Blood Oxygen Level–Dependent MRI of Tissue Oxygenation

Abstract

Objectives-The contribution of endothelial function to tissue oxygenation is not well understood. Muscle blood oxygen level-dependent MRI (BOLD MRI) provides data largely dependent on hemoglobin (Hb) oxygenation. We used BOLD MRI to assess endothelium-dependent signal intensity (SI) changes. Methods and Results-We investigated mean BOLD SI changes in the forearm musculature using a gradient-echo technique at 1.5 T in 9 healthy subjects who underwent a protocol of repeated acetylcholine infusions at 2 different doses (16 and 64 g/min) and N G -monomethyl-L-arginine (L-NMMA; 5 mg/min) into the brachial artery. Sodium nitroprusside was used as a control substance. For additional correlation with standard methods, the same protocol was repeated, and forearm blood flow was measured by strain gauge plethysmography. We obtained a significant increase in BOLD SI during acetylcholine infusion (64 g/min) and a significant decrease for L-NMMA infusion (PϽ0.005 for both). BOLD SI showed a different kinetic signal than did blood flow, particularly after intermittent ischemia and at high flow rates. Key Words: magnetic resonance imaging Ⅲ endothelial function Ⅲ BOLD Ⅲ plethysmography T he vascular endothelium regulates tone and tissue perfusion through release of vasoactive substances such as NO. Numerous studies assessed the effect of endothelial function, and particularly endothelial dysfunction, in humans. However, the contribution of endothelial function to the regulation of tissue oxygenation in humans is poorly understood. 1 Perfusion is not the sole mechanism that determines tissue oxygenation and metabolism. Therefore, blood flow measurements may have limited utility in this regard. Blood oxygen level-dependent MRI (BOLD MRI) reflects changes in the ratio of oxyhemoglobin to deoxyhemoglobin attributable to their different properties in a magnetic field. 2,3 The BOLD technique is well established for functional brain MRI 4 and has also been used to assess myocardial 5-9 and skeletal muscle ischemia. 10,11 More recently, the technique was applied to assess exercise-induced hyperemia in skeletal muscle. 12,13 Available MRI systems are able to generate BOLD-sensitive small volume data sets in Ͻ1 s. Thus, BOLD MRI can noninvasively detect changes in intravascular tissue oxygenation with high spatial and temporal resolution. Furthermore, the tissue access is potentially unrestricted. We investigated changes of tissue oxygenation as defined by BOLD MRI signal intensity (SI) compared with blood flow changes after validated standard effectors on vascular tone and applied direct vasodilation and vasodilation attributable to stimulation of the endothelium. Conclusions-In Methods ProtocolWe studied 9 normal healthy men (25Ϯ4 years of age; 75Ϯ9 kg weight; 180Ϯ9 cm height). They received no medications. Our internal review board approved all studies, and written informed consent was obtained. All studies were conducted between 9 AM and noon after an overnight fast. A catheter (18G; Braun AG) was introduced into the brachial artery ...

Heme arginate improves reperfusion patterns after ischemia: a randomized, placebo-controlled trial in healthy male subjects

“…However, muscular metabolism may also influence oxygen extraction and hemoglobin saturation during reperfusion [27]. Therefore, the BOLD signal cannot be directly compared to reperfusion patterns measured by flow-mediated dilation or strain gauge plethysmography [30]. It seems plausible that a protected endothelial cell function is responsible for faster and increased maximal reperfusion, leading also to more rapid and increased oxygen saturation in the muscles under study.…”

Oxygenation-sensitive cardiovascular magnetic resonance

“…Oxygenation-sensitive CMR was also applied to assess endothelial function in the skeletal muscle [20], but similar studies have not been performed yet in the heart.…”

Noninvasive Estimation of Oxygen Consumption in Human Calf Muscle through Combined NMR Measurements of ASL Perfusion and T₂ Oxymetry

“…The blood O 2 level-dependent (BOLD) contrast exists outside the brain and the resulting tissue T 2 * dependence on hemoglobin saturation can be exploited to monitor venous and/or capillary oxygenation dynamically [13,14,15,16,17]. The multifactorial dependence of BOLD makes it difficult to determine blood oxygenation quantitatively with this approach.…”