Abstract 2337: Apparent Diffusion Coefficient (ADC) Signal Maturation: Rates Of ADC Decline Depend On Severity Of Perfusion Deficit During Hyperacute Ischemic Stroke
Background: While it is known that a reduction of blood flow leads to a decrease in apparent diffusion coefficient (ADC), how ADC evolves as a function of time from ischemia onset is unclear. We evaluated ADC signal change in brain tissue with temporally stable hypoperfusion, examining the relationship between severity of hypoperfusion and the rate of ADC decline during acute ischemia.
Methods: Ischemic stroke patients were sequentially imaged with diffusion-perfusion weighted imaging at <4.5hr (tp1) and at 6hr (tp2) after stroke onset, to directly assess the temporal evolution of ADC. One month FLAIR provided the final infarct region. Registration aligned all images for each patient. Dynamic susceptibility contrast method allowed calculation of mean transit time (MTT). Hypoperfusion was defined as tissue with MTT > 4sec + the contralateral median MTT. In tissue with stable hypoperfusion on tp1 and tp2, ADC regions of interest (ROIs) with normal or moderate reduction on tp1 were evaluated. To avoid capturing tp1 ADC voxels that had already maximally declined (floor effect, <30 ×10-5 mm2/s), ADC values < 60 were excluded. To assess how ADC declined with varying degrees of hypoperfusion, tissue was divided into 6 MTT ranges: 3-6 (ROI1), 6-9 (ROI2), 9-12 (ROI3), 12-15 (ROI4), 15-18 (ROI5) and >18 (ROI6) seconds. Paired t-tests compared tp1 and tp2 ROIs for each patient. Infarct probability based on tp3 FLAIR was computed for each ROI.
Results: 43 patients were imaged at 2.9 (tp1) and 6.4 hrs (tp2) after stroke onset, of which 37 returned for 1 month FLAIR. The 6 ROIs with increasing MTT severity were found in 41, 27, 19, 12, 6, and 10 patients for ROI’s 1-6, respectively. ADC values for all ROIs were similar at tp1 (near normal), despite different tp1 MTT. For ROI1-3, ADC values did not decline between tp1 and tp2 or decreased mildly (ROI3, P=0.079). For severe hypoperfusion, ADC decreased significantly: ROI4 (p=0.006), ROI5 (P=0.038), and ROI6 (P=0.0001). Using linear regression to approximate the ADC decline, the slopes were significantly different from zero with ADC decay rates of -1.87×10-5 mm2/s/hr (R=0.58), -2.86×10-5 mm2/s/hr (R=0.65) and -4.51×10-5 mm2/s /hr (R=0.82) for ROI4-6, respectively (Figure). The median infarct probabilities for the 6 ROI’s increased with increasing MTT severity: 16%, 53%, 57%, 87%, 100%, and 90% for ROI1-6, respectively.
Conclusions: ADC remained normal after ischemic stroke in regions with stable, moderate hypoperfusion. In contrast, with stable, severe hypoperfusion (MTT>12s), ADC decreased from 3-6 hours and the rate of decline was highly dependent on the degree of hypoperfusion.
- © 2012 by American Heart Association, Inc.