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

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

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

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. 

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

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

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

Clinical Examples: Left Adrenal Mass Conventional imaging Tissue Harmonic Imaging

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

Reference https://wiki.engr.illinois.edu/display/BIOE414/ Tissue+Harmonic+Imaging http://radiopaedia.org/articles/tissue- harmonic-imaging

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