Correlation Study Between Oxygen Extraction Fraction (OEF) Changes And Clinical Status (NIHSS) In Ischemic Stroke With Phase Measurement

Objective: The aim of the study was to determine the oxygen extraction fractionchanges (OEF) with the clinical status (NIHSS) in ischemic stroke patients; throughphase value measurement in cerebral veins and white matter using susceptibilityweighted imaging (SWI).Materials and methods: This retrospective study included a total of18acuteischemic stroke patients with age range of20~83(mean age of59.2, M/F=11:7) and24age-matched controls with age range of20~79(mean age of54.2) in number. Theclinical data (age, gender, clinical diagnosis and management plan) of the patients wasrecorded and patients included in this study were not administered with thrombolytictherapy. The clinical evaluation of these ischemic stroke patients was done by an astuteneuro physician with the measurement of National Institute of Health Stroke Scale(NIHSS) scores. The MRI scan including T1WI, T2WI, T2Flair, DWI, SWI sequencesand NIHSS were acquired simultaneously at three different time points(acute, sub acuteand chronic stages) following an ischemic stroke. The location, morphology and extentof the infarct were delineated using DWI and T2WI. The post processing of the rawSWI data was done using SPIN (signal processing in NMR) software (Detroit,Michigan). The Comparison of phase values of the cerebral veins was done for acutestroke patients and the controls, also the affected hemispheres of the stroke patients atthree stages along with phase values of white matter. Correlation of phase values(phase value changes) and NIHSS values (NIHSS changes) was assessed usingSpearman correlation.Results: There was a significant relation between the phase values of strokepatients and controls with the phase values of controls being more than those of strokepatients on an average (p=0.005). The analysis of data (phase values of cerebral veins) acquired3times from stroke patients showed that, the comparison of phase values ofthe cerebral veins in the acute, sub acute and chronic stages showed significant relation(p values0.000,0.005) and the correlation between the phase value changes and NIHSSchanges has good significance for the periods from acute to sub acute(r=-0.492, p=0.001), sub acute to chronic (r=-0.419,p=0.011)and acute to chronic scans (r=-0.327,p=0.006). There is no significant relation between the phase values of white matterobtained during acute, sub acute and chronic stage SWI scans (p=0.361,0.829).Conclusion: This study showed that by using SWI sequence, the phase differencebetween the cerebral veins and surrounding brain tissue, which arises due to increaseddeoxy haemoglobin to oxy haemoglobin ratio in an ischemic stroke patient, can be usedto estimate the oxygenation extraction fraction changes over time through the phasevalue measurement. The phase value and OEF are inversely related. These OEF changeswhich happen over a period of time in stroke patients will aid in predicting the clinicaloutcome of the ischemic stroke patients. This study demonstrated that only the phasevalue changes in the cerebral veins reflected OEF changes but not those of white matter.