Chapter 5 - Working With Scan Modes
Using Spectral Doppler Image Controls
Terason t3000 / Echo Ultrasound System User Guide
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You can also select
Image > Sweep Speed
and then choose a speed, or right-click in the
Time Series window and select a speed.
Setting the Velocity Display Units
The Time Series window shows the velocity of flow in cm/s or kHz. You can change the
units any time. Centimeters per second (cm/s) is available only when the correction angle
(see
Adjusting the Correction Angle
on page 112) is between 0 and ±70º. If you set a
higher angle, the Terason software automatically changes the units to KHz.
To change the velocity display units, click the button for the units you want to use: cm/s or
kHz.
Adjusting Pulse Repetition Frequency (PRF)
Pulse Repetition Frequency defines the velocity range of the display. The maximum value
(in Hz) for the PRF depends on the specific transducer and the location of the sample
volume.
The PRF should be set high enough to prevent aliasing, and low enough to provide
adequate detection of slow blood flow. It may be necessary to vary the PRF during an
exam, depending on the speed of the blood flow, or when pathology is present.
Aliasing occurs when the frequency of what you are observing exceeds one half of the
sample rate. If the blood is moving faster than the pulse repetition rate, then the waveform
on the display will alias, or wrap around, the baseline.
You can only change this setting when viewing a live image, not when an image is frozen.
The Terason software may automatically change the PRF value when you move the region
of interest, to ensure that the maximum PRF value does not exceed its limit.
To adjust the PRF value, click the right or left arrows next to the PRF field.
PRF Control
Note:
In Triplex scanning only: the PRF value is tied to the setting on the 2D mode
(Color Doppler, Directional Power Doppler, or Power Doppler). If you change the
PRF value on one tab, the Terason software also changes the PRF value on the
other tab. This depends on whether you are scanning in simultaneous or non-
simultaneous mode, which is controlled by the Update button.
