Clinical and Radiological Correlates of Reduced CBF Measured Using MRI

Abstract

11 Background and purpose Methods for determining CBF using IV bolus tracking MRI have recently become available. Reduced apparent diffusion coefficient (ADC) values of brain tissue are associated with reductions in regional cerebral blood flow (rCBF). We studied the clinical and radiological features of patients with severe reductions of rCBF on MRI and analysed the relationship between reduced rCBF and ADC. Methods We studied patients with non-lacunar acute ischemic stroke in whom PWI and DWI MRI were performed within 7 hours after symptom onset. A PWI>DWI mismatch of >20% was required. Maps of rCBF, cerebral blood volume (rCBV) and mean transit time (rMTT) were generated after deconvoluting the measured concentration-time curve with the arterial input function using singular value decomposition. The ischemic lesion was outlined on the MTT map and the region of interest (ROI) transferred to the rCBF and rCBV map. ADC-maps were calculated. ADC lesions were defined as regions with ADC values ≤ 550 μm m2/sec. We compared the characteristics of patients with ischemic lesions that had a relative CBF of <50% to the contralateral hemisphere to patients with lesions that had relative CBF of >50%. Characteristics analysed included age, time to MRI, baseline NIHSS, mean ADC, DWI lesion volume, PWI lesion volume and absolute mismatch volume. Results Fifteen patients with an initial PWI>DWI mismatch of >20% were included. Ten had lesions with rCBF of >50% (median 60%) and five patients had rCBF of <50% (median 27.7%). Patients with rCBF <50% had lower ADC values (median 431 μmm2/sec versus 506 μ mm2/sec, p=0.028), larger DWI volumes (median 75.6 cm 3 versus 8.6 cm 3 , p=0.001) and larger PWI lesions as defined by the MTT volume (median 193 cm 3 versus 69 cm 3 , p=0.028) and more severe baseline NIHSS scores (median 18 versus 9, p=0.019). The rMTT and rCBV of the lesions were similar in both groups, as were the age, the absolute mismatch volume and the time from symptom onset to MRI. Conclusion These data indicate that ischemic lesions with severe CBF reductions, measured with new MRI techniques, are associated with a lower mean ADC, larger DWI and PWI lesion volumes and a higher NIHSS score.