The Experimental Study Of The Focal Regions For High Intensity Focused Ultrasound

In recent years, High Intensity Focused Ultrasound(HIFU) has been one of new cancer treatment technologies. Because it’s a non-invasive or minimal invasive therapy, which has been widely used in clinic. At present, many problems including the position, size, and temperature monitoring of focal region have not yet been resolved, so potential complications such as incomplete coagulation of tissue damage may occur, and it cannot guarantee the safety and effectiveness of treatment. In the HIFU tumor treatment, the shape, size, and temperature of focal region are affected by therapy parameters including input power, irradiation time and irradiation depth. Hence, it is necessary to study the influence of these parameters in therapeutic focal region.ObjectiveThrough the experiment of tissue-mimicking phantom involving temperature membrane, excised bovine tissue, bovine muscle, and pig muscle, to evaluate variation rules of therapeutic focal region such as the temperature distribution, size, shape, position, in different input power, irradiation time and irradiation depth. As a result, it provides effective theory date and reference for the determination of clinical therapeutic doses by HIFU.Methods(1) Irradiate tissue-mimicking phantom including temperature membrane in different conditions, and discuss the shape, size and temperature distribution of focal region.(2) Irradiate excised bovine liver, bovine muscle, pig muscle in different conditions, and discuss the size variation of focal region, and contrast the difference.Results1. HIFU tissue-mimicking phantom experiment(1) In the distribution of temperature field study in tissue phantom, the region where temperature is above65.7℃could be observed as ellipse.(2) After setting depth was15mm and irradiating the tissue-mimicking phantom by HIFU, the area where temperature is above65.7℃was larger with increasing input power and irradiation time. In such circumstance the long axis and short axis became longer, while the change in long axis was more obvious than in short axis. When the input power and irradiation time increase, focal region moved towards the transducer.(3) When the input power was20W, and the irradiation depth was increasing, focal region where temperature is above65.7℃became smaller, and the long axis and short axis tend to be smaller, the range of long axis was4mm, and the short axis was1mm, while the change in long axis was obvious than that in short axis.(4) When the irradiation depth was shallow, and the irradiation time was long, focal region performed irregular. And only the irradiation time longer than the threshold, it may appear focal region.2. HIFU excised animal tissue experiment(1) When the irradiation depth was15mm, and the input power was increasing, the long axis and the short one of focal region in excised bovine liver, bovine muscle, pig muscle became larger, while the long axis was more obvious than the short one.(2) When input power increased to190W, the focal region in bovine liver was irregular, while the power was210W in bovine muscle.(3) When the input power, irradiation time and irradiation depth were same, contrasting lesion size among bovine liver, bovine muscle and pig muscle, the result was the lesion in bovine liver was smallest, and which in bovine muscle was largest.Conclusions1. The long axis and short axis of focal region in tissue-mimicking phantom and excised tissue performed larger with increasing input power and irradiation time. When the irradiation depth increasing, the long axis and short one in tissue-mimicking phantom were smaller, while the long axis was more obvious than the short one.2. The focal region in tissue-mimicking phantom moves towards the transducer. And the focal region appeared only when irradiation time was greater than threshold.3. When the irradiation depth was shallow, and input power and irradiation time were big, the focal region in tissue-mimicking phantom and excised tissue was irregular. Compared with bovine muscle and pig muscle, bovine liver was hard to form a lesion, but bovine muscle was easy to form.