NEET-PG 2012 — Radiology
29 Previous Year Questions with Answers & Explanations
Half-life of iodine-131 is
Central stellate scar is typically associated with which of the following conditions?
What is the primary mechanism of heat loss in a modern X-ray tube?
What is the recommended thickness of lead apron to prevent radiation exposure?
Which chamber enlargement shows a double right heart border with a wide subcarinal angle?
Investigation of choice for multiple sclerosis
Which of the following techniques uses piezoelectric crystals?
Which of the following conditions characteristically causes bilateral hypertranslucency of lung fields on chest X-ray?
Which of the following conditions is least likely to cause posterior scalloping of the vertebrae?
The most appropriate first-line imaging modality to detect adrenal metastasis due to bronchogenic carcinoma is:
NEET-PG 2012 - Radiology NEET-PG Practice Questions and MCQs
Question 1: Half-life of iodine-131 is
- A. 8 days (Correct Answer)
- B. 8 hours
- C. 8 weeks
- D. 8 months
Explanation: ***8 days*** - The half-life of **iodine-131** is approximately 8.02 days, which makes it suitable for both diagnostic imaging and therapeutic applications in thyroid conditions. - This specific half-life allows sufficient time for the isotope to localize in the thyroid gland and deliver a therapeutic dose, while also ensuring it clears from the body relatively quickly to minimize long-term radiation exposure. *8 hours* - A half-life of 8 hours would be too short for many therapeutic applications of iodine-131, as it would decay too rapidly to deliver an effective dose to the thyroid. - Isotopes with such short half-lives are typically used for diagnostic imaging where rapid clearance and minimal patient exposure are paramount, such as **technetium-99m**. *8 weeks* - A half-life of 8 weeks would be excessively long for clinical use of iodine-131, leading to prolonged radiation exposure for the patient. - Such long half-lives increase the risk of adverse effects from cumulative radiation, making it unsuitable for routine diagnostic or therapeutic procedures. *8 months* - A half-life of 8 months is impractically long for any medical application requiring regular administration, as it would lead to very high and persistent radiation doses. - This duration would result in significant and unacceptable long-term radiation hazards, making its use unfeasible for imaging or therapy.
Question 2: Central stellate scar is typically associated with which of the following conditions?
- A. Focal nodular hyperplasia (FNH) (Correct Answer)
- B. Hepatic adenoma
- C. Chronic liver disease
- D. Hepatocellular carcinoma
Explanation: ***Focal nodular hyperplasia (FNH)*** - FNH is a benign liver lesion characterized by a central fibrous scar with radiating septa, giving it the characteristic appearance of a **central stellate scar** on imaging. - This scar contains **malformed blood vessels** and bile ductules, which are key diagnostic features. - On dynamic imaging, FNH typically shows **spoke-wheel arterial enhancement** pattern and the central scar shows **delayed enhancement** on MRI. *Hepatic adenoma* - Hepatic adenomas are typically composed of sheets of **hepatocytes** with absent portal triads and are usually **homogeneous** on imaging without a central scar. - They are associated with **oral contraceptive use** and have a risk of hemorrhage and malignant transformation. *Chronic liver disease* - Chronic liver disease, such as **cirrhosis**, is characterized by widespread **fibrosis** and **nodule formation** throughout the liver, but it does not typically present with a solitary lesion with a central stellate scar. - The scarring in cirrhosis is diffuse and leads to architectural distortion, rather than a focal central scar. *Hepatocellular carcinoma* - Hepatocellular carcinoma (HCC) typically presents as a **vascular mass** that may or may not be solitary, usually arising in the context of chronic liver disease or cirrhosis. - Although the **fibrolamellar variant of HCC** (seen in younger patients without cirrhosis) can show a central scar, this is less common and the scar typically shows **hypointensity on T2-weighted imaging**, unlike FNH where the scar is **hyperintense on T2**. - Typical HCC does not show a distinct central stellate scar as a characteristic feature.
Question 3: What is the primary mechanism of heat loss in a modern X-ray tube?
- A. Radiation (Correct Answer)
- B. Evaporation
- C. Conduction
- D. Convection
Explanation: ***Radiation*** - The **primary mechanism** of heat loss in a modern X-ray tube is **radiation** (infrared emission). - The anode surface reaches extremely high temperatures (>1000°C) during X-ray production, causing it to emit significant **infrared radiation**. - Modern X-ray tubes use **high-emissivity materials** (tungsten-rhenium alloys) on the anode to maximize radiative heat transfer. - Since the tube operates in a **vacuum**, radiation is the only effective mechanism for heat dissipation from the anode itself. *Evaporation* - **Evaporation** requires a liquid-to-gas phase change, which is not applicable in the solid-state environment of an X-ray tube anode. - The **vacuum environment** inside the tube prevents any evaporative cooling. - This mechanism is irrelevant for heat loss from the anode. *Conduction* - **Conduction** does transfer heat from the focal spot through the anode body to the rotor bearings. - However, this is heat transfer *within* the tube components, not the primary mechanism for heat loss *from the tube*. - Heat conducted through components must ultimately be dissipated by **radiation** (from anode) or **convection** (from housing via cooling oil). *Convection* - **Convection** requires fluid movement (liquid or gas), which cannot occur in the **vacuum** inside the X-ray tube envelope. - While cooling oil outside the tube uses convection to remove heat from the housing, this is secondary heat removal, not the primary mechanism of heat loss from the anode. - The anode loses heat primarily via **radiation** first, then that heat may be further managed by convection in the cooling system.
Question 4: What is the recommended thickness of lead apron to prevent radiation exposure?
- A. 1 mm
- B. 3 mm
- C. 7 mm
- D. 0.5 mm (Correct Answer)
Explanation: ***0.5 mm*** - A **0.5 mm lead equivalent apron** is the universally accepted standard for protecting against primary beam radiation in most medical imaging procedures, including fluoroscopy and interventional radiology. - This thickness provides adequate **radiation attenuation** to significantly reduce dose to the wearer while maintaining reasonable comfort and mobility. *1 mm* - While offering increased attenuation, a **1 mm lead equivalent apron** is considerably heavier and less practical for routine use, leading to greater physical strain without a proportional increase in necessary protection for most procedures. - The additional weight and bulk can hinder movement and reduce compliance, especially during long procedures. *3 mm* - A **3 mm lead equivalent apron** would be excessively heavy and restrictive for medical personnel, making it highly impractical for general use in radiology departments. - The degree of protection offered by such an apron far exceeds the requirements for standard diagnostic and interventional procedures, incurring unnecessary physical burden. *7 mm* - A **7 mm lead equivalent apron** is an extreme thickness that would be entirely unfeasible for an individual to wear due to its immense weight and stiffness. - This level of shielding is typically found in fixed architectural barriers for radiation protection, such as walls of an X-ray room, not in personal protective equipment.
Question 5: Which chamber enlargement shows a double right heart border with a wide subcarinal angle?
- A. Left atrium (Correct Answer)
- B. Left ventricle
- C. Right atrium
- D. Right ventricle
Explanation: ***Left atrium*** - A **double right heart border** on a chest X-ray is a classic sign of **left atrial enlargement**, as the enlarged left atrium bulges into the right atrial silhouette. - The **wide subcarinal angle** (angle between the mainstem bronchi) also indicates left atrial enlargement, as the expanding left atrium pushes the bronchi apart. *Left ventricle* - **Left ventricular enlargement** primarily manifests as a **downward and leftward displacement of the apex** and increased cardiac silhouette on the left. - It does not typically cause a double right heart border or widening of the subcarinal angle. *Right atrium* - **Right atrial enlargement** usually presents as a **prominent right heart border** that extends further to the right than normal. - It does not result in a double right heart border or affect the subcarinal angle. *Right ventricle* - **Right ventricular enlargement** leads to an **anterior bowing of the sternum** (in severe cases) and an upward and leftward displacement of the cardiac apex. - It pushes the left ventricle posteriorly and does not produce a double right heart border or a wide subcarinal angle.
Question 6: 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 7: Which of the following techniques uses piezoelectric crystals?
- A. Ultrasonography (Correct Answer)
- B. NMR imaging
- C. X-ray diffraction
- D. Xeroradiography
Explanation: ***Ultrasonography*** - **Piezoelectric crystals** are the core component of **ultrasound transducers**, which generate and detect ultrasonic waves. - These crystals convert electrical energy into mechanical vibrations (sound waves) and vice-versa, allowing for the creation of images. *NMR imaging* - **NMR imaging** (Nuclear Magnetic Resonance, now commonly known as **MRI**) uses strong magnetic fields and **radiofrequency pulses** to generate images. - It relies on the magnetic properties of atomic nuclei, particularly hydrogen, rather than piezoelectric effects. *X-ray diffraction* - **X-ray diffraction** is a technique used to study the atomic and molecular structure of materials, and it involves the interaction of **X-rays** with the electron clouds of atoms. - It does not involve piezoelectric crystals; instead, it uses an X-ray source and a detector to measure diffracted X-rays. *Xeroradiography* - **Xeroradiography** is an older imaging technique that used **xerographic plates** coated with a photoconductive material (like selenium) to capture X-ray images. - It relies on electrostatic charges and dry development rather than piezoelectric crystals to produce images.
Question 8: Which of the following conditions characteristically causes bilateral hypertranslucency of lung fields on chest X-ray?
- A. Mcleod syndrome
- B. Poland syndrome
- C. Emphysema (Correct Answer)
- D. Pneumothorax
Explanation: ***Correct: Emphysema*** - **Emphysema** causes destruction of alveolar walls, leading to enlarged air spaces and **air trapping**, making both lungs appear hypertranslucent on X-ray - This **bilateral hypertranslucency** is due to reduced lung tissue density, decreased vascular markings, and increased air volume - Classic radiographic features include flattened diaphragms, increased retrosternal space, and hyperlucent lung fields *Incorrect: Mcleod syndrome* - Also known as **Swyer–James–MacLeod syndrome**, this condition causes **unilateral** lung or lobe hyperlucency due to post-infectious obliterative bronchiolitis - The key differentiating feature is that it's **unilateral**, whereas the question asks for bilateral hypertranslucency - Affected lung shows air trapping on expiratory films *Incorrect: Pneumothorax* - A **pneumothorax** presents as a **unilateral** or focal hypertranslucent area due to air in the pleural space - Characterized by **absence of lung markings** beyond the visceral pleural line and associated lung collapse - This is a pleural space abnormality, not a bilateral parenchymal lung disease *Incorrect: Poland syndrome* - **Poland syndrome** is a congenital condition with absence or underdevelopment of the pectoralis major muscle - Can lead to **unilateral** apparent hyperlucency on the affected side due to missing chest wall muscle - This is a **chest wall anomaly**, not a parenchymal lung disease causing bilateral hypertranslucency
Question 9: Which of the following conditions is least likely to cause posterior scalloping of the vertebrae?
- A. Astrocytoma
- B. Neurofibromatosis
- C. Ependymoma
- D. Aortic aneurysm (Correct Answer)
Explanation: ***Aortic aneurysm*** - An **aortic aneurysm** is located **anterior to the vertebral column** and primarily affects the anterior aspect of the vertebral bodies, causing **anterior scalloping** due to chronic pulsatile erosion, not posterior scalloping. - Posterior scalloping requires intraspinal pathology that expands the spinal canal from within; an aortic aneurysm is extraspinal and anterior, making it the **least likely** cause of posterior scalloping. *Neurofibromatosis* - **Neurofibromatosis** commonly causes posterior vertebral scalloping due to **dural ectasia** (widening of the dural sac) and pressure erosion from expanding neurofibromas within the spinal canal. - This condition is also associated with paraspinal masses, posterior vertebral body erosion, and scoliosis. *Astrocytoma* - An **intramedullary astrocytoma** within the spinal cord can lead to expansion of the cord that causes chronic pressure on the posterior vertebral bodies from within the spinal canal. - This slow-growing intraspinal tumor gradually remodels the bone, causing posterior scalloping. *Ependymoma* - Similar to astrocytoma, an **intramedullary ependymoma** (the most common primary intramedullary tumor in adults) can enlarge the spinal cord, leading to pressure erosion on the posterior vertebral bodies. - This is a characteristic feature of slowly growing intraspinal masses, which cause remodeling of the bony spinal canal.
Question 10: The most appropriate first-line imaging modality to detect adrenal metastasis due to bronchogenic carcinoma is:
- A. PET scan
- B. MRI of the abdomen
- C. Adrenal radionuclide scan
- D. Contrast Enhanced CT abdomen (Correct Answer)
Explanation: **Contrast Enhanced CT abdomen** - **Contrast-enhanced CT abdomen** is generally considered the most sensitive and cost-effective imaging modality for detecting **adrenal metastases**. - It allows for detailed visualization of adrenal gland morphology, including size, shape, and enhancement patterns, which can help differentiate benign from malignant lesions. *PET scan* - While **PET (Positron Emission Tomography) scans** are highly sensitive for detecting metabolically active metastatic disease, they are often used as a secondary imaging modality to characterize indeterminate lesions found on CT or MRI. - **PET scans** can have false positives in benign adrenal tumors (e.g., adenomas rich in fat) and are less readily available or higher in cost for initial screening compared to CT. *MRI of the abdomen* - **MRI of the abdomen** can be very useful for further characterization of adrenal masses, especially for distinguishing between lipid-rich adenomas and metastases. - However, for initial detection, especially in the context of screening for distant metastases from bronchogenic carcinoma, **CT is generally preferred due to its wider availability, speed, and lower cost**. *Adrenal radionuclide scan* - **Adrenal radionuclide scans** (e.g., using MIBG or iodocholesterol) are primarily used for functional imaging of adrenal glands, typically to detect specific types of tumors like pheochromocytomas or aldosteronomas. - These scans are **not sensitive for detecting adrenal metastases** from bronchogenic carcinoma, as the metastatic lesions do not typically exhibit the specific uptake patterns targeted by these radiotracers.