Xu Bo, Liu Tian, Spincemaille Pascal, Prince Martin, Wang Yi
Department of Radiology, Weill Cornell Medical College, New York, New York, USA; Department of Biomedical Engineering, Cornell University, Ithaca, New York, USA.
Magn Reson Med. 2014 Aug;72(2):438-45. doi: 10.1002/mrm.24937. Epub 2013 Sep 4.
Venous blood oxygen saturation is an indicator of brain oxygen consumption and can be measured directly from quantitative susceptibility mapping (QSM) by deconvolving the MR phase signal. However, accurate estimation of the susceptibility of blood may be affected by flow induced phase in the presence of imaging gradient and the inhomogeneous susceptibility field gradient. The purpose of this study is to correct the flow induced error in QSM for improved venous oxygenation quantification.
Flow compensation is proposed for QSM by using a fully flow compensated multi-echo gradient echo sequence for data acquisition. A quadratic fit of the phase with respect to echo time is employed for the flow phase in the presence of inhomogeneity field gradients. Phantom and in vivo experiments were carried out to validate the proposed method.
Phantom experiments demonstrated reduced error in the estimated field map and susceptibility map. Initial data in in vivo human imaging demonstrated improvements in the quantitative susceptibility map and in the estimated venous oxygen saturation values.
Flow compensated multi-echo acquisition and an adaptive-quadratic fit of the phase images improves the quantitative susceptibility map of blood flow. The improved vein susceptibility enables in vivo measurement of venous oxygen saturation throughout the brain.
静脉血氧饱和度是脑氧消耗的一个指标，可通过对磁共振相位信号进行反卷积，直接从定量磁化率成像（QSM）中测量得到。然而，在存在成像梯度和不均匀磁化率场梯度的情况下，血流诱导相位可能会影响血液磁化率的准确估计。本研究的目的是校正QSM中血流诱导的误差，以改进静脉氧合定量分析。
通过使用全血流补偿多回波梯度回波序列进行数据采集，提出了用于QSM的血流补偿方法。在存在不均匀场梯度的情况下，对相位相对于回波时间进行二次拟合以处理血流相位。进行了体模和活体实验以验证所提出的方法。
体模实验表明估计的场图和磁化率图中的误差减小。活体人体成像的初始数据表明定量磁化率图和估计的静脉血氧饱和度值有所改善。
血流补偿多回波采集和相位图像的自适应二次拟合改善了血流的定量磁化率图。改进的静脉磁化率使得能够在全脑范围内进行静脉血氧饱和度的活体测量。
