Validation of quantitative susceptibility mapping with Perls' iron staining for subcortical gray matter
Graphical abstract
Introduction
Iron accumulation in subcortical gray matter (GM) may serve as an important biomarker of normal aging (Aquino et al., 2009, Cherubini et al., 2009, Hallgren and Sourander, 1958, Schenck and Zimmerman, 2004), and of neurological diseases including Alzheimer's disease, Parkinson's disease, Huntington's disease and multiple sclerosis (MS) (Berg and Youdim, 2006, Chen et al., 1993, Dexter et al., 1991, Khalil et al., 2011, LeVine, 1997, Williams et al., 2012). The mechanisms behind iron accumulation are not yet fully understood, although iron may accumulate through inflammatory and destructive processes (Stephenson et al., 2014), and may relate to the presence and extent of neurodegeneration. Measuring the state of brain iron metabolism may provide important information on aging and neurological diseases.
MRI provides a variety of contrast mechanisms that are sensitive to brain iron (Haacke et al., 2005) including transverse relaxation rates R2 and R2*, and susceptibility methods such as phase and susceptibility-weighted imaging. Previous studies in healthy subjects have shown that R2 and R2* increase in iron-rich brain regions and correlate strongly with iron concentration (Drayer et al., 1986, Gelman et al., 1999, Langkammer et al., 2010, Li et al., 2009, Peran et al., 2007, Thomas et al., 1993). While sensitive to iron, R2 and R2* may be affected by other sources such as macromolecular and water content changes (Mitsumori et al., 2012), which makes them not specific to brain iron. The introduction of phase imaging minimizes the influence of changes in macromolecular and water content, and is able to distinguish between negative and positive susceptibility sources (Duyn et al., 2007, Haacke et al., 2004, Rauscher et al., 2005). In addition, phase imaging has demonstrated good correlation to brain iron in subcortical GM (Haacke et al., 2007, Ogg et al., 1999, Yao et al., 2009). However, the non-local field properties of phase imaging cause it to be dependent on the shape and orientation of the object to the main magnetic field (Li and Leigh, 2004, Marques et al., 2009), which complicates interpretation.
The developing field of quantitative susceptibility mapping (QSM) inherits the iron sensitivity from phase imaging while eliminating the problem of non-locality. Derived from a deconvolution process from phase images, QSM unveils the local tissue susceptibility directly (De Rochefort et al., 2010, Kressler et al., 2010, Li et al., 2011, Liu et al., 2009, Liu et al., 2011, Reichenbach, 2012, Schweser et al., 2011, Shmueli et al., 2009, Wharton and Bowtell, 2010). A number of in vivo susceptibility maps have shown good correlations with subcortical GM iron concentrations (Bilgic et al., 2012, Schweser et al., 2011, Wu et al., 2012) as estimated from the hallmark study on brain iron by Hallgren and Sourander (1958). Nevertheless, validation of QSM for brain iron mapping requires postmortem studies that make a direct comparison between MRI and histochemistry. Only two human postmortem studies have been performed to date that compare QSM to histochemically measured iron content in subcortical GM. These studies used mass spectrometry (Langkammer et al., 2012) or X-ray emission and fluorescence (Zheng et al., 2013). The Langkammer et al. (2012) study provided absolute iron values but in small samples that do not provide a full spatial map of the tissue to relate to the susceptibility map, while the work by Zheng et al. (2013) used previously frozen formalin fixed tissue for MRI rather than in situ imaging. Furthermore, both studies examined total iron (ferrous and ferric). Thus to further validate QSM for subcortical GM iron mapping and to verify ferric iron as the main susceptibility source, there remains a need to compare in situ and in vivo susceptibility maps directly to spatial maps of ferric iron. In this study, we make use of Perls' iron staining (Meguro et al., 2007) to obtain full slice spatial maps of relative ferric iron content and compare to in situ and in vivo QSM in subcortical GM.
Section snippets
Subjects
In situ or in vivo QSM followed by Perls' iron staining was performed on three subjects who have been previously studied for phase, R2, and R2* mapping (Walsh et al., 2013). Subject 1 was a 63 year old male imaged in situ 28 h after death. Subject 2 was a 60 year old male imaged in situ 7 h after death. Subject 3 was a 45 year old male imaged in vivo one year before death. Subjects 1 and 2 had secondary progressive MS with Expanded Disability Status Scale (EDSS) scores of 8.5 before death, and
Results
Fig. 3 illustrates three coronal brain images from Subject 3 (in vivo) including field, susceptibility, and R2* maps and the Perls' iron stains. The field maps suffer from strong dipole effects which are resolved in the susceptibility maps, providing clear delineation between iron-rich regions. Subcortical GM hyperintensities in susceptibility and R2* maps correspond well to hypointensities in Perls' iron stains.
The resulting correlations of susceptibility to Perls' iron stain are shown in
Discussion
To compare susceptibility directly to ferric iron, we performed whole slice Perls' iron staining after in vivo or in situ QSM. This process enabled similar large ROI analysis on both MRI and Perls' stains, rather than highly localized samples. Furthermore, we performed in situ MRI shortly after death, to avoid extraction and fixation which can substantially alter MRI properties (Dawe et al., 2009, Van Duijn et al., 2011). Our approach yielded high correlations between susceptibility and ferric
Acknowledgments
Grant support from Canadian Institute of Health Research (MOP102582) and the Multiple Sclerosis Society of Canada (EGID1619) is acknowledged.
References (54)
- et al.
MRI estimates of brain iron concentration in normal aging using quantitative susceptibility mapping
Neuroimage
(2012) - et al.
Aging of subcortical nuclei: microstructural, mineralization and atrophy modifications measured in vivo using MRI
Neuroimage
(2009) - et al.
Imaging iron stores in the brain using magnetic resonance imaging
Magn. Reson. Imaging
(2005) - et al.
Quantitative susceptibility mapping (QSM) as a means to measure brain iron? A post mortem validation study
Neuroimage
(2012) Iron deposits in multiple sclerosis and Alzheimer's disease brains
Brain Res.
(1997)- et al.
Quantitative susceptibility mapping of human brain reflects spatial variation in tissue composition
Neuroimage
(2011) - et al.
On the origin of the MR image phase contrast: an in vivo MR microscopy study of the rat brain at 14.1 T
Neuroimage
(2009) - et al.
The correlation between phase shifts in gradient-echo MR images and regional brain iron concentration
Magn. Reson. Imaging
(1999) The future of susceptibility contrast for assessment of anatomy and function
Neuroimage
(2012)- et al.
Quantitative imaging of intrinsic magnetic tissue properties using MRI signal phase: an approach to in vivo brain iron metabolism?
Neuroimage
(2011)
Whole-brain susceptibility mapping at high field: a comparison of multiple- and single-orientation methods
Neuroimage
Susceptibility contrast in high field MRI of human brain as a function of tissue iron content
Neuroimage
Measuring iron in the brain using quantitative susceptibility mapping and X-ray fluorescence imaging
Neuroimage
Multiple-probe thermography for estimating the postmortem interval: II. Practical versions of the Triple-Exponential Formulae (TEF) for estimating the time of death in the field
J. Forensic Sci.
Age-related iron deposition in the basal ganglia: quantitative analysis in healthy subjects
Radiology
Role of iron in neurodegenerative disorders
Top. Magn. Reson. Imaging
Iron mapping using the temperature dependency of the magnetic susceptibility
Magn. Reson. Med.
Role of iron and ferritin in MR imaging of the brain: a study in primates at different field strengths
Radiology
MR of human postmortem brain tissue: correlative study between T2 and assays of iron and ferritin in Parkinson and Huntington disease
AJNR Am. J. Neuroradiol.
Postmortem MRI of human brain hemispheres: T2 relaxation times during formaldehyde fixation
Magn. Reson. Med.
Quantitative susceptibility map reconstruction from MR phase data using bayesian regularization: validation and application to brain imaging
Magn. Reson. Med.
Alterations in the levels of iron, ferritin and other trace metals in Parkinson's disease and other neurodegenerative diseases affecting the basal ganglia
Brain
MRI of brain iron
AJR Am. J. Roentgenol.
High-field MRI of brain cortical substructure based on signal phase
Proc. Natl. Acad. Sci. U. S. A.
MR imaging of human brain at 3.0 T: preliminary report on transverse relaxation rates and relation to estimated iron content
Radiology
Susceptibility weighted imaging (SWI)
Magn. Reson. Med.
Establishing a baseline phase behavior in magnetic resonance imaging to determine normal vs. abnormal iron content in the brain
J. Magn. Reson. Imaging
Cited by (126)
Improving quantitative susceptibility mapping for the identification of traumatic brain injury neurodegeneration at the individual level
2024, Zeitschrift fur Medizinische PhysikBFRnet: A deep learning-based MR background field removal method for QSM of the brain containing significant pathological susceptibility sources
2023, Zeitschrift fur Medizinische PhysikMagnetic resonance imaging detection of deep gray matter iron deposition in multiple sclerosis: A systematic review
2023, Journal of the Neurological Sciences