Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland.
Magn Reson Med. 2022 Oct;88(4):1937-1947. doi: 10.1002/mrm.29312. Epub 2022 Jun 1.
To analyze the difference between gradient fidelity and acoustic noise of the same MRI scanner operated at product field strength (3 T) and lower field strength (0.75 T).
Gradient modulation transfer functions (GMTFs) were measured using a four-slice 2D phase-encoded chirp-based sequence on the same scanner operated at 3 T and, following ramp-down, at 0.75 T with identical gradient specifications (40 mT/m, 200 T/m/s). Calibrated audio measurements were performed at both field strengths to correlate audio spectra with GMTFs.
While eddy currents were independent of field strength, mechanical resonances were substantially decreased at lower field, resulting in a reduction of GMTF distortions by up to 95% (88% on average) at the mechanical resonances of the gradient system. Audio spectra amplitudes were reduced by up to 87% when comparing 0.75 T versus 3 T.
Lower static fields lead to reduced Lorentz forces on the gradient coil and, in turn, to reduced mechanical resonances, thereby improving gradient fidelity. Simultaneously, the reduction of acoustic noise may help to improve patient comfort.
分析在相同的磁共振成像（MRI）扫描仪产品场强（3T）和较低场强（0.75T）下运行时梯度保真度和噪声的差异。
使用相同的扫描仪在 3T 和降场强至 0.75T 下运行，采用四片 2D 相位编码啁啾基序列测量梯度调制传递函数（GMTF），梯度规格相同（40 mT/m，200T/m/s）。在两个场强下进行校准音频测量，将音频谱与 GMTF 相关联。
尽管涡流与场强无关，但在较低场强下，机械共振明显降低，导致梯度系统的机械共振处的 GMTF 失真降低了高达 95%（平均 88%）。与 3T 相比，0.75T 时音频谱幅度降低了高达 87%。
较低的静态场强导致梯度线圈上的洛伦兹力减小，从而降低机械共振，从而提高梯度保真度。同时，降低噪声可能有助于提高患者舒适度。
