Signal evolution and infarction risk for apparent diffusion coefficient lesions in acute ischemic stroke are both time- and perfusion-dependent

Abstract

Background and purpose: This study aimed to examine the temporal relationship between tissue perfusion and apparent diffusion coefficient (ADC) changes within 6 hours of ischemic stroke onset and how different reperfusion patterns may affect tissue outcome in ADC lesions.

Methods: Thirty-one participants were sequentially imaged at 3 hours, 6 hours, and 1 month post-stroke. Three regions of interest (ROIs) were defined within initial ADC lesions: ROI (1)reperf_3hour hyperacute reperfusion (within 3 hours), ROI (2)reperf_6hour acute reperfusion (3 to 6 hours), and ROI (3)nonreperf no reperfusion (by 6 hours). For each ROI, changes in ADC (ΔADC) from 3 to 6 hours and risks of infarction were examined.

Results: The magnitude of initial ADC reduction was similar in all 3 ROIs (P=0.51). ΔADC was strongly associated with reperfusion (P<0.0001) but not with initial ADC reduction (P=0.83). ΔADC in ROI (1)reperf_3hour and ROI (2)reperf_6hour was significantly larger than that of ROI (3)nonreperf (P<0.05). Positive ΔADC was obtained from 3 to 6 hours in ROI (1)reperf_3hour that had restored perfusion before 3 hours, demonstrating a temporal delay between reperfusion and ADC changes. Risks of infarction were significantly higher in ROI (3)nonreperf than those in ROI (1)reperf_3hour and ROI (2)reperf_6hour.

Conclusions: Improvement in ADC did not occur coincidently with reperfusion but showed a temporal delay. Regions with similar initial ADC reductions at 3 hours had different evolution of ADC and infarction risks depending on when or if tissue reperfused. These findings provide a physiological basis for the observation that a single ADC measurement at a fixed time after stroke onset may not accurately predict tissue outcome.

Fig 1

A schematic representation of the definition of three ROIs within tp1 abnormal ADC regions. Yellow color outlines MTT lesion at tp1 and tp2, and orange color outlines ADC lesion at tp1. Region 1 represents ROI(1)_reperf3hr that exhibits abnormal ADC at tp1but normal MTT at tp1 and tp2; Region 2 represents ROI(2)_reperf6hr that has abnormal ADC and MTT at tp1 and normal MTT at tp2; and region 3 represents ROI(3)_nonreperf that shows abnormal ADC at tp1 and abnormal MTT at tp1 and tp2.

Fig 2

Representative MRI images of the participants exhibiting the three ROIs defined in Figure 1. Shown are MTT tp1 and tp2 (1^st and 2^nd columns), ADC tp1 and tp2 (3^rd and 4^th columns), and FLAIR at tp3 (5^th column). Each representative ROI (defined in Figure 1) was overlaid onto the tp1 ADC (6^th columns): pt 1, ROI_reperf3hr (green); pt 2, ROI_reperf6hr (blue); and pt 3, ROI_nonreperf (red).

Fig 3

Mean ADC from ROI_reperf3hr (a), ROI_reperf6hr (b), and ROI_nonreperf (c) for each individual participant at tp1 and tp2 after stroke onset. Perfusion status was labeled at both tp1 and tp2 in (a) to (c). A scatter plot of ΔADC in the three ROIs (d). † denotes statistical different ΔADC between a ROI and ROI_nonreperf. tPA treated patients were marked in black, while untreated patients were highlighted using red.

Fig 4

Risk of infarction in the three ROIs (box=25^th-75^th percentile; bars = 10^th-90^th percentile). † denotes statistical difference between a specific ROI and ROI_nonreperf using Newman-Keuls multiple comparison.