A magnetic resonance (MR) microscopy system using a microfluidically cryo-cooled planar coil.
A magnetic resonance (MR) microscopy system using a microfluidically cryo-cooled planar coil.
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DOI：
10.1039/c1lc20056a
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发表时间：
2011-07-07
期刊：
影响因子：
6.1
通讯作者：
Han A
中科院分区：
文献类型：
--
作者：
Koo C;Godley RF;Park J;McDougall MP;Wright SM;Han A
我们提出了一种用于磁共振（MR）显微镜的微流体低温冷却平面线圈的发展。低温冷却磁共振成像（MRI）射频（RF）线圈可以提高实验的信噪比（SNR）。常规的低温恒温器通常使用真空间隙来在低温冷却期间将待成像的样本（尤其是生物样本）保持在室温或接近室温。这限制了低温冷却线圈可以放置到样品的近距离。同时，由于平面MR微线圈的成像深度有限，线圈到样本的小距离显著提高了MR成像能力。这两个相互冲突的要求对在MR微弹簧圈中使用低温冷却提出了挑战。使用基于微流体的低温恒温器对MR微线圈进行局部低温冷却是朝着消除这些限制迈出的一步。这里提出的系统由平面仅接收线圈组成，其下方具有集成的低温冷却微流体通道，以及由薄氮气间隙隔开的平面线圈顶部的成像表面。通过软光刻工艺制造的聚合物微流体通道结构用于使液氮在线圈下方流动，以便将平面线圈低温冷却至液氮温度（-196 °C）。低温冷却系统的两个独特特征最小化了线圈和样品之间的距离：1）聚合物微流体通道的小尺寸使得能够局部冷却平面线圈，同时最小化对附近成像表面的热效应。2)成像表面与低温冷却的平面线圈通过薄间隙分开，氮气流过该薄间隙以使成像表面热绝缘，从而使其保持在0°C以上并防止对生物样品的潜在损害。通过仿真、台架测试和MR成像实验验证了局部冷却效果。在4.7 T MR系统内使用这种低温冷却平面线圈系统，相对于类似的室温线圈，平均图像SNR增强1.47 ± 0.11倍。
We present the development of a microfluidically cryo-cooled planar coil for magnetic resonance (MR) microscopy. Cryogenically cooling radiofrequency (RF) coils for magnetic resonance imaging (MRI) can improve the signal to noise ratio (SNR) of the experiment. Conventional cryostats typically use a vacuum gap to keep samples to be imaged, especially biological samples, at or near room temperature during cryo-cooling. This limits how close a cryo-cooled coil can be placed to the sample. At the same time, a small coil-to-sample distance significantly improves the MR imaging capability due to the limited imaging depth of planar MR microcoils. These two conflicting requirements pose challenges to the use of cryo-cooling in MR microcoils. The use of a microfluidic based cryostat for localized cryo-cooling of MR microcoils is a step towards eliminating these constraints. The system presented here consists of planar receive-only coils with integrated cryo-cooling microfluidic channels underneath, and an imaging surface on top of the planar coils separated by a thin nitrogen gas gap. Polymer microfluidic channel structures fabricated through soft lithography processes were used to flow liquid nitrogen under the coils in order to cryo-cool the planar coils to liquid nitrogen temperature (−196°C). Two unique features of the cryo-cooling system minimize the distance between the coil and the sample: 1) The small dimension of the polymer microfluidic channel enables localized cooling of the planar coils, while minimizing thermal effects on the nearby imaging surface. 2) The imaging surface is separated from the cryo-cooled planar coil by a thin gap through which nitrogen gas flows to thermally insulate the imaging surface, keeping it above 0°C and preventing potential damage to biological samples. The localized cooling effect was validated by simulations, bench testing, and MR imaging experiments. Using this cryo-cooled planar coil system inside a 4.7 Tesla MR system resulted in an average image SNR enhancement of 1.47 ± 0.11 times relative to similar room-temperature coils.
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