SPI Ultrasound Physics Review| 296 QUESTIONS| WITH VERIFIED COMPLETE
SOLUTION
Course
Ultrasound Physics
1. Wave Propagation
An ultrasound wave travels through soft tissue at an average speed of:
A. 330 m/s
B. 540 m/s
C. 1540 m/s
D. 3000 m/s
Answer: C. 1540 m/s
Explanation:
Diagnostic ultrasound systems assume sound travels in soft tissue at 1540 m/s. This constant is
used to calculate depth and image formation.
2. Frequency and Resolution
Increasing transducer frequency will:
A. Increase penetration depth
B. Decrease axial resolution
C. Improve resolution but reduce penetration
D. Reduce attenuation
Answer: C. Improve resolution but reduce penetration
Explanation:
Higher frequency waves have shorter wavelengths, producing better image resolution. However,
they attenuate faster, reducing penetration depth.
3. Acoustic Impedance
Acoustic impedance is calculated using:
A. Frequency × wavelength
B. Density × propagation speed
C. Velocity ÷ frequency
D. Pressure × power
Answer: B. Density × propagation speed
,Explanation:
Z=ρcZ=\rho cZ=ρc
Where:
ZZZ = acoustic impedance
ρ\rhoρ = tissue density
ccc = propagation speed
Large impedance differences between tissues create stronger reflections.
4. Doppler Shift
A positive Doppler shift indicates blood flow:
A. Perpendicular to transducer
B. Away from transducer
C. Toward transducer
D. Stationary
Answer: C. Toward transducer
Explanation:
When blood cells move toward the transducer, returning echoes have higher frequency, creating
a positive Doppler shift.
5. Axial Resolution
Axial resolution primarily depends on:
A. Beam width
B. Pulse length
C. Imaging depth
D. Frame rate
Answer: B. Pulse length
Explanation:
Shorter spatial pulse length improves axial resolution by allowing the system to distinguish
structures close together along the beam axis.
6. Attenuation
,The major cause of attenuation in soft tissue is:
A. Reflection
B. Refraction
C. Absorption
D. Interference
Answer: C. Absorption
Explanation:
Absorption converts sound energy into heat and is the main contributor to attenuation in biologic
tissues.
7. Doppler Angle
For the most accurate Doppler velocity measurement, the Doppler angle should ideally be:
A. 90°
B. 0°
C. 120°
D. 180°
Answer: B. 0°
Explanation:
Maximum Doppler shift occurs when flow is parallel to the sound beam. Clinically, angles ≤60°
are preferred.
8. Aliasing
Aliasing occurs when Doppler shift exceeds:
A. Pulse repetition frequency limit
B. Acoustic impedance
C. Dynamic range
D. Temporal resolution
Answer: A. Pulse repetition frequency limit
Explanation:
Aliasing occurs in pulsed Doppler when the Doppler frequency exceeds the Nyquist limit.
The Nyquist limit is:
Nyquist Limit=PRF2Nyquist\ Limit=\frac{PRF}{2}Nyquist Limit=2PRF
, 9. Refraction
Refraction occurs when ultrasound beam:
A. Encounters identical tissues
B. Changes direction crossing tissue boundaries
C. Completely reflects back
D. Stops propagating
Answer: B. Changes direction crossing tissue boundaries
Explanation:
Refraction happens when sound enters a medium with different propagation speed at an oblique
angle.
10. Temporal Resolution
Temporal resolution improves with:
A. Increased frame rate
B. Increased persistence
C. Increased imaging depth
D. Larger sector width
Answer: A. Increased frame rate
Explanation:
Higher frame rates allow the system to display motion more accurately over time, improving
temporal resolution.
11. Pulse Repetition Frequency (PRF)
Increasing PRF will:
A. Increase aliasing
B. Decrease Doppler scale
C. Reduce aliasing risk
D. Decrease penetration depth
Answer: C. Reduce aliasing risk
Explanation:
Higher PRF raises the Nyquist limit, reducing the chance of aliasing in pulsed Doppler systems.
SOLUTION
Course
Ultrasound Physics
1. Wave Propagation
An ultrasound wave travels through soft tissue at an average speed of:
A. 330 m/s
B. 540 m/s
C. 1540 m/s
D. 3000 m/s
Answer: C. 1540 m/s
Explanation:
Diagnostic ultrasound systems assume sound travels in soft tissue at 1540 m/s. This constant is
used to calculate depth and image formation.
2. Frequency and Resolution
Increasing transducer frequency will:
A. Increase penetration depth
B. Decrease axial resolution
C. Improve resolution but reduce penetration
D. Reduce attenuation
Answer: C. Improve resolution but reduce penetration
Explanation:
Higher frequency waves have shorter wavelengths, producing better image resolution. However,
they attenuate faster, reducing penetration depth.
3. Acoustic Impedance
Acoustic impedance is calculated using:
A. Frequency × wavelength
B. Density × propagation speed
C. Velocity ÷ frequency
D. Pressure × power
Answer: B. Density × propagation speed
,Explanation:
Z=ρcZ=\rho cZ=ρc
Where:
ZZZ = acoustic impedance
ρ\rhoρ = tissue density
ccc = propagation speed
Large impedance differences between tissues create stronger reflections.
4. Doppler Shift
A positive Doppler shift indicates blood flow:
A. Perpendicular to transducer
B. Away from transducer
C. Toward transducer
D. Stationary
Answer: C. Toward transducer
Explanation:
When blood cells move toward the transducer, returning echoes have higher frequency, creating
a positive Doppler shift.
5. Axial Resolution
Axial resolution primarily depends on:
A. Beam width
B. Pulse length
C. Imaging depth
D. Frame rate
Answer: B. Pulse length
Explanation:
Shorter spatial pulse length improves axial resolution by allowing the system to distinguish
structures close together along the beam axis.
6. Attenuation
,The major cause of attenuation in soft tissue is:
A. Reflection
B. Refraction
C. Absorption
D. Interference
Answer: C. Absorption
Explanation:
Absorption converts sound energy into heat and is the main contributor to attenuation in biologic
tissues.
7. Doppler Angle
For the most accurate Doppler velocity measurement, the Doppler angle should ideally be:
A. 90°
B. 0°
C. 120°
D. 180°
Answer: B. 0°
Explanation:
Maximum Doppler shift occurs when flow is parallel to the sound beam. Clinically, angles ≤60°
are preferred.
8. Aliasing
Aliasing occurs when Doppler shift exceeds:
A. Pulse repetition frequency limit
B. Acoustic impedance
C. Dynamic range
D. Temporal resolution
Answer: A. Pulse repetition frequency limit
Explanation:
Aliasing occurs in pulsed Doppler when the Doppler frequency exceeds the Nyquist limit.
The Nyquist limit is:
Nyquist Limit=PRF2Nyquist\ Limit=\frac{PRF}{2}Nyquist Limit=2PRF
, 9. Refraction
Refraction occurs when ultrasound beam:
A. Encounters identical tissues
B. Changes direction crossing tissue boundaries
C. Completely reflects back
D. Stops propagating
Answer: B. Changes direction crossing tissue boundaries
Explanation:
Refraction happens when sound enters a medium with different propagation speed at an oblique
angle.
10. Temporal Resolution
Temporal resolution improves with:
A. Increased frame rate
B. Increased persistence
C. Increased imaging depth
D. Larger sector width
Answer: A. Increased frame rate
Explanation:
Higher frame rates allow the system to display motion more accurately over time, improving
temporal resolution.
11. Pulse Repetition Frequency (PRF)
Increasing PRF will:
A. Increase aliasing
B. Decrease Doppler scale
C. Reduce aliasing risk
D. Decrease penetration depth
Answer: C. Reduce aliasing risk
Explanation:
Higher PRF raises the Nyquist limit, reducing the chance of aliasing in pulsed Doppler systems.
