Division of Diagnostic Imaging, Faculty of Veterinary Medicine, Utrecht University
Good quality radiographs of dogs and cats may provide valuable information that is often sufficient to obtain a tentative or even definite positive or negative diagnosis.
Prerequisites for successful radiographic examinations include enthusiasm for this special part of veterinary medicine (including enthusiasm for radiation safety procedures), understanding of radiographic techniques (survey radiography, contrast radiography, special procedures, indications, examination protocols, etc.), basic knowledge of radiographic interpretation (normal radiographic anatomy, radiographic signs of the most common abnormalities), and, last but not least, the willingness to adapt standard routine procedures to individual circumstances ("fit the shoe" procedure).
Radiographic examinations are expensive and increase the costs of a diagnostic work-up considerably. For this reason, veterinarians must always judge the costs of examinations versus the expected yield of diagnostic information. Any radiographic procedure should have an acceptable probability of changing and upgrading the management of the case. In no event should an animal be subjected to an unnecessary radiographic procedure either out of embarrassment with an unsolved diagnostic problem ("maybe it helps") or for no benefit other than the clinician's curiosity or greed of money.
Unnecessary examinations can be avoided when definite and appropriate indications for radiographic examination are established and clinical investigation protocols are followed.
The efficacy of radiography is directly dependent upon the reason(s) for which it is performed, based on the animal's history, clinical examination, and previous laboratory findings.
Next to selection of proper criteria and clinical investigation protocols care must be taken to ensure examination techniques of high diagnostic quality and accuracy, not only in terms of sensitivity (accuracy of positive findings) but also in terms of specificity (accuracy of negative findings). It should be kept in mind that "negative results", as long as they are reliable, may help rule out one or more diseases that had been considered as probable cause of the clinical signs. In that way they are certainly well worth the costs to the client and the endeavors to the veterinarian.
However, the full potential of radiographic examinations is only achieved when the produced radiographs are of excellent technical quality. And, excellent radiographs can only be made with expensive high-powered X-ray machines, good quality cassettes, screens, films and grids, and the use of an automatic film developer. This costs money! Any veterinarian that wants to be a better radiologist must accept the fact that he or she must invest a lot of money. Today, the new types of high-frequency X-ray machines with a capacity of 100 KVP and 200 mAs are readily available to veterinarians, as are the table-top developing machines. Especially the use of these automatic developers may have a very positive effect on radiography under practical circumstances.
In a similar manner, also radiographic interpretation may be improved. Successful interpretation of radiographs depends for the better part upon the quality of the radiographs, but certainly also upon the manner in which they are interpreted and under what circumstances this is done. The method should be systematically, step-by-step, and well-organized with the possibility to compare with normal images (file of normals!). But, much more basically important, the films should be read on a view box that has curtains to close around the radiographic images and that is placed in a semi-light surrounding. Only in this way it is possible also to evaluate the smaller peripheral details that otherwise easily escape attention.
In addition, radiographic interpretation needs time, and deserves time. A hasty radiographic interpretation of a clinician that lacks specialist experience will only yield, at the best, superficial information of larger abnormalities while important details will be overlooked or remain unnoticed. Furthermore, one should take the time to read the entire film including the edges of the picture. It is always a surprise and sometimes very embarrassing how much worthwhile information that is present on the borders of a radiograph has escaped attention during the first reading of the films. As an example, the presence of small nodular densities in the triangular part of the caudal lung field at the border of abdominal films must not be overlooked, even if it is an unexpected finding. Interpretation of radiographic films should be performed with an unbiased mind. However, under practical circumstances, this is an impossibility because the practitioner performed the radiographic examination because of abnormal clinical findings and with the wish to diagnose or exclude certain abnormalities. Under these circumstances it is a good advice to re-interpret the films a second time, at a quiet moment after the busy working hours. It will be a great surprise to find out how easily radiographic abnormalities will be detected that escaped attention during the first reading of the films. Or, how easy radiographic abnormalities are noticed when the presence of the specific abnormality has already been proven by other clinical or surgical findings.
Especially with this attitude, a veterinary practitioner may increase his or hers skill in radiographic interpretation greatly.
Following all these rules, a veterinary clinician can perform as a good radiologist. However, it takes more to become a better radiologist.
The change from good to better is not dependent upon the presence of the most advanced and expensive radiographic machines such as image-intensifying units or CT-scanners (academic circumstances) or upon the strict use of good indications and investigation protocols (academic and practical circumstances).
A better radiologist is a veterinarian that adapts the basic rules of radiography to the special circumstances of the animal under consideration. In the understanding of the possibilities and limitations to perform radiographic examinations under his private practical circumstances, this veterinarian decides at the spot how he will use additional investigation techniques in an optimal way, with this special animal, at this special moment. To make the right choices, a lot of experience is needed.
Radiographic rules should be used as guidelines, but are not strict. They can be changed, adapted or extended to better fit special circumstances. There is only one basic rule: "the animal's life should not be compromised or jeopardized unnecessarily by the radiographic examination". To explain this, the following example may be used.
Routine radiographic examinations of the thorax and abdomen must include two radiographic projections in perpendicular directions, one lateral projection and one dorsoventral or ventrodorsal projection. Without this, a radiographic examination of the thorax or abdomen is not complete. However, with traumatized animals this is not always possible. The animal's discomfort or distress may preclude the taking of more than one radiographic view at the first clinical investigation. Lateral views of the thorax and abdomen are generally more convenient to obtain than dorsoventral or ventrodorsal films. So, at this moment a compromise must be made between the need for radiographic evaluation of the suspected injuries and the stress applied to the animal that will easily risks his life. As a result, the additional views will be made at a later moment when the animal's vital signs have been stabilized properly. In the same way, it is the veterinarian's decision to indicate if sedation or general anesthesia are necessary to perform a radiographic examination.
Routine radiographic procedures may be expanded with special procedures as:
Additional radiographic projections
Additional radiographic projections include horizontal-beam projections with or without special positioning, oblique projections, and vertical projections with the animal in a special position.
Horizontal-beam projections are used to evaluate body cavities that contain free fluid. By way of gravity, fluid will accumulate in the ventral portions of cavities, while free or contained gas or air will accumulate dorsally. In this manner, fluid can be moved away from solid organs and/or mass lesions that now become visible and can be evaluated.
As an example, horizontal beam projections allow visualization of gas-capped fluid levels in distended intestinal loops due to end-stage mechanical or paralytic ileus.
Horizontal-beam projections are especially helpful to evaluate the severity of adhesive changes in a thorax with pleuritis, e.g., encapsulated pyothorax.
Horizontal-beam projections are sometimes used for diagnosing of minor amounts of free pleural air with low-degree pneumothorax.
Oblique projections can be used any time when abnormalities have to be evaluated from different angles such as myelographic changes due to disc herniation. Oblique projections are also used for identification and evaluation of bony abnormalities (fractures, neoplastic and osteomyelitic changes, periosteal new bone formation, etc.), and during intra-oral radiography, Vertical projections with special positioning of the animal are used during radiographic examination of the skull (craniocaudal, intra-oral, and skyline projections). Special projections of the shoulder and stifle joints include skyline projections. Special dorsoventral projections of the cervicothoracic spine are used during myelography, and special ventrodorsal thoracic projections are used to evaluate the cardiac shadow in a liquothorax.
Compression radiography is used during radiographic examination of the abdominal cavity, both during non-contrast routine radiography as during most of the abdominal contrast examinations as excretory urography, cystography or during barium- or air- contrast examinations of the gastrointestinal tract (barium follow-through examination, pneumocolon, or enema procedure).
Localized abdominal compression is performed with the animal in lateral recumbency on the radiographic table. As compression device a plastic compressor or wooden spoon can be used. By applying moderate pressure on a certain region of the abdominal cavity superimposing viscera that conceal underlying structures and abnormalities can be pushed away.
This is especially helpful when barium-filled intestinal loops are crowding the mesogastric region of the abdomen hindering recognition of intestinal abnormalities.
Stress radiography is very helpful for radiographic evaluation of articular or spinal instability (articular (sub)luxation, growth plate injuries, cervical and lumbosacral instability, disc herniation).
Stress maneuvers for evaluation of articular instability and/or growth plate injury include traction, compression, rotation, abduction, adduction, and tibial compression test. For accurate evaluation of spinal instability in the cervical region ("wobbler syndrome") or lumbosacral region ("cauda equina syndrome") stress radiographs with hyperextension and hyperflexion of the specific spinal segments are made. Sometimes also stress radiographs with the neck in lateral hyperflexion are needed. Stress radiography of the spine is also called dynamic spinal radiography because of the dynamic changes that are induced by the stress maneuvers. One should always be careful not to overstress an abnormal joint or spinal region, and one should be careful to keep the hands out of the primary X-ray beam.
Contrast examinations can be performed when routine radiographs produce insufficient evidence of an abnormality that is clinically suspected or when the results of a clinical investigation are not in accordance with the findings of the first set of survey radiographs.
For radiographic evaluation of the gastrointestinal tract barium is not the first choice as contrast medium, but air is the contrast medium of choice.
With air, larger abnormalities of stomach and colon can easily be detected such as dislocations of abdominal viscera, abnormal size, shape or compliance of the stomach or intestinal loops, large filling defects and mass lesions. In case of the stomach, the pyloric region can readily be evaluated with pneumogastrography, while with a pneumocolon the diagnosis of intussusception or colonic neoplasm is only a matter of minutes. Most of the small bowel abnormalities, however, still have to be diagnosed with a barium series.
Abnormalities of the urinary bladder also are easily detected with air-contrast cystography.
These air-contrast examinations are especially suitable for practical circumstances. No long-term preparation or anesthesia is required.
For finer-detailed contrast radiography the academic double-contrast techniques are still used. However, most of these techniques have been replaced by other imaging techniques as endoscopy and ultrasonography.
As a conclusion, the answer to the question "how to become a better radiologist?" is probably not hidden in the urge for better and more expensive machinery and techniques nor in the knowledge of every possible abnormal radiographic pattern, but the answer lies within the veterinarian himself. Guided by his enthusiasm and basic knowledge, he or she will create solutions for difficult problems that threaten the lives of animals.
And by using his creativeness, many of these solutions turn out to be readily available.