Contrast Media and Reactions — MCQs

Contrast Media and Reactions Indian Medical PG Practice Questions and MCQs

Question 31: Excretory urography is contraindicated in:

A. Single kidney
B. Trauma
C. Multiple myeloma (Correct Answer)
D. Renal artery hypertension

Explanation: ***Multiple myeloma*** - Patients with **multiple myeloma** are at high risk of developing **contrast-induced nephropathy** due to the precipitation of Bence Jones proteins in renal tubules when exposed to iodinated contrast agents. - This can lead to **acute kidney injury** or worsening of pre-existing renal impairment, making excretory urography generally contraindicated. *Single kidney* - While careful consideration is needed, having a **single kidney** does not inherently contraindicate excretory urography if renal function is good. - The primary concern is protecting the remaining kidney from **contrast-induced nephropathy** in patients with pre-existing renal dysfunction, not the number of kidneys. *Trauma* - In cases of **renal trauma**, excretory urography (or more commonly, CT urography) can be used to assess the extent of injury and integrity of the urinary tract. - It is often indicated to evaluate **hematuria** or suspected kidney damage, not contraindicated. *Renal artery hypertension* - Excretory urography was historically used to evaluate for **renal artery stenosis**, a cause of **renal artery hypertension**, by looking for delayed contrast excretion or kidney size differences. - While it has largely been replaced by more modern imaging like CT angiography or MRA, it is not considered a contraindication and can provide some diagnostic information.

Question 32: All of the following dyes are water soluble except:

A. Myodil (Correct Answer)
B. Iohexol
C. Conray 420
D. Metrizamide

Explanation: ***Myodil*** - **Myodil** (Iophendylate) is an **oil-based** contrast medium previously used for myelography. - Due to its **oil-based nature**, it is not water-soluble and had to be removed after the procedure to prevent complications. *Iohexol* - **Iohexol** is a **non-ionic, water-soluble** contrast agent commonly used in various radiological procedures, including myelography. - Its water solubility allows for easy absorption and excretion from the body. *Conray 420* - **Conray 420** (Iothalamate meglumine) is an **ionic, water-soluble** contrast agent often used for angiography and urography. - It readily mixes with bodily fluids due to its water-soluble properties. *Metrizamide* - **Metrizamide** was an early **non-ionic, water-soluble** contrast agent specifically developed for myelography. - Although water-soluble, it had a higher incidence of neurotoxicity compared to newer agents like iohexol.

Question 33: Dye used in IV cholangiography is:

A. Billigraffin (Correct Answer)
B. Conray
C. Myodil
D. Dianosil

Explanation: ***Billigraffin*** - **Billigraffin** (also known as sodium **iodipamide**) was historically the **primary contrast agent** used in intravenous (IV) cholangiography. - It is an **iodinated contrast medium** specifically designed for excretion into the **biliary system**, allowing visualization of the bile ducts. *Conray* - **Conray** (iothalamate meglumine) is a general-purpose **ionic iodinated contrast medium** primarily used for **angiography, CT scans**, and **excretory urography**. - It is not specifically formulated for optimal **biliary excretion** and would not provide adequate visualization for IV cholangiography. *Myodil* - **Myodil** (iophendylate) is an **oil-based iodinated contrast medium** that was historically used for **myelography** to visualize the spinal canal. - Due to its **oil-based nature** and different excretion pathway, it is entirely unsuitable for **IV cholangiography**. *Dianosil* - **Dianosil** was a trade name for certain **bronchography contrast agents** containing iodized oil, used to visualize the tracheobronchial tree. - This type of contrast medium is designed for **pulmonary application** and would not be used for imaging the biliary system.

Question 34: Dye used for "Myelography" is:

A. Iohexol (Omnipaque) (Correct Answer)
B. Barium sulfate
C. Iodixanol (Visipaque)
D. Iopamidol (Isovue)

Explanation: ***Iohexol (Omnipaque)*** - Iohexol is a **non-ionic, low-osmolar monomeric contrast agent** and is the **most commonly used agent for myelography** worldwide. - It is **FDA-approved for intrathecal use** and has extensive safety data with **low neurotoxicity**. - Its widespread availability and proven safety profile make it the **standard choice** for myelography in clinical practice. *Iopamidol (Isovue)* - Iopamidol is also a **non-ionic, low-osmolar monomeric agent** that is FDA-approved for myelography. - While it is a suitable alternative to iohexol, **iohexol remains more commonly used** in most centers. - Both agents have similar safety profiles for intrathecal administration. *Iodixanol (Visipaque)* - Iodixanol is an **iso-osmolar dimeric contrast agent** primarily used for **cardiac and vascular imaging**. - While theoretically advantageous due to iso-osmolarity, it has **limited approval and use for myelography** compared to iohexol. - It is **not the standard or most commonly used agent** for this procedure. *Barium sulfate* - This is an **insoluble oral or rectal contrast agent** used exclusively for gastrointestinal imaging. - It is **absolutely contraindicated for intrathecal use** as it causes severe neurotoxicity and potentially fatal reactions. - Only **water-soluble iodinated contrast agents** should be used for myelography.

Question 35: Gadolinium is a contrast agent used for:

A. CT - angiography
B. Bronchography
C. MRI - Imaging (Correct Answer)
D. Contrast Sonography

Explanation: ***MRI - Imaging*** - **Gadolinium** is a paramagnetic substance commonly used as a contrast agent in **Magnetic Resonance Imaging (MRI)**. - It works by altering the **T1 relaxation times** of protons in tissues, enhancing the signal and improving the visibility of certain structures or pathologies like **tumors** or **inflammation**. *CT - angiography* - **CT angiography** typically uses **iodine-based contrast agents**, not gadolinium, to visualize blood vessels. - Iodine contrast agents work by absorbing X-rays, making blood vessels appear bright on CT images. *Bronchography* - **Bronchography** is an older imaging technique that involved introducing an **iodinated contrast medium** directly into the bronchial tree. - It has largely been replaced by **high-resolution CT scans** for evaluating airways. *Contrast Sonography* - **Contrast-enhanced ultrasound (CEUS)**, or contrast sonography, primarily uses **microbubble contrast agents** made of inert gas. - These microbubbles enhance the reflectivity of blood, improving visualization of blood flow and organ perfusion.

Question 36: Non-Iodine containing contrast is

A. Gd DTPA (Correct Answer)
B. Diatrizoate
C. Visipaque
D. Iohexol

Explanation: ***Gd DTPA*** - **Gadolinium-DTPA** (diethylenetriamine pentaacetic acid) is a **gadolinium-based contrast agent** used in MRI, which does not contain iodine. - It enhances images by shortening the **T1 relaxation time** of protons in tissues. *Diatrizoate* - **Diatrizoate** is an **iodinated contrast medium** commonly used in radiography and CT scans. - It contains iodine, which opacifies structures by **attenuating X-rays**. *Visipaque* - **Visipaque** (Iodixanol) is an **iodinated, non-ionic, dimeric contrast medium** with iso-osmolar properties. - It explicitly contains iodine as the contrast-enhancing element. *Iohexol* - **Iohexol** is another widely used **iodinated, non-ionic contrast agent** for various radiological procedures. - Its mechanism of action relies on the presence of iodine atoms to block X-rays.

Question 37: Which of the following statements about contrast in radiography is true:

A. Gadolinium cannot cross an intact blood brain barrier
B. Iohexol is a high osmolar contrast media
C. Non-ionic contrast agents are always high osmolar
D. Ionic monomers have three iodine atoms per two particles in solution (Correct Answer)

Explanation: ***Ionic monomers have three iodine atoms per two particles in solution*** - **Ionic monomeric contrast agents** (e.g., diatrizoate, iothalamate) dissociate in solution, producing **two particles** (one cation and one anion containing three iodine atoms) per molecule. - This dissociation results in a **high osmolality** compared to non-ionic agents, as osmolality is determined by the number of particles in solution. *Gadolinium cannot cross an intact blood brain barrier* - This statement is **FALSE** - **Gadolinium-based contrast agents CAN cross the blood-brain barrier when it is compromised**. - They are used in MRI precisely because they extravasate into tissues where the **blood-brain barrier is disrupted**, such as in tumors, inflammation, or infections. - However, they do **not cross an intact BBB** due to their size and hydrophilicity. *Iohexol is a high osmolar contrast media* - **Iohexol** is a **non-ionic, low osmolality contrast medium** (LOCM). - Its non-ionic nature means it does not dissociate in solution, leading to a significantly lower osmolality compared to older ionic agents. *Non-ionic contrast agents are always high osmolar* - **Non-ionic contrast agents** are characterized by their molecular structure which **does not dissociate into ions** in solution. - This property makes them **low osmolar** or **iso-osmolar**, meaning they have fewer particles in solution compared to ionic agents, thereby reducing osmolality.

Question 38: Which contrast agent is given in perforation peritonitis?

A. Iohexol
B. Metrizoate
C. Diatrizoate (Correct Answer)
D. Iodixanol

Explanation: ***Diatrizoate*** - **Diatrizoate**, a **water-soluble iodinated contrast agent**, is safe for use in suspected bowel perforation because it is absorbed and excreted by the kidneys if it extravasates into the peritoneal cavity. - Unlike barium, it does not cause severe **peritoneal inflammation** or scarring if it leaks into the peritoneum. *Iohexol* - Iohexol is a **non-ionic, low-osmolar contrast medium** primarily used for intravascular administration or for imaging structures like the urinary tract or cerebral arteries. - While water-soluble, it is generally not the first choice for gastrointestinal perforations as **Diatrizoate** has a longer established safety profile and lower cost for this specific indication. *Metrizoate* - Metrizoate is an **ionic, high-osmolar contrast media** that is less commonly used today due to its higher osmolarity and potential for side effects compared to newer agents. - It could theoretically be used in perforation due to its water solubility, but its higher osmolality makes it less preferred than **Diatrizoate**, which is more readily available and widely accepted for this specific application. *Iodixanol* - Iodixanol is an **iso-osmolar, non-ionic contrast medium** mainly used for intravascular procedures, particularly in patients at risk of contrast-induced nephropathy. - While it is water-soluble and safer for intravascular use, it is generally not used for suspected bowel perforations due to its higher cost and the established efficacy and safety of **Diatrizoate** for this specific indication.

Question 39: Which of the following contrast agents is PREFERRED in a patient with renal dysfunction for the prevention of contrast-induced nephropathy?

A. Iso-osmolar contrast (Correct Answer)
B. High osmolar contrast
C. Ionic contrast
D. Low osmolar contrast

Explanation: ***Iso-osmolar contrast*** - **Iso-osmolar contrast agents** (e.g., iodixanol) have an osmolality of ~290 mOsm/kg, which is identical to that of plasma. - **This is the PREFERRED choice** in patients with renal dysfunction as multiple studies demonstrate the lowest risk of contrast-induced nephropathy (CIN). - The iso-osmolar formulation minimizes osmotic stress on renal tubules and reduces the risk of acute kidney injury. - **Current guidelines recommend iso-osmolar agents as first-line** in high-risk patients with pre-existing renal impairment. *Low osmolar contrast* - **Low osmolar contrast agents** have osmolality of 600-900 mOsm/kg, which is significantly lower than high osmolar agents but still 2-3 times higher than plasma. - While **acceptable and safer than high osmolar agents**, they are not as optimal as iso-osmolar contrast for patients with renal dysfunction. - These agents are widely used and represent a reasonable alternative when iso-osmolar agents are not available. *High osmolar contrast* - **High osmolar contrast agents** have osmolality >1400 mOsm/kg (about 5 times that of plasma). - They carry the **highest risk of contrast-induced nephropathy** due to severe osmotic load and direct tubular toxicity. - **Contraindicated or strongly avoided** in patients with pre-existing renal dysfunction. *Ionic contrast* - **Ionic contrast** refers to the chemical structure (dissociates into ions) rather than osmolality. - Can be either high or low osmolar—the ionic nature alone does not determine renal safety. - The critical factor for nephrotoxicity prevention is osmolality, not ionic charge.

Question 40: Which contrast agent is not used for CT scans?

A. CO2 (Correct Answer)
B. Iodinated high-osmolality contrast media
C. Barium compounds
D. Gadolinium-based contrast agents

Explanation: ***CO2*** - **CO2** (carbon dioxide) is **not used as a contrast agent in CT scans**. - CO2 is primarily used in **angiography** (especially for peripheral vessels in patients with iodine allergy or renal insufficiency) where it acts as a negative contrast agent. - In CT, CO2 would appear as air/gas density and create artifacts rather than providing diagnostic enhancement, making it unsuitable for routine CT imaging. *Iodinated high-osmolality contrast media* - These are **iodinated contrast agents** that contain iodine atoms which strongly attenuate X-rays, making them highly effective for **CT imaging**. - High-osmolality contrast media (HOCM) like **diatrizoate** and **iothalamate** were the standard CT contrast agents historically. - They have largely been replaced by **low-osmolality** and **iso-osmolality** agents due to higher incidence of **adverse reactions**, but they are still used for CT scans. *Barium compounds* - **Barium sulfate** suspensions are widely used as **oral or rectal contrast agents** for CT imaging of the gastrointestinal tract. - Barium has high atomic number and effectively attenuates X-rays, making the **GI lumen clearly visible** on CT scans. - Used in **CT enterography**, **CT colonography**, and routine **abdominal/pelvic CT** protocols. *Gadolinium-based contrast agents* - **Gadolinium-based contrast agents (GBCAs)** are primarily designed for **MRI** due to their **paramagnetic properties**. - However, gadolinium DOES attenuate X-rays and can be used **off-label for CT** in patients with **severe iodine allergy** or **contraindications to iodinated contrast**. - While less effective than iodinated agents for CT (requiring higher doses), gadolinium-enhanced CT is a recognized alternative in special clinical circumstances.

Practice by Chapter

Chemistry of Contrast Media

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Pharmacokinetics of Contrast Agents

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Classification of Contrast Reactions

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Risk Factors for Contrast Reactions

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Prevention of Contrast Reactions

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Treatment of Acute Contrast Reactions

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Contrast-Induced Nephropathy

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Nephrogenic Systemic Fibrosis

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Extravasation of Contrast Media

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Guidelines for Contrast Administration

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Alternative Contrast Agents

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Documentation and Medicolegal Aspects

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