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What This Guide Helps With
Troubleshooting CT exposure aborts, warmup interruptions, gantry faults, or generator-ready issues using safe external checks before service escalation.
Step-by-Step Troubleshooting
Ensure Patient Safety First
Confirm whether a patient is on the PET/CT table or positioned inside the gantry.
If the CT exposure abort, gantry fault, or generator issue occurs during an active exam, stop the scan and have clinical staff assess whether the patient can be safely removed or repositioned.
Expected outcome: The patient is not left dependent on a system with unreliable CT exposure, gantry motion, or scan completion.
Confirm the Exact Reported Fault
Ask the technologist what occurred and when the fault appeared.
Identify whether the issue involves:
- CT exposure abort
- Tube warmup failure
- CT generator not ready
- Gantry rotation fault
- Table or gantry coordination issue
- X-ray inhibit
- Error during scout/topogram, helical scan, or CT attenuation correction
- Fault after system startup or idle period
Expected outcome: The failure type is clearly identified before troubleshooting continues.
Check for Active System Messages
Review the operator console for displayed fault messages, warning codes, tube heat messages, interlock warnings, gantry status messages, or generator-ready indicators.
Do not clear or reset messages until they are documented.
Expected outcome: The reported fault is captured accurately for repair escalation if needed.
Verify the Exam Is Not in an Unsafe or Incomplete State
Confirm whether the scan was aborted before, during, or after X-ray exposure.
If patient images may be incomplete or improperly acquired, notify imaging staff so they can determine whether repeat imaging is clinically appropriate.
Expected outcome: Clinical staff understand whether the exam was completed, partially completed, or failed.
Check Emergency Stop and Safety Controls
Inspect the PET/CT room for activated emergency stop buttons, gantry stop controls, table stop controls, or other safety switches.
If an emergency stop is engaged, determine why it was activated before resetting anything.
Expected outcome: The system is not being inhibited by an engaged safety stop, and any safety concern is addressed first.
Inspect the Gantry Area for Obstructions
Look around the CT gantry, patient table, tabletop, mattress, positioning accessories, straps, cables, IV lines, injector tubing, and floor area.
Remove anything that could interfere with gantry clearance, table travel, or patient positioning.
Expected outcome: No external object is blocking gantry operation, table motion, or scan range movement.
Verify Patient Table Position and Scan Range Setup
Confirm the table is properly positioned, the patient is within the intended scan range, and the CT portion of the PET/CT study was planned correctly.
Incorrect positioning or scan planning can appear like a system fault when the system is actually preventing an unsafe or invalid acquisition.
Expected outcome: The CT scan range and table position are appropriate for the selected protocol.
Check Room Door and Interlock Conditions
Confirm the CT room door is fully closed and that any site-specific door, radiation warning, or room safety interlock is satisfied.
Expected outcome: CT exposure is not being blocked by a room safety interlock.
Confirm System Power and Environmental Conditions
Check that the Biograph Horizon system, operator console, CT gantry, acquisition workstation, and supporting equipment appear powered normally.
Look for signs of power disturbance, tripped room power, UPS alarms, unusual heat, burning smell, or abnormal fan noise.
Expected outcome: No obvious facility power or environmental issue is contributing to the fault.
Verify Tube Warmup Requirements
If the issue involves tube warmup, confirm whether the system had been powered off, idle for an extended time, recently restarted, or had heavy CT use.
Follow the normal operator workflow for tube warmup only if the system allows it and no safety faults are present.
Expected outcome: Tube warmup completes normally, or the failure is confirmed as repeatable.
If tube warmup completes and CT exposure becomes available, return the system to clinical staff for appropriate image quality verification and stop.
Allow Appropriate Cooling Time if Heat Is Indicated
If the console indicates tube heat, generator heat, or cooling-related delay, allow the system to cool according to the displayed system guidance.
Do not repeatedly force exposure attempts during heat-related inhibit conditions.
Expected outcome: Exposure becomes available after cooling, or the heat/cooling fault remains and requires escalation.
Check CT Protocol and Workflow Selection
Confirm the selected CT protocol is appropriate for the exam and that the workflow has not been left in an incomplete state from a prior failed acquisition.
Have the technologist attempt a known appropriate non-patient workflow only if site policy allows and no patient safety issue exists.
Expected outcome: The issue is not caused by an invalid protocol selection, incomplete exam state, or workflow mismatch.
Confirm Injector or Accessory Status if Tied to the Exam
If the CT acquisition depends on a contrast injector, respiratory monitor, ECG gating accessory, or other external device, verify that the accessory is ready or intentionally disabled for the protocol.
A connected accessory fault may prevent the scan from proceeding.
Expected outcome: External accessories are not causing the CT acquisition to abort or inhibit.
Restart Only Through Approved Operator Workflow
If the system appears locked in a software-ready state and no patient is involved, coordinate with imaging staff to perform an approved application logout/restart or system restart workflow.
Avoid power cycling gantry or generator components at breakers unless directed by service procedure or vendor support.
Expected outcome: A basic workstation or application lockup is cleared without unsafe equipment handling.
Repeat a Safe Readiness Check
After any reset, warmup, or workflow correction, confirm that the console, gantry, table, and CT acquisition status return to normal ready condition.
If site policy allows, imaging staff may perform the appropriate daily QC, air calibration, or test workflow before returning the system to patient use.
Expected outcome: CT readiness is restored and verified by the appropriate clinical imaging process.
Stop if the Fault Repeats
If the CT exposure abort, tube warmup failure, gantry fault, or generator fault returns after external checks, do not continue repeated exposure attempts.
Repeated faults may indicate a gantry drive, generator, tube, cooling, detector timing, interlock, or system communication problem requiring service evaluation.
Expected outcome: The device is removed from clinical use before repeated failures affect patient care.
If the Problem Persists
If the problem persists, common external causes have been ruled out and the fault is likely internal to the CT gantry, X-ray generator, tube cooling system, gantry rotation system, power distribution, or system control communication.
The Biograph Horizon should be:
- Removed from service
- Labeled Out of Service
- Escalated for Siemens service, repair, or bench/system evaluation
Knowing when to stop is proper troubleshooting. Repeated CT exposure attempts, repeated warmup failures, or unresolved gantry/generator faults should not be treated as routine operator issues.
Clinical Use Tip
Do not troubleshoot CT exposure, gantry motion, or generator faults with a patient positioned in the scanner unless immediate patient safety requires controlled removal. Move the patient to another approved imaging workflow before continuing troubleshooting whenever possible.
Work Order Documentation (CCR Method)
CCR = Complaint, Cause, Resolution
Complaint
What was reported by the clinical staff.
Example:
"CT technologist reported the Biograph Horizon aborted CT exposure during the scout scan and displayed a generator-not-ready message."
Cause
What was observed during troubleshooting.
Example:
"Verified no patient was on the table, checked emergency stops, room door interlock, gantry clearance, scan setup, and tube warmup status; fault repeated during readiness check."
Resolution
What action was taken.
Example:
"Removed the PET/CT system from service, labeled it Out of Service, documented the displayed fault message, and escalated to Siemens service for CT generator and gantry evaluation."
Helpful Details to Include (If Known)
- Whether a patient was on the table when the fault occurred
- Exact console message or fault code
- Whether the issue occurred during startup, warmup, scout, helical scan, or attenuation correction CT
- Whether emergency stop buttons were checked
- Whether room door and radiation interlocks were verified
- Gantry indicator lights or unusual sounds
- Tube heat or cooling messages
- Whether tube warmup completed or failed
- Whether the table and gantry moved normally
- Any unusual heat, smell, vibration, or noise
- Whether the fault cleared after approved restart
- Final device status
Final Thought
CT faults on a PET/CT system should be approached carefully because they can affect patient throughput, image quality, radiation exposure workflow, and scan completion. Start with patient safety, verify simple external causes, document exact messages, and escalate when the system shows repeatable exposure, warmup, gantry, or generator failure.
That is successful troubleshooting.