Radiography of the Equine Spine with Automatic Exposure Detection Digital Radiography Systems
As technology has advanced, it has become easier to achieve high quality equine radiographs out in the field. However, we still need to consider the limitations of portable x-ray equipment.
Most equine DR systems now use AED (automatic exposure detection) technology which requires a short sharp burst of radiation (high mA) for the plate to recognise it. If the radiation exposure is a longer, softer burst (low mA), the plates often do not recognise this and may not trigger the radiograph correctly, resulting in poor image quality and artifacts.
When imaging the extremities, a lightweight generator is preferable. The generator usually needs to be hand-held, and the light weight ones are easier to handle safely around horses, and have small focal spots, giving good image quality. Like all things in life, there must be compromise… To be this light weight, they cannot provide the high outputs that the larger generators can. They normally reach a maximum of 20-30mA, which will decrease to around 6-8mA as the kV is inevitably increased.
This is fine for extremities as the exposure you need is low and the high sensitivity of DR receivers means excellent image quality is achieved. As you move up the leg, soft tissue and bone density increase and more exposure is required, but the generators usually remain within their output range and all is well.
Then you get to the spine. Portable generators will normally cope with the dorsal spinous processes as there is usually relatively little muscle coverage. Image quality achieved should still be good.
Portable generators begin to struggle as the vertebral bodies are imaged. The exposure time needs to be longer to give the required kV and mAs settings. Referring to our earlier comment regarding short bursts of radiation; this can often cause the DR plate to not recognise the exposure. Longer exposures also increase the risk of motion artifact, especially if you are not using a generator or plate stand. We recommend using both when attempting to achieve high quality back radiographs.
The simplest solution is to use a more powerful generator and a generator stand, allowing short sharp bursts of radiation and minimal operator movement, instantly improving image quality.
Older, wired DR systems often cope better with spinal radiography than the AED systems. This is because the synchronisation box of the wired DR system controls when the radiation is produced. As the trigger is pressed, it ensures all the equipment is ready and communicating before allowing the generator to expose. This process ensures the plate will record the exposure correctly. In AED systems, the radiation is controlled only by the operator firing the generator (there is no synchronisation box) and completely relies on the AED panel correctly sensing and reading the exposure.
If you need more help optimising your images, please contact us for help.