The amount of information available to the clinician regarding marine animals is often limited to clinical signs, physical observations, hematology, serum chemistries, cultures and sensitivities, endoscopy, ultrasonography, and radiology. This may seem like a lot of information, but that is if it is all available. More often than not, the diagnosis is based on clinical signs, physical observation, and sometimes hematology and serum chemistries. The value of cultures is questionable even when the affected area is cultured. The species, size, age, temperament, and conditioning are all variables that influence the amount of information available for a diagnosis. A definitive diagnosis is often difficult or impossible to reach in many cases resulting in the necessity to treat the animal symptomatically.

Radiography is a tool that can assist in or confirm a diagnosis in selected cases. We routinely take radiographs on most of our marine animals using a portable machine (Picker 300 Milliamp, 125 Kilovolt, 208 volts) . This unit allows us to take radiographs at our pools as well as in the surgery area.

There are a number of factors that affect the quality of the radiograph. Factors such as film speed, grid, cassettes, and focal film distance are kept constant. The remaining variables that we have to deal with are species, tissue density, and film processing. Many of the techniques are the same or very similar to those developed for companion animals, i.e., the techniques for penguins and otters is the same as for domestic pets. However, the techniques start to vary greatly for pinnipeds and cetaceans. There does not appear to be any constant factor that will allow one to obtain diagnostic radiographs consistently for all species. The radiographs and techniques presented here are the result of extensive trials and modifications. The techniques should be useful as basic reference points for anyone who does not have a technique for a given species or who is just starting to use radiography as a diagnostic tool.

Even though it often changes with the species, a technique chart should be developed for each individual X-ray machine due to machine differences. Variables such as film type, screens, grids, focal film distance, and film processing must be made constant in order to obtain consistent radiographs.

Establishing a radiographic chart for marine animals is similar to establishing one for companion animals. Once you have eliminated as many variables as possible, determine your MaS first and then the KVP. A MaS of 5 and a factor of 40 are considered to be universal and provide a place to start. There are numerous books available on how to develop charts so it will not be dealt with in any detail here.

The MaS that gives the best results on our machine was determined to be 2. 5. The factor 40 works well with this MaS setting as evidenced by the techniques provided for thicknesses of 12 centimeters or less. The thickness in centimeters is multiplied by 2 and the factor of 40 is added to the result to give the required KVP. A grid is not needed for good detail for thicknesses less than 13 centimeters. For thicknesses in excess of 12 centimeters, a grid is usually necessary to obtain a diagnostic image. If the grid is 10:1 or less, 4 times the MaS is often suggested to obtain adequate film exposure. For soft tissue thicknesses between 15 and 25 centimeters, we used 6 times the 2.5 MaS. For soft tissues thicker than 25 centimeters, the MaS was increased to 12 times the original MaS. Thoracic radiographs required a slightly lower MaS. If the KVP is decreased by 10, the density is effectively decreased by 50%. If the KVP is decreased by 10 and the MaS doubled, the contrast is shortened and the density is maintained. A crisp blackness is reflected with overexposure by MaS while a graying or loss of background is seen with overexposure by KVP.

Note that the settings reflected in the chart below for thicknesses 12 centimeters or less, follow the procedure just described, i.e., double the thickness in centimeters and add 40 to determine the KVP when using a MaS of 2.5. If you double the MaS, the KVP can be decreased by 10.

Machine settings for the various species that consistently produced radiographs of diagnostic quality are as follows:

A chart in the following form is handy for easily determining MaS:

MaS Chart

Milliamps (Ma)

Certain problems can be expected when attempting to radiograph marine animals. A few of the problems we consistently encountered were: grid-head alignment, patient motion, adequate positioning of the patient to obtain the desired radiograph, and keeping the equipment dry. Saltwater is extremely corrosive and continuously poses a threat to the X-ray machine when taking radiographs near the pool. Positioning is a particular problem when trying to obtain a lateral thoracic radiograph of a cetacean due to the pectoral flippers.

Most X-ray machines differ from each other enough so as to preclude exact duplication of radiographs utilizing the same technique for each machine. However, most machines are similar enough that a proven technique on one machine will usually produce an acceptable radiograph on a different machine. The radiographs presented here utilized Dupont Cronex 4 film for thicknesses greater than 12 centimeters and Dupont Cronex 10 film for thicknesses less than 13 centimeters, Rare Earth screens, a 10:1 grid for thicknesses over 12 centimeters, and a focal film distance of 40 inches. The film was hand processed using Kodak chemicals following the instructions on the container. Again, the portable Picker machine previously described was used.