Abstract 115: Snapshot MR-OEF for Simultaneous Imaging of Tissue Oxygenation and CVR in 90 Seconds

Abstract

Introduction: Asymmetric hemispheric cerebral Oxygen Extraction Fraction (OEF) has been shown to be an independent predictor of stroke risk. Furthermore, the NIH/NINDS Progress Review Group has recently named tissue oxygenation imaging as a primary research goal in its August 2013 review. We have developed a novel method of imaging OEF with MRI. We present an analysis of MR-OEF images using breath-hold and cardiac-gating as inducers of physiologic stress. Methods: We acquire a 2D k-space volume using a novel rosette trajectory in 65 ms for simultaneous imaging of OEF and vascular reserve. Subjects were tested under 2 transient stress conditions: breath-hold and cardiac-gated. Breath-hold: 20 susceptibility weighted measurements were taken (Δt = 3 secs) with an induced 15 second breath-hold. Cardiac-gated: Because of the speed of PARSE (65 ms) we are able to see the transient hemodynamic fluctuations induced from the cardiac cycle. Images were acquired in 25 ms intervals from the R-wave trigger. Results: Measured mean OEF in normal brain parenchyma of 36.87 ± 6.6% and regions in symptomatic patients reaching 84.05 ± 4.54% correlate well with literature. OEF images taken during the first 125 ms of the cardiac cycle in a symptomatic patient with a right ICA stenosis are shown in Figure 1. Asymmetric hemispheric OEF (right hemispheric 13.06% elevation) is clearly visible. We also see a non-uniform flush in of de-oxygenated hemoglobin with a subsequent uneven outflow, unseen in healthy volunteers, suggesting regions of compromised cerebral vascular reserve. Discussion/Conclusion: Our novel acquisition allows us to simultaneously image single slice OEF and vascular reserve in 65 ms (with total scan time less than 90 seconds). Move over, because of its unprecedented speed, we for the first time, have the temporal resolution to examine the cerebral hemodynamic fluctuations caused by the pressure waveforms induced by the cardiac cycle.