Hypercholestaeremia is the presence of an abnormally large amount of cholesterol in the cells and plasma of blood. If left unchecked it can lead to atherosclerosis – a condition in which fatty material collects along the walls of arteries. This fatty material thickens, hardens and may eventually block the arteries.
One way of detecting high blood cholesterol is magnetocardiography (MCG), a technique that measures the magnetic fields produced by electrical activity in the human heart using extremely sensitive devices, such as superconducting quantum interference devices (SQUIDs). A map of the heart's magnetic field can be obtained, from which it is possible to locate the source of the electrical activity. The map can be used to identify sources of abnormal electrical signals – due to blocked arteries in the heart, for example.
Now, Hong-Chang Yang of the National Taiwan University in Taipei and colleagues at the National Taiwan Normal University, Taiwan University Hospital and the Korea Research Institute of Standards and Science have taken the SQUID-MCG technique a step further by injecting nanoparticles into the subject while taking measurements. The researchers performed their experiments on three normal rabbits and three rabbits with high blood cholesterol levels.
Yang and co-workers begin by injecting a magnetic fluid containing 2 ml of dextran-coated iron oxide particles, about 50 nm across, into the rabbits' ear vein. The fluid quickly travels to the heart and the researchers take SQUID-MCG measurements just before and after injection of the fluid. Subsequent measurements are made at 20 min intervals to obtain MCG contour maps of the rabbits' hearts.
The Taiwan researchers found significantly different behaviour in the MCG contour maps of normal and hypercholesteraemic rabbits. In particular, the peak-to-peak magnetic signal (or ΔB) in normal rabbits decreases while it increases in rabbits with high cholesterol. While they are not sure about the detailed mechanism behind this increase, Yang and colleagues say that it could be due to the iron oxide particles leaking out from the coronary arteries into the myocardium (specialized cardiac muscle cells) through tiny clefts. Surrounding magnetic nanoparticles could therefore modify the electromagnetic signals produced by the action potential of the myocardium.
Another important point of the work is that the difference in the MCG contour maps can be seen in rabbits that have been hypercholesteraemic for just three weeks. In contrast, traditional methods to diagnose hypercholesteremia, such as electrocardiography, only work for rabbits that have had high blood cholesterol for double that time. This technique is therefore a promising early-stage diagnosis for high cholesterol, says the team.
"We would now like to investigate the feasibility of applications using the magnetic nanoparticle assisted MCG for studies or the diagnosis of cardiac functions and diseases in animals, or possibly humans," Yang told our sister site, nanotechweb.org.
The researchers published their results in Appl. Phys. Lett.