1. TISSUE HARMONIC IMAGING (THI)
TIONG WEI SONG (A140479)

2. Tissue Harmonic Imaging (THI)
is a new grayscale imaging technique which results better quality images compared to conventional ultrasound imaging technique.
Tissue Harmonic Imaging has been found to
improve contrast resolution
reduce clutter
sharpen lesion borders

3. Why THI? Conventional THI
the returned signal is less intense, losing strength as it passes through tissue.
Poor image quality leads to uncertainty in diagnosis and costly repeat examinations
THI
the signal returned by the tissue includes not only the transmitted ‘fundamental’ frequency, but also signals ‘harmonic” frequency’
Good image quality

4. Physics
It exploits non-linear propagation of ultrasound through the body tissues. The high pressure portion of the wave travels faster than low pressure resulting in distortion of the shape of the wave.
This change in waveform leads to generation of harmonics from tissue.
At present, 2ndharmonic is being used to produce the image as the subsequent harmonics are of decreasing amplitude and hence insufficient to generate a proper image. 
These harmonic wave which are generated within the tissue, increase with depth to a point of maximum intensity and then decrease with further depth due to attenuation.
Hence the maximum intensity is achieved at an optimum depth below the surface. 

5. Principles of THI Transducer transmits wave at fundamental frequency.
Transducer is focused on the tissue of interest.
Transducer transmits wave at fundamental frequency.
Target tissue begins to oscillate
Echoes from the target tissue contain harmonic frequency backscatter signal, and fundamental frequency backscatter signal
Returning signal is mixed and filtered
Filtered signal contains only harmonic frequency echoes
Filtered signal is displayed, visualizing only resonant tissues near the focus

6. Clinical Benefits of THI
Decreased side lobe artifacts
improves signal-to-noise ratios and reduces artifacts
Increased axial and lateral resolution
improved axial resolution due to higher frequencies and better lateral resolution due to narrower beams.
Cystic clearing
Improved border delineation and contrast resolution
Aberration reduction
due to reduce in tissue aberration, which in turn reduce beam side lobes

7. Tissue Harmonic Imaging
Clinical Examples
liver
liver
aorta
aorta
Conventional imaging
Tissue Harmonic Imaging

8. Clinical Examples: Left Adrenal Mass
Conventional imaging
Tissue Harmonic Imaging

9. Summary
Tissue harmonic imaging benefits from the nonlinear propagation process in tissue
Harmonic beam is generated only where fundamental is strong
Weak fundamental scattered energy does not generate much harmonics
Clutter from tissue aberrations is low in harmonic content
Harmonic beam is low close to transducer where most aberrations occur

10. Reference
Tissue+Harmonic+Imaging
harmonic-imaging

11. Thank You