Susceptibility Weighted Imaging Of Brain Iron

Iron is indispensable for almost all living organisms. In these organisms, iron is involved in a series of very important biochemical functions that include oxygen transport, electron transport, glucose metabolism, and the synthesis of neurotransmitters, myelin, and DNA replication. Thus, iron is essential for normal physiological function.However, iron enhances the production of the highly reactive and toxic hydroxyl radical, thus stimulating oxidative damage. Oxidative injury is considered as a major factor of (accelerated) ageing. Indeed, iron-dependent oxidative injury has been associated with a number of age-related conditions and diseases.In the human brain, a growing body of evidence showed that iron is involved in the mechanisms underlying many neurodegenerative diseases. Abnormal iron deposition in the brain is seen in a variety of neurodegenerative disorders. Estimating the amounts of iron deposits in the brain may be a new biomarker of the presence and progression of neurodegenerative diseases. Thus, clinicians and researchers need a method to measure the brain iron concentration in vivo accurately and non-invasively. Meanwhile, to better understand the disease-related changes that involve iron deposition, it is necessary to know the physiological distribution and change of brain iron of normal subjects.Brain iron stores can be imaged in vivo using magnetic resonance imaging. Iron deposition will increase proton transverse relaxation rate by creating subvoxel magnetic inhomogeneities, which dephase water protons passing nearby. Therefore, investigators attempted to quantify the brain iron content through the effect of iron on transverse relaxation rates. Due to various theorical and technical reasons, however, no quantitative correlations were established reliably between transverse relaxation rate and regional brain iron concentration.A new approach in MR imaging referred to as susceptibility weighted imaging offers a means to quantify iron content differences between tissues in the brain. In this study, we estimated the brain iron levels in vivo in a life-span sample of healthy adults using magnetic susceptibility weighted phase imaging. The purpose of study was to investigate the feasibility and reliability of susceptibility weighted phase imaging in quantifying the brain iron concentration, and to explore the brain iron distribution and change in the physiological condition.Age, gender, and hemispheric location may be the main source of differences in iron concentration in the human brain. The effect of age on the brain iron concentration is relatively well studied. Postmortem and in vivo studies have established that in normal individuals, iron levels increase with ageing in the brain. Until now, only one study reported by Bartzokis and coworkers has focused on gender differences in brain iron levels. They found that women had significantly lower brain iron concentration than men. There is no study focused on the hemispheric asymmetry of the brain iron level.The most striking finding of this study was that our data showed a leftward asymmetry of brain iron deposition. We found that the left hemisphere had higher iron levels than the right in the putamen, globus pallidus, substantia nigra, thalamus, and frontal white matter. We argue that the hemispheric asymmetry of iron content may underlie that of the dopaminergic system and may be related to motor lateralization in humans.In contrast to the previous report, our data showed that there were no gender related differences in iron levels in the brain. We argue that the discrepancy between our data and that reported by Bartzokis and coworkers may be ascribed to the use of different MRI techniques. Finally, our data showed that age-related iron deposition occurred in the brain. However, the rates of iron accumulation are different in various brain structures. The iron concentration in the putamen and frontal white matter increased linearly with age, and the iron concentration in the globus pallidus, substantia nigra, and caudate did not change with age. The patterns of iron accumulation with age in various structures revealed here are consistent with the results derived from postmortem studies.In conclusion, our study demonstrated that the susceptibility weighted phase imaging was a feasible and reliable technique in estimating the human brain iron level in vivo. The results of this study extend our knowledge of the physiological distribution and accumulation of iron in the human brain. The pattern of the distribution and accumulation of iron in the brain with ageing found in this study was a necessary baseline to understand disease-related changes that involve iron deposition.