Harmonics and Contrast Agents Flashcards

Flashcards on Harmonics and Contrast Agents in Ultrasound Imaging

Harmonic Imaging

The creation of an image from sound reflections at twice the frequency of the transmitted sound.

Harmonic Frequency

Frequency of transmitted sound x 2

Fundamental Frequency

The frequency of sound created by the transducer and transmitted into the body

Fundamental Image

Created by processing reflections that have the same frequency as the transmitted sound

Harmonic Image

Created by processing reflections that are twice the fundamental frequency

Linear Behavior

Systems respond in an even manner

Nonlinear Behavior

Behaves unevenly; irregular or disproportionate

Compressions

Squeezed together, higher pressure and density

Rarefactions

Stretched apart, lower pressure and density

Pulse Inversion Harmonics

Reflections contain fundamental and harmonic frequencies

Power Modulation Harmonic Imaging

Technique designed to augment harmonic reflections while eliminating distorted fundamental reflections; two consecutive ultrasound pulses are sent down each scan line (second pulse is twice the strength of the first pulse)

Contrast Agents (Microbubbles)

Gas bubbles encapsulated in a shell

Requirements for Contrast Agents

Safe, metabolically inert, long lasting, strong reflector of ultrasound, small enough to pass through capillaries

Resonance

Nonlinear change in a microbubbles size due to compressions and rarefactions of a sound wave

Oscillation

Regular variation in magnitude or position around a central point

Mechanical Index (MI)

The amount of contrast harmonics produced may be estimated by frequency of transmitted sound and rarefaction pressure of the sound wave