The lithotripsy is a non-invasive treatment device, so the damage to the human body is small, the treatment effect is good, and it is widely used in clinic. It is mainly composed of four systems: work (charging and discharging circuit, shock wave source), positioning, computer aid and operation (operating table and bedside operation panel).
1. Working System
The principle of work: electromagnetic energy is converted into mechanical energy. When ultrasonic waves pass through different media, due to the different density of the media, the impact direction will change. The density of the human body is not much different from the density of water, so there is no change on the surface of the human body in contact with water, and the density of the human body is very different from the density of stones, so the shock wave will produce a mechanical push and pull effect on the surface of the stones. Thus crushing the stone.
The methods of generating shock wave sources can be divided into three categories: hydroelectric shock wave sources, piezoelectric shock wave sources, and electromagnetic shock wave sources. The shock wave source is mostly hydroelectric type. Because of its early development, mature technology and good crushed stone effect, it is widely used. The electromagnetic shock wave source has a relatively new development, stable energy, and the manufacturing process is simpler than the piezoelectric type and the focus is good. The damage to the human body is relatively small, so it is more and more used. The following discusses the comparison between electromagnetic and hydroelectric shock wave sources. Electromagnetic wave gravel discharges an inductive coil through a high-voltage capacitor, and the generated pulse current forms a strong pulse magnetic field, which induces a magnetic field induced by the diaphragm covered by the coil. The interaction between the magnetic field of the diaphragm and the coil generates a repulsive force. Shock waves are formed on the other side of the diaphragm in the medium, and then focused by a lens (double concave lens), the focal point coincides with the stones in the body, and it is crushed. Electromagnetic shock wave is a plane wave. It is focused through the lens. There is no shock wave that directly hits human tissue without focusing, which avoids the damage of direct waves to human tissue. The hydroelectric shock wave is generated by electrode discharge. Spherical wave, the part of the spherical wave reaching the reflecting cup is reflected, and after reflection, it is focused on the second focal point. The reflection cup is open, and a considerable part of the shock wave is not focused, but directly impacts the human body, and the energy of the hydroelectric shock wave is relatively large, thereby causing certain damage to the human body.
The electromagnetic shock wave is generated by the discharge of the magnetic disk. The electric magnetic disk will only be damaged during use without deviation. After the shock wave is focused by the lens (dual concave lens), the focus position will not drift and the focal spot size will not change, as long as it is positioned Accurately, the shock wave energy is concentrated on the stones, so it will not cause harm to human tissues. Electro-hydraulic shock waves use electrode discharge. As the electrode wears out, its tip becomes thicker, and the edge of the electrode tip forms a discharge phenomenon. The resulting shock deviates from the first focus. After being reflected by the reflective cup, the deviation at the focus point will increase Several times, the second focal point will become a large focal spot. The focal spot is too rough to concentrate the shock wave energy on the stones, and some healthy tissues will be impacted, causing some damage.
Second, the positioning system (LocaTIng System)
At present, two positioning systems of medical X-ray and B-ultrasound are used for positioning. In X-ray localization, fixed double bulbs and double image intensifiers were used for positioning in the past, which is economically expensive, and it is difficult to avoid the obstruction of bone tissue, the image cannot be seen clearly, and the operation is also complicated. Mobile C-arm single-tube x-ray machine, C-arm can do plane rotation or spherical motion with the shock wave focus f as the center, X-ray projection center can rotate the C-arm arbitrarily by an angle through the focus f, and then it can be positioned This type of positioning system has accurate and fast positioning and relatively low cost, so its advantages are far greater than the former. The system can position kidney and ureteral stones in all directions.
X-ray positioning: Intuitive, accurate, convenient and fast, it uses three-dimensional coordinate positioning, the cost is relatively high, and it has a certain harm to the human body, so it is required to be exposed as short as possible, the dose of X-ray is as small as possible, Protection requirements are also high; B-ultrasound positioning: it is a polar coordinate positioning method, which can display both yin and yang stones, can be tracked in real time, has little harm to human bodies, has high technical requirements for operators, and has poor image quality X-ray machine is difficult to confirm. It is not as intuitive, convenient and fast as X-ray machine positioning, so now there are many K-ray positioning, and B-ultrasound can assist positioning (when economic conditions permit).
3. Computer Supplementary Systerm
The computer-aided system is equipped with a digital medical imaging system (DMIS: Digital Medical lmaging System). There are two main functions: (1) Data collection and storage (Date CollecTIon / storage). (2) Image capture (Imaging Grasp), a video capture card is added to the computer configuration, that is, a dynamic video capture / playback card, which can capture dynamic video and audio signals at the same time, and compress, store, and playback. Its functions It converts PAL signal to SVGA signal (Super Video Graphic Array).
4. Frequent failures and attention problems 1. The positioning system is faulty. The porcelain core of the X-ray machine high-voltage distribution cabinet is fused, which is usually the breakdown of the high-voltage cable of the X-ray machine. This situation can be repaired (the specific repair method is not repeated, please refer to Relevant information), can be replaced directly under economic conditions.
Constant insurance, when starting the hand brake or pedal (1) The mA meter swings slightly, the bulb filament is bright, it may be that the high-voltage cable of the X-ray machine is broken or the anode and cathode are not in good contact; (2) the bulb filament is not bright The mA meter does not oscillate. This kind of situation rarely occurs, generally the tube is broken; (3) There is a loud noise, like the air is broken or the electrode discharge sound, there may be an X-ray machine tube leaking oil, causing air to enter The tube is broken, the air is broken, this situation can be repaired (please refer to the relevant X-ray machine maintenance information).
2. The capacitor box does not discharge after the trigger switch is activated during the failure treatment of the work and discharge system. Reasons for failure: (1) Capacitor may leak and damage for a long time, and a new capacitor group needs to be replaced; (2) The discharge gap of the trigger ball is too large to trigger. Treatment method: The gap can be adjusted appropriately.
Continuous discharge: (1) When the discharge voltage of the capacitor box is set to low kV, the cause of the failure: the metal copper trigger ball is unclean due to high-frequency discharge, the surface is oxidized and carbonized, and the gap is relatively reduced, causing continuous fire and discharge . Treatment method: The surface can be lightly treated with sandpaper, and then wiped with absolute ethanol or the gap is adjusted appropriately; (2) When set to high kv (kV is within the allowable range), the cause of the failure: the capacitor group is used for a long time , The withstand voltage has not reached the requirements, the capacitor group needs to be replaced; or the gap of the trigger ball is relatively small, and the gap can be adjusted appropriately.
3. Pay attention to the problem. The center of the focus is often calibrated with a positioning pin to avoid positioning errors and inaccuracies, resulting in unnecessary harm to the patient.
The grounding of the capacitor box must meet the standard, and industrial salt must be added regularly to achieve a good conductive function of the grounding, to minimize leakage as much as possible, and to avoid injury to operators and patients.
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