Abstract

Superharmonic Tissue Imaging

A.Bouakaz, N.De Jong (Erasmus University, Experimental Cardiology, Rotterdam )

e-mail: bouakaz@tch.fgg.eur.nl

Medical imaging has recently seen improvement in image quality with second-harmonic (2H) tissue imaging. This was attributed to less reverberations and haze and better sidelobe suppression compared to fundamental imaging. With selective use of 2H, there is a sacrifice however of dynamic range. In addition, to increase the sensitivity of a 2H system the spectral overlap between the fundamental and the 2H must be reduced, which deteriorates the axial-resolution. Consequently, a trade-off is mandatory between the resolution and the sensitivity. We show in this study that higher-harmonics (n>=3) possess superior characteristics to 2H. An elegant way to take advantage of the higher-harmonics is to combine them into a single component that we call SuperHarmonic (SH). We show using measurements and simulations that several advantages are obtained with SH over 2H. 1- at the transducer surface, SH is 30dB lower than 2H. 2- after propagation, the superharmonic builds up more rapidly giving higher SNR. 3- superior removal and elimination of off-axis echoes by damping sidelobes and grating lobes. 4- the lateral resolution shows an improvement by a factor of 2. Moreover, SH imaging does not suffer from the resolution-sensitivity trade-off and since it operates over a wide frequency band, the axial resolution is further improved. In conclusion, SH brings back the lost energy due to distortion into a valuable information giving significant improvements in image quality over 2H imaging. To use SH a special array transducer has been developed and used to cover frequencies from fundamental to 5th harmonic. SH images of a phantom showed exceptionally improved clarity with dramatically cleaner and sharper contrast between the different structures of the phantom

Section : 5