CCI Ultrasound Physics and Instrumentation 3 — Questions and Answers
Question 1: What happens to the Doppler angle as it approaches 90 degrees relative to blood flow?
- Measured velocity increases toward its true value
- Measured velocity approaches zero regardless of true velocity (Correct answer)
- Aliasing is eliminated
- The PRF must be decreased
Correct answer: Measured velocity approaches zero regardless of true velocity
The Doppler equation includes the cosine of the angle; at 90°, cos(90°) = 0, so the detected Doppler shift becomes zero regardless of actual blood velocity.
Question 2: Which transducer type is most commonly used for adult transthoracic echocardiography?
- Linear array
- Curvilinear array
- Phased array (Correct answer)
- Mechanical sector
Correct answer: Phased array
Phased array transducers use electronic steering to create a small footprint with a wide sector image, making them ideal for imaging through narrow intercostal spaces.
Question 3: In color flow Doppler, the variance map (green) indicates:
- High velocity laminar flow
- Turbulent or disturbed flow (Correct answer)
- Retrograde flow only
- Absence of flow
Correct answer: Turbulent or disturbed flow
Green color or color variance in the color flow map indicates turbulent or disturbed flow with multiple velocities present within the sample volume.
Question 4: The lateral resolution of an ultrasound beam is primarily determined by:
- Pulse duration
- Beam width at a given depth (Correct answer)
- Frequency alone
- Depth of the target
Correct answer: Beam width at a given depth
Lateral resolution equals the beam width at the depth of the target; objects closer together than the beam width cannot be resolved as separate structures.
Question 5: Which statement about continuous wave (CW) Doppler is correct?
- It has range resolution and can pinpoint sample depth
- It can measure very high velocities without aliasing (Correct answer)
- It uses a single pulsing crystal
- It has a maximum velocity limit set by the Nyquist theorem
Correct answer: It can measure very high velocities without aliasing
CW Doppler continuously transmits and receives without pulsing, so it has no PRF limit and can accurately measure very high velocities without aliasing.
Question 6: Acoustic shadowing distal to a calcified structure occurs because:
- The structure absorbs and reflects most of the incident sound energy (Correct answer)
- Refraction bends sound around the structure
- The structure enhances sound transmission
- Reverberation fills the distal area with echoes
Correct answer: The structure absorbs and reflects most of the incident sound energy
Dense calcified structures have very high acoustic impedance and absorb or reflect nearly all incident ultrasound, leaving a hypoechoic (shadow) region posterior to the structure.
Question 7: The 'dead zone' near-field artifact is caused by:
- Transducer ringing after pulse transmission that obscures shallow structures (Correct answer)
- Side lobes creating false echoes
- Refraction at tissue interfaces
- High gain settings
Correct answer: Transducer ringing after pulse transmission that obscures shallow structures
After each transmitted pulse, the transducer crystals continue to vibrate briefly (ring-down), masking echoes from very shallow structures during this dead zone period.
CCI Ultrasound Physics and Instrumentation 3
What happens to the Doppler angle as it approaches 90 degrees relative to blood flow?