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What This Guide Helps With
Collimator light, field size, or centering issues caused by setup, SID, positioning, accessory, or collimator alignment problems.
Step-by-Step Troubleshooting
Ensure Patient Safety First
Do not troubleshoot collimator alignment or field size problems during an active exposure or while a patient is positioned for imaging.
Action:
- Move the patient away from the table, wall stand, or imaging area if troubleshooting is needed.
- Confirm the room is safe before activating the collimator light.
- Do not perform test exposures unless clinically approved and radiation safety procedures are followed.
Expected outcome: Troubleshooting is performed without unnecessary patient exposure or positioning risk.
Why it matters: Collimator and centering issues can affect radiation field accuracy, image quality, repeat imaging, and patient dose.
Verify the Reported Problem
Confirm exactly what clinical staff observed.
Action:
- Ask whether the issue involves:
- Collimator light not turning on
- Light field not matching expected image field
- Field size changing unexpectedly
- Centering light or crosshair misaligned
- Collimator blades not opening or closing correctly
- Auto-collimation not working as expected
Expected outcome: The reported symptom is clearly identified before testing.
If the issue was user setup-related and cannot be reproduced, document findings and return the system to service if all checks pass.
Check Room and System Power Status
Verify that the radiographic system is powered on normally and not in a standby or fault condition.
Action:
- Confirm the operator console, overhead tube crane, wall stand, table, and generator are powered normally.
- Check for active system messages, interlocks, or warnings.
- Verify the room is not in emergency stop, exposure inhibit, or safety lockout condition.
Expected outcome: The system is fully powered and ready for positioning and collimator operation.
If system power or room readiness is abnormal, correct that issue first and retest.
Test the Collimator Light Activation
Check whether the collimator lamp or LED activates from the expected control.
Action:
- Press the collimator light button at the tube head or system control.
- Observe whether the light turns on, flickers, times out normally, or does not respond.
- Check whether the light works intermittently when the tube is moved.
Expected outcome: The collimator light turns on consistently and remains visible long enough for positioning.
If the light does not activate but the system otherwise functions, continue checking controls and cabling. If the light works normally, proceed to alignment and field size checks.
Inspect the Collimator Face and Light Window
Look for obvious external obstruction, contamination, or physical damage.
Action:
- Inspect the collimator face, light exit window, mirrors if visible externally, and accessory rails.
- Check for tape, covers, dust, fluid residue, cracked plastic, or damaged external parts.
- Remove only external obstructions that can be safely removed without disassembly.
Expected outcome: The light path is clear and the collimator face is not visibly damaged.
If the light window or collimator face is damaged, remove the system from service and escalate for repair.
Verify Source-to-Image Distance and Positioning
Confirm the system is being tested at the correct SID and detector position.
Action:
- Set the tube, table, or wall stand to a commonly used SID.
- Verify the detector is properly parked, centered, and recognized.
- Confirm the tube is positioned squarely to the table or wall stand.
Expected outcome: The light field and center mark are checked under a normal, repeatable setup condition.
Why it matters: Off-angle tube positioning, incorrect SID, or improper detector positioning can make the field appear miscentered even when the collimator is working correctly.
Check Tube and Detector Centering
Confirm the tube is aligned to the active image receptor.
Action:
- Use the system’s centering indicators, detents, locks, or position displays.
- Check the tube head alignment to the table bucky or wall stand bucky.
- Confirm the detector is seated correctly and not shifted in the tray or holder.
Expected outcome: The tube, detector, and receptor center are physically aligned.
If centering improves after correcting tube or detector position, the issue was setup-related. Document and stop.
Check Collimator Blade Movement
Verify that the field size controls actually move the collimator blades.
Action:
- Adjust the longitudinal and transverse field size controls.
- Watch the light field edges move smoothly.
- Listen for unusual grinding, clicking, binding, or motor noise.
- Confirm both axes respond.
Expected outcome: The field edges move smoothly and predictably.
If the blades do not move, move only one direction, bind, or make abnormal noise, remove the system from service and escalate for collimator evaluation.
Compare Manual and Automatic Collimation Behavior
Determine whether the issue is limited to auto-collimation or affects manual field sizing too.
Action:
- Test manual collimation first.
- Then test auto-collimation, if available and normally used by the site.
- Confirm the detector size and selected exam protocol match the expected field size.
Expected outcome: Manual field size works reliably, and auto-collimation matches the selected receptor and protocol.
If manual collimation works but auto-collimation does not, suspect detector recognition, receptor selection, protocol setup, or system communication issue before assuming collimator failure.
Check Exam Protocol and Receptor Selection
Confirm the selected exam and receptor match the expected field behavior.
Action:
- Review the selected anatomy, view, table or wall stand receptor, and detector size.
- Confirm staff did not select the wrong receptor or a protocol with a preset field size.
- Try a known-good basic exam selection used routinely in the room.
Expected outcome: Field size and centering behavior match the selected receptor and exam setup.
If the issue only occurs on one protocol, escalate for application or configuration review rather than hardware repair.
Inspect External Cables and Movement-Related Symptoms
Check for visible cable strain or intermittent behavior during tube movement.
Action:
- Inspect external cable carriers, tube head cable loops, connectors, and visible strain reliefs.
- Move the tube slowly through normal range while observing the collimator light and field control response.
- Do not open covers or manipulate internal wiring.
Expected outcome: Collimator light and controls remain stable during movement.
If the light flickers, controls drop out, or errors appear during motion, remove the system from service and escalate for cable, harness, or tube head evaluation.
Check for Error Messages or Service Indicators
Look for system messages that point toward collimator, tube stand, detector, or positioning faults.
Action:
- Review the operator console for active warnings.
- Note any messages related to collimator, field size, detector centering, tube position, SID, or system communication.
- Record the exact wording or code in the work order.
Expected outcome: Any system-reported fault is captured accurately for repair follow-up.
If an active collimator or positioning fault remains, remove the system from service and escalate.
Perform a Non-Exposure Light Field Check
If allowed by site policy, compare the projected light field to the expected receptor area without making an exposure.
Action:
- Use the table or wall stand reference markers.
- Set a known SID and center position.
- Adjust the field to a known size.
- Visually confirm whether the light field appears reasonably centered and square.
Expected outcome: The light field appears centered, square, and responsive.
If the light field is obviously skewed, offset, uneven, or not matching control settings, remove the system from service for collimator alignment or calibration evaluation.
Determine Whether the System Can Remain in Service
Make a service decision based on patient safety and imaging accuracy.
Action:
- Return the system to service only if:
- Collimator light works consistently
- Field size controls respond normally
- Tube and detector centering are correct
- No active faults are present
- Staff can reproduce normal operation
Expected outcome: The room is only returned to clinical use when field alignment and collimator behavior appear reliable.
If there is any doubt about radiation field accuracy, remove the system from service.
If the Problem Persists
If the collimator light, centering, or field size issue continues after external checks, common setup and accessory causes have been ruled out. The problem may involve the collimator assembly, lamp or LED circuit, blade drive mechanism, tube stand communication, detector recognition, alignment calibration, or internal system control.
The device should be:
- Removed from service
- Labeled Out of Service
- Sent for repair or bench/service evaluation
Knowing when to stop is proper troubleshooting. Do not perform internal collimator adjustment, calibration, or service manual procedures unless properly trained, authorized, and equipped.
Clinical Use Tip
Do not troubleshoot field size or centering complaints on an active patient. Move the patient to another radiographic room or portable imaging option first if imaging must continue. A questionable collimator can lead to repeat imaging, poor image quality, and unnecessary radiation exposure.
Work Order Documentation (CCR Method)
CCR = Complaint, Cause, Resolution
Complaint
What was reported by the clinical staff.
Example:
"Clinical staff reported that the GE Discovery XR656 collimator light field appeared off-center from the wall stand detector during chest imaging."
Cause
What was observed during troubleshooting.
Example:
"Verified tube and detector centering, checked SID and receptor selection, and found the light field remained visibly offset with no external obstruction present."
Resolution
What action was taken.
Example:
"Removed the room from service, labeled the system Out of Service, and escalated for collimator alignment and service evaluation."
Helpful Details to Include (If Known)
- Outlet or room power status verified
- System startup completed normally
- Alarm behavior
- Any active console messages or fault codes
- Collimator light turns on, flickers, or fails completely
- Manual field size control response
- Auto-collimation behavior
- Accessories swapped
- Power behavior
- Environmental factors
- Indicator lights
- SID used during testing
- Table or wall stand tested
- Detector seated and recognized
- Tube centering indicators checked
- Field appears offset, oversized, undersized, skewed, or uneven
- Unusual collimator noise, binding, heat, or smell
- Final device status
Final Thought
Collimator and field size complaints should be handled carefully because they directly affect radiation field accuracy and patient dose. Start with patient safety, then verify setup, receptor selection, SID, detector position, and external collimator condition before suspecting internal failure. If the field remains unreliable, remove the room from service and document the findings clearly.
That is successful troubleshooting.