Nuclear Medicine — MCQs

Nuclear Medicine Indian Medical PG Practice Questions and MCQs

Question 21: On radionuclide scanning, a toxic adenoma typically appears as which of the following?

A. Hot nodule (Correct Answer)
B. Cold nodule
C. Warm nodule
D. Neutral

Explanation: **Explanation:** In radionuclide thyroid scanning (using **Technetium-99m pertechnetate** or **Iodine-123**), the appearance of a nodule depends on its functional activity compared to the surrounding normal thyroid tissue. **Why "Hot Nodule" is correct:** A **toxic adenoma** is a hyperfunctioning, autonomous nodule. It produces thyroid hormones independently of TSH control. This increased metabolic activity leads to an increased uptake of the radionuclide, appearing as an area of intense radioactivity (a **"Hot Nodule"**). Because the high levels of thyroid hormone suppress TSH secretion via negative feedback, the rest of the normal thyroid gland becomes inactive and often does not visualize on the scan (the "suppressed gland" sign). **Analysis of Incorrect Options:** * **Cold Nodule:** These are non-functional areas with less uptake than the surrounding tissue. While 85% of thyroid nodules are cold, they carry a higher risk of malignancy (approx. 15-20%). Toxic adenomas are almost never malignant. * **Warm Nodule:** These have uptake similar to the surrounding normal thyroid tissue. They are usually benign and represent functioning nodules that are not yet autonomous enough to suppress the rest of the gland. * **Neutral:** This is not a standard term used in radionuclide imaging to describe focal thyroid lesions. **High-Yield Clinical Pearls for NEET-PG:** * **Plummer’s Disease:** This refers to a Toxic Multinodular Goiter, which shows multiple "hot" areas on a scan. * **Marine-Lenhart Syndrome:** A rare condition where Graves' disease coexists with functioning (hot) nodules. * **Rule of Thumb:** "Hot" nodules are rarely malignant (<1%), whereas "Cold" nodules require further evaluation via FNAC to rule out carcinoma. * **Drug Interference:** Patients must stop taking antithyroid drugs or exogenous iodine (e.g., amiodarone, contrast) before the scan to avoid false results.

Question 22: What is a common cause of a "hot nodule" on a liver scan?

A. Hepatic adenoma
B. Focal nodular hyperplasia (Correct Answer)
C. Metastasis
D. Hepatocellular carcinoma (HCC)

Explanation: **Explanation:** The "hot nodule" sign on a Technetium-99m ($^{99m}Tc$) Sulfur Colloid liver scan is a classic diagnostic hallmark for **Focal Nodular Hyperplasia (FNH)**. **1. Why Focal Nodular Hyperplasia (FNH) is correct:** FNH is a benign liver lesion characterized by a disorganized arrangement of normal liver components, including hepatocytes, bile ducts, and, crucially, an abundance of **Kupffer cells**. Sulfur colloid is a particulate matter that is cleared from the bloodstream by the Reticuloendothelial System (RES), specifically Kupffer cells in the liver. Because FNH contains a high concentration of functioning Kupffer cells (often more than the surrounding normal liver), it shows **normal or increased uptake** ("hot nodule") in approximately 60-70% of cases. **2. Why the other options are incorrect:** * **Hepatic Adenoma:** These lesions typically lack a well-developed ductal system and have few to no Kupffer cells. Consequently, they appear as "cold" (photopenic) defects on sulfur colloid scans. * **Metastasis:** Most metastatic tumors are non-functional and do not contain Kupffer cells, resulting in "cold" spots. * **Hepatocellular Carcinoma (HCC):** While HCC arises from hepatocytes, it generally lacks functioning Kupffer cells and typically appears as a "cold" defect. **High-Yield Clinical Pearls for NEET-PG:** * **FNH Triad on Imaging:** Central stellate scar (on CT/MRI), "spoke-wheel" vascularity (on Doppler), and sulfur colloid uptake (on Nuclear Medicine). * **Sulfur Colloid "Colloid Shift":** If you see increased uptake in the spleen and bone marrow with decreased liver uptake, suspect **Cirrhosis/Portal Hypertension**. * **Hot Spot Sign on SVC Obstruction:** A "hot spot" in the **quadrate lobe** (Segment IV) of the liver is seen in Superior Vena Cava obstruction due to collateral flow via the Vein of Sappey.

Question 23: What is the radioisotope of choice for a triple-phase bone scan?

A. Tc99m-Sestamibi
B. Tc99m-Pertechnetate
C. Tc99m-Methylene diphosphonate (Correct Answer)
D. Tc201-Thallium subtraction

Explanation: **Explanation:** **Tc99m-Methylene Diphosphonate (MDP)** is the radioisotope of choice for a triple-phase bone scan because it is a **phosphonate analogue** that localizes to the bone via **chemisorption**. It binds to the hydroxyapatite crystals in the bone matrix, specifically in areas of high osteoblastic activity and increased vascularity. **Why the other options are incorrect:** * **Tc99m-Sestamibi:** Primarily used for myocardial perfusion imaging (MPI) and parathyroid adenoma localization. It is a lipophilic cation that accumulates in mitochondria. * **Tc99m-Pertechnetate:** Used for thyroid imaging, Meckel’s diverticulum scans, and salivary gland imaging. It behaves similarly to iodine but is not organified. * **Tl201-Thallium:** A potassium analogue used for myocardial viability studies and sometimes in tumor imaging (e.g., differentiating lymphoma from toxoplasmosis in the brain). **Triple-Phase Bone Scan Phases:** 1. **Flow Phase (Blood Flow):** Images taken every 2-3 seconds for 1 minute; assesses arterial supply. 2. **Blood Pool Phase:** Images taken at 5 minutes; assesses tissue vascularity/inflammation. 3. **Delayed Phase (Skeletal):** Images taken at 2-4 hours; assesses osteoblastic activity. **High-Yield Clinical Pearls for NEET-PG:** * **Hot Spots:** Seen in fractures, metastases (osteoblastic), and osteomyelitis. * **Cold Spots:** Seen in early avascular necrosis (AVN), multiple myeloma, and some aggressive lytic metastases (e.g., Renal Cell Carcinoma). * **Osteomyelitis vs. Cellulitis:** In osteomyelitis, all three phases are "positive" (increased uptake). In cellulitis, only the first two phases show increased uptake, while the delayed phase is normal or shows diffuse, non-focal uptake. * **Excretion:** Tc99m-MDP is excreted by the kidneys; hence, the bladder is the critical organ (receives the highest radiation dose).

Question 24: A 50-year-old patient with ischemic heart disease develops chest pain. ECG shows ST segment elevation and Q waves. Myocardial necrosis in this patient can be best demonstrated by:

A. Technetium 99m tetrofosmin
B. Sestamibi scan
C. Technetium 99m Pyrophosphate (Correct Answer)
D. Thallium 201

Explanation: **Explanation:** The clinical presentation of chest pain with ST-segment elevation and Q waves indicates an **Acute Myocardial Infarction (AMI)**. To demonstrate myocardial **necrosis** (infarct imaging), we use "hot spot" imaging. **Why Technetium 99m Pyrophosphate (Tc-99m PYP) is correct:** Tc-99m PYP is a bone-seeking agent that also accumulates in acutely infarcted myocardial tissue. The underlying mechanism involves the deposition of **calcium phosphate crystals** within the mitochondria of necrotic myocytes. The tracer binds to these calcium deposits, creating a "hot spot" on the scan. It is most sensitive between **24 to 72 hours** after the onset of infarction and typically becomes negative after 1 to 2 weeks. **Why the other options are incorrect:** * **Technetium 99m Tetrofosmin & Sestamibi (Options A & B):** These are **myocardial perfusion agents**. They are taken up by viable, well-perfused myocardium. In an area of necrosis or ischemia, they show a "cold spot" (defect). They cannot specifically differentiate between acute necrosis and old scar tissue. * **Thallium 201 (Option D):** This is a potassium analogue used for **viability studies** and perfusion. Like Sestamibi, it produces a "cold spot" in infarcted areas. It is primarily used to identify "hibernating myocardium." **High-Yield Clinical Pearls for NEET-PG:** * **Hot Spot Imaging:** Tc-99m Pyrophosphate (detects necrosis). * **Cold Spot Imaging:** Thallium-201, Tc-99m Sestamibi, Tc-99m Tetrofosmin (detects ischemia/infarct as a void). * **Gold Standard for Myocardial Viability:** PET scan using **18-F Fluorodeoxyglucose (FDG)**. * **PYP Scan Utility:** Also the investigation of choice for diagnosing **Transthyretin Cardiac Amyloidosis (ATTR)**.

Question 25: Which imaging modality is primarily used for the calculation of ejection fraction?

A. Multiple Gated Acquisition (MUGA) scan (Correct Answer)
B. Single-Photon Emission Computed Tomography (SPECT) using thallium 201
C. Positron Emission Tomography (PET) myocardial perfusion imaging
D. Sestamibi scan with pharmacological stress

Explanation: **Explanation:** The **Multiple Gated Acquisition (MUGA) scan**, also known as Equilibrium Radionuclide Angiocardiography (ERNA), is considered the "gold standard" in nuclear medicine for the accurate and reproducible calculation of the **Left Ventricular Ejection Fraction (LVEF)**. **Why MUGA is correct:** The procedure involves labeling the patient's red blood cells with **Technetium-99m (Tc-99m)**. An ECG is used to "gate" the acquisition, synchronizing the gamma camera images with the cardiac cycle. By measuring the radioactivity (counts) at end-diastole and end-systole, the computer calculates the EF based on volume changes rather than geometric assumptions. This makes it highly accurate, especially in patients undergoing cardiotoxic chemotherapy (e.g., Doxorubicin). **Why other options are incorrect:** * **B & D (Thallium-201 and Sestamibi):** These are primarily **Myocardial Perfusion Imaging (MPI)** agents. While modern "Gated SPECT" can estimate EF, their primary clinical utility is to detect ischemia (reversible defects) or infarction (fixed defects). * **C (PET Imaging):** PET (using Rubidium-82 or N-13 Ammonia) is the gold standard for **myocardial viability** and absolute blood flow quantification, but it is not the primary or routine modality for simple EF calculation due to high cost and limited availability. **Clinical Pearls for NEET-PG:** * **Radiopharmaceutical:** Tc-99m labeled RBCs (using the *in vivo*, *in vitro*, or modified method). * **Key Advantage:** MUGA is less operator-dependent than Echocardiography and more accurate in patients with irregular body habitus or lung disease. * **High-Yield Fact:** If a patient’s LVEF drops by >10% during chemotherapy (as measured by MUGA), the oncologist may need to stop or adjust the cardiotoxic drug.

Question 26: Which one of the following forms of radiation can penetrate the deepest into body tissue?

A. alpha
B. beta
C. gamma (Correct Answer)
D. positron

Explanation: ### Explanation The depth of radiation penetration into body tissue is inversely proportional to the particle's mass and charge. **Why Gamma is Correct:** Gamma radiation consists of high-energy electromagnetic photons. Unlike alpha or beta particles, gamma rays have **no mass and no electrical charge**. This allows them to travel at the speed of light with minimal interaction with atoms in the tissue, resulting in high penetrating power. In clinical practice, gamma rays can pass entirely through the human body, which is why they are used for diagnostic imaging (e.g., Gamma cameras, SPECT). **Analysis of Incorrect Options:** * **Alpha particles (A):** These are helium nuclei (2 protons, 2 neutrons). They are heavy and carry a +2 charge. Due to their large size, they collide frequently with atoms, losing energy rapidly. They have the **lowest penetration** (stopped by a sheet of paper or the skin's stratum corneum) but the highest ionization density. * **Beta particles (B):** These are high-speed electrons. They are much smaller than alpha particles but still possess mass and a -1 charge. They can penetrate a few millimeters to centimeters into the tissue but are eventually stopped by aluminum or plastic. * **Positrons (D):** These are the antimatter counterparts of electrons (+1 charge). While they have similar mass to beta particles, they undergo **annihilation** almost immediately upon meeting an electron, converting into two 511 keV gamma photons. **NEET-PG Clinical Pearls:** * **Highest Penetration:** Gamma rays (requires lead/concrete shielding). * **Highest Ionizing Power:** Alpha particles (most damaging if internalized). * **Therapeutic Use:** Beta emitters (e.g., I-131, Y-90) are used for internal radiotherapy because their limited penetration localizes the dose to the tumor. * **Diagnostic Use:** Gamma emitters (e.g., Tc-99m) are preferred for imaging because they escape the body to be detected by external sensors.

Question 27: In patients with thyrotoxicosis, which condition is associated with the least radioiodine uptake?

A. Toxic adenoma
B. Graves' disease
C. Multinodular goiter
D. Subacute thyroiditis (Correct Answer)

Explanation: **Explanation:** The core concept in answering this question is distinguishing between **hyperthyroidism** (increased synthesis of hormone) and **thyrotoxicosis due to thyroiditis** (release of pre-formed hormone). **Why Subacute Thyroiditis is correct:** In Subacute (De Quervain’s) Thyroiditis, there is an inflammatory destruction of thyroid follicles. This causes the leakage of stored thyroid hormones into the bloodstream, leading to thyrotoxicosis. However, because the follicular cells are damaged and TSH is suppressed by the high levels of circulating T4/T3, the gland's ability to actively trap iodine is severely impaired. Consequently, the Radioactive Iodine Uptake (RAIU) is **characteristically low or near zero (<5%).** **Why the other options are incorrect:** * **Graves’ Disease:** This is an autoimmune condition where TSH-receptor antibodies stimulate the entire gland, leading to **diffuse, high RAIU.** * **Toxic Adenoma:** This involves a single "hot" nodule that autonomously produces thyroid hormone, showing **increased focal uptake** with suppression of the rest of the gland. * **Multinodular Goiter (Toxic):** This presents with **patchy, heterogeneous increased uptake** in multiple autonomous nodules. **NEET-PG High-Yield Pearls:** * **Low RAIU Thyrotoxicosis:** Remember the mnemonic **"S-I-F-T"**: **S**ubacute thyroiditis, **I**atrogenic/Factitious (exogenous T4), **F**ollicular CA (metastatic), and **T**eratomata (Struma ovarii). * **Subacute Thyroiditis:** Look for a clinical history of a **painful/tender thyroid** following a viral upper respiratory tract infection and an **elevated ESR.** * **Amiodarone:** Can cause both high uptake (Type I) and low uptake (Type II) thyrotoxicosis.

Question 28: Which radioisotope scan is used for diagnosing ectopic gastric mucosa in Meckel's diverticulum?

A. Gallium citrate
B. Thallium
C. Selenium
D. Technetium-99m pertechnetate (Correct Answer)

Explanation: **Explanation:** The correct answer is **Technetium-99m pertechnetate (Tc-99m)**. This scan, often referred to as a **"Meckel’s Scan,"** is the gold standard for detecting ectopic gastric mucosa. **Why Technetium-99m pertechnetate is correct:** The pertechnetate ion ($TcO_4^-$) has a unique affinity for **mucus-secreting cells of the gastric mucosa**. Since approximately 50% of symptomatic Meckel’s diverticula contain ectopic gastric tissue, the isotope concentrates in the diverticulum, appearing as a "hot spot" on gamma camera imaging, typically in the right lower quadrant. **Why other options are incorrect:** * **Gallium citrate (Ga-67):** Primarily used for imaging chronic inflammation, infections (like abscesses), and certain lymphomas. It does not target gastric mucosa. * **Thallium (Tl-201):** A potassium analog used mainly in myocardial perfusion imaging and for differentiating tumor recurrence from radiation necrosis in the brain. * **Selenium (Se-75):** Historically used in the form of Selenomethionine for pancreatic imaging or SeHCAT for bile acid malabsorption; it has no role in Meckel’s diagnosis. **Clinical Pearls for NEET-PG:** * **Rule of 2s:** Meckel’s diverticulum occurs in 2% of the population, is 2 inches long, located 2 feet from the ileocecal valve, and often presents by age 2. * **Pharmacological Augmentation:** To increase the sensitivity of the Meckel’s scan, clinicians may use: 1. **H2 Blockers (e.g., Cimetidine):** Inhibits release of the isotope from the cells into the lumen. 2. **Pentagastrin:** Stimulates uptake of the isotope by the gastric mucosa. 3. **Glucagon:** Decreases peristalsis, preventing the "washout" of the isotope. * **Most common presentation:** Painless lower GI bleeding (melena or hematochezia) in a child.

Question 29: A young female with a history of renal calculi complains of bone pain and abdominal cramps. Investigations reveal multiple fractures and elevated serum calcium and parathyroid hormone (PTH) levels. Which of the following is the best investigation to arrive at a definitive diagnosis?

A. CECT neck
B. Sestamibi scan (Correct Answer)
C. Radioiodine scan
D. Ultrasound neck

Explanation: ### Explanation **Clinical Diagnosis:** The patient presents with the classic triad of "stones, bones, and abdominal groans" (renal calculi, bone pain/fractures, and abdominal cramps), combined with hypercalcemia and elevated PTH. This is a textbook presentation of **Primary Hyperparathyroidism**, most commonly caused by a solitary **Parathyroid Adenoma**. **Why Sestamibi Scan is Correct:** The **Technetium-99m (Tc-99m) Sestamibi scan** is the gold standard for the preoperative localization of parathyroid adenomas. * **Mechanism:** Sestamibi is taken up by both the thyroid and parathyroid glands. However, it **washes out rapidly** from normal thyroid tissue but is **retained** for a longer duration in hyperfunctioning parathyroid tissue (adenomas) due to the high mitochondrial content of oxyphil cells. * **Utility:** It is highly sensitive and allows for minimally invasive parathyroidectomy. **Why Other Options are Incorrect:** * **CECT Neck:** While it provides anatomical detail, it lacks the functional specificity of a Sestamibi scan and involves significant radiation. It is usually reserved for cases where initial imaging fails. * **Radioiodine Scan:** This uses I-131 or I-123 and is specific for **thyroid** pathologies (like Graves' disease or thyroid nodules), not parathyroid glands. * **Ultrasound Neck:** Though often the first-line screening tool due to its low cost and lack of radiation, it is operator-dependent and cannot identify ectopic parathyroid glands (e.g., in the mediastinum), making it less definitive than a Sestamibi scan. **NEET-PG High-Yield Pearls:** * **Dual-phase Sestamibi:** Images are taken at 15 minutes (early) and 2–3 hours (delayed) to observe the "washout" phenomenon. * **SPECT/CT:** Combining Sestamibi with CT (SPECT/CT) further increases sensitivity and precise anatomical localization. * **Hungry Bone Syndrome:** A common post-operative complication of parathyroidectomy characterized by profound hypocalcemia.

Question 30: To detect gastrointestinal protein loss, all are used except?

A. Indium-111 transferrin
B. α-1 antitrypsin
C. 99mTc dextran
D. 99mTc glycoheptone (Correct Answer)

Explanation: **Explanation:** Protein-losing enteropathy (PLE) is characterized by the excessive loss of serum proteins into the gastrointestinal tract. To diagnose this, radiopharmaceuticals must be used that remain within the intravascular space and only appear in the bowel if there is an active leak. **Why 99mTc glycoheptone is the correct answer:** **99mTc glycoheptone** is primarily used in **renal imaging** (specifically for evaluating renal cortical morphology and function). It is rapidly cleared by the kidneys and does not bind to serum proteins in a way that allows for the detection of enteric protein loss. Therefore, it has no role in the diagnosis of PLE. **Analysis of other options:** * **Indium-111 transferrin:** This is a gold-standard radiopharmaceutical for PLE. Transferrin is a large serum protein; when labeled with Indium-111, its presence in the stool or abdominal scans confirms protein leakage. * **α-1 antitrypsin:** While not a radiopharmaceutical, the **fecal α-1 antitrypsin clearance** test is a common biochemical method used to detect and quantify GI protein loss because this protein is resistant to degradation by digestive enzymes. * **99mTc dextran:** This is a macromolecule that mimics the behavior of serum proteins. It is used in scintigraphy to localize the site of protein loss due to its size and intravascular retention. **Clinical Pearls for NEET-PG:** * **99mTc-labeled Human Serum Albumin (HSA)** is another frequently used agent for PLE scintigraphy. * **Chromium-51 (51Cr) chloride** was historically the most common agent but is less used now due to radiation safety and the requirement for 24–96 hour stool collection. * **Scintigraphy Advantage:** Unlike biochemical tests (like α-1 antitrypsin), nuclear medicine scans can **localize** the specific site of the protein leak in the gut.

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Physics of Nuclear Medicine

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Radiopharmaceuticals

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Radiation Detection in Nuclear Medicine

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Thyroid Scintigraphy

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Bone Scintigraphy

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Renal Nuclear Medicine

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Cardiac Nuclear Medicine

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Pulmonary Nuclear Medicine

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Neurological Nuclear Medicine

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PET/CT Principles and Applications

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Radionuclide Therapy

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Radiation Safety in Nuclear Medicine

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