Historical Perspective on Three-Dimensional Echocardiography

Introduction

Three-dimensional echocardiography (3DE) has been in existence since the 1970s, albeit with images that barely resembled a heart at that time. Throughout the 1970s and 1980s, 3DE was limited by computing power, both at the workstation and at the ultrasound level. In the 1990s, as both two-dimensional echocardiography (2DE) image quality and computing power dramatically improved, 3DE began to make strides as a possible clinical entity. During these early attempts at 3DE, it was never real time and was approached from the perspective of capturing multiple 2D images of the heart and either tracing a wire frame of the heart or melding the 2D images together using interpolation methods to create a 3D image. The first attempts at real-time 3DE were undertaken by von Ramm et al at Duke University in the 1990s. The major transition from research to clinical tool for 3DE happened in 2002 when the first reasonably user-friendly version of real-time 3DE (RT3DE) was introduced. This was also the first version of RT3DE to have diagnostic-quality 3DE images performed by an ultrasound system that was capable of both 2DE and 3DE.

Earliest Approaches

3DE had its beginnings in the 1970s with primitive equipment and equally primitive images. By the mid-1980s, there was early 3DE performed with standard B-mode ultrasound and tracking devices designed to locate the transducer in space. The initial approach to 3D echo was to obtain multiple 2D images and reconstruct them into a 3D image. This was accomplished by registering the 2D images such that it could be discerned how the individual images fit together to form the 3D image. Such registration of the images was achieved by tracking the transducer in space via mechanical, acoustic, electromagnetic, or optical detection apparatus. In the mechanical approach, the transducer had an actual mechanical arm attached to it and therefore dictated movement in space ( Figure 1-1 ). Dekker and colleagues are credited with this first iteration of 3DE using the mechanical arm approach in 1974. Next came an acoustic attempt at location, the “spark gap” technique by Moritz and Shreve in 1976. In this technique, the transducer was located by sending pulsed acoustic signals from a device holding the transducer, called a spark gap to a Cartesian locator grid ( Figure 1-2 ). This approach, in theory, allowed free-hand scanning—meaning that the transducer did not have to follow a predetermined pathway and, indeed, was the precursor to free-hand scanning using an electromagnetic locator. Both electrocardiography and respiratory gating were often used, or images were acquired with breath holding. Initially, only end-diastolic and end-systolic images of the left ventricle (LV) were obtained. Over time, complete cardiac cycles could be obtained. Several groups published articles during this period using a variety of primitive transducer tracking systems and the resultant less than pleasing 3D imaging.

In 1977, Raab and colleagues developed the magnetic locator, which ultimately led to the most advanced type of free-hand scanning, but this method for transducer location never caught on until the mid-1990s. This method is still used today by some labs, predominantly for research purposes ( Figure 1-3 ; see also Figures 1-13, 1-14 ).

In between the spark gap and the free-hand magnetic approaches were myriad tactics that used the technique of transducer movement in a preprogrammed, stepwise fashion while attempting to keep the patient and the sonographer as stationary as possible. The mechanical devices then moved the transducer in a linear, fanlike, or rotational direction. An example of a fanlike acquisition is shown in Figure 1-4 .