High intensity focused ultrasound for tumor therapy(一)

Considering the basic requirements of real-time imaging of tumor treatment ,It includes compatibility considerations and cost control requirements of the ultrasound therapy machine itself, the domestic commercial HIFU piezo ceramic ultrasound tumor treatment machine has selected B-ultrasound as for the focus position. As well as real-time evaluation and control of the treatment effect, the B-ultrasound probe should have a detecting depth of between 18 and 25 mm except for size. Generally, non-contacting small convex array transducers should be used, such as EuPc 3 l l T for Hitachi EUB 420 and CSH l for CTS 4 used by domestic Shantou Institute of Ultrasonic Instruments. The patient's body and the B-ultrasound are combined with vacuum water that is close to the acoustic impedance of the human body, and some commercial machines use transducers. The focal plane of the high intensity focused ultrasound transducer falls in the relative fixed position in the B-mode of view and should be calibrated. In order to avoid the influence of high-intensity ultrasound by B-ultrasound imaging, the interval working system is generally adopted, that is, the working time of B-ultrasound is separated from the working time of high intensity focused piezoelectric ceramic.

There are several ways to locate the lesion: CT scan + negative pressure positioning ,First, the patient is fixed in a specific position with a negative pressure and scanned into a CT machine to obtain the spatial position coordinates of the lesion in the negative pressure coordinate system; then the negative pressure is  sent to the focused ultrasound therapy machine along with the patient. The relative position between the ultrasonic therapy machine and the negative pressure has been corrected in advance. Therefore, the absolute position coordinates of the tumor in the therapeutic machine coordinate system can be accurately determined, and treatment can be started. In this way, the main role of B-ultrasound in the treatment process is to evaluate the effect of the treatment point, and to perform therapeutic ultrasound dose , and the treatment position adjustment. The biggest advantage of this method is that its positioning is accurate, but the processing time is too long, and because the negative pressure is used as the reference for the alignment of different coordinate systems, the patient is forced to fix for a long time, and the body feels uncomfortable. 

The intersection of the scanned image is called for the ellipsoid approximation, regardless of the shape of the tumor, an optimal ellipsoid is used instead.Because in general, the ideal focal length of high-intensity focused piezo crystal is ellipsoidal, although the actual shape will first find the center of the tumor through B-ultrasound, and record the coordinates of the center position, record the corresponding B-scan plane.It is the best circumscribing rectangle of the inner tumor; then rotate the B-scan plane to the position of thogonal to the previous scan plane to obtain another optimal rectangle circumscribing ,according to the two orthogonal rectangles ,the smallest volume circumscribes is cube, resulting in such a treatment section ellipse.