A feasibility study of high intensity focused ultrasound for liver biopsy hemostasis

Potential femoral head osteonecrosis model induced by high-intensity focused ultrasound

Osteonecrosis of the femoral head is a common disease that can result in complex hip replacement. To evaluate potential treatments, a model that consistently creates osteonecrosis is needed. We studied and demonstrated the possibility of developing an osteonecrosis model using high-intensity focused ultrasound (HIFU) on canine femora in vitro. To achieve these goals, the temperature in the medullary cavity of the femoral head was measured. A phenomenological model was developed to fit the measured temperature variations with the HIFU parameters for similar HIFU experiments on femoral heads. The average temperature discrepancy between model and measured values was less than 0.83°C. Histology confirmed that the temperature in the medullary cavity can be elevated to a level at which an acute thermal injury is created. HIFU has the potential to be used in a non-invasive model of osteonecrosis.

Calibration and measurement issues for therapeutic ultrasound

This review paper examines some of the issues relating to calibration and measurement of therapeutic medical ultrasonic equipment (MUE). This is not intended to be an all-encompassing review of all aspects of characterising therapeutic ultrasound. Instead it concentrates on issues related to the acoustic output of two applications: physiotherapy and high intensity focused ultrasound surgery (HIFUS or HIFU; also referred to as high intensity therapeutic ultrasound, HITU). Physiotherapy has a well-established standards infrastructure for calibration: the requirements are small in number and well-defined. The issue for physiotherapy is not so much 'How to calibrate?' but rather, 'How to ensure that equipment IS calibrated?' The situation in the much newer area of HIFU is very different: the first steps towards writing standards are just starting and even the very basic questions of what to measure and with what type of sensor are open for debate. Readers whose main interest is in other ultrasound therapies will find ideas of relevance to their own specialty.

Image-guided acoustic hemostasis for hemorrhage in the posterior liver

We investigated the use of ultrasound image-guided high intensity focused ultrasound (HIFU) to stop bleeding from injuries in the posterior liver. A HIFU transducer with focal length of 3.5 cm and frequency of 3.2 MHz was integrated with an intraoperative high-resolution ultrasound-imaging probe. Wedge tissue extractions, 30-mm long, 5-mm wide and 8-mm deep, were made in the posterior liver surface of five pigs to induce bleeding. The device was positioned on the anterior surface of the liver and HIFU was applied using ultrasound image-guidance. Hemostasis was achieved in 66 +/- 18 s (mean +/- standard deviation) for 17 HIFU treatments. During 7 min of sham HIFU treatment, none of the control incisions (n = 7) became hemostatic. Ultrasound image-guided HIFU offers a promising method for hemostasis in surgical settings in which the hemorrhage site is hidden and/or not accessible.

Fluorescence imaging for real-time monitoring of high-intensity focused ultrasound cardiac ablation

Side effects and limitations of radio-frequency ablation of cardiac arrhythmias prompted search for alternative energy sources and means of their application. High-intensity focused ultrasound (HIFU) is becoming an increasingly attractive modality for ablation because of its unique ability for non-invasive or minimally invasive, non-contact focal ablation in 3D volume without affecting intervening and surrounding cells. The purpose of this study is to develop a real-time monitoring technique to elucidate HIFU-induced modifications of electrical conduction in cardiac tissues and to investigate the HIFU cardiac ablation process to help to achieve optimal HIFU ablation outcome. We conducted experimental studies applying HIFU at 4.23 MHz to ablate the atrio-ventricular (AV) node and ventricular tissue of Langendorff-perfused rabbit hearts. We employed fluorescent voltage-sensitive dye imaging and surface electrodes to monitor the electrical conduction activity induced by HIFU application in real time. In ventricular epicardium HIFU ablation, fluorescent imaging revealed gradual reduction of the plateau phase and amplitude of the action potential. Subsequently, conduction block and cell death were observed at the site of ablation. When HIFU was applied to the AV node, fluorescent imaging and electrograms revealed the development of the AV block. The study establishes that real-time fluorescent imaging provides novel monitoring and assessment to study HIFU cardiac ablation, which may be able to provide improved understanding of HIFU cardiac ablation process and mechanism useful for development of successful clinical applications.