Twice the fundamental frequency

Aka second harmonic

Irregular or disproportionate behavior; modeled equation does not progress in a straight path

1) As sound waves travel into the body, a miniscule amount of energy is converted from the fundamental frequency to the harmonic frequency; created during transmission

2) Weak sound beams do not create harmonics; intermediate = miniscule amount; strong sound beams = significant harmonics (created along beam's main axis; fewer artifacts/side lobes/grating lobes)

Strength of the tissue harmonic signal builds up as the wave travels deeper into the tissues then dies down

Tissue harmonics don't exist at superficial depths (increases signal to noise ratio)

A form of harmonic imaging where positive and negative pulses are transmitted down each scan line

Deconstructive interference in fundamental frequency

Constructive interference in harmonic frequency

Disadvantage: frame rate is 1/2 that of fundamental imaging; pulses inversion imaging degrades temporal resolution

Advantage: Improves image accuracy

Sends one weak pulse (no harmonic frequency) and then one strong pulse down each scan line 

During reception, reflections of the first pulse are doubled then subtracted from the second pulse, canceling out the fundamental frequencies

Only the harmonic portion of the second pulse remains

Substances used to enhance the contrast of structures or fluids within the body in medical imaging via microbubbles

Have different acoustic fingerprint than blood or tissue

Can be injected or ingested

Commonly used to enhance visibility of blood vessels and GI tract

Must be safe, metabolically inert, long lasting, strong reflector, and small enough to pass through capillaries

Created by microbubbles that act in non-linear manner when struck by sound waves (resonance)

Bubbles grow greater than they shrink when interacting with a strong beam

Created during reflection 

Peak rarefaction pressure is most important

= peak rarefaction pressure ÷ √F

Amount of estimated contrast harmonics

Increases with lower frequency sound and stronger sound waves

Nonlinear relationship between harmonic creation

Low beams <0.1 -> do not create harmonics

Intermediate beams 0.1-1.0 -> small amount of harmonics

High beams >1.0 -> create substantial harmonics; bubbles may expand and break apart

Trap gas and increase life of bubbles

Bubbles vanish quickly without

Flexible so can change shape without fracturing

Determines stability

Smaller molecules more likely to leak -> shrinkage

Larger molecules makes shell less permeable so molecules remain trapped