Magnetic and ultrasonic thermal effects of magnetic nanoparticles in a tissue phantom

The aim of the paper was a preliminary comparison of heating efficiency by the two physically different modalities, namely ultrasound sonication and alternating magnetic field, of magnetic nanoparticles added to an agar-gel. Special agar-based tissue mimicking material (TMM) were manufactured from agar with the addition of produced by us iron oxide magnetic nanoparticles of order c/a 11 nanometers. To perform comparison of heating by the measured temperature rise curves caused by the two physical fields differently acting on the material sample, in the case of ultrasonic radiation we did not locate the sensor of thermometer in the ultrasonic beam focus, as it was usually studied, but we put it in the place where distribution of ultrasound intensity was more homogeneous. It was motivated by the fact that the “homogeneous heating” by the magnetic iron oxide nanoparticles which are spatially homogeneously distributed should be compared with the ultrasonic heating effects caused by the spatially homogeneous ultrasonic sources. The obtained results confirm that for both fields, ultrasound and magnetic, the temperature increase was caused by the presence of nanoparticles. In the case of heating by magnetic field pure agar-gel was not heated at all, and during sonication the pure agar-gel exhibited very small thermal effect, due only to the structure of the agar-gel crosslinking. We concluded that the ultrasonic absorption was in our experiment greater than magnetic, but the temperature rise after 180 s of magnetic field action was greater than of sonication.