PurposeTo assess the feasibility of functional blood oxygen-level dependent (BOLD) MRI to evaluate intraoperative cerebrovascular reactivity (CVR) at 3 Tesla field strength.MethodsTen consecutive neurosurgical subjects scheduled for a clinical intraoperative MRI examination were enrolled in this study. In addition to the clinical protocol a BOLD sequence was implemented with three cycles of 44 s apnea to calculate CVR values on a voxel-by-voxel basis throughout the brain. The CVR range was then color-coded and superimposed on an anatomical volume to create high spatial resolution CVR maps.ResultsTen subjects (mean age 34.813.4; 2 females) uneventfully underwent the intraoperative BOLD protocol, with no complications occurring. Whole-brain CVR for all subjects was (mean +/- SD) 0.69 +/- 0.42, whereas CVR was markedly higher for tumor subjects as compared to vascular subjects, 0.81 +/- 0.44 versus 0.33 +/- 0.10, respectively. Furthermore, color-coded functional maps could be robustly interpreted for a whole-brain assessment of CVR.ConclusionWe demonstrate that intraoperative BOLD MRI is feasible in creating functional maps to assess cerebrovascular reactivity throughout the brain in subjects undergoing a neurosurgical procedure. Magn Reson Med 77:806-813, 2017. (c) 2016 International Society for Magnetic Resonance in Medicine

INTRODUCTION:Current MRI sequences are limited in identifying brain areas at risk for high grade glioma recurrence. We employed intraoperative 3-Tesla functional MRI to assess cerebrovascular reactivity (CVR) after high-grade glioma resection and analyzed regional CVR responses in areas of tumor recurrence on clinical follow-up imaging. METHODS:Five subjects with high-grade glioma that underwent an intraoperative Blood Oxygen-Level Dependent (BOLD) MRI CVR examination and had a clinical follow-up of at least 18months were selected from a prospective database. For this study, location of tumor recurrence was spatially matched to the intraoperative imaging to assess CVR response in that particular area. CVR is defined as the percent BOLD signal change during repeated cycles of apnea. RESULTS:Of the 5 subjects (mean age 44, 2 females), 4 were diagnosed with a WHO grade III and 1 subject with a WHO grade IV glioma. Three subjects exhibited a tumor recurrence on clinical follow-up MRI (mean: 15months). BOLD CVR measured in the spatially matched area of tumor recurrence was on average 94% increased (range-32% to 183%) as compared to contralateral hemisphere CVR response, 1.50±0.81 versus 1.03±0.46 respectively (p=0.31). CONCLUSION:For this first analysis in a small cohort, we found altered intraoperative CVR in brain areas exhibiting high grade glioma recurrence on clinical follow-up imaging.

The purpose of this study was to measure the regional change of magnetic susceptibility in human brain upon inhalation of 100% oxygen by MRI quantitative susceptibility mapping (QSM). Fourteen healthy volunteers were scanned in a 3 T MR scanner with a 3D multi-gradient-echo sequence while breathing medical air (normoxia) and pure oxygen (hyperoxia). QSM images and R2* maps were calculated. Mean susceptibility differences versus white matter were measured in regions of interest covering veins, gray matter (GM), and cerebrospinal fluid (CSF) under both conditions. Hyperoxia resulted in a strong susceptibility decrease in large veins (-154.4 ± 65.9 ppb, p < 10(-6)), in a smaller reduction in GM (-1.3 ± 1 ppb, p < 0.001), and in a susceptibility increase in ventricular CSF (3.8 ± 1.8 ppb, p < 10(-5)). The susceptibility decrease in veins implied an increase of venous oxygen saturation (SvO2) by 10.1 ± 4.0%. Compared with QSM, R2* was more seriously affected by long-distance effects not related to local tissue oxygenation and increased in cerebral frontal regions (3 ± 2 s(-1), p < 0.0004) due to paramagnetic molecular oxygen in cavities. The results highlight the potential of QSM to yield region-specific quantitative oxygenation information, and, thus, for applications such as oxygen-therapy monitoring or identification of hypoxic tumor tissue during radiotherapy planning.

OBJECTIVES:This study aims to quantify the response of the transverse relaxation rate of the magnetic resonance (MR) signal of the cerebral tissue in healthy volunteers to the administration of air with step-wise increasing percentage of oxygen.MATERIALS AND METHODS:The transverse relaxation rate (R2*) of the MR signal was quantified in seven volunteers under respiratory intake of normobaric gas mixtures containing 21, 50, 75, and 100% oxygen, respectively. End-tidal breath composition, arterial blood saturation (SaO2), and heart pulse rate were monitored during the challenge. R2* maps were computed from multi-echo, gradient-echo magnetic resonance imaging (MRI) data, acquired at 3.0T. The average values in the segmented white matter (WM) and gray matter (GM) were tested by the analysis of variance (ANOVA), with Bonferroni post-hoc correction. The GM R2*-reactivity to hyperoxia was modeled using the Hill's equation.RESULTS:Graded hyperoxia resulted in a progressive and significant (P < 0.05) decrease of the R2* in GM. Under normoxia the GM-R2* was 17.2 ± 1.1 s(-1). At 75% O2 supply, the R2* had reached a saturation level, with 16.4 ± 0.7 s(-1) (P = 0.02), without a significant further decrease for 100% O2. The R2*-response of GM correlated positively with CO2 partial pressure (R = 0.69 ± 0.19) and negatively with SaO2 (R = -0.74 ± 0.17). The WM showed a similar progressive, but non-significant, decrease in the relaxation rates, with an increase in oxygen intake (P = 0.055). The Hill's model predicted a maximum R2* response of the GM, of 3.5%, with half the maximum at 68% oxygen concentration.CONCLUSIONS:The GM-R2* responds to hyperoxia in a concentration-dependent manner, suggesting that monitoring and modeling of the R2*-response may provide new oxygenation biomarkers for tumor therapy or assessment of cerebrovascular reactivity in patients.