Nuclear Medicine Practice Questions

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

Strontium-89 has less toxicity.. **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.

Q: Which radionucleotide is used in Scintimammography?

Sestamibi (MIBI). **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.

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

Gangrenous Cholecystitis. **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.

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

Sarcoidosis. **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.

Q: Which of the following statements are true about the Metaiodobenzylguanidine (MIBG) scan?

Used in Neuroblastoma. **Explanation:** **Metaiodobenzylguanidine (MIBG)** is a structural analog of norepinephrine (guanethidine derivative). It is taken up by the **Type-1 energy-dependent amine uptake mechanism** into the presynaptic storage vesicles of cells derived from the neural crest. 1. **Why Neuroblastoma is the focus:** While MIBG is used for several neuroendocrine tumors, it is the **gold standard** functional imaging modality for **Neuroblastoma** (Option C). It is used for initial staging, assessing response to therapy, and detecting recurrence. In pediatric oncology, MIBG is highly specific for neuroblastoma, often showing bone marrow involvement even when conventional imaging is negative. 2. **Analysis of other options:** * **Options A, B, and D:** Technically, MIBG *does* concentrate in catecholamine-producing cells and is used for Pheochromocytoma and Paraganglioma. However, in the context of NEET-PG "single best answer" questions, **Neuroblastoma** is the most frequent and classic association tested for MIBG. If this were a "Multiple Select" question, all would be correct; as a single choice, Neuroblastoma is the primary clinical application emphasized in standard radiology textbooks (like Grainger & Allison). **High-Yield Clinical Pearls for NEET-PG:** * **Isotopes used:** **I-123 MIBG** is preferred over I-131 because it has a shorter half-life, lower radiation dose, and provides superior image quality (SPECT). * **Thyroid Blockade:** It is mandatory to administer **Lugol’s iodine** or Potassium Iodide before the scan to prevent the uptake of free radioactive iodine by the thyroid gland. * **Drug Interference:** Drugs like Tricyclic Antidepressants (TCAs), Labetalol, and Reserpine must be stopped as they interfere with MIBG uptake. * **Therapeutic Use:** I-131 MIBG can be used for targeted radiotherapy in advanced or refractory neuroblastoma.

Q: Which of the following is NOT a pure beta emitter?

Samarium-153. **Explanation:** In nuclear medicine, radionuclides are classified based on the type of radiation they emit. **Pure beta emitters** are ideal for targeted therapy because they emit electrons that travel short distances, destroying local tissue without significant systemic radiation exposure. However, they are difficult to image because they lack gamma emissions. **Why Samarium-153 is the correct answer:** **Samarium-153 ($^{153}$Sm)** is a **mixed emitter**. It emits both beta particles (for therapy) and **gamma rays** (103 keV). The presence of gamma radiation allows for scintigraphic imaging (dosimetry and localization) while the beta particles treat the pathology. It is commonly used for the palliation of painful bone metastases (e.g., in prostate or breast cancer). **Analysis of Incorrect Options:** * **Yttrium-90 ($^{90}$Y):** A pure beta emitter. It is widely used in **Selective Internal Radiation Therapy (SIRT)** for liver tumors and in radiosynovectomy. * **Strontium-89/90 ($^{89/90}$Sr):** These are pure beta emitters. Strontium-89 is used for bone pain palliation, while Strontium-90 is often used in ophthalmic applicators for pterygium. * **Phosphorus-32 ($^{32}$P):** (Often grouped with these) is also a pure beta emitter used historically for Polycythemia Vera. **High-Yield Clinical Pearls for NEET-PG:** * **Pure Beta Emitters:** Yttrium-90, Phosphorus-32, Strontium-90. (Mnemonic: **Y**oung **P**eople **S**tudy). * **Mixed Emitters (Beta + Gamma):** Iodine-131, Samarium-153, Lutetium-177. These are "theranostic" because they can treat and be imaged simultaneously. * **Alpha Emitter:** Radium-223 (used for bone metastases; improves survival in CRPC). * **Half-life of $^{153}$Sm:** Approximately 46 hours.

Q: Technetium-labeled RBCs are used for the diagnosis of which condition?

Splenic disease. **Explanation:** The correct answer is **Splenic disease**. Technetium-99m labeled Red Blood Cells (RBCs) are a versatile tool in nuclear medicine, but their application depends on how the RBCs are treated before injection. **Why Splenic disease is correct:** To image the spleen specifically, the patient’s RBCs are labeled with **Tc-99m** and then **heat-denatured** (damaged) by heating them to exactly 49.5°C for 15 minutes. The body recognizes these as "damaged" cells, and the spleen—acting as the body's primary filter—sequesters them. This is the gold standard for identifying **ectopic splenic tissue (splenosis)** or a **supplementary spleen** (accessory spleen) when anatomical imaging is inconclusive. **Why other options are incorrect:** * **Biliary tree abnormalities:** These are evaluated using **Tc-99m HIDA** (Hepatobiliary Iminodiacetic Acid) scans, which track bile flow. * **Renal disease:** Renal imaging uses agents like **Tc-99m DTPA** (for GFR), **MAG3** (for tubular secretion), or **DMSA** (for cortical scarring). * **Pulmonary embolism:** This is diagnosed using a **V/Q scan**. The perfusion part uses **Tc-99m MAA** (Macroaggregated Albumin), not RBCs. **High-Yield Clinical Pearls for NEET-PG:** 1. **Tc-99m Labeled RBCs (Non-denatured):** Used for detecting **Gastrointestinal (GI) bleed** (highly sensitive for slow bleeds) and diagnosing **Hepatic Hemangiomas** (showing "delayed filling"). 2. **MUGA Scan:** Uses Tc-99m labeled RBCs to accurately calculate the Left Ventricular Ejection Fraction (LVEF). 3. **Heat-denatured RBCs:** Specifically used for **Spleen Scintigraphy**. If the question mentions "damaged RBCs," always think of the spleen.

Q: What diagnosis is implied by the results of this gallium scan?

Sarcoidosis. ***Sarcoidosis*** - **Gallium-67 scan** shows characteristic **panda sign** (parotid and lacrimal gland uptake) and **lambda sign** (bilateral hilar and right paratracheal lymph node uptake), which are pathognomonic for sarcoidosis. - These specific uptake patterns on gallium scan are highly diagnostic and distinguish sarcoidosis from other inflammatory conditions. *Mumps* - Involves **parotid gland swelling** but lacks the characteristic **bilateral hilar lymphadenopathy** seen on gallium scan. - **Viral parotitis** would not show the **lambda sign** or **systemic inflammatory uptake** pattern typical of sarcoidosis. *Paget's disease* - Primarily affects **bone metabolism** and would show increased uptake in **affected bones** rather than parotid glands or hilar lymph nodes. - **Gallium scan** is not typically used for Paget's disease diagnosis; **bone scan** with technetium-99m is preferred. *Septic emboli* - Would show **multiple scattered hot spots** in lungs corresponding to **infected embolic foci**, not the organized bilateral hilar pattern. - Lacks the characteristic **panda sign** and **lambda sign** that are specific for sarcoidosis on gallium imaging.

Question 1

A patient presents with acute renal failure (ARF) and complete anuria. The ultrasound (USG) is normal. Which of the following investigations will provide the best information regarding renal function?

Accepted Answer

DTPA scan (Radiorenogram)

Answer

Intravenous Pyelogram

Answer

Retrograde Pyelography

Answer

Antegrade Pyelography

Question 2

Increased radioisotopes are seen in all of the following conditions except:

Accepted Answer

Pseudoarthrosis

Answer

Primary bone tumor

Answer

Osteomyelitis

Answer

Paget's disease

Question 3

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

Accepted Answer

Strontium-89 has less toxicity.

Answer

Strontium-89 has a shorter half-life.

Answer

Strontium-89 has deeper penetration.

Answer

None of the above.

Question 4

Which radionucleotide is used in Scintimammography?

Accepted Answer

Sestamibi (MIBI)

Answer

HIDA

Answer

MIBG

Answer

DTPA

Question 5

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

Accepted Answer

Gangrenous Cholecystitis

Answer

Chronic cholecystitis

Answer

Biliary Atresia

Answer

Porcelain Gallbladder

Question 6

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

Accepted Answer

Sarcoidosis

Answer

Systemic lupus erythematosus

Answer

Rheumatoid arthritis

Answer

Seronegative spondyloarthropathy

Question 7

Which of the following statements are true about the Metaiodobenzylguanidine (MIBG) scan?

Accepted Answer

Used in Neuroblastoma

Answer

Concentrates in catecholamine producing tumor cells

Answer

Used in Pheochromocytoma

Answer

Used in Paraganglioma

Question 8

Which of the following is NOT a pure beta emitter?

Accepted Answer

Samarium-153

Answer

Yttrium-90

Answer

Cobalt

Answer

Strontium-90

Question 9

Technetium-labeled RBCs are used for the diagnosis of which condition?

Accepted Answer

Splenic disease

Answer

Biliary tree abnormalities

Answer

Renal disease

Answer

Pulmonary embolism

Question 10

What diagnosis is implied by the results of this gallium scan?

Accepted Answer

Sarcoidosis

Answer

Mumps

Answer

Paget's disease

Answer

Septic emboli

Nuclear Medicine — MCQs

Nuclear Medicine — MCQs

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