Brain iron detected by SWI high pass filtered phase calibrated with synchrotron X-ray fluorescence.
OBJECTIVE
To test the ability of susceptibility weighted images (SWI) and high pass filtered phase images to localize and quantify brain iron.


METHODS
Magnetic resonance (MR) images of human cadaver brain hemispheres were collected using a gradient echo based SWI sequence at 1.5T. For X-ray fluorescence (XRF) mapping, each brain was cut to obtain slices that reasonably matched the MR images and iron was mapped at the iron K-edge at 50 or 100 microm resolution. Iron was quantified using XRF calibration foils. Phase and iron XRF were averaged within anatomic regions of one slice, chosen for its range of iron concentrations and nearly perfect anatomic correspondence. X-ray absorption spectroscopy (XAS) was used to determine if the chemical form of iron was different in regions with poorer correspondence between iron and phase.


RESULTS
Iron XRF maps, SWI, and high pass filtered phase data in nine brain slices from five subjects were visually very similar, particularly in high iron regions. The chemical form of iron could not explain poor matches. The correlation between the concentration of iron and phase in the cadaver brain was estimated as c(Fe) [microg/g tissue] = 850Deltavarpi + 110.


CONCLUSIONS
The phase shift Deltavarpi was found to vary linearly with iron concentration with the best correspondence found in regions with high iron content.
Hopp
Karla
K
Department of Anatomy & Cell Biology, University of Saskatchewan, Saskatoon, SK, Canada.
Popescu
Bogdan F Gh
BF
McCrea
Richard P E
RP
Harder
Sheri L
SL
Robinson
Christopher A
CA
Haacke
Mark E
ME
Rajput
Ali H
AH
Rajput
Alex
A
Nichol
Helen
H
D000544:Alzheimer Disease / Q000473:pathology; D001921:Brain / Q000473:pathology*; D001930:Brain Injuries / Q000473:pathology; D001931:Brain Mapping; D002102:Cadaver; D002138:Calibration; D005557:Formaldehyde / Q000494:pharmacology; D006801:Humans; D007501:Iron / Q000737:chemistry*; D015233:Models, Statistical; D009133:Muscular Atrophy / Q000473:pathology; D010300:Parkinson Disease / Q000473:pathology; D017356:Synchrotrons; D056928:X-Ray Absorption Spectroscopy / Q000379:methods*
D005557:Formaldehyde; D007501:Iron