Development of MRI OEF imaging

Ischemic stroke is the leading cause of death and disability in the industrialized world. Approximately 24 percent of all strokes originate from neurovascular disease. In these patients, a precipitous increase in cerebral oxygen extraction fraction is a precursor to the stroke. The human and economic cost of stroke is high and expected to grow. With the population aging, the number of individuals at risk for stroke along with the associated health care cost is anticipated to rise considerably in the coming years. Consequently, there is an unmet need to identify patients who are mostly likely to suffer an ischemic stroke so that steps can be taken to prevent this devastating event. The goal in treating stroke is to restore oxygen supply to this ischemic penumbra , in a timely manner, in order to prevent it from becoming permanently damaged. Significant work has gone into quantifying stroke risk with advanced imaging; however, unfortunately, there exists no widely available means for doing so. Through positron emission tomography (PET), however, Dr. Colin Derdeyn and colleagues have shown that oxygen extraction fraction (OEF) is an independent indicator of stroke, with 12% hemispheric asymmetry being indicative of significant risk for a future stroke. PET-OEF images, however, require an on-site cyclotron due to the short half-life (~11 min.) of the tracer which has hindered its growth outside academic environments. Currently, fewer than 10 PET sites exist within the United States that can image OEF. Our goal is to translate OEF imaging from PET scanners to the patient population by improving on existing MRI-based OEF methods. We have developed an acquisition method based on the extended MR signal equation introduced by Twieg. With this method we elongate the acquisition window to exacerbate the R2* signal decay and resonant frequency shifts. In a 2003 his paper, Dr. Yablonskiy showed that altered OEF results in subtle changes to tissues R2* and the resonant frequency of water. In other words, MRI has the potential to image OEF. The goal of this pre-doctoral fellowship is multi-faceted. First, the applicant will develop a new MRI pulse sequence, refine and optimize it's image reconstruction software. Second, the applicant will perform a correlation study of the new sequence against the OEF imaging gold standard - PET.