利用表面线圈和对称排列的参考体模探索人体大腿定量钠磁共振成像的新方法。
Exploring a new method for quantitative sodium MRI in the human upper leg with a surface coil and symmetrically arranged reference phantoms.
作者信息
Milani Bastien, Delacoste Jean, Burnier Michel, Pruijm Menno
机构信息
Division of Nephrology and Hypertension, Lausanne University Hospital and University of Lausanne, Lausanne, Switzerland.
Departement de Radiologie, Centre Hospitalier Universitaire Vaudois (CHUV), Lausanne, Switzerland.
出版信息
Quant Imaging Med Surg. 2019 Jun;9(6):985-999. doi: 10.21037/qims.2019.06.08.
BACKGROUND
The aim of this study is to validate and evaluate the reproducibility of a new setup for the quantification of the tissue sodium concentration (TSC) in the human upper leg muscles with sodium MRI at 3 Tesla. This setup is making use of an emit and receive single loop surface coil together with a set of square, symmetrically arranged reference phantoms. As a second aim, the performances of two MRI protocols for the TSC quantification in the upper leg muscles are compared: one using an ultra-short echo time (UTE) 3-dimensional radial sequence (UTE-protocol), and the other one using standard gradient echo sequence (GRE-protocol).
METHODS
A validation test of the quantification of sodium concentration is performed in phantoms. The bias of the method is estimated and compared between both protocols. The reproducibility of TSC quantification is assessed in phantoms by the coefficient of variation (CV) and compared between both protocols. The reproducibility is also assessed in 11 health volunteers. Signal to noise ratio (SNR) maps are acquired in phantoms with both protocols in order to compare the resulting SNR.
RESULTS
The apparatus and post processing were successfully implemented. The bias of the method was smaller than 10% in phantoms (excepted for Na concentration of 10 mmol/L when using the GRE protocol). The reproducibility of the method using symmetrically arranged phantoms was high in phantoms and humans (CV <5%). The GRE-protocol leads to a better SNR than the UTE-protocol in 2D images.
CONCLUSIONS
The use of symmetrically arranged reference phantoms lead to reproducible results in phantoms and humans. Sodium imaging in the human upper leg with a single loop surface coil should be performed with a standard 2-dimensional GRE protocol if an optimal SNR is needed. However, the quantification of the fast and slow decay time constants of the sodium signal, which plays a role in the TSC quantification, still has to be done with a UTE sequence. Moreover, the quantification of sodium concentration is more accurate with the UTE protocol for small sodium concentrations (<20 mmol).
背景
本研究的目的是验证和评估一种用于在3特斯拉下通过钠磁共振成像（MRI）定量人体大腿肌肉组织钠浓度（TSC）的新装置的可重复性。该装置使用一个发射和接收单环表面线圈以及一组方形、对称排列的参考体模。作为第二个目的，比较了两种用于大腿肌肉TSC定量的MRI协议的性能：一种使用超短回波时间（UTE）三维径向序列（UTE协议），另一种使用标准梯度回波序列（GRE协议）。
方法
在体模中进行钠浓度定量的验证测试。估计两种协议之间该方法的偏差并进行比较。通过变异系数（CV）在体模中评估TSC定量的可重复性，并在两种协议之间进行比较。还在11名健康志愿者中评估了可重复性。使用两种协议在体模中采集信噪比（SNR）图，以比较所得的SNR。
结果
该装置和后处理成功实现。在体模中该方法的偏差小于百分之10（使用GRE协议时钠浓度为10 mmol/L的情况除外）。使用对称排列体模的方法在体模和人体中的可重复性都很高（CV<5%）。在二维图像中，GRE协议比UTE协议产生更好的SNR。
结论
使用对称排列的参考体模在体模和人体中都能得到可重复的结果。如果需要最佳SNR，应使用标准二维GRE协议对人体大腿进行单环表面线圈钠成像。然而，在TSC定量中起作用的钠信号快速和慢速衰减时间常数的定量仍需使用UTE序列。此外，对于低钠浓度（<20 mmol），使用UTE协议进行钠浓度定量更准确。
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