Quantitative T2 Values Predict Time From Symptom Onset in Acute Stroke Patients

Abstract

Background and Purpose-We hypothesize that in comparison to diffusion-weighted imaging, quantitative T2 values (qT2) are more directly related to water uptake in ischemic tissue, depending on time from symptom onset. We measured the increase of qT2 in the infarct core to quantify the correlation between time from symptom onset and change in qT2. Methods-Thirty-six patients with acute ischemic stroke in the territory of the proximal middle cerebral artery underwent MRI including diffusion-weighted imaging, fluid-attenuated inversion recovery, and a triple-echo T2 sequence (calculation of T2 maps) within 6 hours after symptom onset. Regions of decreased apparent diffusion coefficient Ͻ550ϫ10 Ϫ9 mm 2 /sec were defined and superimposed onto the corresponding T2 map and the unaffected side in the horizontally flipped maps. Differences of T2/apparent diffusion coefficient values between affected and unaffected side were calculated (differences of T2/differences of apparent diffusion coefficient). Fluid-attenuated inversion recovery images were rated for lesion visibility. Results-Differences of T2 showed a significant correlation with time from symptom onset (Rϭ0.580; PϽ0.001). T2values measured in patients with visible fluid-attenuated inversion recovery lesions were significantly higher than in those without visible hyperintensity (PϽ0.001). The accuracy of qT2 to predict a time from symptom onset Ͻ3 hours was 0.794, whereas the corresponding accuracy for visual assessment of fluid-attenuated inversion recovery images was 0.676. Conclusions-T2

Estimation of the Onset Time of Cerebral Ischemia Using T 1ρ and T 2 MRI in Rats

“…11 Recently, using absolute T 2 relaxation time MRI in a stroke patient population, it was reported that the difference between ischemic and nonischemic contralateral T 2 (⌬T 2 ) increases quadratically between 1 and 6 hours after symptom onset. 12 In agreement with Siemonsen et al, 12 combined information from diffusion and fluidattenuated inversion recovery imaging has been suggested as a means to estimate the time of the ischemia onset. 13,14 The increase in T 2 poststroke has been ascribed chiefly to an increase in tissue water.…”

“…12 However, during the early minutes of ischemia, single Hahn echo T 2 MRI shows T 2 shortening observed both at 4.7 T and 9.4 T due to the negative blood oxygenation level-dependent effect. 18,31 Shortening of T 2 has also been reported acutely in patients imaged at 1.5 T. 32 The presence of such T 2 shortening results in a situation in which there is a time point when T 2 in the stroke tissue shows no difference to contralateral nonischemic tissue.…”

“…13,14 The increase in T 2 poststroke has been ascribed chiefly to an increase in tissue water. 12 that other factors influence T 2 , including the blood oxygenation level-dependent effect. Furthermore, brain T 2 is dependent on the external magnetic field requiring calibration data for each field used.…”

A spatiotemporal theory for MRI T2 relaxation time and apparent diffusion coefficient in the brain during acute ischaemia: Application and validation in a rat acute stroke model

“…Although the excellent agreement between the model's predictions is necessary, but not sufficient to validate its hypotheses, we believe that such a model is of great value in understanding ischaemia and designing MRI experiments for its detection. With an understanding of the parameters which drive ADC and T 2 kinetics in ischaemia, a simplified model may be derived which could be used to extract the most relevant parameters describing ischemia from MRI data, such as time of onset, 15,17,18 which would be of great value in clinical MRI.…”

“…This time dependence in itself could in future be used as a restraint in determining parameters of clinical importance, being more informative than simply the average T 2 over the lesion. 17 An important finding of the simulations is that the T 2 -weighted signal intensity, even at optimal TE, is less sensitive to ischaemia, and apparently more so to tissue type, than T 2 . The latter can therefore be expected to be a more sensitive marker of ischaemia provided it can be experimentally determined with sufficient confidence.…”