Journal
JOURNAL OF MAGNETIC RESONANCE
Volume 193, Issue 2, Pages 267-273Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jmr.2008.05.009
Keywords
MRI; frequency-modulated pulse; adiabatic pulse; correlation spectroscopy; radial imaging
Funding
- NCI NIH HHS [R01 CA092004-05, R01 CA92004, R01 CA092004] Funding Source: Medline
- NCRR NIH HHS [P41 RR008079-080002, P41 RR008079-120069, P41 RR008079, P41 RR008079-050002, P41 RR008079-080009, P41 RR008079-090009, P41 RR008079-100002, P41 RR008079-090002, P41 RR008079-050009, P41 RR008079-080010, P41 RR008079-060002, P41 RR008079-060009] Funding Source: Medline
- NIBIB NIH HHS [P41 EB015894] Funding Source: Medline
- NINDS NIH HHS [P30 NS057091-019005, P30 NS057091] Funding Source: Medline
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A recently introduced method called SWIFT (SWeep Imaging with Fourier Transform) is a fundamentally different approach to MRI which is particularly well suited to imaging objects with extremely fast spin-spin relaxation rates. The method exploits a frequency-swept excitation pulse and virtually simultaneous signal acquisition in a time-shared mode. Correlation of the spin system response with the excitation pulse function is used to extract the signals of interest. With SWIFT, image quality is highly dependent on producing uniform and broadband spin excitation. These requirements are satisfied by using frequency-modulated pulses belonging to the hyperbolic secant family (HSn pulses). This article describes the experimental steps needed to properly implement HSn pulses in SWIFT. In addition, properties of HSn pulses in the rapid passage, linear region are investigated, followed by an analysis of the pulses after inserting the gaps needed for time-shared excitation and acquisition. Finally, compact expressions are presented to estimate the amplitude and flip angle of the HSn pulses, as well as the relative energy deposited by the SWIFT sequence. (c) 2008 Elsevier Inc. All rights reserved.
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