Doppler images of heterogeneous gel dosimeter phantom by multi-frequency vibration

Vibrating biological tissue by external forces and investing of the induced micro-displacements of internal structures is a powerful technique to map relative mechanical properties within the medium. In general, pathological tissue has the stiffness modified. It implies that the range of resonance frequencies and the amplitudes of vibration of pathological tissues may differ from that of normal tissue. In this work, we propose a new apparatus to apply mechanical vibrations to the internal structure of soft tissue. It consists of a permanent magnet disc placed on the sample and a magnetized coil placed close to the magnet. Appling an alternating current in this coil, the oscillating magnetic field will vibrate the magnet. The vibration profile distribution of the internal structures is detected by ultrasound Doppler images. The contrast in the images of tissue-mimicking phantoms is strongly related with the frequency of vibration. The measurements were performed in a gel phantom containing a cylindrical inclusion two times stiffer than the background and in a dosimeter gel phantom containing a stiff inclusion created by ionizing radiation.