Tablet based real-time Doppler spectrum processing

Abstract

By utilizing mobile, low-cost Doppler ultrasound technology in developing countries, the mortality rate of unborn children, small children and pregnant women might be reduced. Two main Doppler techniques which are used in ultrasound are the Doppler spectrum and the Doppler audio. The Doppler spectrum is used for quantitative analysis of the blood-flow while the Doppler audio is used for guidance during recordingThis thesis presents the implementation of a real-time Dopplerspectrum generator and a real-time Doppler stereo audio generator,which is implemented on Android mobile devices; along with real-timeratings and optimizations. The Doppler spectrum implementation wascompared to a Matlab implementation, while the Doppler audio wascompared to a synthetic test signal. The frequency leakage, in theDoppler stereo audio generation, from positive- to negative Dopplershifts and vice versa was at about −20dB with the synthetic testsignal.The performance of a mid- to high-end Android tablet showed high framerates for Fast Fourier-Transform lengths up to 128 with both 75 and 87.5 percent overlap and audio-playback frequencies of 8kHz and 16kHz. The low- to mid-end tablet displayed low framerates with the current implementation.The optimization of the Fast Fourier-transform by utilizing FFTW has shown promising results to increase the framerate on the low- to mid-end tablet. Other ways of improving the framerate on low-end tablets is to turn off the audio or turn off the stereo processing along with reducing the settings on the spectrum generator.