This document discusses contrast media used in radiology. It describes radiolucent and radiopaque materials, different types of contrast agents including barium, iodinated, and gas-based agents. It discusses water-soluble, ionic, and nonionic contrast agents. It also outlines both common mild adverse effects and more severe life-threatening reactions that can potentially occur with the administration of contrast media.
2. Radiolucent
Any material or body through which the x-rays
can pass easily are called radiolucent.
Lung tissues and to some extent soft tissues are
radiolucent.
It may appear black on the radiograph.
Lungs, Soft tissue, Uric Acid stones are
radiolucent
3. Radiopaque
• An material or body structure through which
the x-rays are absorbed are called radiopaque.
• It may appear white on the radiograph. (bone)
• Radio-opaque stones include Calcium Oxalate
(monohydrate),Calcium Phosphate. Bones,
metals, contrast medium
•
4. • All the contrast material used in radiological
procedure are radiopaque whether it may be
given intravenous, oral or rectal.
5. Contrast media
Any substance used to change the imaging
characteristics of the patient, thereby providing
additional information including:
Anatomy: tissue versus fluid, locational information
Physiology: vasculature, vascular integrity, qualitative
assessment of function
Contrast is NOT dye!
Dye is for hair, for clothes, for paintball, etc.
To dye something is to color it.
6. Why consider more contrast
To enhance differences between tissues
To identify normal vs. abnormal
Organes, masses, obstructions, dilations, leaks,
compressions, assessment of function.
To identify changes in vasculature and vascular
integrity, blood flow.
7. Classification by Chemical
Structure
Barium (positive contrast)
Iodinated: (positive contrast)
Ionic ( ultravist, iopamiro, iohexal, iopramide,
Nonionic ( urograffine )
negative contrast
Gas-based:
for ultrasound
Room air or CO2 for lower urogenital or alimentary
use
11. Water soluble contrast media
• Al l conventional ionic water-soluble contrast media or high
osmolar contrast media (HOCM) are hypertonic with
osmolalities of 1200-2000 mosmol/kg water, 4-7 x the
osmolarity of blood.
• Almen first postulated that many of the adverse effects of
contrast media were the result of high osmolality and that by
eliminating the cation, which does not contribute to diagnostic
information but is responsible for up to 50% of the osmotic effect,
it would be possible to reduce the toxicity of contrast media.
12. Iodinated Contrast Agents
• Water-soluble contrast agents, consisting of
molecules containing atoms of iodine, are used
extensively for intravascular applications in CT,
urography, and angiography as well as for
arthrography, cystography, fistulography, and
opacification of the lumen of the GI tract. With
the ever-expanding use of CT, the number of
patients exposed to iodinated contrast agents
continues to increase. Fortunately, the risk of
adverse reaction is low but real risk is inherent in
their use.
13. Continue……
• Any contrast agent administration, regardless
of dose or route of administration, carries a
finite risk of mild to life-threatening reaction.
Older, cheaper high-osmolar ionic agents have
been near completely replaced in most
applications by newer but more expensive,
low-osmolar agents because of safety
considerations.
14. Ionic Contrast Agents
• Ionic Contrast Agents (high osmolality contrast agents)
had been considered safe and effective for more than
70 years. All iodinated contrast agents have a chemical
structure based on a benzene ring containing three
iodine atoms. Ionic media are acid salts that dissociate
in water into an iodine-containing negatively charged
anion (diatrizoate, iothalamate) and a positively
charged cation (sodium or meglumine). To achieve a
sufficient concentration of iodine for radiographic
visualization, ionic agents are markedly hypertonic
(approximately six times the osmolality of plasma).
15. Continue…..
• High osmolality and viscosity cause significant
hemodynamic, cardiac, and subjective effects
including vasodilatation, heat, pain, osmotic
diuresis, and decreased myocardial contractility.
Following IV injection, contrast media are
distributed quickly into the extracellular space.
Excretion is by renal glomerular filtration.
Vicarious excretion through the liver, biliary
system, and intestinal tract occurs when renal
function is impaired.
16. Nonionic Contrast Agents
• Nonionic Contrast Agents (low osmolality
contrast agents) have an osmolality reduced to
one to three times that of blood, resulting in a
significant decrease in the already low incidence
of adverse reactions. Reduction in osmolality is
achieved by making compounds that are nonionic
monomers. Reduced osmolality results in less
hemodynamic alteration on contrast injection.
Nonionic contrast agents continue to be
significantly more expensive than ionic contrast
agents.
17. Adverse Side Effects
• Adverse Side Effects are uncommon ranging from 5% to
12% of intravascular injections with ionic agents to 1% to
3% with nonionic lower osmolality agents. The precise
pathophysiology of adverse reactions to contrast agents is
unknown. However, an increasing body of evidence
suggests that a true allergic reaction mediated by IgE is a
likely precipitating event. Triggering of mast cells to release
histamine is related to severe reactions. Accurate
prediction of contrast reactions is not possible but patients
with a history of allergy, asthma, or previous contrast
reaction are clearly at higher risk. Cardiovascular effects are
more common and more severe in patients with cardiac
disease.
18. Mild adverse effects
• Mild adverse effects are most common.
Nausea, vomiting, urticaria, feeling of warmth
with injection, and pain at the injection site
occur with greater frequency following
injection of ionic agents and is related to their
higher osmolality. Most mild reactions do not
require treatment. Patients should be
observed for 20 to 30 minutes to ensure that
the reaction does not become more severe.
19. Moderate reactions
• Moderate reactions are not life-threatening but
commonly require treatment for symptoms.
Patients with severe hives, vasovagal reactions,
bronchospasm, and mild laryngeal edema should
be monitored until symptoms resolve.
Diphenhydramine is effective for relief of
symptomatic hives. Beta agonist inhalers help
with bronchospasm, and epinephrine is indicated
for laryngeal spasm. Leg elevation is indicated for
vasovagal reactions and hypotension.
20. Severe, potentially life-threatening,
side effects
• Severe, potentially life-threatening, side effects nearly
always occur within the first 20 minutes following
intravascular injection. These are rare but should be
recognized and treated immediately. The risk of death
precipitated by IV injection of iodinated contrast is
conservatively estimated at 1 in 170,000. Severe
bronchospasm or severe laryngeal edema may
progress to loss of consciousness, seizures, and cardiac
arrest. Complete cardiovascular collapse requires life-
support equipment and immediate cardiopulmonary
resuscitation. Cardiotoxic effects include hypotension,
dysrhythmias, and precipitation of acute congestive
heart failure.
21. Local Adverse Effects.
• Venous thrombosis may occur as a result of
endothelial damage precipitated by IV
infusion of contrast. Extravasation of contrast
at the injection site is associated with pain,
edema, skin slough, or deeper tissue necrosis.
If extravasation occurs, the affected limb
should be elevated. Warm compresses may
help absorption of contrast agent, while cold
compresses seem more effective at reducing
pain at the injection site.
