Contrast Media Technique

• When radiographing soft tissues it is often difficult or even impossible to visualize a particular organ or structure clearly owing to its lack of contrast with the surrounding tissues. In these circumstances the use of a contrast medium is often helpful to outline the particular structure under investigation.   

•   The substances employed for this purpose are usually of high atomic number (e.g. compounds of barium or iodine) since such substances are relatively opaque to X-rays. Occasionally gases, which being of low density are more 'transparent' to X-rays than most tissues, are employed with the same object in view. These preparations are introduced so that they nil or outline a particular cavity (e.g. the urinary bladder or the alimentary tract) or are administered in a form which will be excreted through the organ to be demonstrated (e.g. the liver or the kidney).

• Sialography

• Sialography is a technique for making the salivary glands and their ducts visible radiographically and is accomplished by injecting; a radio-opaque contrast agent into the salivary duel. The most commonly used contrast agents for this technique are organic iodines compounds . Sialography is particularly useful for locating the particular salivary gland involved when a salivary cyst is present.  The parotid, mandibular, zygomatic, and sublingual salivary glands can be visualized with this technique. For the procedure, the animal should be anesthetized and a blunt  22 - 25 gauge needle inserted into the duct opening of the gland of interest. The contrast agent should be injected at a dose of 0. 25 – 0.50 ml/10 pounds body weight.

• Figure 1: Monostomatic sublingual salivary glands.

• Figure 2: Mandibular duct.

• Figure 3: Monostomatic sublingual salivary glands.

• Urethrography

• Urethrography is practical for radiographic examination of the urethra. Some in­dications for this procedure are strictures of the urethra, radiolucent urethra calculi, or prostatic abscessation. Because the low incidence of urethra disease in females makes this procedure more applicable to males than lo females, only the technique of exam­ining the male urethra will be described. A positive contrast urethrogram is generally much more informative than a negative con­trast urethrogram. 

• For positive contrast urethrography the contrast agent of choice is one of the organic iodine compounds. It is not necessary to utilize the contrast agent at full strength as a 50% dilution will produce satisfactory results. A 35-ml volume is the proper dose for all but very small dogs- Sedation of the animal is unnecessary in most cases. The animal is catheterized  and the urine removed. After removal of air from a small Bardex catheter by filling its lumen with saline solution or contrast agent, to assure that no air bubbles that may be confused with filling defects will be injected into the urethra, the catheter is inserted into the penile urethra. Its cuff is distended with approximately 1ml of saline solution to prevent the catheter from slipping out during the procedure. Once the catheter is in position the contrast agent is injected through it over a period of about 15 seconds. After approximately 30 of the 35 ml have been injected, the exposure is made with the animal in either the right or left decubitus position.

• The injection is continued during the time the exposure is made. This results in complete filling of the urethra with the contract agent.

• 1. Agents Employed for the Demonstration of the Alimentary Tract:

• The main requirement of substances used for this purpose is that they should be completely insoluble with no possibility of their being acted on by the alimentary secretions or absorbed through the bowel wall. The substance used routinely for this purpose is barium sulphate, usually prepared in a fine colloidal form which provides optimum outlining of the mucosal pattern.

• The chief disadvantage of the use of such inert substances is that, if they introduced into the trachea, or pass through a perforation in the bowel wall into the chest or abdomen, they will not be absorbed or eliminated and may remain in situ indefinitely.

• 2. Water-Soluble Agents

• Substances in this group are practically all iodine preparations, which, being water-soluble, are very rapidly absorbed and eliminated after introduction into the body. They are normally injected into a portion of the vascular system, either for immediate visualization of that system or for subsequent demonstration of the urinary system during excretion through the kidneys. These preparations all have a local irritant effect and should be administered only intravenously

• 3. Agents Excreted Through the Biliary System (Cholecystopaques)

• These are again usually organic iodine preparations which after absorption from the alimentary tract or following intravascular injection  are very largely excreted by the liver and visualize the biliary system.

• 4. Gaseous Agents

• A number of gases have been used as contrast agents but air, oxygen and carbon dioxide are most frequently employed. They are cheap, easy to administer and comparatively sale. They produce less contrast with soft tissues than do substances of high atomic number, but in some circumstances this is advantageous as it avoids complete obliteration of calculi or small foreign bodies. 

• CONTRAST RADIOGRAPHY OF THE ALIMENTARY TRACT

• Indications

• This procedure is employed in an attempt to reveal:

• Obstruction of the alimentary tract by causes such as non-radio-opaque foreign bodies (soft rubber, cloth, etc.), tumour masses or stenosis of the tract.

• Distortions of the wall of the alimentary tract (oesophagcal dilatations, enlargement of the stomach resulting from pyloric stenosis, etc.).

• Lesions of the wall of the alimentary tract (neoplasia, ulcers, etc.).

• Displacement of the alimentary tract, either due to the presence of an intra-abdominal mass or in association with the ruptured diaphragm.

• Normal and abnormal alimentary function.

• Contrast Agents

• Specially prepared colloidal barium sulphate is used routinely for this purpose. It is marketed under a variety of trade names in three main forms:

• Dry powder to be mixed with water to the consistency required. (Micropaque Powder).

• A prepared suspension in water (usually 100 per cent w/v) ('barium meal'). (Micropaque).

• A paste of increased viscosity, used to outline the oesophageal mucosa ('barium swallow'), (Micrqtrast).

• Preparation of the Patient :

• Prior to this examination the alimentary tract should be emptied by with- holding food for some 24 hours, and if necessary, by administering an enema. When dealing with the acutely ill animal there may not be time for such preparation but the tract is likely to have been emptied by vomiting or inappetance.

• Figure 4: Positive gastrography showing normal Duodenum.

• Figure 5: Positive gastrography showing normal GIT.

• Figure 6: Positive gastrography showing normal large intestine.

• Figure 7: Positive gastrography showing normal rectum and colon.

• Figure 8: Negative cyctography.

• Figure 9: Double contrasted radiography.

• UROGRAPHY

• PYELOGRAPHY

• Indications:

• Pyelography is used for the undermentioned purposes:

• To Increase the definition of the kidney shadow and thus aid in the diagnosis of unidentified abdominal masses.

• To demonstrate changes in the shape and structure of the kidney sub­stance due to neoplastic or obstructive changes.

• The procedure can provide some rough indication of kidney function but should not be employed when serious disease of both kidneys is suspected.

• To demonstrate the size and position of the ureters when congenital displacement is suspected.

• Contrast Agents        

• These are organic iodine compounds which, after intravenous administration, are rapidly excreted through the urinary system. These preparation are commonly administered in a dosage of approximately 1 ml per 1 kg body weight for small dogs, and 2 ml per 3 kg body weight for larger dogs.

• Preparation of the Patient

• Whenever possible the dog should be starved for 24 hours prior to the examination and, if necessary, given a mild laxative or an enema, in order to empty the alimentary tract and thus remove extraneous shadows from the abdomen. Water should he withheld for 12 hours and the urinary bladder emptied immediately before the examination

• Figure (8) Intravenous Pyelography.

• Cystography

• Indications:

• To aid in the recognition of small cystic calculi or those of low radio-opacity.

• To demonstrate neoplasia or other lesions of the wall of the-urinary bladder.

• To assist in radiography of prostatic conditions by demonstrating dis­placement of the urinary bladder by an abnormal prostrate gland.

• To check, following an accident, whether the urinary bladder is intact or ruptured.

• Contrast Agents

• These are usually:

• Sterile 20 percent solutions of sodium iodide have been used but this is somewhat irritant on normal mucous membrane and amid be dangerous if there was any risk of it escaping into the abdominal cavity. It would be safer to employ one of the organic iodine preparations intended for pyelography but (as an economy measure) to dilute it to a 5 percent solution.

• Pneumocystography is the most commonly utilized method of radiographically, evaluating the wall of the urinary bladder.

• Before pneumocystography, the animal should be catheterized and all urine with drawn. If the urine is not withdrawn, injection of air will cause bubbles to form and the  bladder wall will not be adequately outlined.

• Next, air is injected into the bladder. Approximately 50 cc of air are satisfactory for a 30-pound dog- The amount can be adjusted according to weight of the animal. If care is taken during the injection procedure, air will usually reflux around the catheter when the bladder becomes fully inflated or resistance can be felt against the plunger of the syringe.

• Following injection of air, ventrodorsal, lateral, and oblique radiographs of the urinary bladder should be secured. Radiographically, the bladder will be seen lo be distended with air; the wall should be easily visualized and appear to be of uniform thickness.

•  Positive contrast cystography is used infrequently in comparison to Pneumocystography. Positive contrast cystography is performated by callinerizing the animal and injecting 10-20 ml of an organic iodine contrast medium. With this technique, spaceoccupying lesions within the urinary bladder an be demonstrated. Evaluation of the urinary bladder can be much more accurately mzde from a pneumocystogram than from a positive contrast cystogram.   

• A duble contrast cystogram can be obtained injection of air followed by injection 5-10 ml of an organic iodine contrast agent into the urinary bladder. Rotation of the animal causes the liquid contrast agent to coat the mucosal surface. Double contrast cystography is the best procedure for radiographically evaluating the mucosa of the urinary bladder. In most cases, however pneumocystography is adequate.

•  Pneumocystography or positive contrast cystography is difficult to perform in cats owing lo the trouble encountered when catheterization is attempted. If catheterizing the animal is not practical, then injection of organic iodine contrast agent, as described in the excretory urography section of this chapter, can be utilized.

• After approximately 15 minutes the medium will collect within the urinary bladder and a positive contrast cystogram will have been obtained. The size of the urinary bladder cannot be controlled with this technique.

• ANGIOGRAPHY

• Angiography, the radiographic demonstration of certain areas of the vascular system by the injection of a water soluble organic iodine compound into a suitable blood vessel (e.g. arteriography, venography, aortography, portal venography angiocardiography  and cerebral angiography).

• Indications

•  The demonstration of occlusion of a particular blood vessel by internal thrombus or external pressure.                    

• To show anatomical variations or pathological lesions of the vascular System.

• Contrast Agents

• They are always water soluble Organic iodine compounds. Apparatus for most procedures the dye may be injected by means of an ordinary surging connected to a hypodermic needle or a catluter which can be mserted into a suitable blood vessel.

• Since the dye will rapidly transported away for the part under examination by circulating blood it is  necessary to expose the X-ray film immediately on completion of the injection.  

• Four people are needed to operate the device. One person will control the x-ray exposure one will inject the dye and two will pass cassettes through the tunnel. All the staff involved must wear protective clothing.

• The first exposure is made just before the end of injection, the cassettes are then advanced and subsequent exposures are usually made at intervals of one or two seconds.

• Figure 10: Arteriography of the tarsal joint after chemical arthrodesis.