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I. Ljungvall1 1 Sweden
Ingrid Ljungvall
Associate Professor, DVM, PhD
Department of Clinical Sciences, Faculty of Veterinary Medicine and Animal Science, Swedish University of Agricultural Sciences, Uppsala, Sweden
Three-dimensional (3D) echocardiography is a recently introduced technique, which offers new possibilities for evaluation of heart size, function and valve integrity. This presentation reviews the potential utility of 3D echocardiography in small animals.
Three-dimensional echocardiographic modalities
Echocardiography has over the last four decades evolved from single-beam and two-dimensional (2D) imaging to 3D techniques. The 3D technique was initially based on dataset reconstructed from series of 2D images, which limited the utility of this technique due to long acquisition and post-processing time as well as image quality and alignment concerns. Technical improvements in 3D hardware and software have enabled a more widespread clinical application of 3D echocardiography. The  rst real-time three-dimensional (RT3D) echocardiographic system was introduced in the early 1990ies, and further developments in design and engineering have led to the recent commercialization of RT3D echocardiographic systems. Modern RT3D echocardiographic systems utilize high-frequency matrix array transducers that consist of more than 3000 individual crystals, which simultaneously acquire data from the heart in a
3D pyramidal fashion in real time; thereby allowing simultaneous visualization of the beating heart. Some currently available RT3D echocardiographic modalities
of imaging acquisition include live 3D, 3D zoom, 3D full volume, and 3D color Doppler  ow analysis. Live 3D is
a real-time live imaging mode, which provides a wedge- shaped 3D sector with a sector volume expanding in height and width at greater imaging depth. 3D zoom mode provides a smaller magni ed real-time pre-cropped image. 3D full-volume acquisition technique is based upon rapid reconstruction of wide-angled pyramidal live 3D volumes, which are stitched together sequentially
beat-by-beat over 4 to 7 ECG gated cardiac cycles.
The 3D color Doppler  ow modality is, in similar fashion to full-volume 3D acquisition, rapidly reconstructed
over several heart beats; resulting in a sample volume approximately half the size of the standard 3D full- volume acquisition but with color Doppler  ow imaging superimposed on the anatomic structures. All 3D modes can be further manipulated, cropped and quanti ed in three orthogonal planes according to the particular region of interest either on the ultrasound platform or off-line using commercial digital software
Assessment of left ventricular size and shape
Evaluation of left ventricular (LV) morphology is one of the most common reasons for performing echocardiography in cardiac patients. RT3D echocardiography allows for superior anatomical delineation of the LV in real time. Due to the ability to manipulate the plane to align the true short- and long-axes of the LV, the problems with chamber foreshortening and oblique imaging planes
can be reduced; thus providing more anatomically correct views than conventional 2D echocardiography. A physics-based modeling algorithm, which makes no assumptions regarding LV geometry, is used in modern RT3D software when assessing global LV volumes. The RT3D dataset can further be divided into regional segments by sectioning the LV from base to apex, perpendicular to the LV long-axis; thereby allowing regional volume assessment. Global and regional function curves, re ecting the ventricular function over time, can also be derived from the LV RT3D dataset. The potential of LV volume and shape assessments
by transthoracic RT3D echocardiography has been demonstrated in dogs with myxomatous mitral valve disease (MMVD), which is the most common heart disease affecting dogs.
Assessment of left atrial size
The left atrium (LA) is a 3-dimensional structure, and LA dilatation may occur in all directions (i.e., cranio-caudal, medio-lateral and ventro-dorsal direction) although perhaps not uniformly. Estimation of LA volume by RT3D echocardiography has been reported to be a major predictor of clinical outcome in human patients with severe LV dysfunction and the clinical value of RT3D techniques was reported superior to 2D techniques. Assessment of LA size provides valuable prognostic information also in dogs with MMVD, and the potential for optimized LA size assessment using RT3D techniques has been demonstrated in dogs.
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