Low-gradient single-sided NMR sensor for one-shot profiling of human skin
Low-gradient single-sided NMR sensor for one-shot profiling of human skin
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DOI：
10.1016/j.jmr.2011.12.010
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发表时间：
2012-02-01
影响因子：
2.2
通讯作者：
Casanova, Federico
中科院分区：
文献类型：
--
作者：
Van Landeghem, Maxime;Danieli, Ernesto;Casanova, Federico
本文介绍了一种匀场方法，用于减少由单面传感器产生的磁场的梯度强度，同时最大化其均匀性沿着横向的磁铁。以这种方式，可以在不损害传感器的深度分辨率的情况下增加被激励的敏感体积的厚度。通过在标准U形磁体上实施该方法，梯度强度降低了一个数量级。在存在约2 T/m的梯度的情况下，2 mm的切片可以以从切片中心处的25 μ m到边界处的50 μ m的范围内的分辨率来描绘轮廓。该传感器对于扫描范围为受激切片量级的应用特别有利。在这些情况下，在单次激发实验中测量整个轮廓，消除了在深度范围内重新定位激发切片以完成轮廓的需要，如标准高梯度传感器所发生的那样。除了简化实验装置外，从逐点测量到同时采集完整轮廓的可能性缩短了实验时间。在较小的静态梯度下进行实验的另一个优点是减少了影响用CPMG序列测量的信号衰减的扩散衰减，使得可以测量具有高扩散率（与水扩散率相当）的样品的T-2。首先评估传感器在分辨率和灵敏度方面的性能，并与使用已知几何形状和弛豫时间的幻影的更高梯度强度的常规单面传感器进行比较。然后，该装置被用来描绘人体皮肤在体内的结构。为了理解不同皮肤层之间的对比度，弛豫时间T-2和扩散系数的分布沿沿着深度方向空间解析。(C)2011 Elsevier Inc. All rights reserved.
This paper describes a shimming approach useful to reduce the gradient strength of the magnetic field generated by single-sided sensors simultaneously maximizing its uniformity along the lateral directions of the magnet. In this way, the thickness of the excited sensitive volume can be increased without compromising the depth resolution of the sensor. By implementing this method on a standard U-shaped magnet, the gradient strength was reduced one order of magnitude. In the presence of a gradient of about 2 T/m, slices of 2 mm could be profiled with a resolution that ranges from 25 mu m at the center of the slice to 50 mu n at the borders. This sensor is of particular advantage for applications, where the scanning range is of the order of the excited slice. In those cases, the full profile is measured in a single excitation experiment, eliminating the need for repositioning the excited slice across the depth range to complete the profile as occurs with standard high gradient sensors. Besides simplifying the experimental setup, the possibility to move from a point-by-point measurement to the simultaneous acquisition of the full profile led to the shortening of the experimental time. A further advantage of performing the experiment under a smaller static gradient is a reduction of the diffusion attenuation affecting the signal decay measured with a CPMG sequence, making it possible to measure the T-2 of samples with high diffusivity (comparable to the water diffusivity). The performance of the sensor in terms of resolution and sensitivity is first evaluated and compared with conventional singled-sided sensors of higher gradient strength using phantoms of known geometry and relaxation times. Then, the device is used to profile the structure of human skin in vivo. To understand the contrast between the different skin layers, the distribution of relaxation times T-2 and diffusion coefficients is spatially resolved along the depth direction. (C) 2011 Elsevier Inc. All rights reserved.