Ultrasound — MCQs

Ultrasound Indian Medical PG Practice Questions and MCQs

Question 131: Ultrasonography is done to visualize all except:

A. Fluid
B. Bile
C. Blood flow
D. Bone (Correct Answer)

Explanation: **Explanation:** The core principle of Ultrasonography (USG) is the transmission of high-frequency sound waves through tissues. The correct answer is **Bone** because of the physical property known as **Acoustic Impedance**. **1. Why Bone is the correct answer:** Bone has extremely high density and acoustic impedance compared to soft tissues. When ultrasound waves hit the surface of a bone, almost 100% of the beam is reflected or absorbed. This results in a "hyperechoic" (bright) white line at the cortex with a complete **posterior acoustic shadow** (black area) behind it. Consequently, USG cannot "see through" bone to visualize its internal structure or the tissues lying deep to it. **2. Why other options are incorrect:** * **Fluid & Bile (Options A & B):** Fluids are "anechoic" (black) because they transmit sound waves with minimal reflection. USG is the gold standard for detecting free fluid (e.g., ascites, pleural effusion) and visualizing bile within the gallbladder or bile ducts. * **Blood Flow (Option C):** Using the **Doppler Effect**, USG can accurately visualize and measure the velocity and direction of blood flow in arteries and veins. **High-Yield Clinical Pearls for NEET-PG:** * **Acoustic Shadowing:** Seen behind highly reflective/absorptive structures like **calcified gallstones** or **bone**. * **Acoustic Enhancement:** Seen behind fluid-filled structures (like a simple cyst), where the area deep to the fluid appears brighter. * **Air/Gas:** Like bone, air is a "natural enemy" of ultrasound because it causes total reflection, which is why USG is limited in evaluating the lungs or gas-filled bowel loops. * **FAST Scan:** A high-yield emergency USG used to detect intraperitoneal fluid (blood) in trauma patients.

Question 132: Ultrasound is useful in detecting which of the following conditions?

A. Placenta previa
B. Intra-uterine growth retardation
C. Foetus associated with ascites
D. All of the above (Correct Answer)

Explanation: **Explanation:** Ultrasound (USG) is the primary imaging modality in obstetrics due to its non-ionizing nature, real-time imaging capabilities, and high sensitivity for soft tissue and fluid assessment. * **Placenta Previa:** USG is the gold standard for placental localization. Transvaginal sonography (TVS) is highly accurate in measuring the distance between the internal os and the placental edge to diagnose low-lying placenta or previa. * **Intra-uterine Growth Retardation (IUGR):** USG is essential for monitoring fetal growth. By measuring parameters such as Biparietal Diameter (BPD), Head Circumference (HC), Abdominal Circumference (AC), and Femur Length (FL), clinicians can calculate the estimated fetal weight (EFW) and identify growth restriction. Doppler USG of the umbilical artery further helps in managing IUGR. * **Fetal Ascites:** USG is highly sensitive in detecting abnormal fluid collections. Fetal ascites (seen as an echo-free rim around abdominal organs) is a key feature of **Hydrops Fetalis**, which can be easily visualized during a routine anomaly scan. **Clinical Pearls for NEET-PG:** * **Best time for Anomaly Scan (Level II):** 18–20 weeks of gestation. * **First sign of IUGR on USG:** Lagging Abdominal Circumference (AC) is often the earliest indicator. * **Safe Modality:** USG uses the "ALARA" (As Low As Reasonably Achievable) principle; there is no documented risk of ionizing radiation to the fetus. * **Full Bladder:** Required for Transabdominal scans (TAS) in early pregnancy to create an acoustic window, but not required for TVS.

Question 133: Which of the following statements is NOT true about antenatal Doppler analysis?

A. Reduction in end diastolic flow is associated with poor outcome.
B. Reduction in end diastolic flow is associated with IUGR.
C. In normal gestation, placental resistance is high. (Correct Answer)
D. S/D ratio is high in IUGR.

Explanation: ### Explanation **Core Concept: The Low-Resistance Placental Bed** In a normal pregnancy, the physiological remodeling of maternal spiral arteries by trophoblastic invasion transforms them into high-capacitance, **low-resistance** vessels. This ensures continuous, high-volume blood flow to the fetus even during diastole. Therefore, the statement that placental resistance is high in normal gestation is **incorrect**. **Analysis of Options:** * **Option C (Correct Answer):** In normal pregnancy, placental resistance is **low**. High resistance is a pathological state often seen in pre-eclampsia or placental insufficiency. * **Option A & B:** As placental resistance increases (due to placental dysfunction), the diastolic flow in the Umbilical Artery decreases. A **reduction in end-diastolic flow (REDF)** or **absent/reversed end-diastolic flow (AREDF/REDF)** is a hallmark of **Intrauterine Growth Restriction (IUGR)** and is strongly associated with poor perinatal outcomes, including fetal hypoxia and acidosis. * **Option D:** The **S/D Ratio** (Systolic/Diastolic) measures the relationship between peak systole and end-diastole. In IUGR, the denominator (diastole) decreases due to high resistance, causing the overall **S/D ratio to increase**. **High-Yield Clinical Pearls for NEET-PG:** * **Umbilical Artery Doppler:** Primarily reflects **placental** health. Normal flow is forward throughout the cardiac cycle. * **Middle Cerebral Artery (MCA) Doppler:** Used to detect the **"Brain Sparing Effect."** In fetal hypoxia, resistance in the MCA decreases (vasodilation) to protect the brain. * **Ductus Venosus:** The most critical indicator of fetal cardiac failure; an "a-wave" reversal is a late sign of fetal distress. * **Uterine Artery Doppler:** High resistance with "diastolic NOTCHING" after 24 weeks is a predictor for the development of Pre-eclampsia.

Question 134: Which of the following conditions cannot be diagnosed by Ultrasound (USG)?

A. Anencephaly
B. Neural tube defect
C. Placenta previa
D. Down's syndrome (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Down’s syndrome**. **1. Why Down’s syndrome is the correct answer:** Down’s syndrome (Trisomy 21) is a **genetic/chromosomal diagnosis**, not a structural one. While Ultrasound (USG) can identify "soft markers" or associated structural anomalies (like an absent nasal bone or endocardial cushion defects), it cannot provide a definitive diagnosis. A definitive diagnosis of Down’s syndrome requires **Karyotyping** or chromosomal analysis via invasive procedures like Amniocentesis or Chorionic Villus Sampling (CVS). **2. Analysis of Incorrect Options:** * **Anencephaly:** This is a major structural defect characterized by the absence of the cranial vault and cerebral hemispheres. It is easily diagnosed on USG (often called the "Frog-eye appearance") as early as the late first trimester. * **Neural Tube Defects (NTDs):** USG is the gold standard for screening structural anomalies like Spina Bifida. Findings such as the "Lemon sign" (scalloping of frontal bones) and "Banana sign" (curved cerebellum) are classic sonographic markers. * **Placenta Previa:** USG is the investigation of choice for placental localization. It accurately identifies the relationship between the placenta and the internal cervical os. **3. Clinical Pearls for NEET-PG:** * **First Trimester Screening for Down’s:** Increased **Nuchal Translucency (NT)** >3mm between 11–13.6 weeks is a high-yield USG marker, but it is a *screening* tool, not diagnostic. * **Combined Test:** Includes NT scan + PAPP-A + β-hCG. * **Level II Scan (Anomaly Scan):** Performed at **18–20 weeks** to detect structural malformations. * **Safe Modality:** USG is preferred in pregnancy because it uses non-ionizing radiation (mechanical sound waves).

Question 135: The Doppler effect results from a change in which property of a wave?

A. Amplitude
B. Frequency (Correct Answer)
C. Direction
D. None of the above

Explanation: **Explanation:** The **Doppler Effect** is a fundamental principle in ultrasound physics defined as the change in the **frequency** (or wavelength) of a wave in relation to an observer who is moving relative to the wave source. In medical imaging, the "source" is the ultrasound transducer, and the "moving targets" are typically red blood cells (RBCs). 1. **Why Frequency is Correct:** When ultrasound waves strike moving RBCs, the reflected frequency shifts. If blood moves toward the transducer, the frequency increases (**positive Doppler shift**); if it moves away, the frequency decreases (**negative Doppler shift**). The magnitude of this shift is directly proportional to the velocity of blood flow, as described by the Doppler Equation: $\Delta f = \frac{2 f_0 v \cos\theta}{c}$. 2. **Why Other Options are Incorrect:** * **Amplitude:** Refers to the height/strength of the wave (loudness). Changes in amplitude relate to attenuation or power, not the Doppler shift. * **Direction:** While the direction of flow determines whether the frequency increases or decreases, the Doppler effect itself is defined by the change in the wave's physical property—its frequency. **Clinical Pearls for NEET-PG:** * **Doppler Shift Range:** Though ultrasound is in the MHz range, the resulting Doppler shift is usually in the **audible range (20 Hz – 20 kHz)**. * **Cosine $\theta$:** The Doppler shift is maximal when the ultrasound beam is parallel to flow ($0^\circ$) and **zero** when the beam is perpendicular ($90^\circ$). * **Color Doppler:** Red typically indicates flow *towards* the probe (BART: Blue Away, Red Towards), while Blue indicates flow *away*. This is a shift in frequency, not a change in the actual color of blood.

Question 136: What material is a USG probe typically made of?

A. Barium
B. Quartz (Correct Answer)
C. Sodium iodide
D. Diamond

Explanation: **Explanation:** The core component of an ultrasound probe is the **piezoelectric crystal**. These materials possess the unique property of converting electrical energy into mechanical energy (ultrasound waves) and vice versa—a phenomenon known as the **Piezoelectric Effect**. **Why Quartz is Correct:** **Quartz** is a naturally occurring piezoelectric crystal. In the early development of ultrasound technology, quartz was the primary material used for transducers because of its ability to vibrate at high frequencies when an electric current is applied. While modern ultrasound probes often use synthetic ceramics like **Lead Zirconate Titanate (PZT)**, Quartz remains the classic textbook answer for the fundamental material used in USG probes. **Why the Other Options are Incorrect:** * **Barium:** While Barium Titanate is a piezoelectric ceramic, pure Barium is a metal and does not possess piezoelectric properties. * **Sodium Iodide:** This is a scintillator material used in **Gamma Cameras (Nuclear Medicine)** and CT scan detectors to convert ionizing radiation into light. It has no role in generating sound waves. * **Diamond:** Although diamond has high thermal conductivity, it does not exhibit the piezoelectric effect required for ultrasound imaging. **High-Yield Clinical Pearls for NEET-PG:** * **Lead Zirconate Titanate (PZT):** This is the most common **synthetic** piezoelectric material used in modern clinical probes due to its higher efficiency compared to quartz. * **Curie Point:** This is the critical temperature above which a piezoelectric crystal loses its magnetic/piezoelectric properties. This is why USG probes **cannot be autoclaved** (heat sterilized). * **Transducer Function:** It acts as both a **transmitter** (Inverse Piezoelectric effect) and a **receiver** (Piezoelectric effect) of sound waves.

Question 137: Which imaging modality utilizes piezoelectric crystals and is safe from radiation?

A. Magnetic Resonance Imaging (MRI)
B. Ultrasound (US) (Correct Answer)
C. Computed Tomography (CT)
D. All of the above

Explanation: ### Explanation **Correct Answer: B. Ultrasound (US)** **Underlying Concept:** Ultrasound imaging is based on the **Piezoelectric Effect**. Inside the ultrasound transducer, there are **piezoelectric crystals** (most commonly Lead Zirconate Titanate or PZT). When an electric current is applied to these crystals, they vibrate and produce high-frequency sound waves (the reverse piezoelectric effect). Conversely, when returning echoes hit the crystals, they generate an electric signal (the piezoelectric effect), which the machine processes into an image. Because ultrasound uses sound waves rather than ionizing electromagnetic waves, it is **non-ionizing** and safe from radiation. **Why Incorrect Options are Wrong:** * **A. Magnetic Resonance Imaging (MRI):** While MRI is also safe from ionizing radiation, it does not use piezoelectric crystals. It utilizes powerful magnetic fields and radiofrequency (RF) pulses to align and flip hydrogen protons in the body. * **C. Computed Tomography (CT):** CT scans utilize **ionizing radiation** (X-rays) to create cross-sectional images. They do not use piezoelectric crystals; instead, they use X-ray tubes and digital detectors. **High-Yield Clinical Pearls for NEET-PG:** * **Safety:** Ultrasound is the modality of choice for imaging in **pregnancy** and for **pediatric** patients due to the absence of radiation (ALARA principle). * **Artifacts:** Knowledge of "Acoustic Shadowing" (seen in gallstones/calcification) and "Acoustic Enhancement" (seen in cysts) is frequently tested. * **Doppler Effect:** Used to evaluate blood flow; it involves a shift in frequency when sound waves reflect off moving Red Blood Cells (RBCs). * **Therapeutic US:** High-intensity focused ultrasound (HIFU) is used for treating conditions like uterine fibroids.

Question 138: In colour Doppler, the colour displayed depends upon which of the following?

A. The strength of the returning echo
B. The relation of the transducer to the direction of blood flow (Correct Answer)
C. The frequency of the Doppler used
D. The type of Doppler machine used

Explanation: ### Explanation The correct answer is **B. The relation of the transducer to the direction of blood flow.** **Why Option B is Correct:** Colour Doppler is based on the **Doppler Shift principle**, where the frequency of sound changes depending on the relative motion between the source (transducer) and the receiver (red blood cells). The direction of blood flow relative to the transducer determines the color assigned: * **Flow toward the transducer:** Results in a positive Doppler shift, conventionally displayed as **Red**. * **Flow away from the transducer:** Results in a negative Doppler shift, conventionally displayed as **Blue**. This is often remembered by the mnemonic **BART** (Blue Away, Red Toward). If the transducer is perpendicular (90°) to the vessel, no shift is detected (cosine 90° = 0), resulting in a "black" signal or dropout. **Why Other Options are Incorrect:** * **A. Strength of the returning echo:** This determines the **brightness (amplitude)** in B-mode (Grey-scale) imaging or Power Doppler, but not the specific color hue in color Doppler. * **C. Frequency of the Doppler used:** While the frequency affects the magnitude of the shift (and depth of penetration), it does not dictate the color assigned to the flow direction. * **D. Type of Doppler machine:** The physics of the Doppler effect is universal; the color assignment is a standardized software convention across all machines. **High-Yield Clinical Pearls for NEET-PG:** * **Doppler Equation:** $\Delta f = \frac{2 f_0 v \cos \theta}{c}$. The angle ($\theta$) is critical; the ideal angle for clinical Doppler is **$\leq$ 60 degrees**. * **Aliasing:** Occurs when the blood velocity exceeds the **Nyquist limit** (PRF/2), causing the color to "wrap around" (e.g., bright red appearing as blue). * **Power Doppler:** More sensitive to slow flow but **does not** provide information on direction or velocity. * **Duplex Ultrasound:** Refers to the simultaneous use of B-mode (structural) and Spectral Doppler (flow).

Question 139: "Lemon sign" and "Banana sign" on Antenatal Ultrasound are seen in which condition?

A. Down syndrome
B. Chiari Malformation (Correct Answer)
C. Turner syndrome
D. Klinefelter syndrome

Explanation: ### Explanation The "Lemon" and "Banana" signs are classic sonographic markers of **Neural Tube Defects (NTDs)**, specifically associated with **Arnold-Chiari Malformation Type II**. **1. Why Chiari Malformation is Correct:** These signs occur due to the downward displacement of the hindbrain through the foramen magnum, which creates a pressure gradient: * **Lemon Sign:** The frontal bones of the fetal skull collapse inward (scalloping), giving the head a shape resembling a lemon. This is due to low intracranial pressure. While it is highly sensitive for spina bifida, it often disappears after 24 weeks as the skull bones ossify. * **Banana Sign:** The cerebellum is pulled downward and wrapped around the brainstem, losing its typical "dumbbell" shape and appearing curved like a banana. This also leads to the obliteration of the **Cisterna Magna**. **2. Why Other Options are Incorrect:** * **Down Syndrome (Trisomy 21):** Associated with an increased **Nuchal Translucency (NT)**, absent nasal bone, echogenic intracardiac focus, and duodenal atresia ("Double bubble sign"). * **Turner Syndrome (45, XO):** Characterized by **Cystic Hygroma** (posterior neck fluid collection) and coarctation of the aorta. * **Klinefelter Syndrome (47, XXY):** Usually does not present with specific structural anomalies detectable on routine antenatal ultrasound. **Clinical Pearls for NEET-PG:** * **Banana sign** is more specific for spina bifida than the lemon sign. * The presence of these signs should prompt a meticulous search for **Spina Bifida Aperta** (Meningomyelocele). * **Strawberry skull** is associated with **Trisomy 18** (Edwards Syndrome). * **Cisterna Magna measurement:** Normal is **2–10 mm**. If <2 mm, suspect Chiari II; if >10 mm, suspect Dandy-Walker malformation.

Question 140: All of the following are ultrasonographic fetal growth parameters except?

A. Biparietal diameter
B. Head circumference
C. Transcerebeller diameter (Correct Answer)
D. Femur length

Explanation: **Explanation:** In fetal ultrasonography, **fetal growth parameters** are specific biometric measurements used to estimate the **Estimated Fetal Weight (EFW)** and assess for conditions like Intrauterine Growth Restriction (IUGR) or macrosomia. 1. **Why Transcerebellar Diameter (TCD) is the correct answer:** While TCD is a vital biometric measurement, it is primarily used for **dating the pregnancy (gestational age)** rather than assessing growth. The cerebellum is relatively resistant to growth restriction (the "brain-sparing effect"), meaning its size remains consistent even if the fetus is malnourished. Therefore, it serves as a reliable baseline to determine the actual age of the fetus when other parameters are lagging. 2. **Analysis of Incorrect Options (Standard Growth Parameters):** * **Biparietal Diameter (BPD) & Head Circumference (HC):** These measure the fetal head. HC is considered more reliable than BPD in cases of abnormal head shapes (dolichocephaly/brachycephaly). * **Femur Length (FL):** This measures the longitudinal growth of the skeletal system. * **Abdominal Circumference (AC):** (Though not listed, it is the most sensitive indicator of fetal growth/nutrition). * *Note:* The combination of BPD, HC, FL, and AC is used in the **Hadlock Formula** to calculate EFW. **High-Yield Clinical Pearls for NEET-PG:** * **Most sensitive parameter for IUGR:** Abdominal Circumference (AC). * **Best parameter for dating in the 1st Trimester:** Crown-Rump Length (CRL). * **TCD Rule of Thumb:** Between 14 and 20 weeks, the TCD in millimeters is roughly equal to the gestational age in weeks. * **Brain-Sparing Effect:** In asymmetrical IUGR, the head and cerebellum are preserved while the AC decreases.

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Ultrasound — MCQs

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