Development of an algorithm for HIFU focus visualization

The ultrasound waves emitted from the HIFU transducer propagate through water and various tissue layers to a focus of the internal body. During propagation the multiple refractions and reflections occur due to in-homogeneity nature of the tissues. These cause the aberration of the focal location. Therefore, in the view of safety for the HIFU treatment it is important to know where the focus is exactly formed. In this study, the method of synchronization control between a HIFU and an imaging devices is proposed for the focus visualization. In order to get a clear focus image, the signal processing with the harmonics of the transmitted HIFU pulses is introduced. The convex imaging probe is installed at the center of the phased-array HIFU transducer. The time delays for the imaging probe as well as the HIFU array-elements are calculated along the HIFU focus location. The HIFU array elements send a short-pulse train of 1 MHz and the imaging probe starts receiving the echo-signal in sequence according to the delays. In this manner, the IQ data were collected using the ultrasound device, ECUBE 9 of ALPINION MEDICAL SYSTEMS. At this stage, the focus is not clear due to the random distribution of the scatters with non-uniform intensity. Through the FFT of the IQ data the spatial distribution of the amplitudes at the fundamental and the harmonic frequencies are extracted. The amplitudes at the harmonic frequencies are divided by the amplitude at the fundamental frequency. And then the results from the division are displayed on the B-mode ultrasound images. This algorithm was tested in ex-vivo and in-vivo. The algorithm was verified through the in-vivo and ex-vivo experiments. It is confirmed that the algorithm can provide the precise information of the focus location in a simple manner.