Clinical 7T MRI for epilepsy care: Value, patient selection, technical issues, and outlook.

Ultra-high-field 7.0 Tesla (T) MRI offers substantial gains in signal-to-noise ratio (SNR) over 3T and 1.5T, but for over two decades has remained a research tool, while 3T scanners have achieved widespread clinical use. This much slower translation of 7T relates to daunting technical challenges encountered in ultra-high-field human MR imaging. The recent introduction of United States Food and Drug Administration (FDA)-approved clinical 7T scanners promises to be a watershed for many 7T neuroimaging applications, including epilepsy imaging. The high SNR of 7T allows clinical imaging of fine neuroanatomic detail at unprecedented spatial resolution, helping with detection and differentiation of subtle, potentially treatable lesions undetectable or suboptimally assessed at 3T. The accompanying research paper reports our group's analysis of 7T MRI efficacy in epilepsy treatment planning. Here, we introduce the technical background and clinical approach we currently use, in order to assist clinical epileptologists and neuroimagers contemplating, creating, or referring patients to a clinical 7T epilepsy imaging service. We describe a tiered epilepsy imaging strategy and protocols designed to optimize 7T value and work around signal intensity variation and signal loss artifacts, which remain significant challenges to full exploitation of 7T clinical value. We describe FDA-approved techniques for mitigating these artifacts and briefly outline techniques currently under development, but not yet FDA approved. Finally, we discuss the major issues in 7T patient safety and toleration, outlining their physical causes and effects on workflow, and provide references to more comprehensive technical reviews for readers seeking greater technical detail.

7T MR Safety.

Magnetic resonance imaging and spectroscopy (MRI/MRS) at 7T represents an exciting advance in MR technology, with intriguing possibilities to enhance image spatial, spectral, and contrast resolution. To ensure the safe use of this technology while still harnessing its potential, clinical staff and researchers need to be cognizant of some safety concerns arising from the increased magnetic field strength and higher Larmor frequency. The higher static magnetic fields give rise to enhanced transient bioeffects and an increased risk of adverse incidents related to electrically conductive implants. Many technical challenges remain and the continuing rapid pace of development of 7T MRI/MRS is likely to present further challenges to ensuring safety of this technology in the years ahead. The recent regulatory clearance for clinical diagnostic imaging at 7T will likely increase the installed base of 7T systems, particularly in hospital environments with little prior ultrahigh-field MR experience. Informed risk/benefit analyses will be required, particularly where implant manufacturer-published 7T safety guidelines for implants are unavailable. On behalf of the International Society for Magnetic Resonance in Medicine, the aim of this article is to provide a reference document to assist institutions developing local institutional policies and procedures that are specific to the safe operation of 7T MRI/MRS. Details of current 7T technology and the physics underpinning its functionality are reviewed, with the aim of supporting efforts to expand the use of 7T MRI/MRS in both research and clinical environments. Current gaps in knowledge are also identified, where additional research and development are required. Level of Evidence 5 Technical Efficacy 2 J. MAGN. RESON. IMAGING 2021;53:333-346.

Clinical utility of a focused hip MRI for assessing suspected hip fracture in the emergency department.

PURPOSE: A focused hip MRI (FHMR) for the detection of radiographically occult hip fractures was implemented in our emergency department (ED) in 2013. The goal of this study was to assess the clinical utility of this protocol. METHODS: We retrospectively reviewed radiology reports of 262 unique patients who underwent 263 FHMR (coronal T1, coronal STIR, axial T2 fat saturated) for suspected hip fracture in the ED from October 2013 to March 2020. Electronic medical records were reviewed for the ED course, follow-up imaging, and clinical management within 90 days. RESULTS: Seventy-one patients had one or more fractures identified by FHMR: one-third had proximal femoral fractures; two-third had pelvic fractures. Of these 71 patients, 53 (74%) had radiographically occult fractures, including 14 (20%) with occult proximal femoral fractures; 4 patients had fractures occult on CT. Nineteen patients with a suspected fracture on radiography were found to have no fracture on FHMR. Four fractures not reported on FHMR were later seen on follow-up imaging: these included 1 isolated greater trochanter, 1 additional ischial tuberosity, 1 additional superior pubic ramus, and 1 additional sacrum. All four fractures were treated non-operatively. Muscle/tendon injury was the most common type of injury, seen in 50% (130/262) patients with the most commonly torn tendons being the hamstring (44%; 15/34) followed by gluteus medius tendon (18%; 6/34). A full-hip or pelvis MRI was done after FHMR in only 5 patients, primarily for the purpose of better characterizing findings already identified on FHMR (2 for fracture, 2 for tendon injury, 1 for soft tissue metastasis). Only one of these five studies provided new information: ruling out a previously questioned fracture. Clinical management of the vast majority of patients was based solely on findings from the FHMR. CONCLUSIONS: FHMR offers reliable identification of radiographically occult hip fractures and muscle/tendon injuries. The protocol is well trusted in guiding patient management in our ED.

Elements of Effective Patient Screening to Improve Safety in MRI.

Conducting magnetic resonance imaging (MRI) safety screening is not a new idea and has developed as a proved method in efforts to ensure patient safety and prevent accidents in the magnetic resonance (MR) environment. A growing number of surgical procedures with implanted medical devices have complicated MR screening and added to the workload of Level 2 personnel. Level 2 staff members are trained to understand and implement screening procedures and should be consulted by all individuals requiring access to the MR environment. All the steps have potential gaps, but as a whole offer efficient and effective tools to alleviate MR-related accidents.

Relative Magnetic Force Measures and Their Potential Role in MRI Safety Practice.

BACKGROUND: Magnetic field markings are occasionally used at MRI sites to provide visual feedback of magnetic field strength at locations within the MRI scan room for safety purposes. In addition to magnetic field line markings, relative magnetic force, or ratio of magnetic to gravitational forces on an object, may be considered a useful complementary metric to quantify the risk associated with bringing objects containing ferromagnetic material into the magnetic field. PURPOSE: To develop and validate methods for deriving useful relative magnetic-force measures including a simple force index for application to MRI safety. STUDY TYPE: Phantom. PHANTOM: A special-purpose rig was built to experimentally measure relative magnetic forces on small ferromagnetic objects. FIELD STRENGTH: Ranging from 1.5T to 7T. ASSESSMENT: Quantitative comparisons were made between theoretical and measured relative magnetic forces on six objects containing ferromagnetic material: a piece of iron, a paper clip, a Kelly clamp, nail clippers, a cell phone, and a small permanent magnet. STATISTICAL TESTS: An analysis based on the Bland-Altman method was employed. RESULTS: After correction of the 1.5T data to account for assumed positioning errors of the test rig, limits of agreement between measured and estimated relative forces in the four MRI systems were ±0.16, where a relative force of 1.0 indicates that the magnetic force is equal to gravitation force. There was no significant bias in the data (P < = 0.05). DATA CONCLUSION: Accurate measures of relative magnetic forces on ferromagnetic objects can be derived for MRI safety purposes. LEVEL OF EVIDENCE: 1 Technical Efficacy Stage: 1 J. Magn. Reson. Imaging 2020;51:1260-1271.

Prostate MRI using an external phased array wearable pelvic coil at 3T: comparison with an endorectal coil.

PURPOSE: To evaluate T2w and DWI image quality using a wearable pelvic coil (WPC) compared with an endorectal coil (ERC). METHODS: Twenty men consecutively presenting to our prostate cancer MRI clinic were prospectively consented to be scanned using a wearable pelvic coil then an endorectal coil and pelvic phased array coil at 3T. Eighteen patients were suitable for inclusion. Axial T2w images were obtained using the WPC and ERC, and DWI images were obtained using the WPC, ERC, and PPA. Analysis was performed in consensus by two readers with experience in prostate MRI. The readers scored the T2w images using six qualitative criteria and the DWI images using five criteria. Signal-to-noise ratio (SNR) was also measured. RESULTS: T2w artifact severity was greater for an ERC than a WPC (p = 0.003). There was no significant difference in T2w qualititatve image quality by other measures. The distinction of zonal anatomy on DWI was superior for an ERC compared with both a WPC and a PPA (p = 0.018 and p < 0.001 respectively), and there was no significant difference in DWI image quality by other measures. SNR was significantly higher for ERC imaging for both T2w and DWI. CONCLUSION: WPC imaging provides comparable image quality to that of an ERC, potentially reducing the need for an ERC. WPC imaging shows reduced T2w artifact severity and inferior DWI zonal anatomy distinction compared with an ERC. Imaging with a WPC produces a lower SNR than an ERC.

Guidelines for documentation and consent for nonclinical, nonresearch MRI in human subjects.

Magnetic resonance imaging (MRI) of human subjects is widely performed for clinical and research purposes. Clinical MRI requires a physician order, while research MRI typically requires an approved protocol from a local Institutional Review Board, as well as informed consent. However, there are several circumstances in which it is appropriate to perform MRI in human subjects, that constitute neither clinical nor research activities. Examples include clinical protocol development, training and teaching, and quality assurance testing. We refer to such activities as nonclinical, nonresearch MRI. The purpose of this document is to provide principles and guidelines for appropriate and safe use of MRI in human subjects for nonclinical, nonresearch purposes. LEVEL OF EVIDENCE: 1 J. Magn. Reson. Imaging 2017;45:36-41.

On replacing the manual measurement of ACR phantom images performed by MRI technologists with an automated measurement approach.

PURPOSE: To assess whether measurements on American College of Radiology (ACR) phantom images performed by magnetic resonance imaging (MRI) technologists as part of a weekly quality control (QC) program could be performed exclusively using an automated system without compromising the integrity of the QC program. MATERIALS AND METHODS: ACR phantom images are acquired on 15 MRI scanners at a number of ACR-accredited sites to fulfill requirements of a weekly QC program. MRI technologists routinely perform several measurements on these images. Software routines are also used to perform the measurements. A set of geometry measurements made by technologists over a five week period and those made using software routines were compared to reference-standard measurements made by two MRI physicists. RESULTS: The geometry measurements performed by software routines had a very high positive correlation (0.92) with the reference-standard measurements. Technologist measurements also had a high positive correlation (0.63), although the correlation was less than for the automated measurements. Bland-Altman analysis revealed overall good agreement between the automated and reference-standard measurements, with the 95% limits of agreement being within ±0.62 mm. Agreement between the technologist and the reference-standard measurements was demonstratively poorer, with 95% limits of agreement being ±1.46 mm. Some of the technologist measurements differed from the reference standard by as much as 2 mm. CONCLUSION: The technologists' geometry measurements may be able to be replaced by automated measurement without compromising the weekly QC program required by the ACR.

MR system operator: recommended minimum requirements for performing MRI in human subjects in a research setting.

This article is intended to provide guidelines for the minimum level of safety and operational knowledge that an MR system operator should exhibit in order to safely perform an MR procedure in a human subject in a research setting. This article represents the position of the International Society for Magnetic Resonance in Medicine (ISMRM) regarding this important topic and was developed by members of this society's MR Safety Committee.