Contrast Media Notes

Glossary of Terms

Acid Group: Contains carbon double-bonded to oxygen, single-bonded to another oxygen, with a negative charge at body pH.
Amine Group: Contains nitrogen bonded to two hydrogen atoms.
Anaphylactoid: Resembles an immune response to a foreign antigen.
Atomic Numbers: Number of protons in an element's nucleus.
Bond: Interactions between atoms' electrons that create a stable group (H-O-H).
Bronchospasm: Involuntary constriction of bronchial tubes, often from an immune reaction.
Compound: Substance of two or more elements in definite ratios, giving specific properties.
Contraindications: Patient history or status factors that make a medical procedure or medication inadvisable.
Creatinine: Nitrogen-containing waste excreted by kidneys; high blood plasma levels indicate poor kidney filtration.
Dimer: Compound formed by bonding two identical, simpler molecules.
Esters: Organic compounds formed by chemically combining alcohols and acids.
Ethyl Group: Two carbon atoms linked to each other and to hydrogen atoms.
Extravasation: Leakage from a vessel into surrounding tissue.
Fatty Acids: Long chains of carbon atoms linked to each other and to hydrogen atoms, with an acid group at one end.
Flocculation: Formation of flaky masses caused by precipitation or coming out of suspension.
Histamine: Molecular substance containing an amine group; causes bronchial constriction and decreased blood pressure.
Hydroxyl: Chemical group with one hydrogen and one oxygen atom; carries a negative charge (anion) when not part of a molecule.
Ionic: Atom or molecule with a negative (anion) or positive (cation) charge.
Methyl Groups: Biochemical groups containing one carbon atom and three hydrogen atoms.
Molecules: Stable groups of bonded atoms with specific chemical properties.
Monomers: Simple molecules of a compound with a relatively low molecular weight.
Osmolality: Measurement of the number of particles that crowd out water molecules in a kilogram of water.
Osmosis: Movement of water from high to 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, causing loss of oxygen and energy.
Solution: Uniform mixture of two or more substances with molecule-sized particles that do not react chemically.
Suspension: Nonuniform mixture with larger-than-molecule-size particles that tend to cluster.

Introduction to Contrast Media

Historical Aspects

Early Use of Air: Walter Dandy (1918) used air for injections to study cerebral ventricles in children with hydrocephalus.
- Air was used to localize brain and spinal cord tumors.
- Later, carbon dioxide, nitrous oxide, and oxygen were also used.
Early Use of Radiopaque Substances: Physiologists used compounds with high atomic numbers mixed with food to monitor the digestive system.
- 1896: Lead subacetate was used but proved toxic.
- 1896: Walter Cannon used bismuth subnitrate to study the digestive system in animals and a child.
  - Cannon is credited with realizing gastrointestinal diseases could be studied using radiopaque media.
Toxicity Issues: Thorotrast, containing thorium, was radioactive.
Barium Sulfate: By 1910, barium sulfate began to be used because of its lack of toxicity, low cost, and availability.
Water-Soluble Iodinated Contrast Media: Introduced by Egas Moniz in 1927 using sodium iodide injected into the cerebrovascular circulation.
- Sodium iodide was a blood vessel irritant.
- Chemical methods improved in the 1930s, allowing iodine atoms to be placed on nontoxic, water-soluble carrier molecules.
- Increased iodine atoms per molecule improved visualization of vascular and urinary systems.
- The use of three iodine atoms per carrier molecule began in the 1950s and became the basis for ionic and nonionic water-soluble iodine contrast media.

Purpose of Contrast Media

Anatomic detail visualization requires differences in radiographic density between the area of interest and surrounding tissue.
Factors affecting radiographic density differences include tissue absorption characteristics, technical factors, image receptor characteristics, image processing, and contrast media.
X-ray Absorption: The body absorbs x-ray photons based on tissues' atomic numbers and 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 absorption.
Low Subject Contrast: Radiographic images of low-subject-contrast areas are difficult to visualize.
Contrast Media: Instilling contrast medium changes absorption characteristics and alters subject contrast, improving visualization of anatomic detail.
Enhancement: Contrast media enhance subject contrast in areas where it's naturally low.
Effectiveness Factors: Effectiveness depends on the atomic number of the element used in the medium and the concentration of atoms per volume.
Classification: Contrast media are classified as negative or positive contrast agents.
- Negative Contrast Agents: Decrease x-ray beam attenuation, producing increased density on the radiograph.
- Positive Contrast Agents: Increase x-ray beam attenuation, producing decreased density on the radiograph.

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 sulfate, iodine compounds.
Combined Use: Negative and positive agents can be used together to visualize the lumen of organs (e.g., colon) or structures within a space (e.g., menisci of the knee).
Specialty Contrast Agents: Used in other modalities like MRI and ultrasound.
- MRI: Gadolinium-DTPA is a metallic and magnetic agent affecting signal intensity.
- Ultrasound: Gas-filled microbubbles affect sound waves to enhance contrast.
- Purpose: Similar to radiographic contrast agents – enhancing subject 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 as a contrast agent because it's quickly absorbed by cells.

Specific Procedures

Air Alone: provides negative contrast for laryngopharyngography.
Combined Use: Radiolucent contrast media are used with radiopaque media to outline lumens or spaces.

Common Double-Contrast Studies

Stomach: Barium sulfate (oral) and carbon dioxide (tablets, crystals, soda water).
Large Intestine: Barium sulfate and air (rectal).
Arthrography (Shoulder, Knee, Wrist, Hip): Water-soluble iodine media and air (injection into joint space).

Patient Preparations

Stomach: NPO after midnight.
Large intestine: Large amount of fluid before examination, cleansing enema before examination.
Arthrography: none.

Patient Instructions and Care

Stomach: Patient should NOT belch.
Large intestine: Provide supportive communication.
Arthrography: Provide supportive communication because stress views performed during procedure can be painful.

Adverse Reactions

Generally minimal; air can cause emboli.
Air Emboli: Small air masses enter the circulatory system, causing pain and loss of oxygen.
Post-Procedure Instructions: Patients receiving barium sulfate with air should drink plenty of fluids.
Administration of water-soluble iodine contrast media along with air in the joint spaces usually does not result in complications.

Positive Contrast Media

Barium Sulfate Contrast Media

Physical Properties

Barium (atomic number 56) is radiopaque.
Barium sulfate (BaSO_4) is an inert powder composed of crystals used for digestive system exams.
- Ratio: One barium atom, one sulfur atom, four oxygen atoms.
Solubility issue: Barium sulfate is not soluble in water, so it must be suspended.
Flocculation: The powder can clump and come out of suspension, so stabilizing agents such as sodium carbonate or sodium citrate are added.
Suspending agents and ingredients are listed on container labels.
Oral barium sulfate may also include vegetable gums, flavoring, and sweeteners.
Barium sulfate suspensions must be concentrated enough to absorb x-rays and flow easily to coat organs. Oral formulations include barium sulfate and methylcellulose.

Specific Procedures

Mixing: For lower GI studies, barium sulfate is mixed with cold tap water to reduce irritation to the colon.
* Room temperature water can also be used for maximal patient comfort.
Water Absorption: The colon absorbs water from waste, but increased absorption can cause hypervolemia (excess fluid in the circulatory system).
- Adding 2 teaspoons of table salt per liter of water reduces the risk of hypervolemia.
Mixing Directions: Following manufacturer's directions is critical.

Specific Procedures - Contraindications

Perforation in the digestive tract is a contraindication.
Barium sulfate is not absorbed naturally and can cause peritonitis if it enters the peritoneal or pelvic cavity.
A water-soluble iodine contrast agent is recommended instead.
Trauma: Barium sulfate can result in trauma such as perforation of the colon.

Specific Procedures - Patient History Factors

Age: Ability to communicate and follow directions.
Diverticulitis or ulcerative colitis: Increased risk of colon perforation.
Long-term steroid therapy: Difficulty holding an enema.
Colon biopsy within previous 2 weeks: Increased risk of colon perforation.
Pregnancy: Lower gastrointestinal series contraindicated.
Mental retardation, confusion, or dizziness: Radiologist should be informed.
Recent onset of constipation or diarrhea: Risk of colon perforation or tumor rupture.
Nausea and vomiting: Risk of aspiration during upper gastrointestinal series.

Common Procedures Using Barium Sulfate Suspensions

Esophagus (Esophagram): 30-50% concentration, oral administration, no patient prep.
Stomach (Upper Gastrointestinal Series): 30-50% concentration, oral, NPO after midnight.
Small Intestine (Small Bowel Series): 40-60%, oral (if included with stomach examination), low-residue diet eaten for 2 days before examination.
Large Intestine (Colon or Barium Enema): 12-25% concentration, rectal, large amount of fluid or fluid diet day before examination, cleansing enema before examination.
Stomach (Computed Tomography): 12-25%, oral, NPO after midnight.

Adverse Reactions

Dehydration & Obstruction: Instruct patients to drink plenty of fluids after receiving barium sulfate.
- Barium sulfate residue can dry and cause an obstruction, with constipation as the major symptom.
Perforation: Perforation of the colon with extravasation into the abdominal cavity can occur, resulting in barium peritonitis.
- Older adults or patients on long-term steroids are at increased risk.
- Patients with diverticulitis and ulcerative colitis are also at risk.
- Patients with toxic megacolon should not have lower GI procedures.
- Recent biopsy of the colon is a contraindication.
- Barium retention catheter can cause colon perforation; inflate gently.
Vaginal Rupture: Incorrect catheter placement during lower GI exams, so ask the patient if they can feel the enema tip in the rectum.
Water Absorption: Water can shift from the colon into the circulatory system, leading to fluid overload, pulmonary edema, seizures, coma, and death.
- Table salt solution reduces the possibility of hypervolemia.
- Observe patients for changes in mental status.
Aspiration: Sedated patients should not undergo upper GI exams because of diminished swallowing reflex.
Allergies: Allergic-type reactions may be caused by preservatives or latex.

Water-Soluble Iodine Contrast Media

Physical Properties

Ionic Iodine Contrast Media

Iodine (atomic number 53) is radiopaque.
Dissociation: Ionic media dissociate into two molecular particles in water or blood plasma.
- Anion (negative charge) and cation (positive charge).
Anion Component: Begins with a six-carbon benzene ring, with iodine atoms at every other carbon bond site.
Triiodinated Structure: Each anion contains three iodine atoms.
Acid Group: One carbon bond site occupied by an acid group, carrying the negative charge.
Solubility and Excretion: Two other carbon bond sites influence solubility and excretion.
Classes:* Diatrizoate, metrizoate, and iothalamate.
Cation Component: Sodium atom or methylglucamine structure.
- Methylglucamine contains six carbons from glucose and a nitrogen with a methyl group.
Osmolality: Most ionic iodine contrast media are identified as higher-osmolality contrast media.
Osmotic Pressure: Osmolality determines osmotic pressure, which controls water movement.
- High-osmolality contrast media draw water toward them.

Nonionic Iodine Contrast Media

Developed to decrease side effects.
Do not dissociate into anions and cations, or are ionic but too large to have osmotic effects (ioxaglate).
Identified as lower-osmolality contrast media.
Ioxaglate: An ionic molecule composed of two connected benzene hexagons, with an acid group that dissociates.
- It is a dimer carrying six iodine atoms per molecule.
Dimers Are large molecules with low osmotic effects and high viscosity.
Iodixanol (Visipaque): A nonionic dimer made isomolal to blood plasma by adding electrolytes.
Hydrophilicity: Lower-osmolality contrast media are more hydrophilic.
Ionic and nonionic agents contain additives such as citrate and calcium disodium edetate.

General Effects of Water-Soluble Iodine Contrast Media

High osmolality and chemical structure characteristics

Major characteristics of water-soluble iodine media are responsible for these effects.
Ionic agents are higher-osmolality contrast media and have greater effects and adverse reactions.
Viscosity, or friction, of a medium is influenced by the concentration and size of molecule.
It affects the injectability, or delivery, of the medium. Heating the medium to body temperature significantly reduces the viscosity and facilitates the ability for rapid injection.

Osmotic Effects

Water Displacement: Injection of ionic media increases plasma particles, displacing water.
Osmosis: Water moves from body cells into the vascular system, causing hypervolemia and blood vessel dilatation.
Blood Pressure: Blood pressure may decrease (vessel dilatation) or increase (hypervolemia and kidney hormone effects).
Intestinal Imaging: High-osmolality media draw fluid into the intestinal tract, aiding in reducing obstructions.
Dehydration: In dehydrated patients, the osmotic effect reduces body cell volume and can result in shock.

Osmolality Measurement

The number of molecular particles is shown on the package insert in units of milliosmoles per kilogram of water at 37° C.
Example: The osmolality of iodixanol at 300 mg of iodine per milliliter is 290 mOsm/kg, equal to that of blood plasma.

Allergic-Like Effects (Anaphylactoid)

Reactions resemble allergies to foreign substances.
Reactions may be minor (urticaria) or severe (wheezing, edema).
Nausea and vomiting are other anaphylactoid effects so technologist should consider these effects are serious.
Caused by the release of histamine from cells in the lungs, stomach, and blood vessels.
Premedication with steroids and antihistamines can reduce allergic effects.

Renal Effects

High-osmolality contrast media can cause renal arteries to expand.
- This results in vasoconstrictors,
- This diminishes blood supply to the kidneys.
Osmotic Diuresis: Osmotic effects cause an increase in molecular substances that cannot be reabsorbed by the renal tubules, resulting in osmotic diuresis (increased secretion of urine) and dehydration.
Indicators: Increased blood urea nitrogen (BUN) and creatinine levels indicate possible contrast medium-induced renal effects.
Patients with renal disease, diabetes, and older patients are at increased risk.
Intravenous fluid can reduce the severity of renal effects.
Theophylline is being investigated as a preventative of toxic renal effects by increasing the filtering action of the kidneys.

Other Effects

Blood-Brain Barrier: Carotid artery injection can alter the blood-brain barrier.
Stimulate areas in the carotid artery that help control heart rate and blood pressure. Clinical symptoms of these effects include increased blood pressure, bradycardia (slow heartbeat), tachycardia (fast heartbeat).
Sickle Cell Anemia: High-osmolality contrast media can cause red blood cells to shrink and sickle, leading to pain and blood clots.
Warmth and Pain: A sensation of warmth and pain on injection is thought to be caused by dissociation of contrast media into anions and cations.
Extravasation In helical computed tomography (CT) procedures, large amount of contrast material is injected at a rate of at least 2.5 mL/sec. The increases the probability of nausea and vomiting and extravasation of the contrast with patient motion as a result.

Drug Interactions

Beta-Adrenergic Blockers: Increase the risk for anaphylactoid reactions.
Calcium-Channel Blockers: Increase the risk for heart block and decreased blood pressure during cardiac catheterization.
Metformin (Glucophage): Should be discontinued 48 hours before and after using iodine contrast media because it can cause Lactic acidosis if renal failure were to occur.

Considerations in the Use of Nonionic Contrast Media

Most adverse reactions are significantly decreased.
Kidney toxicity hasn't been reduced.
Including the patient's BUN and creatinine level in the history is therefore important.

Nonionic Contrast Costs

Nonionic iodine contrast media cost two to three times more than ionic media.

Sample criteria for the use of low-osmolality (nonionic) contrast media might include the following:

Patients with a history of adverse reactions to contrast media, excluding mild reactions such as the sensation of heat or flushing.
Patients with a history of asthma or allergies
Patients with known cardiac problems
Patients with generalized severe debilitating conditions
Patients who will undergo helical CT procedures
These criteria include patients with diabetes mellitus, renal disease or elevated creatinine levels, or sickle cell disease.

Specific Procedures Using Water-Soluble Media

Visualize the urinary and cardiovascular systems.
Used in CT studies of the brain, chest, and abdomen.
Table 21-4 provides a list of the common procedures that use water-soluble iodine contrast agents.

Water-Soluble: Patient History

Pre-administration: The most important aspect is the patient history.
Chemical nature of contrast media provokes severe reactions.
Technologist is responsible for patient observation.

Adverse Reactions Classification

Mild, moderate, and severe reactions are listed.

Oil-Based Iodine Contrast Media

Physical Properties

Physical Properties. Oil-based iodine contrast media are made from fatty acids commonly found in plants and animals. A two-carbon atom chemical group called an ethyl group takes the place of the alcohol chemical group usually found in fatty acids. Then iodine atoms are added at certain areas of the ester molecules.The result is the description seen on the package inserts: iodinated ethyl esters of fatty acids.
Oil-based media are insoluble in water and do not flow easily because they are relatively viscous. When these esters are exposed to light, heat, or air, they decompose. Consequently, these media should be stored in a cool, dark area. Plastic syringes should not be used for injection of oil-based iodine contrast media because toxic substances from the plastic can dissolve into the media. The main disadvantage of oil-based iodine contrast media is that they persist in the body because they are insoluble in water.

Specific Procedures

lymphography, bronchography, dacryocystography, sialography
As with all radiologic procedures, obtaining a complete patient history is important. In particular, the preexisting patient history factors outlined in Table 21-7 may present complications during or after bronchography and lymphography

Adverse Reactions

Any iodine-containing contrast agent may provoke an anaphylactoid (allergic-like) reaction, although this is rare with the use of oil-based media. The persistence of these media in the body generally does not pose problems unless preexisting disease involves the areas examined.

Radiopharmaceuticals

A radiopharmaceutical is a radionuclide that is attached (chemically bound) to a pharmaceutical that has a specific biodistribution in the human body
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 of more or less concentration of the radiopharmaceutical.
Positron Emission Tomography Agents

A positron is a positive electron, which is also known as antimatter. Table 21-9 lists several different PET agents and their clinical uses.

Special Considerations When Working with Unsealed Radiation Sources

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
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. 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.

Health Professional Responsibilities

Qualifications of Personnel. The supervising physician should be a licensed physician with the following qualifications:

Certification in radiology or radiation oncology
A minimum of 6 months of documented
Familiarity with risk factors
Immediate availability to respond
Knowledge of imaging methods

The technologist is responsible for being able to identify the signs and symptoms of adverse reactions and having adequate knowledge of how to treat any adverse reaction.

Patient Selection and Preparation

Patient selection and preparation has two aims: (1) contrast media reaction prevention and (2) preparedness in the event of an adverse reaction.

Patient Care and Surveillance

The patient must remain the focus of the procedure
The radiographer might develop an instruction sheet about mild adverse reactions and discuss these issues with the patient after the procedure is complete but before the patient leaves. Such instructions might include calling the department (direct telephone number) if any of the following occur within 24 hours: hives, flushing, chills, nasal stuffiness, swelling of the eyes or face, or wheezing.