Abstract W P38: Rates of ADC and Flair Signal Maturation Depend on Depth of Ischemia and Time: Helpful for Determining Time of Onset?

Abstract

Listen

Translate article

Background: Imaging biomarkers may be useful to estimate time of stroke onset when it is unknown. We studied FLAIR and ADC signal maturation in acute ischemic stroke patients to understand how the severity of ischemia may influence the rate of signal change. Methods: Ischemic stroke patients with witnessed onset were sequentially imaged with FLAIR, ADC, and PWI (MTT) at 3, 6, and 24 hr after onset. FLAIR and ADC signal intensity (SI) was normalized to the contralesional hemisphere (nFLAIR and nADC). White matter disease was excluded. Regions of stable ischemia between 3-6hr and 6-24hr were stratified based on 6 increments of MTT prolongation (pMTT) ranging from mild to severe ischemia. Rates of nFLAIR and nADC change between 2 time-points (units= /hr and x10-6 mm2/s /hr, respectively) were measured between 3-6hr and 6-24hr for each pMTT increment. % of patients with FLAIR positivity (defined as nFLAIR > 1.15) at 3 and 6 hr was calculated for each pMTT increment. Results: 37 patients were imaged at 2.6, 6.2, and 24 hr after stroke onset. Between 3 and 6 hr (Fig A, blue), rates of SI change for nFLAIR and nADC progressively increased with increasing severity of ischemia (p<0.0001; Kruskal-Willis). Between 6 and 24 hr (Fig A, green), nFLAIR rates of change decreased but continued to depend on ischemic severity, (p=0.0002). However, during this later time period nADC did not change with ischemic severity (p=0.36). The % of patients with FLAIR positivity increased between 3 and 6 hr and with increasing severity of ischemia (p=0.34 and p=0.0003, respectively; Chi-Square); Fig B. Conclusions: Rates of FLAIR and ADC change and FLAIR positivity were influenced by time from stroke onset and severity of ischemia. While FLAIR signal continued to demonstrate perfusion-dependent change beyond 6 hrs, ADC signal matured at 6 hrs, showing little change beyond. Understanding the factors influencing rates of FLAIR and ADC change may help refine an imaging biomarker for determining the time of stroke onset.