Principles of Functional Imaging — MCQs
99m Technetium labeled RBC scintigraphy is PRIMARILY used in the diagnosis of
In radionuclide imaging, the most useful radiopharmaceutical for skeletal imaging is:
A lady presented with a 4 cm tumor in the left parietal lobe for which she underwent surgery and radiotherapy. After 3 months she presented with headache and vomiting. Which of the following would characterize the lesion in the patient?
Which common tracer in PET is usually administered in the form of a glucose sugar?
Which radioisotope is PRIMARILY used for detecting acute myocardial infarction rather than assessing myocardial perfusion?
In a child, non-functioning kidney is best diagnosed by:
MUGA scan is not useful in:
Tc-labeled RBCs are used for all except:
Which one of the following imaging modalities is most sensitive for localizing extra-adrenal pheochromocytoma?
A young male patient presents with dyspnea; auscultation reveals absent breath sounds on the right side, and he has hypotension. What is the immediate next step?
Principles of Functional Imaging Indian Medical PG Practice Questions and MCQs
Question 1: 99m Technetium labeled RBC scintigraphy is PRIMARILY used in the diagnosis of
- A. Hepatoma
- B. Left ventricular function wall motion
- C. Hepatic hemangioma
- D. GI Bleeding (Correct Answer)
Explanation: ***GI Bleeding*** - Technetium-99m labeled RBC scintigraphy (**<sup>99m</sup>Tc-RBC scan**) is highly sensitive for detecting **active gastrointestinal bleeding**, especially slow or intermittent bleeding. - The labeled red blood cells extravasate at the site of bleeding, accumulating and outlining the bleeding focus over time. *Hepatoma* - **Hepatoma** (hepatocellular carcinoma) is primarily diagnosed using imaging modalities like **CT, MRI**, and **ultrasound**, often with contrast enhancement. - While nuclear medicine scans like **FDG-PET** can be used in some cases for staging or assessing viability, <sup>99m</sup>Tc-RBC scans are not a primary diagnostic tool for hepatoma. *Left ventricular function wall motion* - **Left ventricular function** and **wall motion abnormalities** are typically assessed using **echocardiography**, cardiac **MRI**, or **nuclear cardiology studies** like **SPECT** or **PET** using tracers that localize in the myocardium (e.g., <sup>99m</sup>Tc-Sestamibi or Thallium-201). - <sup>99m</sup>Tc-RBC scans are sometimes used for **gated blood pool scans** to assess global ejection fraction, but not directly for wall motion analysis in the same way as other dedicated cardiac modalities. *Hepatic hemangioma* - **Hepatic hemangiomas** can be characterized by **<sup>99m</sup>Tc-RBC scintigraphy**, which shows **early photopenia** followed by **delayed fill-in and retention** of the tracer due to the characteristic slow blood flow within these benign vascular tumors. - While it can be used for confirmation, it's not the most commonly used primary diagnostic tool (which is often **ultrasound** or **MRI** with specific contrast patterns), and GI bleeding is a more direct application where the scan detects extravasation rather than vascular pooling.
Question 2: In radionuclide imaging, the most useful radiopharmaceutical for skeletal imaging is:
- A. Technetium-99m linked to Methylene diphosphonate (Correct Answer)
- B. Gallium 67
- C. Technetium-99m
- D. Technetium-sulfur-colloid
Explanation: ***Technetium-99m linked to Methylene diphosphonate*** - **Technetium-99m MDP** is the most widely used radiopharmaceutical for skeletal imaging due to its **high affinity for hydroxyapatite crystals** in bone and favorable physical properties. - It readily incorporates into areas of **increased bone turnover**, making it excellent for detecting fractures, infections, and metastatic lesions. *Gallium 67* - **Gallium 67** is primarily used for **oncology, infection, and inflammation imaging** and has limited utility for general skeletal imaging. - It accumulates in areas of infection and inflammation, but its **biodistribution is not specific for bone metabolism**. *Technetium-sulfur-colloid* - **Technetium-sulfur-colloid** is mainly used for **liver and spleen imaging** (reticuloendothelial system), not for bone scans. - Its particle size and chemical properties prevent its significant uptake in bone tissue. *Technetium-99m* - **Technetium-99m** is a **radioisotope generator** for many different radiopharmaceuticals, but by itself, it's not directly used for skeletal imaging. - It serves as the **radionuclide scaffold** that is chelated to specific bone-seeking ligands like MDP.
Question 3: A lady presented with a 4 cm tumor in the left parietal lobe for which she underwent surgery and radiotherapy. After 3 months she presented with headache and vomiting. Which of the following would characterize the lesion in the patient?
- A. Digital subtraction angiography with dual source CT scan
- B. Gd-enhanced MRI
- C. 99Tc-HMPAO SPECT brain
- D. 18FDG PET Scan (Correct Answer)
Explanation: ***18FDG PET Scan*** - This patient, presenting with new neurological symptoms after **surgery and radiotherapy** for a cerebral tumor, faces a diagnostic dilemma: differentiating between **tumor recurrence** and **radiation necrosis**. - **18FDG PET scans** effectively distinguish between these two conditions because viable tumor cells exhibit high metabolic activity and thus actively take up **fluorodeoxyglucose (FDG)**, while radiation necrosis is metabolically inactive and shows little to no FDG uptake. *Digital subtraction angiography with dual source CT scan* - **Digital subtraction angiography (DSA)** is primarily used to visualize **vascular structures** and is not the modality of choice for differentiating tumor recurrence from radiation necrosis. - A **dual-source CT scan** is useful for rapid imaging and dynamic studies but lacks the metabolic information needed for this specific differentiation. *Gd-enhanced MRI* - While **Gd-enhanced MRI** is excellent for detecting **structural changes** and **blood-brain barrier disruption**, it often cannot definitively differentiate between **tumor recurrence** and **radiation necrosis**. - Both conditions can present with similar **enhancement patterns** on MRI, making differentiation challenging without additional metabolic information. *99Tc-HMPAO SPECT brain* - **99mTc-HMPAO SPECT** measures **regional cerebral blood flow (rCBF)**, which can be altered in both tumors and areas of radiation injury. - However, it does not provide the specific metabolic information (glucose metabolism) needed to reliably distinguish between **viable tumor cells** and **radiation necrosis** as effectively as FDG PET.
Question 4: Which common tracer in PET is usually administered in the form of a glucose sugar?
- A. Aluminum - 12
- B. Fluorine 18 (Correct Answer)
- C. Carbon 11
- D. Oxygen 15
Explanation: ***Fluorine 18*** - **18F-FDG** (Fluorodeoxyglucose) is the most common PET tracer, utilizing **Fluorine-18** as its radioactive component. - FDG is a glucose analog, meaning it mimics glucose and is taken up by metabolically active cells, allowing for imaging of **glucose metabolism**. *Aluminum - 12* - **Aluminum-12** is not a common radionuclide used in PET imaging. - The most common tracers in PET are **positron emitters** like Fluorine-18, Carbon-11, Nitrogen-13, and Oxygen-15. *Carbon 11* - **Carbon-11** can be used in PET tracers (e.g., 11C-methionine), but it is **less common** than 18F-FDG due to its shorter half-life. - Its short half-life (20 minutes) requires an **on-site cyclotron** for production, limiting its widespread use. *Oxygen 15* - **Oxygen-15** is employed in PET tracers (e.g., 15O-water for cerebral blood flow), but it has an **even shorter half-life** (2 minutes) than Carbon-11. - Its extremely short half-life makes it **impractical** for routine clinical use in the form of a glucose sugar.
Question 5: Which radioisotope is PRIMARILY used for detecting acute myocardial infarction rather than assessing myocardial perfusion?
- A. Thallium 201
- B. Tc-99m Sestamibi
- C. Tc-99m Pyrophosphate (Correct Answer)
- D. 18-FDG PET
Explanation: ***Tc-99m Pyrophosphate*** - This radioisotope binds to **calcium deposits** in infarcted myocardial tissue, which accumulate 12-24 hours after injury. - It is particularly useful for detecting **acute myocardial infarction** (hot spot imaging) when cardiac biomarkers may be unreliable or in cases of delayed presentation. - Shows positive uptake in necrotic tissue, making it a "positive" or "hot spot" agent for acute MI. *Thallium 201* - **Thallium 201** is a potassium analog that is actively transported into viable myocardial cells. - It is primarily used for assessing **myocardial perfusion** and viability, showing areas of reduced blood flow or scar tissue. - Acts as a "cold spot" agent - infarcted areas show reduced uptake. *Tc-99m Sestamibi* - **Tc-99m Sestamibi** is a commonly used tracer for **myocardial perfusion imaging (SPECT)**, indicating blood flow to the heart muscle. - It accumulates in viable myocardial cells in proportion to blood flow and is not specific for acute myocardial necrosis. - Used primarily for stress testing and perfusion assessment, not acute infarct detection. *18-FDG PET* - **18-FDG PET** (Fluorodeoxyglucose Positron Emission Tomography) primarily measures **glucose metabolism** in the myocardium. - It is predominantly used to assess **myocardial viability** in areas of hibernating myocardium rather than acute infarction. - Helps distinguish viable but ischemic tissue from scar tissue.
Question 6: In a child, non-functioning kidney is best diagnosed by:
- A. Ultrasonography
- B. IVU
- C. Creatinine clearance
- D. DTPA renogram (Correct Answer)
Explanation: ***DTPA renogram*** - A **DTPA (diethylenetriamine pentaacetic acid) renogram** is a nuclear medicine study that assesses **renal blood flow**, **glomerular filtration**, and urinary drainage. It directly measures the function of each kidney by quantifying tracer uptake and excretion, making it ideal for diagnosing a non-functioning kidney in a child. - The test provides information on the **relative function** of each kidney and outflow obstruction, which is crucial for determining if a kidney is truly non-functioning rather than just poorly visualized. *Ultrasonography* - While ultrasound can visualize the **anatomy** of the kidney (size, shape, presence of hydronephrosis), it does not directly assess renal function. - It may show a small, atrophic, or poorly developed kidney, but cannot definitively determine if it is non-functioning without functional studies. *IVU (Intravenous Urogram)* - An **IVU** relies on the kidneys' ability to excrete contrast material, which is visualized by X-ray. If a kidney is non-functioning, it will not excrete the contrast, leading to non-visualization. - However, IVU exposes the child to **radiation** and **iodinated contrast**, and newer, safer, and more precise functional studies like renograms are preferred, especially in pediatric cases where radiation exposure should be minimized. *Creatinine clearance* - **Creatinine clearance** is a measure of overall **glomerular filtration rate (GFR)** for both kidneys combined. - It does not provide information on the individual function of each kidney, so it cannot diagnose a non-functioning unilateral kidney.
Question 7: MUGA scan is not useful in:
- A. Stroke volume
- B. Regional wall perfusion (Correct Answer)
- C. Left ventricular ejection fraction
- D. Regional wall motion
Explanation: ***Regional wall perfusion*** - A MUGA scan assesses **ventricular function** through blood pool imaging, evaluating wall motion and ejection fraction. - It does not directly visualize or quantify myocardial perfusion, which is the flow of blood through the coronary arteries to the heart muscle. *Stroke volume* - A MUGA scan accurately measures **end-diastolic volume** and **end-systolic volume**, from which stroke volume (EDV – ESV) can be calculated. - This parameter directly reflects the amount of blood pumped out by the ventricle with each beat. *Left ventricular ejection fraction* - The MUGA scan is considered a gold standard for calculating **left ventricular ejection fraction** (LVEF), a key indicator of cardiac pump function. - It uses a count-based method from gated blood pool images to determine the percentage of blood ejected from the left ventricle. *Regional wall motion* - MUGA scans are highly effective in assessing **regional wall motion abnormalities**, identifying areas of **hypokinesis**, **akinesis**, or **dyskinesis**. - This is crucial for diagnosing and monitoring conditions like myocardial ischemia or infarction, and is a primary utility of the scan.
Question 8: Tc-labeled RBCs are used for all except:
- A. Liver adenoma (Correct Answer)
- B. LV function
- C. GI bleeding
- D. Liver hemangioma
Explanation: ***Liver adenoma*** - Tc-labeled RBCs are primarily used to highlight a specific type of tissue or process. **Liver adenomas** do not typically show an affinity for **Tc-labeled RBCs**, as they are benign epithelial tumors with a different vascular composition. - While adenomas can be vascular, they do not inherently contain the **vascular pooling** or blood volume characteristics that would be specifically targeted by **Tc-labeled RBCs** for diagnostic imaging. *LV function* - **Tc-labeled RBCs** (or Tc-99m-pertechnetate) are commonly used in **gated blood pool imaging** (MUGA scan) to assess **left ventricular (LV) function**, including **ejection fraction** and wall motion abnormalities. - This technique directly visualizes the blood pool within the cardiac chambers, making it suitable for assessing functional parameters of the heart. *GI bleeding* - **Tc-labeled RBCs** are a standard imaging agent for detecting and localizing **active gastrointestinal (GI) bleeding**, especially when the bleeding rate is intermittent or slow. - The labeled RBCs extravasate at the site of hemorrhage, creating a 'hot spot' that can be identified over time. *Liver hemangioma* - **Tc-labeled RBCs** are highly effective in diagnosing **liver hemangiomas**, which are benign vascular tumors composed of large, dilated blood vessels. - These lesions show characteristic uptake and retention of **labeled RBCs** due to their slow blood flow and large intravascular space, appearing as early peripheral enhancement with subsequent centripetal filling.
Question 9: Which one of the following imaging modalities is most sensitive for localizing extra-adrenal pheochromocytoma?
- A. USG
- B. MRI
- C. MIBG scan
- D. 68Ga-DOTATATE PET/CT (Correct Answer)
Explanation: ***68Ga-DOTATATE PET/CT*** - **68Ga-DOTATATE PET/CT** is highly sensitive for detecting **neuroendocrine tumors**, including pheochromocytomas and paragangliomas, due to its affinity for **somatostatin receptors** which are overexpressed on these cells. - This modality offers superior sensitivity in localizing both adrenal and **extra-adrenal pheochromocytomas**, particularly in cases of metastatic disease or multifocal lesions. *USG* - **Ultrasound (USG)** has limited utility for localizing **extra-adrenal pheochromocytomas**, especially if they are small, located in less accessible anatomical sites, or obscured by bowel gas. - While useful for initial screening of adrenal masses, its sensitivity for **extra-adrenal disease** is low. *MRI* - **MRI** is a valuable imaging modality for pheochromocytoma localization, offering good soft tissue contrast, but its overall sensitivity for detecting **extra-adrenal lesions** may be surpassed by more specific functional imaging techniques like 68Ga-DOTATATE PET/CT. - It is particularly useful for assessing the extent of disease and anatomical proximity to vital structures once a lesion is identified, but less sensitive for identifying occult **extra-adrenal tumors**. *MIBG scan* - **MIBG scintigraphy** relies on the uptake of a chemical analog of norepinephrine by **sympathetic neurosecretory cells**, making it useful for detecting pheochromocytomas. - However, its sensitivity in detecting **extra-adrenal pheochromocytomas** and metastatic disease is generally lower compared to 68Ga-DOTATATE PET/CT, particularly for certain genetic subtypes.
Question 10: A young male patient presents with dyspnea; auscultation reveals absent breath sounds on the right side, and he has hypotension. What is the immediate next step?
- A. Needle insertion in 2nd intercostal space, midclavicular line (Correct Answer)
- B. Chest X-ray
- C. Intubate the patient
- D. Urgent IV fluid administration
Explanation: ***Needle insertion in 2nd intercostal space, midclavicular line*** - The combination of **dyspnea**, **absent breath sounds** on one side, and **hypotension** points to a **tension pneumothorax**, which is a medical emergency. - **Needle decompression** at the 2nd intercostal space, midclavicular line is the immediate life-saving intervention to relieve the pressure. *Chest X-ray* - While a Chest X-ray would confirm the diagnosis, it would **delay the urgent intervention** required for a tension pneumothorax. - The clinical picture dictates immediate treatment rather than diagnostic confirmation when a life-threatening condition is suspected. *Intubate the patient* - **Intubation** is not the primary treatment for a tension pneumothorax; it addresses airway compromise but not the underlying lung collapse and mediastinal shift. - It might even worsen the condition if **positive pressure ventilation** is applied before decompression. *Urgent IV fluid administration* - **IV fluids** are important for managing hypotension, but they do not address the **mechanical compression** of the heart and good lung by the tension pneumothorax. - Without relieving the tension, fluid administration alone will not improve the patient's cardiorespiratory status.
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