PET/CT Principles and Applications Indian Medical PG Practice Questions and MCQs
Practice Indian Medical PG questions for PET/CT Principles and Applications. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
PET/CT Principles and Applications Indian Medical PG 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
PET/CT Principles and Applications 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.
PET/CT Principles and Applications Indian Medical PG Question 2: 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
PET/CT Principles and Applications 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.
PET/CT Principles and Applications Indian Medical PG 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)
PET/CT Principles and Applications 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.
PET/CT Principles and Applications Indian Medical PG Question 4: Investigation of choice for vascular ring around airway:
- A. PET
- B. Catheter directed angiography
- C. MRI
- D. CT (Correct Answer)
PET/CT Principles and Applications Explanation: ***CT***
- **CT angiography (CTA)** is the **investigation of choice** for diagnosing vascular rings due to its ability to provide detailed anatomical visualization of the great vessels and their relationship to the trachea and esophagus.
- It offers high spatial resolution, allowing precise identification of the type of vascular anomaly, the degree of **airway and esophageal compression**, and guiding surgical planning.
*PET*
- **PET scans** are primarily used for assessing **metabolic activity**, particularly in oncology or to evaluate organ function, and do not provide sufficient anatomical detail for vascular rings.
- While it can detect metabolically active lesions, it is **not suitable** for visualizing the structural abnormalities of blood vessels and their compressive effects on the airway.
*Catheter directed angiography*
- **Catheter-directed angiography** is an **invasive procedure** involving radiation and contrast, primarily used for assessing blood flow dynamics, identifying stenosis, or guiding interventions.
- While it can visualize vessels, CTA is **less invasive**, provides comparable or superior anatomical detail for vascular rings, and is generally preferred for initial diagnosis.
*MRI*
- **MRI** can provide good soft tissue contrast and visualize vascular structures without radiation, but it is often **less readily available** and can be more challenging for pediatric patients due to the need for sedation and longer scan times.
- For comprehensive anatomical detail including bone and calcifications, and in patients who might struggle with breath-holding, **CT angiography** often offers clearer and more consistent images of complex vascular anatomy.
PET/CT Principles and Applications Indian Medical PG Question 5: Investigation of choice for leptomeningeal carcinomatosis:
- A. Gd enhanced MRI (Correct Answer)
- B. CT scan
- C. SPECT
- D. PET
PET/CT Principles and Applications 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.
PET/CT Principles and Applications Indian Medical PG Question 6: 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
PET/CT Principles and Applications 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.
PET/CT Principles and Applications Indian Medical PG Question 7: 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
PET/CT Principles and Applications 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.
PET/CT Principles and Applications Indian Medical PG Question 8: Statement 1 - A 59-year-old patient presents with flaccid bullae. Histopathology shows a suprabasal acantholytic split.
Statement 2 - The row of tombstones appearance is diagnostic of Pemphigus vulgaris.
- A. Statements 1 & 2 are correct, 2 is not explaining 1 (Correct Answer)
- B. Statements 1 and 2 are correct and 2 is the correct explanation for 1
- C. Statements 1 and 2 are incorrect
- D. Statement 1 is incorrect
PET/CT Principles and Applications Explanation: ***Correct: Statements 1 & 2 are correct, 2 is not explaining 1***
**Analysis of Statement 1:**
- A 59-year-old patient with **flaccid bullae** and **suprabasal acantholytic split** on histopathology is the classic presentation of **Pemphigus vulgaris**
- The flaccid (easily ruptured) nature of bullae distinguishes it from tense bullae seen in bullous pemphigoid
- The suprabasal location of the split (just above the basal layer) with acantholysis (loss of cell-to-cell adhesion) is pathognomonic
- **Statement 1 is CORRECT** ✓
**Analysis of Statement 2:**
- The **"row of tombstones" or "tombstone appearance"** is indeed a diagnostic histopathological feature of Pemphigus vulgaris
- This appearance results from basal keratinocytes remaining attached to the basement membrane while suprabasal cells separate due to acantholysis
- The intact basal cells standing upright resemble a row of tombstones
- **Statement 2 is CORRECT** ✓
**Does Statement 2 explain Statement 1?**
- Statement 2 describes a **histopathological appearance** (tombstone pattern) that is a **consequence** of the suprabasal split
- However, it does NOT explain the **underlying cause** of the flaccid bullae or the suprabasal split
- The true explanation involves **IgG autoantibodies against desmoglein 3 (and desmoglein 1)**, which attack intercellular adhesion structures (desmosomes), causing **acantholysis**
- Therefore, **Statement 2 does NOT explain Statement 1** ✗
*Incorrect: Statement 2 is the correct explanation for Statement 1*
- While both statements describe features of Pemphigus vulgaris, the tombstone appearance is a descriptive finding, not an explanatory mechanism
*Incorrect: Statements 1 and 2 are incorrect*
- Both statements are medically accurate descriptions of Pemphigus vulgaris features
*Incorrect: Statement 1 is incorrect*
- Statement 1 correctly describes the cardinal clinical and histopathological features of Pemphigus vulgaris
PET/CT Principles and Applications Indian Medical PG Question 9: Which artificial radioisotopes are used in nuclear medicine?
- A. Radium
- B. Uranium
- C. Plutonium (Correct Answer)
- D. Iridium
PET/CT Principles and Applications Explanation: ### Explanation
**Correct Answer: C. Plutonium**
In nuclear medicine, radioisotopes are categorized as either **natural** (found in nature) or **artificial** (man-made via nuclear reactors or cyclotrons).
**Plutonium (specifically Pu-238)** is an artificial radioisotope produced in nuclear reactors. While not used as a diagnostic tracer or therapeutic agent for internal administration, it has a significant historical and niche clinical application as a power source for **Radioisotope Thermoelectric Generators (RTGs)** in long-lived **cardiac pacemakers**. Its high energy density and long half-life made it ideal for devices requiring decades of operation without battery replacement.
**Analysis of Incorrect Options:**
* **A. Radium:** This is a **naturally occurring** radioactive metal found in uranium ores. While Radium-223 is used in treating bone metastases (Xofigo), the element itself is classified as natural.
* **B. Uranium:** This is a **naturally occurring** heavy metal. It is the raw material used to produce artificial isotopes but is not used directly in clinical nuclear medicine.
* **C. Iridium:** While Iridium-192 is used in Brachytherapy, it is generally classified as a transition metal used in "sealed sources" for radiotherapy rather than being the classic example of an "artificial radioisotope" in the context of general nuclear medicine tracers (like Technetium-99m). However, in the context of this specific question, Plutonium is the most distinct "artificial/man-made" element.
**High-Yield Clinical Pearls for NEET-PG:**
* **Technetium-99m (Tc-99m):** The most commonly used artificial radioisotope in diagnostic nuclear medicine (produced in a Mo-99/Tc-99m generator).
* **Cyclotron-produced isotopes:** Include F-18 (used in PET scans), I-123, and Thallium-201.
* **Reactor-produced isotopes:** Include I-131, Mo-99, and Xenon-133.
* **Therapeutic Alpha Emitter:** Radium-223 is the first alpha-emitting radiopharmaceutical approved to improve survival in castration-resistant prostate cancer with bone metastases.
PET/CT Principles and Applications Indian Medical PG Question 10: Which radiopharmaceutical is used for a liver scan?
- A. Tc-99m sulphur colloid (Correct Answer)
- B. Tc-99m mebrofenin
- C. Tc-99m MIBI
- D. Tc-99m DTPA
PET/CT Principles and Applications Explanation: **Explanation:**
The correct answer is **Tc-99m sulphur colloid**. The underlying principle for a liver-spleen scan is the **phagocytic activity of the Reticuloendothelial System (RES)**. When Tc-99m sulphur colloid is injected intravenously, the particles (sized 0.1–1.0 μm) are cleared from the blood by Kupffer cells in the liver (80–90%), splenic macrophages (5–10%), and bone marrow. This scan is primarily used to evaluate functional liver anatomy and detect "cold nodules" (e.g., abscesses or tumors) or "hot spots" (e.g., Focal Nodular Hyperplasia).
**Analysis of Incorrect Options:**
* **Tc-99m Mebrofenin:** This is an IDA (Iminodiacetic acid) derivative used for **HIDA scans**. It evaluates the **hepatobiliary system** (hepatocyte uptake and biliary excretion) and is the gold standard for diagnosing Acute Cholecystitis.
* **Tc-99m MIBI:** Primarily used for **Myocardial Perfusion Imaging** and Parathyroid imaging. It is taken up by mitochondria.
* **Tc-99m DTPA:** A chelating agent cleared by glomerular filtration, used for **Renal Dynamic Scans** to assess GFR and obstructive uropathy.
**High-Yield Clinical Pearls for NEET-PG:**
1. **Colloid Shift:** In portal hypertension or cirrhosis, there is decreased liver uptake and increased uptake in the spleen and bone marrow.
2. **Focal Nodular Hyperplasia (FNH):** This is the only liver lesion that typically appears "hot" or "isointense" on a sulphur colloid scan due to the presence of Kupffer cells.
3. **Hot Spot on Liver Scan:** Classically seen in **Superior Vena Cava (SVC) Obstruction** (due to collateral flow via the vein of Sappey).
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