With the rapid development of science and technology and China's medical and health care industry, medical X-ray and CT machines have been upgraded in municipal and county-level hospitals in China, and multi-slice spiral CT has also been gradually applied in provincial and municipal key hospitals. The tube is an expensive and consumable central component in CT, with a purchase price ranging from tens of thousands to over a million yuan. During the scanning process (especially for tubes with sufficient exposure times), tube faults are often reported. A thorough inspection and analysis should be carried out. Non-fatal faults should be repaired and eliminated in a timely manner to restore normal scanning. This not only reduces downtime, ensures good social benefits, but also effectively extends the service life of the tubes and creates good economic benefits. This article separates the relevant materials and my own understanding in work to briefly discuss some issues related to ball tubes, hoping to serve as a starting point for further discussion. We sincerely hope that all experts and fellow teachers will offer corrections if there are any inappropriate points.

The structure and composition of a tube

A common CT tube is composed of a tube core, a tube sleeve and a matching oil circulation cooling part. The tube core is further made up of a rotating anode, a filament, a tube core glass shell, etc.

2. Factors Affecting the service life of tubes

The main factors affecting the service life of CT tube balls are as follows:

2.1 Commissioning of the tube ball device

The filament voltage, current, etc. should be strictly adjusted in accordance with the technical parameters of the tube ball. Calibration of the front and back positions, kV, mA, etc. should be done well. Regular detection of various parameters and timely adjustment should be carried out. Otherwise, it will not only affect the lifespan of the tube ball, but also the image quality, and even lead to artifacts.

2.2 Setting of Scanning technical conditions

The main conditions include: kV, mA, scanning time (the time required for the tube ball to rotate once), layer thickness, pitch, scanning range, reconstruction method and other parameters.

2.3 Working status of the tube ball cooling system

Most CT tube cooling systems adopt the method of air-cooled and oil-cooled tube balls. It is extremely important to pay close attention to the working efficiency of the tube ball cooling system. The important task is to regularly clean the dust on the filter screen and the radiator to keep the air flow rate in a good state and improve the cooling efficiency.

2.4 Quality issues of the tube balls themselves

The rational application of the tube ball is mainly manifested in the control of the scanning heat capacity. Under the condition of not affecting the image quality, the MAS should be appropriately reduced according to the scanning requirements and the actual human body scanning images. Patients undergoing spiral scanning and axial scanning should be examined in combination, and the pitch should be adjusted according to different parts. Regularly check the power supply parameters of the tube balls and the working status of the cooling system. After formulating the working routine for each CT machine through the above methods, it is requested that the operators strictly implement it. After more than two years of observation, the uniform service life of the tube balls has improved significantly.

Daily maintenance and care of 3-CT tubes

3.1 External three-phase power supply detection.

This includes the phase of the three-phase power supply, the balance and stability of the phase amplitude, the balance of the phase amplitude without phase shifting, the resistance value of the ground wire, and whether the grounding is good or not.

3.2 Eliminate animals such as rats and cockroaches.

It is not uncommon for them to bite through wires and contaminate circuit boards, causing fires.

3.3 Temperature and humidity in the computer room.

If the temperature is too high or too low, the electronic circuit cannot work properly. The working environment is too dry, which can easily cause static electricity. A too humid working environment can easily cause short circuits in the circuit due to moisture such as oxides and dust. The working environment temperature is usually maintained between 20 and 300 degrees Celsius, with a temperature change rate of no more than 30 degrees Celsius per hour. The humidity is 75%, and the humidity change rate is no more than 5% per hour.

3.4 Detection of various working parameters of the CT tube, including kV, Ma, temperature, etc. of the CT tube.

3.5 The high-voltage cable has good contact with the ball pipe, and the contact components are free of impurities. It should be inspected once every two years.

Common faults and maintenance of 4-ball tubes

Regarding the fault phenomena caused by the ball tube and its high pressure, we roughly summarize them according to the composition as follows:

4.1 Filament issues: Common filaments are open or semi-open

The problem is manifested as follows: no exposure after applying high voltage, no tube current or unstable current, and a filament open circuit (or Low mA) prompt. Under the condition that the filament power supply is normal after checking, the filament resistance is mostly an open circuit of the bulb filament. It should be noted that sometimes the filament is in a semi-open circuit state, sometimes on and sometimes off. During operation, heating causes an open circuit, and when power is cut off, cooling causes it to reconnect. This often leads to misjudgment and requires repeated identification.

4.2 The vacuum degree of the core drops or the core glass shell is damaged

The fault is manifested as: when checking the fault code, it usually prompts an overload alarm. One situation is that after long-term use of the core, the filament evaporates, the target surface is damaged and vaporized, and the vacuum degree of the core decreases. Secondly, if the tube is not used for a long time, gas may seep into the core, or the core shell may age and crack, allowing oil to seep in. High-temperature carbonization generates gas, causing the vacuum degree of the core to drop.

4.3 The rotating anode does not rotate

Fault manifestation: The alarm shows a fault with the rotating anode. This problem usually has the following two causes: One is that the stator coil of the rotating anode is damaged (open circuit or short circuit); The second reason is that the rotor of the rotating anode gets stuck or the bearing wears out, resulting in excessive clearance. After being powered on, the distributed magnetic field becomes unbalanced and gets stuck.

4.4 High-pressure ignition inside the pipe sleeve

When such faults occur, the alarm shows overload. Loose high-voltage cable plugs, reduced sealing and insulation between them and sockets, or cracked high-voltage plugs can all cause intermittent sparking. In severe cases, overload alarms will occur and the scanning will be interrupted. In the image reconstructed from the sparking, thin interference lines will appear. When the high-voltage cable plug is pulled out for inspection, it can be found that there are obvious discharge, carbonization and burning marks on the plug and socket, accompanied by a pungent smell. After cleaning thoroughly with anhydrous alcohol and gauze, it can be restored to normal by resealing the high-pressure rubber pad, high-pressure silicone or insulating oil.

4.5 Internal ignition of the core

The fault is manifested as: Overload immediately upon startup of exposure, indicating overload (Over mA), which usually occurs in tubes with a large exposure count. Sometimes, it can still be scanned after reducing the kV and mA, but the image quality is poor. After long-term use of the core, the filament evaporates, the target surface is damaged and vaporized, and the vacuum degree of the core decreases. Or due to cracks in the glass shell under high-temperature oil pressure, gas may seep into the core. Or the core shell ages and cracks, oil seeps in, high-temperature carbonization generates gas, the vacuum degree of the tube core drops, and the tube is scrapped.

4.6 The pipe sleeve is leaking oil

Slight oil leakage does not affect work. However, when the oil leakage is significant, there will be bubbles inside the tube sleeve, and during scanning, overload (sparking inside the sleeve) will be presented. Visual inspection can reveal the leakage. Careful examination can locate the leakage point, which is mostly caused by loose pipe joints or aging of the sealing gasket. Tightening the joint or replacing the gasket can restore normal operation.

4.7 The tube is overheating

The faults are manifested as: too long waiting time for cooling during scanning, indicating temperature or oil pressure problems, mostly faults in the ball tube oil circulation cooling system. It can be detailed into:

4.7.1 The radiator grille was clogged with dust, resulting in poor heat dissipation. It returned to normal after dust removal.

4.7.2 If the cooling fan does not rotate, it is mostly due to damaged windings or stuck bearings. Change the fan.

4.7.3 The circulating oil pump is broken. If the oil pump motor is broken, the bearing is stuck or the oil pump is damaged, repair or replace it.

4.7.4 The filter screen of the CT spherical tube oil circuit is blocked. If there are too many impurities or foreign substances in the insulating oil, cleaning and changing the oil can work normally.

There are many factors related to the identification of tube faults. How to clearly distinguish whether it is a tube problem is rather complex. We can break it down into:

(1) Fault in the high-voltage control circuit; (2) High-voltage inverter (trigger) fault; (3) Malfunction of the anode rotation controller; (4) Anode inverter trigger fault; (5) Filament circuit failure; (6) High-voltage cable breakdown; (7) Abnormal reaction resistance in the high-pressure oil tank; (8) Breakdown of silicon stacks in high-voltage oil tanks, etc.

The rational application of the tube ball is mainly manifested in the control of the scanning heat capacity. Under the condition of not affecting the image quality, the mAS should be appropriately reduced according to the requirements of the scanning area and the actual human body scanning image. Regularly check the power supply parameters of the tube balls and the working status of the cooling system. By formulating the working routine for each CT through the above methods and requesting the operators to strictly follow them, the service life of the CT can be greatly improved.