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Low duty cycle pulse trains for exchange rate insensitive chemical exchange saturation transfer MRI
Author(s) -
Chung Julius Juhyun,
Jin Tao
Publication year - 2021
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.28896
Subject(s) - duty cycle , saturation (graph theory) , nuclear magnetic resonance , pulse (music) , train , chemistry , materials science , environmental science , analytical chemistry (journal) , physics , thermodynamics , chromatography , mathematics , optics , power (physics) , cartography , geography , combinatorics , detector
Purpose To introduce and validate a pulse scheme that uses low duty cycle trains of π‐pulses to achieve saturation that is relatively insensitive to exchange rate yet linearly dependent on labile proton concentration. Methods Simulations were performed to explore the exchange rate sensitivity of π‐pulse trains and continuous wave chemical exchange saturation transfer (CEST) signals. Creatine phantoms with varying pH and varying concentrations were imaged to demonstrate pH insensitivity and concentration dependence of low duty cycle π‐pulse saturation. Results Simulations show decreasing the duty cycle of π‐pulse saturation decreases peak sensitivity to exchange rate, and this range of insensitivity can be tuned to different exchange rates through average B 1 power. The range of insensitivity is unaffected by changes in relaxation and magnetization transfer, while the sensitivity of CEST signal maintains linear dependence on labile proton concentration. Under B 1, avg = 0.48 μT, 30 mM creatine with pHs ranging between 6.36 and 8.21 exhibited CEST contrast ranging between ~6 and 11% under continuous wave and ~4% across all pHs using 10% duty cycle π‐pulses. Imaging these phantoms using duty cycles of 5, 10, 25, and 50% showed decreasing pH sensitivity with decreased duty cycle. Creatine phantoms with varied concentrations and pHs reveal that π‐pulse train saturation exhibited stricter correlation to concentration at lower DCs. Conclusion Low DC π‐pulse train is an easy‐to‐implement way of providing labile proton concentration‐dependent CEST MRI signal that is insensitive to exchange rate. This approach can be useful in studies where a change of chemical exchange rate may interfere with accurate assessments of physiology or pathology.