Hot Spots:

VSOP particle with yellow molecules indicating the citrate bound to the iron oxide surface (grey). Functionalisation of the particle by specific peptides e.g. Annexin V

‘The tiny particles under investigation are less than seven nanometres across, with an iron core that is highly responsive to the intense magnetism of an MR system. Most MR imaging of coronary arteries already employs contrast agents to improve image quality. Coronary arteries are small and due to the movement of the heart during the cardiac cycle, there is very little net imaging time, so you need a contrast agent to get a sufficient signal-to-noise ratio. The super paramagnetic iron oxide particles under development have an optimal signal-enhancing effect far above that of existing contrast agents. An ongoing phase II trial is measuring blood flow through coronary arteries. The goal is to compare images made with the nanocontrast agent to those made with traditional X-ray angiography.

A second application for the highly responsive nanoscale particles is more speculative, but could prove more valuable. With assistance from Siemens, the consortium leader of Nano AG, Prof. Taupitz and colleagues at other luminary academic sites are trying to attach the tiny particles to peptides that bind to specific structures in the body, which could turn the nanoparticles into disease–hunters inside the body.

To detect arterial plaque, the nanoscale iron oxide particles could be attached to a factor that would, in turn, attach to compounds involved in apoptosis. Programmed cell death in the artery wall is one sign of vulnerable plaque. A second tactic could link to compounds associated with angiogenesis, which often occurs in unstable plaque. In either case, the tiny particles will enrich within the pathologic vessel walls and generate hot spots on a MR image.

Currently, physicians must rely on indirect methods to specifically image diseased arteries. It is a change in paradigm for vascular diagnosis. We may have to look not so much at flow-limiting stenosis, or narrowing, but at the composition of the plaques and the change in the vessel walls. Using a specific contrast medium means to get functional information and then to make a prediction of the risk of plaque rupture in the artery.‘

01.09.2007