Image Processing Reference
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response is more important than the frequency feature clinically, and the target performance
in Table 4 is fulfilled mostly, we consider the complex IIR filter system to be the best device
for the direction separation of the Doppler audio system.
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(a) mod./demod. system: BLS=0
(b) mod./demod. System: BLS=+0.4・ fs
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Fig. 20. Frequency characterization of Doppler audio output
4.5 Implementation of complex IIR filter system
4.5.1 Signal processing simulation
We examine the possibility of using the complex IIR filter system in signal processing
simulation. The input signal is conceived to be for the actual venous blood model. The
model consists of a noise component (white noise), a blood vessel wall component (clutter:
low frequency high power), and a blood flow component. The powers and frequencies of
these components are shown in Table 8. The input and output waveforms and power
spectra of the processing blocks in the complex IIR filter system are shown in Fig. 21. The
amplitude of the left-hand-side waveform is normalized by clutter amplitude to be 2.
Moreover, 256-point FFT with a Hanning window is applied to the calculation of the right-
hand-side power spectrum. Figures 21(a) and 21(c) show the input and output waveforms of
zero insertion processing, respectively. A solid line denotes the I-component, and a dashed
line, the Q-component. Figures 21(e) and 21(g) show the Doppler audio outputs of both
directions at the zero baseline-shift. A solid line denotes the real component, and a dashed
line, the imaginary component. Figures 21(i) and 21(k) show the Doppler audio outputs of
both directions at the +0.4* fs baseline-shift. A solid line denotes the real-component, and a
dashed line, the imaginary-component. Figures 21(b), 21(d), 21(f), 21(h), 21(i) and 21(l) show
power spectra corresponding to the waveforms in the time domain. The aliasing spectra of
blood flow and clutter are observed in Fig. 21(d) for a zero insertion processing output.
Moreover, the approximately -20 dB DC component is observed at the center of the spectra.
This DC component, which is not removed using the Hanning window, does not affect the
latter complex band-pass filter processing. From the positive-side output waveform at the
zero baseline-shift shown in Fig. 21(e), we confirm that the blood flow component of +0.24* fs
frequency is separated on the positive-side. Moreover, in the power spectrum shown in Fig.
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