Nuclear Medicine Practice Questions

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 the investigation of choice for reversible myocardial ischemia?

Thallium scan. ### Explanation The investigation of choice for **reversible myocardial ischemia** is a **Thallium scan** (Myocardial Perfusion Imaging). [1] **1. Why Thallium Scan is Correct:** Thallium-201 is a potassium analogue that enters viable myocardial cells via the Na+/K+ ATPase pump. In a stress-redistribution protocol, areas of ischemia appear as "cold spots" during exercise (due to decreased blood flow) but "fill in" during rest (redistribution) [1]. This ability to demonstrate **reversible perfusion defects** distinguishes viable but ischemic myocardium from infarcted (scarred) tissue, which remains a "cold spot" even at rest. [1] **2. Why Other Options are Incorrect:** * **MUGA Scan:** This is the gold standard for accurately measuring the **Left Ventricular Ejection Fraction (LVEF)**. It does not assess perfusion or ischemia. * **Resting Echocardiogram:** While it can show regional wall motion abnormalities (RWMA), a resting echo cannot differentiate between an old infarct and active ischemia. It is often normal in patients with stable angina at rest. * **Coronary Angiography (CAG):** This is the gold standard for visualizing **coronary anatomy** and the degree of luminal stenosis [2]. However, it is an anatomical study, not a functional one; it cannot definitively prove if a specific stenosis is causing reversible ischemia at the cellular level. [2] **Clinical Pearls for NEET-PG:** * **Gold Standard for Viability:** PET scan (using FDG) is the most sensitive, but Thallium-201 is the standard clinical choice for "reversible ischemia." * **Hibernating Myocardium:** Chronic but reversible ischemia where wall motion is impaired; it improves after revascularization. * **Stunned Myocardium:** Temporary dysfunction persisting after reperfusion (e.g., post-PCI), despite restored blood flow.

Q: A cold lesion on a bone scan suggests which of the following?

Lytic lesion. **Explanation:** A **bone scan** (Technetium-99m MDP) depends on two factors: blood flow and **osteoblastic activity** (bone formation). A "hot lesion" indicates increased bone turnover, while a **"cold lesion" (photopenia)** occurs when there is localized bone destruction or absent blood supply that prevents the uptake of the radiopharmaceutical. **1. Why Lytic Lesion is correct:** Purely lytic lesions (e.g., Multiple Myeloma, certain metastases like Renal Cell Carcinoma) involve rapid bone destruction without a compensatory osteoblastic response. Because there is no new bone formation to take up the tracer, these appear as "cold" or "punched-out" areas on a scan. **2. Why other options are incorrect:** * **Osteomyelitis:** Typically presents as a "hot lesion" due to increased vascularity and reactive bone formation. (Note: In very early stages or if there is compromised blood flow, it can rarely be cold, but "hot" is the classic finding). * **Osteoblastic lesion:** These (e.g., Prostate cancer mets, Osteoid osteoma) show intense tracer uptake and appear "hot" due to active bone mineral deposition. * **Sequestrum:** While a sequestrum is necrotic bone, the surrounding involucrum and granulation tissue in chronic osteomyelitis usually result in an overall "hot" appearance on a bone scan. **Clinical Pearls for NEET-PG:** * **The "Cold" Differential:** Multiple Myeloma (most common cause of false-negative bone scans), aggressive lytic metastases (RCC, Thyroid), early infarction/Avascular Necrosis (Stage 1), and prosthesis. * **Sensitivity vs. Specificity:** Bone scans are highly sensitive for detecting bone pathology but have low specificity. * **Multiple Myeloma:** Always remember that a Skeletal Survey (X-ray) is preferred over a Bone Scan for Myeloma because the lesions are often cold and missed on scintigraphy.

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

Thallium scan. **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 1

Which of the following statements regarding the use of nitrates in myocardial perfusion studies is true?

Accepted Answer

Nitrates enhance the detection of myocardial viability when using Thallium-201 as a radiopharmaceutical.

Answer

Nitrates act as a stress agent.

Answer

Nitrates cause decreased myocardial flow in areas of ischemia.

Answer

Nitrates result in reduced collateral flow into the ischemic zone.

Question 2

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 3

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 4

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 5

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 6

Which of the following is the investigation of choice for reversible myocardial ischemia?

Accepted Answer

Thallium scan

Answer

MUGA scan

Answer

Resting echocardiogram

Answer

Coronary angiography

Question 7

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 8

A cold lesion on a bone scan suggests which of the following?

Accepted Answer

Lytic lesion

Answer

Osteomyelitis

Answer

Osteoblastic lesion

Answer

Sequestrum

Question 9

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

Accepted Answer

Thallium scan

Answer

MUGA scan

Answer

MDCT

Answer

Stress Echocardiography

Question 10

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

Nuclear Medicine — MCQs

Nuclear Medicine — MCQs

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