NEET-PG 2013 - Radiology Practice Questions

Q: Which imaging modality delivers the highest dose of radiation?

Cardiac perfusion scan. ***Cardiac perfusion scan*** - A **cardiac perfusion scan (nuclear cardiology)** involves the administration of a radioactive tracer, and the radiation dose can be significant due to the nature and energy of the isotopes used. - While varying, the effective dose for these scans can range from **10 to 30 mSv**, placing it among some of the highest radiation exposures from medical imaging. *CT scan of the chest* - A **CT scan of the chest** provides a relatively high radiation dose compared to plain X-rays, typically ranging from **5 to 7 mSv**. - This is generally lower than some nuclear medicine studies, particularly complex or prolonged cardiac perfusion scans. *Mammogram* - A **mammogram** involves a relatively low dose of radiation, typically in the range of **0.2 to 0.7 mSv**. - Its objective is to image the breast tissue with minimal exposure, making it one of the lower-dose imaging modalities available. *CT scan of the brain* - A **CT scan of the brain** usually delivers a moderate radiation dose, estimated to be around **1 to 2 mSv**. - This is often less than a chest CT due to the smaller volume and different shielding considerations, and significantly less than a cardiac perfusion scan.

Q: Gyromagnetic property of proton is seen in -

MRI. ***MRI*** - Magnetic Resonance Imaging (MRI) relies on the **gyromagnetic properties of protons**, primarily hydrogen nuclei in water and fat. - These protons align with a strong magnetic field and, when pulsed with radiofrequency waves, emit detectable signals that form the image. *CT* - Computed Tomography (CT) utilizes **X-rays** and their differential absorption by various tissues to create cross-sectional images. - It does not involve the gyromagnetic properties of protons. *PET scan* - Positron Emission Tomography (PET) scans detect **gamma rays** emitted from radiotracers, typically radionuclides like Fluorine-18, that accumulate in metabolically active tissues. - This imaging modality is based on radioactive decay, not proton spin. *USG* - Ultrasonography (USG) generates images by sending **high-frequency sound waves** into the body and detecting the echoes that bounce back from various tissues. - It relies on acoustic properties and tissue interfaces, not magnetic properties of protons.

Q: What condition is indicated by the double bubble sign on an abdominal X-ray?

Duodenal atresia. ***Duodenal atresia*** - The **double bubble sign** on an abdominal X-ray is pathognomonic for **duodenal atresia**, characterized by two air-filled bubbles: one in the stomach and one in the proximal duodenum, separated by the pylorus. - This congenital anomaly results from a complete obstruction of the duodenum, preventing the passage of air and fluid past this point. *Duodenal stenosis* - While also an obstruction of the duodenum, **duodenal stenosis** is an incomplete obstruction, meaning some gas will pass beyond the duodenum. - This would result in gas being present in the distal bowel, which is not seen with a classic "double bubble" where the bowel distal to the duodenum is gasless. *Volvulus* - **Volvulus** involves the twisting of a loop of intestine, leading to obstruction and potentially ischemia. - While it can cause obstruction, it typically presents with a "corkscrew" appearance on an upper GI series or signs of diffuse bowel distension, not the isolated double bubble. *All of the options* - The double bubble sign is highly specific to **duodenal atresia** due to the complete obstruction it signifies. - Other conditions like duodenal stenosis and volvulus cause different radiological patterns, making this option incorrect.

Q: What is the echogenic lesion size criterion for chronic pancreatitis?

> 3 mm. ***> 3 mm*** - An echogenic lesion **greater than 3 mm** in size is a diagnostic criterion for **chronic pancreatitis** when observed on ultrasound imaging. - This represents one of the **major features** in ultrasound diagnosis of chronic pancreatitis, particularly when echogenic foci demonstrate acoustic shadowing (suggesting calcifications). - This criterion is part of established diagnostic frameworks and helps differentiate pathological calcifications from minor, non-specific findings. *> 4 mm* - While a **4 mm threshold** would indicate significant findings, the established diagnostic criterion for chronic pancreatitis uses **> 3 mm** as the cutoff. - Using a higher threshold would reduce sensitivity for detecting chronic pancreatitis. *> 2 mm* - A lesion larger than **2 mm** is generally considered below the established diagnostic threshold for **chronic pancreatitis**. - This size may represent early changes or incidental findings that are not yet definitive for diagnosis. *> 1 mm* - A lesion **greater than 1 mm** is too small to be a definitive criterion for **chronic pancreatitis** and could represent minor, non-pathological findings. - Such small echogenic foci lack sufficient specificity for diagnosing chronic pancreatic disease.

Q: Investigation with least radiation dose in the diagnosis of Meckel's diverticulum is -

Technetium -99m scanning. ***Technetium-99m scanning*** - **Technetium-99m pertechnetate scan** (Meckel's scan) is the **gold standard investigation** for diagnosing Meckel's diverticulum with ectopic gastric mucosa - Among the investigations that can actually **diagnose Meckel's diverticulum**, it has the **lowest radiation dose** (approximately 1-2 mSv) - The radioisotope is specifically taken up by ectopic gastric mucosa, providing both diagnostic utility and relatively low radiation exposure - **Sensitivity: 85-95%** for detecting ectopic gastric mucosa in Meckel's diverticulum - The radiation dose is comparable to a few months of natural background radiation and significantly lower than CT or contrast studies *MRI* - While **MRI uses no ionizing radiation**, it is **not a standard or practical investigation** for diagnosing Meckel's diverticulum - MRI cannot identify ectopic gastric mucosa specifically - It is rarely used in clinical practice for this indication - The question asks about investigation "in the diagnosis" of Meckel's diverticulum, implying a test that is actually used diagnostically *CT* - **Computed Tomography (CT)** delivers a **high radiation dose** (typically 5-10 mSv or more) - While it can identify structural abnormalities, it is not specific for Meckel's diverticulum - Not the first-line investigation for this condition *Contrast radiography* - **Contrast studies** (barium studies) use **moderate ionizing radiation** (3-5 mSv) - Limited utility in diagnosing Meckel's diverticulum as it primarily assesses luminal patency - Cannot identify ectopic gastric mucosa - Lower sensitivity compared to Tc-99m scanning

Q: What is the maximum radiation dose (in Gray) that bone tissue can tolerate?

50 Gray. ***Correct Option: 50 Gray*** - The **maximum radiation tolerance dose** for bone tissue is approximately **50-60 Gray (Gy)** based on radiobiology literature and clinical practice. - Among the given options, **50 Gy** represents the most appropriate threshold for bone tolerance. - According to **Emami et al. tolerance doses** and **QUANTEC guidelines**, bone can typically tolerate up to 60 Gy without significant risk of complications. - Doses approaching or exceeding **60 Gy** carry increased risk of **osteoradionecrosis**, particularly in the **mandible and weight-bearing bones**. - **Clinical significance**: In radiation therapy planning, doses of 50-60 Gy to bone are commonly used therapeutically for tumors involving or adjacent to bone. *Incorrect Option: 40 Gray* - 40 Gy is **below the accepted tolerance threshold** for bone tissue. - This dose is generally **well-tolerated** by bone without significant risk of necrosis or fracture. - Commonly used in palliative and definitive radiation protocols without major bone complications. *Incorrect Option: 30 Gray* - 30 Gy is **considerably below** the tolerance limit for bone. - This dose level is **safe for bone tissue** and carries minimal risk of radiation-induced bone damage. - Often used in palliative treatments with excellent bone tolerance. *Incorrect Option: 20 Gray* - 20 Gy is a **low radiation dose** from the perspective of bone tolerance. - This dose is **highly unlikely** to cause any significant bone damage or complications. - Represents a conservative therapeutic dose well within safety margins.

Q: What is the investigation of choice for whole body imaging in metastatic breast cancer?

CT Scan. ***CT Scan (Correct answer for NEET 2013)*** - **Contrast-enhanced CT scan** was the standard imaging modality for **whole-body staging** in metastatic breast cancer at the time of this exam (2013). - CT offers **excellent spatial resolution** for detecting metastases in **bone, lung, liver, and lymph nodes**. - It is widely available, relatively quick, and provides comprehensive anatomical information. - **Modern Update:** While CT was the standard in 2013, **PET-CT (FDG-PET/CT) is now considered the gold standard** for whole-body staging in metastatic breast cancer due to its combined metabolic and anatomical imaging capabilities. However, PET-CT was not among the options in this historical question. *Magnetic Resonance Imaging* - **MRI** is highly sensitive for specific sites, particularly for **brain metastases** and **bone metastases (especially spine and bone marrow)**. - **Whole-body MRI** protocols are emerging but require longer acquisition times and specialized equipment. - Not ideal as a single first-line modality for comprehensive whole-body staging compared to CT (or modern PET-CT). *Angiography* - **Angiography** is an invasive vascular imaging procedure used to visualize **arterial blood flow**. - It has **no role in routine metastatic screening or staging** of breast cancer. - Reserved for specific indications like preoperative vascular mapping or interventional procedures. *Venography* - **Venography** specifically visualizes **venous structures** and is used to detect venous thrombosis or venous obstructions. - It is **not applicable** for detecting solid organ metastases, bone lesions, or lymph node involvement in cancer staging.

Q: Barium swallow is used for -

Esophagus. ***Esophagus*** - A **barium swallow** specifically visualizes the **esophagus**, pharynx, and sometimes the early stomach. - It's used to identify abnormalities like **dysphagia**, strictures, **achalasia**, or tumors by coating the mucosal lining. *Colon* - The colon is typically examined using a **barium enema**, where barium sulfate is administered rectally. - This procedure is effective for visualizing the large intestine for conditions like **polyps**, diverticula, or inflammatory bowel disease. *Duodenum* - While a barium swallow may transiently show the **duodenum**, its primary target is the esophagus and stomach. - More detailed imaging of the duodenum often requires an **upper GI series (UGI)**, which is a broader study of the upper digestive tract. *Jejunum* - The jejunum is part of the small intestine and is best visualized through a **small bowel follow-through (SBFT)** procedure. - This involves ingesting barium and taking serial X-rays as it progresses through the small bowel, to detect conditions like **Crohn's disease** or obstructions.

Q: Enhancement in CT contrast is due to -

Iodine. ***Iodine*** - **Iodine-based contrast agents** are commonly used in CT scans to enhance the visualization of blood vessels, organs, and certain lesions due to their **high atomic number** and ability to absorb X-rays. - The degree of enhancement observed on a CT image is directly proportional to the concentration of **iodine** in the tissue or blood. *Gadolinium* - **Gadolinium-based contrast agents** are predominantly used in **Magnetic Resonance Imaging (MRI)**, not CT scans. - Gadolinium works by altering the **magnetic properties** of water molecules in tissues, thereby improving MRI signal intensity. *Mercury* - **Mercury** is a highly toxic heavy metal and is **not used as a contrast agent** in any imaging modality due to its severe health risks. - While historically used in some medical applications, it has been replaced by safer alternatives. *Silver* - **Silver** is not used as a contrast agent in medical imaging; it has no suitable properties for enhancing images in CT or other common modalities. - It is known for its **antimicrobial properties** and is sometimes used in wound dressings.

Q: Normal prevertebral soft tissue thickness in adults at C3 level is

7 mm. ***7 mm*** * The normal prevertebral soft tissue thickness in adults at the **C3 level** is approximately **7 mm** (upper limit 5-7 mm) on a lateral cervical spine radiograph. * The **C1-C4 levels** have relatively thin prevertebral soft tissue as they lie above the hypopharynx and esophagus. * Exceeding this measurement can indicate **prevertebral hematoma, edema, abscess**, or other pathologies such as retropharyngeal abscess or cervical spine fracture with soft tissue swelling. *Incorrect: 15 mm* * A measurement of 15 mm at the **C3 level** would be considered **abnormal** and indicates prevertebral soft tissue swelling. * This value exceeds the normal limit by more than double and warrants further investigation. *Incorrect: 22 mm* * A measurement of 22 mm at the **C3 level** is significantly **abnormal** and highly suggestive of serious pathology such as retropharyngeal hematoma, abscess, or cervical spine injury. * Note that 22 mm may be within normal limits at the **C6-C7 level** where the esophagus widens the prevertebral space. *Incorrect: 30 mm* * 30 mm is severely abnormal at the **C3 level**. * While prevertebral soft tissue thickness can be greater at lower cervical levels (C5-C7) due to the esophagus, even at those levels 30 mm would suggest pathology. * Such measurements indicate significant conditions like large hematoma, abscess, or tumor.

Question 1

Which imaging modality delivers the highest dose of radiation?

Accepted Answer

Cardiac perfusion scan

Answer

CT scan of the chest

Answer

Mammogram

Answer

CT scan of the brain

Question 2

Gyromagnetic property of proton is seen in -

Accepted Answer

MRI

Answer

CT

Answer

PET scan

Answer

USG

Question 3

What condition is indicated by the double bubble sign on an abdominal X-ray?

Accepted Answer

Duodenal atresia

Answer

Duodenal stenosis

Answer

Volvulus

Answer

All of the options

Question 4

What is the echogenic lesion size criterion for chronic pancreatitis?

Accepted Answer

> 3 mm

Answer

> 2 mm

Answer

> 1 mm

Answer

> 4 mm

Question 5

Investigation with least radiation dose in the diagnosis of Meckel's diverticulum is -

Accepted Answer

Technetium -99m scanning

Answer

MRI

Answer

CT

Answer

Contrast radiography

Question 6

What is the maximum radiation dose (in Gray) that bone tissue can tolerate?

Accepted Answer

50 Gray

Answer

30 Gray

Answer

20 Gray

Answer

40 Gray

Question 7

What is the investigation of choice for whole body imaging in metastatic breast cancer?

Accepted Answer

CT Scan

Answer

Angiography

Answer

Venography

Answer

Magnetic Resonance Imaging

Question 8

Barium swallow is used for -

Accepted Answer

Esophagus

Answer

Colon

Answer

Duodenum

Answer

Jejunum

Question 9

Enhancement in CT contrast is due to -

Accepted Answer

Iodine

Answer

Gadolinium

Answer

Mercury

Answer

Silver

Question 10

Normal prevertebral soft tissue thickness in adults at C3 level is

Accepted Answer

7 mm

Answer

15 mm

Answer

22 mm

Answer

30 mm

NEET-PG 2013 — Radiology