In the last blog post, we talked about under-exposed radiographs and how to get better results.
But, it’s important to remember that overcompensating too far in the other direction can give you a problem in the other extreme: that is, over-exposed images.
This is basically the opposite of an overly white or light radiograph. Instead, the image may appear “burnt out,” and overly dark or black, making it difficult to see all the information you need to make your diagnosis.
Over-exposed radiographs can make your life difficult because of the obliteration of normal anatomy
An over-exposure usually means the x-ray beam was too powerful, and that a larger percentage of x-rays passed through the patient’s tissues to reach the film or plate. So, rather than seeing information about the patient, you end up with a blackened image with not nearly enough detail.
Some structures, such as small blood vessels in the thorax, might not be visible at all.
In other words, over-exposure could cause you to miss important lesions or interfere with your interpretation of normal anatomical structures.
Reasons why your radiographs might be over-exposed
Here are some possible culprits…
An error in technique (kVp or mAs settings).
A machine or equipment error.
Using grid technique without a grid.
Variations in screens.
Too short of a distance between the x-ray source and the film or plate.
Also, scatter radiation can contribute to darkening an already over-exposed image.
What to do about over-exposed images
To decrease your radiograph procedure time and minimize x-ray exposure to patients and staff, it’s best to get your shots right the first time. But if your images are overexposed, try…
Using a “hot light.” Sometimes, an overexposed radiograph can still be read by holding it up to an extra bright light known as a “hot light.”
However, if that doesn’t work, you will probably need to retake the radiograph. Here are some tips for getting a better shot the next time…
Adjust your settings. Typically, lighter images can be obtained by lowering the kVp or mAs.
Check for errors in technique, such as using or not using a grid setting.
Collimate. That way, you reduce the area of the primary beam and reduce scatter radiation, giving your image an overall better quality.
Measure patients in the position they will be in during the shot. For example, when taking a lateral thorax view, the thorax may be thinner when the patient is laying on their side than it was when they were standing up. If that happens, your settings would probably be too high based on the measurement obtained from a standing patient.
Also, be sure to follow these general tips for producing good X-ray images…
Use technique charts for a good starting point for exposure settings. A good technique chart will remove much of the guesswork.
Keep your equipment in good repair, including routine maintenance as necessary.
Consider digital radiography, which can take film development out of the equation, and shorten the waiting time between views (allowing you to adjust settings prior to taking more shots).
Use appropriate patient restraint to minimize artifacts from movement.
With practice, good quality equipment, and a few tips for adjusting your settings… Getting a properly exposed image doesn’t have to be hard!
And getting the right exposure will help you save time, avoid the headaches of struggling with poor-quality images, and get to your diagnoses faster.
Disclaimer: This article is for general informational purposes only, and not intended as a guide to the medical treatment of any specific animal.
Written by: Dr. Tammy Powell, DVM
