UTC Ultrasound Physics & Instrumentation 1 — Questions and Answers
Question 1: What is the accepted average speed of sound in soft tissue used as the standard for ultrasound imaging calculations?
- 1,450 m/s
- 1,540 m/s (Correct answer)
- 1,620 m/s
- 1,330 m/s
Correct answer: 1,540 m/s
The accepted average speed of sound in soft tissue is 1,540 m/s, which is the standard value used by all ultrasound systems for depth calculations.
Question 2: The piezoelectric effect in ultrasound transducers refers to which property?
- Absorption of sound waves by tissue
- Conversion of electrical energy to mechanical vibrations and vice versa (Correct answer)
- Reflection of sound at tissue interfaces
- Attenuation of sound waves in fluid
Correct answer: Conversion of electrical energy to mechanical vibrations and vice versa
The piezoelectric effect is the ability of certain crystals to convert electrical energy into mechanical vibrations (and vice versa), which is the fundamental operating principle of ultrasound transducers.
Question 3: Acoustic impedance (Z) is calculated using which two factors?
- Frequency and wavelength
- Amplitude and phase
- Density and propagation speed (Correct answer)
- Power and intensity
Correct answer: Density and propagation speed
Acoustic impedance Z = density (ρ) × propagation speed (c); differences in impedance at tissue interfaces determine how much sound is reflected versus transmitted.
Question 4: Which type of resolution describes the ability to distinguish two adjacent structures lying side by side perpendicular to the ultrasound beam?
- Axial resolution
- Lateral resolution (Correct answer)
- Temporal resolution
- Contrast resolution
Correct answer: Lateral resolution
Lateral resolution (also called azimuthal or transverse resolution) is the ability to distinguish two structures that are side by side in the direction perpendicular to the beam.
Question 5: What happens to the wavelength of an ultrasound wave when the frequency is increased while propagation speed remains constant?
- Wavelength increases proportionally
- Wavelength remains unchanged
- Wavelength decreases proportionally (Correct answer)
- Wavelength doubles
Correct answer: Wavelength decreases proportionally
Since wavelength = velocity/frequency (λ = v/f), increasing frequency while velocity remains constant in tissue causes wavelength to decrease proportionally.
Question 6: Which unit is used to measure the total acoustic power output of an ultrasound transducer?
- Decibels (dB)
- Watts (W) (Correct answer)
- Hertz (Hz)
- Pascal (Pa)
Correct answer: Watts (W)
Acoustic power is measured in watts (W), representing the total energy output per unit time from the transducer.
Question 7: Axial resolution in ultrasound is primarily determined by which factor?
- Beam width at the focal zone
- Spatial pulse length (Correct answer)
- Pulse repetition frequency
- Transducer diameter
Correct answer: Spatial pulse length
Axial resolution equals half the spatial pulse length; shorter pulses (higher frequency, fewer cycles) produce better axial resolution for distinguishing structures along the beam axis.
UTC Ultrasound Physics & Instrumentation 1
What is the accepted average speed of sound in soft tissue used as the standard for ultrasound imaging calculations?