Sodium Imaging Intensity Increases with Time after Human Ischemic Stroke

Objective: Establishing time of onset is important in acute stroke management. Current imaging modalities do not allow determination of stroke onset time. Although correlations between sodium magnetic resonance imaging signal intensity within ischemic lesions and time of onset have been shown in animal models, the relation to onset time has not been established in human stroke. Utilizing high-quality, sodium images, we tested the hypothesis that sodium signal intensity increases with time from symptom onset in human ischemic stroke. Methods: Twenty-one stroke patients (63 +/- 15 years old) were scanned 4 to 104 hours after symptom onset. Follow-up images were obtained in 10 patients at 23 to 161 hours after onset, yielding a total of 32 time points. A standard stroke imaging protocol was acquired at 1.5 Tesla, followed by sodium magnetic resonance imaging at 4.7 Tesla. Relative sodium signal intensity within each lesion was measured with respect to the contralateral side. Results: The sodium image quality was sufficient to visualize each acute lesion (lesion volume range, 1.7-217cm(3)). Relative sodium signal intensity increased nonlinearly over time after stroke onset. Sodium images acquired within 7 hours (n = 5) demonstrated a relative increase in lesion intensity of 10% or less, whereas the majority beyond 9 hours demonstrated increases of 23% or more, with an eventual leveling at 69 +/- 18%. Interpretation: Increases of sodium signal intensity within the ischemic lesion are related to time after stroke onset. Thus, noninvasive imaging of sodium may be a novel metabolic biomarker related to stroke progression.