Pharma

• Lead subacetate was used to study the digestive system of the guinea pig which later proved to be toxic


  1896
• Walter Cannon


  Used Bismuth subnitrate in his series of experiments to study the digestive system, subjects included: geese, cats, and a 7-year old girl
• Thorotrast, which incorporated thorium, proved to be radioactive
• Articles about the advantages of the inert in insoluble compound barium sulfate began to appear in the medical literature


  1910
• Barium sulfate was used rapidly due to low toxicity, cost, and availability
• Walter Dandy used air to study cerebral ventricles in children with hydrocephalus (Pneumoencephalography)


  1918
• Hydrocephalus


  A chronic, neurological condition caused by an abnormal accumulation of cerebrospinal fluid (CSF) within cavities of the brain called ventricles, resulting in pressure on the brain
• Dandy-Walker Malformation


  Congenital malformation that involves the cerebellum and fourth ventricle
• Carbon dioxide, nitrous oxide, and oxygen came into use
• Egaz Moniz injected sodium iodide into the cerebrovascular circulation via carotid arteries which proved to be a blood vessel irritant


  1927
• Atoms with high atomic numbers could be placed on a non-toxic water soluble carrier molecules
• Three iodine atoms per carrier molecule

  1950
• Contrast agents


  Agents that are instilled into body orifices or injected into the vascular system joints and ducts to enhance subject contrast in anatomic areas where low subject contrast exists
• Negative contrast media


  Radiolucent, appear dark (black) on radiographs, composed of low atomic number elements, administered as gas or gas producing tablets, crystal or soda water
• Positive contrast media


  Radiopaque, appear white on radiograph, composed of elements with high atomic numbers, barium sulfate, iodinated contrast
• MRI contrast agent


  Gadolinium diethylenetriaminepentaacetic acid (gadolinium-DTPA), a metallic and magnetic agent that will affect the signal intensity used to image the anatomic area of interest
• Ultrasound contrast agents


  Generally gas-filled microbubbles that affect the sound wave to enhance ultrasound contrast
• Double contrast studies


  Positive and negative contrast agents are used together, positive coats the part under study, negative fills the space and permits visualization through the gaseous medium
• Common double contrast studies

  • Upper gastrointestinal series (UGIS)
  • Barium enema
  • Retrograde arthrography (shoulder, knee, hip, wrist)
• Desirable features of a contrast agent

  • Easy to administer
  • No toxicity/carcinogenicity
  • Stable compound
  • Concentrates in area of interest
  • Proper demonstration of the organ system
  • Should have rapid elimination
  • Minimal distress to patients (viscosity)
  • Cost effective
• Barium sulfate


  Inert powder composed of crystals that is used for examining the digestive system, chemical formula: BaSO4, not soluble in water, must be mixed or shaken into a suspension
• Flocculation


  Tendency of barium sulfate to clump
• Vegetable gums, flavoring, and sweeteners are added to barium sulfate to increase palatability
• Small intestine studies


  • Oral formulations of barium sulfate and methylcellulose
  • Give see through effect to better diagnose small lesions
• Lower GI series


  Barium sulfate mixed with cold tap water to reduce irritation, aid the patient in holding the enema, and reduce spasm and cramping
• Hypervolemia


  Introduction of contrast medium may result in increased water absorption by the colon leading to excess fluid entering the circulatory system
• Addition of 2 teaspoons of table salt per liter of water is applied in the enema concentration to address hypervolemia
• Contraindications of barium sulfate

  • Patients who do not absorb barium naturally (could cause peritonitis)
  • Obstruction
  • Perforation of the colon with extravasation
  • Leakage could result in inflammation of the abdominal cavity (barium peritonitis)
  • Older patients with long term use of steroids (higher risk for colon perforation)
  • Patients with diverticulitis and ulcerative colitis (result in inflammation and degradation of the colon)
  • Patients with toxic megacolon (should not have lower GI procedures, risk of rupture)
  • Recent biopsy of the colon
  • Vaginal rupture
  • Sedated patients for UGIS examinations (higher aspiration risk)
  • Mentally handicapped patients (higher aspiration risk)
• Patient history factors in barium sulfate examinations

  • Age
  • Ability to communicate, hear and follow directions
  • Risk of colon perforation caused by loss of tissue tone
  • Diverticulosis/ulcerative colitis
  • Difficulty in holding an enema
  • Recent colon biopsy
  • Mental retardation, confusion, dizziness
  • Risk of aspiration during UGIS
  • Recent onset of constipation or diarrhea
  • Tumor rupture
  • Nausea or vomiting
• Osmolality


  Measure of the number of dissolved particles in a medium, measure of the number of particles (molecules, ions, cations)
• Ion


  Atom or molecule having a negative charge or a positive charge
• Ionic iodine contrast media

  Atomic number of iodine 53, dissociate into two molecular particles in water or blood plasma, anion: negative, cation: positive
• Primary anions employed


  • Diatrizoate
  • Iothalamate
  • Metrizoate
• Cations

  Positively charged ions, located at number 1, increases the solubility of the medium
• Non ionic iodine contrast media

  Molecules that do not dissociate into anion and cation (nonionics) or ionic but are too big to have osmotic effects (ioxaglate), lower osmolality contrast media
• Ioxaglate


  Ionic molecule composed of two connected benzene hexagons, dimer, carries six iodine atoms per molecule, ionic
• Iodixanol (visipaque)


  Nonionic dimer, isomolar (same number of particles to blood plasma by the addition of electrolytes)
• Advantage of lower osmolality

  Hydrophilic (water soluble) which make it less likely to be reactive with cells that can trigger allergic effects
• General effects of water soluble contrast media

  • High osmolality and chemical nature
  • Viscosity/friction: concentration and size of molecule affects the injectability or delivery of media, warmer temperature decreases viscosity

  
• Osmotic effects


  Increase in the number of particles in the blood plasma due to the dissociation of ionic media, displacement of plasma water by contrast particles causes water from body cells to move into the vascular system resulting in hypervolemia