Nuclear microscopy measurement of copper in atherosclerosis – Sensitivity and limitations to spatial resolution

Nuclear microscopy studies at the Centre for Ion Beam Applications have indicated a link between iron, zinc and the development of atherosclerosis. In the present study, we have extended this study to copper, since copper is also capable of inducing free radical mediated damage. As copper in biological tissue occurs at the parts per million level and therefore close to the detection limits for PIXE analysis, we have substantially increased the beam intensity and scanning time to obtain adequate statistics and analytical sensitivity. The experiments were conducted on male New Zealand White rabbits, weighing approximately 2.5 kg and fed on high cholesterol diets for 8 weeks. Unlike iron concentrations, which were observed to be increased in the atherosclerotic lesion, our experiments show that copper is depleted in the lesion (1.9 ppm) compared with the adjacent artery wall (4.1 ppm). The concentration of copper present in the lesion is also much less than iron (approximately 30 times less on average), indicating that iron, rather than copper, is more likely to induce atherosclerosis through free radical mediated damage, purely on the basis of greatly reduced concentrations.To obtain adequate statistics for copper, a 2.1 MeV proton beam focused to 2 μm with a relatively high beam current (from about 800 pA to 1 nA) was scanned over the sample for approximately 4 h. The effects of beam damage due to these high beam currents have been investigated and it was found that the tissue shrinks 10% each in the X and Y direction contributing to total area shrinkage of 20%. Despite tissue shrinkage problems, our results indicate that even with 1 nA beam currents, 4 h scan times and scan sizes of around 1 × 1 mm2, we can still extract accurate trace elemental concentrations.