HIFU & Focused Ultrasound
Ultrasound is a form of vibrational wave. It can transmit harmlessly through living tissues, and this makes it possible to use an extracorporeal source of ultrasound for therapeutic purposes. If ultrasound beams are focused and sufficient ultrasonic energy is concentrated within volume while they propagate through tissues, the temperature in the focal region may be raised to levels at which the tumors are cooked, resulting in tissue ablation. This process occurs without any damage to surrounding or overlying tissues, and the tissue ablation technique that employs such beams is known interchangeably as high intensity focused ultrasound (HIFU).

HIFU is a different therapy from conventional hyperthermia, which has been used as an adjuvant to radiotherapy and chemotherapy for cancer treatment since the 1980s. The purpose of hyperthermia to raise the temperature of the tumor from 37℃ to 42-45℃, and to maintain uniform temperature distributions in a narrow therapeutic range for 60 minutes. However, the temperature distributions induced in vivo are usually non-uniform because of tissue cooling by blood flow, and it is extremely difficult to avoid local cold spots that do not reach the necessary therapeutic temperature level. With HIFU, the temperature within the focal zone is rapidly raised to temperatures between 56℃ to 90℃ and is held for one second. The rapid deposition of HIFU thermal energy causes a peak temperature rise that is unaffected by blood flow cooling. Therefore, it can avoid the problem of non-uniform temperature distribution in hyperthermia, and there is no need for inserting thermocouple probes into the targeted tumor to describe temperature distribution during HIFU procedures.