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

Clinical MR imaging of patients with spinal hardware at 0.55T: comparison of diagnostic assessment and metal artifact appearance with 1.5T

PURPOSE

The aim of this study is to assess inter-reader agreement of imaging findings and compare readers' assessment of image quality (IQ) and appearance of metal artifact (MA) in patients with spinal implants between 0.55T and 1.5T MRI.

METHODS

Patients imaged on Siemens Healthineers Magnetom Free.Max 0.55T (n = 42; avg. age 55 yrs.) with spinal hardware between 12/2021 and 3/2024 were included. Of these, 18 patients had a paired exam at 1.5T. All exams were reviewed independently by three neuroradiologists (R1-3). Readers selected imaging findings from a pick-list and rated sequences using a 4-point Likert scale for IQ and MA.

RESULTS

At both 0.55T and 1.5T, raw agreement for the following findings ranged between 81 and 95%: cord signal abnormality, osteomyelitis/discitis, osseous metastatic disease, and compression fracture. Agreement on post-operative fluid collection and spinal canal stenosis was 64.3% and 66.7% at 0.55T, and 77.7% and 50.0% at 1.5T. Agreement on neural foraminal stenosis was low in both cohorts, 47.6% and 33.3% at 0.55T and 1.5T. No sequence at 0.55T was rated inferior to 1.5T in IQ or MA. Sequences rated higher at 0.55T compared to 1.5T were as follows for IQ: sagittal T1w TSE (R1) and as follows for MA: axial T1w TSE (R1, R2), sagittal T1w TSE (R1), axial T2w TSE (R1), sagittal T1w TSE Dixon post-contrast (R2), sagittal T2w STIR (R2: p = 0.01).

CONCLUSION

Imaging patients with spinal hardware at 0.55T results in comparable inter-reader agreement for clinically-relevant imaging findings and equivalent or improved image quality compared to 1.5T.

Low-field MRI for use in neurological diseases

PURPOSE OF REVIEW

To review recent clinical uses of low-field magnetic resonance imaging (MRI) to guide incorporation into neurological practice.

RECENT FINDINGS

Use of low-field MRI has been demonstrated in applications including tumours, vascular pathologies, multiple sclerosis, brain injury, and paediatrics. Safety, workflow, and image quality have also been evaluated.

SUMMARY

Low-field MRI has the potential to increase access to critical brain imaging for patients who otherwise may not obtain imaging in a timely manner. This includes areas such as the intensive care unit and emergency room, where patients could be imaged at the point of care rather than be transported to the MRI scanner. Such systems are often more affordable than conventional systems, allowing them to be more easily deployed in resource constrained settings. A variety of systems are available on the market or in a research setting and are currently being used to determine clinical uses for these devices. The utility of such devices must be fully evaluated in clinical scenarios before adoption into standard practice can be achieved. This review summarizes recent clinical uses of low-field MR as well as safety, workflows, and image quality to aid practitioners in assessing this new technology.

Abdominal MRI on a Commercial 0.55T System: Initial Evaluation and Comparison to Higher Field Strengths

RATIONALE AND OBJECTIVES

This study aims to assess the quality of abdominal MR images acquired on a commercial 0.55T scanner and compare these images with those acquired on conventional 1.5T/3T scanners in both healthy subjects and patients.

MATERIALS AND METHODS

Fifteen healthy subjects and 52 patients underwent abdominal Magnetic Resonance Imaging at 0.55T. Images were also collected in healthy subjects at 1.5T, and comparison 1.5/3T images identified for 28 of the 52 patients. Image quality was rated by two radiologists on a 4-point Likert scale. Readers were asked whether they could answer the clinical question for patient studies. Wilcoxon signed-rank test was used to test for significant differences in image ratings and acquisition times, and inter-reader reliability was computed.

RESULTS

The overall image quality of all sequences at 0.55T were rated as acceptable in healthy subjects. Sequences were modified to improve signal-to-noise ratio and reduce artifacts and deployed for clinical use; 52 patients were enrolled in this study. Radiologists were able to answer the clinical question in 52 (reader 1) and 46 (reader 2) of the patient cases. Average image quality was considered to be diagnostic (>3) for all sequences except arterial phase FS 3D T1w gradient echo (GRE) and 3D magnetic resonance cholangiopancreatography for one reader. In comparison to higher field images, significantly lower scores were given to 0.55T IP 2D GRE and arterial phase FS 3D T1w GRE, and significantly higher scores to diffusion-weighted echo planar imaging at 0.55T; other sequences were equivalent. The average scan time at 0.55T was 54 ± 10 minutes vs 36 ± 11 minutes at higher field strengths (P < .001).

CONCLUSION

Diagnostic-quality abdominal MR images can be obtained on a commercial 0.55T scanner at a longer overall acquisition time compared to higher field systems, although some sequences may benefit from additional optimization.

Comparison of image quality and diagnostic efficacy of routine clinical lumbar spine imaging at 0.55T and 1.5/3T

PURPOSE

To compare image quality, assess inter-reader variability, and evaluate the diagnostic efficacy of routine clinical lumbar spine sequences at 0.55T compared with those collected at 1.5/3T to assess common spine pathology.

METHODS

665 image series across 70 studies, collected at 0.55T and 1.5/3T, were assessed by two neuroradiology fellows for overall imaging quality (OIQ), artifacts, and accurate visualization of anatomical features (intervertebral discs, neural foramina, spinal cord, bone marrow, and conus / cauda equina nerve roots) using a 4-point Likert scale (1 = non-diagnostic to 4 = excellent). For the 0.55T scans, the most appropriate diagnosis(es) from a picklist of common spine pathologies was selected. The mean ± SD of all scores for all features for each sequence and reader at 0.55T and 1.5/3T were calculated. Paired t-tests (p ≤ 0.05) were used to compare ratings between field strengths. The inter-reader agreement was calculated using linear-weighted Cohen's Kappa coefficient (p ≤ 0.05). Unpaired VCG analysis for OIQ was additionally employed to represent differences between 0.55T and 1.5/3T (95 % CI).

RESULTS

All sequences at 0.55T were rated as acceptable (≥2) for diagnostic use by both readers despite significantly lower scores for some compared to those at 1.5/3T. While there was low inter-reader agreement on individual scores, the agreement on the diagnosis was high, demonstrating the potential of this system for detecting routine spine pathology.

CONCLUSIONS

Clinical lumbar spine imaging at 0.55T produces diagnostic-quality images demonstrating the feasibility of its use in diagnosing spinal pathology, including osteomyelitis/discitis, post-surgical changes with complications, and metastatic disease.