FujiFilm Sonosite PX Service Manual page 39

Color In color Doppler, a real-time, two-dimensional cross-section of blood flow is displayed.
Doppler The 2D cross-section may be presented as a rectangle, parallelogram, trapezoid,
(Color) sector, or a full circle, depending on the particular transducer used.
The 2D cross-section is presented as a full color display, with various colors being used
to represent the velocity, both positive and negative, of the blood flow echoes. Often, to
provide spatial orientation, the full color blood flow cross-section is overlaid on top of
the gray scale cross-section of soft tissue structure (2D echo). For each pixel in the
overlay, the decision of whether to display Velocity Color Doppler (VCD), gray scale
(echo) information or a blended combination is based on the relative strength of echoes
from the soft-tissue structures and from the red blood battery.
A high pass filter (wall filter) is used to remove the signals from stationary or slowly
moving structures. Tissue motion is discriminated from blood flow by assuming that
blood is moving faster than the surrounding tissue, although additional parameters may
also be used to enhance the discrimination. The remaining signal after wall filtering
may be averaged over time (persistence) to present a steady state image of blood flow
distribution. Variance information may also be displayed to provide information when
large variance is observed in the velocity information.
Color Power In CPD, a real-time two-dimensional cross-section of blood flow is displayed. The 2D
Doppler cross-section may be presented as a rectangle, parallelogram, trapezoid, sector, or a
(CPD) full circle, depending on the particular transducer used.
The 2D cross-section is presented as a full color display, with various colors being used
to represent the power in blood flow echoes. Often, to provide spatial orientation, the
full color blood flow cross-section is overlaid on top of the gray scale cross-section of
soft tissue structure (2D echo). For each pixel in the overlay, the decision of whether to
display CPD, gray scale (echo) information, or a blended combination is based on the
relative strength of echoes from the soft-tissue structures and from the red blood
battery.
A high pass filter (wall filter) is used to remove the signals from stationary or slowly
moving structures. Tissue motion is discriminated from blood flow by assuming that
blood is moving faster than the surrounding tissue, although additional parameters may
also be used to enhance the discrimination. The power in the remaining signal after
wall filtering may be averaged over time (persistence) to present a steady state image
of blood flow distribution.
Continuous CW provides a real-time representation of blood flow and is displayed as a
Wave (CW) velocity-versus-time sweeping output. Velocity (or frequency) is presented as the
Doppler vertical axis with time along the horizontal axis. The magnitude of the detected signal is
represented as different gray scale values.
CW Doppler mode provides the clinician with the ability to obtain blood flow velocities
focused about a user specified focal region. A continuous transmit waveform of
ultrasound energy with a known frequency is transmitted and focused by the system;
on the receive side, the transducer receive echoes are continuously amplified, focused
about the focal region and converted to a base band quadrature signal. The signal is
analyzed by a quadrature phase detector that establishes two receive channels to
allow detection of flow direction. These two channels are then analyzed by a fast
complex Fourier transform (FFT) circuit to establish the spectrum of frequencies
present in the echoes. The data are displayed as spectrum frequencies with respect to
time.
CW can be used alone but is normally used in conjunction with a 2D image for spatial
reference. The 2D image has a graphical line (D-line) superimposed on the 2D image
indicating where the M-mode beam is located.
Chapter 4: System Overview 31