NEET-PG 2012 — Radiology

Q: Half-life of iodine-131 is

8 days. ***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. [Practice more Radiology PYQs on OnCourse]

Q: Central stellate scar is typically associated with which of the following conditions?

Focal nodular hyperplasia (FNH). ***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. [Practice more Radiology PYQs on OnCourse]

Q: What is the primary mechanism of heat loss in a modern X-ray tube?

Radiation. ***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. [Practice more Radiology PYQs on OnCourse]

Q: What is the recommended thickness of lead apron to prevent radiation exposure?

0.5 mm. ***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. [Practice more Radiology PYQs on OnCourse]

Q: What is the most effective imaging method for the diagnosis of adenomyosis?

MRI. ***MRI*** - **MRI** offers superior soft tissue contrast, allowing for detailed visualization of the **junctional zone** and **myometrial thickening** characteristic of adenomyosis. - It can effectively differentiate adenomyosis from other uterine pathologies like **leiomyomas**, due to its ability to detect **heterogeneous myometrial signal** and small myometrial cysts. *CT scan* - **CT scans** have limited utility in diagnosing adenomyosis due to their **poor soft tissue contrast** in evaluating diffuse uterine conditions. - They expose the patient to **ionizing radiation** and are generally reserved for detecting calcifications or larger structural abnormalities in the pelvis. *Ultrasound* - **Transvaginal ultrasound** is often the first-line imaging modality due to its accessibility and non-invasiveness, but its diagnostic accuracy for adenomyosis is **operator-dependent** and can be limited in subtle cases. - While it can suggest adenomyosis through findings like **globular uterus** or **heterogeneous myometrium**, it often lacks the resolution to definitively characterize the extent and nature of the lesion compared to MRI. *Hysterosalpingography* - **Hysterosalpingography** is primarily used to evaluate the patency of the **fallopian tubes** and the contour of the uterine cavity, making it unsuitable for direct visualization of myometrial pathology. - While it might show an **irregular uterine cavity** if adenomyosis is severe and extends to the endometrium, it cannot definitively diagnose or characterize the condition within the myometrium. [Practice more Radiology PYQs on OnCourse]

29 Previous Year Questions with Answers & Explanations

Questions

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?

What is the most effective imaging method for the diagnosis of adenomyosis?

Which of the following techniques uses piezoelectric crystals?

Step ladder pattern of gas shadow is seen in

Which chamber enlargement shows a double right heart border with a wide subcarinal angle?

Parrot beak appearance is seen in which of the following conditions?

Q10

Which of the following conditions is least likely to cause posterior scalloping of the vertebrae?

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: What is the most effective imaging method for the diagnosis of adenomyosis?

A. CT scan
B. Hysterosalpingography
C. Ultrasound
D. MRI (Correct Answer)

Explanation: ***MRI*** - **MRI** offers superior soft tissue contrast, allowing for detailed visualization of the **junctional zone** and **myometrial thickening** characteristic of adenomyosis. - It can effectively differentiate adenomyosis from other uterine pathologies like **leiomyomas**, due to its ability to detect **heterogeneous myometrial signal** and small myometrial cysts. *CT scan* - **CT scans** have limited utility in diagnosing adenomyosis due to their **poor soft tissue contrast** in evaluating diffuse uterine conditions. - They expose the patient to **ionizing radiation** and are generally reserved for detecting calcifications or larger structural abnormalities in the pelvis. *Ultrasound* - **Transvaginal ultrasound** is often the first-line imaging modality due to its accessibility and non-invasiveness, but its diagnostic accuracy for adenomyosis is **operator-dependent** and can be limited in subtle cases. - While it can suggest adenomyosis through findings like **globular uterus** or **heterogeneous myometrium**, it often lacks the resolution to definitively characterize the extent and nature of the lesion compared to MRI. *Hysterosalpingography* - **Hysterosalpingography** is primarily used to evaluate the patency of the **fallopian tubes** and the contour of the uterine cavity, making it unsuitable for direct visualization of myometrial pathology. - While it might show an **irregular uterine cavity** if adenomyosis is severe and extends to the endometrium, it cannot definitively diagnose or characterize the condition within the myometrium.

Question 6: 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 7: Step ladder pattern of gas shadow is seen in

A. Intestinal obstruction (Correct Answer)
B. Gastric outlet obstruction
C. Duodenal obstruction
D. Sigmoid volvulus

Explanation: ***Intestinal obstruction*** - A **step-ladder pattern** of gas shadows is a classic radiological sign seen in **small bowel obstruction** due to dilated, fluid-filled loops of small bowel stacked on top of each other. - This pattern results from the accumulation of gas and fluid proximal to the obstruction, causing dilated bowel loops to arrange horizontally. *Gastric outlet obstruction* - This condition primarily results in a **dilated stomach** with fluid and gas, not typically a step-ladder pattern in the small bowel. - Vomiting is usually a prominent symptom, and imaging would show a large fluid-filled stomach. *Duodenal obstruction* - Causes dilatation of the stomach and duodenum, leading to a "**double-bubble sign**" (dilated stomach and proximal duodenum). - It does not typically produce the extensive, stacked small bowel loops seen in a step-ladder pattern. *Sigmoid volvulus* - Characterized by a distinctive large, dilated loop of sigmoid colon, often described as a "**coffee bean sign**" or an **inverted U-shape**. - This is a large bowel obstruction and does not typically present with a step-ladder pattern of small bowel gas.

Question 8: 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 9: Parrot beak appearance is seen in which of the following conditions?

A. Volvulus (Correct Answer)
B. Rectal atresia
C. CA colon
D. Intussusception

Explanation: ***Volvulus*** - A **parrot beak** appearance, or bird's beak sign, is characteristic of a **volvulus** on barium enema or CT imaging, representing the twisted lumen of the bowel. - This finding indicates a **torsion** of a segment of the bowel, which can lead to obstruction and ischemia. *Intussusception* - Intussusception typically presents with a **"target sign"** or **"donut sign"** on ultrasound, indicating concentric layers of bowel within bowel. - The classic presentation is a **"currant jelly stool"** and a palpable **sausage-shaped mass**. *Rectal atresia* - Rectal atresia involves a **complete blockage** or absence of the rectum, preventing passage of stool. - Imaging typically shows a **dilated colon** proximal to the atretic segment, without a specific "parrot beak" appearance. *CA colon* - Colon cancer (CA colon) appears as a **filling defect** or an **"apple core" lesion** on barium enema due to tumoral constriction. - It does not present with a "parrot beak" sign, which is indicative of a twisted bowel segment.

Question 10: 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.