Contrast radiography



            When the radiodensity of the tissue itself or its surrounding structures is deliberately altered to obtain a radiograph with enhanced visualization and demarcation, it is called contrast radiography. The substance used for this purpose is called a contrast medium. The materials which increase radiodensity of the structure of the tissue in relation to surrounding tissue are called a positive contrast medium and those, which decrease the radiodensity, are negative contrast medium. In double-contrast radiography, both contrast media are used. Contrast radiography has the following advantages:

                                                                                         

  1. Organs or structures can be evaluated more effectively for their size, shape, and position.
  2. Valuable information can be gained regarding the serosal and mucosal surface of hollow organs.
  3. In some instances idea of the function of the organ can be formed.

Positive Contrast Media



            The atomic number (Z) is generally positively correlated with the radiodensity of a compound. The highest Z in the body is that of bone (138) and the lowest Z is of air-filled lungs (4). For compounds to be used as positive contrast agents, Z of the element has to be above 50 e.g. barium (Z=56) and iodine (Z=53).

Ideal Positive Contrast Media



  1. It should have the desired Z number
  2. It should be inert or its metabolites should not be toxic
  3. It should be retained in the area of interest only for the desired period
  4. Agents used for outlining excretory organs must specifically excrete through that route insufficient concentration so as to produce radiodensity of the desired value.

Adverse Reactions


  1. Chemotoxic or local reactions: includes all types of allergic responses; urticarial, head jerks, muscle fasciculation, etc.
  2. Systemic and hypersensitivity reactions: may be due to a mediator release (histamine), antigen-antibody reaction or due to involvement of acute activation systems (complement the system, coagulation system, kinin system, etc). Premedication with steroids reduces adverse effects.


Broad Classification of Positive Contrast Media


                I.      Barium sulfate preparations: exclusively used for outlining the alimentary tract. It is insoluble and is not absorbed in the body. Its use should be avoided if perforations are suspected. It is available in powder, paste, or suspension formulations.

             II.      Water soluble iodine preparations: all conventional and low osmolarity contrast media fall in this group.  Commonest conventional agents are the sodium and meglumine salts of iothalmic, diatrizioc, and metrizioc acid.  

         III.      Cholycystapaques: water-soluble organic iodine preparations, but exclusively excreted through the biliary system. These agents are exclusively used for outlining the biliary tract and gall bladder.


          IV.      Viscous and oily agents: viscous and oily preparations are indicated when less elimination of the contrast media is required.


Negative Contrast Media


            Room air, carbon dioxide, and oxygen are the most commonly used negative contrast media. An ideal negative contrast media should be inert, quickly dissolved in the body fluids, and quickly eliminated from the body. Room air is cheap and readily available negative contrast media but it less readily absorbed. Gases provide poor contrast and are best used in double-contrast studies. 


Contrast Radiography of the Digestive System


  1. Sialography: contrast radiographic study of salivary glands and ducts. Its main indications are to diagnose;
    1. Space occupying lesions of the parotid gland
    2. Site of obstruction in ducts
    3. Site of leakage of saliva

Technique: In the retrograde technique, sedate the animal in lateral recumbency; cannulate the salivary duct through its opening in the oral cavity. Secure the cannula tightly with suture to prevent the backflow of the contrast agent. Infuse 3-6 ml of water-soluble     contrast agent and obtain a radiograph at the end of injection.

In the antegrade technique, a water-soluble contrast agent is injected into the glandular tissue aseptically and serial radiographs are taken. Any agent which decreases the flow of saliva e.g. atropine should not be used before sialography.



  1. Barium Swallow (Oesophagraphy): this is used to evaluate both the structural and functional status of the esophagus after the introduction of a positive contrast agent. This is indicated to diagnose cases of oesophageal obstruction, stenosis, diverticulum, perforations, and mucosal disease. It should not be done rupture of the thoracic part of the oesophagus is suspected. Barium sulfate solution (cream like) is usually used as a contrast agent. Water-soluble iodine-based agents are recommended if cervical oesophageal rupture is suspected.



Technique: a survey radiograph of the area is obtained before the administration of contrast media. Administer slowly orally contrast agent i.e. 1-2 ml/kg barium sulfate. A lateral radiograph is made after the administration of the last swallow. In absence of obstruction, the mucosal folds will appear as linear streaks and barium meal is quickly cleared into the stomach. Any obstruction in the passage will lead to the accumulation of barium cranial to the obstruction site. The diverticulum is identified as an oesophageal out pouch filled with contrast agent. 



  1. Barium Series: this is used to examine radiographically the gastrointestinal tract. The procedure is indicated to evaluate the structural and functional status of the GI tract. The technique should be avoided if a rupture of the stomach or intestine is suspected.



Technique: keep the animal off feed for 36 hours and off water for 12 hours. Administer 0.5 kg of magnesium sulfate 24 hours before the study. Administer 100 grams of activated charcoal orally 12 hours before the study in an attempt to clear the GI tract of gases. Perform worm soap water enema 3 hours before the study. After taking the survey radiograph, administer orally 70% W/V solution of barium sulfate @ 25-30 ml/kg. Obtain lateral and ventrodorsal radiographs at different intervals. Most organs up to caecum are visualized at 4 hours, while the colon gets demarcated between 6-8 hours after administration (in large animals and sheep and goat). Use 15-20% barium sulfate suspension in case of a dog.



  1. Barium Enema: This is indicated in suspected cases of intraluminal or extraluminal obstructions. If perforations are suspected the technique should not be used.



Technique: keep the animal off feed for 36 hours and off water for 12 hours. Administer orally laxative dose of magnesium sulfate 12 hours before the study. Warm-soap water enema will be given to the animal 2 hours before the study until the returning fluid is clear. Sedate the animal and place it in lateral recumbency. Raise the hindquarter, insert a well-lubricated catheter into the rectum, and inflate the cuff. Attach the catheter with the enema pump filled with 15-25% W/V barium sulfate solution and infuse it @ 15-20 ml/kg to fill the colon. Obtain the right lateral and ventrodorsal projections.



Contrast Radiography of Urinary System




1.      Intravenous Pyelography (Excretory Urography): IVP (Intravenous Pyelography) refers to contrast radiographic examination of kidney and ureters after the intravenous introduction of positive contrast media. Water-soluble iodine-based contrast agents are excreted through urine, intravenous injections of these agents are used for contrast radiography of this system. This technique also serves as a rough index of kidney function.



Technique: animal preparation is the same as in the case of barium series contrast radiography. In the case of ruminants, pneumoperitoneum is created to provide a negative contrast. Contrast media can be infused either through a bolus technique (low volume rapid infusion) or drip technique (high volume drip infusion). Sodium iothalamate (70% W/V) or sodium tri-iodinated organic compounds (23% W/V) are generally used for this purpose.  The usual dose is 2-3 ml/kg in small ruminants, 0.5 ml/kg for large ruminants. In the dog, the total dose should not contain more than 35 g of iodine. In case of bolus method, the entire dose is injected as a bolus, while in the case of the drip technique entire volume is injected intravenously over a period of about 10 minutes. Standing right lateral and ventrodorsal radiographs are taken. The first radiograph should be taken soon after the completion of injection than after intervals. A 10 minutes radiograph show both kidneys and Ureters. Usually, in 20 minutes, the contrast media reaches the urinary bladder.



  1. Urethrography: to diagnose abnormalities of the urethra (mostly in the male).

Technique: the animal is kept off feed for 24 hours and off water for 12 hours. Sedate the animal and prepare the area. Lubricate a catheter with lignocaine gel and insert it into the urethra. Insert 5-10 ml of lignocaine in the urethra to desensitize urethral mucosa. Insert the water-soluble iodinated agent through the catheter and take a lateral radiograph during the last phase of injection. In the case of ram and buck intravenous pyelography can be performed and when most of the contrast media reaches the bladder, the abdomen is pressed extremely so that a few drops of urine appear at the urethral opening.



  1. Cystogrpahy: contrast radiographic examination of the urinary bladder. To diagnose structural abnormalities and diseases of the bladder.
Technique: preparation of the animal is the same as in the case of barium series. Sedate and restrain the animal in lateral recumbency. Place the catheter and evacuate the bladder as much as possible. Infuse 2% lignocaine (5-10 ml) into the bladder. Remove air from the catheter. A water-soluble an iodinated contrast agent (sodium iothalamate 70% W/V, diluted to a concentration of 10-15%) or a negative contrast media (room air, etc.) is injected into the bladder through a catheter. In the dog, the dose is 6-12 ml/kg. For a double-contrast study, inject 15-20 ml of positive contrast media, roll the animal, and then infuse negative contrast to fill the bladder. For triple contrast, pneumoperitoneum is created. Obtain the right lateral and ventrodorsal radiographs.

Comments

Post a Comment

Popular posts from this blog

Sugar •        Sugar has been described both in history and recently as a topical wound treatment. •        The basis for its use is its high osmolality. •        Thus, it is effective in reducing edema due to its hydrophilic action. •        It has also been reported to attract macrophages, accelerate slough of devitalized tissue, provide cellular energy, and promote granulation tissue. •        Its use should be discontinued after the wound has a good bed of granulation tissue. •        It has been reported to be effective against Staph., Strep., Enterobacter, E. coli, Klebsiella, Pseudomonas, and Serratia organisms. •          It reportedly does not cause hyperglycemia. •        It should be used with caution on large wounds. I...
Read more

Nematodes

Image
    General Characteristics: Nematodes are commonly called roundworms because, as the name suggests, they are round when viewed in cross section. They are cylindrical in structure and taper towards their anterior and posterior ends. They are bilaterally symmetrical. The sexes are separate in most species, a few are hermaphrodite. Nematodes that parasitize domestic animals are found in all parts of the body but are most commonly found in the digestive and respiratory tracts, and in the circulatory system.
Read more
PHYSICAL EXAM PROCESS 1)  Signalment / History 2)  General Appearance / Initial Observations 3)  Vital Signs 4)  Physical Exam (Systems Approach or Head to Toe) 5)  Surgical / Anesthetic Risk Assessment 6)  RAVS Animal Condition (RAC) Score
Read more