Ultrasound Physics and Instrumentation Flashcards

Which property of ultrasound determines the maximum depth of penetration in tissue?

Answer: Frequency

Lower frequencies penetrate deeper because attenuation increases with frequency, so lower frequencies lose less energy per unit depth.

The term 'acoustic impedance' is defined as the product of:

Answer: Density and propagation velocity

Acoustic impedance (Z) equals tissue density (ρ) multiplied by the speed of sound (c) in that medium, expressed as Z = ρc.

What artifact occurs when a strong reflector causes repeated echo returns at equally spaced intervals?

Answer: Reverberation artifact

Reverberation artifacts occur when sound bounces repeatedly between two strong reflectors, creating equally spaced false echoes at multiples of the true depth.

In pulsed wave Doppler, the Nyquist limit determines the maximum:

Answer: Velocity that can be accurately measured without aliasing

The Nyquist limit is half the pulse repetition frequency; velocities causing Doppler shifts exceeding this value will alias and display incorrectly.

Which mode of echocardiography provides the highest temporal resolution for cardiac motion analysis?

Answer: M-mode

M-mode records a single line of information at a very high frame rate (typically 1,000 frames/sec), providing superior temporal resolution for cardiac motion.

The speed of sound in soft tissue is approximately:

Answer: 1,540 m/s

Ultrasound machines assume a constant propagation speed of 1,540 m/s in soft tissue to calculate depth from echo return time.

Harmonic imaging improves image quality primarily by:

Answer: Reducing side lobe and reverberation artifacts

Tissue harmonic imaging uses the second harmonic frequency generated within tissue, which has a narrower beam and fewer near-field artifacts than the fundamental frequency.