Neurological Nuclear Medicine — MCQs
Which imaging modality is most sensitive for detecting early ischemic stroke?
Investigation of choice for multiple sclerosis
Substance used for PET scan is
Which of the following is used in the treatment of well-differentiated thyroid carcinoma?
Which radioisotope is PRIMARILY used for detecting acute myocardial infarction rather than assessing myocardial perfusion?
Non-Iodine containing contrast is
A patient presents with seizures that were controlled with midazolam. Lumbar puncture (LP) revealed no pathology. What is the confirmatory test in the condition shown in the MRI below?
Which one of the following hepatic lesions can be diagnosed with high accuracy by using nuclear imaging?
A dense nephrogram is obtained by
The T1/2 of Iodine-131 is:
Neurological Nuclear Medicine Indian Medical PG Practice Questions and MCQs
Question 1: Which imaging modality is most sensitive for detecting early ischemic stroke?
- A. Ultrasound
- B. PET scan
- C. CT
- D. MRI with DWI (Correct Answer)
Explanation: ***MRI with DWI*** - **Diffusion-weighted imaging (DWI)** within an MRI scan is highly sensitive in detecting **cytotoxic edema** within minutes of **ischemic stroke** onset. This makes it crucial for early diagnosis and treatment decisions. - DWI can identify areas of restricted water diffusion, which is a hallmark of acute cellular injury due to **ischemia**, even before changes are visible on conventional T1 or T2-weighted MRI sequences. *CT* - While frequently used in acute stroke settings, **non-contrast CT** is primarily used to **rule out hemorrhagic stroke** and may only show subtle or no signs of acute ischemia in the first few hours. - Early ischemic changes on CT, often referred to as the **"ischemic penumbra"**, may appear hours after stroke onset, making it less sensitive for very early detection compared to DWI. *Ultrasound* - **Transcranial Doppler (TCD) ultrasound** can evaluate blood flow velocities in intracranial arteries and detect stenoses or occlusions but is not a primary imaging modality for directly visualizing brain parenchymal ischemia. - Cervical ultrasound (e.g., **carotid duplex**) assesses extracranial vessels but cannot directly detect **ischemic changes** within the brain tissue itself. *PET scan* - **PET (Positron Emission Tomography)** can assess brain metabolism and blood flow but is typically not the preferred or most sensitive modality for **early detection of acute ischemic stroke** due to its complexity, cost, and limited availability in emergency settings. - PET is more commonly used in research or for assessing chronic conditions and **metabolic abnormalities**, rather than acute stroke diagnosis.
Question 2: Investigation of choice for multiple sclerosis
- A. CT
- B. MRI (Correct Answer)
- C. USG
- D. PET
Explanation: ***MRI*** - **Magnetic Resonance Imaging (MRI)** is the investigation of choice for **multiple sclerosis** due to its superior ability to visualize **demyelinating plaques** in the brain and spinal cord. - It can detect both **new and old lesions**, crucial for diagnosis and monitoring disease progression, according to the **McDonald criteria**. *CT* - **Computed Tomography (CT) scans** are generally less sensitive than MRI in detecting the subtle **demyelinating lesions** characteristic of multiple sclerosis. - While it can sometimes show larger lesions, it often misses smaller or early-stage plaques, making it less suitable for initial diagnosis. *USG* - **Ultrasound (USG)** is primarily used for visualizing soft tissues and vascular structures, not for detailed imaging of the brain or spinal cord parenchyma. - It has no role in the diagnosis or monitoring of **multiple sclerosis**. *PET* - **Positron Emission Tomography (PET) scans** are used to assess metabolic activity and perfusion, often in oncology or certain neurological disorders like Alzheimer's or Parkinson's disease. - It is not routinely used for the diagnosis of **multiple sclerosis**, as it does not clearly visualize the **demyelinating lesions**.
Question 3: Substance used for PET scan is
- A. Gadolinium
- B. Gastrografin
- C. Iodine
- D. 18F-FDG (Correct Answer)
Explanation: ***18F-FDG*** - **18F-FDG (Fluorodeoxyglucose)** is a glucose analog labeled with a **positron-emitting radioisotope**, fluorine-18 (18F). - It is the most commonly used radiotracer in PET scans, as it accumulates in cells with high metabolic activity, particularly **cancer cells** and activated brain cells. *Gadolinium* - **Gadolinium** is a paramagnetic contrast agent primarily used in **MRI scans** to enhance the visualization of blood vessels and abnormal tissues. - It does not emit positrons and is therefore not suitable for PET imaging. *Gastrografin* - **Gastrografin** is an oral, water-soluble contrast agent containing **iodine**, typically used in **X-rays** and **CT scans** of the gastrointestinal tract. - It is not a radioactive tracer and has no application in PET imaging. *Iodine* - **Iodine** in various forms can be used as a contrast agent in **X-rays** and **CT scans**, or as a radioactive isotope (e.g., **I-131**) for **thyroid imaging** and treatment. - While some isotopes of iodine are radioactive, they are not typically used for PET imaging, which relies on positron emission.
Question 4: Which of the following is used in the treatment of well-differentiated thyroid carcinoma?
- A. I131 (Correct Answer)
- B. 99m Tc
- C. 32p
- D. MIBG
Explanation: ***I131*** - **Radioactive iodine (I131)** is specifically absorbed by **well-differentiated thyroid cancer cells** because these cells retain the ability to uptake iodine, unlike other types of cancer cells. - Used for **ablating residual thyroid tissue** after surgery and for treating **metastatic well-differentiated thyroid carcinoma** [1]. *99m Tc* - **Technetium-99m (99m Tc)** is primarily used for **diagnostic imaging** (e.g., thyroid scans, bone scans), not for therapeutic treatment of thyroid cancer. - It has a short half-life and emits gamma rays, making it suitable for imaging but generally not for delivering sustained radiation for therapeutic effect. *32p* - **Phosphorus-32 (32p)** is a beta-emitting radionuclide used in the treatment of certain hematological malignancies, such as **polycythemia vera**, and for palliative treatment of bone metastases. - It is not selectively taken up by thyroid cancer cells and therefore is not used in the treatment of thyroid carcinoma. *MIBG* - **Metaiodobenzylguanidine (MIBG)**, often labeled with I123 (diagnostic) or I131 (therapeutic), is used in the diagnosis and treatment of **neuroendocrine tumors** like **pheochromocytoma** and **neuroblastoma**. - Its uptake mechanism targets cells of neuroectodermal origin, which is distinct from the iodine uptake mechanism of thyroid cells.
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: Non-Iodine containing contrast is
- A. Gd DTPA (Correct Answer)
- B. Diatrizoate
- C. Visipaque
- D. Iohexol
Explanation: ***Gd DTPA*** - **Gadolinium-DTPA** (diethylenetriamine pentaacetic acid) is a **gadolinium-based contrast agent** used in MRI, which does not contain iodine. - It enhances images by shortening the **T1 relaxation time** of protons in tissues. *Diatrizoate* - **Diatrizoate** is an **iodinated contrast medium** commonly used in radiography and CT scans. - It contains iodine, which opacifies structures by **attenuating X-rays**. *Visipaque* - **Visipaque** (Iodixanol) is an **iodinated, non-ionic, dimeric contrast medium** with iso-osmolar properties. - It explicitly contains iodine as the contrast-enhancing element. *Iohexol* - **Iohexol** is another widely used **iodinated, non-ionic contrast agent** for various radiological procedures. - Its mechanism of action relies on the presence of iodine atoms to block X-rays.
Question 7: A patient presents with seizures that were controlled with midazolam. Lumbar puncture (LP) revealed no pathology. What is the confirmatory test in the condition shown in the MRI below?
- A. PET scan
- B. CBNAAT
- C. MR spectroscopy (Correct Answer)
- D. MRI serial scan
Explanation: ***MR spectroscopy*** - The MRI shows multiple **ring-enhancing lesions**, which, combined with the history of seizures and normal LP, strongly suggests **neurocysticercosis**. - **MR spectroscopy** can detect the specific biochemical markers (e.g., lactate, succinate) within the cyst, which are indicative of the parasitic infection, and can help differentiate it from other lesions like tumors or abscesses. *PET scan* - A **PET scan** primarily assesses metabolic activity and is more commonly used in the evaluation of tumors or neurodegenerative diseases. - It is generally not the primary or confirmatory test for neurocysticercosis, as it does not directly visualize the parasite or its specific biochemical markers. *CBNAAT* - **CBNAAT (Cartridge-Based Nucleic Acid Amplification Test)** is a rapid molecular test primarily used for the diagnosis of **tuberculosis**, not neurocysticercosis. - While tuberculosis can cause CNS lesions, the clinical and imaging presentation (multiple ring-enhancing lesions) is more suggestive of neurocysticercosis, and CBNAAT would not confirm this diagnosis. *MRI serial scan* - **Serial MRI scans** are useful for monitoring the progression or resolution of lesions over time, especially in response to treatment. - However, a serial scan is not a "confirmatory test" for the initial diagnosis; it provides prognostic or follow-up information rather than confirming the etiology.
Question 8: Which one of the following hepatic lesions can be diagnosed with high accuracy by using nuclear imaging?
- A. Cholangiocarcinoma
- B. Hepatocellular carcinoma
- C. Hepatic adenoma
- D. Focal nodular hyperplasia (Correct Answer)
Explanation: ***Focal nodular hyperplasia*** - **Focal nodular hyperplasia** (FNH) contains functioning Kupffer cells, which take up **Technetium-99m sulfur colloid** used in nuclear imaging. - FNH typically shows **normal or increased uptake** on sulfur colloid scans, which distinguishes it from other hepatic lesions with high accuracy. - The presence of functional **Kupffer cells and hepatocytes** allows FNH to be diagnosed with high specificity using nuclear imaging. *Cholangiocarcinoma* - **Cholangiocarcinoma** is a malignant tumor of the bile ducts and does not contain Kupffer cells. - It appears as a **photopenic defect** (decreased or absent uptake) on nuclear scans due to its lack of functional liver cells. *Hepatocellular carcinoma* - **Hepatocellular carcinoma** (HCC) is a primary liver malignancy that typically lacks functional Kupffer cells. - HCC usually shows **decreased or absent uptake** on **Technetium-99m sulfur colloid scans**, appearing as a cold lesion. *Hepatic adenoma* - A **hepatic adenoma** is a benign liver tumor that lacks Kupffer cells and thus does not take up the tracer in nuclear imaging. - Adenomas appear as **photopenic defects** on sulfur colloid scans and are better characterized by their enhancement patterns on MRI or CT.
Question 9: A dense nephrogram is obtained by
- A. Dehydrating the patient
- B. Rapid (Bolus) injection of dye (Correct Answer)
- C. Using non ionic media
- D. Increasing the dose of contrast media
Explanation: ***Rapid (Bolus) injection of dye*** - A **rapid bolus injection** of contrast material ensures a high concentration reaches the kidneys simultaneously, leading to optimal opacification and a **dense nephrogram**. - This method allows for the collection of a **large bolus of undiluted contrast** in the renal vessels and parenchyma, improving visualization of the renal parenchyma during the nephrographic phase. - The dense nephrogram phase occurs when contrast is within the renal tubules and interstitium, producing uniform opacification. *Dehydrating the patient* - **Dehydration** would concentrate the urine in the collecting system, but it does not directly contribute to the **dense nephrogram** appearance of the renal parenchyma. - While dehydration may improve visualization of the pelvicalyceal system on delayed images, it can increase the risk of **contrast-induced nephropathy**. *Using non ionic media* - **Non-ionic contrast media** are associated with fewer adverse reactions and greater patient safety compared to ionic media due to their lower osmolality. - However, the type of contrast media (ionic vs. non-ionic) does not primarily determine the **density of the nephrogram** itself, but rather patient tolerability and safety profile. *Increasing the dose of contrast media* - While increasing the dose might provide more contrast overall, it does not guarantee a **dense nephrogram**, which requires a high concentration of contrast to be present acutely in the renal parenchyma. - A dense nephrogram is better achieved by **rapid bolus injection technique** rather than simply increasing the total dose. - Excessive contrast increases the risk of **adverse reactions** and contrast-induced nephropathy without necessarily improving nephrographic density proportionally.
Question 10: The T1/2 of Iodine-131 is:
- A. 8 days (Correct Answer)
- B. 12 hours
- C. 13 days
- D. 2 days
Explanation: ***8 days*** - Iodine-131 (¹³¹I) has a relatively short half-life of **8.02 days**, making it suitable for diagnostic and therapeutic uses with a controlled radiation exposure window. - This **half-life** allows for effective patient monitoring and targeted treatment while minimizing long-term radiation risks. *12 hours* - This is an incorrect value; 12 hours is a significantly shorter half-life than that of **Iodine-131**. - Other isotopes, such as **Iodine-123**, have a half-life of 13.2 hours, which is closer to this value but still distinct from **Iodine-131**. *13 days* - This value is close but incorrect; the correct half-life for **Iodine-131** is approximately **8 days**. - A 13-day half-life would imply a longer period of radioactivity, altering its clinical applications. *2 days* - This is an incorrect half-life for **Iodine-131**, which has a significantly longer half-life of approximately 8 days. - A 2-day half-life would mean the isotope decays much faster than it actually does.
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