Nuclear Medicine — MCQs

Nuclear Medicine Indian Medical PG Practice Questions and MCQs

Question 71: What is the investigation of choice in parathyroid pathology?

A. CT scan
B. Gallium scan
C. Thallium scan
D. Technetium-99m sestamibi scan (Correct Answer)

Explanation: **Explanation:** **Technetium-99m (Tc-99m) Sestamibi scan** is the investigation of choice for localizing parathyroid adenomas (the most common cause of primary hyperparathyroidism). The underlying principle is based on **differential washout**. Sestamibi is a lipophilic cation taken up by both thyroid and parathyroid tissues. However, it clears rapidly from normal thyroid tissue but is retained much longer in hyperfunctioning parathyroid tissue (adenomas or hyperplasia) due to the high concentration of mitochondria-rich oxyphil cells. This allows for clear visualization on delayed images (usually taken at 2 hours). **Analysis of Incorrect Options:** * **CT Scan:** While useful for identifying ectopic parathyroid glands in the mediastinum, it lacks the functional specificity of nuclear imaging and is not the first-line investigation. * **Gallium Scan:** Primarily used for detecting inflammation, infections, or certain malignancies (like lymphoma); it has no role in parathyroid imaging. * **Thallium Scan:** Historically, Thallium-201 was used in combination with Technetium-99m pertechnetate (subtraction technique). However, it has been largely replaced by Sestamibi due to Sestamibi’s superior image quality and lower radiation dose. **High-Yield Clinical Pearls for NEET-PG:** * **SPECT/CT:** Combining Sestamibi with SPECT/CT provides anatomical localization and is currently considered the "gold standard" for preoperative planning. * **4D-CT:** This is an emerging highly sensitive modality used specifically for surgical planning in cases where Sestamibi is negative or in re-operative cases. * **Ectopic Glands:** The most common site for an ectopic parathyroid gland is the **thymus** (inferior gland) or the **tracheoesophageal groove** (superior gland). Sestamibi is excellent for detecting these.

Question 72: What is the half-life of Technetium-99m?

A. 2 hours
B. 6 hours (Correct Answer)
C. 12 hours
D. 24 hours

Explanation: **Explanation:** **Technetium-99m (Tc-99m)** is the most widely used radioisotope in diagnostic nuclear medicine. The correct answer is **6 hours**, which represents its physical half-life ($T_{1/2}$). 1. **Why 6 hours is correct:** Tc-99m is a metastable nuclear isomer of Technetium-99. It decays via **isomeric transition**, emitting a pure **gamma photon of 140 keV**. A 6-hour half-life is considered "ideal" for clinical imaging: it is long enough to allow for complex metabolic labeling and imaging procedures, yet short enough to minimize the radiation dose to the patient. 2. **Why other options are incorrect:** * **2 hours:** Too short for most diagnostic protocols; however, Fluorine-18 (used in PET scans) has a similar half-life (~110 minutes). * **12 hours:** Incorrect for Tc-99m; Iodine-123 (used in thyroid imaging) has a half-life of approximately 13 hours. * **24 hours:** Too long for a standard diagnostic tracer, as it would result in unnecessary prolonged radiation exposure. **High-Yield Clinical Pearls for NEET-PG:** * **Source:** Tc-99m is obtained from a **Molybdenum-99 (Mo-99) generator** (often called a "Moly cow"). * **Energy:** The 140 keV energy is optimal for detection by modern **Gamma Cameras**. * **Pure Gamma Emitter:** Unlike isotopes that emit alpha or beta particles, Tc-99m is a pure gamma emitter, which reduces tissue damage (low particulate radiation). * **Common Uses:** Bone scans (MDP), Renal scans (DTPA/MAG3), Thyroid scans (Pertechnetate), and Cardiac perfusion (Sestamibi).

Question 73: What is an Isotope Renogram used for?

A. Study of the renin mechanism
B. Contrast study of the kidneys, ureter, and bladder
C. Mapping the anatomy of the kidneys
D. Graphic representation of the radioactivity of the kidneys (Correct Answer)

Explanation: An **Isotope Renogram** (Radionuclide Renography) is a functional nuclear medicine study used to evaluate renal perfusion and excretion. ### Why Option D is Correct The test involves the intravenous administration of a radiopharmaceutical (commonly **99mTc-DTPA** or **99mTc-MAG3**). As the kidneys filter or secrete these tracers, a gamma camera records the radioactivity over time. This data is plotted as a **time-activity curve**, providing a graphic representation of the uptake, transit, and excretion of the tracer by each kidney individually. ### Why Other Options are Incorrect * **Option A:** While renal artery stenosis (which triggers the renin mechanism) can be evaluated using a **Captopril Renogram**, the renogram itself measures tracer kinetics, not the biochemical renin levels. * **Option B:** Contrast studies involving the kidneys, ureters, and bladder (like IVP or CT Urography) use iodinated contrast media and X-rays to visualize anatomy, not radioactive isotopes. * **Option C:** Mapping anatomy is the primary goal of **Static Renal Scintigraphy** (using **99mTc-DMSA**), which binds to the renal cortex. A renogram is a *dynamic* study focused on function rather than detailed structural anatomy. ### High-Yield Clinical Pearls for NEET-PG * **Tracer of Choice for GFR:** 99mTc-DTPA (filtered by the glomerulus). * **Tracer of Choice for ERPF:** 99mTc-MAG3 (secreted by tubules; preferred in pediatric patients or those with renal failure). * **DMSA Scan:** Used for detecting **renal scars** (e.g., in chronic pyelonephritis) and ectopic kidneys. * **Diuretic Renogram (Lasix):** Used to differentiate between mechanical obstruction and functional stasis (dilated pelvis).

Question 74: A young man presented with hyperparathyroidism. Which radionuclide scan is done for parathyroid adenoma?

A. Sesta MIBI scan (Correct Answer)
B. Iodine-123 scan
C. 99mTc-sulphur colloid
D. Gallium scan

Explanation: ### Explanation **Correct Answer: A. Sesta MIBI scan** The **99mTc-Sestamibi (MIBI) scan** is the gold standard radionuclide imaging modality for localizing parathyroid adenomas. Sestamibi is a lipophilic cationic compound that is taken up by mitochondria-rich cells. Parathyroid adenomas contain a high density of **oxyphil cells**, which are packed with mitochondria. The scan typically uses a **dual-phase technique**: 1. **Early Phase (15 mins):** Uptake is seen in both the thyroid and parathyroid glands. 2. **Delayed Phase (2–3 hours):** Sestamibi washes out rapidly from normal thyroid tissue but is **retained** in the parathyroid adenoma due to the slow mitochondria turnover in oxyphil cells. This differential washout allows for clear visualization of the adenoma. --- ### Why other options are incorrect: * **B. Iodine-123 scan:** This is used primarily for imaging thyroid morphology and function (e.g., Graves' disease or toxic nodules) as it is trapped and organified by thyroid follicular cells, not parathyroid tissue. * **C. 99mTc-sulphur colloid:** This agent is taken up by the Reticuloendothelial System (RES). It is used for liver-spleen imaging, bone marrow scanning, and detecting gastrointestinal bleeds. * **D. Gallium-67 scan:** This is used to image chronic inflammation, infections (like sarcoidosis), or certain malignancies (like lymphomas). It has no role in parathyroid localization. --- ### High-Yield Clinical Pearls for NEET-PG: * **Dual-Isotope Subtraction:** Another method involves using **99mTc-Pertechnetate** (thyroid only) and **Sestamibi** (both); subtracting the thyroid image leaves only the parathyroid adenoma visible. * **Ectopic Adenoma:** Sestamibi is particularly useful for identifying ectopic parathyroid glands (e.g., in the mediastinum). * **SPECT/CT:** Combining Sestamibi with CT (SPECT/CT) significantly improves anatomical localization and is now the preferred advanced imaging protocol. * **Hungry Bone Syndrome:** A common post-operative complication after parathyroidectomy, characterized by profound hypocalcemia.

Question 75: Which radiotracer is used to demonstrate vesicoureteric reflux?

A. Tc-99 - DTPA
B. Tc-99 - DMSA (Correct Answer)
C. Tc-99 - MAG-3
D. I - 123 - OIH

Explanation: ### Explanation **Correct Answer: B. Tc-99m DMSA** In the context of Vesicoureteric Reflux (VUR), the primary goal of nuclear imaging is to detect **renal cortical scarring**, which is the most significant long-term complication of reflux (Reflux Nephropathy). **Tc-99m DMSA (Dimercaptosuccinic Acid)** is a static renal imaging agent that binds to the proximal convoluted tubules in the renal cortex. It is the **gold standard** for detecting cortical scars, assessing differential renal function, and diagnosing acute pyelonephritis. While a "Radionuclide Cystogram" (RNC) is used to *diagnose* the reflux itself, DMSA is the tracer used to *demonstrate the clinical impact* (scarring) of that reflux on the kidney. #### Analysis of Incorrect Options: * **A. Tc-99m DTPA:** A glomerular filtration agent used primarily for calculating GFR and evaluating obstructive uropathy. It is cleared rapidly and is not ideal for visualizing cortical morphology. * **C. Tc-99m MAG-3:** A tubular secretion agent used for dynamic renography (diuretic renograms). It is the agent of choice for assessing renal perfusion and drainage but not for permanent cortical scarring. * **D. I-123 OIH (Orthoiodohippurate):** Historically used to measure effective renal plasma flow (ERPF). It has been largely replaced by MAG-3 due to better imaging characteristics and lower radiation dose of Technetium-based tracers. #### NEET-PG High-Yield Pearls: * **Static Imaging:** DMSA (Best for Scars/Pyelonephritis). * **Dynamic Imaging:** DTPA (GFR) and MAG-3 (Best for Obstruction/Transplant evaluation). * **VUR Diagnosis:** The **Radionuclide Cystogram (RNC)** is more sensitive than MCU (Micturating Cystourethrogram) for follow-up and screening siblings, as it involves lower radiation. * **DMSA Timing:** For scar detection, DMSA should be performed 4–6 months after an acute UTI to avoid confusing acute inflammation with permanent scarring.

Question 76: PET Scan is useful in evaluating all the following conditions except?

A. Solitary pulmonary nodule
B. Skeletal metastasis
C. Myocardial viability
D. Dysphagia lusoria (Correct Answer)

Explanation: **Explanation:** **Dysphagia lusoria** is the correct answer because it is a **structural/mechanical condition**, not a metabolic one. It is caused by an aberrant right subclavian artery that arises from the aortic arch and crosses behind the esophagus, causing extrinsic compression. Diagnosis is primarily made via **Barium swallow** (showing a posterior indentation) or **CT/MRI Angiography** to visualize the vascular anatomy. Since PET scans measure metabolic activity (glucose uptake), they have no role in evaluating mechanical vascular anomalies. **Why the other options are incorrect:** * **Solitary Pulmonary Nodule (SPN):** FDG-PET is a gold-standard non-invasive tool to differentiate between benign and malignant nodules. A high Standardized Uptake Value (SUV) suggests malignancy. * **Skeletal Metastasis:** PET scans (especially using FDG or F-18 Sodium Fluoride) are highly sensitive for detecting bone metastases by identifying areas of increased mineral turnover or tumor cell metabolism, often outperforming traditional bone scans in lytic lesions. * **Myocardial Viability:** FDG-PET is the **"Gold Standard"** for assessing myocardial viability. It identifies "hibernating myocardium" (areas with reduced blood flow but preserved glucose metabolism), helping surgeons decide if revascularization (CABG/PCI) will be beneficial. **Clinical Pearls for NEET-PG:** * **PET Radiopharmaceutical:** Most common is **18-FDG** (Fluorodeoxyglucose), a glucose analog. * **Mechanism:** PET detects **annihilation photons** (511 keV) produced when a positron meets an electron. * **Normal High Uptake:** Brain, Heart, Kidneys, and Bladder (due to excretion) normally show high FDG uptake; this should not be confused with pathology. * **False Positives:** Infection and inflammation (e.g., Tuberculosis) can cause high FDG uptake, mimicking malignancy.

Question 77: Which of the following is used to detect mucosa in Meckel's diverticulum?

A. Technetium-99 scan (Correct Answer)
B. Barium meal
C. CT scan
D. MRI scan

Explanation: **Explanation:** The correct answer is **Technetium-99m pertechnetate scan**, commonly referred to as a **Meckel’s Scan**. **Why it is correct:** Meckel’s diverticulum is the most common congenital anomaly of the gastrointestinal tract. Approximately 50% of symptomatic cases contain **ectopic gastric mucosa**. The pertechnetate ion ($Tc^{99m}O_4^-$) has a natural affinity for gastric mucosal cells (specifically the mucoid surface cells). When injected intravenously, the radionuclide concentrates in the stomach and any ectopic gastric tissue, appearing as a "hot spot" on scintigraphy. This is the investigation of choice for diagnosing a bleeding Meckel’s diverticulum. **Why the other options are incorrect:** * **Barium meal:** This is generally insensitive for Meckel’s diverticulum as the diverticulum may not fill with contrast or may be obscured by overlying loops of small bowel. * **CT and MRI scans:** While these can identify complications like diverticulitis or bowel obstruction, they lack the functional sensitivity to specifically identify ectopic gastric mucosa, which is the hallmark of the condition. **High-Yield Clinical Pearls for NEET-PG:** * **Rule of 2s:** 2% of the population, 2 feet from the ileocecal valve, 2 inches long, 2 types of ectopic tissue (Gastric > Pancreatic), and usually presents before age 2. * **Pharmacological Augmentation:** To increase the sensitivity of the Meckel’s scan, the following can be used: 1. **Pentagastrin:** Stimulates uptake of pertechnetate. 2. **H2 Blockers (Ranitidine/Cimetidine):** Prevents the release of the tracer from the cells into the lumen. 3. **Glucagon:** Decreases peristalsis, preventing the "washout" of the tracer. * **False Negatives:** Can occur if there is no ectopic gastric mucosa present or if there is brisk active bleeding washing away the tracer.

Question 78: Tc-99m labeled red blood cells are used for which of the following diagnostic purposes?

A. Assessment of myocardial function
B. Diagnosis of spleen diseases (Correct Answer)
C. Evaluation of liver and biliary function
D. Assessment of lung ventilation

Explanation: **Explanation:** The correct answer is **B. Diagnosis of spleen diseases.** **Why it is correct:** Technetium-99m (Tc-99m) labeled red blood cells (RBCs) are primarily used for splenic imaging when they are **heat-denatured** (damaged). The spleen’s physiological role is to filter out aged or damaged erythrocytes from the circulation. When heat-damaged Tc-99m RBCs are injected, they are selectively sequestered by the splenic parenchyma, making this the "gold standard" for identifying ectopic splenic tissue (splenosis) or a **splenunculus** (accessory spleen). **Analysis of Incorrect Options:** * **Option A:** Myocardial function is typically assessed using **Tc-99m Sestamibi** or **Thallium-201** (for perfusion) or **Tc-99m labeled RBCs** (non-denatured) for MUGA scans to calculate Ejection Fraction. However, in the context of specific organ diagnosis, spleen imaging is the classic association for labeled RBCs. * **Option C:** Liver and biliary functions are evaluated using **Tc-99m HIDA** (Hepatobiliary Iminodiacetic Acid) scans. * **Option D:** Lung ventilation is assessed using **Xe-133 gas** or **Tc-99m DTPA aerosol**. **High-Yield Clinical Pearls for NEET-PG:** * **Heat-denatured RBCs:** Used for Spleen imaging (sequestration). * **Non-denatured (In-vivo/In-vitro) RBCs:** Used for detecting **Gastrointestinal (GI) bleed** (specifically slow/intermittent bleeds) and **Hemangioma** of the liver (shows "delayed filling"). * **Sulfur Colloid:** Another agent for spleen imaging, but it also labels the liver and bone marrow (Reticuloendothelial system). Heat-denatured RBCs are more specific for the spleen.

Question 79: Which investigation is used to assess the functionality of the gallbladder?

A. MRCP (Magnetic Resonance Cholangiopancreatography)
B. PTC (Percutaneous Transhepatic Cholangiography)
C. HIDA scan (Hepatobiliary Iminodiacetic Acid scan) (Correct Answer)
D. EUS scan (Endoscopic Ultrasound scan)

Explanation: **Explanation:** The correct answer is **HIDA scan (Hepatobiliary Iminodiacetic Acid scan)**, also known as cholescintigraphy. **Why HIDA scan is correct:** The HIDA scan is a **functional (physiological) imaging** study. It involves the intravenous injection of a technetium-99m labeled iminodiacetic acid derivative, which is taken up by hepatocytes and excreted into the bile, mimicking the pathway of bilirubin. It is the gold standard for assessing gallbladder functionality because it can measure the **Gallbladder Ejection Fraction (GBEF)** following the administration of Cholecystokinin (CCK). A low GBEF indicates biliary dyskinesia or chronic acalculous cholecystitis. **Why other options are incorrect:** * **MRCP:** This is a non-invasive **anatomical** imaging technique using MRI to visualize the biliary and pancreatic ducts. While excellent for detecting stones (choledocholithiasis) or strictures, it does not assess the dynamic function or emptying of the gallbladder. * **PTC:** This is an invasive **radiological procedure** where contrast is injected directly into the intrahepatic bile ducts. It is used for mapping anatomy in obstructive jaundice or for therapeutic interventions (e.g., stenting), not for functional assessment. * **EUS:** This combines endoscopy and ultrasound to provide high-resolution **structural** images of the gallbladder wall and distal biliary tree. It is highly sensitive for microlithiasis and tumors but cannot evaluate gallbladder motility. **Clinical Pearls for NEET-PG:** * **Acute Cholecystitis:** The HIDA scan is the most sensitive test. **Non-visualization** of the gallbladder after 4 hours (due to cystic duct obstruction) is diagnostic. * **Biliary Atresia:** HIDA is used in neonates; failure of the tracer to reach the duodenum confirms the diagnosis. * **Rim Sign:** Increased tracer uptake in the liver parenchyma surrounding the gallbladder fossa on HIDA scan suggests gangrenous cholecystitis.

Question 80: Which of the following is an alpha emitter?

A. Plutonium-236 (Correct Answer)
B. Carbon-11
C. Oxygen-15
D. Samarium-153

Explanation: **Explanation:** **Plutonium-236 (Option A)** is an alpha emitter. Alpha particles consist of two protons and two neutrons (helium nucleus). Alpha emitters are characterized by high Linear Energy Transfer (LET) and short range in tissue, making them highly effective for targeted alpha therapy (TAT) in oncology, as they cause dense ionization and double-stranded DNA breaks within a very small radius. **Why the other options are incorrect:** * **Carbon-11 (Option B) and Oxygen-15 (Option C):** These are **Positron ($\beta^+$) emitters**. They are produced in a cyclotron and are used in Positron Emission Tomography (PET) imaging due to their short half-lives (C-11: ~20 mins; O-15: ~2 mins). * **Samarium-153 (Option D):** This is primarily a **Beta ($\beta^-$) emitter** (with a gamma component for imaging). It is used clinically for the palliative treatment of bone pain in patients with osteoblastic skeletal metastases (e.g., prostate cancer). **High-Yield Clinical Pearls for NEET-PG:** * **Alpha Emitters in Medicine:** Radium-223 (used for bone metastases in CRPC), Actinium-225, and Bismuth-213. * **Pure Beta Emitters:** Yttrium-90 (used in TARE/Radioembolization) and Phosphorus-32. * **Gamma Emitter (Gold Standard for Imaging):** Technetium-99m (Tc-99m) is the most widely used radiopharmaceutical in diagnostic nuclear medicine. * **Theranostics:** Iodine-131 is a classic example, emitting both beta particles (for therapy of thyroid cancer/hyperthyroidism) and gamma rays (for imaging).

Practice by Chapter

Physics of Nuclear Medicine

Practice Questions

Radiopharmaceuticals

Practice Questions

Radiation Detection in Nuclear Medicine

Practice Questions

Thyroid Scintigraphy

Practice Questions

Bone Scintigraphy

Practice Questions

Renal Nuclear Medicine

Practice Questions

Cardiac Nuclear Medicine

Practice Questions

Pulmonary Nuclear Medicine

Practice Questions

Neurological Nuclear Medicine

Practice Questions

PET/CT Principles and Applications

Practice Questions

Radionuclide Therapy

Practice Questions

Radiation Safety in Nuclear Medicine

Practice Questions

Want unlimited practice?

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

Start For Free