Potential of Stroke Imaging Using a New Prototype of Low-Field MRI: A Prospective Direct 0.55 T/1.5 T Scanner Comparison

Abstract

Objectives: Ischemic stroke is a leading cause of mortality and acquired disability worldwide and thus plays an enormous health-economic role. Imaging of choice is computed-tomographic (CT) or magnetic resonance imaging (MRI), especially diffusion-weighted (DW) sequences. However, MR imaging is associated with high costs and therefore has a limited availability leading to low-field-MRI techniques increasingly coming into focus. Thus, the aim of our study was to assess the potential of stroke imaging with low-field MRI. Material and Methods: A scanner comparison was performed including 27 patients (17 stroke cohort, 10 control group). For each patient, a brain scan was performed first with a 1.5T scanner and afterwards with a 0.55T scanner. Scan protocols were as identical as possible and optimized. Data analysis was performed in three steps: All DWI/ADC (apparent diffusion coefficient) and FLAIR (fluid attenuated inversion recovery) sequences underwent Likert rating with respect to image impression, resolution, noise, contrast, and diagnostic quality and were evaluated by two radiologists regarding number and localization of DWI and FLAIR lesions in a blinded fashion. Then segmentation of lesion volumes was performed by two other radiologists on DWI/ADC and FLAIR. Results: DWI/ADC lesions could be diagnosed with the same reliability by the most experienced reader in the 0.55T and 1.5T sequences (specificity 100% and sensitivity 92.9%, respectively). False positive findings did not occur. Detection of number/location of FLAIR lesions was mostly equivalent between 0.55T and 1.5T sequences. No significant difference (p = 0.789–0.104) for FLAIR resolution and contrast was observed regarding Likert scaling. For DWI/ADC noise, the 0.55T sequences were significantly superior (p < 0.026). Otherwise, the 1.5T sequences were significantly superior (p < 0.029). There was no significant difference in infarct volume and volume of infarct demarcation between the 0.55T and 1.5T sequences, when detectable. Conclusions: Low-field MRI stroke imaging at 0.55T may not be inferior to scanners with higher field strengths and thus has great potential as a low-cost alternative in future stroke diagnostics. However, there are limitations in the detection of very small infarcts. Further technical developments with follow-up studies must show whether this problem can be solved.

Low‐field MRI: A report on the 2022 ISMRM workshop

“…Alternatively, mid-field systems could facilitate deployment of MRI to good effect for general purpose radiology imaging in lower-resource regions and outpatient settings where 1.5T or 3T systems are scarce, as long as suitable diagnostic information can be gleaned. 83 Additionally, these systems offer advantages in niche applications, such as imaging high-susceptibility anatomy (e.g., lung and bowel), imaging near metallic implanted devices, or performing MRI-guided interventions. 70 Furthermore, the lower cost of these systems may encourage the adoption of applications that are difficult to justify, economically, with current high field system -for example, cardiac imaging may be achievable at mid-field, and is currently underutilized at ≥1.5T due to cost and complexity, despite clinical evidence of its diagnostic and prognostic value.…”

“…Mid‐field system may be acquired at a lower cost and then can allow conventional ≥1.5T clinical MRI systems to be used when they are necessary, enabling departments to complete more MRI exams at an overall lower cost. Alternatively, mid‐field systems could facilitate deployment of MRI to good effect for general purpose radiology imaging in lower‐resource regions and outpatient settings where 1.5T or 3T systems are scarce, as long as suitable diagnostic information can be gleaned 83 . Additionally, these systems offer advantages in niche applications, such as imaging high‐susceptibility anatomy (e.g., lung and bowel), imaging near metallic implanted devices, or performing MRI‐guided interventions 70 .…”

Quality assessment of routine brain imaging at 0.55 T: initial experience in a clinical workflow

“…Pogarell et al reported excellent‐quality musculoskeletal images of knee and hip with metallic implant at 0.55 T 18 . Finally, Rusche et al showed that the 0.55 T MRI system may be deployed for imaging of stroke patients, demonstrating image quality comparable with that at 1.5 T 19 …”

“…16 In a case report by Breit et al images collected at 0.55 T demonstrated improved quality in postoperative thoracic spine in comparison with 3 T MRI, with substantially reduced metal artifacts. 17 Pogarell et al reported excellent-quality musculoskeletal images of knee and hip with metallic implant at 0.55 T. 18 Finally, Rusche et al showed that the 0.55 T MRI system may be deployed for imaging of stroke patients, demonstrating image quality comparable with that at 1.5 T. 19 However, the general utility of 0.55 T systems for routine brain imaging has not yet been assessed. In order for 0.55 T MRI scanners to be incorporated into healthcare systems, they must offer a high level of diagnostic certainty despite their potential disadvantages, such as reduced SNR compared with higher-field systems.…”

Current Status of and Future Developments in Acute Stroke Management

“…At the same time, steps are being taken toward popularizing the use of magnetic resonance (MR) imaging for stroke. New evidence suggests that low-field MR imaging can offer a feasible alternative to its expensive 1.5-T counterparts, thus making MR imaging available to a broader spectrum of healthcare systems and, subsequently, patients [ 10 , 11 ].…”