Nuclear Medicine — MCQs

Nuclear Medicine Indian Medical PG Practice Questions and MCQs

Question 231: What is the primary clinical application of Technetium-99m labeled red blood cells (Tc-99m RBC)?

A. Detection of gastrointestinal bleeding (Correct Answer)
B. Assessment of myocardial perfusion
C. Assessment of liver function
D. Evaluation of lung ventilation

Explanation: ***Detection of gastrointestinal bleeding*** - **Tc-99m labeled red blood cells** remain in the intravascular space, allowing for prolonged imaging to detect intermittent or slow **gastrointestinal bleeding** sites as extravasation of the labeled cells. - The high sensitivity makes it useful for localizing bleeding when endoscopy is negative or difficult, as the tracer accumulates at the site of active hemorrhage. *Assessment of myocardial perfusion* - **Myocardial perfusion** is typically assessed using different radiopharmaceuticals like **Tc-99m sestamibi** or **thallium-201**, which concentrate in viable myocardial tissue. - While Tc-99m is used, it is complexed with different agents (e.g., sestamibi) to target myocardial perfusion, not directly as labeled RBCs. *Assessment of liver function* - **Liver function** is generally evaluated using radiopharmaceuticals like **Tc-99m disofenin (HIDA)** scans for biliary excretion or blood tests for enzyme levels. - **Tc-99m RBCs** are primarily used for their intravascular residence and are not selectively taken up or metabolized by hepatocytes to assess liver function. *Evaluation of lung ventilation* - **Lung ventilation** is typically assessed using inhaled radioactive gases like **Xenon-133** or **Tc-99m DTPA aerosols**. - **Tc-99m RBCs** are administered intravenously and are not suitable for evaluating the air spaces of the lungs.

Question 232: What is the imaging modality of choice for localizing neuroendocrine tumors?

A. USG
B. CT
C. MRI
D. Somatostatin receptor scintigraphy (Correct Answer)

Explanation: ***Somatostatin receptor scintigraphy*** - **Somatostatin receptor scintigraphy** is the imaging modality of choice given that most neuroendocrine tumors (NETs) express a high density of somatostatin receptors. - **68Ga-DOTATATE PET/CT** is the **current preferred technique**, offering superior sensitivity (>90%) and specificity compared to older methods like Indium-111 pentetreotide (Octreoscan). - This functional imaging allows for **whole-body evaluation** and can detect both primary tumors and metastases, including small lesions that may be missed on conventional anatomical imaging. - Particularly valuable for detecting occult primary tumors and staging metastatic disease. *USG* - **Ultrasound** is useful for initial screening or evaluating superficial NETs, particularly in organs like the pancreas or liver. - However, its utility is limited by **operator dependence**, gas artifact, and its inability to detect small or deeply located tumors effectively. - Does not provide functional information about somatostatin receptor expression. *CT* - **Computed tomography** provides good anatomical detail and is useful for assessing tumor size, local invasion, and detecting liver metastases. - While helpful for anatomical characterization, CT can **miss small lesions** (especially <1 cm) and does not provide functional information about receptor status. - Often used in combination with functional imaging for treatment planning. *MRI* - **Magnetic resonance imaging** offers excellent soft tissue contrast and is particularly useful for NETs in the liver and pancreas. - Superior to CT for detecting liver metastases due to better soft tissue resolution. - However, MRI has **lower sensitivity for small or widespread lesions** compared to somatostatin receptor imaging and does not provide functional receptor information.

Question 233: Which of the following parotid gland tumors shows a hot spot on a Tc99 pertechnetate scan?

A. adenolymphoma (Correct Answer)
B. adenocarcinoma
C. acinic cell carcinoma
D. adenoid cystic carcinoma

Explanation: ***adenolymphoma*** - **Adenolymphoma**, also known as **Warthin's tumor**, is a benign parotid gland tumor characterized by epithelial and lymphoid components. - Its epithelial cells concentrate **technetium-99m pertechnetate**, leading to a characteristic "hot spot" on scintigraphy, a feature that distinguishes it from most other parotid masses. *adenoid cystic carcinoma* - This is a malignant tumor known for **perineural invasion** and is not typically associated with increased uptake of **Tc99m pertechnetate**. - It often presents as a slowly growing mass with potential for pain and **facial nerve palsy**. *acinic cell carcinoma* - This is a low-grade malignant tumor of the salivary glands that does not exhibit increased uptake of **Tc99m pertechnetate**. - It arises from serous acinar cells and can sometimes recur locally, but rarely metastasizes. *adenocarcinoma* - This is a general term for a malignant tumor arising from glandular tissue and does not typically show a "hot spot" on a **Tc99m pertechnetate scan**. - Its imaging characteristics are variable but generally involve a **cold spot** or no specific uptake pattern on scintigraphy, indicating a non-functioning tumor.

Question 234: Gamma rays are used in which diagnostic modality?

A. Fluoroscopy
B. CT Scan
C. MRI
D. Bone scan (Correct Answer)

Explanation: ***Bone scan*** - **Bone scans** are a type of **nuclear medicine imaging** that uses **radiopharmaceuticals** (typically Tc-99m labeled compounds) that emit **gamma rays**, which are detected by a gamma camera to create images. - Gamma ray detection is the fundamental principle of **all nuclear medicine procedures** including SPECT, PET scans, thyroid scans, and renal scans. - This modality is particularly useful for detecting **bone metastases**, infections, and fractures due to the targeted uptake of the tracer. *Fluoroscopy* - **Fluoroscopy** utilizes continuous **X-rays** to produce real-time images of internal structures, often used for guiding procedures. - It does not involve the detection of gamma rays emitted from a patient. *CT Scan* - A **CT scan** (Computed Tomography) uses a rotating **X-ray tube** and detectors to create detailed cross-sectional images of the body. - While it uses X-rays, it does not detect gamma rays for image formation. *MRI* - **MRI** (Magnetic Resonance Imaging) uses strong **magnetic fields** and **radio waves** to generate detailed images of organs and soft tissues. - It operates on the principle of nuclear magnetic resonance and does not involve gamma rays at all.

Question 235: The best method of investigation in case of acute cholecystitis is:

A. OCG
B. Ultrasound
C. ERCP
D. Radionuclide imaging (Correct Answer)

Explanation: ***Radionuclide imaging (HIDA scan)*** - **Most accurate and specific test** for acute cholecystitis with **sensitivity 95-98%** and **specificity 90-95%** - **Directly demonstrates cystic duct obstruction** (pathognomonic feature of acute cholecystitis) by showing non-visualization of gallbladder when bile ducts and small bowel are visualized - **Gold standard diagnostic test** when definitive diagnosis is required, particularly in equivocal cases - Functional imaging that assesses **biliary patency** and confirms acute cholecystitis diagnosis *Ultrasound* - **First-line imaging modality** in clinical practice due to **availability**, **cost-effectiveness**, and **non-invasiveness** - Detects **gallstones**, **gallbladder wall thickening >3mm**, **pericholecystic fluid**, and **sonographic Murphy's sign** - **Lower specificity (80-85%)** compared to HIDA scan, may miss cases with incomplete obstruction - Excellent screening tool but HIDA scan reserved for **definitive diagnosis** when ultrasound is inconclusive *OCG (Oral cholecystography)* - **Obsolete imaging technique** replaced by modern modalities - Requires **12-14 hours** for contrast concentration, unsuitable for **acute settings** requiring rapid diagnosis - Contraindicated in patients with **impaired hepatic function** or **hyperbilirubinemia** *ERCP* - **Therapeutic endoscopic procedure**, not a diagnostic imaging test for cholecystitis - Indicated for **bile duct stones (choledocholithiasis)** or **biliary strictures**, not gallbladder pathology - **Invasive with significant risks** including pancreatitis, bleeding, and perforation

Question 236: Sensitive investigation to detect ectopic parathyroid glands is

A. CECT neck
B. MRI
C. Sestamibi scan (Correct Answer)
D. Thallium scan

Explanation: ***Sestamibi scan*** - A **sestamibi scan** is highly sensitive for detecting abnormal parathyroid glands, including **ectopic glands**, due to their increased uptake and retention of the tracer. - It works by differentiating parathyroid tissue from thyroid tissue because parathyroid adenomas retain the tracer longer than thyroid tissue. *CECT neck* - While **CECT (Contrast-Enhanced Computed Tomography) neck** can identify larger parathyroid glands and delineate their anatomical location, its sensitivity for small or ectopic glands is lower compared to nuclear medicine scans. - It's often used for **preoperative localization** but may miss smaller adenomas or those located in unusual positions. *MRI* - **MRI** provides good soft tissue contrast but is generally less sensitive than sestamibi scans for identifying hyperfunctioning parathyroid glands. - Its utility in detecting small or ectopic parathyroid glands can be limited by **motion artifacts** and lack of functional information. *Thallium scan* - **Thallium scans** were historically used for parathyroid localization but have largely been replaced by **sestamibi scans** due to their lower sensitivity and specificity. - Thallium-201 uptake by both thyroid and parathyroid tissue often made differentiation challenging, leading to less clear imaging.

Question 237: What is the most commonly used radioisotope in a PET scan?

A. Iodine 123
B. Iodine 131
C. Fluoride-18 (Correct Answer)
D. Technetium 99m

Explanation: ***Fluoride-18*** - **18F-FDG** (Fluorodeoxyglucose) is the most common radiotracer used in PET scans, as it mimics glucose and highlights areas of high metabolic activity, such as tumors. - The **fluorine-18** isotope is a positron emitter, decaying to form a positron that subsequently annihilates with an electron, producing two gamma rays detected by the PET scanner. *Technetium 99m* - **Technetium 99m** is a commonly used radioisotope in **SPECT scans** (Single-Photon Emission Computed Tomography), not PET scans. - It decays by **gamma emission** directly, without positron emission, making it unsuitable for PET imaging. *Iodine 123* - **Iodine-123** is primarily used in **SPECT imaging** for thyroid and neuroendocrine studies due to its gamma emission. - While it is a useful diagnostic radioisotope, it is not a **positron emitter** and therefore not used in typical PET scans. *Iodine 131* - **Iodine-131** is primarily used for **therapeutic purposes** in treating thyroid cancer and hyperthyroidism, due to its beta emission. - Although it also emits gamma rays, its primary application is not in diagnostic imaging, and it is not a positron emitter for PET.

Question 238: A 22-year-old man presents with a solitary 2 cm space-occupying lesion of mixed echogenicity in the right lobe of the liver on ultrasound examination. The rest of the liver is normal. Which of the following tests should be done next?

A. Ultrasound-guided biopsy of the lesion
B. Hepatic scintigraphy
C. Contrast-enhanced CT scan of the liver (Correct Answer)
D. Hepatic angiography

Explanation: ***Contrast-enhanced CT scan of the liver*** - A **contrast-enhanced CT scan** offers superior anatomical detail and lesion characterization compared to ultrasound, which is crucial for evaluating a newly discovered **space-occupying liver lesion**. - It can help differentiate between benign and malignant lesions, provide information on vascularity, and guide further management or **biopsy planning**. *Ultrasound-guided biopsy of the lesion* - While a biopsy might eventually be needed, it is generally performed **after further imaging** has better characterized the lesion. - Biopsy can be invasive and carries risks; a CT scan can often narrow down the differential diagnosis and determine if a biopsy is truly necessary. *Hepatic scintigraphy* - **Hepatic scintigraphy** (e.g., Tc-99m sulfur colloid scan) is primarily used for evaluating diffuse liver disease, bile duct obstruction, or specific entities like **focal nodular hyperplasia** (FNH) with certain tracers. - It is not the most appropriate initial imaging test for general characterization of a solitary, unspecific liver lesion. *Hepatic angiography* - **Hepatic angiography** is an invasive procedure typically reserved for detailed assessment of liver vascularity, embolization, or pre-surgical planning for highly vascular tumors. - It is not a first-line diagnostic test for an unexplained solitary liver mass after an initial ultrasound.

Question 239: Which scan is used to identify viable myocardium after myocardial infarction?

A. PET scan (Correct Answer)
B. Strontium 90 scan
C. Tc 99 scan
D. Thallium 201 scan

Explanation: ***PET scan*** - Positron Emission Tomography (PET) is the **gold standard** for assessing myocardial viability, particularly using **FDG-PET**, which identifies metabolically active (viable) tissue. - Areas that show perfusion but no metabolic activity on FDG-PET indicate **hibernating myocardium**, which can recover function after revascularization. *Tc 99 scan* - **Technetium-99m sestamibi** scans assess myocardial perfusion, identifying areas of reduced blood flow (ischemia) or absent flow (infarction). - While useful for perfusion, it is **less sensitive** than PET for distinguishing between necrotic tissue and viable, but dysfunctional, myocardium. *Strontium 90 scan* - **Strontium-90** is primarily a beta emitter used in brachytherapy and **radiation sources**, not typically in diagnostic cardiac imaging for myocardial viability. - It is **not a standard radiotracer** for assessing myocardial perfusion or metabolism. *Thallium 201 scan* - **Thallium-201** is a potassium analog used in myocardial perfusion imaging to detect ischemia and infarction. - While it can show **redistribution** into viable myocardium, its resolution and ability to differentiate viable from non-viable tissue are **inferior to PET imaging**.

Question 240: Most sensitive investigation for preoperative localization of abnormal parathyroid glands is

A. Neck ultrasound
B. (99mTc) labelled Sestamibi isotope scan (Correct Answer)
C. CT scan
D. MRI

Explanation: ***(99mTc) labelled Sestamibi isotope scan*** - This scan uses a **radioactive tracer** that is preferentially taken up and retained by hyperfunctioning parathyroid tissue, making it highly sensitive for identifying **abnormal parathyroid glands**, especially parathyroid adenomas. - It is particularly useful for detecting **ectopic parathyroid glands** and in cases of persistent or recurrent hyperparathyroidism. *Neck ultrasound* - While useful for localizing parathyroid glands, its sensitivity can be limited by **operator dependence**, gland size, and location (e.g., retrosternal). - It is generally good for initial screening but not as sensitive as Sestamibi for identifying all abnormal glands, especially those located in challenging areas. *CT scan* - CT scans can visualize larger parathyroid adenomas, but their sensitivity is lower than Sestamibi scans for smaller lesions or those with **atypical locations**. - It is often used as a **second-line imaging modality** when Sestamibi is inconclusive or to complement findings. *MRI* - MRI can provide detailed anatomical information and identify parathyroid glands, but its sensitivity for detecting abnormal parathyroid tissue is generally **comparable to or slightly less** than CT and inferior to Sestamibi scanning. - It may be considered in cases of unclear findings from other modalities or when radiation exposure is a concern.

Practice by Chapter

Physics of Nuclear Medicine

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Radiopharmaceuticals

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Radiation Detection in Nuclear Medicine

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Thyroid Scintigraphy

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Bone Scintigraphy

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Renal Nuclear Medicine

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Cardiac Nuclear Medicine

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Pulmonary Nuclear Medicine

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Neurological Nuclear Medicine

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PET/CT Principles and Applications

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Radionuclide Therapy

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Radiation Safety in Nuclear Medicine

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