Ex vivo ovine liver model simulating respiratory motion and blood perfusion for validating image-guided HIFU systems

Methods The respiratory liver motion simulator consists of a physical ovine liver, agar-gelatine block surrounding the liver, a medical air balloon which is connected to a lung ventilator, and two water balloons which are used to move the phantom back to its original position. The whole setup was MR compatible, including the ventilator which is used to provide simulation of respiratory motion. The movement generated by the simulator was analysed via an MR compatible ultrasound system, and this real-time motion information was used to guide a dynamic high intensity focused ultrasound system (Exablate 2100 system, 0.55MHz) to steer its focus to follow this motion (Figure 1). The liver model is perfused via an extracorporeal circuit driven by a heart lung bypass machine (HL30 Maquet, Germany). Continuous non pulsatile input into the portal vein of 220 ml/min saline, with output free draining into the venous system, forming a perfusion circuit. (Figure 2). Digital Subtraction Angiography contrast images of the vasculature (OEC 9900, GE USA: Ultravist 370, Bayer HealthCare) to scanning with the MR and ultrasound doppler. The perfused vessel was then scanned in the 1.5 T Signa HDxGE (GE, USA) and ultrasound wireless scanner (Accuson SIEMENS, GERMANY).