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Structure or Exchange? On the Feasibility of Chemical Exchange Detection with Balanced Steady‐State Free Precession in Tissue – An In Vitro Study
Author(s) -
Heule Rahel,
Deshmane Anagha,
Zaiss Moritz,
Herz Kai,
Ehses Philipp,
Scheffler Klaus
Publication year - 2020
Publication title -
nmr in biomedicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.278
H-Index - 114
eISSN - 1099-1492
pISSN - 0952-3480
DOI - 10.1002/nbm.4200
Subject(s) - asymmetry , white matter , chemistry , biophysics , nuclear magnetic resonance , biology , magnetic resonance imaging , physics , medicine , quantum mechanics , radiology
Balanced steady‐state free precession imaging has recently been suggested for chemical exchange detection (bSSFPX). The objective of this work is to investigate the contributions of microstructural, chemical shift and chemical exchange effects to the asymmetry of the bSSFP profile at field strengths of 3 T and 9.4 T. To this end, in vitro bSSFPX experiments are performed for a range of repetition times and flip angles in glucose water solutions with different MnCl 2 concentrations and tissue homogenates obtained from the brainstem of pig brains. The experimental results are compared to multi‐pool Bloch‐McConnell simulations. Additionally, the influence of white matter tract geometry is analyzed ex vivo in pig brain hemispheres measured at two different angles with respect to B 0 . The detectable bSSFP profile asymmetry in glucose solutions with tissue‐like relaxation times and white matter homogenates was consistent with Bloch‐McConnell simulations but relatively small. In intact white matter tracts, the asymmetry was dominated by structural effects with a strong dependency on tract orientation relative to B 0 . In tracts perpendicular to B 0 , the asymmetry was ≈ 3‐4 times higher than in the homogenates, thus barely affected by chemical exchange effects. In conclusion, chemical exchange‐related bSSFP profile asymmetries are detectable in tissue homogenates, however, the observed asymmetry level is generally low and prone to confounding structural effects rendering in vivo chemical exchange detection with bSSFP challenging in the brain.