X-rays, or radiographs, are a helpful tool for diagnosing many disease problems in fish. They allow veterinarians to evaluate the health or disease status of the bony structures of the fish. They can also be helpful in diagnosing swim-bladder problems and certain other conditions such as tumors. Radiography has its limitations, however. It is difficult to determine the health status of any soft tissue structures such as liver, muscle or kidney.
Radiography of fish is fairly easy to accomplish when proper techniques and methods are used. The advantage of radiographic imaging is that it is a relatively low-cost way to get a snapshot of the inside of an animal.
Radiographs of fish can be made either at the client's home using portable equipment or in the office or hospital using stationary equipment. As a general rule, radiographing the patient in the office or hospital is a better alternative for several reasons. First, if a radiograph does not turn out well it can easily be retaken in the office. Generally, better radiographs are taken in the office because everything is carefully measured and calibrated.
With portable equipment the film has to be taken back to the office to be developed. Should a radiograph turn out to be unsatisfactory, the veterinarian would need to return to the home and handle the fish a second time. This would increase costs, as well as causing additional stress to what may already be a sick animal. Second, the office or hospital is a more controlled environment. If an emergency occurred during the X-ray, equipment would be on hand to deal with it better.
Lastly, office or hospital machines are safer to use. These machines allow the user to leave the room and stand behind shielded walls while the animal is exposed to the X-rays. Portable machines often require the user to hold the machine in place while taking the radiograph.
Despite these disadvantages portable radiography is still a useful tool for cases where the patient cannot be transported to the office or hospital, such as in the case of a very large fish, an incapacitated owner, or when the veterinarian has a mobile practice.
Whether the radiographs are being made at the office or in the field, the same basic procedures are necessary to produce diagnostic quality images in a safe manner. Protective clothing should be worn. This includes a lead apron, thyroid shield and possibly lead gloves. People are exposed to X-rays in small amounts everyday with little harm; however, veterinarians are exposed much more often and to greater amounts than what is normal for the ordinary person. An X-ray badge is also worn which measures the amount of X-ray radiation exposure so technicians do not exceed acceptable levels.
Once their safety equipment is in place the film cassette is covered in plastic to prevent the film from becoming wet. A film cassette is a special film holder that allows X-rays to penetrate and expose the film while keeping out all other light. Film cassettes have to be loaded in a darkroom to prevent exposure of the film. The inner surface of these cassettes is often lined with special material to enhance the ability of the X-rays to expose the film inside.
Radiographic film and cassettes come in many sizes and shapes for radiographing different sized animals and various body parts. The fish is measured to determine which technique will be used to make diagnostic quality images of the animal. The technique is the combination of settings on the radiograph machine which produce the X-rays. These settings control the strength, number and duration of X-rays that are produced.
With the machine set, the patient is anesthetized. Sometimes a particularly sick fish or one that is very docile does not need anesthetics. However, it is usually recommended to ensure the safety of the fish and to permit the most complete X-rays.
Anesthesia-laden water can be flushed over the gills with a syringe periodically to keep the fish anesthetized during the procedure. The fish can be kept out of the water for several minutes so long as they are kept moist. For longer procedures, or when available, an anesthesia machine can be used to supply a continuous flow of water over the gills. These machines have been used to carry out successful anesthetic procedures of several hours duration. Latex gloves are worn during all contact with the animal to prevent removal of the mucus or slime coating, which is important to prevent infection and to regulate the fish's temperature.
Once anesthetized, the fish is placed on its right side on the plastic covered cassette. Personnel then leave the room and the image is made. This process takes only seconds to complete. The people then return to the room and replace the cassette with a second plastic covered cassette. This time the fish is placed with its belly against the cassette. Often times this requires the animal be propped up with sand bags or other material to help the animal remain in this position.
Once the radiographs are made the film is removed from the cassettes and the veterinarian evaluates the entire radiograph for any abnormalities. Sometimes it may be necessary to radiograph a normal fish of the same size and species for comparison. This is because each species may have its own unique anatomy which has not been previously described. In these cases reference images are necessary to determine if any apparent abnormality is merely a normal feature of that particular species.
Besides radiography there are other imaging modalities available for evaluating the fish patient. These other modalities include: magnetic resonance imaging (MRI), computed tomography (CT scan), fluoroscopy (moving radiograph) and nuclear scintigraphy. In addition, there are many contrast studies that can be done to evaluate specific structures within the body. These include but are not limited to swim-bladder studies (pneumocystography), intestinal studies (barium or GI series), kidney studies, and vascular studies (angiography). All these additional techniques can be quite complicated and costly but they are available for those cases where the added information is needed and desired.