(Download) "Methods for Brain Iron Evaluation in Normal Aging" by Georgeta Mihai # Book PDF Kindle ePub Free
eBook details
- Title: Methods for Brain Iron Evaluation in Normal Aging
- Author : Georgeta Mihai
- Release Date : January 18, 2013
- Genre: Medical,Books,Professional & Technical,
- Pages : * pages
- Size : 16029 KB
Description
During the last few years, magnetic resonance imaging (MRI) systems operating at high (≥3 Tesla) and ultra-high (≥7 Tesla) magnetic field strength, have been extensively developed and used. However, there are still open questions about what determines the improved contrast among tissues in the brain, visible in susceptibility weighted, T2, T2*, and phase images. Brain iron deposition is age and region specific, with a pattern that is disturbed in neurological diseases (Alzheimer, Parkinson). Understanding the effect of tissue iron in the transverse relaxation and contrast mechanism in susceptibility weighted T2* images may be useful to non-invasively detect the distribution of iron in the brain. Studies of normal subjects and age related changes are needed to provide baseline data. Iron is capable of affecting the MRI signal by influencing the phase of the diffusing spins. This causes an increased transverse relaxation rate, visible in a T2 or a T2* weighted image, and a strong dephasing of spins, which effects are seen in a gradient echo T2* weighted image with a long echo time. Our experiments, conducted at both 3 Tesla and 7 Tesla, looked into the relationship between measured T2 using the commercially available Dual Echo and GRASE sequences, and the published estimated regional brain iron content, in the first study. The second study was dedicated to the correlation between phase spin quantifications, using phase images obtained from a gradient echo T2* acquisition and the same estimated brain iron content. We found that T2 correlated with brain tissue iron concentrations at both 3T and 7T. However, accurate relaxation measurements using the vendor supplied sequences are difficult to obtain, especially at 7 Tesla. RF inhomogeneities probably caused the failure to detect significant correlation between T2 values and normal brain iron distribution using GRASE. The correlation between brain iron and phase shift proved to be dependent on the region of interest. Moreover, the high visual resemblance between the phase images at the midbrain level and the same region on postmortem India ink stained microvasculature suggests that tissue iron may not be the sole influence in the contrast mechanism at ultra-high field strength.
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