University Honors

Iron deposition and demyelination are commonly observed in the aging brain and neurodegenerative diseases. Magnetic resonance imaging (MRI) allows for characterization of iron deposition and myelination in vivo. Quantitative susceptibility mapping is a MRI technique that measures magnetic susceptibility, the degree a material is magnetized in response to an applied magnetic field, and quantitative susceptibility source separation allows for the separation of paramagnetic (i.e. positive susceptibility) and diamagnetic (i.e. negative susceptibility). components. Iron is paramagnetic and myelin is diamagnetic and the magnetic susceptibility of different tissues will vary based on the relative content of iron and myelin. Here, we examine the relationship between age and susceptibility in 54 healthy older adults (aged 60-87 years; interquartile range: 65-73, median: 68, mean: 69.3 ± 6.02 years; 24 males and 30 females) recruited from the community surrounding University of California, Riverside. All subjects provided written informed consent. Statistically significant correlations were seen between age and diamagnetic susceptibility in the frontal lobe (r = 0.412, p<0.01), temporal lobe (r = 0.286, p<0.01), occipital lobe (r = 0.402, p<0.01), and parietal lobe (r = 0.348, p<0.01). No significant relationship was observed between age and the paramagnetic susceptibility component in any cortical region. The positive correlation between diamagnetic susceptibility and age may be due to grey matter volume loss. Older adults experience a loss of cortical grey matter and myelin may make up a larger percentage of brain tissue in older adults. This may lead to a relative increase in diamagnetic susceptibility.