Terason t3000, Руководство пользователя

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Chapter 5 - Working With Scan Modes Using Color and Power Doppler Image Controls
Terason t3000 / Echo Ultrasound System User Guide 120
Resizing the Scan Area
4. Click to anchor the region of interest.
You can also type a period ( . ) twice to select the region of interest. Then use the left/right
arrow keys to decrease or increase the width, or the up and down arrow keys to increase or
decrease the height.
The Terason application may automatically adjust the PRF value when you move the
region of interest to ensure that the maximum PRF is not exceeded for the new depth.
Adjusting Pulse Repetition Frequency (PRF)
Pulse Repetition Frequency (PRF) 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 region
of interest.
The PRF should be set high enough to prevent aliasing, and low enough to provide
adequate detection of low flow. It may be necessary to vary the PRF during an exam,
depending on the speed of the blood flow, or if 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 Doppler
display will alias, or wrap-around, the baseline. Aliasing may occur for Color Doppler or
Directional Power Doppler, but does not occur with Power Doppler.
If the PRF is set too high, low-frequency shifts caused by low-velocity flow may not show.
Typically, the PRF is set higher for cardiac and arterial applications than it is for venous or
small-parts applications.
As PRF increases, the maximum Doppler shift that can display without aliasing also
increases.
You can only use this control when viewing a live image. When an image is frozen, you
cannot change this control setting.
To adjust the PRF value, click the right or left arrows next to the PRF field.
PRF Control