Temporary Hearing Threshold Shift in Healthy Volunteers with Hearing Protection Caused by Acoustic Noise Exposure during 3-T Multisequence MR Neuroimaging

MRI noise and auditory health: Can one hundred scans be linked to hearing loss? The case of the Courtois NeuroMod project

Magnetic resonance imaging (MRI) is one of the most commonly used tools in neuroscience. However, it implies exposure to high noise levels. Exposure to noise can lead to temporary or permanent hearing loss, especially when the exposure is long and/or repeated. Little is known about the hearing risks for people undergoing several MRI examinations, especially in the context of longitudinal studies. The goal of this study was to assess the potential impact of repeated exposure to MRI noise on hearing in research participants undergoing dozens of MRI scans. This investigation was made possible thanks to an unprecedented intensive MRI research data collection effort (the Courtois NeuroMod project) where participants have been scanned weekly (up to twice a week), with the use of hearing protection, since 2018. Their hearing was tested periodically, over a period of 1.5 years. First, baseline pure-tone thresholds and distortion product otoacoustic emission (DPOAE) amplitudes were acquired before the beginning of this study. Hearing tests were then scheduled immediately before/immediately after a scan and with a delay of two to seven days after a scan. Pure-tone thresholds and DPOAE amplitudes showed no scanner noise impact right after the scan session when compared to the values acquired right before the scan session. Pure-tone thresholds and DPOAE amplitudes acquired in the delayed condition and compared to the baseline showed similar results. These results suggest an absence of impact from MRI noise exposure. Overall, our results show that an intensive longitudinal MRI study like the Courtois NeuroMod project likely does not cause hearing damage to participants when they properly utilize adequate hearing protection.

Auditory Effects of Acoustic Noise From 3-T Brain MRI in Neonates With Hearing Protection

BACKGROUND

Neonates with immature auditory function (eg, weak/absent middle ear muscle reflex) could conceivably be vulnerable to noise-induced hearing loss; however, it is unclear if neonates show evidence of hearing loss following MRI acoustic noise exposure.

PURPOSE

To explore the auditory effects of MRI acoustic noise in neonates.

STUDY TYPE

Prospective.

SUBJECTS

Two independent cohorts of neonates (N = 19 and N = 18; mean gestational-age, 38.75 ± 2.18 and 39.01 ± 1.83 weeks).

FIELD STRENGTH/SEQUENCE

T1-weighted three-dimensional gradient-echo sequence, T2-weighted fast spin-echo sequence, single-shot echo-planar imaging-based diffusion-tensor imaging, single-shot echo-planar imaging-based diffusion-kurtosis imaging and T2-weighted fluid-attenuated inversion recovery sequence at 3.0 T.

ASSESSMENT

All neonates wore ear protection during scan protocols lasted ~40 minutes. Equivalent sound pressure levels (SPLs) were measured for both cohorts. In cohort1, left- and right-ear auditory brainstem response (ABR) was measured before (baseline) and after (follow-up) MRI, included assessment of ABR threshold, wave I, III and V latencies and interpeak interval to determine the functional status of auditory nerve and brainstem. In cohort2, baseline and follow-up left- and right-ear distortion product otoacoustic emission (DPOAE) amplitudes were assessed at 1.2 to 7.0 kHz to determine cochlear function.

STATISTICAL TEST

Wilcoxon signed-rank or paired t-tests with Bonferroni's correction were used to compare the differences between baseline and follow-up ABR and DPOAE measures.

RESULTS

Equivalent SPLs ranged from 103.5 to 113.6 dBA. No significant differences between baseline and follow-up were detected in left- or right-ear ABR measures (P > 0.999, Bonferroni corrected) in cohort1, or in DPOAE levels at 1.2 to 7.0 kHz in cohort2 (all P > 0.999 Bonferroni corrected except for left-ear levels at 3.5 and 7.0 kHz with corrected P = 0.138 and P = 0.533).

DATA CONCLUSION

A single 40-minute 3-T MRI with equivalent SPLs of 103.5-113.6 dBA did not result in significant transient disruption of auditory function, as measured by ABR and DPOAE, in neonates with adequate hearing protection.

EVIDENCE LEVEL

2.

TECHNICAL EFFICACY

Stage 5.

AAPM Task Group 334: A guidance document to using radiotherapy immobilization devices and accessories in an MR environment

Use of magnetic resonance (MR) imaging in radiation therapy has increased substantially in recent years as more radiotherapy centers are having MR simulators installed, requesting more time on clinical diagnostic MR systems, or even treating with combination MR linear accelerator (MR-linac) systems. With this increased use, to ensure the most accurate integration of images into radiotherapy (RT), RT immobilization devices and accessories must be able to be used safely in the MR environment and produce minimal perturbations. The determination of the safety profile and considerations often falls to the medical physicist or other support staff members who at a minimum should be a Level 2 personnel as per the ACR. The purpose of this guidance document will be to help guide the user in making determinations on MR Safety labeling (i.e., MR Safe, Conditional, or Unsafe) including standard testing, and verification of image quality, when using RT immobilization devices and accessories in an MR environment.

Whole-body magnetic resonance imaging at 0.05 Tesla

Despite a half-century of advancements, global magnetic resonance imaging (MRI) accessibility remains limited and uneven, hindering its full potential in health care. Initially, MRI development focused on low fields around 0.05 Tesla, but progress halted after the introduction of the 1.5 Tesla whole-body superconducting scanner in 1983. Using a permanent 0.05 Tesla magnet and deep learning for electromagnetic interference elimination, we developed a whole-body scanner that operates using a standard wall power outlet and without radiofrequency and magnetic shielding. We demonstrated its wide-ranging applicability for imaging various anatomical structures. Furthermore, we developed three-dimensional deep learning reconstruction to boost image quality by harnessing extensive high-field MRI data. These advances pave the way for affordable deep learning-powered ultra-low-field MRI scanners, addressing unmet clinical needs in diverse health care settings worldwide.

Zero Echo Time Magnetic Resonance Imaging; Techniques and Clinical Utility in Musculoskeletal System

Zero echo time (ZTE) sequence is recent advanced magnetic resonance technique that utilizes ultrafast readouts to capture signals from short-T2 tissues. This sequence enables T2- and T2* weighted imaging of tissues with short intrinsic relaxation times by using an extremely short TE, and are increasingly used in the musculoskeletal system. We review the imaging physics of these sequences, practical limitations, and image reconstruction, and then discuss the clinical utilities in various disorders of the musculoskeletal system. ZTE can be readily incorporated into the clinical workflow, and is a promising technique to avoid unnecessary radiation exposure, cost, and time-consuming by computed tomography in some cases. LEVEL OF EVIDENCE: 4 TECHNICAL EFFICACY: Stage 1.

Evaluation of hearing loss in young adults after exposure to 3.0T MRI with standard hearing protection

Standard clinical protocols require hearing protection during magnetic resonance imaging (MRI) for patient safety. This investigation prospectively evaluated the auditory function impact of acoustic noise exposure during a 3.0T MRI in healthy adults. Twenty-nine participants with normal hearing underwent a comprehensive audiologic assessment before and immediately following a clinically indicated head MRI. Appropriate hearing protection with earplugs (and pads) was used per standard of practice. To characterize noise hazards, current sound monitoring tools were used to measure levels of pulse sequences measured. A third audiologic test was performed if a significant threshold shift (STS) was identified at the second test, within 30 days post MRI. Some sequences produced high levels (up to 114.5 dBA; 129 dB peak SPL) that required hearing protection but did not exceed 100% daily noise dose. One participant exhibited an STS in the frequency region most highly associated with noise-induced hearing loss. No participants experienced OSHA-defined STS in either ear. Overall, OAE measures did not show evidence of changes in cochlear function after MRI. In conclusion, hearing threshold shifts associated with hearing loss or OAE level shifts reflecting underlying cochlear damage were not detected in any of the 3.0T MRI study participants who used the current recommended hearing protection.

A low-cost and shielding-free ultra-low-field brain MRI scanner

Magnetic resonance imaging is a key diagnostic tool in modern healthcare, yet it can be cost-prohibitive given the high installation, maintenance and operation costs of the machinery. There are approximately seven scanners per million inhabitants and over 90% are concentrated in high-income countries. We describe an ultra-low-field brain MRI scanner that operates using a standard AC power outlet and is low cost to build. Using a permanent 0.055 Tesla Samarium-cobalt magnet and deep learning for cancellation of electromagnetic interference, it requires neither magnetic nor radiofrequency shielding cages. The scanner is compact, mobile, and acoustically quiet during scanning. We implement four standard clinical neuroimaging protocols (T1- and T2-weighted, fluid-attenuated inversion recovery like, and diffusion-weighted imaging) on this system, and demonstrate preliminary feasibility in diagnosing brain tumor and stroke. Such technology has the potential to meet clinical needs at point of care or in low and middle income countries.

Survey of Acoustic Output in Neonatal Brain Protocols

BACKGROUND

Auditory and non-auditory safety concerns associated with the appreciable sound levels inherent to magnetic resonance imaging (MRI) procedures exist for neonates. However, current gaps in knowledge preclude making an adequate risk assessment.

PURPOSE

To measure acoustic exposure (duration, intensity, and frequency) during neonatal brain MRI and compare these values to existing hearing safety limits and data.

STUDY TYPE

Phantom.

PHANTOM

Cylindrical doped water phantom.

FIELD STRENGTH/SEQUENCE

Neonatal brain protocols acquired at 1-3 T. Scans in the model protocol included a diffusion tensor imaging scan, a gradient echo, a three-dimensional (3D) fast spin echo, 3D fast spin-echo single-shots, a spin echo, a turbo spin echo, a 3D arterial spin labeling scan, and a susceptibility-weighted fast spin-echo scan.

ASSESSMENT

The sound pressure levels (SPLs), frequency profile, and durations of five neonatal brain protocols on five MR scanners (scanner A [3 T, whole-body], scanner B [1.5 T, whole-body], scanner C [1 T, dedicated neonatal], scanner D [1.5 T, whole-body], and scanner E [3 T, whole-body]) located at three different sites were recorded. The SPLs were then compared to the International Electrotechnical Commission (IEC) hearing safety limit and existing data of infant non-auditory responses to loud sounds to assess risk.

STATISTICAL TESTS

Mann-Whitney U test to assess whether the dedicated neonatal scanner was quieter than the other machines.

RESULTS

The average level A-weighted equivalent value (LAEQ) across all five MR scanners and scans was 92.88 dBA and the range of LAEQs across all five MR scanners and scans was 80.8-105.31 dBA. The duration of the recorded neonatal protocols maintained by neonatal scanning facilities (from scanners A, B, and C) ranged from 27:33 to 37:06 minutes.

DATA CONCLUSION

Neonatal protocol sound levels straddled existing notions of risk, exceeding sound levels known to cause non-auditory responses in neonates but not exceeding the IEC MRI SPL safety limit.

LEVEL OF EVIDENCE

5 TECHNICAL EFFICACY: Stage 5.

Silent zero TE MR neuroimaging: Current state-of-the-art and future directions

Magnetic Resonance Imaging (MRI) scanners produce loud acoustic noise originating from vibrational Lorentz forces induced by rapidly changing currents in the magnetic field gradient coils. Using zero echo time (ZTE) MRI pulse sequences, gradient switching can be reduced to a minimum, which enables near silent operation.Besides silent MRI, ZTE offers further interesting characteristics, including a nominal echo time of TE = 0 (thus capturing short-lived signals from MR tissues which are otherwise MR-invisible), 3D radial sampling (providing motion robustness), and ultra-short repetition times (providing fast and efficient scanning).In this work we describe the main concepts behind ZTE imaging with a focus on conceptual understanding of the imaging sequences, relevant acquisition parameters, commonly observed image artefacts, and image contrasts. We will further describe a range of methods for anatomical and functional neuroimaging, together with recommendations for successful implementation.

Maintaining Image Quality While Reducing Acoustic Noise and Switched Gradient Field Exposure During Lumbar MRI

BACKGROUND

MR-generated acoustic noise can contribute to patient discomfort and potentially be harmful. One way to reduce this noise is by altering the gradient output and/or waveform using software optimization. Such modifications might influence image quality and switched gradient field exposure, and different techniques appear to affect sound pressure levels (SPLs) to various degrees.

PURPOSE

To evaluate SPLs, image quality, switched gradient field exposure, and participants' perceived noise levels during two different acoustic noise reduction (ANR) techniques, Quiet Suite (QS) and Whisper Mode (WM), and to compare them with conventional T2-weighted turbo spin echo (T2W TSE) of the lumbar spine.

DESIGN

Prospective.

SUBJECTS

Forty adults referred for lumbar MRI.

FIELD STRENGTH/SEQUENCE

Conventional T2W TSE, T2W TSE with QS, and T2W TSE with WM were acquired at 1.5 T.

ASSESSMENT

Peak SPL (A-weighted decibels, dBA), perceived noise levels (Borg CR10®-scale), signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), three radiologists' qualitative assessments in image quality on an ordinal scale 1-4, switched gradient field exposure (% general public), and gradient currents were measured. Interobserver reliability was reported as percentage agreement.

STATISTICAL TESTS

Repeated measures ANOVA, Friedman's ANOVA, and Wilcoxon's Signed-Rank Test for acoustic noise measurements and image quality assessments.

RESULTS

Mean peak SPLs were 89.9 dBA, 74.3 dBA, and 78.8 dBA for conventional, QS, and WM, respectively (P < 0.05). Participants perceived QS as the quietest and conventional as the loudest sequence (P < 0.05). No qualitative differences in image quality were seen (P > 0.05), although QS showed significantly improved SNR and CNR (P < 0.05). Switched gradient field exposure was reduced by 66% and 48% for QS and WM, respectively.

DATA CONCLUSION

Without degrading image quality, both QS and WM are viable ANR techniques in lumbar T2W TSE. QS provided the lowest SPL, the lowest gradient field exposure and was perceived as the most silent among the three sequences.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY STAGE: 5.

Evaluation of the possible effect of magnetic resonance imaging noise on peripheral hearing organ with the otoacoustic emission

PURPOSE

The aim of this study is to evaluate the effect of noise produced by magnetic resonance imaging (MRI) device on hearing by using objective and subjective audiological assessments.

METHODS

A total of 38 patients between the ages of 18 and 50 without hearing loss, and had performed MRI for brain, head, neck or cervical imaging were included in this prospective clinical study. Pure tone audiometry, speech audiometry, high frequency audiometry, transient evoked otoacoustic emissions (TEOAE) and distortion product otoacoustic emission (DPOAE) were performed before and after MRI.

RESULTS

There was no statistically significant difference in TEOAE, pure tone audiogram, high frequency audiogram and speech audiogram thresholds. In DPOAE, the median value before and after MRI at the frequency of the left ear at 4.0 kHz was 13.6 (8.5-19.9) and 15.7 (8.9-20.7) SNR respectively (p > .05). The median value before MRI at the right ear 4.0 kHz frequency was 14.1 (9.1-20.5) SNR, whereas the median value after MRI was 13.2 (8.8-19.8 SNR (p = 0,03). There was no statistically significant difference in other frequencies in DPOAE.

CONCLUSIONS

This is the first objective study that examines the MRI noise on speech audiometry and otoacoustic emission together. However, the effect of MRI noise on hearing pathway is still doubt. Based on the difference at 4 kHz frequency on DPOAE; on-earphones may not sufficiently protect the patients from the MRI noise and this issue should deserve further research.

Key Elements of Clinical Magnetic Resonance Imaging Safety: It Takes a Village

Magnetic resonance (MR) imaging-related injuries have continued to occur at an alarming rate during more than 3 decades of use. Persistently reported MR imaging-related injuries are caused by (1) radiofrequency thermal effect burns, (2) bruising from table top and coil-related mechanical injuries, (3) magnetic field-related support equipment malfunction, (4) magnetic field-related projectile trauma, (5) gradient switching noise hearing loss. A cohesive and educated MR imaging community under the guidance of a defined management structure is essential for monitoring and mitigating MR imaging risks. This article offers an approach for decreasing MR imaging-related injury risks.

Silent 3D MR sequence for quantitative and multicontrast T1 and proton density imaging

This study aims to develop a silent, fast and 3D method for T1 and proton density (PD) mapping, while generating time series of T1-weighted (T1w) images with bias-field correction. Undersampled T1w images at different effective inversion times (TIs) were acquired using the inversion recovery prepared RUFIS sequence with an interleaved k-space trajectory. Unaliased images were reconstructed by constraining the signal evolution to a temporal subspace which was learned from the signal model. Parameter maps were obtained by fitting the data to the signal model, and bias-field correction was conducted on T1w images. Accuracy and repeatability of the method was accessed in repeated experiments with phantom and volunteers. For the phantom study, T1 values obtained by the proposed method were highly consistent with values from the gold standard method, R² = 0.9976. Coefficients of variation (CVs) ranged from 0.09% to 0.83%. For the volunteer study, T1 values from gray and white matter regions were consistent with literature values, and peaks of gray and white matter can be clearly delineated on whole-brain T1 histograms. CVs ranged from 0.01% to 2.30%. The acoustic noise measured at the scanner isocenter was 2.6 dBA higher compared to the in-bore background. Rapid and with low acoustic noise, the proposed method is shown to produce accurate T1 and PD maps with high repeatability by reconstructing sparsely sampled T1w images at different TIs using temporal subspace. Our approach can greatly enhance patient comfort during examination and therefore increase the acceptance of the procedure.

Silent myelin-weighted magnetic resonance imaging

Background: Inhomogeneous Magnetization Transfer (ihMT) is an emerging, uniquely myelin-specific magnetic resonance imaging (MRI) contrast. Current ihMT acquisitions utilise fast Gradient Echo sequences which are among the most acoustically noisy MRI sequences, reducing patient comfort during acquisition. We sought to address this by modifying a near silent MRI sequence to include ihMT contrast.

Methods: A Magnetization Transfer preparation module was incorporated into a radial Zero Echo-Time sequence. Repeatability of the ihMT ratio and inverse ihMT ratio were assessed in a cohort of healthy subjects. We also investigated how head orientation affects ihMT across subjects, as a previous study in a single subject suggests this as a potential confound.

Results: We demonstrated that ihMT ratios comparable to existing, acoustically loud, implementations could be obtained with the silent sequence. We observed a small but significant effect of head orientation on inverse ihMTR.

Conclusions: Silent ihMT imaging is a comparable alternative to conventional, noisy, alternatives. For all future ihMT studies we recommend careful positioning of the subject within the scanner.

Silent myelin-weighted magnetic resonance imaging

Background: Inhomogeneous Magnetization Transfer (ihMT) is an emerging, uniquely myelin-specific magnetic resonance imaging (MRI) contrast. Current ihMT acquisitions utilise fast Gradient Echo sequences which are among the most acoustically noisy MRI sequences, reducing patient comfort during acquisition. We sought to address this by modifying a near silent MRI sequence to include ihMT contrast. Methods: A Magnetization Transfer preparation module was incorporated into a radial Zero Echo-Time sequence. Repeatability of the ihMT ratio and inverse ihMT ratio were assessed in a cohort of healthy subjects. We also investigated how head orientation affects ihMT across subjects, as a previous study in a single subject suggests this as a potential confound. Results: We demonstrated that ihMT ratios comparable to existing, acoustically loud, implementations could be obtained with the silent sequence. We observed a small but significant effect of head orientation on inverse ihMTR. Conclusions: Silent ihMT imaging is a comparable alternative to conventional, noisy, alternatives. For all future ihMT studies we recommend careful positioning of the subject within the scanner.

[Sedative effect of intranasal midazolam in neonates undergoing magnetic resonance imaging: a prospective single-blind randomized controlled study]

OBJECTIVE

To compare intranasal midazolam and intramuscular phenobarbital sodium for their sedative effect in neonates undergoing magnetic resonance imaging (MRI).

METHODS

A total of 70 neonates who underwent cranial MRI from September 2017 to March 2019 were randomized into an observation group and a control group, with 35 cases in each group. The observation group received intranasal drops of midazolam (0.3 mg/kg), and the control group received intramuscular injection of phenobarbital sodium (10 mg/kg). The sedation status of the neonates was evaluated using the Ramsay Sedation Scale. Meanwhile, the two groups were compared for the success rate of MRI procedure and incidence of adverse reactions.

RESULTS

In the observation group, the sedation score was the highest at 20 minutes post administration, then was gradually decreasing, and decreased to the lowest level at 70 minutes post administration. In the control group, the sedation score was the lowest at 10 minutes post administration, then was gradually increasing, and increased to the highest level at 40 minutes and 50 minutes post administration, followed by a gradual decrease. Comparison of the sedation score at each time period suggested that the sedation score was significantly higher in the observation group than in the control group within 40 minutes post administration (P<0.05), while there were no significant differences between the two groups in the sedation score after 40 minutes post administration (P>0.05). The success rate of MRI procedure was significantly higher in the observation group than in the control group (89% vs 69%, P<0.05). There was no significant difference between the two groups in the incidence of adverse reactions (P>0.05).

CONCLUSIONS

Intranasal midazolam is superior to intramuscular phenobarbital sodium in the sedative effect in neonates undergoing MRI, with the benefits of being fast, convenient, safe, and effective.

Review of Audiovestibular Symptoms Following Exposure to Acoustic and Electromagnetic Energy Outside Conventional Human Hearing

Objective: We aim to examine the existing literature on, and identify knowledge gaps in, the study of adverse animal and human audiovestibular effects from exposure to acoustic or electromagnetic waves that are outside of conventional human hearing. Design/Setting/Participants: A review was performed, which included searches of relevant MeSH terms using PubMed, Embase, and Scopus. Primary outcomes included documented auditory and/or vestibular signs or symptoms in animals or humans exposed to infrasound, ultrasound, radiofrequency, and magnetic resonance imaging. The references of these articles were then reviewed in order to identify primary sources and literature not captured by electronic search databases. Results: Infrasound and ultrasound acoustic waves have been described in the literature to result in audiovestibular symptomology following exposure. Technology emitting infrasound such as wind turbines and rocket engines have produced isolated reports of vestibular symptoms, including dizziness and nausea and auditory complaints, such as tinnitus following exposure. Occupational exposure to both low frequency and high frequency ultrasound has resulted in reports of wide-ranging audiovestibular symptoms, with less robust evidence of symptomology following modern-day exposure via new technology such as remote controls, automated door openers, and wireless phone chargers. Radiofrequency exposure has been linked to both auditory and vestibular dysfunction in animal models, with additional historical evidence of human audiovestibular disturbance following unquantifiable exposure. While several theories, such as the cavitation theory, have been postulated as a cause for symptomology, there is extremely limited knowledge of the pathophysiology behind the adverse effects that particular exposure frequencies, intensities, and durations have on animals and humans. This has created a knowledge gap in which much of our understanding is derived from retrospective examination of patients who develop symptoms after postulated exposures. Conclusion and Relevance: Evidence for adverse human audiovestibular symptomology following exposure to acoustic waves and electromagnetic energy outside the spectrum of human hearing is largely rooted in case series or small cohort studies. Further research on the pathogenesis of audiovestibular dysfunction following acoustic exposure to these frequencies is critical to understand reported symptoms.

Transplantation and Tracking of the Human Umbilical Cord Mesenchymal Stem Cell Labeled with Superparamagnetic Iron Oxide in Deaf Pigs

The purpose of this study was to establish a safe and effective approach to label the human umbilical cord mesenchymal stem cells (UC-MSCs) derived from the Wharton's Jelly with superparamagnetic iron oxide (SPIO) nanoparticles as a cell tracer. The cytotoxicity of the SPIO was screened in vitro by cytochemical experiments. The results showed the new infection protocol of SPIO-Lip2000 mixture had high efficiency and the optimal labeling concentration was a 50 μg/ml SPIO suspension. Transmission electron microscope (TEM) confirmed the distribution of the intracellular SPIO. We transplanted the labeled UC-MSCs into the sensorineural hearing loss (SNHL) minipigs at 1 week after noise exposure. Auditory brainstem response results demonstrated the transplantation of UC-MSCs was an efficient therapy for SNHL. The positive sediments in cochlear blood vessels, the bony wall of scala tympani, and spiral ganglion nerve fibers were found in the stem cell recipients' cochlea. We did not detect iron elements in the inner/outer hair cells' stereocilia, cuticular plate, or pillar cells from the basal to apex turns of the stem cell recipients' cochlea. In addition, TEM found SPIO in the medulla oblongata and the cerebrum in the SNHL minipigs after stem cell transplantation. In conclusion, we established a safe and effective approach to labeled human UC-MSCs derived from Wharton's Jelly by using SPIO nanoparticles as a cell tracer in vitro and in vivo. This protocol showed a wide promising application in stem cell therapy and tracing in vivo for experiments with large mammals. Anat Rec, 303:494-505, 2020. © 2019 American Association for Anatomy.

Silent susceptibility-weighted angiography to detect hemorrhagic lesions in the brain: a clinical and phantom study

PURPOSE

To compare the effectiveness of silent susceptibility-weighted angiography (sSWAN), a new imaging technique with lower acoustic noise, with conventional susceptibility-weighted angiography (cSWAN) in the detection of intracranial hemorrhagic lesions.

METHODS

We measured the acoustic and background noise during sSWAN and cSWAN imaging and calculated the contrast-to-noise ratio (CNR) of the phantom consisting of eight chambers with different concentrations of superparamagnetic iron oxide. In the clinical study, we calculated the CNRs of hemorrhagic lesions in 15 patients and evaluated the images for conspicuity and artifact on each sequence and scored them on a 4-point scale. We also evaluated whether hypointense areas observed on sSWAN or cSWAN increased in size from those on T2*-weighted imaging (T2*-WI).

RESULTS

Acoustic noise for sSWAN (57.9 ± 0.32 dB [background noise 51.3 dB]) was significantly less than that for cSWAN (89.0 ± 0.22 dB [background noise 50.9 dB]). The CNRs of phantoms for sSWAN were slightly but not significantly lower than those for cSWAN (P = 0.18). The CNRs of hemorrhagic lesions did not show significant differences between sSWAN and cSWAN (P = 0.17). There were no significant differences between sSWAN and cSWAN with respect to the scores for conspicuity, artifact, and change in size of hypointense areas from T2*-WI.

CONCLUSION

sSWAN is equivalent to cSWAN with respect to the image quality for the detection of hemorrhagic lesions but has lower acoustic noise.

Acoustic trauma from continuous noise: Minimum exposures, issues in clinical trial design, and comments on magnetic resonance imaging exposures

Acoustic trauma (AT) is permanent hearing loss after a single noise exposure. A few human cases resulting from continuous, i.e., nonimpulsive noise, have been reported as reviewed by Ward [(1991). "Hearing loss from noise and music," presented at Audio Engineering Society, New York, October 4-8]. This paper updates that review by examining 11 cases in nine reports, from 1950 to 2006, with the intention of determining minimum exposures that may cause AT, including the potential risk of exposure to noise from magnetic resonance imaging machines. Diffuse-field related levels above 120 dBA for 10 s or more, or above 130 dBA for 2-3 s (values well above OSHA's unprotected exposure limits), can lead to AT. These cases appear to represent a susceptible fraction of the population, because much more intense exposures (e.g., 130 dBA for 32 min) have been tolerated by groups of volunteers who suffered only temporary threshold shifts. AT from continuous noise is unlikely to occur in OSHA-compliant hearing conservation programs, and probably rare enough in the general civilian population that clinical trials of drugs aimed at treating it are unlikely to be practical. AT from impulse noise, such as gunfire, which is specifically not the topic of the current work, is more amenable to clinical trials, especially in military settings.

Hearing Thresholds Changes after MRI 1.5T of Head and Neck

Introduction

Exposure to high intensity noise produced by MRI is a cause for concern. This study was conducted to determine the temporary and permanent effects of exposure to noise created by performing MRI on the hearing threshold of the subjects using conventional and extended high frequency audiometry.

Methods

This semiexperimental study was performed on 35 patients referred to Shahid Rahnemoun Hospital for head and neck MRI due to different clinical conditions. The hearing threshold of patients was measured before, immediately after, and 24 hours after performing 1.5 Tesla MRI using conventional and extended high frequency audiometry. SPSS version 18 was used to compare the mean hearing thresholds before and after MRI using paired T test and repeated measures analysis.

Results

Comparison of auditory thresholds in conventional and extended high frequencies before and immediately after MRI showed a significant shift at 4 KHz (P = 0.008 and P = 0.08 for right and left ears), 6 KHz (P = 0.03 and P = 0.01 for right and left ears), and 14 KHz (P =0.03 and P = 0.31 for right and left ears). However, there was no significant difference between audiometric thresholds before and 24 hours after MRI.

Conclusion

Noise due to 1.5 Tesla MRI can only cause transient threshold shift.

Dissociation between Cerebellar and Cerebral Neural Activities in Humans with Long-Term Bilateral Sensorineural Hearing Loss

Abnormal neural activity in the cerebellum has been implicated in hearing impairments, but the effects of long-term hearing loss on cerebellar function are poorly understood. To further explore the role of long-term bilateral sensorineural hearing loss on cerebellar function, we investigated hearing loss-induced changes among neural networks within cerebellar subregions and the changes in cerebellar-cerebral connectivity patterns using resting-state functional MRI. Twenty-one subjects with long-term bilateral moderate-to-severe sensorineural hearing loss and 21 matched controls with clinically normal hearing underwent MRI scanning and a series of neuropsychological tests targeting cognition and emotion. Voxel-wise functional connectivity (FC) analysis demonstrated decreased couplings between the cerebellum and other cerebral areas, including the temporal pole (TP), insula, supramarginal gyrus, inferior frontal gyrus (IFG), medial frontal gyrus, and thalamus, in long-term bilateral sensorineural hearing loss patients. An ROI-wise FC analysis found weakened interregional connections within cerebellar subdivisions. Moreover, there was a negative correlation between anxiety and FC between the left cerebellar lobe VI and left insula. Hearing ability and anxiety scores were also correlated with FC between the left cerebellar lobe VI and left TP, as well as the right cerebellar lobule VI and left IFG. Our results suggest that sensorineural hearing loss disrupts cerebellar-cerebral circuits, some potentially linked to anxiety, and interregional cerebellar connectivity. The findings contribute to a growing body showing that auditory deprivation caused by cochlear hearing loss disrupts not only activity with the classical auditory pathway but also portions of the cerebellum that communicates with other cortical networks.

Software-based noise reduction in cranial magnetic resonance imaging: Influence on image quality

Objectives

To investigate acoustic noise reduction, image quality and white matter lesion detection rates of cranial magnetic resonance imaging (MRI) scans acquired with and without sequence-based acoustic noise reduction software.

Material and methods

Thirty-one patients, including 18 men and 13 women, with a mean age of 58.3±14.5 years underwent cranial MRI. A fluid-attenuated inversion recovery (FLAIR) sequence was acquired with and without acoustic noise reduction using the Quiet Suite (QS) software (Siemens Healthcare). During data acquisition, peak sound pressure levels were measured with a sound level meter (Testo, Typ 815). In addition, two observers assessed subjective image quality for both sequences using a five-point scale (1 very good—5 inadequate). Signal-to-noise ratio (SNR) was measured for both sequences in the following regions: white matter, gray matter, and cerebrospinal fluid. Furthermore, lesion detection rates in white matter pathologies were evaluated by two observers for both sequences. Acoustic noise, image quality including SNR and white matter lesion detection rates were compared using the Mann-Whitney-U-test.

Results

Peak sound pressure levels were slightly but significantly reduced using QS, P≤0.017. Effective sound pressure, measured in Pascal, was decreased by 19.7%. There was no significant difference in subjective image quality between FLAIR sequences acquired without/with QS: observer 1: 2.03/2.07, P = 0.730; observer 2: 1.98/2.10, P = 0.362. In addition, SNR was significantly increased in white matter, P≤0.001, and gray matter, P = 0.006, using QS. The lesion detection rates did not decline utilizing QS: observer 1: P = 0.944 observer 2: P = 0.952.

Conclusions

Sequence-based noise reduction software such as QS can significantly reduce peak sound pressure levels, without a loss of subjective image quality and increase SNR at constant lesion detection rates.