Contrast Media and Reactions — MCQs

Contrast Media and Reactions Indian Medical PG Practice Questions and MCQs

Question 11: Which MRI contrast agent is specifically used for liver imaging?

A. Gadoterate
B. Gadoxetate (Correct Answer)
C. Gadoteridol
D. Gadopenate

Explanation: **Explanation:** **Gadoxetate disodium (Primovist/Eovist)** is the correct answer because it is a **hepatobiliary-specific** MRI contrast agent. Unlike standard extracellular agents, gadoxetate is taken up by functioning hepatocytes via OATP1 receptors and subsequently excreted into the bile. This dual-phase property allows for both dynamic vascular imaging and a delayed **hepatobiliary phase** (typically at 20 minutes). In this phase, normal liver tissue enhances (appears bright), while lesions lacking functioning hepatocytes—such as **Hepatocellular Carcinoma (HCC)** or metastases—appear hypointense (dark), significantly increasing diagnostic sensitivity. **Analysis of Incorrect Options:** * **A. Gadoterate (Dotarem):** A macrocyclic, ionic, extracellular fluid (ECF) agent. It is used for general CNS and body imaging but lacks hepatocyte-specific uptake. * **C. Gadoteridol (ProHance):** A macrocyclic, non-ionic ECF agent. Similar to Gadoterate, it distributes in the interstitial space and does not provide hepatobiliary phase imaging. * **D. Gadopentetate (Magnevist):** A linear, ionic ECF agent. While historically common, it is a non-specific agent and is increasingly avoided due to a higher risk of Nephrogenic Systemic Fibrosis (NSF) compared to macrocyclic agents. **High-Yield Clinical Pearls for NEET-PG:** * **Hepatobiliary Agents:** Gadoxetate (Eovist) and Gadobenate (MultiHance) are the two main agents. Gadoxetate has higher biliary excretion (~50%) compared to Gadobenate (~5%). * **Focal Nodular Hyperplasia (FNH):** Characteristically appears **hyperintense** or isointense on the hepatobiliary phase because it contains functioning hepatocytes and abnormal bile ducts that retain contrast. * **Safety:** Macrocyclic agents (Gadoterate, Gadoteridol) are generally considered safer than linear agents regarding the risk of NSF and brain deposition.

Question 12: Which of the following is an ionic dimer?

A. Diatrizoate
B. Metrizoate
C. Ioxaglate (Correct Answer)
D. Iothalamate

Explanation: **Explanation:** The classification of iodinated contrast media is based on two factors: **osmolality** (High vs. Low) and **ionic nature** (Ionic vs. Non-ionic). **Ioxaglate** is the correct answer because it is the only clinically significant **Low Osmolar Ionic Dimer**. It consists of two benzene rings (a dimer) but still contains a carboxyl group that dissociates in solution, making it ionic. Because it provides six iodine atoms for every two particles in solution (a 6:2 or 3:1 ratio), it has lower osmolality than traditional ionic monomers, reducing side effects while maintaining ionic properties. **Analysis of Incorrect Options:** * **A. Diatrizoate:** A High Osmolar Ionic Monomer (HOCM). It is the prototype of older contrast agents with high osmolality and higher risk of adverse reactions. * **B. Metrizoate:** Another High Osmolar Ionic Monomer, similar to Diatrizoate. * **D. Iothalamate:** Also a High Osmolar Ionic Monomer. **High-Yield NEET-PG Pearls:** 1. **Classification Summary:** * **Ionic Monomer (HOCM):** Diatrizoate, Iothalamate, Metrizoate. * **Ionic Dimer (LOCM):** Ioxaglate (The "Odd One Out"). * **Non-ionic Monomer (LOCM):** Iohexol, Iopamidol, Ioversol. * **Non-ionic Dimer (IOCM):** Iodixanol (Iso-osmolar; safest for kidneys). 2. **Osmolality:** Non-ionic dimers (Iodixanol) are **iso-osmolar** to blood (approx. 290 mOsm/kg), making them the preferred choice for patients with renal impairment. 3. **Adverse Reactions:** Most idiosyncratic (allergic-like) reactions are more common with ionic agents due to their high osmolality and chemotoxicity.

Question 13: Which of the following statements regarding radiocontrast media (RCM) reactions is NOT true?

A. Hypersensitivity reactions are independent of the rate of infusion.
B. Seizures and arrhythmias are noticed in RCM reactions. (Correct Answer)
C. Physiologic reactions are related to the chemical properties of RCM agents.
D. Physiologic reactions are dependent on the rate and dose of administration.

Explanation: ### Explanation Contrast media reactions are broadly classified into two categories: **Anaphylactoid (Hypersensitivity)** and **Physiologic (Chemotoxic)**. **Why Option B is the "Correct" (False) Statement:** In the context of standard NEET-PG classification, **seizures and arrhythmias** are classified as **Physiologic reactions**, not hypersensitivity reactions. They occur due to the direct chemotoxic effects of the contrast media (osmolality, calcium binding, or direct organ toxicity) rather than an idiosyncratic immune-mediated response. While they *are* noticed in RCM reactions, the question likely seeks to distinguish between the mechanisms of reaction types. **Analysis of Other Options:** * **Option A (True):** Hypersensitivity (anaphylactoid) reactions are **idiosyncratic**. They are independent of the dose or rate of infusion; even a tiny amount can trigger a severe reaction. * **Option C (True):** Physiologic reactions are related to the **chemical properties** (high osmolality, ionic nature, or toxicity) of the RCM. Common examples include nausea, vomiting, and a sensation of warmth. * **Option D (True):** Unlike hypersensitivity, physiologic reactions are **dose and rate-dependent**. Rapid infusion of high-osmolality contrast is more likely to cause cardiac strain or vasovagal responses. **High-Yield Clinical Pearls for NEET-PG:** * **Risk Factors:** A prior reaction to RCM is the strongest predictor of a future reaction. Asthma and significant allergies also increase risk. * **Pre-medication:** For high-risk patients, use **Corticosteroids** (e.g., Prednisolone 50mg orally 13, 7, and 1 hour before) and H1-antihistamines. * **Drug of Choice:** **Adrenaline (1:1000, 0.3–0.5 mg IM)** is the first-line treatment for severe anaphylactoid reactions. * **LOCM vs. HOCM:** Low-Osmolar Contrast Media (LOCM) have significantly lower rates of both physiologic and hypersensitivity reactions compared to High-Osmolar Contrast Media (HOCM).

Question 14: All of the following pharmacological agents may be used for reducing the risk of contrast nephropathy, except?

A. Fenoldopam
B. N-Acetylcysteine
C. Prostaglandins
D. Furosemide (Correct Answer)

Explanation: **Explanation:** Contrast-Induced Nephropathy (CIN) is a form of acute kidney injury occurring after the administration of iodinated contrast media. The pathophysiology involves renal vasoconstriction and direct tubular toxicity. **Why Furosemide is the correct answer:** Furosemide (a loop diuretic) is **not** used for prophylaxis; in fact, it is **contraindicated** for this purpose. Diuretics can lead to intravascular volume depletion, which activates the renin-angiotensin-aldosterone system and increases the concentration of contrast within the renal tubules. This exacerbates medullary hypoxia and direct toxicity, thereby **increasing the risk** of CIN. **Analysis of other options:** * **N-Acetylcysteine (NAC):** It is an antioxidant that scavenges free radicals and has vasodilatory properties. While its clinical efficacy is debated in recent trials, it is traditionally used in protocols to prevent CIN. * **Fenoldopam:** A selective dopamine-1 receptor agonist that causes renal vasodilation and increases renal blood flow. It has been studied for its potential to counteract contrast-induced vasoconstriction. * **Prostaglandins:** Agents like PGE1 have been explored for their vasodilatory effects on the renal vasculature to maintain perfusion during contrast administration. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Prophylaxis:** The most effective method to prevent CIN is **Isotonic Saline (0.9% NaCl) hydration**. * **Definition of CIN:** An increase in serum creatinine of >0.5 mg/dL or >25% from baseline within 48–72 hours of contrast exposure. * **Risk Factors:** Pre-existing chronic kidney disease (CKD), Diabetes Mellitus, dehydration, and high-osmolar contrast media (HOCM). * **Management:** Use Low-Osmolar (LOCM) or Iso-Osmolar Contrast Media (IOCM) and ensure adequate hydration.

Question 15: What contrast agent is commonly used in CT scans?

A. Gadolinium
B. Technetium
C. Iodine (Correct Answer)
D. Chromium

Explanation: ### Explanation **Correct Option: C (Iodine)** Iodine is the primary contrast agent used in Computed Tomography (CT) because of its **high atomic number (Z=53)**. In CT imaging, contrast depends on the attenuation of X-rays. Iodine atoms are highly effective at absorbing X-rays via the photoelectric effect, which increases the density of blood vessels and organs on the scan, making them appear "bright" (hyperdense). Modern CT contrast agents are typically **non-ionic, low-osmolar iodinated compounds** (e.g., Iohexol, Iopromide) to minimize adverse reactions. **Incorrect Options:** * **A. Gadolinium:** This is the gold-standard contrast agent for **MRI**, not CT. It works by altering the relaxation times of nearby water protons rather than blocking X-rays. * **B. Technetium (Tc-99m):** This is a radioisotope used in **Nuclear Medicine** (e.g., bone scans, SPECT). It emits gamma radiation from within the body, which is detected by a gamma camera. * **D. Chromium:** Chromium (specifically Cr-51) was historically used in specialized nuclear medicine tests (like red cell mass studies) but has no role as a routine CT contrast medium. **High-Yield Clinical Pearls for NEET-PG:** 1. **Route of Excretion:** Iodinated contrast is primarily excreted by the **kidneys** via glomerular filtration. 2. **Contrast-Induced Nephropathy (CIN):** A key risk factor. Always check **Serum Creatinine/eGFR** before administration in high-risk patients. 3. **Metformin Rule:** Metformin should be withheld for 48 hours *after* the procedure if the patient has renal impairment to prevent lactic acidosis. 4. **Adverse Reactions:** Most are idiosyncratic. Pre-medication with **steroids and H1 blockers** is indicated for patients with a history of prior moderate-to-severe reactions.

Question 16: After contrast media injection, a patient develops severe hypotension, bronchospasm, and cyanosis. Which one of the following drugs should be used for treatment?

A. Atropine
B. Aminophylline
C. Dopamine
D. Adrenaline (Correct Answer)

Explanation: ### Explanation The clinical presentation of **severe hypotension, bronchospasm, and cyanosis** following contrast administration indicates a **Grade III (Severe) Anaphylactoid Reaction**. **1. Why Adrenaline is the Correct Answer:** Adrenaline (Epinephrine) is the drug of choice for severe anaphylaxis due to its multi-receptor action: * **Alpha-1 agonist:** Causes vasoconstriction, which reverses hypotension and reduces mucosal edema. * **Beta-1 agonist:** Increases heart rate and myocardial contractility (positive inotropy). * **Beta-2 agonist:** Induces bronchodilation to relieve bronchospasm and inhibits further mediator release from mast cells and basophils. * **Route:** In an emergency, the preferred route is **Intramuscular (IM)** in the anterolateral thigh (1:1000 concentration). **2. Why Other Options are Incorrect:** * **Atropine:** Used specifically for **Vasovagal reactions** characterized by hypotension accompanied by **bradycardia**. In anaphylaxis, the patient usually has tachycardia. * **Aminophylline:** A bronchodilator that is no longer first-line. It does not address hypotension or the systemic allergic cascade. * **Dopamine:** An inotrope used for cardiogenic or septic shock, but it lacks the potent bronchodilatory effects required to treat anaphylaxis. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mild Reactions (Urticaria/Pruritus):** Treat with H1-blockers (e.g., Pheniramine maleate). * **Moderate Reactions (Mild bronchospasm/Isolated hypotension):** Require oxygen, IV fluids, and potentially hydrocortisone. * **Adrenaline Dosage:** 0.3–0.5 mg IM (1:1000) for adults; 0.01 mg/kg for children. * **Contrast Media:** Non-ionic, low-osmolar contrast media (LOCM) have a significantly lower incidence of adverse reactions compared to ionic, high-osmolar media (HOCM).

Question 17: A 60-year-old diabetic woman with a creatinine of 2.2 requires a coronary angiogram for evaluation of coronary artery disease. Which of the following is the most effective in reducing the risk of contrast-induced nephropathy?

A. Administer mannitol immediately after the contrast is given.
B. Perform prophylactic hemodialysis after the procedure.
C. Give IV hydration with normal saline or sodium bicarbonate prior to and following the procedure. (Correct Answer)
D. Administer indomethacin 25 mg the morning of the procedure.

Explanation: **Explanation:** **Contrast-Induced Nephropathy (CIN)** is defined as an absolute increase in serum creatinine of $\geq$ 0.5 mg/dL or a relative increase of $\geq$ 25% from baseline within 48–72 hours of intravascular contrast administration. This patient is at high risk due to pre-existing renal insufficiency (Creatinine 2.2) and diabetes mellitus. **Why Option C is Correct:** Intravenous hydration is the **single most effective** and proven strategy to prevent CIN. Hydration works by expanding intravascular volume, which decreases the concentration of contrast in the renal tubules, promotes rapid excretion, and reduces renal vasoconstriction. Both 0.9% Normal Saline and Sodium Bicarbonate are effective; Sodium Bicarbonate is thought to reduce free radical damage by alkalinizing the tubular fluid. **Why Other Options are Incorrect:** * **Option A (Mannitol):** Diuretics like mannitol or furosemide do not prevent CIN and may actually worsen it by causing dehydration and increasing the concentration of contrast in the tubules. * **Option B (Prophylactic Hemodialysis):** While dialysis removes contrast from the blood, studies have shown it does **not** prevent the development of CIN and is not recommended as a prophylactic measure. * **Option D (Indomethacin):** NSAIDs like indomethacin inhibit prostaglandins, leading to renal afferent arteriolar vasoconstriction. This exacerbates renal ischemia and significantly **increases** the risk of CIN. **High-Yield Clinical Pearls for NEET-PG:** * **Risk Factors:** Pre-existing renal disease (most important), Diabetes, Congestive Heart Failure, and Advanced Age. * **Prevention:** Use **Low-Osmolar (LOCM)** or **Iso-Osmolar Contrast Media (IOCM)**; minimize contrast volume. * **N-Acetylcysteine (NAC):** Previously popular due to antioxidant properties, but recent large trials (PRESERVE trial) show it offers no significant benefit over hydration alone. * **Metformin:** Must be withheld for 48 hours **after** the procedure in patients with renal impairment to avoid lactic acidosis if CIN occurs.

Question 18: Which of the following is a hepatocyte-specific MR contrast agent?

A. Mn-DPDP (Correct Answer)
B. Iohexol
C. Starch-coated iron oxide
D. DMSA

Explanation: **Explanation:** **Mn-DPDP (Mangafodipir trisodium)** is a hepatocyte-specific MRI contrast agent. It is an intracellular agent taken up by functional hepatocytes via the vitamin B6 transport mechanism and excreted into the bile. On T1-weighted imaging, it causes significant shortening of T1 relaxation time, leading to **hyperintensity (bright signal)** in normal liver parenchyma. This enhances the detection of focal liver lesions (like metastases or hemangiomas) which do not contain hepatocytes and thus appear hypointense against the enhanced liver. **Analysis of Incorrect Options:** * **B. Iohexol:** This is a non-ionic, low-osmolar **iodinated contrast agent** used primarily in CT imaging and fluoroscopy, not MRI. It is excreted by the kidneys via glomerular filtration. * **C. Starch-coated iron oxide (SPIO):** These are **reticuloendothelial system (RES) agents**. They are taken up by Kupffer cells in the liver, not hepatocytes. They primarily cause T2* shortening, making the liver appear dark. * **D. DMSA (Dimercaptosuccinic acid):** This is a **radiopharmaceutical** used in Nuclear Medicine (Gamma camera/SPECT) for renal cortical imaging, not an MRI contrast agent. **High-Yield Clinical Pearls for NEET-PG:** * **Hepatocyte-specific agents:** Include Mn-DPDP, **Gadobenate dimeglumine (Gd-BOPTA)**, and **Gadoxetic acid (Gd-EOB-DTPA/Primovist)**. * **Focal Nodular Hyperplasia (FNH):** Characteristically shows uptake/retention of hepatocyte-specific agents because it contains functional hepatocytes and abnormal bile ducts. * **Metastases:** Typically lack hepatocytes and Kupffer cells, appearing "cold" or dark on post-contrast hepatobiliary phase images. * **Safety Note:** Mn-DPDP is less commonly used now compared to Gadoxetic acid due to the clinical efficiency of the latter.

Question 19: All of the following are strategies to prevent contrast nephropathy, except?

A. Intravenous Hydration
B. Use of High Osmolar Contrast Agents (Correct Answer)
C. Theophylline administration
D. Hemodialysis

Explanation: **Explanation:** Contrast-Induced Nephropathy (CIN) is a form of acute kidney injury occurring after the administration of iodinated contrast. The primary goal in management is prevention, especially in high-risk patients (e.g., diabetics, pre-existing renal insufficiency). **Why Option B is the Correct Answer:** High Osmolar Contrast Media (HOCM), such as Diatrizoate, have an osmolality significantly higher than plasma (~1500–2000 mOsm/kg). This high osmolality causes osmotic diuresis, renal vasoconstriction, and direct tubular toxicity. To **prevent** CIN, one should use **Low Osmolar Contrast Media (LOCM)** or **Iso-osmolar Contrast Media (IOCM)** like Iodixanol, which are significantly less nephrotoxic. **Analysis of Other Options:** * **A. Intravenous Hydration:** This is the **most effective** and gold-standard preventive strategy. Normal saline (0.9% NaCl) or Sodium Bicarbonate helps by expanding intravascular volume and diluting the contrast in the renal tubules. * **C. Theophylline administration:** Adenosine is a mediator of renal vasoconstriction in CIN. Adenosine antagonists like Theophylline or Aminophylline have shown some benefit in clinical trials for preventing CIN, though they are not first-line. * **D. Hemodialysis:** While not a routine preventive measure for everyone, prophylactic hemodialysis or hemofiltration can be used in end-stage renal disease patients to rapidly clear contrast, though its efficacy in preventing CIN in non-dialysis patients is controversial. **High-Yield Clinical Pearls for NEET-PG:** * **Definition of CIN:** An increase in serum creatinine >0.5 mg/dL or >25% from baseline within 48–72 hours of contrast exposure. * **Best Fluid:** Isotonic saline (0.9% NaCl) is preferred over half-normal saline. * **N-Acetylcysteine (NAC):** Often used in exams as a preventive strategy (antioxidant), though recent large trials (PRESERVE) show limited benefit. * **Metformin:** Must be withheld for 48 hours **after** the procedure to avoid lactic acidosis if CIN develops.

Question 20: Which of the following are risk factors for precipitation of renal failure while performing intravenous urography (IVP)?

A. Myeloma
B. Diabetes
C. Old age
D. All of the above (Correct Answer)

Explanation: **Explanation:** The primary concern when administering iodinated contrast media for Intravenous Pyelography (IVP) is **Contrast-Induced Nephropathy (CIN)**. This occurs due to direct tubular toxicity and renal medullary ischemia caused by the hyperosmolality and vasoconstrictive properties of the contrast agent. **Why "All of the Above" is correct:** * **Myeloma (Multiple Myeloma):** This is a classic high-yield risk factor. In patients with myeloma, Bence-Jones proteins can precipitate in the renal tubules when they interact with contrast media, leading to intratubular obstruction and acute renal failure. * **Diabetes Mellitus:** Diabetic nephropathy is the most significant independent risk factor for CIN. Pre-existing renal insufficiency in diabetics severely impairs the kidney's ability to clear the contrast load. * **Old Age:** Elderly patients often have a physiological decline in Glomerular Filtration Rate (GFR), reduced renal reserve, and are more prone to dehydration, making them highly susceptible to nephrotoxicity. **Clinical Pearls for NEET-PG:** * **Prevention:** The most effective strategy to prevent CIN is **adequate hydration** (usually with Normal Saline) before and after the procedure. * **Metformin Caution:** In diabetic patients, Metformin should be withheld for 48 hours after contrast administration to prevent **Lactic Acidosis** if renal impairment occurs. * **Creatinine Levels:** Always check serum creatinine/eGFR before IVP. A creatinine level >1.5 mg/dL is generally considered a contraindication for conventional IVP. * **Alternative:** In high-risk patients (like those with the factors mentioned above), Non-Contrast CT or Ultrasound is preferred over IVP.

Practice by Chapter

Chemistry of Contrast Media

Practice Questions

Pharmacokinetics of Contrast Agents

Practice Questions

Classification of Contrast Reactions

Practice Questions

Risk Factors for Contrast Reactions

Practice Questions

Prevention of Contrast Reactions

Practice Questions

Treatment of Acute Contrast Reactions

Practice Questions

Contrast-Induced Nephropathy

Practice Questions

Nephrogenic Systemic Fibrosis

Practice Questions

Extravasation of Contrast Media

Practice Questions

Guidelines for Contrast Administration

Practice Questions

Alternative Contrast Agents

Practice Questions

Documentation and Medicolegal Aspects

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free