Contrast Media Notes

Glossary of Terms:

  • Acid Group: Contains carbon double bonded to oxygen, single bonded to another oxygen, and has a negative charge at body pH.
  • Amine Group: Contains nitrogen bonded to two hydrogen atoms.
  • Anaphylactoid: Resembles an immune system response to a foreign material (antigen).
  • Atomic Numbers: Number of protons in the nuclei of different elements.
  • Bond: Interactions between electrons of atoms that hold atoms together in a stable group.
  • Bronchospasm: Involuntary constriction of bronchial tubes, usually from an immune system reaction.
  • Compound: Substance composed of two or more elements combined in definite ratios.
  • Contraindications: Factors in a patient's history that indicate a medical procedure should not be performed or a medication given.
  • Creatinine: Nitrogen-containing waste product of metabolism, excreted by the kidneys; high blood levels indicate poor kidney filtration.
  • Dimer: Compound formed by bonding two identical simpler molecules.
  • Esters: Organic compounds formed when alcohols and acids are combined chemically.
  • Ethyl Group: Two carbon atoms linked to each other and to hydrogen atoms.
  • Extravasation: Leakage from a vessel into the tissue.
  • Fatty Acids: Long chains of carbon atoms linked to one another and to hydrogen atoms; one end has an acid group.
  • Flocculation: Formation of flaky masses resulting from precipitation or coming out of a suspension or solution.
  • Histamine: Molecular substance containing an amine group; causes bronchial constriction and a decrease in blood pressure.
  • Hydroxyl: Chemical group containing one hydrogen atom and one oxygen atom; carries a negative charge (anion) when not part of a molecule.
  • Ionic: Atom or molecule having a negative charge (anion) or positive charge (cation).
  • Methyl Groups: Biochemical groups containing one carbon atom and three hydrogen atoms.
  • Molecules: Stable groups of bonded atoms having specific chemical properties.
  • Monomers: Simple molecules of a compound of relatively low molecular weight.
  • Osmolality: Measurement of the number of particles that can crowd out water molecules in a kilogram of water.
  • Osmosis: Movement of water from an area of high concentration to an area of low concentration through a semipermeable membrane.
  • pH: Relative acidity or basicity of a solution; below 7.0 is acidic, above 7.0 is alkaline.
  • Radiopharmaceutical: Pharmaceutical compound attached to a radioisotope.
  • Shock: Inadequate blood flow with resulting loss of oxygen.
  • Solution: Uniform mixture of two or more substances composed of molecule-sized particles that do not react chemically.
  • Suspension: Nonuniform mixture of two or more substances, one of which is composed of larger-than-molecule-size particles that tend to cluster.

Introduction to Contrast Media

  • Historical Aspects:
    • 1918: Walter Dandy used air (a negative contrast medium) to study cerebral ventricles in children with hydrocephalus.
      • Use of air was initiated to localize tumors in the brain and spinal cord.
      • Later, carbon dioxide, nitrous oxide, and oxygen were also used.
    • Following Roentgen's discovery of x-rays, physiologists used high atomic number compounds mixed with food to monitor digestive systems in animals.
      • 1896: Lead subacetate was used, but proved toxic.
      • Walter Cannon used bismuth subnitrate to study the digestive system.
        • Credited with realizing GI tract diseases could be studied using radiopaque media.
    • Thorotrast, which incorporated thorium, was radioactive.
    • Barium sulfate began to be used due to its lack of toxicity, low cost, and availability.
    • 1927: Egas Moniz introduced water-soluble iodinated contrast media, injecting sodium iodide into the cerebrovascular circulation; however, sodium iodide was a blood vessel irritant.
    • 1930s: Chemical methods improved to place high atomic number atoms (iodine) on nontoxic water-soluble carrier molecules.
      • More iodine atoms per molecule were added to increase visualization of vascular and urinary systems.
    • 1950s: Use of three iodine atoms per carrier molecule began (triiodinated molecules).
      • Basic chemical structures for ionic and nonionic water-soluble iodine contrast media originated.
  • Purpose of Contrast Media:
    • Anatomic detail is visualized when the area of interest differs in radiographic density from surrounding tissue.
    • Radiographic density differences are affected by:
      • Absorption characteristics of tissues.
      • Technical factors.
      • Image receptor characteristics.
      • Automatic image processing.
      • Use of contrast media agents.
    • The body absorbs x-ray photons based on tissue atomic numbers and amount of matter per volume.
      • High-atomic-number tissues (e.g., bone with calcium) absorb more x-ray photons.
      • Soft tissues transmit/scatter x-ray photons more easily, resulting in decreased x-ray absorption.
    • Low subject contrast results in few density differences, making visualization difficult.
      • Contrast media changes absorption characteristics, altering subject contrast and radiographic density differences.
    • Contrast media enhances density differences to improve anatomical detail visualization.
    • Contrast media are diagnostic agents instilled into body orifices or injected into the vascular system, joints, and ducts to enhance subject contrast.
    • The ability of contrast media to enhance subject contrast depends on:
      • Atomic number of the element used.
      • Concentration of atoms per volume of the medium.
    • Contrast media are classified as:
      • Negative contrast agents.
      • Positive contrast agents.
  • General Types of Contrast Agents:
    • Radiolucent (Negative):
      • Easily transmit or scatter x-ray photons.
      • Appear dark (increased density) on radiographs.
      • Composed of low atomic number elements.
      • Examples: Air, carbon dioxide.
    • Radiopaque (Positive):
      • Absorb x-ray photons.
      • Appear light (decreased density) on radiographs.
      • Composed of high atomic number elements.
      • Examples: Barium, iodine.
    • Negative and positive agents can be used together.
      • Examples: Colon visualization, knee menisci visualization.
    • Specialty Contrast Agents:
      • Used in MRI (e.g., gadolinium-DTPA).
        • Metallic and magnetic agent affecting signal intensity.
      • Ultrasound (gas-filled microbubbles).
        • Affect sound waves to enhance contrast.

Negative Contrast Media

  • Physical Properties:
    • Composed of low atomic number elements.
    • Administered as gas (air) or gas-producing tablets, crystals, or soda water (carbon dioxide).
    • Oxygen is rarely used alone because cells absorb it quickly.
  • Specific Procedures:
    • Air alone can provide negative contrast for laryngopharyngography because upper respiratory structures contain air naturally.
    • Radiolucent contrast media are often used in combination with radiopaque media to outline lumens or spaces within body structures.
  • Adverse Reactions
    • Complications are generally minimal. Air can cause emboli (small air masses lodged in blood vessels, causing pain and loss of oxygen).
    • Patients receiving barium sulfate with air should drink plenty of fluids after the procedure to dilute and eliminate the barium sulfate.
    • Water-soluble iodine contrast media with air in joint spaces usually does not result in complications.

Positive Contrast Media

  • Barium Sulfate Contrast Media

    • Physical Properties
      • Barium has an atomic number of 56 (radiopaque).
      • Barium sulfate (BaSO_4) is an inert powder composed of crystals used for examining the digestive system. It has a 1:1:4 ratio of barium, sulfur, and oxygen atoms.
      • It is not soluble in water and must be mixed into a suspension.
      • Flocculation (clumping) can occur, especially in acidic environments such as the stomach.
      • Stabilizing agents like sodium carbonate or sodium citrate are used to prevent flocculation (listed as suspending agents on labels).
      • Oral formulations may contain vegetable gums, flavoring, and sweeteners for palatability.
      • Suspensions must be concentrated enough to absorb x-rays and flow easily to coat organs.
      • For small intestine studies, barium sulfate and methylcellulose (nondigestible starch) can be used to provide a see-through effect for better lesion diagnosis.
      • For lower GI studies, barium sulfate is mixed with cold tap water to reduce irritation and aid in enema retention. Room temperature water can also be used for maximal patient comfort.
      • The colon absorbs water, and increased absorption can cause hypervolemia (excess fluid in the circulatory system). Adding 2 teaspoons of table salt per liter of water reduces this risk.
      • Following the manufacturer's directions is critical when mixing barium sulfate suspensions for diagnostic radiographs.
    • Specific Procedures
      • Contraindicated if a patient has a suspected digestive tract perforation. Barium sulfate is not absorbed naturally and can cause peritonitis if it enters the peritoneal or pelvic cavity, requiring surgical removal.
      • Water-soluble iodine contrast agent is recommended as the alternative.
      • The radiologic technologist must obtain a detailed patient history to give appropriate patient care.
    • Adverse Reactions
      • Patients should be instructed to drink plenty of fluids after receiving barium sulfate to prevent constipation caused by water absorption in the colon.
      • Perforation of the colon with extravasation (leakage) into the abdominal cavity can occur, leading to barium peritonitis.
      • Older adults or patients on long-term steroid medication are at increased risk due to tissue atrophy.
      • Patients with diverticulitis, ulcerative colitis, or toxic megacolon are also at risk.
      • Recent colon biopsy is a contraindication until the area heals.
      • The barium retention catheter can cause colon perforation. Inflate the retention cuff gently.
      • Vaginal rupture is a rare complication of incorrect catheter placement.
      • Water absorption from the colon can lead to hypervolemia, resulting in pulmonary edema, seizures, coma, and death. Saline solution reduces the possibility of hypervolemia.
      • Sedated patients should not undergo upper GI examinations due to the risk of aspiration, as well as mentally handicapped patients or patients with altered mental status.
      • Allergic-type reactions may be caused by preservatives in the barium sulfate preparation or latex in barium enema retention catheters.
      • Occasionally, barium sulfate has collected within the appendix.

  • Water-Soluble Iodine Contrast Media:

    • Physical Properties:
      • Iodine has an atomic number of 53 (radiopaque).
      • Ionic Iodine Contrast Media:
        • Dissociate into two molecular particles (anion and cation) in water or blood plasma.
        • Anion part begins with a benzene ring (six-carbon hexagon).
        • Each anion contains three iodine atoms (triiodinated).
        • One carbon bond site is occupied by an acid group (negative charge at physiologic pH). Anion and cation dissociate upon injection.
        • Two carbon bond sites occupied by chemical structures to increase solubility or excretion rate.
        • Cation part is either a sodium atom or methylglucamine.
        • Methylglucamine contains six carbons bonded to one another and bonded to oxygens and hydrogens (hydroxyl groups) from glucose.
        • Most ionic iodine contrast media are identified as higher-osmolality contrast media due to their osmotic effects.
          • Osmolality is a measure of the total number of particles in solution per kilogram of water.
          • Adverse reactions are often related to osmolality because it determines osmotic pressure, controlling water movement in the body.
          • High-osmolality contrast media have an increased number of particles, pulling water toward them.
      • Nonionic Iodine Contrast Media:
        • Molecules do not dissociate into anions and cations.
        • Examples: ioxaglate (Hexabrix).
        • Identified as lower-osmolality contrast media.
        • Ioxaglate is an ionic dimer composed of two connected benzene hexagons, with one carrying an acid group that dissociates on injection.
          *Ioxaglate carries six iodine atoms per molecule.
        • Most ionic iodine contrast media are monomers (simple molecules of relatively low molecular weight).
        • Nonionic dimers (e.g., iodixanol [Visipaque]) are isomolar (having the same number of particles) to blood plasma.
          • Achieved by adding electrolytes (small anions and cations).
        • Lower-osmolality contrast media are more hydrophilic (water soluble).
          • Less reactive with cells that trigger allergic effects.
        • Both ionic and nonionic agents contain additives (e.g., citrate, calcium disodium edetate) to prevent iodine atoms from being removed from the contrast molecules.
    • General Effects:
      • High osmolality and chemical structure are major characteristics of water-soluble media responsible for physiologic effects.
      • Ionic agents are typically higher-osmolality contrast media and show greater effects and adverse reactions.
      • Viscosity (friction) affects injectability and is influenced by concentration and size of the molecule.
      • Heating the medium to body temperature reduces viscosity and facilitates rapid injection.
      • Osmotic Effects:
        • Ionic media dissociate in water, increasing the number of particles in plasma and displacing water.
        • Water moves from high to low concentration (osmosis).
        • Water from body cells moves into the vascular system, causing hypervolemia and blood vessel dilatation, producing pain and discomfort.
        • Blood pressure may decrease (vessel dilatation) or increase (hypervolemia/hormones in kidneys).
        • When high-osmolality contrast media are given for intestinal tract imaging, fluid is drawn from cells into these areas.
          • Can reduce obstructions by increasing peristalsis.
          • Can cause shock in dehydrated patients.
        • Package inserts list milliosmoles per kilogram of water at 37° C, indicating the number of particles that can produce osmotic effects.
      • Allergic-Like Effects (Anaphylactoid):
        • Resemble allergic reactions to foreign substances.
        • May be minor (urticaria) or severe (wheezing, edema, bronchospasm).
        • May also cause Nausea and vomiting
        • Thought to be caused by histamine release from cells in lungs, stomach, and blood vessel linings.
        • Radiologic technologist should consider these effects as serious. Premedication (steroids, antihistamines) can reduce or eliminate allergic effects.
      • Renal Effects:
        • High-osmolality contrast media can cause expansion of kidney arteries due to osmotic effect.
        • Arterial expansion releases vasoconstrictors, causing renal artery constriction.
        • Diminished blood supply to the kidneys.
        • Osmotic effects lead to increased molecular substances that cannot be reabsorbed by renal tubules, resulting in osmotic diuresis and dehydration.
        • Increased BUN and creatinine levels indicate possible contrast medium-induced renal effects.
        • Patients with renal disease, diabetes, and older patients are at increased risk.
        • Intravenous fluids can reduce the severity of renal effects.
        • Theophylline may prevent toxic renal effects by increasing kidney filtering action.
      • Other Effects:
        • Carotid artery injection can alter the blood-brain barrier by causing capillary cells to shrivel due to water loss.
        • Can stimulate areas in the carotid artery controlling heart rate and blood pressure.
        • Symptoms include increased blood pressure, bradycardia, and tachycardia.
        • In patients with sickle cell anemia, high-osmolality contrast media can cause red blood cells to shrink and sickle.
        • Common effect: sensation of warmth and pain on injection into arterial vessels.
        • Helical CT procedures may increase the probability of nausea and vomiting and extravasation.
    • Drug Interactions and Considerations:
      • Beta-Adrenergic Blockers:
        • Reduce cardiac output, bronchial smooth muscle dilatation, and epinephrine effect.
        • Increase risk for anaphylactoid reactions.
      • Calcium-Channel Blockers:
        • Reduce hypertension by relaxing electrical conduction of cell membranes in arterioles and heart muscle.
        • Risk for heart block and abrupt decrease in blood pressure if ionic contrast media are used during cardiac catheterization.
      • Metformin (Glucophage):
        • Used to treat non-insulin-dependent diabetes.
        • Should be discontinued 48 hours before and 48 hours after iodine contrast media use.
        • If renal failure occurs due to iodine contrast administration, metformin levels accumulate, leading to lactic acidosis.
    • Considerations in the Use of Nonionic Contrast Media:
      • Most adverse reactions associated with water-soluble ionic iodine contrast media are significantly decreased with nonionic media due to decreased osmolality; however, kidney toxicity has not been reduced.
      • Injection of nonionics during angiography is less painful.

  • Oil-Based Iodine Contrast Media

    • Rarely used in radiography, mainly for lymphangiography (studies of the lymphatic system).
    • Once used for myelography (spinal cord), hysterosalpingography (female reproductive system), bronchography (bronchial tree), sialography (salivary glands), and dacryocystography (tear ducts), but now replaced by water-soluble iodinated nonionic contrast media.
    • Physical Properties
      • Made from fatty acids found in plants and animals.
      • An ethyl group takes the place of the alcohol chemical group in fatty acids, changing them into esters.
      • Iodine atoms are added at certain areas of the ester molecules, resulting in "iodinated ethyl esters of fatty acids."
      • Insoluble in water and do not flow easily because they are viscous.
      • Decompose when exposed to light, heat, or air; therefore, they should be stored in a cool, dark area.
      • Do not use any media that have darkened from their original pale yellow or pale amber color.
      • Plastic syringes should not be used for injection because toxic substances can dissolve into the media.
      • Main disadvantage: persist in the body because they are insoluble in water.
    • Specific Procedures
      • Used for procedures like bronchography, dacryocystography, sialography, and lymphography.
      • Myelography was a common procedure using an oil-based medium before nonionic contrast media were introduced.
      • Pre-existing patient history factors may present complications during or after bronchography and lymphography.
    • Adverse Reactions
      • May provoke an anaphylactoid (allergic-like) reaction, although this is rare.
      • Persistence of these media in the body generally does not pose problems unless pre-existing disease involves the areas examined.
      • Specific examinations may have adverse reactions.
      • During bronchography, pulmonary function is temporarily reduced. Encourage the patient to cough up the contrast medium after the procedure. Nausea, vomiting, and headache can also occur.
      • During dacryocystography and sialography, small ducts are dilated. Extravasation may occur if an accidental tear occurs.
      • Iodine contrast injected into the parotid salivary gland causes inflammation of the gland (iodine parotitis) in some patients.
      • During lymphography, extravasation may also occur. Itchy skin rashes, temporary lymphedema, and thrombophlebitis have been reported, although these reactions are infrequent.

Radiopharmaceuticals

  • General Characteristics

    • Radiopharmaceutical vs. Contrast Agent
      • A radiopharmaceutical is not a contrast agent. A radiopharmaceutical is a radionuclide that is attached (chemically bound) to a pharmaceutical that has a specific biodistribution in the human body.
      • This biodistribution is dependent on many factors such as route of administration, gas, liquid, or solid state of the radiopharmaceutical; and sensitivity, as well as specificity of the pharmaceutical in the body as it is taken up.
    • Imaging Mechanism
      • The radioisotope attached to the pharmaceutical is imaged using a gamma camera, which sees or detects where the radiopharmaceutical is in the body and forms an image more or less concentration of the radiopharmaceutical.
      • Physicians read the images knowing the normal biodistribution patterns and look for pathologic conditions within the body based on where the radiopharmaceuticals is taken.
    • Functionality
      • The functionality of this procedure lies in the ability of many radiopharmaceuticals to be taken up by an organ of interest and then be metabolized and used or be eliminated by the body.
      • A prime example would be renal imaging, whereby the radiopharmaceutical is taken up by the kidneys, metabolized into urine, and collected in the bladder. If a patient has a kidney stone that is blocking the path of urine in one of the ureters, then this stone would show up while the study is being performed.
      • Physicians can also determine the rate of uptake and elimination of the radiopharmaceutical in the kidneys and determine if they are functioning normally or not. This method is how an effective renal plasma flow is determined.
    • Table 21-8 lists several radionuclides, their characteristics, and associated pharmaceuticals for some typical nuclear medicine studies.

  • Positron Emission Tomography Agents

    • Nature of Positrons
      • A positron is a positive electron, which is also known as antimatter. Antimatter cannot exist for long because when it comes into contact with a negative electron, it annihilates itself into two 511-keV photons of energy that are approximately 180 degrees apart from each other.
    • Imaging Principle
      • Positron emission tomography (PET) imaging takes advantage of these two 511-keV photons nearly 180 degrees opposite each other to do coincidence imaging whereby the gamma camera accepts only two 180-degree opposing events to form an image.
    • Production and Characteristics
      • Positron emitters are formed in a cyclotron and often have very short half-lives.
    • Table 21-9 lists several different PET agents and their clinical uses.

  • Special Considerations When Working with Unsealed Radiation Sources

    • Primary Concern: Contamination
      • The primary concern when working with short-lived (small half-lives of hours, minutes, or seconds) unsealed radiation sources is contamination, which can occur on patients, personnel, floors, tables, or imaging equipment, that might be misconstrued as part of the image produced for physicians to read.
      • These artifacts may not be easily ascertained and might be misinterpreted by a physician as a pathologic abnormality in a patient when reading a study.
    • Radiation Exposure
      • Another concern with contamination of unsealed sources is increased radiation exposure to personnel and patients that might occur. This contamination might be in the form of external or internal contamination.
    • Types of Contamination
      • External contamination would be dropped, splashed, or spilled unsealed sources deposited on someone or something.
      • Internal contamination might occur if these dropped, splashed, or spilled unsealed sources were internalized via inhalation, absorption, or ingestion.
    • Containment Protocol
      • Unsealed sources must be contained as much as possible before, during, and after their use.
      • This contamination is why nuclear medicine personnel recap needles on a syringe, whereas all other medical personnel do not.

Health Professional Responsibilities

  • Qualifications of Personnel

    • Supervising Physician should:
      • Be a licensed physician certified in radiology or radiation oncology.
      • Have documented training in general radiography interpretation and reporting.
      • Demonstrate knowledge of pharmacology, indications, contraindications, and safe administration.
      • Initiate treatment for adverse reactions.
      • Be familiar with risk factors, premedication strategies, and preprocedural screening.
      • Be immediately available to respond to adverse reactions.
      • Know appropriate alternate imaging methods.
      • Be aware of adverse reaction signs and symptoms and how to monitor patients.
    • Technologist Responsibilities:
      • Ensure patient comfort throughout the procedure.
      • Identify adverse reaction signs and symptoms.
      • Possess adequate knowledge of how to treat adverse reactions.

  • Patient Selection and Preparation

    • Aims:
      • Contrast media reaction prevention.
      • Preparedness in the event of an adverse reaction.
    • Prevention Depends On:
      • Obtaining a thorough patient history.
      • Preprocedural preparations and instructions.
      • Adequate knowledge regarding treatment and use of emergency equipment.

  • Patient Care and Surveillance

    • Remain the focus of the procedure
    • Professional Demeanor Reduce the Possibility of reactions
      • Adverse may occur hours later, if so report immediately