Getting the most from exposure charts

Exposure charts should be simple to use – but frequently things go wrong. Here are 5 straightforward tips to ensure optimal use of exposure charts.

Determining measurements

Don’t overlook the importance of measuring distance before taking X-rays. FFD (focal to film distance) is critical for correct exposure. A 20cm adjustment requires a doubling of mAs, or an increment in kV by a factor of 10. The critical distance to measure is to the X-ray cassette or plate – and not simply to the animal. Distance drift can occur occasionally, where FFD has varied, which often leads to less than optimal image quality.

No one exposure chart does it all

There is no universal exposure chart which applies to all veterinary digital radiography systems in operation nowadays. There are always variations between different systems such as CR or DDR systems, and although recommended exposures may be taken as a guide; experimentation and adjustment to the specs of a given system are essential in order to obtain optimal image quality consistently. So make sure to annotate all settings and exposures commonly used within your practice on your exposure chart for easy reference by others.

Consider the animal to be X-rayed

The general physical build of an animal can influence the exposure when taking X-rays. A big muscular animal will typically require an increase in kV; for example, in the case of a muscular dog, because it is easier to scan through fat than more solid muscle mass. Other examples where greater exposure might be required would include: an animal with the chest fluid present, or alternatively, an animal whose abdomen is filled with fluid.

Purpose of the radiography

Exposure settings must be appropriate for highlighting the aspects of the animal requiring examination. For example, abdominal and chest exposure settings will vary due to the fact that the chest area naturally provides high contrast, which may need to be reduced somewhat in order to expose details of the lungs, heart and/or ribs, etc. This will typically require lower mAs and higher kV values. Meanwhile, for the abdominal area, it may be necessary to generate greater contrast in order to highlight differences between the soft tissues of the organs. In such cases, higher mAs and lower kV are normally best.

In the case of orthopaedic radiography, enhanced images can be obtained by the use of a lower kV setting while using higher mAs. This enables easier identification of soft tissue, trabecular bone pattern, and in addition avoids burning out any small chips which may be present in the bones.

Climate change!

Yes, changes in weather, specifically temperature can generate variations in the quality of images obtained. If a previously successful exposure setting suddenly produces less than desired results – check all equipment for mechanical/technical issues, and bear in mind that extremely hot weather can cause conventional wet processors to overheat. In such cases, overheating can produce darker than normal images, or images which appear ‘foggy’ or flat. In contrast, extremely cold weather may lead to brighter than normal images, making identification of detail somewhat more difficult. Make sure to note any necessary adjustments on your exposure chart. 

Exposure Technique

In radiography, the exposure charts need to be adjusted for the patients, since they may vary from obese adults to premature infants. The radiographers are expected to select maximum kVp for penetrating the anatomy of patient under study.

Keeping note of such factors, not only ensure optimal usage of the exposure charts, but also help in studying the anatomy in a detailed and hassle-free manner. 

Author Bio:

Simon Hopes is an eminent writer who has earned extensive experience in writing informative articles relating to veterinary digital radiography.