The USC Andrew and Erna Viterbi School of Engineering USC Signal and Image Processing Institute USC Ming Hsieh Department of Electrical Engineering University of Southern California

Technical Report USC-SIPI-394

“Wideband Steady-State Free Precession for Cardiac MRI”

by Hsu-Lei Lee

December 2008

Balanced steady-state free precession (SSFP) is an MRI pulse sequence that is widely used for cardiac imaging, because it provides superior SNR and excellent contrast between blood and myocardium compared to the alternatives. Its primary drawback is sensitivity to off-resonance, which is related to the reciprocal of the sequence repetition time (TR) and results in banding artifacts.In this thesis, I introduce a novel technique that overcomes this limitation, and apply it to two clinically important cardiac imaging applications. The new technique, called wideband SSFP, utilizes two alternating repetition times to establish a steady state that is more resistant to banding artifacts, because the spacing between nulls in its frequency response is up to twice as large as that of conventional balanced SSFP. Wideband SSFP provides an efficient scheme for acquiring SSFP cardiac images with long readouts, which allows the high SNR of SSFP to be used for achieving higher spatial resolution. This technique is particularly suited for higher field strengths (such as 3 Tesla).A theoretical description of wideband SSFP is provided, including its spectral response, contrast, and SNR efficiency, with phantom experiments demonstrating excellent agreement between simulation and measurement. I then describe an initial magnetization preparation scheme based on scaled Kaiser-Bessel windowing functions to optimally stabilize the alternating-TR SSFP signal. Successful implementations of wideband SSFP for left ventricular function imaging and high-resolution coronary artery imaging in humans at 3 Tesla are then presented. In both cases, wideband SSFP provided improved spatial resolution and reduced image artifact, while maintaining a blood-myocardium contrast comparable to conventional balanced SSFP.


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