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Hyperpolarized 13C Metabolic Magnetic Resonance Spectroscopy and Imaging
Published on: December 30, 2016
Steady-state free precession with hyperpolarized 3He: experiments and theory
Jim M Wild1, Kevin Teh, Neil Woodhouse
1Unit of Academic Radiology, University of Sheffield, C floor, Royal Hallamshire Hospital, Glossop Road, S10 2JF, UK. j.m.wild@sheffield.ac.uk
Journal of Magnetic Resonance (San Diego, Calif. : 1997)
|August 8, 2006
Summary
Steady-state free precession (SSFP) sequences offer increased signal-to-noise ratio (SNR) for hyperpolarized 3He gas imaging compared to spoiled gradient echo (SPGR) sequences, especially at higher flip angles. Optimization is key to balancing SNR gains with potential image quality compromises.
Area of Science:
- Magnetic Resonance Imaging (MRI)
- Hyperpolarized Gas Imaging
- Nuclear Magnetic Resonance (NMR)
Background:
- Hyperpolarized 3He gas MRI offers unique advantages for lung imaging due to its high sensitivity.
- Steady-state free precession (SSFP) sequences are known for efficient signal generation in MRI.
- Understanding SSFP sequence performance is crucial for optimizing hyperpolarized gas imaging protocols.
Purpose of the Study:
- To simulate and experimentally validate the magnetization response of hyperpolarized 3He gas to SSFP sequences.
- To compare the signal-to-noise ratio (SNR) and image quality of SSFP with spoiled gradient echo (SPGR) sequences.
- To investigate the effects of various parameters, including flip angle and diffusion, on SSFP performance.
Main Methods:
- Simulations of hyperpolarized 3He gas magnetization response using matrix product operators.
- Inclusion of parameters such as flip angle, timings, resonant frequency, diffusion, gradients, T1, and T2 in simulations.
- Experimental validation at 1.5 T using gas phantoms and healthy human subjects.
Main Results:
- SSFP sequences demonstrate increased SNR compared to SPGR, particularly with higher flip angles (e.g., 20 degrees).
- Diffusion dephasing and slice-mixing effects can compromise SNR and broaden the point spread function at high flip angles.
- Radiation damping was identified as a source of signal deviation in initial phases under specific experimental conditions.
Conclusions:
- Optimized SSFP sequences (e.g., alpha=20 degrees) provide superior SNR for hyperpolarized 3He imaging compared to SPGR.
- Careful selection of flip angle is necessary to balance SNR enhancement with potential image quality degradation.
- SSFP shows promise for hyperpolarized 3He MRI, despite challenges like off-resonance banding artifacts in vivo.
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