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Page 2 of 23 Rao. Vessel Plus 2022;6:24 https://dx.doi.org/10.20517/2574-1209.2021.91

The purpose of this review is to present an overview of echocardiography in pediatric practice. For a more
thorough appraisal, standard text books of Pediatric Cardiology or Pediatric Echocardiography may be
reviewed. In this review, the author will describe principles of echocardiography and Doppler, outline the
techniques of echocardiography and Doppler studies, describe methods of estimation of pulmonary artery
(PA) pressures, discuss methods used to evaluate ventricular function, and illustrate the utility of
echocardiography in evaluating multiple neonatal issues. Echocardiographic findings of commonly
encountered heart defects will be presented in Parts II and III of this series.

[1,2]
There are several specialized types of echocardiographic evaluation such as contrast echocardiography ,
trans-esophageal echocardiography , intra-cardiac echocardiography , intravascular ultrasound [5,8,9] , fetal
[3-5]
[6,7]
echocardiography [10,11] , 3-dimentional echocardiography [12,13] and others; these specialized techniques will not
be discussed in this review.

PRINCIPLES OF ECHO-DOPPLER - WHAT IS IT?
Ultrasound
Ultrasound is a sound beyond the perceptible (by the human ear) range, typically higher than twenty-
thousand cycles/s [14-18] . The ultrasound utilized for clinical evaluation is between two and ten MHz (millions
of cycles/s). The ultrasound follows the rules of reflection (echo). The ultrasound is created by
“Piezoelectric” quartzes; these are either naturally available crystals or manufactured lead zirconate or
barium titanate. The present transducers send out ultrasound for a tiny fraction of a second and perceive
the reflected echoes for more than one thousand times longer.

Echo
When the transmitted ultrasound hits a border between two substances that have dissimilar sound
resistances (acoustic impedance), the ultrasound is returned, and an echo is created. When this echo is
received by the transducer, the quartz in the transducer shudders. This said shuddering is presented as a
dot. The resultant dot, when documented against time on the horizontal-axis, will appear as a straight line.
The “M” or motion mode echo [Figure 1] is thus produced.

2D echo
A 2D echo is obtained in a manner similar to that of M-mode echocardiogram; however, spatial data are
included with regard to the position of the echoes at the period the data are returned; this is with the aid of
line locater circuitry built into the system. This 2D echo [Figure 2] is commonly utilized in the appraisal of
cardiac anatomy.

Doppler
In the preceding paragraphs, describing imaging echoes, the targets for echo reflections are cardiac valves,
myocardium, walls of the blood vessels, and additional heart anatomy. The echoes from the red (and white)
blood cells are very low in strength and are disregarded. During the Doppler examination, these poor
intensity echo signals from red (and white) blood cells are augmented and examined with the use of the
Doppler principle, which states that an apparent shift of the transmitted frequency takes place due to the
movement of the target. This frequency change of transmitted vs. returned wave fronts is examined by fast
Fourier transformation, zero-crossing detector or Chirp-Z analysis, and the blood flow velocity is
determined [Table 1]. The velocity data so secured is of utility in the Doppler evaluation. Several types of
Doppler methods have been used to obtain the physiologic info and include pulsed wave (PW), continuous
wave (CW), high pulse repetition frequency (HPRF), and color flow Doppler. All of these have a different
and definitive rationale [14-19] .