Tissue Oxygen Saturation Mapping with Magnetic Resonance Imaging

Abstract

A quantitative estimate of cerebral blood oxygen saturation is of critical importance in the investigation of cerebrovascular disease. While positron emission tomography can map in vivo the oxygen level in blood, it has limited availability and requires ionizing radiation. Magnetic resonance imaging (MRI) offers an alternative through the blood oxygen level-dependent contrast. Here, we describe an in vivo and non-invasive approach to map brain tissue oxygen saturation (StO 2 ) with high spatial resolution. StO 2 obtained with MRI correlated well with results from blood gas analyses for various oxygen and hematocrit challenges. In a stroke model, the hypoxic areas delineated in vivo by MRI spatially matched those observed ex vivo by pimonidazole staining. In a model of diffuse traumatic brain injury, MRI was able to detect even a reduction in StO 2 that was too small to be detected by histology. In a F98 glioma model, MRI was able to map oxygenation heterogeneity. Thus, the MRI technique may improve our understanding of the pathophysiology of several brain diseases involving impaired oxygenation. Journal of Cerebral Blood INTRODUCTIONThe sensitivity of magnetic resonance imaging (MRI) to changes in oxygenation through the blood oxygen level-dependent (BOLD) effect 1 is the basis of functional MRI. This technique allows a noninvasive exploration of the functions and dysfunctions of the human brain and has revolutionized cognitive neuroscience over the last 20 years. Less appreciated is the potential of BOLD MRI to study baseline brain oxygenation. In a clinical environment, MRI oximetry would offer definitive advantages over brain oxygenation mapping with positron emission tomography (PET), 2 a technique not widely available and that requires ionizing radiations.Several authors have laid out the foundations of a theoretical framework named quantitative BOLD (qBOLD) imaging that aims to extract quantitative vascular information from baseline scans.

MR Vascular Fingerprinting in Stroke and Brain Tumors Models

“…StO 2 maps were estimated using the quantitative BOLD approach described in refs 4 and 21. Briefly, a T 2 map was derived from the MSME data using a non-linear fitting algorithm.…”

“…This includes steady-state or dynamic susceptibility contrast enhanced1, dynamic contrast enhanced2, arterial spin labeling3, and quantitative BOLD imaging45 that provide measurements of microvessel blood volume fraction, average vessel diameter and density, permeability, blood flow, or blood oxygenation. Clinical studies have benefited from these techniques with special attention paid to diagnosis, prediction of disease progression, and assessment of treatment interventions in stroke6 and cancer imaging78.…”

“…Three different rat models of brain tumors (9 L, C6, F98) known to contain irregular microvascular architectures121314 were analyzed. We also studied a stroke model in which the geometry of blood vessels is less affected but blood flow and blood oxygenation have large variations4. We studied the effects of increasing the complexity of the numerical models by adding a new dimension to the dictionary (water diffusion), increasing the size of the dictionary by extending the range of parameters accessible, and finally designing special cases where the voxels contain abnormally large blood vessels with preferential orientations.…”

“…We studied the effects of increasing the complexity of the numerical models by adding a new dimension to the dictionary (water diffusion), increasing the size of the dictionary by extending the range of parameters accessible, and finally designing special cases where the voxels contain abnormally large blood vessels with preferential orientations. The results were compared to those obtained from conventional analytical MR methods: steady-state susceptibility contrast imaging for BVf and vessel size imaging (VSI)15; and multiparametric quantitative BOLD (mqBOLD) imaging for StO 2 measurements4.…”

Algorithm for mapping cutaneous tissue oxygen concentration using hyperspectral imaging

“…Various methods for directly or indirectly determination of the tissue oxygenation have been developed and are currently used in both clinical practice and experimental studies such as: blood gas analysis [1], polarographic electrode technique [2], transcutaneous oxygen measurement [3], pulse oximetry [4], near-infrared spectroscopy [5], magnetic resonance imaging [6], electron paramagnetic resonance [7], and positron emission tomography [8]. Each of these methods has however its own limitations, in terms of accuracy, invasiveness, time-consuming, expensiveness, etc.…”