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Optimizing brain tissue contrast with EPI: A simulated annealing approach
Author(s) -
Ikonomidou Vasiliki N.,
van Gelderen Peter,
de Zwart Jacco A.,
Fukunaga Masaki,
Duyn Jeff H.
Publication year - 2005
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.20561
Subject(s) - flip angle , image contrast , nuclear magnetic resonance , magnetic resonance imaging , contrast (vision) , pulse sequence , white matter , image resolution , computer science , simulated annealing , magnetization transfer , echo planar imaging , biomedical engineering , materials science , artificial intelligence , physics , algorithm , radiology , medicine
Abstract A new magnetization preparation and image acquisition scheme was developed to obtain high‐resolution brain images with optimal tissue contrast. The pulse sequence was derived from an optimization process using simulated annealing, without prior assumptions with regard to the number of radiofrequency (RF) pulses and flip angles. The resulting scheme combined two inversion pulses with the acquisition of three images with varying contrast. The combination of the three images allowed separation of gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) based on T 1 , contrast. It also enabled the correction of small errors in the initial T 1 estimates in postprocessing. The use of three‐dimensional (3D) sensitivity‐encoded (SENSE) echo‐planar imaging (EPI) for image acquisition made it possible to achieve a 1.15 3 mm 3 isotropic resolution within a scan time of 10 min 21 s. The cortical GM signal‐to‐noise ratio (SNR) in the calculated GM‐only image varied between 30 and 100. The novel technique was evaluated in combination with blood oxygen level‐dependent (BOLD) functional magnetic resonance imaging (fMRI) on human subjects, and provided for excellent coregistration of anatomical and functional data. Magn Reson Med 54:373–385, 2005. Published 2005 Wiley‐Liss, Inc.