Molecular Imaging in Oncology — MCQs
Which radiopharmaceutical is commonly used in positron emission tomography (PET) imaging?
Most sensitive modality for detecting bone metastases
99m Technetium labeled RBC scintigraphy is PRIMARILY used in the diagnosis of
Which of the following investigations work on the same principle?
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?
Investigation of choice for leptomeningeal carcinomatosis:
Which of the following is used in the treatment of well-differentiated thyroid carcinoma?
Distant bone metastases can be best detected by which of the following imaging techniques?
Which radioisotope is PRIMARILY used for detecting acute myocardial infarction rather than assessing myocardial perfusion?
What is the best investigation for diagnosis and staging of renal cell carcinoma with thrombus extending into the IVC?
Molecular Imaging in Oncology Indian Medical PG Practice Questions and MCQs
Question 1: Which radiopharmaceutical is commonly used in positron emission tomography (PET) imaging?
- A. 18F-FDG (Fluorodeoxyglucose) (Correct Answer)
- B. Oxygen-15 (used in specific PET scans)
- C. Carbon-11 acetate
- D. Nitrogen-13 ammonia
Explanation: ***18F-FDG (Fluorodeoxyglucose)*** - **18F-FDG** is the most widely used radiopharmaceutical in PET imaging, particularly for **oncology**, as it's a glucose analog that accumulates in metabolically active cells. - Its widespread use is due to its favorable physical properties for PET and its ability to reflect **tumor metabolism**. *Carbon-11 acetate* - **Carbon-11 acetate** is used in specific PET applications, primarily for **cardiac imaging** to assess myocardial oxidative metabolism. - It has a very short half-life (around 20 minutes) which limits its availability to centers with on-site cyclotrons. *Oxygen-15 (used in specific PET scans)* - **Oxygen-15** (e.g., O-15 water) is used in highly specialized PET scans for measuring **blood flow** and oxygen metabolism, especially in brain studies. - Its extremely short half-life (approximately 2 minutes) necessitates an on-site cyclotron and immediate use. *Nitrogen-13 ammonia* - **Nitrogen-13 ammonia** is a common radiopharmaceutical for **myocardial perfusion imaging** with PET, reflecting regional blood flow to the heart. - Like other C-11 and O-15 tracers, its short half-life (about 10 minutes) requires proximity to a cyclotron facility.
Question 2: Most sensitive modality for detecting bone metastases
- A. Bone scan
- B. PET-CT
- C. Plain radiograph
- D. MRI (Correct Answer)
Explanation: ***MRI*** - **MRI**, especially **whole-body MRI (WB-MRI)**, has the **highest sensitivity (90-100%)** for detecting bone metastases among all imaging modalities. - It directly visualizes **bone marrow changes** before cortical bone destruction occurs, allowing for earlier detection than other modalities. - Excellent for detecting both **lytic and sclerotic lesions** and provides superior soft tissue contrast for assessing marrow involvement. - Particularly sensitive for **spine and pelvic metastases**, and whole-body protocols enable comprehensive skeletal assessment. *PET-CT* - **PET-CT with 18F-FDG** is highly sensitive for detecting metabolically active lesions and provides whole-body assessment with both metabolic and anatomical information. - However, its sensitivity varies by primary tumor type and is **limited for sclerotic/osteoblastic metastases** which may not be FDG-avid. - While excellent for many malignancies, it has **lower sensitivity than MRI** for pure bone metastases detection, particularly in low-metabolism lesions. *Bone scan* - **Bone scan (Tc-99m MDP)** detects increased osteoblastic activity and has been the traditional screening tool with good sensitivity (62-89%). - Effective for detecting osteoblastic lesions and provides whole-body skeletal survey at relatively low cost. - However, it is **less sensitive than MRI** and can miss purely lytic metastases or early marrow involvement before osteoblastic response occurs. *Plain radiograph* - **Plain radiographs** require significant bone mineral loss (30-50%) to visualize lesions, making them the **least sensitive modality** for bone metastases. - Useful for assessing established lesions and complications like pathological fractures, but inadequate for screening or early detection.
Question 3: 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 4: Which of the following investigations work on the same principle?
- A. MRI and PET Scan
- B. CT and MRI
- C. CT and X-ray (Correct Answer)
- D. USG and HIDA Scan
Explanation: ***CT and X-ray*** - Both **Computed Tomography (CT)** and **X-ray** imaging utilize **ionizing radiation** to generate images of the body's internal structures. - They work by passing X-ray beams through the patient, with different tissues absorbing the radiation to varying degrees, which is then detected to create an image. *MRI and PET Scan* - **Magnetic Resonance Imaging (MRI)** uses **strong magnetic fields and radio waves** to create detailed images of soft tissues, based on water content. - **Positron Emission Tomography (PET) scans** use **radioactive tracers** to visualize metabolic activity and blood flow, detecting gamma rays emitted from the patient. *CT and MRI* - **CT scans** use **ionizing radiation** (X-rays) to produce cross-sectional images. - **MRI scans** use **magnetic fields and radio waves** and do not involve ionizing radiation. *USG and HIDA Scan* - **Ultrasound (USG)** uses **high-frequency sound waves** to create real-time images of organs and structures. - **Hepatobiliary Iminodiacetic Acid (HIDA) scans** are a type of nuclear medicine study that uses a **radioactive tracer** to evaluate liver and gallbladder function.
Question 5: 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 6: Investigation of choice for leptomeningeal carcinomatosis:
- A. Gd enhanced MRI (Correct Answer)
- B. CT scan
- C. SPECT
- D. PET
Explanation: ***Gd enhanced MRI*** - **Gadolinium-enhanced MRI** is the investigation of choice for **leptomeningeal carcinomatosis** as it can visualize the subtle nodular or linear enhancement along the leptomeninges, indicating tumor dissemination. - It offers superior **soft tissue contrast** and spatial resolution compared to CT, enabling detection of small lesions and accurate mapping of disease extent. *CT scan* - A **CT scan** has limited sensitivity for detecting leptomeningeal involvement due to poor contrast resolution of soft tissues and the dura/arachnoid spaces. - It might show hydrocephalus or large tumor deposits, but subtle leptomeningeal enhancement is often missed. *SPECT* - **Single photon emission computed tomography (SPECT)** is primarily used for functional imaging and is not the investigation of choice for anatomical visualization of leptomeningeal carcinomatosis. - Its resolution is too low to detect the fine structural changes associated with leptomeningeal spread. *PET* - **Positron emission tomography (PET)**, often combined with CT, identifies metabolically active tumor cells and can detect diffuse metastatic disease. - While useful for overall cancer staging and identifying primary lesions, it is less effective than gadolinium-enhanced MRI for directly visualizing the morphology and enhancement patterns of leptomeningeal carcinomatosis due to limited spatial resolution in the CSF spaces.
Question 7: 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 8: Distant bone metastases can be best detected by which of the following imaging techniques?
- A. Bone scan (Correct Answer)
- B. CT
- C. Intravenous venogram
- D. PET scan
Explanation: ***Bone scan*** - A **bone scan** is highly sensitive for detecting **osteoblastic activity**, which is characteristic of most bone metastases. - It involves injecting a **radioactive tracer** (usually technetium-99m methylene diphosphonate) that accumulates in areas of increased bone turnover, making it excellent for surveying the entire skeletal system. *PET scan* - While a **PET scan** (Positron Emission Tomography) can detect bone metastases, especially with **FDG-PET**, it is generally more expensive and may not be as sensitive for purely **osteoblastic lesions** as a bone scan. - Its primary role is often in assessing metabolic activity of the primary tumor and other distant soft tissue metastases. *CT* - **CT scans** (Computed Tomography) are excellent for assessing bone anatomy, cortical destruction, and soft tissue involvement, but they are generally less sensitive for detecting early or widespread **osseous metastatic disease** compared to a bone scan. - CT provides detailed anatomical information but may miss early **marrow involvement** that alters bone metabolism. *Intravenous venogram* - An **intravenous venogram** is an imaging technique used to visualize veins, primarily for detecting **thrombosis** or venous insufficiency. - It has no role in the detection of **bone metastases**, as it provides no information about bone structure or metabolic activity.
Question 9: 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 10: What is the best investigation for diagnosis and staging of renal cell carcinoma with thrombus extending into the IVC?
- A. CT scan (Correct Answer)
- B. Angiography
- C. Colour doppler imaging
- D. IVP
Explanation: ***CT scan*** - **CT scan** with contrast is the gold standard for diagnosing renal cell carcinoma and evaluating the extent of tumor thrombus into the **IVC**. - It provides detailed anatomical information on the tumor, staging, and involvement of adjacent structures. *Angiography* - **Angiography** is an invasive procedure primarily used for mapping the vascular supply of the tumor preoperatively or for embolization, not as a primary diagnostic tool. - It carries risks associated with contrast agents and catheterization and provides less comprehensive detail on tumor extension compared to CT. *Colour doppler imaging* - While useful for detecting blood flow and confirming the presence of a thrombus, **color Doppler imaging** (ultrasound) has limitations in accurately assessing the cranial extent of an IVC thrombus. - Its diagnostic accuracy is highly operator-dependent and less reliable for deep structures like the IVC compared to CT. *IVP* - **Intravenous Pyelogram (IVP)** assesses the urinary tract's structure and function but has limited utility in detecting soft tissue masses like renal cell carcinoma or IVC thrombus. - It involves radiation exposure and contrast material, and has largely been replaced by more advanced imaging techniques like CT and MRI for renal masses.
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