Nuclear Medicine Practice Questions

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

Detection of gastrointestinal bleeding. ***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.

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

Somatostatin receptor scintigraphy. ***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.

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

adenolymphoma. ***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.

Q: A patient presents with acute renal failure and a normal ultrasound abdomen report. What is the next most useful investigation?

DTPA scan. ***DTPA scan*** - A **DTPA (diethylenetriamine pentaacetate) scan** assesses **renal perfusion** and **glomerular filtration rate (GFR)**, which is crucial for evaluating functional impairment in acute renal failure [1]. - Since the ultrasound is normal, ruling out structural obstruction [2], the next step is to evaluate the kidneys' functional status, and the DTPA scan is excellent for this. *Intravenous pyelography (IVP)* - **IVP** uses **iodinated contrast**, which is potentially **nephrotoxic** and should be avoided in patients with acute renal failure [3]. - It primarily evaluates the **collecting system** and **ureters** for structural abnormalities, which were already deemed normal by the ultrasound in this case. *Retrograde pyelography (RGP)* - **RGP** is an **invasive procedure** involving the retrograde injection of contrast into the ureters and renal pelvis. - While it can visualize the upper urinary tract, it is typically reserved for cases where **obstruction is suspected** after less invasive methods or when definitive delineation of an obstruction is required, which is not indicated here given the normal ultrasound. *CT scan for renal evaluation* - A **CT scan for renal evaluation** often involves **contrast administration**, posing a risk of **contrast-induced nephropathy** in acute renal failure [3]. - While it provides detailed anatomical information, the initial ultrasound has already ruled out significant structural abnormalities, and a functional assessment is now more critical.

Q: Gamma rays are used in which diagnostic modality?

Bone scan. ***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.

Q: Sensitive investigation to detect ectopic parathyroid glands is

Sestamibi scan. ***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.

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

Fluoride-18. ***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.

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

PET scan. ***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**.

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

(99mTc) labelled Sestamibi isotope scan. ***(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.

Q: Most commonly used isotope in myocardial perfusion scan is:

Technetium. ***Technetium*** - **Technetium-99m (Tc-99m)** is the most widely used radionuclide in myocardial perfusion imaging (MPI) due to its favorable physical properties, including a short half-life and suitable gamma energy. - It is often chelated with agents like **sestamibi** or **tetrofosmin** to allow uptake by viable myocardial cells proportional to blood flow. *Thallium* - **Thallium-201** was historically used for MPI but has been largely replaced by technetium-based agents due to its longer half-life and lower energy photons, which result in poorer image quality. - While still used in some specific cases, it is not the primary isotope for modern myocardial perfusion scans. *Stannous pyrophosphate* - **Stannous pyrophosphate (PYP)** is used for imaging **amyloidosis** and **myocardial infarction** (specifically for detecting acutely necrotic myocardium), not for routine myocardial perfusion imaging. - It localizes to areas of **calcium deposition** in damaged myocardial tissue. *Gallium* - **Gallium-67** is primarily used for imaging **inflammation** and **infection**, such as in detecting lymphomas or osteomyelitis. - It is not used for assessing myocardial perfusion.

Question 1

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

Accepted Answer

Detection of gastrointestinal bleeding

Answer

Assessment of myocardial perfusion

Answer

Assessment of liver function

Answer

Evaluation of lung ventilation

Question 2

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

Accepted Answer

Somatostatin receptor scintigraphy

Answer

USG

Answer

CT

Answer

MRI

Question 3

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

Accepted Answer

adenolymphoma

Answer

adenocarcinoma

Answer

acinic cell carcinoma

Answer

adenoid cystic carcinoma

Question 4

A patient presents with acute renal failure and a normal ultrasound abdomen report. What is the next most useful investigation?

Accepted Answer

DTPA scan

Answer

Intravenous pyelography (IVP)

Answer

CT scan for renal evaluation

Answer

Retrograde pyelography (RGP)

Question 5

Gamma rays are used in which diagnostic modality?

Accepted Answer

Bone scan

Answer

Fluoroscopy

Answer

CT Scan

Answer

MRI

Question 6

Sensitive investigation to detect ectopic parathyroid glands is

Accepted Answer

Sestamibi scan

Answer

CECT neck

Answer

MRI

Answer

Thallium scan

Question 7

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

Accepted Answer

Fluoride-18

Answer

Iodine 123

Answer

Iodine 131

Answer

Technetium 99m

Question 8

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

Accepted Answer

PET scan

Answer

Strontium 90 scan

Answer

Tc 99 scan

Answer

Thallium 201 scan

Question 9

Most sensitive investigation for preoperative localization of abnormal parathyroid glands is

Accepted Answer

(99mTc) labelled Sestamibi isotope scan

Answer

Neck ultrasound

Answer

CT scan

Answer

MRI

Question 10

Most commonly used isotope in myocardial perfusion scan is:

Accepted Answer

Technetium

Answer

Stannous pyrophosphate

Answer

Gallium

Answer

Thallium

Nuclear Medicine — MCQs

Nuclear Medicine — MCQs

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