Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Medical Biophysics

Supervisor

Dr. Neil Gelman

2nd Supervisor

Dr. Donna Goldhawk

Joint Supervisor

Abstract

Using magnetic resonance imaging, relaxation rate measurements were

performed in cancer cells overexpressing a magnetotactic bacterial gene, MagA.

Measurements of magnetic resonance relaxation rates in this expression

system is important for optimizing cell detection and specificity, for developing

quantification methods, and for refinement of gene-based iron contrast using

magnetosome associated genes. We measured the total transverse

relaxation rate (R2*), its irreversible and reversible components (R2 and R2′,

respectively) and the longitudinal relaxation rate (R1) in MDA-MB-435 tumor cells.

Clonal lines overexpressing MagA were cultured in the presence and absence of

iron supplementation, and mounted in a spherical phantom for relaxation rate

measurements at 3Tesla. In addition to MR measures, cellular changes in iron

were evaluated by inductively-coupled plasma mass spectrometry. Values of R2*

and R2ʹ were significantly higher (p < .01, accounting for multiple comparisons)

in iron-supplemented, MagA- expressing cells compared to unsupplemented

cells. R2* provided the greatest absolute difference and R2′ showed the greatest

relative difference, consistent with the notion that R2′ may be a more specific

indicator of iron-based contrast than R2, as has been observed in brain tissue.

R2 differences between the supplemented and non-supplement MagA-

expressing cells showed a trend (p < .05) toward significance. R1 differences

between these conditions were not significant. For parental cells, no significant

differences between iron-supplemented and unsupplemented cells were

observed in any of the relaxation rates. The results highlight the

potential of magnetotactic bacterial gene expression for detecting labeled cells.

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