Ultrasonic Doppler and duplex systems: possibilities and limitations.
In order to utilize Doppler modalities in an optimal manner, one should both be aware of their potential and respect their limitations. To this end, a variety of technical and physical factors affecting the performance of Doppler devices are discussed: (1) the velocity of propagation limiting the temporal resolution of pulsed systems; (2) intervening tissue that may weaken the echo considerably; (3) the size of the sample volume that could be too small to provide a transvascular mean velocity or too large to discriminate flow in adjacent vessels; (4) the principles of continuous wave mode lacking depth resolution, and pulsed mode being prone to aliasing; (5) the additional complexity of duplex/triplex systems; (6) the tight temporal restrictions of 2-dimensional color mappers which cause poor velocity resolution, and (7) the angle of incidence that needs to be assessed in order to measure absolute velocity and the cross-sectional area that must be measured additionally for the calculation of the volume flow rate. Based on this discussion, some hints on selecting instruments or instrument parameters are given.
Institute of Biomedical Engineering and Medical Informatics, University of Zürich, Switzerland.
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D001783:Blood Flow Velocity; D006801:Humans; D014465:Ultrasonics; D014463:Ultrasonography; D014570:Urologic Diseases / Q000175:diagnosis