Moelker Adriaan, Wielopolski Piotr A, Pattynama Peter M T
Department of Radiology, Erasmus Medical Center Rotterdam, 50 Dr Molewaterplein, 3000 DR Rotterdam, The Netherlands.
MAGMA. 2003 Feb;16(1):52-5. doi: 10.1007/s10334-003-0005-9.
The need for better signal-to-noise ratios and resolution has pushed magnetic resonance imaging (MRI) towards high-field MR-scanners for which only little data on MR-related acoustic noise production have been published. The purpose of this study was to validate the theoretical relationship of sound pressure level (SPL) and static magnetic field strength. This is relevant for allowing adequate comparisons of acoustic data of MR systems at various magnetic field strengths. Acoustic data were acquired during various pulse sequences at field strengths of 0.5, 1.0, 1.5 and 2.0 Tesla using the same MRI unit by means of a Helicon rampable magnet. Continuous-equivalent, i.e. time-averaged, linear SPLs and 1/3-octave band frequencies were recorded. Ramping from 0.5 to 1.0 Tesla and from 1.0 to 2.0 Tesla resulted in an SPL increase of 5.7 and 5.2 dB(L), respectively, when averaged over the various pulse sequences. Most of the acoustic energy was in the 1-kHz frequency band, irrespective of magnetic field strength. The relation between field strength and SPL was slightly non-linear, i.e. a slightly less increase at higher field strengths, presumably caused by the elastic properties of the gradient coil encasings.
对更好的信噪比和分辨率的需求推动磁共振成像（MRI）朝着高场强MR扫描仪发展，而关于与MR相关的噪声产生的此类数据仅有少量发表。本研究的目的是验证声压级（SPL）与静磁场强度之间的理论关系。这对于在不同磁场强度下对MR系统的声学数据进行充分比较具有重要意义。利用一个可斜坡式磁铁，通过同一MRI设备，在0.5、1.0、1.5和2.0特斯拉的场强下，于各种脉冲序列期间采集声学数据。记录连续等效即时间平均的线性声压级和1/3倍频程带频率。在各种脉冲序列上进行平均时，从0.5特斯拉升至1.0特斯拉以及从1.0特斯拉升至2.0特斯拉分别导致声压级增加5.7和5.2分贝（L）。不论磁场强度如何，大部分声能都集中在1千赫兹频段。场强与声压级之间的关系略呈非线性，即在较高场强下增加幅度略小，这大概是由梯度线圈外壳的弹性特性所致。
