MASiVar: Multisite, multiscanner, and multisubject acquisitions for studying variability in diffusion weighted MRI.

PURPOSE: Diffusion-weighted imaging allows investigators to identify structural, microstructural, and connectivity-based differences between subjects, but variability due to session and scanner biases is a challenge. METHODS: To investigate DWI variability, we present MASiVar, a multisite data set consisting of 319 diffusion scans acquired at 3 T from b = 1000 to 3000 s/mm2 across 14 healthy adults, 83 healthy children (5 to 8 years), three sites, and four scanners as a publicly available, preprocessed, and de-identified data set. With the adult data, we demonstrate the capacity of MASiVar to simultaneously quantify the intrasession, intersession, interscanner, and intersubject variability of four common DWI processing approaches: (1) a tensor signal representation, (2) a multi-compartment neurite orientation dispersion and density model, (3) white-matter bundle segmentation, and (4) structural connectomics. Respectively, we evaluate region-wise fractional anisotropy, mean diffusivity, and principal eigenvector; region-wise CSF volume fraction, intracellular volume fraction, and orientation dispersion index; bundle-wise shape, volume, fractional anisotropy, and length; and whole connectome correlation and maximized modularity, global efficiency, and characteristic path length. RESULTS: We plot the variability in these measures at each level and find that it consistently increases with intrasession to intersession to interscanner to intersubject effects across all processing approaches and that sometimes interscanner variability can approach intersubject variability. CONCLUSIONS: This study demonstrates the potential of MASiVar to more globally investigate DWI variability across multiple levels and processing approaches simultaneously and suggests harmonization between scanners for multisite analyses should be considered before inference of group differences on subjects.

Safety and Image Quality of 1.5-T Endorectal Coil Multiparametric MRI of the Prostate or Prostatectomy Fossa for Patients With Pacemaker or Implantable Cardioverter-Defibrillator.

OBJECTIVE: The purpose of this study is to report the patient safety and image quality of 1.5-T multiparametric MRI of the prostate in patients with cardiac implantable electronic devices (CIEDs). MATERIALS AND METHODS: In this retrospective study, a database was searched to identify prostate multiparametric 1.5-T MRI examinations performed with endorectal coils for patients with CIEDs from 2012 to 2016 (study group) and matched patients without CIEDs (control group). Clinical safety in the study group was reviewed. The specific absorption rate (SAR) and signal-to-noise ratio (SNR) were measured in both groups. Imaging quality and artifact on T2-weighted images, DW images, and dynamic contrast-enhanced images were rated on a 5-point scale by two independent readers. RESULTS: The study group consisted of total 28 multiparametric MRI examinations in 25 patients. There were no serious device-related adverse effects observed (0/28; 0%), and the estimated whole-body SAR in the study group was never greater than 1.5 W/kg. The SNR values tended to be lower in the study group than in the control group. However, overall perceived image preferences and influences of artifacts on image quality for the study group were not significantly different from those for the control group (p > 0.05), which were rated above average (rating 3) by both readers 1 and 2. CONCLUSION: Multiparametric 1.5-T MRI examination of the prostate can be safely performed in selected patients with CIEDs under controlled conditions with applicable image quality while maintaining a SAR less than 1.5 W/kg.

MR Imaging and Cochlear Implants with Retained Internal Magnets: Reducing Artifacts near Highly Inhomogeneous Magnetic Fields.

The number of patients receiving cochlear implants and auditory brainstem implants for severe to profound sensorineural hearing loss has rapidly increased. These implants consist of an internal component implanted between the skull and the temporal scalp and an external removable speech processor unit. A small magnet within the internal component is commonly used to hold the external speech processor unit in place. Several cochlear implant models have recently received U.S. Food and Drug Administration and European Economic Area regulatory approval to allow magnetic resonance (MR) imaging examinations to be performed under certain specified conditions. The small internal magnet presents a challenge for imaging of the head and neck near the implant, creating a nonlinear magnetic field inhomogeneity and significant MR imaging artifacts. Fat-saturation failures and susceptibility artifacts severely degrade image quality. Typical artifacts at diffusion-weighted imaging and accelerated imaging are exacerbated. Each examination may require impromptu adjustments to allow visualization of the tissue or contrast of interest. Patients may also be quite uncomfortable during the examination, as a result of either imposed magnetic forces or a tight head wrap that is often applied to minimize internal magnet movement. Translational forces and torque sometimes displace the implanted magnet even when a head wrap is used. Diseases such as neurofibromatosis type 2 that are associated with bilateral vestibular schwannomas and hearing loss often require lifelong tumor surveillance with MR imaging. A collaborative team of radiologists, technologists, and/or medical physicists or MR imaging scientists, armed with strategies to mitigate artifacts near implanted magnets, can customize the examination for better visualization of tissue and consistent comparison examinations over time. ©RSNA, 2018.

Magnetic Resonance Imaging in Patients with Cochlear Implants without Magnet Removal: A Radiology-Administered Protocol to Enhance Operational Efficiency and Improve Workflow.

OBJECTIVE: To describe the development, implementation, and validation of a radiology-administered protocol to obtain magnetic resonance imaging (MRI) in patients with cochlear implants and auditory brainstem implants without magnet removal. STUDY DESIGN: Retrospective review and description of novel care pathway. METHODS: A radiology-administered protocol was designed based on careful input from the radiology safety committee and neurotology. Radiology technologist training modules, consent instructions, patient educational material, clinical audits, and other safeguards were implemented, with samples provided in this report. The primary outcomes measured included instances of magnet displacement during MRI and premature termination of MRI studies secondary to pain. RESULTS: Between June 19, 2018, and October 12, 2021, 301 implanted ears underwent MRI without magnet removal, including 153 devices housing diametric MRI-conditional magnets, and 148 implants with conventional axial (i.e., nondiametric) magnets. Among cases with diametric MRI-conditional magnets, all studies were completed without magnet dislodgement or need to terminate imaging early due to pain. Among cases with conventional axial (nondiametric) magnets, 29 (19.6%) MRI studies were stopped prematurely secondary to pain or discomfort; the overall rate of this event was 9.6% (29 of 301) among the entire study cohort. In addition, 6.1% (9 of 148) experienced confirmed magnet displacement despite headwrap placement; the overall rate among all cases was 3.0% (9 of 301). Eight of these patients received successful external magnet reseating through manual pressure on the external scalp without surgery, and one required surgical replacement of the magnet in the operating room. There were no documented instances of hematoma, infection, device or magnet extrusion, internal device movement (i.e., gross receiver-stimulator migration), or device malfunction in this cohort related to MRI. CONCLUSIONS: We present the successful implementation of a radiology-administered protocol designed to streamline care for cochlear implant and auditory brainstem implant recipients who require MRI and ease clinical demands for otolaryngology providers. Examples of resources developed, including a process map, radiology training modules, consent instructions, patient educational materials, clinical audit, and other procedural safety measures are provided so interested groups may consider adapting and implementing related measures according to need.

Magnetic resonance-guided focused ultrasound of uterine leiomyomas: review of a 12-month outcome of 130 clinical patients.

PURPOSE: To assess 12-month outcomes and safety of clinical magnetic resonance (MR)-guided focused ultrasound (US) treatments of uterine leiomyomas. MATERIALS AND METHODS: Between March 2005 and December 2009, 150 women with symptomatic uterine leiomyomas were clinically treated with MR-guided focused US at a single institution; 130 patients completed treatment and agreed to have their data used for research purposes. Patients were followed through retrospective review of medical records and phone interviews conducted at 3-, 6-, and 12-month intervals after treatment to assess additional procedures and symptom relief. Outcome measures and treatment complications were analyzed for possible correlations with the appearance of the tumors on T2-weighted imaging. RESULTS: The cumulative incidence of additional tumor-related treatments 12 months after MR-guided focused US was 7.4% by the Kaplan-Meier method. At 3-, 6-, and 12-month follow-up, 86% (90 of 105), 93% (92 of 99), and 88% (78 of 89) of patients reported relief of symptoms, respectively. No statistically significant correlation between tumor appearance on T2-weighted imaging and 12-month outcome was found. Treatment-related complications were observed in 17 patients (13.1%): 16 patients had minor complications and one had a major complication (deep vein thrombosis). All complications were resolved within the 12-month follow-up period. CONCLUSIONS: MR-guided focused US is a noninvasive treatment option that can be used to effectively and safely treat uterine leiomyomas and delivers significant and lasting symptom relief for at least 12 months. The incidence of additional treatment during this time period is comparable with those in previous reports of uterine artery embolization.

Comparison of Clinical Performance Between Two Generations of Magnetic Resonance-guided Focused Ultrasound Systems in Treatments of Uterine Leiomyomas.

OBJECTIVES: The aim of this study was to evaluate the impact of technology improvements on the outcomes of magnetic resonance-guided focused ultrasound (MRgFUS) treatments of symptomatic uterine leiomyomas (uterine fibroids). The study compared ablation volumes and incidence of adverse events in patient groups treated with two generations of MRgFUS systems from a single vendor. METHODS: The present study describes the results of a retrospective comparative study of two groups of women with symptomatic uterine leiomyomas who were clinically treated with MRgFUS at a single institution. Group 1 (n = 130) was treated using the first-generation system between March 2005 and December 2009. Group 2 (n = 71) was treated using the second-generation between December 2013 and September 2019. RESULTS: The second-generation MRgFUS system resulted in significantly improved nonperfused volume ratios in both dark and bright T2 fibroid categories compared with the first-generation system (dark - 80% versus46 %, p = 0.00002 and bright - 46% versus 32%, p = 0.001). There have been no recorded hospital admissions, no skins burns, and no reported major adverse events since the introduction of this second-generation ExAblate 2100 system with advanced safety and treatment planning features. CONCLUSION: This study has demonstrated that improvements to current MRgFUS technology resulted in significantly increased efficacy and patient safety of clinical treatments of patients with symptomatic uterine leiomyomas.

MR Safety: Active Implanted Electronic Devices.

New implanted medical devices continue to be made available for treatment of medical conditions. Many recipients can benefit from the diagnostic power of MR imaging. Provisions must be made to determine if these patients can be safely scanned. Metal-containing devices can be considered either MR unsafe or conditional. It is essential that all components of an implanted system are completely and accurately identified, with the most restrictive MR safety condition dictating the scanning approach. MR safety considerations for major classes of implanted devices are discussed, recognizing that there have been reports of serious device-related MR safety incidents.

Evaluation of feasibility of 1.5 Tesla prostate MRI using body coil RF transmit in a patient with an implanted vagus nerve stimulator.

PURPOSE: To assess risks of RF-heating of a vagus nerve stimulator (VNS) during 1.5 T prostate MRI using body coil transmit and to compare these risks with those associated with MRI head exams using a transmit/receive head coil. METHODS: Spatial distributions of radio-frequency (RF) B1 fields generated by transmit/receive (T/R) body and head coils were empirically assessed along the long axis of a 1.5 T MRI scanner bore. Measurements were obtained along the center axis of the scanner and laterally offset by 15 cm (body coil) and 7 cm (head coil). RF-field measurements were supplemented with direct measurements of RF-heating of 15 cm long copper wires affixed to and submerged in the "neck" region of the gelled saline-filled (sodium chloride and polyacrylic acid) "head-and-torso" phantom. Temperature elevations at the lead tips were measured using fiber-optic thermometers with the phantom positioned at systematically increased distances from the scanner isocenter. RESULTS: B1 field measurements demonstrated greater than 10 dB reduction in RF power at distances beyond 28 cm and 24 cm from isocenter for body and head coil, respectively. Moreover, RF power from body coil transmit at distances greater than 32 cm from isocenter was found to be lower than from the RF power from head coil transmit measured at locations adjacent to the coil array at its opening. Correspondingly, maximum temperature elevations at the tips of the copper wires decreased with increasing distance from isocenter - from 7.4°C at 0 cm to no appreciable heating at locations beyond 40 cm. CONCLUSIONS: For the particular scanner model evaluated in this study, positioning an implanted VNS farther than 32 cm from isocenter (configuration achievable for prostate exams) can reduce risks of RF-heating resulting from the body coil transmit to those associated with using a T/R head coil.

Use of a radio frequency shield during 1.5 and 3.0 Tesla magnetic resonance imaging: experimental evaluation.

Radiofrequency (RF) shields have been recently developed for the purpose of shielding portions of the patient's body during magnetic resonance imaging (MRI) examinations. We present an experimental evaluation of a commercially available RF shield in the MRI environment. All tests were performed on 1.5 T and 3.0 T clinical MRI scanners. The tests were repeated with and without the RF shield present in the bore, for comparison. Effects of the shield, placed within the scanner bore, on the RF fields generated by the scanner were measured directly using tuned pick-up coils. Attenuation, by as much as 35 dB, of RF field power was found inside the RF shield. These results were supported by temperature measurements of metallic leads placed inside the shield, in which no measurable RF heating was found. In addition, there was a small, simultaneous detectable increase (∼1 dB) of RF power just outside the edges of the shield. For these particular scanners, the autocalibrated RF power levels were reduced for scan locations prescribed just outside the edges of the shield, which corresponded with estimations based on the pick-up coil measurements. Additionally, no significant heating during MRI scanning was observed on the shield surface. The impact of the RF shield on the RF fields inside the magnet bore is likely to be dependent on the particular model of the RF shield or the MRI scanner. These results suggest that the RF shield could be a valuable tool for clinical MRI practices.

Clinical correlates of white matter tract degeneration in progressive supranuclear palsy.

OBJECTIVES: To use diffusion tensor imaging to assess white matter tract degeneration in progressive supranuclear palsy (PSP) and to investigate correlates between tract integrity and clinical measures. DESIGN: Case-control study. SETTING: Tertiary care medical center. PATIENTS/PARTICIPANTS: Twenty patients with probable PSP and 20 age- and sex-matched healthy controls were enrolled. All patients with PSP underwent standardized clinical testing, including the Frontal Behavioral Inventory and Frontal Assessment Battery to assess behavioral change, the PSP Rating Scale to measure disease severity, the Movement Disorder Society-sponsored revision of the Unified Parkinson's Disease Rating Scale (parts II and III) to measure motor function, and the PSP Saccadic Impairment Scale to measure eye movement abnormalities. METHODS: Fractional anisotropy and mean diffusivity were measured using region of interest analysis and tract-based spatial statistics. RESULTS: Compared with controls, abnormal diffusivity was observed predominantly in the superior cerebellar peduncles, body of the corpus callosum, inferior longitudinal fasciculus, and superior longitudinal fasciculus in patients with PSP. Fractional anisotropy values in the superior cerebellar peduncles correlated with disease severity (r = -0.59, P = .006), inferior longitudinal fasciculus correlated with motor function (r = -0.51, P = .02), and superior longitudinal fasciculus correlated with severity of saccadic impairments (r = -0.45, P = .047). CONCLUSIONS: The results of this study demonstrate that PSP is associated with degeneration of the brainstem, association, and commissural fibers and that this degeneration likely plays an important role in clinical dysfunction.