Abstract WP228: Measurement Of Oxygen Extraction Fraction (OEF) By A Novel MRI Technique

Abstract

We report a novel application of an MRI technique called Parameter Assessment by Retrieval from Signal Encoding (PARSE) to measure OEF. OEF is of crucial importance, providing information about the stage of neurovascular impairment in a patient and the risk of stroke in such a patient. In this study, we test the hypothesis that PARSE can be used to measure oxygen extraction in the brain. This method uses a more accurate MR signal model, employs a non-Cartesian Rosette trajectory to encode multiple parameters and can simultaneously estimate M 0 , R 2 *, and local frequency in a single, non-invasive 5 second acquisition. Of particular interest here, is the feasibility to directly measure susceptibility related frequency changes from local frequency estimates. Since OEF abnormalities are focal, contralateral measurements were used to estimate the relative frequency change. We acquired data on 5 human subjects. In the series of 5 normal volunteers (M/F 3/2, <age> = 26 +/-10 years) we acquired a single slice, 5.0 mm thick, 220 mm x 220 mm FOV, 64 x 64 matrix, image resolution = 3 x 3 x 5.0 mm 3 ) 2D PARSE images. The total sequence time was 5 seconds. One arterio-venous malformation (AVM) patient was also tested with the PARSE-OEF sequence. The parameters were identical to the volunteer scans. For the 5 volunteers, the average frequency change (δω) across the brain image slice was 15.49 Hz ±2.77 Hz. This corresponded to an average whole brain-slice OEF of 37.23 ± 6.60%. This is in agreement with gold-standard Positron Emission Tomography (PET) OEF studies of normative values from Carpenter (35±7%), Yamauchi (42±5%), Diringer (41±6%) and Raichle (40±9%). Our current values are in excellent agreement with PET literature values. Upon further validation, this technique may be a viable clinical alternative to PET-OEF.