Nuclear Medicine — MCQs

Nuclear Medicine Indian Medical PG Practice Questions and MCQs

Question 81: Which of the following is the best test for assessing myocardial viability after myocardial infarction?

A. Thallium scan (Correct Answer)
B. MUGA scan
C. MDCT
D. Stress Echocardiography

Explanation: **Explanation:** **1. Why Thallium-201 Scan is Correct:** Thallium-201 is a potassium analog that enters cardiomyocytes via the active **Na+/K+ ATPase pump**. For Thallium to be taken up, the cell membrane must be intact and the cell must be metabolically active. Therefore, Thallium uptake is a direct marker of **myocardial viability**. In clinical practice, the "Rest-Redistribution" protocol is used: if an initial defect "fills in" (redistributes) after 3–4 hours, it indicates hibernating but viable myocardium rather than a permanent scar. **2. Analysis of Incorrect Options:** * **MUGA Scan (Multi-Gated Acquisition):** This is the gold standard for calculating the **Left Ventricular Ejection Fraction (LVEF)**. It assesses ventricular function and wall motion, not cellular viability. * **MDCT (Multidetector CT):** Primarily used for **Coronary Angiography** to visualize anatomical stenosis or calcium scoring. It is not a functional or metabolic test for viability. * **Stress Echocardiography:** This assesses "Inotropic Reserve." While it can detect viable tissue (demonstrated by improved wall motion with low-dose dobutamine), nuclear imaging (Thallium/PET) is generally considered more sensitive for detecting hibernating myocardium. **3. Clinical Pearls for NEET-PG:** * **Gold Standard:** While Thallium is the "best" among these options, **FDG-PET Scan** is the overall gold standard for myocardial viability (detecting glucose metabolism). * **Hibernating Myocardium:** Chronic ischemia leading to reversible LV dysfunction; it shows decreased perfusion but preserved viability (uptake on PET/Thallium). * **Stunned Myocardium:** Acute ischemia followed by reperfusion; the tissue is viable but function is temporarily depressed. * **Technetium-99m Sestamibi:** Unlike Thallium, it does not redistribute; it is used primarily for perfusion imaging rather than viability.

Question 82: All of the following conditions show increased uptake (hot spot) on a bone scan except?

A. Multiple Myeloma (Correct Answer)
B. Fibrous Dysplasia
C. Paget's Disease
D. Osteomyelitis

Explanation: **Explanation:** The standard bone scan (Technetium-99m MDP) relies on **osteoblastic activity** (new bone formation) and local blood flow. For a lesion to appear as a "hot spot," there must be a reactive bone formation response to the underlying pathology. **1. Why Multiple Myeloma is the Correct Answer:** Multiple Myeloma is characterized by purely **osteolytic lesions**. The plasma cells produce "Osteoclast Activating Factors" (like RANK-L), which trigger massive bone resorption without stimulating any compensatory osteoblastic activity. Because there is no new bone formation, the Tc-99m MDP cannot incorporate into the bone, often resulting in **"cold spots"** or appearing completely normal (false negative). Skeletal surveys (X-rays) or MRI/PET-CT are preferred over bone scans for Myeloma. **2. Analysis of Incorrect Options:** * **Fibrous Dysplasia:** This involves the replacement of normal bone with fibrous connective tissue and immature bone. It typically shows **intense, uniform increased uptake** due to high bone turnover. * **Paget’s Disease:** Characterized by disordered and excessive bone remodeling. It shows the **marked increased uptake** (often involving the entire bone, e.g., "Mickey Mouse sign" in vertebrae) due to the hyperactive osteoblastic phase. * **Osteomyelitis:** Infection triggers an inflammatory response and reactive bone repair. It shows increased uptake in all three phases of a bone scan (Flow, Blood pool, and Delayed). **High-Yield Clinical Pearls for NEET-PG:** * **"Cold" Lesions on Bone Scan:** Multiple Myeloma, Renal Cell Carcinoma (often), Thyroid Carcinoma, Anaplastic tumors, and early Infarction/Avascular Necrosis. * **Super Scan:** A bone scan with intense symmetrical skeletal uptake and **absent renal activity**. Seen in Metastatic Prostate CA, Hyperparathyroidism, and Myelofibrosis. * **Flare Phenomenon:** A temporary increase in uptake seen 2 weeks to 3 months after successful chemotherapy, which should not be confused with disease progression.

Question 83: Which of the following investigations is NOT used in the diagnosis of protein-losing enteropathy?

A. Technetium-99m (Tc) albumin scan
B. Technetium-99m (Tc) dextran scan
C. Indium-111 (In) transferrin scan
D. Technetium-99m (Tc) sevelamer scan (Correct Answer)

Explanation: **Explanation:** Protein-losing enteropathy (PLE) is characterized by the excessive loss of serum proteins into the gastrointestinal tract. Diagnostic imaging relies on labeling plasma proteins (or large molecules that mimic them) with radioactive isotopes and detecting their leakage into the bowel lumen via scintigraphy. **Why Option D is Correct:** **Technetium-99m (Tc) sevelamer** is not a diagnostic agent for PLE. Sevelamer is a phosphate-binding medication used to treat hyperphosphatemia in chronic kidney disease. It is not used as a radiopharmaceutical for protein-leakage studies. **Why the other options are incorrect:** * **A. Tc-99m Albumin scan:** This is a commonly used investigation. Human serum albumin is labeled with Tc-99m; its appearance in the bowel on delayed images confirms protein loss. * **B. Tc-99m Dextran scan:** Dextran is a large polysaccharide. When radiolabeled, it serves as an excellent macromolecular tracer to identify the site of protein leakage, often providing better image quality than albumin due to lower background activity. * **C. In-111 Transferrin scan:** Transferrin is a plasma protein that can be labeled with Indium-111. It is highly effective for diagnosing PLE, especially in cases where longer imaging windows (up to 24–48 hours) are required due to the longer half-life of Indium-111 compared to Technetium. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard:** The biochemical gold standard for diagnosing PLE is the **Alpha-1 antitrypsin clearance** (fecal excretion). * **Nuclear Medicine Advantage:** While fecal clearance confirms the diagnosis, scintigraphy (using Tc-99m albumin/dextran) is superior for **localizing the specific site** of the leak. * **Common Causes of PLE:** Primary lymphangiectasia (Waldmann's disease), Menetrier’s disease, and post-Fontan procedure complications.

Question 84: Which is the best scan for assessing myocardial viability?

A. Thallium scan
B. MIBI scan
C. Technetium-99m pyrophosphate scan
D. FDG PET scan (Correct Answer)

Explanation: **Explanation:** The assessment of myocardial viability is crucial in patients with ischemic heart disease to determine if revascularization (CABG or PCI) will improve cardiac function. **1. Why FDG PET is the Correct Answer:** **FDG-PET (Fluorodeoxyglucose Positron Emission Tomography)** is considered the **Gold Standard** for assessing myocardial viability. It relies on the "metabolic shift" concept: while normal myocardium uses fatty acids for energy, ischemic but viable (hibernating) myocardium shifts to **glucose metabolism** to survive. A "mismatch" pattern—where there is reduced blood flow (on ammonia/rubidium scan) but preserved FDG uptake (metabolism)—confirms that the tissue is alive and will benefit from surgery. **2. Analysis of Incorrect Options:** * **A. Thallium-201 Scan:** Historically used for viability (redistribution studies). While sensitive, it has lower resolution and higher radiation compared to PET. It is often the "second best" but not the gold standard. * **B. MIBI (Tc-99m Sestamibi) Scan:** Primarily used for **myocardial perfusion** (stress tests). Since MIBI uptake depends on active mitochondrial membrane potential, it can underestimate viability in hibernating segments. * **C. Tc-99m Pyrophosphate Scan:** This is used for "Hot Spot" imaging to detect **acute myocardial infarction** (it binds to calcium in necrotic cells) or to diagnose Transthyretin (ATTR) Cardiac Amyloidosis. It is not used for viability. **3. High-Yield Clinical Pearls for NEET-PG:** * **Hibernating Myocardium:** Chronic ischemia leading to reversible LV dysfunction; viable on PET. * **Stunned Myocardium:** Acute ischemia followed by reperfusion; temporary dysfunction with normal flow. * **Cardiac MRI (Late Gadolinium Enhancement):** Another excellent tool; if transmural enhancement is <50%, the tissue is considered viable. * **Dobutamine Stress Echo:** Checks for "contractile reserve" as a sign of viability.

Question 85: Which of the following radiopharmaceuticals is used in imaging of the reticuloendothelial system?

A. Tc-99m Red blood cells
B. Tc-99m Pyrophosphate
C. Tc-99m Sulfur Colloid (Correct Answer)
D. Tc-99m Teboroxime

Explanation: **Explanation:** **Tc-99m Sulfur Colloid** is the correct answer because of the physiological process of **phagocytosis**. When injected intravenously, these colloidal particles (ranging from 0.1 to 1.0 μm) are recognized as foreign bodies and are cleared from the circulation by the **Reticuloendothelial System (RES)**, specifically the Kupffer cells in the liver (80–90%), the spleen (5–10%), and the bone marrow. This makes it the gold standard for liver-spleen imaging and assessing RES function. **Analysis of Incorrect Options:** * **Tc-99m Red Blood Cells (RBCs):** Used primarily for **blood pool imaging**. Clinical applications include detecting gastrointestinal bleeds, mapping hepatic hemangiomas, and performing MUGA scans for cardiac ejection fraction. * **Tc-99m Pyrophosphate (PYP):** This is a bone-seeking agent. While historically used for myocardial infarction imaging ("hot spot" imaging), it is currently the investigation of choice for diagnosing **Transthyretin (ATTR) Cardiac Amyloidosis**. * **Tc-99m Teboroxime:** A lipophilic myocardial perfusion agent. It has very high extraction efficiency but suffers from rapid myocardial washout, making it less commonly used than Sestamibi or Tetrofosmin. **High-Yield Clinical Pearls for NEET-PG:** 1. **Colloid Shift:** In cases of portal hypertension or cirrhosis, there is decreased uptake in the liver and increased uptake in the spleen and bone marrow. This phenomenon is known as "Colloid Shift." 2. **Particle Size:** If the sulfur colloid particles are too large, they will trap in the lungs; if they are too small, they will show increased bone marrow uptake. 3. **Oral Use:** Tc-99m Sulfur Colloid can also be administered orally for **Gastric Emptying Studies** and to detect gastroesophageal reflux.

Question 86: Thyroid radioiodine ablation therapy is useful in all except?

A. Residual papillary carcinoma
B. Anaplastic carcinoma
C. Follicular carcinoma
D. Medullary carcinoma (Correct Answer)

Explanation: ### Explanation The effectiveness of **Radioiodine (I-131) therapy** depends entirely on the ability of thyroid cells to express the **Sodium-Iodide Symporter (NIS)**, which allows for the active uptake of iodine. **Why Medullary Carcinoma is the Correct Answer:** Medullary Thyroid Carcinoma (MTC) originates from the **parafollicular C-cells** (neuroendocrine cells), which produce calcitonin. Unlike follicular cells, C-cells do **not** concentrate iodine and do not express NIS. Therefore, I-131 therapy has no therapeutic role in MTC. The primary treatment for MTC is surgical resection. **Analysis of Other Options:** * **Papillary (A) and Follicular (C) Carcinoma:** These are "Differentiated Thyroid Cancers" (DTC) arising from follicular epithelium. They retain the machinery to trap iodine. I-131 is the gold standard for ablating residual microscopic disease post-surgery and treating distant metastases. * **Anaplastic Carcinoma (B):** While Anaplastic carcinoma is undifferentiated and generally does not take up iodine, the question asks where ablation is "useful." In clinical practice, if a patient has a mixed component or if the tumor shows any focal uptake on a diagnostic scan, I-131 might be attempted, though it is rarely effective. However, **Medullary carcinoma is the absolute "except"** because it physiologically lacks the mechanism for iodine uptake entirely. **NEET-PG High-Yield Pearls:** 1. **Drug of Choice for I-131:** It is the treatment of choice for Grave’s disease and toxic multinodular goiter. 2. **Pre-requisite:** Patients must have high TSH levels (>30 mIU/L) and a low-iodine diet before ablation to maximize I-131 uptake. 3. **MTC Marker:** Calcitonin and CEA are the tumor markers for Medullary carcinoma, not Thyroglobulin. 4. **Contraindication:** I-131 is strictly contraindicated in pregnancy and breastfeeding.

Question 87: Radioactive gold (Au-198) is used in the treatment of which condition?

A. Bladder tumours
B. Malignant ascites (Correct Answer)
C. Gliomas
D. None of the above

Explanation: **Explanation:** **Gold-198 (Au-198)** is a radioisotope that emits both **beta particles** (responsible for the therapeutic effect) and **gamma rays** (used for imaging). It has a physical half-life of approximately 2.7 days. **Why Malignant Ascites is the correct answer:** Au-198 is primarily used in the form of a **colloidal suspension** for the intracavitary treatment of malignant effusions, specifically **malignant ascites** and pleural effusions. When injected into the peritoneal cavity, the colloidal particles are phagocytosed by macrophages and fixed onto the serosal surfaces. The short-range beta radiation then works to suppress the production of fluid by the malignant cells and the peritoneal lining, providing palliative relief from recurrent fluid accumulation. **Analysis of Incorrect Options:** * **A. Bladder tumours:** While various isotopes have been used intravesically, Au-198 is not the standard treatment. Radio-frequency ablation or BCG immunotherapy are more common for superficial tumors. * **C. Gliomas:** Treatment for gliomas typically involves external beam radiation or interstitial brachytherapy using Iodine-125 or Iridium-192 seeds, rather than colloidal Gold-198. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Au-198 therapeutic action is via **Beta emission** (max energy 0.96 MeV). * **Half-life:** 2.7 days (Easy to remember: "Gold is 24 carats, 2+7=9, close to 2.7"). * **Other uses:** Historically used in permanent interstitial implants (brachytherapy) for prostate cancer, though largely replaced by I-125 and Pd-103. * **Safety Note:** Due to its significant gamma emission, it poses a higher radiation safety risk to healthcare workers compared to pure beta emitters like Phosphorus-32 (P-32), which is also used for malignant effusions.

Question 88: Which of the following imaging techniques is best able to measure regional brain substrate uptake and metabolic kinetics?

A. Magnetic Resonance Imaging (MRI)
B. Computed Tomography (CT)
C. Positron Emission Tomography (PET) (Correct Answer)
D. Serial Thallium Scintigrams

Explanation: **Explanation:** **Positron Emission Tomography (PET)** is the gold standard for measuring regional brain substrate uptake and metabolic kinetics. This is because PET utilizes radiopharmaceuticals labeled with positron-emitting isotopes (such as **18F-Fluorodeoxyglucose or FDG**) that act as analogs to biological substrates. By tracking the distribution and rate of decay of these tracers, PET can quantify glucose metabolism, oxygen consumption, and neurotransmitter activity in specific brain regions, providing a functional map of cerebral activity. **Why other options are incorrect:** * **MRI (Option A):** Primarily provides high-resolution **anatomical and structural** detail. While Functional MRI (fMRI) can detect changes in blood oxygenation (BOLD signal), it does not directly measure substrate uptake or metabolic kinetics as precisely as PET. * **CT (Option B):** Uses X-rays to create structural cross-sectional images. It is excellent for detecting acute hemorrhage or bone abnormalities but has no role in measuring metabolic processes. * **Serial Thallium Scintigrams (Option D):** Thallium-201 is a potassium analog primarily used in myocardial perfusion imaging or to differentiate tumor recurrence from radiation necrosis. It is not the standard for measuring general brain metabolic kinetics. **High-Yield Clinical Pearls for NEET-PG:** * **FDG-PET in Neurology:** The most common tracer used is **18F-FDG**, which reflects glucose metabolism. * **Alzheimer’s Disease:** Characteristically shows **hypometabolism** in the temporoparietal regions on PET. * **Epilepsy:** PET is used for pre-surgical evaluation; it shows **interictal hypometabolism** at the seizure focus. * **PET vs. SPECT:** PET has higher spatial resolution and sensitivity compared to Single Photon Emission Computed Tomography (SPECT).

Question 89: What is the parent compound of Tc-99m?

A. Strontium-99
B. Molybdenum-99 (Correct Answer)
C. Rubidium-99
D. Cs-137

Explanation: **Explanation:** Technetium-99m (Tc-99m) is the most widely used radioisotope in diagnostic nuclear medicine. It is produced through the radioactive decay of its parent isotope, **Molybdenum-99 (Mo-99)**. **1. Why Molybdenum-99 is correct:** Mo-99 has a half-life of approximately **66 hours**, which is long enough to allow for transport from nuclear reactors to hospitals. It decays via beta emission into Tc-99m. In a clinical setting, Tc-99m is extracted using a **Technetium-99m generator** (often called a "Moly cow"). Tc-99m is preferred for imaging because it has a short half-life (6 hours) and emits pure gamma rays at **140 keV**, which is ideal for gamma camera detection while minimizing patient radiation dose. **2. Analysis of Incorrect Options:** * **Strontium-99:** This is not a standard parent isotope for medical imaging. However, *Strontium-82* is the parent of Rubidium-82 (used in PET cardiac imaging), and *Strontium-89* is used for bone pain palliation. * **Rubidium-99:** This isotope does not exist in a stable or clinically relevant form for Tc-99m production. Rubidium-82 is the isotope used in clinical practice. * **Cs-137 (Cesium-137):** This is a long-lived radioactive isotope (half-life ~30 years) used primarily in radiotherapy (brachytherapy) and for calibrating equipment, not as a parent for Tc-99m. **High-Yield Clinical Pearls for NEET-PG:** * **Generator Mechanism:** The process of extracting Tc-99m from Mo-99 is called **"milking."** * **Decay Type:** Mo-99 decays to Tc-99m via **Beta (β-) decay**, whereas Tc-99m decays to Tc-99 via **Isomeric Transition**. * **Transient Equilibrium:** This is the physical principle where the ratio of the parent (Mo-99) and daughter (Tc-99m) activity becomes constant over time. * **Common Uses:** Tc-99m is used in MDP bone scans, HIDA scans, and Sestamibi cardiac imaging.

Question 90: Fluorodeoxyglucose-positron emission tomography (FDG-PET) does not detect which of the following?

A. Typical carcinoid (Correct Answer)
B. Atypical carcinoid
C. Small cell neuroendocrine tumor
D. Large cell neuroendocrine tumor

Explanation: **Explanation:** The core concept behind FDG-PET imaging is the **Warburg effect**, where malignant cells exhibit increased glucose metabolism and overexpression of GLUT-1 transporters. The sensitivity of FDG-PET in neuroendocrine tumors (NETs) is directly proportional to the **metabolic rate and proliferation index (Ki-67)** of the tumor. * **Typical Carcinoid (Correct Answer):** These are well-differentiated, low-grade (Grade 1) tumors with a low mitotic rate (<2 mitoses/10mm²) and low metabolic activity. Because they grow slowly and often lack significant GLUT-1 expression, they are frequently **FDG-avid negative**. For these tumors, Somatostatin Receptor Scintigraphy (e.g., **Ga-68 DOTATATE PET/CT**) is the imaging modality of choice. * **Atypical Carcinoid:** These are intermediate-grade (Grade 2) tumors. They have higher mitotic indices and a greater likelihood of being FDG-positive compared to typical carcinoids, as they transition toward more aggressive metabolic pathways. * **Small Cell & Large Cell Neuroendocrine Tumors:** These are high-grade (Grade 3), poorly differentiated carcinomas. They are highly aggressive with rapid cell turnover and high glucose utilization. Consequently, they are consistently **FDG-avid** and are better visualized with FDG-PET than with DOTATATE scans. **Clinical Pearls for NEET-PG:** 1. **The "Flip-Flop" Phenomenon:** Low-grade NETs are DOTATATE positive/FDG negative; High-grade NETs are DOTATATE negative/FDG positive. 2. **Other FDG-PET "Cold" Tumors:** Bronchoalveolar carcinoma (Adenocarcinoma in situ), Renal Cell Carcinoma (clear cell), Prostate cancer, and Mucinous tumors. 3. **Brain & Bladder:** FDG-PET has limited utility in the brain (high baseline glucose use) and urinary tract (excretion of tracer).

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Physics of Nuclear Medicine

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Renal Nuclear Medicine

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Pulmonary Nuclear Medicine

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Neurological Nuclear Medicine

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