[3D-spectrogram of the doppler signal in real time]

Doppler signals are normally displayed as an x/y-graph. The frequency is plotted in the y-direction, and the intensity is represented by the brightness. This represents less information than is contained in the acoustic signal: often one can hear more one can see. We are investigating the question as to whether it is feasible to render the complete information visible without the use of expensive additional equipment.

The sound card (SB16 P&P value edition) in a Pentium-PC (200 MHz 32 MB RAM) was used as a 16 bit dual channel a/d converter and connected to the ultrasound system Sonoline Elegra (Siemens, Erlangen, Germany). We used a standard 32 bit dual channel real-time FFT-software (SpectraPro, Sound Technology, California) to display a 3D-spectrogram on the PC-screen in real-time mode. This system was first tested on a flow model both with laminar steady flow and with pulsatile flow. Following this, measurements were made of the arteries and veins in healthy volunteers.

In the 3D-Spectrogram the character of the flow can easily be seen. The quantitative parameters of velocity (Doppler frequency), direction and intensity of flow can be readily determined. Additional information about quality of flow, erythrocyte clusters and changes occurring in areas of slight stenoses can be used for diagnostic evaluation. The orthograde and retrograde flow are displayed separately using the dual channel technique. The arterial and venous flow in small and closely neighbouring vessels, such as the central retinal artery and vein, can easily be differentiated. The venous flow in particular is more turbulent in the 3D-spectrogram than would be expected from the normal display mode.

The 3D-spectrogram provides much additional information in comparison with the normal Doppler spectrogram of the ultrasound system. This 3D-spectrogram can be easily obtained using inexpensive standard hard- and software.