Effect of saturation pulse power on chemical exchange saturation transfer imaging in patients with acute ischemic stroke.

OBJECTIVES

To determine the optimal saturation power for chemical exchange saturation transfer (CEST) imaging and evaluate the prognostic value of CEST parameters at different saturation powers in patients with acute ischemic stroke (AIS).

MATERIALS AND METHODS

Seventy-nine AIS patients underwent CEST imaging at saturation powers of 1, 1.5, and 2 μT. Amide proton transfer (APT) and nuclear overhauser enhancement (NOE) signals were quantified using the numerical fitting of the extrapolated semi-solid magnetization transfer reference (NEMR) method and compared to conventional amide proton transfer-weighted (APTw) signals based on the magnetization transfer ratio asymmetry at 3.5 ppm. Infarction visibility and hypointense artifacts on APT, NOE, and APTw images were graded on a three-point scale and compared using the Friedman test. Independent t-tests were used to compare CEST parameters between patients with favorable and unfavorable outcomes at 90 days.

RESULTS

Hypointense artifacts were most pronounced at 2 μT and minimized at 1 μT on APT and NOE images (p < 0.001). Infarctions were best visualized at 1 μT in 78.6% and 64.3% of patients on APT and NOE images, respectively, whereas APTw images provided poor lesion visibility at all saturation powers. Ischemic lesions showed decreasing APT and NOE values with increasing saturation power. Patients with favorable outcomes had significantly higher APT values and smaller percent change of APT at 1 μT compared to those with unfavorable outcomes (p < 0.05).

CONCLUSIONS

APT images at 1 μT provided superior image quality and demonstrated a significant correlation with 90-day neurological outcomes in AIS patients.

KEY POINTS

Question Standardized scanning parameters for chemical exchange saturation transfer (CEST) imaging in the evaluation of acute ischemic stroke (AIS) have not yet been established. Findings Amide proton transfer (APT) images acquired with 1-μT saturation power provided optimal image quality and were significantly associated with 90-day neurological outcomes in AIS patients. Clinical relevance Scanning parameters affect image contrast and the CEST effect. Our study supports the use of 1-μT saturation power for improved diagnostic quality and prognostic evaluation, contributing to the standardization of CEST imaging in clinical stroke assessment and future research.