Nuclear Medicine Practice Questions

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

Technetium-99m (Tc) sevelamer scan. **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.

Q: Which of the following imaging modalities is used to differentiate tumor recurrence from radiation necrosis?

PET scan. **Explanation:** The differentiation between **tumor recurrence** and **radiation necrosis** is a classic clinical challenge because both entities often appear identical on conventional structural imaging (like CT or MRI), showing contrast enhancement and perilesional edema. **1. Why PET Scan is the Correct Answer:** The distinction relies on **metabolic activity** rather than anatomy. * **Tumor Recurrence:** Malignant cells are hypermetabolic and demonstrate high uptake of radiopharmaceuticals like **18F-FDG** (Fluorodeoxyglucose) or amino acid tracers (e.g., 11C-Methionine). * **Radiation Necrosis:** This represents dead tissue and vascular injury; it is metabolically inactive (hypometabolic) and shows little to no tracer uptake. Therefore, PET imaging provides the functional data necessary to distinguish "hot" viable tumor from "cold" necrotic tissue. **2. Why Other Options are Incorrect:** * **MRI:** While advanced sequences like MR Spectroscopy (showing high Choline/NAA ratios) can help, standard MRI often fails because both necrosis and recurrence cause blood-brain barrier breakdown and enhancement. * **3D CT:** CT provides excellent structural detail of bone and acute hemorrhage but lacks the metabolic sensitivity to differentiate viable tumor cells from post-radiation changes. * **USG:** Ultrasound has no role in evaluating deep-seated brain tumors or post-radiation changes due to the inability of sound waves to penetrate the adult cranium. **Clinical Pearls for NEET-PG:** * **Gold Standard:** While PET is the preferred functional imaging, **MR Spectroscopy (MRS)** is the most common "advanced MRI" alternative mentioned in exams. * **Tracer of Choice:** In the brain, **18F-FET** or **11C-Methionine** are often superior to FDG because the brain has high baseline glucose uptake, which can mask tumors. * **Hot vs. Cold:** Remember: **Recurrence = Hot (Hypermetabolic)**; **Necrosis = Cold (Hypometabolic).**

Q: Which is the best scan for assessing myocardial viability?

FDG PET scan. **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.

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

Tc-99m Sulfur Colloid. **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.

Q: A patient presented with pentad of symptoms: kidney stones, painful bones, abdominal groans, psychic moans, and fatigue. The imaging investigation done for him is shown below. What is this investigation?

Tc 99 m Sestamibi scan. ***Tc 99 m Sestamibi scan*** - The classic **pentad of hypercalcemia** (stones, bones, groans, psychic moans, fatigue) indicates **primary hyperparathyroidism**, most commonly caused by **parathyroid adenoma**. - **Tc-99m Sestamibi scan** is the gold standard imaging for localizing **parathyroid adenomas** before surgical removal, showing increased uptake in hyperfunctioning parathyroid tissue. *Sulphur Colloid Scan* - This nuclear medicine scan is specifically used for imaging the **reticuloendothelial system**, particularly **liver and spleen** evaluation. - It has no role in **parathyroid pathology** assessment and would not help localize parathyroid adenomas causing hypercalcemia. *MIBG scan* - **MIBG (Meta-iodobenzylguanidine) scan** is used to detect **pheochromocytomas**, **paragangliomas**, and **neuroblastomas** that take up norepinephrine analogs. - It is completely unrelated to **calcium metabolism disorders** and would not be useful in primary hyperparathyroidism evaluation. *VMA scan* - **VMA (Vanillylmandelic acid)** is not actually a scan but a **24-hour urine test** measuring catecholamine metabolites for pheochromocytoma diagnosis. - This test is irrelevant to **parathyroid disorders** and hypercalcemia workup, as it evaluates adrenal medulla function.

Q: Thyroid radioiodine ablation therapy is useful in all except?

Medullary carcinoma. ### 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.

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

Malignant ascites. **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.

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

Positron Emission Tomography (PET). **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).

Q: The provided image is a thyroid scan. Based on the scan, what is the most probable diagnosis?

Hypersecreting adenoma. ***Hypersecreting adenoma*** - Shows a **hot nodule** with increased uptake and **suppression of the remaining thyroid gland**, characteristic of a **toxic adenoma**. - The autonomous hyperfunctioning nodule produces excess thyroid hormone, causing feedback inhibition of **TSH** and suppression of normal thyroid tissue. *Papillary carcinoma of the thyroid* - Typically appears as a **cold nodule** with decreased or absent uptake on thyroid scan due to loss of iodine-concentrating ability. - Most thyroid malignancies are **non-functional** and do not suppress normal thyroid tissue. *Lateral aberrant thyroid* - Represents **ectopic thyroid tissue** located laterally in the neck, often appearing as uptake outside the normal thyroid location. - Would show uptake in an **abnormal anatomical position**, not within the thyroid gland itself. *Graves disease* - Characterized by **diffuse increased uptake** throughout the entire thyroid gland on scintigraphy. - Shows **uniform hyperactivity** of the whole gland rather than a single hyperfunctioning nodule with suppressed surrounding tissue.

Question 1

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

Accepted Answer

Multiple Myeloma

Answer

Fibrous Dysplasia

Answer

Paget's Disease

Answer

Osteomyelitis

Question 2

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

Accepted Answer

Technetium-99m (Tc) sevelamer scan

Answer

Technetium-99m (Tc) albumin scan

Answer

Technetium-99m (Tc) dextran scan

Answer

Indium-111 (In) transferrin scan

Question 3

Which of the following imaging modalities is used to differentiate tumor recurrence from radiation necrosis?

Accepted Answer

PET scan

Answer

MRI

Answer

3D CT

Answer

USG

Question 4

Which is the best scan for assessing myocardial viability?

Accepted Answer

FDG PET scan

Answer

Thallium scan

Answer

MIBI scan

Answer

Technetium-99m pyrophosphate scan

Question 5

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

Accepted Answer

Tc-99m Sulfur Colloid

Answer

Tc-99m Red blood cells

Answer

Tc-99m Pyrophosphate

Answer

Tc-99m Teboroxime

Question 6

A patient presented with pentad of symptoms: kidney stones, painful bones, abdominal groans, psychic moans, and fatigue. The imaging investigation done for him is shown below. What is this investigation?

Accepted Answer

Tc 99 m Sestamibi scan

Answer

Sulphur Colloid Scan

Answer

MIBG scan

Answer

VMA scan

Question 7

Thyroid radioiodine ablation therapy is useful in all except?

Accepted Answer

Medullary carcinoma

Answer

Residual papillary carcinoma

Answer

Anaplastic carcinoma

Answer

Follicular carcinoma

Question 8

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

Accepted Answer

Malignant ascites

Answer

Bladder tumours

Answer

Gliomas

Answer

None of the above

Question 9

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

Accepted Answer

Positron Emission Tomography (PET)

Answer

Magnetic Resonance Imaging (MRI)

Answer

Computed Tomography (CT)

Answer

Serial Thallium Scintigrams

Question 10

The provided image is a thyroid scan. Based on the scan, what is the most probable diagnosis?

Accepted Answer

Hypersecreting adenoma

Answer

Papillary carcinoma of the thyroid

Answer

Lateral aberrant thyroid

Answer

Graves disease

Nuclear Medicine — MCQs

Nuclear Medicine — MCQs

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