Introduction

Magnetic resonance (MR) diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) offer a unique insight into ischemic stroke pathophysiology.¹ An absolute quantitative dynamic susceptibility contrast (DSC) cerebral PWI technique has recently been proposed. It is based on the self-calibrated EPI sequence (SCALE-PWI),² and could provide reliable quantitative measurement of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) in a short scan time. This technique may offer the opportunity to make a personalized therapy plan for each patient with ischemic stroke, based on complete quantitative hemodynamic information. The purpose of this study was to investigate the clinical value of SCALE-PWI in detecting salvageable areas in stroke patients.

Methods

Eleven patients with ischemic stroke underwent routine MRI (T1WI, T2WI, FLAIR, DWI) and SCALE-PWI scanning in a 3T Magnetom Prisma MR scanner (Siemens Healthcare, Erlangen, Germany) with a 64-channel head coil. The parameters of the prototype SCALE-PWI protocol were as follows: TR/TE = 1600/30 ms, matrix size = 128 × 128, flip angle = 20º, field of view = 220 × 220 mm², slice thickness = 6 mm, and acquisition time = 2:14 mins. The subjects were scanned with a delay of 46 secs. between consecutive modules of SCALE-PWI. A single dose (0.1 mmol/kg body weight) of Gd-DTPA contrast agent (Magnevist, Berlex, Montville, NJ, USA) was injected during the DSC module of SCALE-PWI, followed by a 20 mL saline flush, at a rate of 4 mL/sec. The quantitative CBV, CBF, and MTT maps were inline processed immediately after the scan. Two radiologists independently drew the region of interest (ROI) of the lesion on each map for the statistical analyses. The ROI₁ contained the entire abnormal areas on the CBV, CBF, and MTT images, and the ROI₂ contained the lesions that appeared hyperintense on DWI. We subsequently calculated the value of CBV_m, CBF_m, and MTT_m in the DWI/PWI mismatch areas. Paired t-tests were performed to detect differences in the CBV and CBV_m, CBF and CBF_m, and MTT and MTT_m, using SPSS 17.0 (IBM Corp., Armonk/NY, USA). P < 0.05 was considered statistically significant.

Results

The images and quantitative results for one representative subject are shown in Fig. 1. All the values are shown in the form of mean ± standard deviation. The CBF values of the infarct core (ROI₂) were significantly lower than the CBF_m values of the DWI/PWI mismatch areas [(25.53 ± 16.57) ml/100g/min vs. (33.90 ± 17.65) ml/100g/min, P = 0.03] in patients with ischemic stroke (Fig. 2). The CBV values were: (1.56 ± 0.75) ml/100g, and the CBV_m values were: (2.23 ± 1.39) ml/100g. The MTT values were: (4.19 ± 1.21) secs, and the MTT_m values were: (9.43 ± 17.00) secs. However, no significant differences were observed between the CBV and CBV_m, or MTT and MTT_m (P = 0.08 and 0.25, respectively).

Discussion

The research on ischemic stroke has focused not only on the early detection of lesions but also on the goal of tissue-based decision-making and personalized acute stroke treatment1, which are associated with the differentiation of infarcted and salvageable areas. This project found that the CBF values in DWI/PWI mismatch areas (traditionally considered to be salvageable areas) were significantly higher than the CBF values in the infarct core, suggesting that the quantitative CBF value obtained by the SCALE-PWI technique may be a promising indicator for distinguishing the salvageable area. Our findings show that the tissues whose CBF values are higher than 52.7 ml/100g/min could be salvageable, which is useful information for deducing tissue-based treatment. Different from the previous semi-quantitative method, the SCALE-PWI technique could provide complete quantitative information in a relatively short scan time (only 2:14 mins). The values of the CBV_m and CBF_m were similar to previous findings in the ischemic penumbra, showing hypoperfusion.³ But no significant difference was observed between the CBV and CBV_m, or the MTT and MTT_m. We speculate that it may be caused by recanalization therapy, collateral circulation, or a small sample size. The value of SCALE-PWI in acute ischemic stroke needs to be further investigated in the future.

Conclusion

SCALE-PWI could provide useful quantitative hemodynamic information to detect the ischemic penumbra in a relatively short scan time, and thus may serve as a guide for tissue-based decision-making and personalized treatment planning in acute stroke.

Acknowledgements

This research was supported by the NNSFC (81720108021, 81772009, 81601466, 81641168, 31470047), National Key R&D Program of China (YS2017YFGH000397), Scientific and Technological Research Project of Henan Province (182102310162) and the Key Project of Henan Medical Science and Technology Project (201501011).