Nuclear Medicine Practice Questions

Q: What is the investigation of choice in parathyroid pathology?

Technetium-99m sestamibi scan. **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.

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

6 hours. **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).

Q: What is an Isotope Renogram used for?

Graphic representation of the radioactivity of the kidneys. 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).

Q: Which radiotracer is used to demonstrate vesicoureteric reflux?

Tc-99 - DMSA. ### 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.

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

Dysphagia lusoria. **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.

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

Technetium-99 scan. **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.

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

Diagnosis of spleen diseases. **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.

Q: Which of the following is an alpha emitter?

Plutonium-236. **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).

Question 1

What is the investigation of choice in parathyroid pathology?

Accepted Answer

Technetium-99m sestamibi scan

Answer

CT scan

Answer

Gallium scan

Answer

Thallium scan

Question 2

What is the half-life of Technetium-99m?

Accepted Answer

6 hours

Answer

2 hours

Answer

12 hours

Answer

24 hours

Question 3

What is an Isotope Renogram used for?

Accepted Answer

Graphic representation of the radioactivity of the kidneys

Answer

Study of the renin mechanism

Answer

Contrast study of the kidneys, ureter, and bladder

Answer

Mapping the anatomy of the kidneys

Question 4

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

Accepted Answer

Sesta MIBI scan

Answer

Iodine-123 scan

Answer

99mTc-sulphur colloid

Answer

Gallium scan

Question 5

Which radiotracer is used to demonstrate vesicoureteric reflux?

Accepted Answer

Tc-99 - DMSA

Answer

Tc-99 - DTPA

Answer

Tc-99 - MAG-3

Answer

I - 123 - OIH

Question 6

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

Accepted Answer

Dysphagia lusoria

Answer

Solitary pulmonary nodule

Answer

Skeletal metastasis

Answer

Myocardial viability

Question 7

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

Accepted Answer

Technetium-99 scan

Answer

Barium meal

Answer

CT scan

Answer

MRI scan

Question 8

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

Accepted Answer

Diagnosis of spleen diseases

Answer

Assessment of myocardial function

Answer

Evaluation of liver and biliary function

Answer

Assessment of lung ventilation

Question 9

Which investigation is used to assess the functionality of the gallbladder?

Accepted Answer

HIDA scan (Hepatobiliary Iminodiacetic Acid scan)

Answer

MRCP (Magnetic Resonance Cholangiopancreatography)

Answer

PTC (Percutaneous Transhepatic Cholangiography)

Answer

EUS scan (Endoscopic Ultrasound scan)

Question 10

Which of the following is an alpha emitter?

Accepted Answer

Plutonium-236

Answer

Carbon-11

Answer

Oxygen-15

Answer

Samarium-153

Nuclear Medicine — MCQs

Nuclear Medicine — MCQs

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