Nuclear Medicine — MCQs

Nuclear Medicine Indian Medical PG Practice Questions and MCQs

Question 101: A bone scan in multiple myeloma typically shows which of the following?

A. Hot spot
B. Cold spot (Correct Answer)
C. Diffusely increased uptake
D. Diffusely decreased uptake

Explanation: **Explanation:** In **Multiple Myeloma (MM)**, the characteristic bone lesions are purely **osteolytic**. The pathophysiology involves the activation of osteoclasts by myeloma cells (via RANKL expression) and the simultaneous inhibition of osteoblasts. A standard **Technetium-99m MDP Bone Scan** relies on osteoblastic activity (bone formation) to show "hot spots." Because MM lacks a reactive osteoblastic response, the lesions do not take up the tracer. Instead, they appear as **"Cold spots"** (areas of decreased or absent uptake) or may even appear normal, leading to a high false-negative rate (approx. 30-50%). **Analysis of Options:** * **A. Hot spot:** This is the typical finding for osteoblastic or mixed lesions (e.g., Prostate cancer metastases, Paget’s disease, or healing fractures). It is rarely seen in MM unless a pathological fracture is actively healing. * **C & D. Diffuse uptake patterns:** "Diffusely increased uptake" (Super scan) is characteristic of metabolic bone diseases (Hyperparathyroidism) or widespread osteoblastic metastases. MM does not present with diffuse metabolic alterations of the entire skeleton in this manner. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard for Imaging MM:** Whole-body Low-Dose CT (WBLDCT) or MRI is now preferred over the traditional skeletal survey. * **Bone Scan vs. Skeletal Survey:** A skeletal survey (X-ray) is more sensitive than a bone scan for MM, but even X-rays require 30-50% bone mineral loss to be visible. * **Punch-out Lesions:** The classic radiographic description of MM on X-ray. * **Exception:** If a bone scan *is* positive (hot) in a suspected MM patient, always rule out a pathological fracture.

Question 102: Distant metastasis of bone can be best detected by?

A. NMI
B. Bone scan (Correct Answer)
C. CT
D. Intravenous venogram

Explanation: **Explanation:** **Why Bone Scan is the Correct Answer:** Technetium-99m Methyl Diphosphonate (Tc-99m MDP) **Bone Scan** is the gold standard for screening distant bone metastasis. Its superiority lies in its **high sensitivity** and ability to perform a **whole-body survey** in a single session. The mechanism is based on osteoblastic activity; the radiopharmaceutical concentrates in areas of increased bone turnover (remodeling). Crucially, a bone scan can detect metastatic lesions **2–6 months earlier** than a conventional X-ray, as it identifies functional changes before significant structural damage (30–50% calcium loss) occurs. **Analysis of Incorrect Options:** * **NMI (Nuclear Medicine Imaging):** This is a broad category that includes bone scans, PET scans, and thyroid scans. While technically correct in classification, "Bone Scan" is the specific and most appropriate clinical answer. * **CT (Computed Tomography):** While excellent for evaluating cortical bone destruction and detailed anatomy, CT is not used for primary screening of distant metastasis because it is difficult to scan the entire skeleton efficiently and involves high radiation doses. * **Intravenous Venogram:** This is an invasive procedure used to visualize veins (e.g., for DVT). It has no role in detecting bone metastasis. **NEET-PG High-Yield Pearls:** * **Most Sensitive Modality:** While Bone Scan is the screening tool of choice, **MRI** is the most sensitive for detecting early marrow involvement. * **The "Cold" Exception:** Bone scans may show "cold defects" (false negatives) in purely lytic lesions, such as **Multiple Myeloma**, or very aggressive tumors where there is no osteoblastic response. * **Flare Phenomenon:** An apparent increase in uptake on a bone scan shortly after starting chemotherapy, which actually indicates healing rather than disease progression. * **Common Primary Sites:** The most common cancers metastasizing to bone are **Breast, Prostate, and Lung**.

Question 103: What does 18-FDG stand for?

A. 18-Fluorodeoxy glucose (Correct Answer)
B. 18-Fluorodioxy glucose
C. 18-Fluorodeoxy galactose
D. 18-Fluorodioxy galactose

Explanation: **Explanation:** **18-FDG** stands for **18-Fluorodeoxyglucose**. It is the most commonly used radiopharmaceutical in Positron Emission Tomography (PET) imaging. **Why Option A is correct:** 18-FDG is a glucose analog where the hydroxyl group at the C-2 position of the glucose molecule is replaced by a radioactive **Fluorine-18** isotope. It is transported into cells by **GLUT transporters** and phosphorylated by **hexokinase** into FDG-6-phosphate. Unlike normal glucose, FDG-6-phosphate cannot undergo further glycolysis and becomes "trapped" inside the cell. This process, known as **metabolic trapping**, allows for the visualization of tissues with high glucose metabolism. **Why other options are incorrect:** * **Options B & D (Dioxy):** The term "dioxy" implies two oxygen atoms, whereas "deoxy" correctly indicates the removal of an oxygen atom (specifically from the hydroxyl group) to facilitate the substitution with Fluorine-18. * **Options C & D (Galactose):** While galactose is a sugar, it is not the primary substrate used for routine PET oncological imaging. Glucose is the universal fuel for most malignant cells; hence, a glucose analog is used. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Based on the **Warburg Effect** (cancer cells exhibit increased glycolysis even in aerobic conditions). * **Half-life:** The physical half-life of Fluorine-18 is approximately **110 minutes**. * **Clinical Use:** Staging, restaging, and monitoring treatment response in various cancers (except those with low metabolic rates like prostate cancer or certain neuroendocrine tumors). * **Patient Preparation:** Patients must fast for 4–6 hours, and blood glucose should ideally be **<150–200 mg/dL** to prevent competition between endogenous glucose and FDG. * **Physiological Uptake:** Normal "hot spots" include the brain, heart, kidneys, and urinary bladder (excretion route). Brown fat uptake can be minimized by keeping the patient warm.

Question 104: Which statement is true regarding Strontium-89 when compared to Phosphorus-32?

A. Strontium-89 has a shorter half-life.
B. Strontium-89 has less toxicity. (Correct Answer)
C. Strontium-89 has deeper penetration.
D. None of the above.

Explanation: **Explanation:** Both Strontium-89 ($^{89}$Sr) and Phosphorus-32 ($^{32}$P) are beta-emitting radionuclides used for the palliative treatment of painful bone metastases. However, their pharmacological profiles differ significantly. **Why Option B is Correct:** Strontium-89 is a calcium analog that selectively localizes to areas of high osteoblastic activity (bone metastases). In contrast, Phosphorus-32 is a phosphate analog that incorporates into the hydroxyapatite crystal of the bone but also into the **rapidly dividing cells of the bone marrow**. Consequently, $^{32}$P causes significant and prolonged **myelosuppression** (leukopenia and thrombocytopenia). Strontium-89 has a more targeted uptake, resulting in **less hematologic toxicity** compared to $^{32}$P. **Analysis of Incorrect Options:** * **Option A:** Strontium-89 has a **longer** physical half-life (~50.5 days) compared to Phosphorus-32 (~14.3 days). * **Option C:** Phosphorus-32 actually has a higher maximum beta energy (1.71 MeV) compared to Strontium-89 (1.46 MeV). Therefore, $^{32}$P generally has a slightly **deeper** tissue penetration (average 3.0 mm) than $^{89}$Sr (average 2.4 mm). **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Both are pure beta emitters (ideal for therapy, not imaging). * **Indications:** Primarily used for osteoblastic metastases (e.g., Prostate and Breast cancer). * **Samarium-153 ($^{153}$Sm):** Another common agent; unlike the others, it also emits a small amount of gamma radiation, allowing for post-therapy scintigraphic imaging. It has the shortest half-life (approx. 1.9 days). * **Flare Phenomenon:** Patients may experience a transient increase in bone pain 2–3 days after injection before relief begins.

Question 105: Radioisotopes emit all the following types of radiation except?

A. Alpha Rays
B. Beta Rays
C. Gamma Rays
D. X-rays (Correct Answer)

Explanation: ### Explanation The core concept behind this question lies in the **origin of the radiation**. Radioisotopes (radionuclides) are unstable atoms that undergo **nuclear decay** to reach a stable state. Therefore, the radiation they emit originates from the **nucleus**. **Why X-rays is the correct answer:** X-rays are **extranuclear** in origin. They are produced when electrons transition between atomic shells (Characteristic X-rays) or when high-speed electrons are decelerated near a nucleus (Bremmstrahlung radiation). Since X-rays do not originate from the radioactive decay of the nucleus itself, they are not considered a primary emission of radioisotopes. **Analysis of incorrect options:** * **Alpha Rays (α):** These consist of two protons and two neutrons (Helium nucleus). They are emitted by heavy unstable nuclei (e.g., Radium-226) during alpha decay. * **Beta Rays (β):** These are high-speed electrons ($\beta^-$) or positrons ($\beta^+$) emitted from the nucleus when a neutron converts to a proton or vice versa. * **Gamma Rays (γ):** These are high-energy electromagnetic photons emitted from an excited nucleus as it transitions to a lower energy state. This is the most common emission used in diagnostic Nuclear Medicine (e.g., Technetium-99m). **High-Yield Clinical Pearls for NEET-PG:** * **Technetium-99m (Tc-99m):** The most widely used radioisotope in diagnostic imaging; it is a pure **Gamma** emitter with a half-life of 6 hours and energy of 140 keV. * **Therapeutic Isotopes:** Usually emit **Beta particles** (e.g., I-131 for hyperthyroidism, Yttrium-90 for radioembolization) because they have a short path length and cause local tissue destruction. * **PET Scans:** Utilize **Positron ($\beta^+$) emitters** like Fluorine-18 (F-18). * **Alpha emitters:** Used in targeted alpha therapy (e.g., Radium-223 for bone metastases) due to high linear energy transfer (LET).

Question 106: Which radionucleotide is used in Scintimammography?

A. HIDA
B. MIBG
C. Sestamibi (MIBI) (Correct Answer)
D. DTPA

Explanation: **Explanation:** **Scintimammography** (also known as Molecular Breast Imaging) is a functional imaging technique used to detect breast cancer, particularly in women with dense breast tissue where traditional mammography may be less sensitive. **Why Sestamibi (MIBI) is correct:** **Technetium-99m Sestamibi** is a lipophilic cationic compound. It is taken up by breast cancer cells due to their high metabolic activity and increased mitochondrial density. The tracer crosses the cell membrane and accumulates within the mitochondria via a passive transport mechanism driven by the negative transmembrane potential. Malignant cells, having higher metabolic demands, show significantly higher uptake compared to normal breast tissue. **Analysis of Incorrect Options:** * **A. HIDA (Hepatic Iminodiacetic Acid):** Used for **Cholescintigraphy** to evaluate the gallbladder and biliary tree (e.g., diagnosing acute cholecystitis). * **B. MIBG (Metaiodobenzylguanidine):** An analogue of norepinephrine used to image neuroendocrine tumors like **Pheochromocytoma** and Neuroblastoma. * **D. DTPA (Diethylene Triamine Pentaacetic Acid):** Primarily used for **Renal Scintigraphy** to assess Glomerular Filtration Rate (GFR) and evaluate obstructive uropathy. **High-Yield Clinical Pearls for NEET-PG:** * **Sestamibi** is also the gold standard for **Parathyroid Scintigraphy** (to locate adenomas) and **Myocardial Perfusion Imaging** (Stress Thallium/MIBI). * **Washout phenomenon:** Sestamibi is a substrate for the **P-glycoprotein (Pgp)** pump. Rapid washout of the tracer from a breast lesion is often associated with multidrug resistance (MDR) in tumors. * Scintimammography is particularly useful when mammography is inconclusive due to breast implants or severe scarring.

Question 107: Which of the following factors contribute to the development of duodenal ulcer?

A. I-131 (Correct Answer)
B. I-125
C. Tc-99
D. P-32

Explanation: **Explanation:** The correct answer is **I-131**. This question relates to the side effects of radionuclide therapy, specifically in the treatment of thyroid disorders. **1. Why I-131 is correct:** Radioactive Iodine-131 (I-131) is a beta-emitter used for treating hyperthyroidism and thyroid carcinoma. While it is primarily concentrated in the thyroid gland, it is also secreted by the **gastric mucosa** and salivary glands. High doses of I-131 can lead to radiation-induced mucosal damage. Specifically, the concentration of I-131 in the stomach can cause gastritis and, in some cases, lead to the development of **duodenal or gastric ulcers** due to direct radiation injury to the mucosal lining. **2. Why other options are incorrect:** * **I-125:** This isotope is primarily used in brachytherapy (e.g., prostate cancer) and RIA (Radioimmunoassay). It emits low-energy gamma rays and Auger electrons with a much shorter range than I-131, making it less likely to cause systemic mucosal damage like duodenal ulcers. * **Tc-99m:** Technetium-99m is a pure gamma emitter used for diagnostic imaging (scintigraphy). It has a short half-life (6 hours) and does not emit corpuscular radiation (beta particles), meaning it does not cause tissue destruction or ulceration. * **P-32:** Phosphorus-32 is a pure beta emitter used for treating polycythemia vera and malignant effusions. While it affects rapidly dividing cells (bone marrow), it is not selectively secreted by the gastric mucosa and is not a recognized cause of duodenal ulcers. **Clinical Pearls for NEET-PG:** * **I-131 Radiation:** Emits both **Beta particles** (for therapy) and **Gamma rays** (for imaging). * **Protective Measure:** Patients receiving high-dose I-131 are often advised to stay hydrated and sometimes use H2 blockers or proton pump inhibitors (PPIs) to reduce gastric irritation. * **Common Side Effects of I-131:** Sialadenitis (salivary gland swelling), radiation thyroiditis, and transient gastritis.

Question 108: Hot rim sign on hepatobiliary scintigraphy (Tc99m-HIDA) is seen in which of the following conditions?

A. Chronic cholecystitis
B. Biliary Atresia
C. Gangrenous Cholecystitis (Correct Answer)
D. Porcelain Gallbladder

Explanation: **Explanation:** The **Hot Rim Sign** (also known as the "Rim Sign") on Tc99m-HIDA scintigraphy refers to a curvilinear area of increased radioactivity in the liver parenchyma immediately adjacent to the gallbladder fossa. **1. Why Gangrenous Cholecystitis is correct:** The Hot Rim Sign is a highly specific indicator of **acute severe cholecystitis**, often associated with complications like **gangrenous cholecystitis** or perforation. The underlying mechanism is increased blood flow (hyperemia) and inflammatory changes in the liver bed surrounding the inflamed gallbladder. While HIDA scans typically show non-visualization of the gallbladder in acute cholecystitis, the presence of this "rim" of activity suggests a more advanced or necrotic disease process. **2. Why the other options are incorrect:** * **Chronic Cholecystitis:** Typically shows delayed visualization of the gallbladder (after 1–4 hours) rather than a hot rim sign. * **Biliary Atresia:** Characterized by good hepatic uptake of the tracer but a total **absence of excretion** into the small intestine, even on delayed 24-hour images. * **Porcelain Gallbladder:** This is a surgical/radiological diagnosis (calcification of the gallbladder wall) seen on X-ray or CT; it is not a primary finding on HIDA scans. **Clinical Pearls for NEET-PG:** * **Gold Standard:** HIDA scan is the most sensitive imaging modality for diagnosing **Acute Cholecystitis** (due to cystic duct obstruction). * **Normal HIDA:** Visualization of the gallbladder, common bile duct, and duodenum within 60 minutes. * **False Positives:** Can occur in patients with prolonged fasting (>24 hours), total parenteral nutrition (TPN), or severe liver disease. * **Morphine Augmentation:** Used to differentiate acute from chronic cholecystitis by increasing sphincter of Oddi pressure to force tracer into the gallbladder.

Question 109: The Panda sign in a gallium scan is characteristic of which condition?

A. Sarcoidosis (Correct Answer)
B. Systemic lupus erythematosus
C. Rheumatoid arthritis
D. Seronegative spondyloarthropathy

Explanation: **Explanation:** The **Panda sign** is a classic nuclear medicine finding on a **Gallium-67 (Ga-67) citrate scan**. It occurs due to bilateral, symmetrical uptake of the radiotracer in the **lacrimal glands, parotid glands, and nasopharyngeal mucosa**. When these areas of uptake are visualized together on an anterior head/neck image, they resemble the face of a giant panda. 1. **Why Sarcoidosis is correct:** Sarcoidosis is a multisystem granulomatous disease. Gallium-67 is an iron analog that binds to lactoferrin and accumulates in areas of active inflammation and granuloma formation. The Panda sign specifically indicates bilateral dacryoadenitis and parotitis. When combined with the **"Lambda sign"** (symmetrical uptake in the hilar and paratracheal lymph nodes), the specificity for Sarcoidosis increases significantly. 2. **Why other options are incorrect:** * **SLE, Rheumatoid Arthritis, and Seronegative Spondyloarthropathy:** While these are systemic inflammatory conditions, they do not typically cause the specific pattern of symmetrical lacrimal and salivary gland inflammation required to produce the Panda sign. While Gallium scans may show joint or visceral uptake in these diseases, the findings are non-specific. **High-Yield Clinical Pearls for NEET-PG:** * **Panda Sign:** Seen in Sarcoidosis, Sjögren’s syndrome, and occasionally after neck irradiation or in lymphoma (post-treatment). * **Lambda Sign:** Symmetrical uptake in right paratracheal and bilateral hilar lymph nodes (resembling the Greek letter $\lambda$). * **Gallium-67:** It has a physical half-life of **78 hours** and emits four photopeaks (approx. 93, 184, 300, and 394 keV). * **Hot Potato Sign:** Another name sometimes used for the combination of Panda and Lambda signs in Sarcoidosis.

Question 110: Renal cortical imaging is done by which of the following modalities?

A. DTPA (Diethylene triamine pentaacetic acid)
B. DMSA (Dimercaptosuccinic acid) (Correct Answer)
C. MAG3 (Mercaptoacetyltriglycine)
D. UIH (Unknown abbreviation - likely incorrect)

Explanation: **Explanation:** **DMSA (Dimercaptosuccinic acid)** is the gold standard for **renal cortical imaging**. The underlying mechanism involves its accumulation in the **proximal convoluted tubules** of the renal cortex. Approximately 40-50% of the injected dose is bound to the cortical tubular cells and remains there for several hours, allowing for high-resolution static imaging. It is primarily used to detect **renal scarring** (post-pyelonephritis), ectopic kidneys, and to calculate **differential renal function**. **Analysis of Incorrect Options:** * **DTPA (Diethylene triamine pentaacetic acid):** This is a glomerular agent. It is filtered solely by the **glomerulus** and is not reabsorbed or secreted. It is used for measuring **GFR** and dynamic renography to assess obstructive uropathy. * **MAG3 (Mercaptoacetyltriglycine):** This is a tubular secretion agent. It is primarily secreted by the **proximal tubules** and rapidly excreted into the urine. It is the agent of choice for **dynamic renography** (diuretic renogram) to evaluate drainage and renal perfusion, especially in patients with impaired renal function. * **UIH:** This is likely a distractor or a typo for OIH (Ortho-iodohippurate), which was historically used for effective renal plasma flow (ERPF) but has been largely replaced by MAG3. **High-Yield Clinical Pearls for NEET-PG:** * **Static Imaging:** DMSA (Think "S" for Static/Scarring). * **Dynamic Imaging:** DTPA and MAG3 (Think "D" for Drainage/Dynamic). * **Best agent for Neonates/Renal Failure:** MAG3 (due to high extraction fraction). * **Glucoheptonate (GHA):** A unique agent that can be used for both cortical imaging and GFR estimation.

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