Velocity encoding with the slice select refocusing gradient for faster imaging and reduced chemical shift-induced...

Area of Science:

• Cardiovascular Imaging
• Magnetic Resonance Imaging Physics

Background:

• Phase-contrast MRI (PC-MRI) is crucial for quantifying blood flow.
• Conventional PC-MRI techniques can be limited by long acquisition times and chemical shift artifacts.
• Faster imaging and reduced artifacts are essential for improved clinical utility.

Purpose of the Study:

• To evaluate a novel velocity-encoding technique using slice select refocusing gradients in PC-MRI.
• To assess the potential for faster imaging and mitigation of chemical shift-induced phase errors.
• To compare the accuracy of this new technique against conventional methods for blood flow quantification.

Main Methods:

• A novel velocity-encoding method was developed by time-shifting the refocusing gradient to enable minimum in-phase echo time (TE).
• This technique was implemented on a 3 Tesla scanner.
• Net forward flow was measured in the aorta and pulmonary arteries of 10 healthy subjects, comparing the novel method with conventional flow-compensated and flow-encoded PC-MRI.

Main Results:

• The slice select refocused gradient technique demonstrated significantly improved agreement in net forward flow measurements across all assessed vessels compared to conventional methods.
• Specifically, agreement between ascending aorta and pulmonary artery flow was 1.7% ± 1.9% versus 5.8% ± 2.8% (P=.002).
• The novel technique also increased temporal resolution by 35% and signal-to-noise ratio by 33%.

Conclusions:

• Slice select refocused gradient PC-MRI with a high receiver bandwidth and minimum in-phase TE offers more accurate and reproducible blood flow measurements.
• This method effectively reduces chemical shift-induced phase errors and shortens TE/repetition time.
• The technique allows for enhanced temporal/spatial resolution and potentially shorter breath-hold durations in cardiovascular MRI.