Novel gradient echo sequence‑based amide proton transfer magnetic resonance imaging in hyperacute cerebral infarction

Area of Science:

• Biomedical imaging
• Magnetic Resonance Imaging (MRI)
• Neuroscience

Background:

• Tissue pH is crucial in understanding metabolic disruption, acidosis, and damage during ischemia.
• Chemical exchange-dependent saturation transfer (CEST) imaging, particularly amide proton transfer (APT) MRI, can detect tissue pH and ischemic lesions.
• Existing CEST sequences require optimization for sensitive in vivo pH imaging.

Purpose of the Study:

• To develop and validate a novel gradient echo-based APT (GRE-APT) MRI sequence for hyperacute stroke imaging.
• To assess the efficacy of GRE-APT MRI in detecting ischemic acidosis and tissue damage in a rat model.
• To compare the diagnostic capabilities of GRE-APT MRI with diffusion-weighted imaging (DWI) in the hyperacute phase of stroke.

Main Methods:

• A novel GRE sequence incorporating a magnetization transfer pulse and minimized repetition time (TR) was developed for APT imaging.
• The GRE-APT MRI method was validated using a pH phantom and optimized for in vivo imaging.
• Rats subjected to middle cerebral artery occlusion (MCAO) underwent multiparametric MRI, including diffusion, GRE-APT, and T2-weighted imaging.

Main Results:

• The GRE-APT MRI achieved high spatial resolution and homogeneous signals, clearly delineating cerebral anatomy.
• GRE-APT and diffusion MRI findings correlated significantly with lactate content and infarct area.
• APT maps identified tissue not yet irreversibly damaged, unlike ADC maps, during the hyperacute stroke phase.

Conclusions:

• GRE-APT MRI effectively detects ischemic lactic acidosis with high sensitivity and spatiotemporal resolution.
• This pH MRI technique shows potential as a surrogate imaging marker for impaired tissue metabolism in hyperacute stroke.
• GRE-APT MRI may improve the diagnosis and prognosis of hyperacute stroke by providing earlier insights into metabolic changes.