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Common Issues With X-Ray Collimator Heads

The three things that can go wrong with General X-ray collimator heads

When working with X-ray tubes and images very little thought is given to the collimator head which is a significant part to the X-ray unit.

Collimators contain a series of mirrors, lights and lead leaves or strips to direct and filter the X-ray beam. Any one of these parts can go bad and need replacing or repairing. In this article we will cover the three common problems encountered with collimator heads and what to do about them.

The light bulb, lead glass enclosure and collimator leaves are the major components of the collimator head that need maintenance and or replacement. They are on every X-ray unit, including general rad rooms, C-arms, and portable machines.  

 The collimator lead strips inside the glass enclosure, guide the x-rays to the imaging surface.  While at the same time the collimator prevents the divergent beam from exposing the patient and healthcare personnel.  The final image is “coned down” or cropped to focus on the body part being imaged such as a finger, toe, or a chest X-ray.

The general X-ray collimator assembly contain four metal strips inserted around the edges of the collimator head.  These strips are manually controlled by two knobs one for the vertical half and the other for the horizontal section. In both stationery and portable C-arms, the leaves are arranged in a circular or hexagonal pattern which narrows the beam down to an inch diameter.  

Collimators can also automatically “cone down” or “close down” to the film size loaded in the chest stand and table buckys.

Three things that can go wrong with the collimators under normal operating conditions

  1. No light field and the collimator leaves won’t open. Non-opening collimators are usually caused by a X-ray tube that is misaligned to the table or chest board. Be sure to center the tube to the chest or table bucky tray and make sure it is properly “detented” or locked into position.  Adjust the tube carriage to the proper distances either 40” or 72” inches by moving the tube along the railings until it clicks into place.
  2. Collimator leaves Become misaligned. Nothing worse than have an x-ray imaged “coned off” or part of the image cut off due to misaligned leaf in the collimator assembly. Unfortunately, the Biomed team or qualified service engineer must be called in to make the adjustments. For a quick fix, just open the collimators during the exposure until the biomed team can repair it.
  3. Collimator head becomes loose. Usually caused by mishandling. Be sure to loosen the collimator screw when twisting the head and don’t force the head to move. Doing so will strip the screws and the whole head assembly will need replacement.

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To recap

Basically, collimators don’t need much maintenance.  However, they are not indestructible and will break or loosen if the head is mishandled.  Always loosen the screws around the collimators when turning or twisting the head. never move the tube along the rails without pressing the appropriate lock on the collimator head assembly.

Non-opening and misaligned collimators are the two most common things that can go wrong. A non-opening collimator can be easily fixed by following a few simple steps listed above: For instance, checking the detent and cassette placement. A misaligned collimator and light bulb replacement needs to be performed by a biomed engineer.

 Collimators are important for image production and radiation safety.  A poorly collimated x ray beam results in more radiation exposure and low quality images. The alignment of the leaves should be included in a scheduled PM to keep the collimator leaves aligned and accurate.



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