Cerebral oxygen extraction fraction and cerebral venous blood volume measurements using MRI: Effects of magnetic field variation

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Abstract
The presence of magnetic background field inhomogeneity (ΔB) may confound quantitative measures of cerebral venous blood volume (vCBV) and cerebral oxygen extraction fraction (MR_OEF) with T-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 ΔB maps by two algorithms. The ΔB 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 ΔB- 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 ΔB correction, while the measured vCBV was substantially reduced after ΔB correction. Whole brain vCBV of 2.97 ± 0.44% and 2.68 ± 0.47% were obtained by the two different ΔB correction methods, in excellent agreement with the reported results in the literature. Furthermore, when MR_OEF was compared with and without ΔB 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. Magn Reson Med 47:958–966, 2002.