Visualization of cancer distribution for living tissues using acoustic impedance microscope

Two-dimensional acoustic impedance imaging is useful for observation of tissue conditions without chemical fixation or histochemical processing. Previously, we showed that direct or immunological heavy metal binding to particular proteins of cerebellar tissues made them featuring as higher acoustic impedance, and visualized their distribution in the tissues acoustically. In this report, we would propose a new technique of the acoustic impedance imaging to visualize cancer cells in living sliced organs. Zn²⁺ ions are required for dividing cells as an important element of cell mitogenic proteins, zinc finger proteins. Some types of cancers, for example, hepatoma and brain tumor, accumulate applied Zn²⁺ in their organs. STAM mouse is an useful model animal of non-alcoholic steatohepatitis (NASH) based hepatocellular carcinoma (HCC) generation. After 16 weeks old, many tumors develop and grow in liver. We prepared fresh slices of 17 week-STAM mouse livers and treated them with 400 μM ZnSO4 solution. Their acoustic impedances were observed with 120 MHz transducer using acoustic microscope : HMS 2000 (Honda Electronics Co. Ltd.). The slices and reference water were mounted on a hydrophilic silane-treated flat culture dish made of 0.7 mm thick polystyrene. Either silane treatment or vacuum ultraviolet (VUV) treatment was useful for stabilization of acoustic measurement. Observed slices were fixed and stained with anti-glypican 3 antibodies in order to confirm the HCC distribution traditionally. The acoustic images of rat healthy liver slices showed hepatic lobules and blood vessels clearly. In HCC mouse liver slices, round tumor tissue was observed with high impedance. After Zn²⁺ application, some regions in the tumor increased their impedance in zigzag lines. Subtraction image showed the increased region in the tumor. Immunohistochemical staining with glypican 3 antibodies showed the HCC distributed there in the tumor. We conclude- that some specific metal-treatment would become a new technique for the visualization of cancer cells in the living organs acoustically.