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Estimation of bloch model MT spin system parameters from Z ‐spectral data
Author(s) -
Holt R. W.,
Duerk J. L.,
Hua J.,
Hurst Gregoly C.
Publication year - 1994
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.1910310205
Subject(s) - magnetization transfer , magnetization , spectral line , saturation (graph theory) , bloch equations , irradiation , offset (computer science) , nuclear magnetic resonance , physics , computational physics , materials science , mathematics , computer science , magnetic field , quantum mechanics , combinatorics , magnetic resonance imaging , medicine , radiology , programming language
Previous studies have described magnetization transfer (MT) Z ‐spectra in terms of a two‐pool Bloch model, with six spin‐system parameters K A , F , T 1 A , T 1 B , and T 2 B . By simulation, we show that a process including nonlinear constrained optimization can be used to accurately and uniquely estimate spin‐system parameters from MT 2‐spectra prepared by continuous wave (CW) RF irradiation. Experiments producing Z ‐spectra by pulsed RF irradiation give substantially different magnetization values, relative to MT acquisitions obtained by CW RF irradiation, at small offset frequencies, with a consequence that only T 2 B can be uniquely determined. However, several equalities and bounds involving four of the other parameters ( K A , F , T 1 A , T 1 B ) are derived, which are applicable to pulsed data. These relationships allow calculation of “free pool” magnetization corresponding to complete saturation of the restricted pool, without requiring that this complete saturation be experimentally achieved. MT experimental data from pulsed RF irradiation on boiled egg albumin, obtained using a clinical whole‐body MRI system, are analyzed using an optimization algorithm and the derived expressions.