磁共振微波吸收成像：信号检测的可行性。
Magnetic resonance microwave absorption imaging: feasibility of signal detection.
机构信息
Thayer School of Engineering, Dartmouth College, Hanover New Hampshire 03755, USA.
出版信息
Med Phys. 2009 Nov;36(11):5190-7. doi: 10.1118/1.3215533.
PURPOSE
Magnetic resonance (MR) technique was used to detect small displacements induced by localized absorption of pulsed 434 MHz microwave power as a potential method for tumor detection.
METHODS
Phase contrast subtraction was used to separate the phase change due to motion from thermoelastic expansion from other contributions to phase variation such as the bulk temperature rise of the medium and phase offsets from the MR scanner itself. A simple set of experiments was performed where the motion was constrained to be one dimensional which provided controls on the data acquisition and motion extraction procedures. Specifically, the MR-detected motion signal was isolated by altering the direction of the microwave-induced motion and sampling the response with motion encoding gradients in all three directions when the microwave power was turned on and turned off.
RESULTS
Successful signal detection, as evidenced by the recording of a systematic alternating (zigzag) phase pattern, occurred only when the motion encoding was in parallel with either the vertical or horizontal direction of the microwave-induced motion on both 10 and 4 mm spatial scales.
CONCLUSIONS
These results demonstrate, for the first time, that motion associated with thermoelastic expansion from the absorption of pulsed microwave power can be detected with MR.
目的
磁共振（MR）技术被用于探测局部吸收脉冲 434MHz 微波功率所引起的小位移，这可能是一种肿瘤探测的方法。
方法
采用相位对比减影技术将运动引起的相位变化与热弹性膨胀引起的相位变化区分开来，其他导致相位变化的因素有介质的体升温以及来自 MR 扫描仪本身的相位偏移等。我们进行了一套简单的实验，运动被限制在一维，这为数据采集和运动提取过程提供了控制。具体来说，通过改变微波诱导运动的方向，并在微波功率开启和关闭时在所有三个方向上施加运动编码梯度来采样响应，从而分离出由 MR 检测到的运动信号。
结果
只有当运动编码与微波诱导运动的垂直或水平方向之一平行时，才会成功检测到信号，这在 10 和 4mm 空间尺度上都得到了证实。
结论
这些结果首次证明，通过 MR 可以探测到与吸收脉冲微波功率相关的热弹性膨胀引起的运动。
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