TY - JOUR

T1 - Effects of biological tissue structural anisotropy and anisotropy of magnetic susceptibility on the gradient echo MRI signal phase

T2 - theoretical background

AU - Yablonskiy, Dmitriy A.

AU - Sukstanskii, Alexander L.

N1 - Publisher Copyright:
Copyright © 2016 John Wiley & Sons, Ltd.

PY - 2017/4/1

Y1 - 2017/4/1

N2 - Quantitative susceptibility mapping is a potentially powerful technique for mapping tissue magnetic susceptibility from gradient recalled echo (GRE) MRI signal phase. In this review, we present up-to-date theoretical developments in analyzing the relationships between GRE signal phase and the underlying tissue microstructure and magnetic susceptibility at the cellular level. Two important phenomena contributing to the GRE signal phase are at the focus of this review – tissue structural anisotropy (e.g. cylindrical axonal bundles in white matter) and magnetic susceptibility anisotropy. One of the most intriguing and challenging problems in this field is calculating the so-called Lorentzian contribution to the phase shift induced by the local environment – magnetized tissue structures that have dimensions smaller than the imaging voxel (e.g. cells, cellular components, blood capillaries). In this review, we briefly discuss a “standard” approach to this problem, based on introduction of an imaginary Lorentzian cavity, as well as a more recent method – the generalized Lorentzian tensor approach (GLTA) – that is based on a statistical approach and a direct solution of the magnetostatic Maxwell equations. The latter adequately accounts for both types of anisotropy: the anisotropy of magnetic susceptibility and the structural tissue anisotropy. In the GLTA the frequency shift due to the local environment is characterized by the Lorentzian tensor (Formula presented.), which has a substantially different structure than the susceptibility tensor (Formula presented.). While the components of (Formula presented.) are compartmental susceptibilities “weighted” by their volume fractions, the components of (Formula presented.) are weighted by specific numerical factors depending on tissue geometrical microsymmetry. In multi-compartment structures, the components of the Lorentzian tensor also depend on the compartmental relaxation properties, hence the MR pulse sequence settings.

AB - Quantitative susceptibility mapping is a potentially powerful technique for mapping tissue magnetic susceptibility from gradient recalled echo (GRE) MRI signal phase. In this review, we present up-to-date theoretical developments in analyzing the relationships between GRE signal phase and the underlying tissue microstructure and magnetic susceptibility at the cellular level. Two important phenomena contributing to the GRE signal phase are at the focus of this review – tissue structural anisotropy (e.g. cylindrical axonal bundles in white matter) and magnetic susceptibility anisotropy. One of the most intriguing and challenging problems in this field is calculating the so-called Lorentzian contribution to the phase shift induced by the local environment – magnetized tissue structures that have dimensions smaller than the imaging voxel (e.g. cells, cellular components, blood capillaries). In this review, we briefly discuss a “standard” approach to this problem, based on introduction of an imaginary Lorentzian cavity, as well as a more recent method – the generalized Lorentzian tensor approach (GLTA) – that is based on a statistical approach and a direct solution of the magnetostatic Maxwell equations. The latter adequately accounts for both types of anisotropy: the anisotropy of magnetic susceptibility and the structural tissue anisotropy. In the GLTA the frequency shift due to the local environment is characterized by the Lorentzian tensor (Formula presented.), which has a substantially different structure than the susceptibility tensor (Formula presented.). While the components of (Formula presented.) are compartmental susceptibilities “weighted” by their volume fractions, the components of (Formula presented.) are weighted by specific numerical factors depending on tissue geometrical microsymmetry. In multi-compartment structures, the components of the Lorentzian tensor also depend on the compartmental relaxation properties, hence the MR pulse sequence settings.

KW - generalized Lorentzian tensor approach

KW - magnetic susceptibility

KW - phase contrast

KW - quantitative susceptibility mapping

KW - white matter

UR - http://www.scopus.com/inward/record.url?scp=85003674264&partnerID=8YFLogxK

U2 - 10.1002/nbm.3655

DO - 10.1002/nbm.3655

M3 - Review article

C2 - 27862452

AN - SCOPUS:85003674264

SN - 0952-3480

VL - 30

JO - NMR in Biomedicine

JF - NMR in Biomedicine

IS - 4

M1 - e3655

ER -