Conventional Diffusion Weighted Imaging In Acute Stroke Overestimates Apparent Diffusion Coefficient (ADC): Improved Accuracy of ADC Measurements of Brain Using Fluid-Inversion Prepared Diffusion (FLIPD) Imaging
Background: The measurement of ADC of water in brains of stroke patients is used in developing tissue models of reversible from irreversible injury. Cerebrospinal fluid (CSF) has a higher ADC and T2 value than parenchyma and measurement of lesion ADC by conventional EPI methods may be overestimated by the presence of CSF in sulci and perivascular spaces. We investigated whether the suppression of signal from CSF using an inversion recovery MRI method would give different ADC values than with the conventional DWI technique. Methods: Thirteen consecutive patients with stroke onset of less than 6 hours and an acute lesion on conventional DWI were studied. Conventional isotropic DWI was a T2-weighted single shot EPI technique with a b value of 1000 s/mm2. CSF suppression was achieved by the addition of an inversion pulse (TI = 2200 ms) at the beginning of the DWI sequence. The method is termed Fluid-Inversion Prepared Diffusion (FLIPD), and it is a combination of FLAIR and DWI in a single sequence. The region of the acute lesion was identified on the conventional DWI and the ADC of that region was measured in both the conventional and FLIPD ADC images. Results: In all 13 patients, FLIPD ADC was lower than conventional ADC. The mean (SD) of the 13 patients’ lesion ADC was 0.587 (0.075) x 10-3mm/s with FLIPD and 0.696 (0.078) x 10-3mm/s with conventional DWI (p < 0.0001). The distribution of ADC values in all voxels pooled across all subjects indicated a narrower distribution of for FLIPD ADC (SD = 0.128 vs. 0.220 x 10-3mm/s for lesions and (SD = 0.151 vs. 0.514 x 10-3mm/s for normal brain). The reduced variance in FLIPD ADC improved the diagnostic conspicuity of FLIPD ADC lesions. Conclusions: Suppression of CSF leads to lesion ADC values more homogeneous and greater than 15% lower than with conventional EPI DWI techniques. We suggest that FLIPD ADC measurements are more accurate and give more diagnostically useful images than conventional ADC maps. Because FLIPD measures water diffusion within parenchyma only, it should be more sensitive to ischemic changes.