Physics of Ultrasound — MCQs
Pulse echo principle is used by which modality?
Which of the following is the best in-vivo screening choice for carotid artery stenosis?
Which of the following techniques uses piezoelectric crystals?
Which is not echogenic while doing ultrasonography:
'Triphasic waveform' on colour Doppler is of
Acoustic shadow is produced by the following except
Causes of thickened gallbladder wall on ultrasound examination are all except:
Investigation of choice for hypertrophic pyloric stenosis is
What is the investigation of choice for an 8-year-old child presenting with an acute abdomen?
Which condition shows a 'comet tail artifact' on gallbladder ultrasound?
Physics of Ultrasound Indian Medical PG Practice Questions and MCQs
Question 1: Pulse echo principle is used by which modality?
- A. X-ray
- B. CT
- C. MRI
- D. USG (Correct Answer)
Explanation: ***USG*** - **Ultrasound (USG)** imaging relies on the **pulse echo principle**, where high-frequency sound waves are emitted and their reflections (echoes) are detected to create images. - The transducer sends out a short **ultrasound pulse** and then listens for the echoes returning from structures within the body. *X-ray* - **X-ray** imaging uses **ionizing radiation** to produce images, where X-rays pass through the body and are absorbed differently by various tissues. - It does not involve emitting pulses or detecting echoes; instead, it measures the **attenuation of X-rays**. *CT* - **Computed Tomography (CT)** also uses **X-rays** but in a cross-sectional manner, rotating an X-ray source and detector around the patient. - It reconstructs detailed 3D images based on varying **X-ray absorption** and does not use sound waves or the pulse echo principle. *MRI* - **Magnetic Resonance Imaging (MRI)** utilizes strong **magnetic fields** and **radio waves** to produce detailed anatomical images. - It measures the signals emitted by **protons in water molecules** after they are excited by radiofrequency pulses, which is distinct from sound wave echoes.
Question 2: Which of the following is the best in-vivo screening choice for carotid artery stenosis?
- A. Digital Subtraction Angiography (DSA)
- B. CT
- C. MRI
- D. USG (Correct Answer)
Explanation: ***USG*** - **Ultrasound** (USG), specifically **carotid duplex ultrasonography**, is the **safest**, most cost-effective, and readily available initial screening tool for carotid artery stenosis due to its non-invasive nature and ability to visualize blood flow and vessel morphology. - It combines **B-mode imaging** with **Doppler flow analysis** to provide real-time images and flow velocity measurements, allowing for assessment of the degree of **stenosis** and plaque characteristics without radiation or contrast agents. - Sensitivity and specificity exceed 85-90% for detecting significant stenosis, making it the preferred first-line screening modality. *Digital Subtraction Angiography (DSA)* - **DSA** is the **gold standard** for anatomical detail and remains the most accurate method for quantifying carotid stenosis, but it is **invasive** and requires arterial catheterization. - It involves **ionizing radiation** and **iodinated contrast agents**, carrying risks of stroke (0.5-1%), arterial dissection, nephrotoxicity, and contrast allergic reactions. - Due to its invasive nature and associated risks, DSA is reserved for **pre-surgical planning** or when non-invasive imaging is inconclusive, not for initial screening. *CT* - **Computed tomography angiography (CTA)** involves **ionizing radiation** and typically requires an **iodinated contrast agent**, which carries risks of allergy and nephrotoxicity. - Though CTA provides excellent anatomical detail and can visualize vessel wall calcification, it is generally reserved for confirmation or surgical planning rather than initial screening due to its higher cost, radiation exposure, and contrast-related risks. *MRI* - **Magnetic resonance angiography (MRA)** can visualize carotid arteries well but is more expensive, less accessible than ultrasound, and may require a **gadolinium-based contrast agent**, which can have adverse effects (nephrogenic systemic fibrosis in renal impairment). - It is often used when ultrasound findings are equivocal or in cases where CTA is contraindicated, but it's not the preferred initial screening method due to its complexity, cost, longer examination time, and contraindications (pacemakers, metallic implants).
Question 3: 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 4: Which is not echogenic while doing ultrasonography:
- A. Bile (Correct Answer)
- B. Bone
- C. Gas
- D. Gall stones
Explanation: ***Bile*** - Bile is largely composed of **water**, which allows ultrasound waves to pass through it with minimal reflection, appearing **anechoic** (black) on ultrasound. - This property makes the gallbladder lumen, when filled with bile, appear anechoic, which is crucial for identifying structures like gallstones. *Bone* - **Bone** is highly dense and reflects a significant portion of ultrasound waves, making it appear very **echogenic** (bright) on ultrasonography. - Due to its high reflectivity, bone often produces a strong **acoustic shadow** behind it, obscuring deeper structures. *Gas* - **Gas** (air) is a strong reflector of ultrasound waves and appears brightly echogenic, often with a characteristic **dirty shadowing** or **reverberation artifact**. - The presence of gas can significantly hinder visualization of underlying tissues due to its strong reflection and scatter of the ultrasound beam. *Gall stones* - **Gallstones** are solid concretions that are highly reflective of ultrasound waves, appearing as bright, **echogenic foci** within the gallbladder lumen. - A classic ultrasound sign of gallstones is an echogenic structure with strong **posterior acoustic shadowing**.
Question 5: 'Triphasic waveform' on colour Doppler is of
- A. Portal vein
- B. Hepatic artery
- C. Hepatic vein (Correct Answer)
- D. All of the options
Explanation: ***Hepatic vein*** - A normal hepatic vein Doppler waveform is **triphasic**, showing two antegrade (towards the heart) waves corresponding to **ventricular systole (S wave)** and **diastole (D wave)**, and one small retrograde (away from the heart) wave corresponding to **atrial contraction (a wave)**. - This triphasic pattern reflects the cyclic pressure changes in the right atrium and is crucial for assessing **right heart function** and conditions affecting hepatic venous outflow. *Portal vein* - The portal vein typically exhibits a **monophasic waveform** with continuous, low-velocity, hepatopetal (towards the liver) flow, often with slight undulations due to respiration. - The absence of a triphasic pattern differentiates it from the hepatic veins, as its flow is driven by pressure differences from the mesenteric circulation, not directly by cardiac cycles. *Hepatic artery* - The hepatic artery demonstrates a **high-resistive, biphasic waveform** with a sharp systolic peak and continuous diastolic flow, reflecting its essential role in supplying oxygenated blood to the liver parenchyma. - It does not show a triphasic pattern, which is characteristic of venous structures influenced by right atrial pressures. *All of the options* - This option is incorrect because only the **hepatic veins** typically display a triphasic waveform; the portal vein and hepatic artery have distinct, different waveform patterns. - Each vessel's unique flow pattern is indicative of its specific physiological role and anatomical connection to the cardiac cycle.
Question 6: Acoustic shadow is produced by the following except
- A. Calculus
- B. Bone
- C. Gas
- D. Fat (Correct Answer)
Explanation: ***Fat*** - Fat has a **low acoustic impedance** and typically allows ultrasound waves to pass through with minimal reflection, thus it does not produce an **acoustic shadow**. - Instead of shadowing, fat often appears **hyperechoic** or **isoechoic** to surrounding tissues with good sound transmission. *Calculus* - **Calculi** (e.g., gallstones, kidney stones) are extremely dense and highly reflective, causing almost all ultrasound waves to be **absorbed or reflected**. - This leads to a distinct **anechoic area** (shadow) behind the calculus, as no sound waves penetrate beyond it. *Bone* - **Bone** is a hard, dense structure with high acoustic impedance, causing significant **reflection and attenuation** of ultrasound waves. - This blockage of sound waves results in a prominent **acoustic shadow** posterior to the bone, making structures behind it difficult to visualize. *Gas* - **Gas** (e.g., in bowel loops) has a very low acoustic impedance compared to soft tissue, creating a large **impedance mismatch** that leads to almost complete **reflection of ultrasound waves**. - The rapid scattering and reflection of sound waves by gas create a "dirty" or **"reverberation" shadow**, characterized by multiple bright echoes and lack of posterior visualization.
Question 7: Causes of thickened gallbladder wall on ultrasound examination are all except:
- A. Congestive cardiac failure
- B. Postprandial state
- C. Kawasaki disease (Correct Answer)
- D. Cholecystitis
Explanation: ***Kawasaki disease*** (Correct Answer) - While Kawasaki disease can cause **gallbladder hydrops** (distension with bile), the primary ultrasound finding is an **enlarged, distended gallbladder** rather than isolated wall thickening. - When gallbladder involvement occurs in Kawasaki disease, it manifests as **acalculous cholecystitis** with hydrops, but this is **not a typical or common presentation** compared to the other causes listed. - The hallmark features of Kawasaki disease are **coronary artery aneurysms** and systemic vasculitis, not primary gallbladder pathology. - In clinical practice, gallbladder wall thickening would **not be attributed to Kawasaki disease** as a primary differential diagnosis. *Incorrect: Congestive cardiac failure* - **Systemic fluid overload** and venous congestion in CHF leads to gallbladder wall thickening due to **transudative edema**. - This is a **common cause** of non-inflammatory gallbladder wall thickening (>3mm). - The wall appears thickened, hypoechoic, and **edematous** without pericholecystic fluid. *Incorrect: Postprandial state* - After eating, the gallbladder **contracts to release bile**, causing the wall to appear thicker on ultrasound due to **accordion-like folding** of the mucosa. - This is a **normal physiological finding** and typically resolves within 1-2 hours. - Scanning should ideally be done after **6-8 hours of fasting** to avoid this pseudo-thickening. *Incorrect: Cholecystitis* - **Acute cholecystitis** is the **classic cause** of gallbladder wall thickening (>3mm, often >5mm). - Associated findings include **gallstones, pericholecystic fluid, positive sonographic Murphy's sign**, and wall edema. - The wall shows **layering** (subserosal edema) and hyperemia on Doppler imaging.
Question 8: Investigation of choice for hypertrophic pyloric stenosis is
- A. USG (Correct Answer)
- B. X-ray
- C. CT
- D. MRI
Explanation: ***USG*** - **Ultrasound** is the preferred imaging modality for diagnosing **hypertrophic pyloric stenosis** due to its non-invasive nature, lack of radiation, and ability to directly visualize the thickened pyloric muscle. - Diagnostic criteria on ultrasound include a **pyloric muscle thickness** greater than 3-4 mm and a **pyloric channel length** greater than 14-17 mm. *X-ray* - An **X-ray** may show a dilated stomach with a **small amount of gas** in the distal bowel, but it is not specific for hypertrophic pyloric stenosis and cannot directly visualize the pylorus. - Barium studies (upper GI series) were historically used but have largely been replaced by ultrasound due to **radiation exposure** and diagnostic inferiority. *CT* - **CT scans** involve significant **radiation exposure** and are generally not recommended for infants due to risks, especially when a definitive diagnosis can be made effectively with ultrasound. - While CT can visualize the pylorus, it offers no significant advantage over ultrasound for this specific condition and carries **higher risks**. *MRI* - **MRI** is a sophisticated imaging technique that offers excellent soft tissue contrast, but it is **time-consuming**, expensive, and often requires sedation in infants. - It is not the investigation of choice for hypertrophic pyloric stenosis where **ultrasound is readily available** and provides sufficient diagnostic information without sedation or radiation.
Question 9: What is the investigation of choice for an 8-year-old child presenting with an acute abdomen?
- A. USG (Correct Answer)
- B. CT Scan
- C. X-ray
- D. MRI
Explanation: ***USG*** - An **ultrasound (USG)** is the preferred initial imaging modality in pediatric acute abdomen due to its **lack of ionizing radiation**, ease of use, and ability to visualize common causes like appendicitis and intussusception. - It is particularly useful for assessing **fluid collections**, inflammation, and obstruction in a non-invasive manner suitable for children. *CT Scan* - While it offers detailed anatomical views, **CT scans** involve significant **ionizing radiation**, which is a concern in children due to increased lifetime cancer risk. - It is typically reserved for cases where **USG is inconclusive** or if there is a high suspicion of conditions not well visualized by ultrasound. *X-ray* - **X-rays** provide limited information for soft tissue pathologies and are primarily useful for detecting **bowel obstruction (air-fluid levels)** or **free air** (perforation). - They lack the resolution to diagnose many common causes of acute abdomen in children, such as appendicitis or intussusception. *MRI* - **MRI** provides excellent soft tissue contrast without ionizing radiation but often requires **sedation** in young children due to the long scan times and need for stillness. - It is less readily available and more expensive than USG, making it a less practical first-line investigation for an acute presentation.
Question 10: Which condition shows a 'comet tail artifact' on gallbladder ultrasound?
- A. Cholecystitis
- B. Gallstones
- C. Hepatic cyst
- D. Adenomyomatosis (Correct Answer)
Explanation: ***Adenomyomatosis*** - This condition is characterized by **hypertrophy of the muscular layer** and **outpouchings of the mucosa** through the muscular layer (Rokitansky-Aschoff sinuses). - The tiny cholesterol crystals or sludge within these sinuses cause a specific type of reverberation artifact known as the "**comet tail artifact**" or V-shaped artifact on ultrasound. *Cholecystitis* - **Acute cholecystitis** generally presents with gallbladder wall thickening, pericholecystic fluid, and a positive sonographic Murphy's sign, but not typically a comet tail artifact. - The hallmark is **inflammation** of the gallbladder, often due to cystic duct obstruction by a gallstone. *Gallstones* - Gallstones are commonly seen as **echogenic structures with posterior acoustic shadowing** within the gallbladder lumen. - While they can cause cholecystitis, they do not directly produce a comet tail artifact themselves. *Hepatic cyst* - A **hepatic cyst** is a simple fluid-filled lesion in the liver and appears on ultrasound as an anechoic (black) structure with well-defined walls and **posterior acoustic enhancement**. - It does not involve the gallbladder and therefore would not exhibit a comet tail artifact within the gallbladder.
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