Cirs 069A, Руководство пользователя, Страница: 10 / 16

VELOCITY ACCURACY
1 . Set flow pump so that the average flow velocity is 20 cm/s. See “Pump Calibration” (page 11) for
instructions on converting volume flow rate to average flow velocity.
2 . To ensure laminar flow, the scan region should be placed outside the minimum entrance length (>6 cm at
maximum flow velocity).
3 . Enable Pulse-Wave mode. Image the tube in cross-section, set angle correction to that vessel angle and
set the pulse wave window to encompass the entire lumen. Estimate the maximum velocity (center of the
tube). For laminar flow, the maximum velocity will be double the average flow velocity.
4 . Enable Color Flow mode. Scan flow tube in the cross-sectional position. Set the pulse repetition frequency
(PRF) to avoid aliasing and decrease until aliasing sets in. The maximum velocity corresponding to the PRF
setting is the maximum velocity in the flow tube.
Note: Color Flow only yields an average velocity, which should match the calibrated average flow velocity of
the flow pump.
ANGLE ERROR TEST
1. Set the flow circuit for constant velocity flow.
2 . Enable Color Flow mode. Scan the flow tube in the longitudinal sectional position.
3 . For orientation 1, which tests for abdominal applications, the angle between the membrane and the vessel
is 45°. Thus, the Doppler angle is 45° if the probe is placed normal to the membrane. The transducer should
be placed closer to the shallow end to measure the angle at the middle region of the tubing.
4 . For orientation 2, which tests for peripheral applications, the angle between the membrane and the vessel is
20°. The Doppler angle is 70° if the probe is placed normal to the membrane.
5 . Position the Doppler window on the center of the tube and correct the angle to that of the vessel. Record the
observed angle and freeze the image.
6 . Measure the angle between the membrane and beam direction by using the caliper application. The corrected
Doppler angle is given by the equation given below: