Abdominal Positioning & Small Animal Special Procedures Chapters 18 & 25

Learning Objectives: Abdomen & Soft Tissue Understand radiographic concerns associated with the abdomen Properly and safely position a small animal for two common radiographic views, with the ability to: Measure accurately Center the x-ray beam appropriately Image with correct borders Properly position the patient Understand alternate views Identify normal abdominal anatomy, including major differences between cats and dogs

Small Animal Abdomen: Anatomy

SA Abdomen: Radiographic Concerns Less natural contrast than thorax Similar densities & multiple organ systems GI gas & fat provide contrast Contrast media often required Generally use a higher kVp and lower mAs Try for higher mA and lower time to shorten exposure May need two views in deep-chested dogs Can average measurements on smaller animals Higher kVp = More shades of grey Lower mAs = Shorter exposure less motion artifacts

SA Abdomen: Radiographic Concerns Use nonmanual restraint whenever possible Expose at end of expiration during pause Allows maximum space for abdominal organs Minimize intestinal artifacts by: Fasting 12 hours Cleansing enema 3-4 hours prior Abdominal compression can reduce thickness Can use a compression paddle Moves underlying organ to aid in visualization Reduces thickness so lessens scatter Usually a brief pause at end of expiration Maximum space for stomach contents as lungs contract & diaphragm relaxes The Pneumatic Compression Paddle is used for guided compression during radiographic studies of the gastro-intestinal tract. The paddle is inflated beneath the patient to increase pressure in a concentrated area.

Radiographing the Abdomen: Positioning

Lateral Abdomen – Dog vs Cat

Abdominal Positioning: Lateral L/R marker at ventral aspect Sternum & spine on same plane Aim is symmetry & superimposition Hind limbs caudal to prevent superimposition of femoral muscles Center the beam differently in dogs & cats Cats more caudal than dog Right lateral separates kidneys better Left lateral is preferable in vomiting patients Gas in pylorus can highlight a foreign body Left lateral may be required in contrast studies

Liver Mass

Abdominal Mass – Lateral View

Gastric Trichobezoar A trichobezoar is a bezoar (a mass found trapped in the gastrointestinal system) formed from the ingestion of hair.

Gastric Dilitation & Volvulus (GDV) “Double bubble”

Uterine Inertia/Rupture

Abdominal Positioning: Ventrodorsal Measure at liver Central ray positioning differs between cat & dog Imagine a straight line connecting nose & caudal midline * DV can be used as alternative if animal is compromised by VD Dog Cat

Abdominal Mass – VD View

Abdomen: Modified Lateral & Lateral Oblique Used when radiographing the entire male urinary tract Moves hind limbs so they don’t overlap penile urethra or bladder

Abdominal Anatomy: Notes Fat animals image better than emaciated ones Fat serves as a contrasting opacity Many normal structures hidden radiographically Ureters, urethra, adrenals, pancreas, etc. Abnormalities can make them visible Liver – Normally lies beneath ribs Best evaluated via lateral radiograph Stomach – Normally within rib cage – include caudal ribs in radiograph Food images as granular material of mixed opacity Can be 2-3 times larger after a meal Gas rises and fluid moves with gravity

Chocolate Ingestion Chloe - Full stomach

Abdominal Anatomy: Kidneys Dogs: Canine kidneys elongated Only the left kidney & part of the right can be seen Bladder is cranial to the pelvis Cats: Feline kidneys more rounded Both kidneys can generally be seen Bladder more rounded & cranial than dog Both Left kidney is generally more caudal

Bladder Stones

Switching gears now to… Small Animal Special Procedures

Special Procedures: Learning Objectives Understand the differences between types of contrast media Understand the appropriate patient preparation for contrast studies Know procedures & protocols for various studies Understand the additional modalities that can be used in addition to contrast studies ID normal contrast anatomy

Special Procedures: General Principles Contrast media attenuates the x-ray beam & can show previously unseen differences in abdominal structures. 2 types of contrast media: Positive-contrast: Appears white or radio-opaque Negative-contrast: Appears dark or radiolucent Contrast agents are used in 2 ways: Demonstrate anatomy by outlining or filling Demonstrate physiology via excretion through an organ Attenuates = lowers the intensity of the x-ray beam

Special Procedures: General Principles Contrast studies are used to: Provide information to make a diagnosis Evaluate a suspected lesion Determine proper treatment Injected contrast substance: Used to cause a difference in density & organ visibility yet still be harmless to patient Higher kVps typically needed in contrast studies Should never replace a simple survey radiograph Ultrasound & other imaging has replaced contrast radiography in many evaluations Barium can be USED as a treatment

Positive-Contrast Media: Barium Sulfate Used to radiograph the GI tract Administer orally or rectally Low cost & palatable Does not alter normal physiologic function Delineates mucosal walls well Not absorbed in intestines Cautions: Cannot be used if a gastric perforation is suspected Aspiration in lung can be fatal Atomic numbers of barium & iodide higher than tissues/bones

Barium Aspiration: Lungs

Positive-Contrast Media: Iodine Use for suspected gastric perforation or obstructions Instead of barium Used for functional studies Oral or injectable forms Has a bitter taste Nonirritating if aspirated or leaked into body cavities Mixes with blood or body fluids & is excreted via the kidneys More expensive than barium Functional/physiology vs anatomic

Negative & Double-Contrast Media Negative-contrast media: Low atomic number or low-density agents Air, nitrous oxide, oxygen, and carbon dioxide Absorb fewer x-rays & appear dark on radiographs Less mucosal detail with negative vs positive-contrast Be careful not to over-inflate organs (bladder, etc.) Air embolism can lead to cardiac arrest Double-contrast procedures: Use both positive & negative agents Normally used to image the urinary bladder, stomach, or colon Negative-contrast administered first to avoid air bubbles

Negative Contrast

GI Tract Studies Patient preparation: Indications: Fasting + a cathartic/laxative and enema Take a survey radiograph prior Take required number of radiographs 4 views generally needed Oblique views or compression may be required Indications: Vomiting, diarrhea, or constipation Hematochezia or melena Masses or foreign bodies Abdominal pain Post-abdominal trauma Cathartic - laxative Barium spill behind the screen

GI Tract Studies Contraindications: Contrast agents: Fluid-filled esophagus or stomach Atonic bowel Gastric torsion Gastric perforation Contrast agents: Barium is typically used because it doesn’t separate Shake prior to use Chilling barium for upper GI series speeds up transit time Possibility for contamination once opened Spilling barium on the coat will cause a radiographic artifact Barium-impregnated polyurethane spheres (BIPS) – A way to quantify gastric emptying Dosage is number of large & small spheres Gastric emptying rate is calculated based on number in areas of GI tract Large spheres are designed to stop at obstruction Pics on p.384 in book

Esophagography Contrast radiography of the esophagus to identify lesions Evaluates morphological or structural alterations Uses a paste of positive contrast media Indications: Dysphagia Regurgitation, gagging, or retching Megaesophagus Abnormal swallowing Esophageal dysfunction Foreign bodies Blockage d/t neoplasm in a cat

Esophagography Precautions: Patient preparation: Comments & tips: Patients with dysphagia are at risk for aspiration Contrast may not be needed if esophagus is fluid or food-filled Patient preparation: If evaluating megaesophagus – empty prior to administration Fast if further GI studies are planned Comments & tips: Avoid barium artifacts Pharyngeal issues are best evaluated mid-swallow

Esophagography

Megaesophagus

Upper GI Study Barium is given orally, then images are taken during transit through stomach and small bowel Studies can be done for: Morphology – Form & structure of organs Size, shape, and position or organs Character of stomach wall & contents Lesions in the GI tract Function – How organ works Gastric motility Intestinal function Indications: Any GI irregularities (vomiting, diarrhea, anorexia, weight loss, etc.) Inconclusive results of survey radiograph

Upper GI Study Precautions: Patient preparation: For suspected perforation or rupture, use iodides Unless dehydrated or compromised – ultrasonography preferred Delay study if full stomach Gastric distention is not recommended immediately after gastric surgery Patient preparation: GI tract should be empty – fast at least 12 hours prior Administer enema 2-4 hours prior If using orogastric tube - verify placement in esophagus Before removing, clear with small amount of air and kink to prevent aspiration

Upper GI Study Procedure: Comments & tips: Administer barium (slowly) Take 4 radiographs centering over cranial abdomen Both VD and lateral views at 15, 30, and 60 minutes post Hourly radiographs until study is completed Label films carefully Comments & tips: If slow GI emptying is suspected, start study early in the day Give a sufficient volume of barium Gastrogram is finished when the majority of barium is no longer visible in the stomach Upper GI is complete when the barium is in the colon Ultrasound is safer in compromised patients Barium doses: 8-10 mls/kg in dogs < 10 kg 5-8 mls/kg in dogs 10-40 kgs 3-5 mls/kg in dogs > 40 kg

Barium Upper GI Study: Dog 15 minutes 30 minutes 60 minutes 2 hours: Stomach, complete small intestine, cecum 4 hours: Small & large intestine (Stomach, duodenum) (Stomach, duodenum, jejunum)

Lower GI Study Used for examination of the cecum, colon, and rectum Evaluates for masses and lesions Full distention with removal of feces is required Rectal administration of barium may be required Sedation is usually warranted Used when lumen narrowing prevents passing an endoscope Indications (examples): Abnormal defecation Excessive mucus or bright red stool Strictures or obstructions Neoplasia Colitis

Lower GI Study Precautions: Patient preparation: No barium if a perforation is suspected Transient spasms may occur Patient preparation: Fast for 24-36 hours (water allowed until 4 hours prior) Colon should be free of fecal matter Cathartic & warm water enemas the night before Avoid soapy-water enemas Sedate or anesthetize Take survey lateral & VD radiographs

Lower GI Study Procedure: Comments & tips: Exposure factors may need to be increased Have chemically restrained patient on the table Insert catheter rectally & inflate cuff Stop infusion if any resistance Take 3-view radiographs Oblique view may be required in males Process the films, then remove as much contrast medium as possible before removing catheter Comments & tips: Remove catheter away from x-ray table Give barium in small increments

Lower GI Study (barium)

Links to Case Studies Barium Study in a Dog (Virtuavet)- http://virtuavet.wordpress.com/2010/ 10/26/barium-study-in-a-dog/ 8-Year Old Curly-Coat Retriever Takes a Long Road to a Simple Answer (Virtuavet)- http://virtuavet.wordpress.com/2010/03/28/8-year-old-curly-coat-retriever-takes-a-long-road-to-a-simple-answer/ “Titus”