Contrast Media in Radiology

Contrast Media in Radiology

• Contrast media (CM) or "dyes" are special liquids used to enhance differences between body tissues during radiographic scans or examinations.
• Contrast enhancement is requested to delineate anatomical structures when there is poor inherent contrast between tissues.
• Physicians determine if contrast enhancement is necessary for a procedure.
• CM increases subject contrast, aiding in diagnosis by improving the visibility of specific organs, blood vessels, or tissues.
• Contrast isn't needed to rule out fractures, since bone has inherent contrast, nor hemorrhage in the brain, due to blood's inherent contrast.
• CM can be administered intravenously, orally, or rectally.
• Radiologic Technologist (RTOD) injects contrast media manually (bolus) or via injector.
• Examinations commonly requesting contrast enhancement include digestive, biliary, urinary, reproductive, circulatory, and CNS scans.

Types of Scans Requiring Contrast Media:

• MRI
• CT Scan
• Other radiographic or fluoroscopic procedures

Classification of Contrast Media based on Atomic Weight:

• Positive (radiopaque) CM has a higher atomic weight than surrounding tissue, absorbs more photons, and produces lower radiographic density. Examples include barium sulfate and iodinated CM.
• Negative (radiolucent) CM has a lower atomic weight, absorbs fewer photons, and produces higher radiographic density, like gases such as air, O2, and CO2.

Types of Contrast Media

• Both Gadolinium and Iodinated contrast media have a similar consistency to sugar syrup and are sticky
• Gadolinium for MRI scans
• Iodinated dyes for CT Scans and other radiographic or fluoroscopic procedures

Gadolinium

• Chemical element with the symbol Gd and atomic number 64.
• It is a non-toxic paramagnetic contrast enhancement agent due to its 7 unpaired electrons.
• Paramagnetism is the intrinsic property of materials to become temporarily magnetized in an external magnetic field.
• Potent paramagnetic properties make Gadolinium useful as an MR contrast agent.
• May be nephrotoxic in very high doses.
• Gadolinium influences the relaxation of nearby hydrogen protons, and isn't directly seen in MR images.
• During T1-weighted imaging, Gadolinium changes signal intensities by shortening T1, resulting in bright T1-weighted images.
• Enhanced images are useful for visualizing vascular structures and blood-brain barrier breakdown, such as tumors, abscesses, and inflammation.

Iodine

• Iodine, a non-metallic element with symbol I and atomic number 53, enhances images using X-rays.

Osmolality

• Osmolality the concentration of dissolved particles in a solution, High osmolality induces greater osmotic pressure, causing fluid to flow into the solution.
• When it's greater than body fluid, water moves from low osmolal body fluid to high osmolal CM, leading to dehydration and increased CM reactions.
• Higher CM osmolality increases the chances of CM reactions, while osmolality near body fluid reduces them.

Solubility

• Solubility is the measure of how much substance can be dissolved in a solvent.

Classification of Contrast Media Based on Water Solubility:

• Water Insoluble Contrast Media
• Barium Sulfate (BaSO4)
  • In powder form it is a semi-solid colloidal suspension
  • Administered orally or rectally as an enema.
  • insoluble in water.
  • Not easily absorbed or excreted, remaining in the body cavity for longer.
  • Used in GIT and examples include Barium Swallow for esophagus, Barium Meal for stomach, SI series, and Barium Enema for a large intestine study
  • Is contraindicated in cases of suspected perforation and obstruction to prevent Barium Peritonitis from leakage into the peritoneal cavity leading to potential death.
  • Following GI or BE examinations, patients should expect light-colored stools, drink plenty of fluids, and increase fiber intake.
• Water Soluble Contrast Media
  • Organic Iodine
    • It is in liquid form
    • Soluble in water for quick kidney absorption and excretion with a fast clearance time
    • Used in the Urinary, Biliary, CNS, CVS, and some GIT systems, especially when perforation and obstruction are suspected
    • Includes multiple types of Organic Iodinated CM:
      • High Osmolar CM (HOCM)
        • An older, less expensive iodinated CM
        • Has a high concentration of dissolved particles (high osmolality), 5-8x greater than the body fluid, leading to higher CM reaction chances.
        • When introduced to a solution, HOCM breaks down to anion (iodine) and cation (sodium/meglumine), naming it Ionic CM.
        • Examples of the above include UROGRAFIN (Diatrizoate Sodium/Meglumine) and CONRAY (Iothalmate Sodium/Meglumine) – Low Osmolar CM (LOCM)
        • More expensive but advanced compared to HOCM
        • Has a lower concentration of dissolved particles in contrast.
        • Ionic LOCM breaks down in the solution but releases fewer particles
        • Non-ionic LOCM will not break apart into charged particles
        • Examples of Ionic LOCM include HEXABRIX (Ioxaglate).
        • Non-Ionic LOCM include IOPAMIRON (Iopamidol) VISIPAQUE (Iodixanol), OMNIPAQUE (Iohexol) and OPTIRAY (Ioversol) it is less likely to exhibit CM reactions

Iodine-Based Contrast Media

• Ionic Contrast Media
  • High toxicity and Osmolality that causes a high chance of CM
  • Dissolves into charged particles
  • Dissociates from iodine, forming anion and cation

Non Ionic Contrast Media

• Has a low osmolality, less toxicity compared to ionic media, does not break down into particles, and causes fewer CM reactions.
• It doesn't contain salt, so it has no dissociation or charged particles.
• CM reaction are less common is it's widely used because it's osmolality is closer to body fluids

General Classification of CM Reactions:

• Dose-Dependent Reactions
  • Occur with high doses (HOCM) or high flow rates, especially in critical organs (brain, spinal cord, kidneys, myocardium) or in patients with kidney failure or allergic reactions.
• Dose-Independent Reactions
  • These reactions can occur even with low doses and flow rates, irrespective of known predisposing conditions.
  • This type is called idiosyncratic reactions and requires constant patient attendance, immediate assistance, and standby emergency resuscitation equipment.
  • Mechanism of idiosyncratic reactions stem from HOCM or widespread allergy history

Mechanism of Idiosyncratic Reactions

• Histamine Release
  • Leukocytes (Mast cells & Basophils), they protect the body from foreign things like infectious germs and allergens
  • Chemicals like histamine release to destroy and engulf these, and causes flushing, itching and Edema.
• Complement System Activation
  • Relies on certain proteins in the immune system to enhance the ability of WBC to destroy germs and allergens.
  • It's inactive when there are no germ or allergens, and activates upon threat detection.
  • CM causes damage to blood vessel endothelium, causing complement system activation
• Enzyme Binding
  • Enzymes are proteins that regulate rate of chemical reaction.
  • The processes are food breakdown and energy build up.
  • CM binds to cholinergic enzymes in muscles and nerves, which inhibits function and causes toxicity, leading to vasodilation, bradycardia, bronchospasm, blurry vision, and urticaria.
• Chemotoxicity
  • The electrical charge of dissolved CM particles can increase convulsions and cardiac arrhythmia.
• Anxiety
  • Anxious patients are prone to sympathetic nervous system activation.
  • Additional stimulation of the sympathetic nervous system can cause dyspnea, sweating, and diarrhea.

Contrast Media Reactions Based on Severity

• Mild/Minor reaction
  • 3% chance of having Metallic taste, Nausea & vomiting, itchiness, dizziness, flushing, sneezing, skin rash, chills, heat sensation
  • Provide a vomit basin, promote ventilation and monitor the patient
• Moderate reaction
  • 1% chance of having Tachycardia/bradycardia, hypertension or hypotension, coughing and wheezing/bronchospasm, severe hives, dyspnea or severe skin rash
  • Call for help, treat symptoms, and ensure respiratory function by elevating the head and shoulder.
• Severe Reaction
  • 0.02% chance of extreme low blood pressure, cardiac arrhythmia, cardiac arrest, convulsions, unresponsiveness and anaphylactic shock.
  • Call for a code, and provide artificial respiration
• Injection Site reaction
  • 0.9% chance of extravasation, with pain and swelling from leakage outside the vein and burning sensation.
• Staff must be informed of any underlying conditions like allergies, asthma, or prior operations during the screening.

Extravasation vs. Infiltration:

• Extravasation
  • Medication or contrast media leakage from a vein rupture or unintentional introduction into tissue
  • The leakage is vesicant (irritates tissues)
• Infiltration
  • Diffusion of injected material into adjacent tissues
  • Injected material is non-vesicant
  • Treatment includes removing the needle, applying pressure, elevating the affected side, and applying dry cold/warm compresses to relieve pain/increase blood flow

Vesicants

• Drugs that can result in tissue necrosis or formation of blisters when accidentally infused into tissue surrounding a vein.
• The difference between an infiltration and extravasation is the type of medicine or fluid that is leaked

Compress Treatments

• Warm Compress: Vasodilatation to increase drug absorption.
• Cold Compress: Vasoconstriction to limit drug diffusion, reducing inflammation and pain.

Phlebotomy vs. Venipuncture

• Venipuncture: A broad concept of entering a vein for withdrawing blood or administering IV fluids for extended period, or medication.
• Phlebotomy: Uses a needle to draw blood specimen from the arm, and is limited to obtaining blood samples for tests only.

High Risk Groups

• Pediatric patients
• Geriatric patients
• Diabetic Patients
• Patients with Cardiac impairment
• Patients with renal impairment
• Asthmatic patients
• Patient with history of CM reactions
• Patients with wide history of allergies

Special Factors for Contrast Use

• Age poses risks to children and the elderly.
• Weight influences dosage.
• Pre-existing medications.
• Impaired renal or liver function.
• Laboratory results like creatinine, BUN (Blood Urea Nitrogen).
• Perforated bowels.

Priority Patients

• Fasting patients
• Emergency patients
• Pediatric and geriatric patients that are NPO
• Diabetics forgoing insulin due exams

Prophylaxis for CM Reactions:

• Test Doses
  • Administer 10 cc of solution (9 cc Saline and 1 cc CM) and observe mild reaction after 2-10 mins.
  • If it occurs, it will likely to cause moderate to severe reaction.
  • inform the physician and halt exam if it occurs
• Pretreatment with steroids.
• Pretreatment with antihistamines.
• Reducing the anxiety by reassuring the patient
• Use of LOCM instead of HOCM

Sequencing of scheduled examinations:

• All radiographic examinations not requiring contrast media.
• Laboratory studies for iodine uptake (thyroid uptake).
• Radiographic examinations of the urinary tract.
• Radiographic examinations of the biliary tract.
• Lower gastrointestinal series (barium enema).
• Upper gastrointestinal series.