Three experiments are described. In each of the experiments, displacement data was collected from the left and right radiation force push. The axicon focus described in the companion paper (Part 1) was selected to lower the peak intensity while creating a longer axial source, as compared to conventional focus. The displacement data was used to create crawling wave movies by using the convolution method, and the crawling wave movie was analyzed to extract the shear wave speed for the vibration frequency. The constructed phantoms include a gelatin phantom with a cylindrical inclusion, an oil-gelatin phantom, and two mouse livers ex-vivo.
A gelatin phantom (an ‘inclusion’ phantom) with a cylindrical inclusion was fabricated with an inclusion, 6mm in diameter, of 16% gelatin against a background of 8% gelatin. The procedure to fabricate the phantom is as follows: 51.5g gelatin (300 Bloom Pork Gelatin, Gelatin Innovations Inc., Schiller Park, IL, USA), 4.5 g NaCl and 0.75 g of agar were added to 500 mL of de-ionized water, and the mixture was heated to 55 °C. After all the components dissolved, the mixture was further cooled to approximately 30 °C, and poured into cylindrical molds and allowed to rest at 4 °C overnight. Once formed, the inclusion was removed from the mold and suspended in a cubic phantom mold. An 8% gelatin background was created by heating a mixture of 1.8 L de-ionized water, 148.3 g gelatin, 16.2 g NaCl, and 2.7 g agar to 55 °C. The mixture was then cooled in an ice water bath to approximately 30 °C and poured into the cubic gelatin mold containing the cylindrical inclusion. The mold was then allowed to rest at 4 °C overnight. The 8% gelatin background was also used to suspend the mouse livers as will be discussed in the next section.
Another phantom, an oil-based gelatin phantom, was created to check the dispersion. It consisted of 11% gelatin and 25% castor oil. 110g gelatin (300 Bloom Pork Gelatin, Gelatin Innovations Inc., Schiller Park, IL, USA) and 1 g antibacterium (Germall Plus, Lotioncrafter, Olga, WA, USA) were added to 1 L of de-ionized water, and the mixture was heated to 90 °C (molten gelatin). The molten gelatin was placed in an ice water bath and cooled to roughly 55 °C at which point 30mL castor oil and 7.7mL surfactant (Ultra Ivory, Procter & Gamble, Cincinnati, OH, USA) were emulsified into the mixture. The mixture was further cooled to approximately 30 °C, poured in a cubic mold and allowed to rest at 4 °C overnight.
A third phantom, mouse phantom, is a gelatin phantom containing mouse livers. The livers, obtained by hepatectomy, were suspended in a cube-shaped mold of dimension 8.5 cm × 10cm × 19cm. Two mo use livers were suspended in the mold and the 8% gelatin phantom previously described was poured into the cubed gelatin mold containing the mouse livers. The mold was then placed in an ice water bath for roughly 90 minutes, cooling it from 35 °C to 15 °C. The size of the liver in the scanning cross-section was approximately 2 cm × 3cm for the fatty liver, and 1.5 cm × 1.4 cm for the normal liver.