12 Chapter 3: System Overview
The Doppler functional processing platform is in Figure 3.2.
Continuous
Wave (CW)
Doppler
CW provides a real-time representation of blood flow and is displayed as a
velocity-versus-time sweeping output. Velocity (or frequency) is presented as the 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.
Pulsed Wave
(PW) Doppler
PW provides a real-time representation of blood flow and is displayed as a
velocity-versus-time sweeping output. Velocity (or frequency) is presented as the vertical
axis with time along the horizontal axis. The magnitude of the detected signal is represented
as different gray scale values. The ultrasound data is derived from a single area, the sample
volume, on a stationary beam.
PW Doppler mode provides the clinician with the ability to obtain blood flow velocities
about a spatial sample volume. A burst of ultrasound with a known spectrum is transmitted
by the System; on the receive side, the transducer receive echoes are amplified and range
gated at the appropriate depth. 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.
PW 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. The sample volume position (depth) and size
are also indicated on the D-Line.
To Next Page
Loading...