High Intensity Focused Ultrasound technology (HIFU)
HIFU technology uses a high-intensity convergent ultrasound beam generated by high power transducers to produce heat.
HIFU is intended to allow the surgeon to necrose prostatic tissue without damaging surrounding tissue, thus eliminating the need for incisions, transfusions, general anesthesia and their resulting complications. The development of ultrasound transducers started with the work of P. Langevin, who used, in the 20th century, the piezoelectric properties of quartz crystal to build the first submarine sonar.
History : How, when and where it started
In the 1950s, the Fry brothers - Francis and William - invented the first medical application of ultrasonic waves.
Their first works were related to the extra-corporeal treatment of neurologic disorders - Parkinson disease. Using a set of ultrasound transducers focused on the area to be treated, they could realize tiny biological lesions located deep inside the cerebral cortex. But the lack of an imaging device with enough performances and accuracy stopped the development of this type of therapies.
The use of HIFU in the treatment of cancer in both human and animal models was examined by Burov in 1986. Irradiation of experimental tumors using HIFU followed in the late 1970s and early 1980s and in 1986, Lizzy applied HIFU in the treatment of certain ocular cancers and glaucoma. This approach has been rapidly replaced by laser.
At the end of the 80s, the Inserm - French Institute for Medical Research - Lyon Hospitals and EDAP TMS, engaged in a research program on the interaction of High Intensity Focused Ultrasound (HIFU) on tissues. The main purpose of this work was to develop applications to treat malignant tumors: the prototype of the Ablatherm® was born.
Mechanism of HIFU action
The basic principle of transrectal high intensity focused ultrasound (HIFU) is the precise destruction of prostatic tissue in one session, which is achieved by depositing large amounts of energy into it. Ultrasound waves, generated by the high frequency vibration (0.5 – 10 MHz) of a piezoelectric or piezoceramic transducer, are focused into a small discrete region (the focal point) by concave or parabolic arrangement.
Coupling and cooling is performed by degassed colored liquid as interface between the source and the patient’s rectal wall. Due to the similar physical properties of water and tissue as well as the broad flat coupling surface, ultrasound waves penetrate with minimal absorption or reflection. As the converging ultrasound approaches the focal point, the power density increases.
The two principle mechanisms of action of HIFU are based on thermal and mechanical effects.
The thermal effect of HIFU is associated with the absorption of ultrasound energy into the tissue, which is converted into heat. Temperature elevation in the tissues depends on the absorption coefficient of the tissue as well as the size, shape and thermal response. The biological changes that are induced by heating depend on the temperature reached and the duration of the exposure (the thermal dose). Above a certain threshold, thermal doses induce irreversible tissue damage in the form of coagulative necrosis. Below the threshold, thermal dose effects depend on the sensitivity of the neighboring tissue, as can be seen in the sharp temperature gradient between the necrotic lesion and the normal cells in histological samples.
From the mechanical standpoint, bubbles form inside the cells due to negative pressure of the ultrasound wave and these increase in size to the point at which resonance is achieved. When the bubbles suddenly collapse, high pressure of 20,000 – 30,000 bars develops and damages nearby cells. This acoustic cavitation is complex and must be controlled in its extension. The two activities together lead to a reduction in prostate volume down to 5 ml.
Hifu Planet a patient web site
HIFU PLANET website was set up to provide patients with useful information relating to prostate cancer treatments and particularly on Ablatherm® HIFU treatment. The web site is now available in several languages.