Principles of viewing and interpreting x-ray films
Veterinary students should learn how to apply diagnostic imaging investigation and how to recognise basic radiological signs, by the time they graduate and become hospital doctors. Quality radiographs, detection knowledge and correlation of significant radiographic findings with clinical data are essential. Radiography is not an absolute diagnostic tool but only an adjunct to clinical diagnosis.
It is important to relate the changes seen to known behaviour of tissues under consideration, rather than relating radiographic appearance to a clinical condition seen before. It is important to remember that each radiograph can only represent a fraction of a second in the life of a patient, and the development of disease process. The x-ray picture is a static image of a dynamic process. All the changes from the normal, should be used to build up an impression which can be related to disease process known to occur in that region.
In order to interpret a radiograph for pathological lesion, it is essential that radiographic appearance of normal structures are known. The radiograph should be interpreted without any preconceived idea. Radiography is an aid to diagnosis and not the ultimate diagnosis itself.
For a given site, adequate evaluation usually requires a minimum of two views, to be made at 90o to each other (orthogonal views). To evaluate fractures and postoperative fracture repairs radiographs of the long bones must include the joints above and below the bone of interest. Serial radiographs are necessary for correct interpretation of dynamic process e.g. fracture healing and growth of bone tumors.
Radiographic interpretation should be done when the film is dry. The emulsion swells when wet and details cannot be appreciated on wet films. It is helpful if the radiographs are always viewed using the same orientation, i.e. with the animal facing the viewer’s left. Satisfactory radiographic interpretation is dependent on complete and systematic evaluation of all the information that is found on the film. Close attention should be paid to the variations in the outline and densities of the images in the film. Fine details of the radiograph should be examined minutely.
Principles of viewing Skiagram (x-ray Radiograph)
Important Factors for Accurate Interpretation
- The period of time during which the clinical signs have been present
- The age, sex and breed of the animal
- The validity of history
- Possible complicating factors
Viewing Box
X-ray should be viewed only on a viewing box with subdued light. This optimise the ability of the reader to differentiate the structures and to obtain the maximum information from the film. The darker the film, the more important is to read the film under ideal conditions. Radiograph has variable grey shades. Black areas indicate areas or structures of low density e.g. Air in Lungs. White areas indicate structures that have relatively high density e.g. Bone.
Distant Evaluation of X-ray
Prior to closer view, initially the film should be evaluated from a distance of several feet, in order to get an overall impression before concentrating on details. Then start assessing the radiograph itself for;
- Quality of the film
- Processing artifacts and other artifacts
- Exposure factors & penetration of the part of interest
- Sufficient radiographic density & contrast
- Elimination of motion during exposure
- Approximate age of the patient
- Soft tissue abnormalities
- Bone outline and internal structures
Asses the Identified Abnormality
Ensure that it is real and confirm it on another view.Asses the possibilities due to overlapping of bones or soft tissues.Differentiate normal variations and real abnormalities e.g. Nutrient foramen.Explain the radiolucent zone – whether due to introduction of air during injection of local analgesics.
Describe the radiographic lesion in radiographic terms
Terms like smooth, regular, well defined etc. It will lead towards a conclusion of normal, benign or long standing lesion.Other terms such as roughened, irregular, sharp, poorly demarcated or destructive, lead to conclusions of active disease.Other pathological lesions also should be considered.
Assessment of the Duration Of The Lesion
- Osteophite formation less than three weeks
- Incomplete fracture takes 2 weeks to become visible
- Active bone lesions have irregular margins and less opaque than parent bone
- Inactive bone changes appear generally smooth, regular and uniformly opaque
- Scars in bone, as in other tissue, do not model.
The purpose of x-ray in fracture is to asses
- The type and severity
- The degree of displacement
- The damage to adjacent joint
- The damage to soft tissue
- The degree of reduction achieved.
For Interpretation of Skeletal X-Rays
- For detection fractures and dislocations, one x-ray is not enough
- For correct assessment of fracture at times more than one view is required
- Obtain minimum two views at right angles for all suspected fractures and dislocations
- The films must show the joint above and below any suspected fracture of the limbs
- The tendon or vascular damage cannot be seen on routine x-rays
- Fractures of the shaft of bones are easily seen when there is break in the thick cortex
- When an obvious injury is seen, continue searching, as there may be other abnormalities
- In non-union, the fracture line persists, the broken ends of the bone appear whiter
- For best visualisation of a fracture, the x-ray beam must be parallel with the plane of fracture
- All the changes from the normal should be used to build up an impression, which can be related to disease process known to occur in that region
- Serial radiographs are necessary for correct interpretation of dynamic process e.g. fracture healing and growth of bone tumors.
A working diagnosis can then be formed, which will complement any laboratory findings and other imaging techniques and to help to confirm a clinical diagnosis.
There is no substitute for a good clinical diagnosis and examination, and radiograph should only be used as an aid to clinical diagnosis.