An Hongyu, Lin Weili
Department of Biomedical Engineering, Washington University, St. Louis, Missouri.
Magn Reson Med. 2002 May;47(5):958-66. doi: 10.1002/mrm.10148.
The presence of magnetic background field inhomogeneity (DeltaB) may confound quantitative measures of cerebral venous blood volume (vCBV) and cerebral oxygen extraction fraction (MR_OEF) with T2*-based methods. The goal of this study was to correct its effect and obtain more accurate estimates of vCBV and MR_OEF. A 3D high-resolution gradient echo sequence was employed to obtain DeltaB maps by two algorithms. The DeltaB maps were then used to recover the signal loss in images acquired by a 2D multiecho gradient echo / spin echo sequence. Finally, both quantitative estimates of MR_OEF and vCBV were obtained from the DeltaB- corrected 2D multiecho gradient echo / spin echo images. A total of 12 normal subjects were studied. An overestimated vCBV was observed in the brain (4.29 +/- 0.78%) prior to DeltaB correction, while the measured vCBV was substantially reduced after DeltaB correction. Whole brain vCBV of 2.97 +/- 0.44% and 2.68 +/- 0.47% were obtained by the two different DeltaB correction methods, in excellent agreement with the reported results in the literature. Furthermore, when MR_OEF was compared with and without DeltaB correction, no significant differences (P = 0.467) were observed. The ability to simultaneously obtain vCBV and MR_OEF noninvasively may have profound clinical implications for the studies of cerebrovascular disease.
磁背景场不均匀性（ΔB）的存在可能会使基于T2*的方法对脑静脉血容量（vCBV）和脑氧摄取分数（MR_OEF）的定量测量产生混淆。本研究的目的是校正其影响并获得更准确的vCBV和MR_OEF估计值。采用3D高分辨率梯度回波序列通过两种算法获得ΔB图。然后使用ΔB图来恢复由2D多回波梯度回波/自旋回波序列采集的图像中的信号损失。最后，从经ΔB校正的2D多回波梯度回波/自旋回波图像中获得MR_OEF和vCBV的定量估计值。共研究了12名正常受试者。在进行ΔB校正之前，观察到大脑中的vCBV被高估（4.29±0.78%），而在进行ΔB校正后，测量的vCBV大幅降低。通过两种不同的ΔB校正方法获得的全脑vCBV分别为2.97±0.44%和2.68±0.47%，与文献报道的结果高度一致。此外，比较校正和未校正ΔB时的MR_OEF，未观察到显著差异（P = 0.467）。同时无创获得vCBV和MR_OEF的能力可能对脑血管疾病的研究具有深远的临床意义。
