MRI of brain iron

Drayer, B P; Burger, Peter C.; Darwin, Robert H.; Riederer, Stephen J.; Herfkens, R. J.; Johnson, G. Allan

doi:10.2214/ajr.147.1.103

Cited by 350 publications

(291 citation statements)

References 20 publications

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“…63 Most iron is chelated and stored in the protein ferritin as Fe 3+ , 23,63 which shortens water proton T 1 and T 2 relaxation times. 23,64 Accordingly, several studies reported T 1 and T 2 effects as a function of iron content 10,[23][24][25]65 in the human brain, with concentration in the globus pallidus (GP) among the highest. Though T 2 W MR imaging shows a similar pattern of signal reduction around the GP (white arrows in Fig.…”

Section: Nerve Cellsmentioning

confidence: 99%

<i>In Vivo</i> Brain MR Imaging at Subnanoliter Resolution: Contrast and Histology

2016

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This article provides an overview of in vivo magnetic resonance (MR) imaging contrasts obtained for mammalian brain in relation to histological knowledge. Emphasis is paid to the (1) significance of high spatial resolution for the optimization of T 1 , T 2 , and magnetization transfer contrast, (2) use of exogenous extra-and intracellular contrast agents for validating endogenous contrast sources, and (3) histological structures and biochemical compounds underlying these contrasts and (4) their relevance to neuroradiology. Comparisons between MR imaging at subnanoliter resolution and histological data indicate that (a) myelin sheaths, (b) nerve cells, and (c) the neuropil are most responsible for observed MR imaging contrasts, while (a) diamagnetic macromolecules, (b) intracellular paramagnetic ions, and (c) extracellular free water, respectively, emerge as the dominant factors. Enhanced relaxation rates due to paramagnetic ions, such as iron and manganese, have been observed for oligodendrocytes, astrocytes, microglia, and blood cells in the brain as well as for nerve cells. Taken together, a plethora of observations suggests that the delineation of specific structures in high-resolution MR imaging of mammalian brain and the absence of corresponding contrasts in MR imaging of the human brain do not necessarily indicate differences between species but may be explained by partial volume effects. Second, paramagnetic ions are required in active cells in vivo which may reduce the magnetization transfer ratio in the brain through accelerated T 1 recovery. Third, reductions of the magnetization transfer ratio may be more sensitive to a particular pathological condition, such as astrocytosis, microglial activation, inflammation, and demyelination, than changes in relaxation. This is because the simultaneous occurrence of increased paramagnetic ions (i.e., shorter relaxation times) and increased free water (i.e., longer relaxation times) may cancel T 1 or T 2 effects, whereas both processes reduce the magnetization transfer ratio.

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Section: Nerve Cellsmentioning

confidence: 99%

<i>In Vivo</i> Brain MR Imaging at Subnanoliter Resolution: Contrast and Histology

2016

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“…It has been reported (3,20) that there is an uneven distribution of nonheme iron in different regions of the adult brain. This brain iron is progressively accumulated with age, particularly in the first three decades.…”

Section: Effect Of Brain Ironmentioning

confidence: 99%

“…The extrapyramidal nuclei have a high concentration of nonheme iron: 21.30 Ϯ 33.49 mg iron / 100 g fresh weight in the globus pallidus and 19.48 Ϯ 6.86 mg iron / 100 g fresh weight in the red nucleus in the age range of 30 -100 years (20). By comparison, the iron concentration in cerebral cortex and WM is quite low with a variation of a few mg / 100 g between the different regions (3,20). The data indicate that the occipital cortex has a greater nonheme iron content than the frontal cortex (20), while the frontal WM has a greater iron content than the occipital WM (3).…”

Section: Effect Of Brain Ironmentioning

confidence: 99%

“…Several studies (2)(3)(4)(5)(6)(7)(8)(9)(10)(11) have shown that T 2 varies across brain regions and during different stages of brain maturation and aging (5,10). Numerous studies in normal adults at multiple field strengths (2)(3)(4)9) have concluded that T 2 of cortical gray matter (GM) is longer than that of white matter (WM). On the contrary, gray matter T 2 was found to be shorter than that of WM in the brains of newborns (10) and in spinal cord (12).…”

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Inverse T₂ contrast at 1.5 Tesla between gray matter and white matter in the occipital lobe of normal adult human brain

Zhou

Golay

Zijl

et al. 2001

Magnetic Resonance in Med

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T 2 of cortical gray matter is generally assumed to be longer than that of white matter. It is shown here that this is not the case in the occipital lobe, but that this effect is often obscured at lower resolution and concealed in standard T 2 -weighted images. Using a high-resolution (1 ؋ 1.3 ؋ 2 mm 3 ) segmented EPI CarrPurcell-Meiboom-Gill sequence, T 2 relaxation times of the brain were measured at 1.5 T for eight healthy adult volunteers. The average T 2 values of cortical gray and white matter were found to be 88 ؎ 2 and 84 ؎ 3 msec in the frontal lobe, 84 ؎ 2 and 83 ؎ 3 msec in the parietal lobe, and 79 ؎ 1 and 87 ؎ 3 msec in the occipital lobe, respectively. This unexpected occipital T 2 contrast between gray and white matter is attributed to regional differences in iron concentration. The transverse relaxation time T 2 is one of the most commonly employed MRI contrast parameters. We have recently shown that absolute T 2 values can be used to quantify cerebral hemodynamics and oxygen extraction (1). As such, it is useful to accurately map T 2 of various normal and abnormal tissues. Several studies (2-11) have shown that T 2 varies across brain regions and during different stages of brain maturation and aging (5,10). Numerous studies in normal adults at multiple field strengths (2-4,9) have concluded that T 2 of cortical gray matter (GM) is longer than that of white matter (WM). On the contrary, gray matter T 2 was found to be shorter than that of WM in the brains of newborns (10) and in spinal cord (12). Several factors are likely to contribute to the heterogeneity of T 2 values. Among these may be regional variations in brain iron concentration, as well as variations in the microarchitecture of the cellular constituents and myelin structure (cytoarchitecture and myeloarchitecture, respectively). Recently, investigators examining the superior temporal gyrus and primary auditory cortex region have shown that the T 2 -weighted signal intensities can vary appreciably even between neighboring regions of the cortex (11). We found a similar pattern in our studies of the visual cortex, where typically an oblique slice through the calcarine fissure is studied. In order to better quantify the T 2 contrast between GM and WM in this location, we used very-high spatial resolution absolute T 2 measurements to minimize the likelihood of including WM and CSF (cerebrospinal fluid) in voxels nominally occupied by GM. MATERIALS AND METHODSMeasurements were performed on a 1.5 T ACS-NT clinical MRI scanner (Philips Medical Systems, Best, Netherlands). A body coil was used for RF transmission and a head coil was used for signal reception. Eight normal adult volunteers (four male, four female, age range 22-44 years, mean 32 Ϯ 8 SD years) were studied in accordance with institutional guidelines. A multiecho Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence with 13-shot segmented EPI acquisition was utilized at an echo-spacing of 25 msec. A single slice was acquired with 30 averages at the level of the dorsal-most aspects of the ...

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“…Using conventional MRI, iron deposition in the brain has been observed to appear in the globus pallidus as early as 6 months after birth. 75 The same study showed evidence of iron deposition in the substantia nigra at 9 to 12 months, the red nucleus at 18 to 24 months, and the dentate nucleus at 3 to 7 years of age. In a landmark postmortem study of 81 normal brains, Hallgren and Sourander 76 showed a progressive increase in whole brain iron deposition until the end of the third decade of life.…”

Section: Endogenous Protection From Iron-related Damagementioning

confidence: 80%

Iron in Chronic Brain Disorders: Imaging and Neurotherapeutic Implications

et al. 2007

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Summary:Iron is important for brain oxygen transport, electron transfer, neurotransmitter synthesis, and myelin production. Though iron deposition has been observed in the brain with normal aging, increased iron has also been shown in many chronic neurological disorders including Alzheimer's disease, Parkinson's disease, and multiple sclerosis. In vitro studies have demonstrated that excessive iron can lead to free radical production, which can promote neurotoxicity. However, the link between observed iron deposition and pathological processes underlying various diseases of the brain is not well understood. It is not known whether excessive in vivo iron directly contributes to tissue damage or is solely an epiphenomenon. In this article, we focus on the imaging of brain iron and the underlying physiology and metabolism relating to iron deposition. We conclude with a discussion of the potential implications of iron-related toxicity to neurotherapeutic development.

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MRI of brain iron

Cited by 350 publications

References 20 publications

<i>In Vivo</i> Brain MR Imaging at Subnanoliter Resolution: Contrast and Histology

<i>In Vivo</i> Brain MR Imaging at Subnanoliter Resolution: Contrast and Histology

Inverse T₂ contrast at 1.5 Tesla between gray matter and white matter in the occipital lobe of normal adult human brain

Iron in Chronic Brain Disorders: Imaging and Neurotherapeutic Implications

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MRI of brain iron

Cited by 350 publications

References 20 publications

<i>In Vivo</i> Brain MR Imaging at Subnanoliter Resolution: Contrast and Histology

<i>In Vivo</i> Brain MR Imaging at Subnanoliter Resolution: Contrast and Histology

Inverse T2 contrast at 1.5 Tesla between gray matter and white matter in the occipital lobe of normal adult human brain

Iron in Chronic Brain Disorders: Imaging and Neurotherapeutic Implications

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Inverse T₂ contrast at 1.5 Tesla between gray matter and white matter in the occipital lobe of normal adult human brain