Evaluation of Software-Optimized Protocols for Acoustic Noise Reduction During Brain MRI at 7 Tesla

Abstract

Background: MR-generated acoustic noise may be particularly concerning at 7-Tesla (T) systems. Noise levels can be reduced by altering gradient output using software optimization. However, such alterations might influence image quality or prolong scan times, and these optimizations have not been well characterized.

Purpose: To evaluate image quality, sound pressure levels (SPLs), and perceived noise levels when using the acoustic noise reduction technique SofTone for T₂-weighted fast spin echo (T₂W FSE) and three-dimensional T₁-weighted turbo field echo (3D T₁W TFE), and to compare with conventional imaging during 7-T brain MRI.

Study type: Prospective.

Subjects: Twenty-eight volunteers underwent brain MRI, with n = 26 for image quality evaluations.

Field strength/sequence: Conventional and SofTone versions of T₂W FSE and 3D T₁W TFE at 7 T.

Assessment: Peak SPLs (A-weighted decibels, dBA), participant-perceived noise levels (Borg CR10-scale), qualitative image assessments by three neuroradiologists (four-graded ordinal scales), interrater reliability, and percentage agreement.

Statistical test: Paired t-test, Wilcoxon's Signed-Rank Test, and Krippendorff's alpha; p < 0.05 were considered statistically significant.

Results: SofTone significantly reduced peak SPLs: from 116.3 to 97.0 dBA on T₂W FSE, and from 123.7 to 101.5 dBA on 3D T₁W TFE. SofTone was perceived as significantly quieter than conventional scanning. T₂W FSE showed no significant differences in image quality assessments (p = 0.21-1.00), except one radiologist noting significantly less artifact interference with SofTone. General image quality remained acceptable for 3D T₁W TFE, though one radiologist scored it significantly lower with SofTone (mean scores: 3.08 vs. 3.65), and two radiologists observed significantly worse white and gray matter differentiation with SofTone (mean scores: 3.19 vs. 3.54; 2.27 vs. 2.81).

Data conclusion: SofTone can significantly reduce sound intensity and perceived noise levels while maintaining acceptable image quality with T₂W FSE and 3D T₁W TFE in brain MRI. It appears to be an effective tool for providing a safer, quieter 7-T scan environment.

Evidence level: 4 Technical Efficacy: Stage 5.

Keywords: MR safety; hearing protection; software optimization; ultra‐high field MRI.

FIGURE 1

Box plot showing the distribution of peak sound pressure levels in A‐weighted decibels (dBA) for T₂‐weighted fast spin echo (T₂W FSE) and three‐dimensional T₁‐weighted turbo field echo (3D T₁W TFE), with and without SofTone (n = 28). The black centerlines show the median; the boxes show the data ranges between the first and third quartiles; dark gray boxes represent SofTone scanning; light gray boxes represent conventional scanning; * = extreme outlier; ° = mild outlier. While the cause of these outliers remains unclear, potential pressure doubling [17] cannot be ruled out, that is, reflected sound waves undergoing in‐phase enhancements in the vicinity of the scanned participant.

FIGURE 2

Example images produced using T₂‐weighted fast spin echo (T₂W FSE) and three‐dimensional T₁‐weighted turbo field echo (3D T₁W TFE) from a healthy volunteer. (a) T₂W FSE Conventional, 116.1 dBA (peak sound pressure level in A‐weighted decibels); (b) T₂W FSE SofTone, 97.4 dBA; (c) 3D T₁W TFE Conventional, 123.5 dBA; (d) 3D T₁W TFE SofTone, 101.2 dBA. The three radiologists rated the general image quality of all of these images as either “3, good” or “4, excellent”. Images reproduced with permission from Glans [32].

FIGURE 3

Example images from a healthy volunteer, illustrating image quality differences between conventional and SofTone scanning with three‐dimensional T₁‐weighted turbo field echo (3D T₁W TFE). (a) Conventional, 122.2 dBA (peak sound pressure level in A‐weighted decibels); (b) SofTone, 100.7 dBA. Red arrows illustrate slightly more image blurring, contours, and signal loss using SofTone compared to the conventional imaging, along with less detailed white and gray matter discrimination. For SofTone, the white and gray matter discrimination and the general image quality were rated as either “3, good” or “2, fair”, whereas the ratings for the conventional sequence were either “4, excellent” or “3, good”.