This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. INTRODUCTION: Eddy current induced fields impart phase on the acquired signal that can distort both magnitude images and phase estimates used to measure tissue velocities, displacements, and temperatures. Eddy current pre-emphasis provides first-order correction, but more sophisticated techniques are needed to account for a broad range of short and long time constants and spatial non-linearities. A pulse sequence designed to measure the system s eddy current response was modeled with Bloch and Monte-Carlo simulation to characterize the sensitivity and bandwidth of measured time constants (?). METHODS: In order to measure phase shifts that arise from short ? eddy currents the pulse sequence was designed to acquire data (DAQ) for 62ms immediately after a large test gradient. Simulated, steady-state eddy current induced mono-exponential gradients were generated with 0.01ms<?<200ms and peak eddy current gradient strengths of 0.1Gmax/?. Bloch simulation was used to simulate the signal response over a broad range of ?. Monte-Carlo simulation was used to demonstrate the sensitivity to quantifying the phase response of each eddy current ?. RESULTS: The pulse sequence with the DGs doesn t stimulate and is therefore insensitive to long ? eddy current effects, but is sensitive (phase accumulation >?) to 25 s<?<25ms. Error associated with fitting the time constant of a mono-exponential function to the phase response of a gradient induced eddy-current with a single ? are lowest near ?=5ms indicating maximum sensitivity to estimating time constants of this magnitude. CONCLUSIONS: The Bloch simulation demonstrates that the pulse sequence is maximally sensitive to short ? of ~5ms, but with good sensitivity to 25 s<?<25ms. The fact that DAQ begins immediately after a gradient slew, combined with the high SNR of the sequence and the fact that short ? effects are not sensitive to T2 decay combine to make measurement of short ? effects possible.
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