Preclinical Evaluation of the Accuracy of HIFU Treatments Using a Tumor-Mimic Model. Results of Animal Experiments

Presented in this paper is a tumor-mimic model that allows the evaluation at a preclinical stage of the targeting accuracy of HIFU treatments in the liver. The tumor-mimics were made by injecting a warm mixture of agarose, cellulose, and glycerol that polymerizes immediately in hepatic tissue and forms a 1 cm discrete lesion that is detectable by ultrasound imaging and gross pathology. Three studies were conducted: (i) in vitro experiments were conducted to study acoustical proprieties of the tumor-mimics, (ii) animal experiments were conducted in ten pigs to evaluate the tolerance of the tumor-mimics at mid-term (30 days), (iii) ultrasound-guided HIFU ablation has been performed in ten pigs with tumor-mimics to demonstrate that it is possible to treat a predetermined zone accurately. The attenuation of tumor-mimics was 0.39 dB.cm-1 at 1 MHz, the ultrasound propagation velocity was 1523 m.s-1, and the acoustic impedance was 1.9 MRayls. The pigs tolerated tumor-mimics and treatment well over the experimental period. Tumor-mimics were visible with high contrast on ultrasound images. In addition, it has been demonstrated by using the tumor-mimic as a reference target, that tissue destruction induced by HIFU and observed on gross pathology corresponded to the targeted area on the ultrasound images. The average difference between the predetermined location of the HIFU ablation and the actual coagulated area was 16%. These tumor-mimics are identifiable by ultrasound imaging, they do not modify the geometry of HIFU lesions and thus constitutes a viable mimic of tumors indicated for HIFU therapy.