Dynamic Range and Harmonics in Ultrasound Physics

This set of flashcards covers key concepts related to dynamic range, harmonics, and contrast agents in ultrasound physics as presented in the lecture notes.

What is dynamic range in ultrasound physics?

describing the extent to which a signal can vary and still maintain accuracy.

What units are used to measure dynamic range?

Decibels.

What happens to the dynamic range of information as it is processed?

It decreases.

What is the dynamic range of a transducer?

120 dB.

What is the dynamic range of a receiver?

100 to 120 dB.

What is the dynamic range of a scan converter?

40 to 50 dB.

What is the dynamic range of a display?

20 to 30 dB.

What is compression in ultrasound physics?

reducing the dynamic range of a signal without introducing errors.

Why is compression beneficial for images?

It allows us to effectively see the meaningful clinical information.

What issue may arise without compression of dynamic range?

Inaccuracies when signals pass from the receiver to the scan converter.

What is a narrow dynamic range?

few gray shades; (a bistable image)

What does a wide dynamic range indicate?

many shades of gray; (a grayscale image)

What are the two forms of harmonic imaging?

Tissue and contrast

What creates harmonic frequencies?

Nonlinear behavior

How does tissue harmonics occur?

Energy converts from fundamental to harmonic frequency during transmission.

What is the primary cause of tissue harmonics?

Sound traveling at slightly different speeds through soft tissue.

Why do strong artifacts appear in fundamental imaging?

Strong beam and superficial anatomic layers distorting the sound beam.

What do harmonics arise only in?

The non-distorted main beam.

What is pulse inversion harmonics?

A technique that utilizes harmonic reflections while eliminating distorted fundamental reflections.

What effect does pulse inversion have on frame rate?

It halves the frame rate.

What is power modulation harmonic imaging designed for?

To augment harmonic reflections and eliminate distorted fundamental reflections.

How is power modulation different from pulse inversion?

In power modulation, the second pulse is twice the strength of the first pulse.

What are contrast agents also known as?

Microbubbles.

What requirements must contrast agents meet?

They must be safe, metabolically inert, long-lasting, strong reflectors of ultrasound, and small enough to pass through capillaries.

What creates contrast harmonics?

Nonlinear changes in the sizes of microbubbles exposed to sound beams.

How is the mechanical index calculated?

Peak rarefaction pressure divided by frequency.

What are Microbubbles used for

To creat strong reflection that light up blood chambers, vessels, or other anatomic regions

What is the comparison between tissue and contrast harmonics?

Contrast harmonics are stronger and occur during reflection off microbubbles.

How do tissue harmonics and contrast harmonics differ in terms of occurrence?

Tissue harmonics occur during transmission, contrast harmonics require a contrast agents.

What is a key characteristic of contrast harmonics?

resonance and bubble disruption.

What influence does the outer shell of microbubbles have?

It affects their behavior and strength as contrast agents.

What is the significance of the mechanical index in ultrasound?

It relates to the amount of contrast harmonics produced based on pressure and frequency.

What type of behavior do microbubbles exhibit?

Nonlinear behavior

What indicates a higher mechanical index in ultrasound imaging?

Larger pressure variation and lower frequency.

Why are microbubbles considered strong scatterers of sound?

They can produce large oscillations or resonance from a small driving force.