secondary focusing principle of HIFU piezo

HIFU uses secondary HIFU piezo ceramic technology to transmit ultrasonic waves from multiple probes to outside the patient's body, and focuses of the lesion to form a high-intensity focal spot similar to the size of rice. Producing high temperature to burn cancer cells. For the purpose of treatment, the ultrasound intensity of a single probe through the body is much lower,it is no harm to the human body. High-energy Hifu piezoelectric ceramic transducer has obvious advantages such as no pain, no surgery, few side effects, short treatment and recovery time. It has become a hot spot in the research of tumor treatment equipment, and has now entered clinical application. However, because the accuracy of HIFU focal spot is difficult to control, even in the course of treatment, even the phenomenon of off-target and other surrounding organs is seriously affected, and HIFU piezoelectric crystal has not become a reliable tumor treatment.

There are many factors affecting the accuracy of HIFU focal spot. From the probe to the human lesion, the ultrasound should pass through the water medium, the sound-permeable membrane, the coupling agent, the human skin fat and the internal organs. All the factors affecting the ultrasound propagation will affect the accuracy of the HIFU focal spot. This paper only introduces the research and exploration to improve the accuracy of HIFU focal spot during the development of equipment from the perspective of HIFU equipment.

Piezoelectric ceramic sheets in a single ultrasonic probe generally have a flat sheet and a spherical sheet. The spherical sheet can be used to obtain a contract sound field, which is one focus, The focal spot depth of a single probe is too small. Generally, the HIFU treatment contains multiple probes, up to more than 500. Several probes are mounted on the spherical inner surface of the treatment head, and the sound field axis intersects at the center of the sphere. The focal spot with high intensity is formed. This is the “secondary focus”. The treatment head can realize three-dimensional movement under the control of the three-dimensional motion mechanism. The doctor scans the lesion with the B-ultrasound probe at the center of the treatment head and processes it through computer software. According to the information, the computer controls the three-dimensional motion mechanism according to the information, and uses the focal spot of the treatment head to irradiate the lesion according to a certain “travel route”. The local high temperature generated by the focal spot of high intensity focused piezo is enough to organize the tissue at the lesion. "burned to death." In order to reduce the damage of the ultrasound through the single probe of the human body, the treatment head slowly swings during the treatment. Ultrasound attenuates rapidly in the air, and refraction and reflection occurs at the interface of different media. Therefore, the treatment head must be placed in the degassed water. The bottom of the pool is a film with good sound permeability, coated between the human body and the sound-permeable membrane.

The multi-probe secondary focus mainly controls the angular deviation of the center normal of the positioning surface of the spherical focusing body probe. Practice has shown that if the beta value of the probe is too small,There are too many piezoelectric ceramic sheets, so the value should be reduced, and the measurements are taken are mainly combined with the design and manufacture of the focusing body. The treatment head is connected to the movement mechanism through the upper flange, and is positioned by the flange end face and the center hole. The treatment head adopts stainless steel castings, firstly it flanges the end face and the outer circle,which completes the center hole, and then fix it with the flange end face and the outer circle is positioning clamp and the center hole, it rotates the horizontal worktable 25° to process the probe mounting hole,The indexing head rotates the treatment head 45° around the central hole axis to process the next probe mounting hole. Since the machining of the center hole and the probe mounting hole for positioning is performed in one setup, as long as the machine precision is ensured,ultrasonic high focus piezoelectric ceramics ensures that the probe mounting hole axes intersect on the center hole axis.