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Intravascular contrast agent T 2 * relaxivity in brain tissue
Author(s) -
Patil Vishal,
Jensen Jens H.,
Johnson Glyn
Publication year - 2013
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.2876
Subject(s) - dephasing , nuclear magnetic resonance , contrast (vision) , linearity , white matter , nuclear medicine , relaxation (psychology) , pulse (music) , chemistry , magnetic resonance imaging , biomedical engineering , physics , medicine , radiology , quantum mechanics , optics , detector
Dynamic susceptibility‐weighted contrast‐enhanced (DSC) MRI perfusion measurements depend on estimating intravascular contrast agent (CA) concentrations ( C ) from signal intensity changes in T 2 * ‐weighted images after bolus injection. Generally, linearity is assumed between relaxation and C , but previous studies have shown that compartmentalization of CA and secondary magnetic field perturbations generate deviations from linearity. Physical phantoms using bulk blood have been used to empirically determine the relationship between relaxation rate and C in large vessels. However, the relaxivity of CA in the microvasculature is not easily measured since constructing appropriate phantoms is difficult. Instead, theoretical relaxivity models have been developed. In this study, we empirically tested a non‐linear expression based on static dephasing regime (SDR) and linear approximation. Signal‐time curves in white (WM) and grey matter (GM) were converted to concentration time curves (CTCs) using both expressions. Parameters for both linear and non‐linear formulations were adjusted to give a best agreement between cerebral blood volumes (CBV) calculated from WM and arterial CTCs in a group of normal subjects scanned at 3T. Optimized parameters were used to calculate blood volume in WM and GM in healthy subjects scanned at 3T and in meningioma patients scanned at 1.5T. Results from this study showed that a non‐linear SDR formulation gave an acceptable functional form for tissue relaxivity, giving reliable CBV estimates at different field strengths and echo times. Copyright © 2012 John Wiley & Sons, Ltd.