Paraffin-gel tissue-mimicking material for ultrasound-guided needle biopsy phantom.

Paraffin-gel waxes have been investigated as new soft tissue-mimicking materials for ultrasound-guided breast biopsy training. Breast phantoms were produced with a broad range of acoustical properties. The speed of sound for the phantoms ranged from 1425.4 ± 0.6 to 1480.3 ± 1.7 m/s at room temperature. The attenuation coefficients were easily controlled between 0.32 ± 0.27 dB/cm and 2.04 ± 0.65 dB/cm at 7.5 MHz, depending on the amount of carnauba wax added to the base material. The materials do not suffer dehydration and provide adequate needle penetration, with a Young's storage modulus varying between 14.7 ± 0.2 kPa and 34.9 ± 0.3 kPa. The phantom background material possesses long-term stability and can be employed in a supine position without changes in geometry. These results indicate that paraffin-gel waxes may be promising materials for training radiologists in ultrasound biopsy procedures.

Evaluation of vibro-acoustography techniques to map absorbed dose distribution in irradiated phantoms.

This work presents Vibro-acoustography (VA) as a tool to visualize absorbed dose distributions in a polymer gel dosimeter. VA uses the radiation force of focused ultrasound to vibrate a small region of the sample. Different modalities of VA were used to investigate the feasibility of this technique to evaluate dose distribution in irradiated 'MAGIC' polymer gel. A phantom was designed using this polymer with 2% w/w added glass microspheres having an average diameter range between 40-75 microm. The phantom was irradiated using conventional 10 MeV X-rays from a linear accelerator at a distance of 100 cm. An absorbed dose of 50 gray was delivered to the gel. To study the phenomena of dose distribution, continuous wave (CW), toneburst and multifrequency VA were applied to the phantom. Images were generated from the phase and magnitude of the emitted sound from the irradiated area. The comparative accuracy of the different VA results were validated using transverse relaxation rate (R2) image analysis by Magnetic Resonance Imaging (MRI) and a treatment planning system. A contour map of R2 was registered with the transverse CW images, obtained with the focal point on the top surface, and a good correlation was found between the images. The axial profile of irradiated inclusion from the toneburst VA image obtained with excitation frequency of 75 kHz showed the best accuracy compared to other VA modalities. The results show that VA imaging has potential to visualize dose distribution in a polymer gel dosimeter.