Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

52 Small Animal Radiolo g y and Ultrasono graphy
FIG. 2-20 Graphs showing the normal
values (predicted value ±95%
confidence interval) of the normal
ventricular septal thickness in diastole
(A) and systole (B). (From
Bonagura JD, O’Grady MR, Herring
DS: Echocardiography: principles of
interpretation. Vet Clin North Am
1985; 15:1190.)
A
B
Duplex Doppler units capable of simultaneously displaying both a two-dimensional
and a pulsed Doppler image are helpful, because the site from which the Doppler signal
originates is visible. In areas with high flow rates or in areas that are relatively distant from
the transducer, a continuous wave Doppler (nonimaging) system is more accurate. As a
general rule, lower-frequency transducers are better for Doppler studies and higherfrequency
transducers produce better images (at the cost of less depth penetration). A compromise
often must be made in transducer selection.
Doppler studies may be performed to investigate blood flow characteristics at
any site in the heart. The method for evaluating the common sites has been described (Fig.
2-33). 25,67-69 An example of the detailed information available using Doppler echocardiography
can be seen in studies of the left atrium. Sampling usually is performed using a left
caudal parasternal view, a four-chamber inflow view. To evaluate mitral valve competence,
the sample volume position should be in the left atrium one fourth of the distance
between the mitral annulus and the dorsal wall. To evaluate the flow across the mitral