B-K Medical Pro Focus 2202, User Manual

Page: 157 / 356

Doppler Mode – Spectral Doppler 157
Range
In Doppler mode, as in Color mode, you can vary the PRF (pulse repetition
frequency) to select the range of Doppler frequencies that are included in the spectral
analysis.
To adjust the velocity range:
• Press
[
Scale
z
]
to step through the available ranges.
or
•
Click PRF under Doppler on the left side of the screen and select the value you
want (or point at PRF and press
[
+/-
]
).
The vertical scale is updated to correspond to the new range of velocities.
The current setting is displayed on the screen next to PRF.
Note: The wall filter value will be changed automatically when you change the
PRF value.
HPRF
To measure higher flow speeds (high range setting) in a sample volume placed deep
in the tissue, HPRF (high PRF) is automatically used. When HPRF is active, the
Doppler line shows the actual sample volume, false sample volumes (indicated by
holes in the line), and dead space areas where Doppler information cannot be
achieved at the current PRF (indicated by a thick line). See Fig 11-2 on page 154.
The false sample volumes should always be placed outside a vessel. The “thick” parts
of the line (see Fig 11-2 on page 154) can be moved by adjusting the range.
When HPRF is used and the actual sample volume is placed in a dead space, the
system automatically adjusts the range so that the signal can be received.
Wall Filter
In Doppler mode, you can set the cutoff frequency for the wall filter.
To set the cutoff frequency for the wall filter:
• Click Wall Filter under Doppler on the left side of the screen and select the
value you want (or point at Wall Filter and press
[
+/-
]
).
or
• Press
[
Filter
F
]
to step through the available values.
The current setting is displayed on the screen next to Wall Filter.
Invert
In PW Doppler mode, you can invert the spectrum on the screen.