The purpose of this study was to measure gantry angle-related eddy currents in a 0.35-T MRI-Linac and determine if B₀ (zeroth order) eddy currents are the primary cause of gantry angle-dependent imaging isocenter shifts vs other potential causes like B₀ inhomogeneities and gradient (first order) eddy currents. For conventional Cartesian acquisitions, B₀ eddy currents can cause imaging isocenter shifts along both phase encode and readout directions. Gradient eddy currents can cause spatial distortion along both the phase encode and readout directions. Center frequency offsets can cause imaging isocenter shifts along the readout direction that vary with readout gradient polarity.

中文翻译：

---

B0涡流对0.35-T MRI引导放疗（MR-IGRT）系统成像等中心位移的影响

本研究的目的是在 0.35-T MRI-Linac 中测量与机架角度相关的涡流，并确定 B ₀（零阶）涡流是否是机架角度相关成像等中心偏移的主要原因与其他潜在原因，如B ₀不均匀性和梯度（一阶）涡流。对于传统的笛卡尔采集，B ₀涡流会导致沿相位编码和读出方向的成像等中心偏移。梯度涡流会导致沿相位编码和读出方向的空间失真。中心频率偏移会导致沿读出方向的成像等中心偏移，该偏移随读出梯度极性而变化。