flow within the vessel to portray flow in the wrong direction. The disadvantage of using a
higher PRF is a loss of sensitivity to low flow velocities.
Use the [PRF] control to adjust the velocity range. Selecting up - increases the PRF
Selecting down - decreases the PRF
If a selected PRF is unavailable for the selected depth the PRF will be automatically
reduced. Changing the PRF display unit from kHz to m/s or cm/s can be done in the CF Sub
Menu: 'CF Sub Menu'
on page 8-15
Remarks:
•
The current sampling frequency is displayed on the screen [PRF ...].
8.7.22.1 HPPRF
The maximum clearly measurable flow velocity (Nyquist Limit) is determined by the measuring
depth of the sample volume and the related run time of the ultrasound. By a further increase of
the Doppler PRF (High PRF mode, HPRF) the Nyquist Limit can be increased. Thus in
addition to the main sample volume one or more sample volume gates appear along the D-
cursor. During examinations make sure that these additional sample volumes (virtual gates) do
not interfere with echo-rich areas, as these lead to interferences in the Doppler signal. Further
it has to be noted that blood flows recorded by these virtual gates are overlaying the actual
Doppler signal of the main sample volume.
When the maximum PRF is exceeded, the HPRF mode is automatically switched on. Virtual
gates are being displayed and the [HPRF] appears on the monitor.
Changing of the velocity range display from kHz to m/s or cm/s is to be performed in the PW
Sub Menu
(chapter
'PW Sub Menu'
on page 8-6
)
.
Remarks:
•
The current sampling frequency is displayed on the screen [PRF.... respectively
HPRF...].
•
The HPRF mode does not work in simultaneous Duplex- and Triplex mode.
•
The HPRF mode is not possible with linear array probes.
8.7.23 Wall Motion Filter (WMF)
PW CW CF PD HD-Flow TD
- - X X X X
Wall motion filters are used to eliminate vessel wall motion noise that is low in velocity but high
in intensity. Use a wall filter that is high enough to remove motion artefacts, but that is
sensitive enough to display low velocity flows in small vessels.The WMF control is used to
change the wall motion filter. The settings are: low1, low2, mid1, mid2, high1, high2 and max.
Use the [WMF] flipswitch to adjust the required Wall Motion Filter.
Remarks:
Doppler Modes
Voluson® S6/S8 Basic User Manual
5433669-100 Revision 4 8-41
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