ALLPCB
To use a helical CT properly, it is essential to apply practical measures from installation through normal operation. Equipment should operate in a suitable environment, and operators should understand key principles so they can use the system correctly. Proper practice helps the scanner perform reliably while minimizing operating costs.
Helical CT scanners have been rapidly adopted in many hospitals in recent years, improving diagnostic imaging quality. However, rapid adoption has left some hospitals, especially at the district and county level, with questions about how to use the equipment efficiently, extend component life, and reduce wear. Insufficient training from distributors and manufacturers has led to avoidable wear and higher failure rates. CT users should acquire a basic understanding of their helical CT's working principle and characteristics, and accumulate operational experience to keep the system in good condition.
Many helical CTs currently in use were installed after 2000. Based on operational experience, the following recommendations are offered for reference.
1. Room selection and installation requirements
The CT room should be sited where vibration is low, there is no significant electromagnetic interference, noise is low, and air cleanliness is relatively high. If possible, consider proximity to the power distribution room and convenient patient access and equipment installation. Placement of major components should balance operational safety, maintenance access, patient flow, operator convenience, and ventilation. Minimize interference between work areas, for example the locations of voltage stabilizers, power distribution equipment, workstations, cameras, film processors, and high-pressure injectors.
Cable routing should avoid AC electromagnetic sources such as transformers, inductors, and motors. Signal lines and power lines should be shielded and routed separately. Where necessary, use cable ducts lined with sheet metal and fitted with covers and rodent protection. If cable runs are long, lay them in serpentine loops rather than folding or coiling them tightly.
The system computer should be backed by a UPS to prevent sudden power loss that could corrupt data or damage software. The CT system power feeder capacity should exceed the unit's rated total power by 10%–20%. The CT must have a good grounding arrangement; the grounding resistance should be less than 2 Ω and checked semiannually. The resistance between the grounding terminal and all grounded metal parts should be less than 0.1 Ω.
2. Fully warm up the system after power-on
Before scanning the first patient after power-on, fully warm up the system so the X-ray tube filament is thoroughly heated. Running a scan before the filament and associated circuitry are warmed can damage the tube and degrade image quality.
3. Maintain a clean environment and keep the machine interior dust-free
Clean the CT room daily and remove dust inside the system at regular intervals. Minimizing dust ingress lowers the failure rate of electronic components, reduces contamination of the slip ring, and reduces friction between slip ring and carbon brushes. Good ventilation and heat dissipation preserve system reliability.
4. Regular inspection of wear parts
Based on workload and patient volume, perform periodic maintenance of slip rings and carbon brushes. Under conditions where 5,000 patients are scanned or the slip ring has rotated about 400,000 revolutions, clean the slip ring and carbon brushes and check carbon brush wear. Carbon brushes have replacement marks; replace them when they reach or approach the mark to prevent copper leads from contacting and damaging the slip ring. Regularly inspect frequently rotating parts and verify lubrication status.
5. Start and stop scans promptly
When the gantry has reached constant rotation speed and is ready for helical exposure, the tube filament is driven into full-load heating. The operator should start exposure promptly. Failure to start exposure wastes slip ring and carbon brush life and subjects the filament to unnecessary full-load heating. After a scan, promptly exit the scanning state so the filament returns from full-load to standby preheat and the slip ring stops rotating. This extends the service life of the tube, slip ring, and carbon brushes. In other words, minimize the ratio of slip ring revolutions to tube exposures; generally control it within 10:1 or lower. The exact ratio depends on the machine and vendor definitions of exposure counting.
The table below (from GE's HIS-PEED DXI single-slice helical CT) shows minimum ratios of slip ring revolutions to tube exposures for several exposure modes and the effect of repeated scans in an adrenal study due to poor patient cooperation. During helical scanning, the exposure counter registers one exposure per second; in axial scanning the counter registers one exposure per reconstructed image; each topogram (localizer) counts as one exposure.
Based on these principles, when an operator receives a scan request, review the patient's condition and plan the scan sequence carefully. Define the primary scan region and aim to complete necessary exposures within a single planned sequence to avoid unnecessary pauses, additions, and waits. For organs influenced by respiration, it is better to design a slightly larger scan range to avoid supplemental scans, since waiting and supplementary scans impose significant wear. Diagnostic physicians should understand scanning technique in addition to interpreting images; breaking the old model where technologists only scan and physicians only read images reduces missed lesions and unnecessary exposures. When appropriate, the diagnostic physician performing the scan can reduce patient dose and equipment wear while improving diagnostic accuracy.
