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T 2 Accuracy on a whole‐body imager
Author(s) -
Foltz Warren D.,
Stainsby Jeffery A.,
Wright Graham A.
Publication year - 1997
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.1910380512
Subject(s) - signal (programming language) , physics , pulse (music) , nuclear magnetic resonance , time constant , simple (philosophy) , imaging phantom , optics , computational physics , materials science , computer science , electrical engineering , philosophy , epistemology , detector , programming language , engineering
MR oximetry requires a T 2 measurement that is accurate within 5% in vivo. Simple methods are susceptible to signal loss and tend to underestimate T 2 . Current methods utilize RF pulses or RF cycling patterns that prevent signal loss at each data acquisition. However, using these methods with imperfect pulses, T 2 tends to be overestimated due to temporary storage of the magnetization along the longitudinal axis where it decays more slowly with a time constant T 1 T 2 . To reduce the T 1 dependence while preventing signal loss, we utilize simple 90 x 180 y 90 x composite pulses and good RF cycling patterns. These trains are critical for T 2 accuracy over typical ranges of RF and static field inhomogeneities and refocusing intervals. T 1 signal decay during each 90 x 180 y 90 x pulse must be accounted for to yield accuracy within 5% when the pulse‐width is 10% or more of the refocusing interval. A simple correction scheme compensates for this T 1 ‐related error effectively.