Acoustic noise in magnetic resonance imaging: An ongoing issue

Safety of Magnetic Resonance Imaging in Pregnancy

Magnetic resonance imaging is being increasingly used to diagnose and follow up a variety of medical conditions in pregnancy, both for maternal and fetal indications. However, limited data regarding its safe use in pregnancy may be a source of anxiety and avoidance for both patients and their healthcare providers. In this review, we critically discuss the main safety concerns of Magnetic Resonance Imaging (MRI) in pregnancy including energy deposition, acoustic noise, and use of contrast agents, supported by data from animal and human studies. Use of maternal sedatives and concerns related to occupational exposure in pregnant personnel are also addressed. Exposure to gadolinium-based contrast agents and sedation for MRI during pregnancy should be avoided whenever feasible.

Image quality and subject experience of quiet T1-weighted 7-T brain imaging using a silent gradient coil

Objectives

Acoustic noise in magnetic resonance imaging (MRI) negatively impacts patients. We assessed a silent gradient coil switched at 20 kHz combined with a T₁-weighted magnetisation prepared rapid gradient-echo (MPRAGE) sequence at 7 T.

Methods

Five healthy subjects (21–29 years; three females) without previous 7-T MRI experience underwent both a quiet MPRAGE (Q-MPRAGE) and conventional MPRAGE (C-MPRAGE) sequence twice. Image quality was assessed quantitatively, and qualitatively by two neuroradiologists. Sound level was measured objectively and rated subjectively on a 0 to 10 scale by all subjects immediately following each sequence and after the whole examination (delayed). All subjects also reported comfort level, overall experience and willingness to undergo the sequence again.

Results

Compared to C-MPRAGE, Q-MPRAGE showed higher signal-to-noise ratio (10%; p = 0.012) and lower contrast-to-noise ratio (20%; p < 0.001) as well as acceptable to good image quality. Q-MPRAGE produced 27 dB lower sound level (76 versus 103 dB). Subjects reported lower sound level for Q-MPRAGE both immediate (4.4 ± 1.4 versus 6.4 ± 1.3; p = 0.007) and delayed (4.6 ± 1.4 versus 6.3 ± 1.3; p = 0.005), while they rated comfort level (7.4 ± 1.0 versus 6.1 ± 1.7; p = 0.016) and overall experience (7.6 ± 1.0 versus 6.0 ± 0.9; p = 0.005) higher. Willingness to undergo the sequence again was also higher, however not significantly (8.1 ± 1.0 versus 7.2 ± 1.3; p = 0.066).

Conclusion

Q-MPRAGE using a silent gradient coil reduced sound level by 27 dB compared to C-MPRAGE at 7 T while featuring acceptable-to-good image quality and a quieter and more pleasant subject experience.

Accelerating Brain Imaging Using a Silent Spatial Encoding Axis

Purpose

To characterize the acceleration capabilities of a silent head insert gradient axis that operates at the inaudible frequency of 20 kHz and a maximum gradient amplitude of 40 mT/m without inducing peripheral nerve stimulation.

Methods

The silent gradient axis' acquisitions feature an oscillating gradient in the phase‐encoding direction that is played out on top of a cartesian readout, similarly as done in Wave‐CAIPI. The additional spatial encoding fills k‐space in readout lanes allowing for the acquisition of fewer phase‐encoding steps without increasing aliasing artifacts. Fully sampled 2D gradient echo datasets were acquired both with and without the silent readout. All scans were retrospectively undersampled (acceleration factors R = 1 to 12) to compare conventional SENSE acceleration and acceleration using the silent gradient. The silent gradient amplitude and the readout bandwidth were varied to investigate the effect on artifacts and g‐factor.

Results

The silent readout reduced the g‐factor for all acceleration factors when compared to SENSE acceleration. Increasing the silent gradient amplitude from 31.5 mT/m to 40 mT/m at an acceleration factor of 10 yielded a reduction in the average g‐factor (g_avg) from 1.3 ± 0.14 (g_max = 1.9) to 1.1 ± 0.09 (g_max = 1.6)_. Furthermore, reducing the number of cycles increased the readout bandwidth and the g‐factor that reached g_avg = 1.5 ± 0.16 for a readout bandwidth of 651 Hz/pixel and an acceleration factor of R = 8.

Conclusion

A silent gradient axis enables high acceleration factors up to R = 10 while maintaining a g‐factor close to unity (g_avg = 1.1 and g_max = 1.6) and can be acquired with clinically relevant readout bandwidths.

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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 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.

Validation of Zero TE-MRA in the Characterization of Cerebrovascular Diseases: A Feasibility Study

BACKGROUND AND PURPOSE

Zero TE-MRA is less sensitive to field heterogeneity, complex flow, and acquisition noise. This study aimed to prospectively validate the feasibility of zero TE-MRA for cerebrovascular diseases assessment, compared with TOF-MRA.

MATERIALS AND METHODS

Seventy patients suspected of having cerebrovascular disorders were recruited. Sound levels were estimated for each MRA subjectively and objectively in different modes. MRA image quality was estimated by 2 neuroradiologists. The degree of stenosis (grades 0-4) and the z-diameter of aneurysms (tiny group ≤3 mm and large group >3 mm) were measured for further quantitative analysis. CTA was used as the criterion standard.

RESULTS

Zero TE-MRA achieved significantly lower subjective perception and objective noise reduction (37.53%). Zero TE-MRA images showed higher signal homogeneity (3.29 ± 0.59 versus 3.04 ± 0.43) and quality of venous signal suppression (3.67 ± 0.47 versus 2.75 ± 0.46). The intermodality agreement was higher for zero TE-MRA than for TOF-MRA (zero TE, 0.90; TOF, 0.81) in the grading of stenosis. Zero TE-MRA had a higher correlation than TOF-MRA (zero TE, 0.84; TOF, 0.74) in the tiny group and a higher consistency with CTA (intraclass correlation coefficient, 0.83; intercept, -0.5084-1.1794; slope -0.4952 to -0.2093) than TOF-MRA (intraclass correlation coefficient, 0.64; intercept, 0.7000-2.6133; slope -1.0344 to -0.1923). Zero TE-MRA and TOF-MRA were comparable in the large group. Zero TE-MRA had more accurate details than TOF-MRA of AVM and Moyamoya lesions.

CONCLUSIONS

Compared with TOF-MRA, zero TE-MRA achieved more robust performance in depicting cerebrovascular diseases. Therefore, zero TE-MRA was shown to be a promising MRA technique for further routine application in the clinic in patients with cerebrovascular diseases.

MRI acoustic noise-modulated computer animations for patient distraction and entertainment with application in pediatric psychiatric patients

PURPOSE

To reduce patient anxiety caused by the MRI scanner acoustic noise.

MATERIAL AND METHODS

We developed a simple and low-cost system for patient distraction using visual computer animations that were synchronized to the MRI scanner's acoustic noise during the MRI exam. The system was implemented on a 3T MRI system and tested in 28 pediatric patients with bipolar disorder. The patients were randomized to receive noise-synchronized animations in the form of abstract animations in addition to music (n = 13, F/M = 6/7, age = 10.9 ± 2.5 years) or, as a control, receive only music (n = 15, F/M = 7/8, age = 11.6 ± 2.3 years). After completion of the scans, all subjects answered a questionnaire about their scan experience and the perceived scan duration.

RESULTS

The scan duration with multisensory input (animations and music) was perceived to be ~15% shorter than in the control group (43 min vs. 50 min, P < 0.05). However, the overall scan experience was scored less favorably (3.9 vs. 4.6 in the control group, P < 0.04).

CONCLUSIONS

This simple system provided patient distraction and entertainment leading to perceived shorter scan times, but the provided visualization with abstract animations was not favored by this patient cohort.

Comparison of image quality characteristics on Silent MR versus conventional MR imaging of brain lesions at 3 Tesla

OBJECTIVE:

To compare signal- and contrast-to-noise-ratio (SNR, CNR), conspicuity values and subjective image quality characteristics of Silent MRI and conventional MRI in brain disorders at 3 T.

METHODS:

26 patients were prospectively examined with a 3 T MRI. Silent Scan was added to standardized MR protocol. Silenz T₁ weighted (Tlw) and Silent T₂ weighted (T2w) sequences were compared to standard Tlw and T2w. Analysis was performed quantitatively (SNR, CNR, conspicuity values) and by visual assessment on a 4-point scale with regard to lesion visibility, lesion delineation, grey-white differentiation and diagnostic usefulness. Data were analyzed using Wilcoxon signed-rank and Sign test. p ≤ 0.05 was considered significant.

RESULTS:

Silenz Tlw vs Tlw provided decreased SNR, but increased CNR (SNRparenchyma, SNRlesion: p = 0.000, CNRlesion: p = 0.003). Silent T2w vs T2w showed better SNR and CNR values (SNR_parenchyma, p = 0.014; SNR_lesion, p = 0.005; CNR_lesion, p = 0.005). Conspicuity values were not significantly different on Silenz Tlw vs Tlw and Silent T2w vs T2w. The visual assessment revealed Silenz Tlw to be significantly superior to Tlw in terms of grey- white differentiation (p = 0.000), lesion visibility (p = 0.003) and overall diagnostic usefulness (p = 0.001). In terms of Silent T2w vs T2w, there was a significant difference in grey-white differentiation in favour of Silent T2w (p = 0.016).

CONCLUSION:

Silent Scan is suitable for 3 T with image quality characteristics comparable to conventional MRI.

ADVANCES IN KNOWLEDGE:

Silent Scan has a diagnostic value comparable to conventional MRI, with the advantage of a quiet MR exam improving patient MR experience.

Interventions to reduce anxiety, distress and the need for sedation in adult patients undergoing magnetic resonance imaging: a systematic review

PURPOSE

Adults undergoing MRI scans can experience anxiety, claustrophobia and fear during the scanning experience and, in some cases, require sedation. The aim of this systematic review was to determine what strategies are effective in reducing fear, anxiety and claustrophobia, and the need for sedation in adults undergoing MRI.

METHODS

A quantitative systematic review, according to the methodology of the Joanna Briggs Institute, was carried out. A systematic search of a number of databases was performed. Studies were then screened and critically appraised by two independent reviewers before being included in the review.

RESULTS

In total, 21 studies met the inclusion criteria for the review, which assessed the following interventions: MRI design features, cognitive-behavioural strategies, prone positioning, information, fragrance administration and team training. All of these had some positive impact on outcomes.

CONCLUSION

Healthcare professionals working with adults undergoing MRI may consider some of the strategies included in this review to implement in their practice to reduce anxiety and increase patient comfort while reducing the need for sedation.

A finite difference method for the design of gradient coils in MRI--an initial framework

This paper proposes a finite-difference (FD)-based method for the design of gradient coils in MRI. The design method first uses the FD approximation to describe the continuous current density of the coil space and then employs the stream function method to extract the coil patterns. During the numerical implementation, a linear equation is constructed and solved using a regularization scheme. The algorithm details have been exemplified through biplanar and cylindrical gradient coil design examples. The design method can be applied to unusual coil designs such as ultrashort or dedicated gradient coils. The proposed gradient coil design scheme can be integrated into a FD-based electromagnetic framework, which can then provide a unified computational framework for gradient and RF design and patient-field interactions.

The effectiveness of interventions to reduce anxiety, claustrophobia, sedation and non-completion rates of patients undergoing high technology medical imaging

BACKGROUND

Advanced, high technology medical imaging, such as Computed Tomography (CT), Magnetic Resonance Imaging (MRI), Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT), have seen significant increases in their use. A number of interventions have been developed with the aim of reducing anxiety, fear and claustrophobia prior to and during imaging.

OBJECTIVE

To determine the effectiveness of interventions aiming to improve the patient experience of high technology medical imaging.

INCLUSION CRITERIA

Any patients who have undergone high technology (MRI, CT, PET, Nuclear medicine and SPECT) imaging in a medical imaging department. Interventional scans were not considered for inclusion.Considered interventions were: MRI scanner designs, quieter machines, information, psychological support, anxiety reduction protocols, mock MRI, team training, prone scanning, audiovisual (AV) systems, cognitive behavioural therapies, fragrance administration, guided imagery, patient positioning devices and paediatric preparation booklets.Experimental and observational studies were included in the review.Primary patient outcomes:Secondary patient outcome measures included: SEARCH STRATEGY: A comprehensive, three-step search strategy conducted during August to October 2011 aimed to find both published and unpublished English language studies across 14 major databases. No time restrictions.

METHODOLOGICAL QUALITY

Retrieved papers were assessed by two independent reviewers prior to inclusion in the review using standardised critical appraisal instruments from the Joanna Briggs Institute Meta Analysis of Statistics Assessment and Review Instrument (JBI-MAStARI).

DATA COLLECTION

Data was extracted from papers included in the review using the standardised data extraction tool from JBI-MAStARI.

DATA SYNTHESIS

Quantitative data was, where possible pooled in statistical meta-analysis using JBI-MAStARI. All results were subject to double data entry.

RESULTS

Thirty-eight studies met the inclusion criteria and were considered to be of suitable methodological quality. The quality of the studies varied; however, all the studies included had at a minimum a comparison group. Of the final 38 studies, 29 assessed interventions for MRI, 8 Nuclear Medicine procedures, and one in CT. Meta-analysis was performed for two interventions; additional information and an AV system.Significantly fewer children (10-18 years) required sedation prior to a MRI scan when given an audiovisual intervention (n=1785) OR 0.42% (CI 0.25 - 0.70), compared with the control group. Open MRI, newer MRI scanners, quieter machines, information in combination with psychological support or an anxiety reduction protocol, mock MRI, team training, prone scanning, AV systems, cognitive behavioural therapies, fragrance administration, guided imagery, patient positioning devices and paediatric preparation booklets were all found to have some positive effect on at least one outcome, whilst the findings for additional information were mixed.

CONCLUSIONS

This review identified 38 studies that assessed interventions to reduce anxiety, claustrophobia, sedation and non-completions and improve satisfaction for patients undergoing medical imaging. The majority of the interventions studied had some positive effect on at least one outcome.Healthcare professionals need to be aware of the potential for patients undergoing medical imaging to experience anxiety, fear and claustrophobia during scanning. A number of interventions can be selected and tailored to the patient group.There is still a significant amount of research required to establish the effectiveness for a number of interventions aimed to reduce anxiety, fear and claustrophobia in medical imaging, particularly in CT.