A. Basic structure of CT scanner

 

After years of development, CT scanners have undergone significant improvements, including an increase in the number of detector layers and faster scanning speed. However, their hardware components remain largely the same and can be divided into three main parts:

 

1）X-ray detector gantry

2）Computerized console

3）Patient table for positioning

4）Structurally and functionally, CT scanners consist of the following components:

 

The part responsible for controlling computer scanning and image reconstruction

The mechanical part for patient positioning and scanning, which includes the scanning gantry and the bed

High-voltage X-ray generator and X-ray tube for producing X-rays

Data acquisition and detection component for extracting information and data

Based on these fundamental structural characteristics of CT scanners, one can determine the basic direction for troubleshooting in case of malfunctions.

 

Two classifications, sources, and characteristics of CT machine faults

 

CT machine failures can be classified into three types: failures caused by environmental factors, faults resulting from improper operation, and failures due to aging and component deterioration within the CT system, leading to parameter drift and mechanical wear.

 

1）Failures caused by environmental factors

Environmental factors such as temperature, humidity, air purification, and power supply stability can contribute to CT machine failures. Insufficient ventilation and high room temperatures can cause appliances such as power supplies or transformers to overheat, potentially leading to circuit board damage. Machine interruptions and excessive temperature drift resulting from inadequate cooling can generate image artifacts. Surges in CT supply voltage can disrupt proper computer functioning, causing instability in machine operations, abnormal pressure, X-ray instability, and ultimately affecting image quality. Poor air purification can result in dust accumulation, leading to malfunctions in optical signal transmission control. Excessive humidity can cause short-circuits and electronic device failures. Environmental factors can pose significant harm to CT machines, sometimes even causing permanent damage. Therefore, maintaining an optimal operating environment is crucial for minimizing CT machine faults and extending their service life.

 

2）Faults caused by human error and improper operation

Common factors contributing to human error include lack of time for warm-up routines or calibration, resulting in abnormal image uniformity or quality issues, and incorrect patient positioning leading to undesirable images. Metal artifacts can be produced when patients are wearing metallic objects during scans. Operating multiple CT machines simultaneously can lead to crashes, and improper selection of scanning parameters can introduce image artifacts. Typically, human errors do not cause severe consequences, as long as the underlying reasons are identified, proper procedures are followed, and the system is restarted or re-operated, thereby successfully troubleshooting the issues.

 

3) Hardware failures and damage within the CT system

CT hardware components may experience their own production failures. In most mature CT systems, failures occur according to a saddle-shaped trend over time, following statistical probability. The installation period is characterized by a higher failure rate in the first six months, followed by a relatively stable low failure rate during a long period of five to eight years. After this period, the failure rate gradually increases.

 

 

a. Mechanical part failures

 

The following major faults are mainly discussed:

 

As equipment ages, mechanical failures increase every year. In the early days of CT, a reverse rotation mode was used in the scan cycle, with a very short rotation speed that switched from uniform to slow and stopped repeatedly. This led to a higher rate of mechanical failure. Issues such as unstable speed, uncontrollable spinning, braking problems, and belt tension issues were common. Additionally, cable wear and fractures occurred. Nowadays, the majority of CT machines use slip ring technology for smooth one-way rotation, and some high-end machines even incorporate magnetic drive technology, significantly reducing breakdowns in rotating machinery. However, slip rings introduce their own set of faults, as prolonged friction can result in poor contact and trigger mechanical and electrical failures such as uncontrolled spinning, high-pressure control, ignition (in the case of high slip rings), and loss of control signals (in the case of slip ring transmission). Regular maintenance and replacement of slip rings is essential. Other components, like X-ray collimators, are also prone to mechanical failures such as getting stuck or going out of control, while fans may fail after long-term operation. The pulse generator responsible for motor rotation control signals may experience wear or damage, leading to pulse loss phenomena.

 

b. X-ray component-generated faults

 

X-ray CT machine production control relies on several components including high-frequency inverters, high-voltage transformers, X-ray tubes, control circuits, and high-voltage cables. Common faults include:

 

X-ray tube failures: These include rotating anode failure, manifested by loud rotating noise, and serious cases where switching becomes impossible or the anode gets stuck, resulting in overcurrent when exposed. Filament failures can cause no radiation. Glass core leakage leads to rupture or leakage, preventing exposure and causing vacuum drop and high-voltage ignition.

 

High-voltage generation failures: Faults in the inverter circuit, breakdowns, short-circuits in the high-voltage transformer, and ignition or breakdown of high-voltage capacitors often cause the corresponding fuse to blow. Exposure becomes impossible or is automatically interrupted due to protection.

 

High-voltage cable faults: Common issues include loose connectors causing ignition, overvoltage, or high voltage. In early CT machines, prolonged use can lead to wear and tear on high-voltage ignition cables, resulting in internal short-circuits. These failures usually correspond to a blown fuse.

 

c. Computer-related faults

 

Failures in the computer part of CT machines are relatively rare and usually easy to repair. They mainly involve minor issues with components such as keyboards, mice, trackballs, etc. However, failures in hard disks, tape drives, and magneto-optical devices can occur as a result of prolonged use, with an increase in bad zones leading to total damage.

 

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