TISSUE HARMONIC IMAGING (THI) Aimi Alwani bt Mat Nawi A141042

WHAT IS THI? Tissue harmonic imaging (THI) is a sonographic technique that can potentially provide images of higher quality than can conventional sonographic techniques does. The physical basis for improvement of image quality with THI sonography is associated with two factors: - narrowing of the width of the ultrasound beam - reduction of side lobe artifacts.

Harmonics are frequency that occur at multiples of the fundamental (first harmonic) or transmitted sonographic frequency. Tissue harmonic images are formed by utilizing the harmonic signals that are generated by tissue and by electronically filtering out the fundamental frequency and its grating lobes.

Because harmonics are generated within the tissue itself, a certain distance from the sender is required in order for the harmonic wave to build up. Near-field imaging does not permit this. Conversely, signal intensity and sensitivity are lost in the far field. Therefore, harmonic imaging is most applicable when scanning structures in the middle range.

ADVANTAGE OF THI Imaging using harmonic frequencies offers several potential advantages,including : - improved lateral resolution - reduced side lobe artifact - improved signal-to-noise ratio  These characteristics of harmonic imaging significantly improve the quality of the sonogram.

DISADVANTAGE OF THI In very thin individuals, where the transducer is in very close proximity to the heart, the near field is almost entirely composed of fundamental frequencies and hence the apex is often inadequately visualized Conversely, in obese patients, the very far field will also have poor harmonics and thus poor image resolution.

Image showing the portal vein comparison between the fundamental sonographic (A), and THI (B)

THANK YOU... :)