Keywords:
Education and training, Imaging sequences, MR, MR physics
Authors:
M. Wyss1, I. Dobrev1, J. H. Sim1, T. D. J. Sartoretti2, A. Najafi2, M. Koepfli3, A. M. Huber1, C. A. Binkert2; 1Zürich/CH, 2Winterthur/CH, 3Lucerne/CH
DOI:
10.1594/ecr2018/C-2186
Results
Acoustic noise control resulted in an average reduction of 12.5 dB (A) which equals a reduction of the average acoustic noise level of 74% (range: 56% - 90%) for the A-weighted scale (Figure 5).
As averaged over the complete brain protocols,
an A-weighted RMS SPL of 90.5 dB (range: 61.4 dB – 100.5 dB) without acoustic noise reduction and an A-weighted RMS SPL of 78 dB (range: 69.5 dB – 85.7 dB) with acoustic noise reduction were measured.
Peak acoustic noise levels without noise reduction were found at frequencies between 380 and 1100 Hz (mean of all sequences: 650Hz).
A shift of peak acoustic levels with noise reduction towards lower frequencies (200 - 500 Hz,
mean of all sequences: 340 Hz) was observed.
While low frequencies up to 100 Hz were not or just slightly reduced with acoustic noise control,
frequencies above 1 kHz were noticeably attenuated.
Application of noise reduction technique increased total acquisition time for the complete brain protocol by two minutes (+ 12%) (Figure 6a).
The TR was lengthened for the coil survey scan (2.1ms to 5.6ms),
reference scan (3.9ms to 6.4ms),
DWI (2944ms to 3794ms),
survey scan (15ms to 17ms),
TOF (23ms to 25ms) and T1w SE (581ms to 607ms).
No changes were observed for the T2w TSE and the FLAIR sequence (Figure 6b).
The TE was increased for the reference scan (0.57ms to 1.65ms),
survey scan (5.2ms to 9.2ms),
DWI (89ms to 106ms) and the coil survey scan (1.27ms to 1.36ms).
No changes occurred for the T1w SE,
T2w TSE,
FLAIR and TOF sequence (Figure 6c).
Higher receiver bandwidth were observed for the T1w SE (109 to 148 Hz/pixel),
T2w TSE (140 to 204 Hz/pixel),
lower receiver bandwidth were observed on the reference scan (3100 to 1320 Hz/pixel) and the DWI (23 to 12 Hz/pixel).
No changes in the receiver bandwidth were perceived for the coil survey scan,
survey scan,
FLAIR and TOF.
(Figure 6d).
Relative signal level increased for the reference scan (154%),
FLAIR (110%),
DWI (109%) and survey (104%).
Signal level decreased for the T2w TSE (-17%) and the T1w SE (-11%) (Figure 6e).
Visual inspection of image quality with and without acoustic noise reduction revealed no obvious differences,
apart from the DWI sequence.
The DWI images with acoustic noise control appear slightly more distorted due to changes in TE and receiver bandwidth (Figure 7).