CCI Ultrasound Physics and Instrumentation 4 — Questions and Answers
Question 1: The piezoelectric effect in ultrasound transducers refers to:
- Generation of heat from electrical current
- Conversion of electrical energy to mechanical vibration and vice versa (Correct answer)
- Reflection of sound at tissue interfaces
- Absorption of sound energy by tissue
Correct answer: Conversion of electrical energy to mechanical vibration and vice versa
Piezoelectric crystals deform mechanically when voltage is applied (transmit) and generate voltage when mechanically deformed by returning echoes (receive).
Question 2: Increasing the gain on an ultrasound system primarily affects:
- The frequency of transmitted pulses
- The amplification of returning echo signals (Correct answer)
- The depth of field
- The pulse repetition frequency
Correct answer: The amplification of returning echo signals
Gain uniformly amplifies all returning echo signals electronically without changing transmission power or depth penetration.
Question 3: Which Doppler equation component must the sonographer manually align to minimize velocity measurement error?
- Pulse repetition frequency
- Doppler angle (θ) (Correct answer)
- Sample volume depth
- Wall filter setting
Correct answer: Doppler angle (θ)
Velocity = (Doppler shift × c) / (2 × frequency × cos θ); the angle θ must be estimated and corrected by the operator to calculate true velocity.
Question 4: A spectral Doppler waveform showing systolic flow above and diastolic flow below the baseline in an arterial study most likely indicates:
- Laminar antegrade flow throughout the cycle
- Bidirectional flow with forward systole and reverse diastole (triphasic pattern) (Correct answer)
- Continuous venous contamination
- Severe aliasing artifact
Correct answer: Bidirectional flow with forward systole and reverse diastole (triphasic pattern)
A triphasic arterial waveform shows rapid systolic forward flow, brief early diastolic flow reversal, and then slow antegrade late diastolic flow, characteristic of normal peripheral arteries.
Question 5: The axial resolution of an ultrasound system is best improved by:
- Decreasing transducer frequency
- Shortening pulse duration (using higher frequency or damped transducers) (Correct answer)
- Increasing gain
- Widening the sector angle
Correct answer: Shortening pulse duration (using higher frequency or damped transducers)
Axial resolution = spatial pulse length / 2; shorter pulses achieved with higher frequencies or heavy damping allow discrimination of closely spaced objects along the beam axis.
Question 6: In echocardiography, the term 'frame rate' refers to:
- The number of Doppler samples per cardiac cycle
- The number of 2D images acquired per second (Correct answer)
- The speed of sound in tissue
- The pulse repetition frequency of M-mode
Correct answer: The number of 2D images acquired per second
Frame rate is the number of complete 2D image frames acquired per second and determines the temporal resolution of real-time imaging.
Question 7: Which bioeffect mechanism is most relevant to diagnostic ultrasound safety concerns at standard clinical intensities?
- Cavitation (both stable and inertial) (Correct answer)
- Thermal damage from continuous heating
- Radiation pressure effects
- Ionizing radiation exposure
Correct answer: Cavitation (both stable and inertial)
Cavitation—oscillation and possible collapse of microbubbles in tissue—is the primary non-thermal bioeffect concern, though significant risk at diagnostic power levels is not established.
CCI Ultrasound Physics and Instrumentation 4
The piezoelectric effect in ultrasound transducers refers to: