Susceptibility contrast in high field MRI of human brain as a function of tissue iron content

  • Yao B
  • Li T
  • Gelderen P
 et al. 
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Magnetic susceptibility provides an important contrast mechanism for
MRI. Increasingly, susceptibility-based contrast is being exploited
to investigate brain tissue microstructure and to detect abnormal
levels of brain iron as these have been implicated in a variety of
neuro-degenerative diseases. However, it remains unclear to what
extent magnetic susceptibility-related contrast at high field relates
to actual brain iron concentrations. In this study, we performed
susceptibility weighted imaging as a function of field strength on
healthy brains in vivo and post-mortem brain tissues at 1.5 T, 3
T and 7 T. Iron histology was performed on the tissue samples for
comparison. The calculated susceptibility-related parameters R(2)(*)
and signal frequency shift in four iron-rich regions (putamen, globus
pallidus, caudate, and thalamus) showed an almost linear dependence
(r>or=0.90 for R(2)(*); r>or=0.83 for phase, psuggesting that potential ferritin saturation effects are not relevant
to susceptibility-weighted contrast for field strengths up to 7 T.
The R(2)(*) dependence on the putative (literature-based) iron concentration
was 0.048 Hz/T/ppm. The histological data from brain samples confirmed
the linear dependence of R(2)(*) on field strength and showed a slope
against iron concentration of 0.0099 Hz/T/ppm dry-weight, which is
equivalent to 0.05 Hz/T/ppm wet-weight and closely matched the calculated
value in vivo. These results confirm the validity of using susceptibility-weighted
contrast as an indicator of iron content in iron-rich brain regions.
The absence of saturation effects opens the way to exploit the benefits
of MRI at high field strengths for the detection of iron distributions
with high sensitivity and resolution.

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  • B Yao

  • T Q Li

  • P Gelderen

  • K Shmueli

  • J A de Zwart

  • J H Duyn

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