Fast phase-contrast velocity measurement in the steady state

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Cardiovascular Imaging
• Flow Quantification

Background:

• Standard phase contrast (PC) imaging is crucial for flow quantification but can be limited by scan time and signal-to-noise ratio.
• Steady-state free precession (SSFP) sequences offer high signal but traditionally have not been optimized for direct velocity encoding.
• Developing rapid and efficient flow imaging techniques is essential for clinical applications.

Purpose of the Study:

• To introduce and evaluate a new method, steady-state phase contrast (SSPC), for rapid velocity encoding using refocused SSFP.
• To compare the performance of SSPC against conventional RF-spoiled PC imaging.
• To assess the signal-to-noise ratio (SNR) and phase-noise ratio (PNR) of SSPC in phantom studies.

Main Methods:

• Implementation of SSPC by encoding flow velocity as image phase within a refocused SSFP sequence.
• Simultaneous acquisition of magnitude images with refocused-SSFP contrast.
• Comparison with standard RF-spoiled PC imaging at various repetition intervals (TRs).
• Validation using a 2D Fast Fourier Transform (2DFT) sequence in phantom studies.

Main Results:

• SSPC demonstrated more than double the phase-signal to phase-noise ratio (PNR) compared to standard PC at reasonable TRs.
• The PNR advantage of SSPC increased exponentially as TR decreased, enabling faster scans with high efficiency.
• Good SNR and PNR were observed in stationary structures like the descending aorta and carotid bifurcation.
• Preliminary results suggest potential for TR reduction for improved cardiac imaging.

Conclusions:

• SSPC is a promising technique for rapid and high-quality velocity imaging with superior PNR compared to standard PC.
• The method facilitates efficient flow quantification, particularly in less dynamic vascular structures.
• Further optimization of TR may enhance its utility for dynamic applications like cardiac imaging.