Department of Medical Radiation Physics, Lund University, Lund, Sweden.
Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States.
J Neuroimaging. 2022 May;32(3):442-458. doi: 10.1111/jon.12975. Epub 2022 Feb 6.
Cerebral tissue oxygenation is a critical brain viability parameter, and the magnetic properties of hemoglobin offer the opportunity to noninvasively quantify oxygen extraction fraction (OEF) by magnetic resonance imaging (MRI). Ultrahigh-field MRI shows advantages such as increased sensitivity to magnetic susceptibility differences and improved signal-to-noise ratio that can be translated into smaller voxel size, but also increased sensitivity to static and B1 field inhomogeneities. The aim was to produce a systematic comparison of three MRI-based methods for estimation of OEF.
OEF estimates in 16 healthy subjects were obtained at 7T utilizing susceptometry-based oximetry (SBO), quantitative susceptibility mapping (QSM), and transverse relaxation rate (R2*). Two major draining veins, that is, the superior sagittal sinus (SSS) and the straight sinus (SS), were investigated, including mutual agreement between the methods in each of the two different vessels, agreement between vessels as well as potential vessel angle and vessel size dependences.
Very good correlation (r = .88) was found between SBO-based and QSM-based OEF estimates in SSS. Only QSM showed a moderate correlation (r = .61) between corresponding OEF estimates in SSS and SS. For SBO, a trend of increasing OEF estimates was observed as the SS vessel angle relative to the main magnetic field increased. No obvious size dependence could be established for any method. The R2*-based OEF estimates were reasonable (35%-36%), but the observed range was somewhat low.
The results indicate that QSM is a promising candidate for assessment of OEF estimates, for example, providing reasonably robust estimates across a wide range of vessel orientations.
脑组织氧合是一个关键的脑存活参数，血红蛋白的磁特性提供了通过磁共振成像（MRI）非侵入性地定量氧摄取分数（OEF）的机会。超高场 MRI 具有增加对磁化率差异的灵敏度和提高信噪比的优势，这可以转化为更小的体素大小，但也增加了对静态和 B1 场不均匀性的灵敏度。目的是对三种基于 MRI 的 OEF 估计方法进行系统比较。
在 7T 下，利用基于磁化率的血氧计（SBO）、定量磁化率映射（QSM）和横向弛豫率（R2*），在 16 名健康受试者中获得 OEF 估计值。研究了两个主要引流静脉，即上矢状窦（SSS）和直窦（SS），包括在两种不同血管中的每种方法之间的相互一致性、血管之间的一致性以及潜在的血管角度和血管大小依赖性。
在 SSS 中，SBO 与 QSM 基于 OEF 估计值之间存在非常好的相关性（r=.88）。只有 QSM 在 SSS 和 SS 中对应的 OEF 估计值之间显示出中等相关性（r=.61）。对于 SBO，随着 SS 血管相对于主磁场的角度增加，OEF 估计值呈上升趋势。任何方法都没有明显的尺寸依赖性。R2*-基于的 OEF 估计值是合理的（35%-36%），但观察到的范围有些低。
结果表明，QSM 是评估 OEF 估计值的有前途的候选方法，例如，在广泛的血管取向范围内提供相当稳健的估计值。
