Effects of ribs in high intensity focused ultrasound beam path on formation of coagulated necrosis in cattle liver in vitro

Abstract

Objective To investigate the effects of ribs in high intensity focused ultrasound (HIFU)beam path on formation of coagulative necrosis in cattle liver in vitro in the same acoustic power. Methods The HIFU ablation was carried out in the manner of a single dot in the liver in vitro. The liver was ablated by HIFU in free field,then the ribs were placed between the focal plane and transducer,directing the beam axis through the intercostals space, lied at the rib edge and on the centre of middle rib. For each of these axial arrangements,the plane of the front surface of ribs was placed 3 cm,6 cm or 9 cm in front of the focus. After HIFU exposure,the tissue necrosis rate(TNR),the maximum length,width,depth and position of the coagulated necrosis in the liver were measured. Results ①The TNR was 100% in the free field. When the ribs were placed 3 cm in front of the focal plane,directing the beam axis through the intercostals space, the TNR was 100%. When directing the beam axis lied at the rib edge and on the centre of middle rib,the TNR decreased sharply. When the ribs were placed 6cm and 9cm in front of the focal plane, the TNR was more than 50%. ②When the ribs were placed in HIFU beam path, the volume of necrosis decreased compared with those in free field. The relationship between the ribs and beam axis, the location of ribs placed away from the focal plane different,the volume,length,width and position of the coagulated necrosis different. ③ When the ribs were close to the focal plane,unacceptable damage could been observed on the surface of ribs.When the ribs were far away from the focal plane, the ribs were safe. Conclusions The volume of necrosis decrease when the ribs are placed in HIFU beam path. The relative location of ribs and HIFU beam axis, the location of ribs away from the focal plane are relative with the volume of the coagulated necrosis. When directing the beam axis through the intercostals space, the volume of necrosis is large, and the shape of coagulated necrosis is regulated. When the ribs are closed with the focal plane,ribs are damaged probably. Key words: Ultrasound,high intensity focused; Ribs; Coagulated necrosis; Rib-like barrier