterpreted as R waves resulting in erroneous triggering together with motion corrupted image quality. This issue is pronounced at higher magnetic fields. These artefacts render MHD effects detrimental for reliable synchronization of MRI or image registration with the cardiac cycle and constitute a practical impediment (Original Image from Ref.⁷⁹).

Figure 5

Example of boosting SNR using spiral-out acquisition to enhance sampling efficiency at low-field bSSFP CMR in a 23-year-old woman (Original Image from Ref.¹¹³).

Figure 6

Image comparisons of breath held cine bSSFP at 0.55 T and 1.5 T, taken in the short axis (A) and the long axis (B). These images were taken from a patient with non-ischaemic cardiomyopathy (Original Image from Ref.³¹).