Acoustic noise reduction in MRI using Silent Scan: an initial experience

Abstract

Purpose: Acoustic noise during magnetic resonance imaging (MRI) is the main source for patient discomfort and leads to verbal communication problems, difficulties in sedation, and hearing impairment. Silent Scan technology uses less changes in gradient excitation levels, which is directly related to noise levels. Here, we report our preliminary experience with this technique in neuroimaging with regard to subjective and objective noise levels and image quality.

Materials and methods: Ten patients underwent routine brain MRI with 3 Tesla MR750w system and 12-channel head coil. T1-weighted gradient echo (BRAVO) and Silenz pulse sequence (TE=0, 3D radial center-out k-space filling and data sampling with relatively small gradient steps) were performed. Patients rated subjective sound impression for both sequences on a 6-point scale. Objective sound level measurements were performed with a dedicated device in gantry at different operation modes. Image quality was subjectively assessed in consensus by two radiologists on a 3-point scale.

Results: Readers rated image quality as fully diagnostic in all patients. Measured mean noise was reduced significantly with Silenz sequence (68.8 dB vs. 104.65 dB with BRAVO, P = 0.024) corresponding to 34.3% reduction in sound intensity and 99,97% reduction in sound pressure. No significant difference was observed between Silenz sound levels and ambient sounds (i.e., background noise in the scanner room, 68.8 dB vs. 68.73 dB, P = 0.5). The patients' subjective sound level score was lower for Silenz compared with conventional sequence (1.1 vs. 2.3, P = 0.003).

Conclusion: T1-weighted Silent Scan is a promising technique for acoustic noise reduction and improved patient comfort.

Figure 1.

Silenz acquisition and k-space readout scheme. Silenz uses a 3D radial center-out data acquisition scheme between radio frequency pulses (RF), stepping through k-space by increasing gradients in small steps. Ramp-up and ramp-down of gradients (Gx, Gy, Gz) between spokes are eliminated, resulting in the silent properties of the pulse sequence.

Figure 2.

The sound level meter is placed in the gantry at a position corresponding to the right ear of the patient.

Figure 3.

Silenz vs. BRAVO image. Contrast enhanced sample image from a 3D T1-weighted Silenz scan (left) and 3D BRAVO scan (right) are shown (screenshots from a transverse reconstruction of 3D source images).