American College of Cardiology<BR>
Anaheim, CA<BR>
March 16-19, 1997<BR>
<BR>
<B>Three-Dimensional Echocardiography by Rapid Free Scanning 
From Multiple Transthoracic Windows</B>
<BR>
<BR>
Daniel Leotta, Brad Munt, Malcolm Legget, Roy Martin, Xiang-Ning Li, 
Edward Bolson, Todd  Zwink, Carol Kraft, Gerard 
Bashein, Murali Sivarajan, Catherine Otto, Florence Sheehan.<BR> 
<I>University of Washington, Seattle, WA</I>
<BR>
<BR>
<BR>
Three-dimensional (3D) echocardiography has recently been 
shown to improve the accuracy and reproducibility of estimates of 
left ventricular (LV) mass and volume.  However, accuracy of 3D 
cardiac reconstructions can be limited by such factors as lengthy 
image acquisition times, limited acoustic viewing windows, a need 
for respiratory gating, and geometric assumptions of LV shape.<P>

   We present a method for quickly acquiring a 3D scan using a 
commercial ultrasound scanner equipped with a magnetic position 
locating device (Ascension Technology Flock of Birds).  Digital 
images are captured continuously while freely tilting, translating 
and/or rotating the probe.  In four breath holds of eight seconds 
each, complete scans from the parasternal (short and long axis) and 
apical windows are obtained.<P>
   The digital image files are linked to their spatial coordinates and 
the electrocardiogram.  Object borders are manually traced using 
custom software that allows interactive 3D visualization and 
editing of the outlines.  The scanned objects are reconstructed 
using a piecewise-smooth subdivision surface-fitting algorithm.<P>
   Phantom imaging indicates that the system accurately reproduces 
volume (true volume = 0.96 calculated volume + 2.2 ml, r2 = 0.999, 
SEE = 1.0 ml, n = 14 balloons) and shape (rms distance of 
reconstructed surface to ideal surface < 1 mm, n = 3 cylinders).  
Initial scans in ten normal subjects indicate that LV reconstructions 
are feasible in awake patients. These results suggest that LV 
volume and shape can be calculated accurately from images 
acquired during rapid free scanning in vivo.  With this technique, 
images are acquired quickly from one or more acoustic windows 
without respiratory gating, and reconstructions of the LV are 
performed without geometric assumptions.