Contrast Material

Prepared by Midrar ullah khan Lecturer radiology

IPMS KMU

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

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

•

• All the contrast material used in radiological procedure are radiopaque whether it may be given intravenous, oral or rectal.

Contrast media

Any substance used to change the imagingcharacteristics of the patient, thereby providingadditional information including:Anatomy: tissue versus fluid, locational informationPhysiology: vasculature, vascular integrity, qualitativeassessment of functionContrast is NOT dye!Dye is for hair, for clothes, for paintball, etc.To dye something is to color it.

Why consider more contrast

To enhance differences between tissuesTo identify normal vs. abnormal Organes, masses, obstructions, dilations, leaks,compressions, assessment of function. To identify changes in vasculature and vascularintegrity, blood flow.

Classification by ChemicalStructure

Barium (positive contrast) Iodinated: (positive contrast) Ionic ( ultravist, iopamiro, iohexal, iopramide, Nonionic ( urograffine ) negative contrastGas-based: for ultrasound Room air or CO2 for lower urogenital or alimentaryuse

Single contrast Double contrast

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.

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.

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• 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.

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).

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• 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.

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.

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.

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.

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.

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.

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.