A Tissue Mimicking Polyacrylamide Hydrogel Phantom for Visualizing Thermal Lesions Generated by High Intensity Focused Ultrasound

An optically transparent tissue-mimicking (TM) phantom whose acoustic properties are close to those of tissue was constructed for visualizing therapeutic effects by high intensity focused ultrasound (HIFU). The TM phantom was designed to improve a widely used standard bovine serum albumin (BSA) polyacrylamide hydrogel (PAG), which attenuated ultrasound far less than tissue and, unlike tissue, did not scatter ultrasound. A modified recipe has been proposed in the study by adding scattering glass beads with diameters of 40-80 μm (0.002% w/v) and by raising the concentration of acrylamide (30% v/v). The TM BSA-PAG constructed has an acoustic impedance of 1.67 MRayls, a speed of sound of 1576 m/s, an attenuation coefficient of 0.52 dB/cm at 1 MHz, a backscattering coefficient of 0.242 × 10−3 1/sr/cm at 1 MHz and a nonlinear parameter (B/A) of 5.7. These parameters are close to those of liver. The thermal and optical properties are almost the same as the standard BSA-PAG. The characteristic features of the thermal lesions by HIFU were observed to be more accurately visualized in the TM BSA-PAG than in the standard BSA-PAG. In conclusion, the proposed TM BSA-PAG acoustically mimics tissue better than the standard BSA-PAG and is expected to be preferentially used for assuring if a clinical HIFU device produces the thermal lesion as planned.