What is an Overexposed X-Ray and What do they Look Like?

With almost all types of veterinary diagnostic imagery, the effort is in the prep work!

That means getting the correct measurements, exposure settings, and positioning off the bat leads to the best results.

In a previous blog, we discussed why we get underexposed X-rays and how to identify them.

However, it’s easy to overcompensate when adjusting exposure settings and get the opposite effect: overexposed X-rays.

With proper knowledge, practice, and technique, getting a well-balanced exposure rate is simple!

What is an Overexposed X-Ray?

Overexposed X-rays are a result of X-ray settings being too high (using an increased kVp and mAs). This causes too much energy build up in the primary beam.

With excessive energy build-up, the patient absorbs little energy, and an overdose of radiation is absorbed into the detector. A detector starts white and darkens as it’s met with radiation.

As a result, the image will be overexposed (or too dark) to be considered diagnostic. The X-rays are essentially “burning” the plate, causing significant internal structures and tissues to appear less visible.

As you can imagine, this inhibits a clear interpretation by the Veterinarian or Veterinary Specialist and delays a proper diagnosis and treatment.

How Will I Know the X-Ray is Overexposed?

It’s not hard to identify veterinary X-rays that have been overexposed.

Here are a few characteristics that will stand out:

• · Image has a darkened appearance

• · Poor visibility of internal structures

• · Blur or distortion

• · Scatter Radiation (reduces image contrast and clarity as a result of the x-ray changing direction –“scattering” - when it meets the patient)

To be appropriately interpreted by a Veterinarian or Veterinary Specialist, you’ll likely need a retake to visualize lesions, growths, or other abnormalities clearly.

Why is My X-ray overexposed?

Capturing an overexposed image is frustrating. Now that we’re pretty clear on what they look like, let’s talk about what may have caused it:

• · Incorrect kVp or mAs settings (if settings appear correct, consider re-measuring to confirm measurements were accurate)

• · Forgetting to move the x-ray tube head to the correct position (if it’s too close to the cassette, it’s easy to cause overexposure)

• · Possible technical error

If I Need a Retake, How Can I Avoid Another Overexposed X-Ray?

Here are a few easy-to-follow tips to avoid overexposed X-rays with your next image:

1. Correctly measure the anatomical part of the patient you’ll be radiographing using a set of calipers (remember, it’s best to measure in the position they’ll be in for the image)

2. Confirm X-ray settings using your veterinary X-ray technique chart

3. Ensure the x-ray tube head is in the correct position (raised if the plate is on the tabletop or lowered if it’s in the bucky tray)

4. Don’t forget to collimate (helps to reduce scatter radiation for a better image quality)

For best results, use computed radiography software tools to reduce artifacts, distortion, and scatter radiation (not to mention hassle-free transfers of DICOM or JPEG images for diagnostic review).

The Quick Take Away

If we think of X-ray exposure like a toaster, when the toaster produces too much energy, we’re left with toast that’s burnt to a crisp.

Just as we’d need to decrease the time on our toaster for a better breakfast, the x-ray settings will need to be reduced on the machine for a balanced diagnostic image.

We want to aim for images that have:

· Sharpness (in focus, clear, and distinct)

· Visual characteristics of density and contrast (adequate representation of tissue density)

· Clear visualization of internal structures

· No distortion or artifacts (no patient motion, technical errors, unnecessary objects, etc.)

Avoid the hassle of retakes by putting effort into the prep work—accurate measuring, exposure settings, and positioning—and getting back to what truly matters to you and your patients. 

The Impact of Over-Exposed X-Rays in Animal Radiography

What is an over-exposed X-ray and how can I avoid that in my animal clinic's X-ray room?

X-rays are a vital and commonly used tool in every animal hospital. However, they are only of use if the X-ray image is of good diagnostic quality. If radiographs are of poor quality, for example through inadequate positioning or incorrect exposure, this can lead to errors in interpretation.

If X-rays taken in the animal clinic are over-exposed, this can be very frustrating to veterinary staff. The radiographs may need to be repeated, leading to increased exposure to X-ray beams for patients, and higher time and cost penalties.   

X-rays being over or under-exposed is a common problem in veterinary clinics. In this blog, we’ll go through over-exposure, why it happens, and how to help. To learn more about the opposite problem, under-exposure, check out our blog here.

What is exposure?

Exposure is the term used to describe the number of X-ray photons present at a certain point. Over-exposure to animal X-rays happens when the concentration of these photons is too high, leading to excessive darkening of the film. 

Four radiographic factors affect exposure:

1. Kilovoltage (kV) – the voltage applied across the X-ray generator, affecting the energy of the X-ray, and therefore the penetrating power of the beam

2. Milliampere (mA) – the current applied to the cathode to generate X-rays, affecting the number of electrons and thus of X-ray photons

3. Exposure time

4. The distance from the X-ray source to the patient (FFD – focus-film distance) – as distance decreases, the intensity of the beam increases.

The exposure of the X-ray is determined by changes to any of these four factors.

Why does an over-exposed X-ray matter?

A radiograph should be properly exposed so that all structures in the targeted anatomical region can be visualized.

In a film-based radiograph, over-exposure makes an X-ray very dark, making it hard to interpret but easy to detect. Using an over-exposed X-ray as a diagnostic tool may lead to subtle lesions being missed, or to artifacts being seen.

However, in a DR system, there are very few signs of over-exposure, as the computer will automatically filter the image and return an “optimal” radiograph.

If the exposure is massively excessive, however, there may be other artifacts generated, in particular, blocky or geometric shapes superimposed over the image.

This is more apparent in some systems than others but seems to be due to the local vs regional adjustment patterns generated by the filtering software.

So, an over-exposed DR radiograph rarely leads to a non-diagnostic image. However, over-exposure is also a safety concern, with animals and potentially staff being exposed to unnecessary levels of X-rays.

Correctly exposed X-rays are important for accurate diagnosis but above all for safety in the animal hospital.

 "Exposure Creep” is a common problem with digital radiography, and with our increasing knowledge of the health concerns associated with cumulative X-ray exposure, something that all clinicians need to work to minimize – even in jurisdictions with relatively relaxed radiation safety limits, such as the USA.

Why is my X-ray over-exposed?

It can be frustrating to have an over-exposed X-ray, and difficult to determine the underlying problem. Here are some common reasons for over-exposure in animal radiography.

A common issue when struggling with exposure is non-deliberate changes in the distance between the film and the X-ray generator.

A small change in distance can have a huge effect on exposure, as the relationship between FFD and exposure is an exponential function.

If your X-ray is overexposed, the FFD may be too small, and require adjustment – or a corresponding change to the mAs.

In animal hospitals, moveable and adjustable X-ray tables can make changes to the FFD a common problem. 

Technical errors in the choice of kV and mA levels are also common. If the kV setting is too high, the X-rays will have more power and penetrate straight through the patient, leaving a film that is overexposed and too dark to interpret.

Over-exposed X-rays require a decrease in the kV level and mAs. The omission of a grid when one is needed – or accounted for in the exposure chart - can also affect exposure. 

Tips for avoiding an over-exposed X-ray

Interpreting X-rays requires films of high quality, excellent positioning, and good exposure. 

A simple response to avoid over-exposed radiographs in the animal clinic is to ensure the kV and mA settings are correct. Over-exposure implies the settings are too high.

The use of an exposure chart can be invaluable to ensure accurate levels. A comprehensive chart, with suggested settings for all different species and sizes of animals, as well as differing anatomical locations, can help avoid mistakes when calculating appropriate settings. 

It should be remembered that X-rays need to be of good quality and exposed correctly for the anatomical area. Different bodily areas have varying needs for good interpretation.
For example, the thorax has both soft tissue and bone which all need to be detailed whereas the abdomen contains high volumes of soft tissue structures, requiring excellent contrast.

Understanding this principle may lead to small adjustments to kV and mAs to maximize the quality of the X-ray. 

Most DR systems are now equipped with Exposure Indicators, and these are invaluable for detecting higher-than-optimal exposures.

Ensure that you are familiar with how this works on your system and that you know how to interpret the numbers generated. LINK?

Remember to keep X-ray machines well-maintained and regularly serviced, for optimal performance.

Summing up

One of the reasons for observing overexposed X-rays is the failure to make necessary adjustments to the imaging technique when transitioning from film to CR to DR, or between different DR panels.

X-rays are a regularly used tool in animal clinics and have great diagnostic value. However, accurate interpretation relies upon good-quality X-rays.

Over-exposure rarely leads to a non-diagnostic radiograph but does lead to excessive radiation exposure to the patient and, potentially, staff.

​​Over-exposure can be caused by changes to the exposure factors: kV, mA, time, and distance.

Using accurate settings for the size, species, and anatomical location of the desired image, and knowing how to interpret the Exposure Indicator, are essential for optimal exposure and good quality X-ray. 
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Many instances of under or overexposure can be attributed to doctors failing to measure animals or consult the technique chart.
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The DynaVue Duo x-ray machine for veterinarians automatically adjusts the exposure based on animal size, optimizing imaging and reducing radiation exposure.

​​This feature saves time, minimizes errors, and enhances diagnostic quality, improving veterinary care.

References

Mattoon, J. (2006) ‘Digital Radiography’ Vet Comp Orthop Traumatol 19(03) pp.123-132

Kirberger, R. (2005) ‘Radiograph quality evaluation for exposure variables – a review’ Veterinary Radiology and Ultrasound 40(3) pp.220-226

What Is an Over-Exposed X-Ray, and How to Avoid Over-Exposed

An over-exposed radiograph is one in which the X-ray beam was too powerful, resulting in an excessively dark or “burnt-out” image. 

Unfortunately, this can make it difficult or impossible to interpret the radiograph, which can lead to frustrating retakes or even non-diagnostic images.

Here are some important things to know about over-exposed X-rays and how to avoid them…

Why Are Over-Exposed Radiographs a Bad Thing?

Radiographs are about balance. A veterinary professional may feel like Goldilocks—wanting to avoid too few or too many X-rays passing through the patient and onto the film or sensor/plate, and instead, find the x-ray beam strength that is “just right.”

What happens otherwise?

Too few X-rays (or a beam that’s weaker) means an under-exposed (or whited out) image. Too many X-rays (a beam that’s too powerful) result in an over-exposed image. 

In general, an over-exposed image may be more useful than an under-exposed image when working with physical X-ray films, thanks to the availability of hot light, an extra bright light that may allow a veterinarian to see more details when viewing an over-exposed film.

However, even a hot light can’t save a very over-exposed image. It’s always best to go for high-quality radiographs.

High-quality X-ray images are more diagnostic because they allow for the visualization of fine details that could otherwise be missed. For example, pulmonary vessels and small nodules might not be visible in an over-exposed radiograph.

How to Avoid Over-Exposed Radiographs 

Improving the quality of radiographs involves troubleshooting. By figuring out WHY there is an issue with image quality, a veterinarian can most effectively improve their radiographs.

Here are some possible causes of over-exposed X-rays…

• Machine errors. Sometimes, a generator, developer, or digital plate needs to be serviced in order to correct the problem. 

An equipment issue may be more likely if ALL patient radiographs are showing the same issue, such as an exposure error. Keeping up with routine x-ray equipment maintenance can help to prevent this type of problem.

• Technical errors. This is less common with digital machines that have preprogrammed settings. 

However, it’s still possible, especially if the wrong part of the body has been selected for the study. Or, maybe the clinic has different sensors/plates with slightly differing sensitivities to the same exposure settings. 

For film machines, errors in technique are common. Technique charts can help vet professionals select the best settings and reduce time-consuming retakes. 

Either way, to obtain a lighter image, lower the kVp or mAs for the shot.

• Operator errors. For film and digital studies alike, errors in measuring the patient are common. For example, when performing an abdominal or thoracic study, remember to take the patient’s measurement while they are lying on their side—this number could be surprisingly different from the patient’s width while standing up. 

Also, the X-ray operator should remember to collimate the field. This improves the detail and reduces scatter radiation that could otherwise darken an image.

Training and practice can help veterinary team members master these protocols and obtain high-quality images. 

Also, digital radiographs can help remove some potential human error (such as manually setting the technique) by automating much of the process.

Getting the exposure right the first time will help the whole team save time, reduce stress for patients and staff by avoiding frustrating retakes, and produce images of a higher diagnostic quality for excellent patient care.

Written by: Dr. Tammy Powell, DVM