Read e-book online Cardiac Doppler Diagnosis PDF

By J. Geoffrey Stevenson M.D. (auth.), Merrill P. Spencer MD (eds.)

ISBN-10: 940094988X

ISBN-13: 9789400949881

ISBN-10: 9401087083

ISBN-13: 9789401087087

`Those who've realised the significance of the extra information which might be received by means of the complementary use of Doppler ultrasound will locate that this e-book is a concenient resource of reference. those that stay to be confident will locate that it places the topic properly into perspective.'
The British magazine of Radiology, 57:681 (September 1984)

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Extra resources for Cardiac Doppler Diagnosis

Sample text

Small sampIe volumes. To achieve a high spatial resolution it is necessary to employ a high emission frequency reducing the velocity-range product of the system. Then, it will become more likely that high velocities are wrongly evaluated due to aliasing. It is, therefore, essen- tial to develop a processing scheme that automatically corrects for aliasing. The tracking technique as developed for peripheral applications seems to be promising since it automatically corrects for aliasing while at the same time, it reduces the susceptibility 50 of the system output for a low signal-to-noise ratio.

These two channels are commonly called the "in-phase" and "quadrature" channels, the term quadrature being derived from the fact that the second reference signal is one-quarter wavelength out of phase with the first reference signal. After these two channels of signal have been produced, the signal is both high pass and low pass filtered, a step not shown in Fig. 2. The high pass filter, the cutoff frequency of which is typically chosen to be 500-1000 Hz for cardiac applications, removes all echoes from stationary structures as well as the very low frequency, large amplitude signals associated with heart wall motions.

Several approaches have been pro- prosed depending on the application. One may limit the presenta- tion of velocity signals as function of depth to the most relevant volumes stressing its value and temporal behaviour. other approach the velocity distribution as sensed along the ultrasound beam is presented as function of time (velocity profiles) emphasizing their value and spatial behavior. Other investigators (Brandestini, 1979; Eyer, 1981) propose the display of coded in color in an overlay of an M-mode echo-display.

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Cardiac Doppler Diagnosis by J. Geoffrey Stevenson M.D. (auth.), Merrill P. Spencer MD (eds.)


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