NEET-PG Radiology Previous Year Questions (2017–2026)

Correct answer: A. Ultrasound scanner.

Ultrasonography uses high-frequency sound waves, not ionising radiation, so it falls outside AERB radiation licensing. In India it is instead regulated under the PC-PNDT Act (to prevent sex determination and female foeticide). All X-ray-based devices - mammography, C-arm and radiography units - emit ionising radiation and require AERB registration and licensing.

Incorrect Options:

• Mammography unit: a dedicated low-kV X-ray system that needs AERB licensing. Mammography X-ray unit.
• Mobile C-arm: an intra-operative fluoroscopy unit emitting continuous X-rays, requires AERB licence. Draped C-arm fluoroscopy unit.
• Portable radiography: a mobile X-ray generator that also needs AERB registration. Portable radiography unit in use.

High-Yield Facts:

• AERB licenses equipment that emits ionising radiation (X-ray and gamma).
• Ultrasound and MRI are non-ionising and need no AERB radiation licence.
• Ultrasound is governed by the PC-PNDT Act in India.
• Radiography, mammography, fluoroscopy (C-arm), CT and cath-lab units all need AERB clearance.

Correct Answer: B. The intensity of radiation falls inversely with the square of the distance from the emitting source

This is simply the inverse square law applied to brachytherapy. Because sources sit directly within or against the tumor, a lethal dose lands on the immediate tissue while intensity collapses exponentially just a few millimeters out, sparing structures further away. The broader radiobiology principle at play is the Law of Bergonie and Tribondeau: ionizing radiation preferentially kills rapidly dividing cells by inflicting DNA damage they cannot repair before the next division, which is exactly why tumors and other high-turnover tissues take the brunt of the dose.

Why the other options fail

• A. The mucosal lining of the small intestine exhibits high radioresistance: intestinal crypt epithelium divides continuously and is among the most radiosensitive tissue in the body, not resistant.
• C. Microvasculature is significantly more radioresistant than larger caliber blood vessels: the opposite is true -- small vessels are more radiosensitive than large ones.
• D. Cellular populations with high mitotic rates demonstrate the greatest radioresistance: high mitotic activity means high radiosensitivity per Bergonie-Tribondeau, not resistance.

Pearl: in brachytherapy the dose dies off with distance squared, and cells die off with how fast they divide -- remember both curves point the same direction.

The correct answer is Focused Assessment with Sonography for Trauma (FAST).

The patient presents with blunt abdominal trauma, signs of left lower rib and potential splenic injury (left hypochondriac tenderness), and frank hemodynamic instability (hypotension and tachycardia). According to Advanced Trauma Life Support (ATLS) guidelines, in any hemodynamically unstable patient with blunt abdominal trauma, the immediate diagnostic goal is to rapidly identify the presence of life-threatening intra-abdominal hemorrhage. The best initial bedside investigation is the Focused Assessment with Sonography for Trauma (FAST) exam. FAST is a rapid, non-invasive, and highly specific ultrasound evaluation that assesses four key dependent regions for free fluid (blood): the right upper quadrant (perihepatic space/Morison's pouch), the left upper quadrant (perisplenic space), the pelvis (Pouch of Douglas/rectovesical pouch), and the subxiphoid view for the pericardium. Crucially, it can be performed concurrently with active fluid and blood resuscitation right in the emergency department without delaying patient care.

Incorrect Options:

• Plain abdominal radiography: While an upright chest X-ray is useful for ruling out a pneumothorax or hemothorax in the primary survey, a plain abdominal X-ray has extremely low sensitivity for detecting free intra-abdominal fluid or solid organ injury. It is not a priority in an unstable trauma patient.
• Diagnostic peritoneal lavage (DPL): Historically used before the widespread availability of ultrasound, DPL is an invasive surgical procedure. It has largely been replaced by the FAST exam in modern trauma algorithms due to the non-invasive nature, repeatability, and speed of ultrasonography. It is now rarely indicated unless FAST and CT are completely unavailable.
• Contrast-enhanced computed tomography (CT) of the abdomen: CT is the gold standard for diagnosing the exact grade and location of solid organ injuries (e.g., a splenic laceration). However, it requires transporting the patient out of the resuscitation bay to the scanner. Therefore, it is strictly contraindicated in a hemodynamically unstable patient (BP 88/50 mmHg) until they respond adequately to resuscitation.

High-Yield Facts:

• If a hemodynamically unstable patient has a positive FAST exam indicating hemoperitoneum, the next immediate step in management is an emergency exploratory laparotomy in the operating room.
• The most commonly injured solid organ in blunt abdominal trauma is the spleen, which is highly associated with left lower rib fractures.
• The "eFAST" (extended FAST) adds bilateral anterior thoracic views to the standard protocol to quickly detect the presence of a pneumothorax or hemothorax.