Tissue Harmonic Imaging + Contrast

sound pressure waves are caused by a __

mechanical action

Transmitted frequency is called the __ FREQUENCY (operating frequency) 

fundamental

Pressure waves travel through ___ propagation 

non-linear

The harmonic signal gets __ as it goes deeper 

stronger 

Fundamental frequency is the same for __ and __  

transmission and reception 

Harmonic signals are — the fundamental frequency

Double

Harmonic signals are generated by —

Tissue

Attenuation limits the - of harmonic signal

Depth

Harmonic signals are generated with __

Depth

TISSUE HARMONIC IMAGING IS VERY DEPENDENT ON THE —- AND ON —- 

Acoustic output power and depth

The stronger the output power the stronger the -

Harmonic signal

HARMONICS HAVE BETTER — BECAUSE THE BEAM IS MORE —- 

Lateral resolution, narrow

Tissue harmonic imaging improves quality because

Primary beam is much NARROWER, eliminates grating lobes (artifact), harmonic beam is generated deep to area where many artifacts occur (superficial reverberation)

PULSE INVERSION is one way to eliminate the — signal 

Fundamental

In pulse inversion machine sends one regular pulse and then another pulse inverted — degrees. When it overlaps, they — each other out 

180, cancel

Other methods to eliminate the fundamental signal

side by side phase cancellation or pulse-coded harmonics 

Superficial

Weak harmonic signal

Deep

attenuation eats the sound

Vibrating tissue creates its own sound at - the incident (fundamental, f0) frequency 

Double

We image with the - (2f0) and the fundamental is filtered out 

Second harmonic

Advantages of THI

decreases grating lobes & reverberation, improved lateral resolution, improved border definition, decrease in image noise, enhanced contrast resolution 

subharmonic imaging images at —

half the fundamental frequency 

Subharmonic imaging has — spatial resolution

Poor, due to suppressed tissue

Subharmonic imaging is used with — to evaluate blood flow

Contrast imaging

Subharmonic imaging is used for

intravascular pressure estimation, intracardiac pressures, portal-venous, intracranial, etc

Benefits of Subharmonic imaging: __ of tissue signal, allows better visualization of , more — than color and power doppler

Suppression, tumor microcirculation, sensitive

In spatial compounding - beams from different angles are sent out of the transducer instead of 1

3

Spatial compounding eliminates — and reduces —-

Eliminates edge shadows, speckle artifact