CT Tube Arcing
Vacuum-integrity loss inside a rotating-anode CT X-ray tube — the most common end-of-life failure mode on modern CT tubes. As tube vacuum degrades over the operational lifetime (gradual outgassing of internal materials, anode-track erosion releasing tungsten / molybdenum vapor, eventual filament wear), the ability to sustain high kVp without ionization breakdown decreases. The failure manifests progressively, then abruptly.
Symptoms
- kVp instability during high-power protocols — most visible on cardiac CCTA and high-mA chest / abdomen scans.
- Dose-output spikes / drops during acquisition, sometimes as transient mA fluctuations on the scanner log.
- Acquisition interlocks / aborts mid-scan as the system protective circuitry detects an arc event.
- Audible discharge in some cases — popping / clicking from the tube during ramp-up. Operators sometimes notice this before the scanner does.
- Image artifacts — streak artifacts on reconstruction during the affected acquisition.
Diagnosis
- Tube-arc counter in the service log — most modern CT systems track arc events and trend them. Rising arc count is the canonical predictive indicator.
- kVp linearity test — acceptance test reveals instability before clinical impact.
- Tube conditioning history — if the system has been performing extended tube conditioning cycles automatically more often than baseline, vacuum degradation is in progress.
- Tube-hour and scan-count correlation — arc events accelerate sharply past tube end-of-life thresholds.
Affected parts
- Siemens STRATON
- Siemens Vectron
- Canon MegaCool
- Philips MRC
- GE Gemstone Clarity
- GE Performix HDw
- GE Performix Pro VCT
Operational implications
- Predictable end-of-life event — arc-counter trending typically gives weeks-to-months of warning before clinical impact, enabling scheduled tube replacement vs emergency-room downtime.
- Tube conditioning cycles can extend lifetime modestly but do not reverse vacuum loss.
- Refurb tubes generally exhibit accelerated arc-counter ramp vs OEM-new tubes — relevant for refurb-deal underwriting.
Replacement path
See the individual tube parts pages and CT Decommissioning. Tube replacement is a full-day scheduled service event with calibration suite + acceptance testing.