Mechanism of chirp excitation
In design of a chirp inversion pulse, we keep the sweep rate a≪ω12, where ω1 is the amplitude of the pulse. This is the adiabaticity condition for the inversion to work. We can convert a chirp inversion pulse to an excitation pulse by keeping the chirp rate high, with a>ω12. To be precise a=2.8ω1...
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ftdoajarticles:oai:doaj.org/article:b4f91dade15c4d1f97988ddd6a6527c0 2023-05-15T17:39:54+02:00 Mechanism of chirp excitation Sreya Das Justin Jacob Navin Khaneja 2022-06-01T00:00:00Z https://doi.org/10.1016/j.jmro.2021.100026 https://doaj.org/article/b4f91dade15c4d1f97988ddd6a6527c0 EN eng Elsevier http://www.sciencedirect.com/science/article/pii/S2666441021000170 https://doaj.org/toc/2666-4410 2666-4410 doi:10.1016/j.jmro.2021.100026 https://doaj.org/article/b4f91dade15c4d1f97988ddd6a6527c0 Journal of Magnetic Resonance Open, Vol 10, Iss , Pp 100026- (2022) Medical physics. Medical radiology. Nuclear medicine R895-920 Physics QC1-999 article 2022 ftdoajarticles https://doi.org/10.1016/j.jmro.2021.100026 2022-12-30T23:21:03Z In design of a chirp inversion pulse, we keep the sweep rate a≪ω12, where ω1 is the amplitude of the pulse. This is the adiabaticity condition for the inversion to work. We can convert a chirp inversion pulse to an excitation pulse by keeping the chirp rate high, with a>ω12. To be precise a=2.8ω12. The analysis of such a pulse breaks the evolution into three phases. The first and third phase are adiabatic phases while the second phase is non-adiabatic. Starting from north pole such a pulse brings the magnetization to equator, however there is a nonuniform phase which depends on the resonance offsets. We show how by following this pulse with a chirp inversion pulse at twice the sweep rate of excitation pulse, we can refocus this uniform phase. We find there is still some phase dispersion. This can be further eliminated by bringing in a second inversion pulse. The combination of these three chirp pulses allows us to excite arbitrary large bandwidth without increasing the peak amplitude of the pulse. Refocusing properties of pair of chirp has been studied before but our description is very different. Article in Journal/Newspaper North Pole Directory of Open Access Journals: DOAJ Articles North Pole Journal of Magnetic Resonance Open 10-11 100026 |
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Directory of Open Access Journals: DOAJ Articles |
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English |
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Medical physics. Medical radiology. Nuclear medicine R895-920 Physics QC1-999 |
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Medical physics. Medical radiology. Nuclear medicine R895-920 Physics QC1-999 Sreya Das Justin Jacob Navin Khaneja Mechanism of chirp excitation |
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Medical physics. Medical radiology. Nuclear medicine R895-920 Physics QC1-999 |
description |
In design of a chirp inversion pulse, we keep the sweep rate a≪ω12, where ω1 is the amplitude of the pulse. This is the adiabaticity condition for the inversion to work. We can convert a chirp inversion pulse to an excitation pulse by keeping the chirp rate high, with a>ω12. To be precise a=2.8ω12. The analysis of such a pulse breaks the evolution into three phases. The first and third phase are adiabatic phases while the second phase is non-adiabatic. Starting from north pole such a pulse brings the magnetization to equator, however there is a nonuniform phase which depends on the resonance offsets. We show how by following this pulse with a chirp inversion pulse at twice the sweep rate of excitation pulse, we can refocus this uniform phase. We find there is still some phase dispersion. This can be further eliminated by bringing in a second inversion pulse. The combination of these three chirp pulses allows us to excite arbitrary large bandwidth without increasing the peak amplitude of the pulse. Refocusing properties of pair of chirp has been studied before but our description is very different. |
format |
Article in Journal/Newspaper |
author |
Sreya Das Justin Jacob Navin Khaneja |
author_facet |
Sreya Das Justin Jacob Navin Khaneja |
author_sort |
Sreya Das |
title |
Mechanism of chirp excitation |
title_short |
Mechanism of chirp excitation |
title_full |
Mechanism of chirp excitation |
title_fullStr |
Mechanism of chirp excitation |
title_full_unstemmed |
Mechanism of chirp excitation |
title_sort |
mechanism of chirp excitation |
publisher |
Elsevier |
publishDate |
2022 |
url |
https://doi.org/10.1016/j.jmro.2021.100026 https://doaj.org/article/b4f91dade15c4d1f97988ddd6a6527c0 |
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North Pole |
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North Pole |
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North Pole |
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North Pole |
op_source |
Journal of Magnetic Resonance Open, Vol 10, Iss , Pp 100026- (2022) |
op_relation |
http://www.sciencedirect.com/science/article/pii/S2666441021000170 https://doaj.org/toc/2666-4410 2666-4410 doi:10.1016/j.jmro.2021.100026 https://doaj.org/article/b4f91dade15c4d1f97988ddd6a6527c0 |
op_doi |
https://doi.org/10.1016/j.jmro.2021.100026 |
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Journal of Magnetic Resonance Open |
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10-11 |
container_start_page |
100026 |
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1766140664755519488 |