期刊
MAGNETIC RESONANCE IN MEDICINE
卷 87, 期 5, 页码 2130-2144出版社
WILEY
DOI: 10.1002/mrm.29110
关键词
hyperpolarized; metabolism; MRI; numerical optimization; pulse sequence
资金
- Cancer Research UK Cambridge Institute Biological Resources Unit and Preclinical Imaging Core Facilities
- European Union [858149]
- Cancer Research UK [C197/A16465, C55296/A26605, C9685/A25177]
The method described in the study utilizes a stochastic numerical solver for optimizing pulse sequences, providing a simple framework for incorporating constraints and complex cost functions. Experimental results show improved signal-to-noise ratio with optimized polarization transfer pulses and achieve J-coupling modulation-free excitation.
Purpose: The performance of pulse sequences in vivo can be limited by fast relaxation rates, magnetic field inhomogeneity, and nonuniform spin excitation. We describe here a method for pulse sequence optimization that uses a stochastic numerical solver that in principle is capable of finding a global optimum. The method provides a simple framework for incorporating any constraint and implementing arbitrarily complex cost functions. Efficient methods for simulating spin dynamics and incorporating frequency selectivity are also described. Methods: Optimized pulse sequences for polarization transfer between protons and X-nuclei and excitation pulses that eliminate J-coupling modulation were evaluated experimentally using a surface coil on phantoms, and also the detection of hyperpolarized [2-C-13]lactate in vivo in the case of J-coupling modulation-free excitation. Results: The optimized polarization transfer pulses improved the SNR by similar to 50% with a more than twofold reduction in the B-1 field, and J-coupling modulation-free excitation was achieved with a more than threefold reduction in pulse length. Conclusion: This process could be used to optimize any pulse when there is a need to improve the uniformity and frequency selectivity of excitation as well as to design new pulses to steer the spin system to any desired achievable state.
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