Andersons pediatric cardiology 497

In 1990, von Ramm and Smith described a transducer that provided live 3DE images of the heart.2 This transducer was unable to be steered in the third dimension, which has since been term

Echocardiography

Early approaches were based on 2DE images that were acquired, stacked, and aligned based on the phases of the cardiac cycle to produce a 3DE dataset.1 The need for time and equipment for offline processing imposed fundamental

limitations on their clinical applicability In 1990, von Ramm and Smith

described a transducer that provided live 3DE images of the heart.2 This

transducer was unable to be steered in the third dimension, which has since been termed the plane of elevation; the latter capability, and the ability to render the image in real time, have been developed over the past 15 years.3

Key advances that have facilitated enhancements in 3DE include matrix-array transducers, piezoelectric materials, and innovations to visualize and quantitate 3D data

Matrix-Array Transducers

These transducers comprise as many elements in the elevation dimension as they

do in the azimuthal dimension, with over 60 elements in each, thus totaling more than 3600 elements To be able to steer in the plane of elevation, each element must be electrically active and independent; this advance became commercially available in 2002 In 2006, advances in the ability to miniaturize these complex connections led to the development and introduction of a high-frequency

pediatric transthoracic 3DE transducer as well as a transesophageal 3DE probe for use in adults.4,5

Piezoelectrical Materials

The piezoelectrical material in a transducer fundamentally determines the quality

of the image Piezoelectrical elements are responsible for delivery of ultrasonic energy into the tissue that is scanned, and for converting waves of reflected

ultrasound into electric signals Their efficiency in converting electrical energy

to mechanical energy, and vice versa, is a key determinant of the quality of the image, sensitivity to Doppler shifts, and the ability of transmitted ultrasound to penetrate to increasing depths One example of new piezoelectrical material involves growing crystals from molten ceramic material, resulting in a

homogenous crystal that enables a near-perfect alignment of dipoles, resulting in enhanced electromechanical properties including miniaturization and increased bandwidth and sensitivity, resulting in improvements in both penetration and resolution.6

Visualization of Three-Dimensional

Echocardiograms

While 3DE techniques provide the ability to acquire wide, trapezoid-shaped

fundamentally challenged within the construct of the 2DE display Early

iterations of software featured variations of grayscale, which limited the

perception of depth Enhancements over the past decade include the use of

dynamic schemes that automatically code the near and far fields in contrasting colors (Fig 20.1, Videos 20.1 and 20.2) More recently, tools such as directional lighting have been used to provide shadows of structures such as wires or

devices A separate advance in visualization has come from the ability to

manipulate 3DE images after they have been acquired (Fig 20.2, Video 20.3).7 Today, the viewer can interact with the image, performing virtual dissections (cropping) and tilting or rotating the image as desired More recently, interactive digital holograms have been developed using intraprocedural data from 3D transesophageal echocardiograms.8 Together, these capabilities constitute

fundamental changes to the scope and practice of echocardiography

FIG 20.1 Parasternal short-axis view of partial atrioventricular septal defect, with an asterisk marking the “cleft” (zone of apposition between the

superior and inferior bridging leaflets) The left panel demonstrates a traditional grayscale map This color scheme leads to difficulties in appreciation of perspective (depth) The right panel has been colorized

using a holographic color map: structures that are in the near field are colored orange; in contrast, structures in the far field are colored blue This

is a dynamic colorization scheme: as the image is rotated or tilted, the

colors change in keeping with the new orientation.