Molecular Imaging in Inflammation and Infection — MCQs
Which radiopharmaceutical is commonly used in positron emission tomography (PET) imaging?
A child presents with painful limp and restricted hip rotation. ESR and CRP are elevated. Initial plain radiograph is normal. What is the next best imaging study?
What is the best imaging modality for detecting early osteomyelitis?
Isotope selectively concentrated in abscess cavities:
Tc-labeled RBCs are used for all except:
Which one of the following hepatic lesions can be diagnosed with high accuracy by using nuclear imaging?
Apple jelly nodule on diascopy is a feature of:
Which one of the following regarding Pancreatic effusion is correct?
A patient with a history of chronic ear infection now presents with manifestations, including headache and vomiting. A CT brain image is shown. What is the most probable diagnosis?
In which condition is the Prehn sign typically positive?
Molecular Imaging in Inflammation and Infection 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: A child presents with painful limp and restricted hip rotation. ESR and CRP are elevated. Initial plain radiograph is normal. What is the next best imaging study?
- A. CT Scan
- B. MRI with contrast (Correct Answer)
- C. Bone Scan
- D. Plain Radiograph
Explanation: ***MRI with contrast*** - An **MRI with contrast** is the most sensitive and specific imaging modality for detecting early changes in **osteomyelitis** or **septic arthritis**, which are serious conditions given the child's symptoms and elevated inflammatory markers. - It can visualize soft tissue and bone marrow edema, joint effusions, and abscesses, guiding immediate treatment. *CT Scan* - While useful for bony detail, a CT scan is **less sensitive than MRI** for detecting early bone marrow changes or soft tissue inflammation in the hip joint. - It also involves **radiation exposure**, which should be limited in children when other effective modalities are available. *Bone Scan* - A bone scan using **technetium-99m** is sensitive for detecting increased bone turnover, but it is **not specific for infection** and cannot differentiate between inflammatory processes, tumors, or fractures. - It provides less anatomical detail compared to MRI, making precise localization of an infection more challenging. *Plain Radiograph* - Plain radiographs are typically the **initial imaging study** for orthopedic complaints but are often **normal in early stages** of septic arthritis or osteomyelitis. - Significant radiographic changes, such as bone erosion or joint space widening, usually appear much later in the disease process.
Question 3: What is the best imaging modality for detecting early osteomyelitis?
- A. CT scan
- B. X-ray
- C. MRI (Correct Answer)
- D. Bone scintigraphy
Explanation: ***MRI*** - **Magnetic Resonance Imaging (MRI)** is considered the **gold standard** for detecting early osteomyelitis due to its excellent soft tissue contrast and ability to visualize **bone marrow edema**, which is an early sign of infection. - It can identify changes within **3-5 days** of infection onset, much earlier than other modalities. *CT scan* - While useful for showing **bone destruction**, cortical integrity, and sequestra, **CT scans** are less sensitive than MRI for detecting early marrow edema. - Its ability to diagnose osteomyelitis is usually delayed until significant **bony changes** have occurred, typically around 1-2 weeks. *X-ray* - **Plain radiographs** are often the initial imaging study but are **insensitive** for early osteomyelitis, showing changes only after 10-14 days or more. - Early findings on X-rays can be subtle, such as **periosteal elevation** or **soft tissue swelling**, but frank bone destruction is a late finding. *Bone scintigraphy* - **Bone scintigraphy** (e.g., technetium-99m) is sensitive for detecting increased bone turnover associated with infection but lacks **specificity**, as it can be positive in other conditions like trauma or tumors. - While it can detect changes earlier than X-rays, typically within 2-3 days, it cannot clearly differentiate infection from other processes, and its spatial resolution is poor compared to MRI.
Question 4: Isotope selectively concentrated in abscess cavities:
- A. Technetium
- B. Gallium (Correct Answer)
- C. Chromium
- D. Selenium
Explanation: ***Gallium*** - **Gallium-67 citrate** is incorporated into lactoferrin and transferrin, proteins that are drawn to inflammatory sites, including abscesses. - Its accumulation reflects the cellular activity and **increased vascular permeability** at the site of infection. *Technetium* - **Technetium-99m** is widely used in many different imaging studies, but it is not specifically concentrated in abscess cavities. - While it can be used to label white blood cells for infection imaging, it's not the isotope itself that is selectively concentrated in an abscess. *Chromium* - **Chromium-51** is primarily used for imaging related to red blood cell survival or gastrointestinal bleeding. - It does not have a mechanism for selective accumulation in abscess cavities. *Selenium* - **Selenium-75** is used in imaging, primarily for pancreatic or adrenal gland studies, and for assessing protein-losing enteropathy. - It does not show selective concentration in abscess cavities.
Question 5: 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 6: 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 7: Apple jelly nodule on diascopy is a feature of:
- A. Aspergillosis
- B. Lupus vulgaris (Correct Answer)
- C. Erysipelas
- D. Rhinoscleroma
Explanation: ***Lupus vulgaris*** - An **apple jelly nodule** on diascopy is a classic clinical sign of **lupus vulgaris**, a severe form of cutaneous tuberculosis. - Diascopy reveals the characteristic yellowish-brown discoloration due to **tuberculous granulomas** in the dermis. *Aspergillosis* - This is a fungal infection that typically affects the **respiratory tract** and less commonly the skin, especially in immunocompromised individuals. - Skin lesions in aspergillosis are usually **necrotic ulcers** or plaques, not apple jelly nodules on diascopy. *Erysipelas* - This is a **superficial bacterial infection** of the skin and subcutaneous tissue, typically caused by *Streptococcus pyogenes*. - It presents as a bright red, swollen, raised lesion with a **distinct border**, and does not produce apple jelly nodules. *Rhinoscleroma* - This is a chronic, progressive granulomatous disease affecting the **upper respiratory tract**, caused by *Klebsiella rhinoscleromatis*. - It leads to **hard, nodular masses** in the nose and pharynx, often described as ligneous, but does not present as apple jelly nodules on diascopy.
Question 8: Which one of the following regarding Pancreatic effusion is correct?
- A. Pancreatic stenting is to be done
- B. Free fluid collection in Pleural cavity
- C. Percutaneous drainage under image guidance is indicated for symptomatic effusions (Correct Answer)
- D. Never associated with abdominal collection
Explanation: ***Percutaneous drainage under image guidance is indicated for symptomatic effusions*** - For **symptomatic pancreatic effusions**, particularly those causing pain, infection, or organ compression, percutaneous drainage offers an effective and less invasive management option. - This procedure is typically performed under **ultrasound or CT guidance** to ensure accurate placement of the drainage catheter, minimizing complications. *Pancreatic stenting is to be done* - **Pancreatic stenting** is primarily indicated for managing pancreatic duct strictures or leaks, often in the context of chronic pancreatitis or postsurgical complications. - It is not a direct treatment for a pancreatic effusion itself, which is a collection of fluid outside the ductal system. *Free fluid collection in Pleural cavity* - Pancreatic effusion refers to the **leakage of pancreatic fluid** into the abdominal cavity, typically surrounding the pancreas or in the peritoneum. - While pancreatic diseases can sometimes lead to **pleural effusions** (fluid in the chest cavity) due to translocation of fluid through the diaphragm, a pancreatic effusion itself is defined as an abdominal collection. *Never associated with abdominal collection* - This statement is incorrect as a **pancreatic effusion is by definition an abdominal collection** of fluid originating from the pancreas. - These collections can arise from disruptions in the pancreatic duct or parenchyma, leading to the accumulation of pancreatic enzymes, fluid, and debris in the peripancreatic region or elsewhere within the abdomen.
Question 9: A patient with a history of chronic ear infection now presents with manifestations, including headache and vomiting. A CT brain image is shown. What is the most probable diagnosis?
- A. Meningitis
- B. Extradural Abscess
- C. Cerebral Abscess
- D. Temporal lobe Abscess (Correct Answer)
Explanation: ***Temporal lobe Abscess*** - The CT scan shows a **ring-enhancing lesion** with significant surrounding edema, which is characteristic of a **brain abscess**. - Given the history of a **chronic ear infection**, the temporal lobe is a common site for bacterial spread from the mastoid air cells or middle ear. *Meningitis* - Meningitis involves inflammation of the **meninges** and typically presents with diffuse changes on imaging, such as sulcal effacement or leptomeningeal enhancement, rather than a focal, encapsulated lesion. - While it can cause headache and vomiting, the CT image does not show findings typical of meningitis. *Extradural Abscess* - An extradural (or epidural) abscess is located **between the dura mater and the skull bone**. - It would typically appear as a collection outside the brain parenchyma, potentially causing mass effect but distinct from an intraparenchymal lesion seen in the image. *Cerebral Abscess* - The image does show a **cerebral abscess**, but this option is less specific than "Temporal lobe abscess." - The question asks for the **most probable diagnosis**, and combining the imaging findings with the patient's history of ear infection points to a specific location within the cerebrum.
Question 10: In which condition is the Prehn sign typically positive?
- A. Acute epididymitis (Correct Answer)
- B. Chronic epididymitis
- C. Testicular torsion
- D. Acute scrotal pain due to other causes
Explanation: ***Acute epididymitis*** - **Prehn sign** is positive when lifting the scrotal sac alleviates pain, as it reduces pressure on the inflamed epididymis. - This sign is commonly used to differentiate **epididymitis** from **testicular torsion**, where pain typically worsens or remains unchanged with elevation. *Chronic epididymitis* - While potentially painful, **chronic epididymitis** usually presents with persistent, dull pain that is less likely to be acutely relieved by scrotal elevation. - The **Prehn sign** is primarily a diagnostic tool for **acute inflammatory conditions** of the epididymis. *Testicular torsion* - In **testicular torsion**, the pain is often sudden, severe, and typically **not relieved** by elevating the testicle; in fact, it may worsen. - This condition is a **surgical emergency** where blood flow to the testicle is compromised. *Acute scrotal pain due to other causes* - Other causes of **acute scrotal pain**, such as **trauma** or **incarcerated hernias**, generally do not exhibit a positive Prehn sign. - The **Prehn sign** is quite specific to the **inflammatory process** of epididymitis affecting pain perception.
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