Histologic analysis of rabbit liver cancer treated by bulk ultrasound ablation

VX2 rabbit liver cancer, treated in vivo using bulk ultrasound ablation by miniaturized image-ablate arrays, was histologically analyzed using TTC vital stain and DAPI nucleic acid stain. VX2 cells were implanted into rabbit liver lobes and allowed to grow for 11-21 days. Liver lobes containing solid VX2 tumors were then treated with 4.8 MHz, 22.5-38.5 W/cm² in situ intensity, unfocused ultrasound for exposure times of 20-120 s. After animal sacrifice, thermal lesions were bisected along the imaging/treatment plane, one face stained with TTC, and the other with DAPI. Levels of TTC uptake (no uptake, partial uptake, and complete uptake) in liver parenchyma corresponded to three discrete regions of tan, pink and red color. By processing images of DAPI-stained parenchymal tissue from these three regions, cellular damage was quantified. A viability index parameter incorporating the size and shape of DAPI-stained nuclei correlated significantly with levels of TTC uptake, and thus with local tissue viability. For ablation of normal liver, viability indices for parenchymal regions of no TTC uptake and partial TTC uptake were significantly different from those for viable tissue. For ablation of VX2 tumor, differences in viability index between regions of no TTC uptake and complete TTC uptake were smaller, but significant overall.