Observation of the reaction of a contrast agent to cells or tissue (Blood Pool Contrast Agent)

Quite a range of factors influence the gray level of a standard MRI picture. Beside the microscopic structure and the temperature we want to point out the influence of the local contrast agent concentration. If the sum of all influencing factors of two adjacent regions lead to the same gray level, these regions cannot be distinguished by means of MRI. Thus, a contrast agent has to accumulate in the region of interest to be beneficial for the interpreting physician.

Since the MRI signal is always the sum of various factors you can hardly ever tell which factor was responsible for the differences in the gray values of adjacent regions.

Both limitations of MRI are overcome by application of resonant ultrasound if magnetic nanoparticles (MNP) are used as contrast agents. We can prepare MNPs in such a way that they change their influence on the MRI signal if resonant ultrasound is applied. Thus, their contribution to the overall MRI signal can be quantified.

Additionally, the contribution of the MNPs to the MRI gray level under influence of resonant ultrasound changes if the prepared MNPs react with a cell or organic macromolecule. This reaction can be observed independently from any accumulation of the contrast agent.