Real-Time Processing of Three Dimensional Ultrasound for Intracardiac Surgery

Real-time three-dimensional ultrasound has been demonstrated as a viable tool for guiding surgical procedures. This visualization technique enables a range of new minimally invasive techniques in cardiac surgery. Ultrasound permits visualization through the opaque blood pool in the heart, and the advent of real-time 3DUS overcomes difficulties with 3D spatial perception in conventional 2D ultrasound. These procedures eliminate the need for a cardiopulminary bypass and its well documented adverse effects. However, challenges remain before clinical implementation of ultrasound-guided intracardiac surgery can be made practical. 3D ultrasound provides limited spatial perception due to distorted appearance of tissue and instruments. The low quality imaging when combined with the confined dynamic environment of a beating heart makes complex tasks difficult for surgeons to perform.

These challenges are addressed by improving the display of 3D ultrasound with stereo displays, tracked surgical instruments, and introducing robotics for handling the dynamic cardiac tissue. A study is presented that demonstrates stereo displays improve surgical performance, reducing error rates by 50% and procedure times by 28%. The stereo display was found to help surgeons better interpret the low resolution ultrasound volumes. However, a large source of ultrasound distortion is imaging artifacts created by surgical instruments. A detection technique is presented that identifies the position of the instrument within the ultrasound volume. The algorithm uses a form of the generalized Radon transform and passive markers to identify the full position and orientation of the instrument. This detection technique is amenable to rapid execution on parallel computer architectures and as a result real-time instrument tracking was attained. With a tracked instrument location, it is now possible to develop enhanced surgical displays. Instrument tracking also enables robot guidance that is ideally suited to compensate for the highly dynamic environment of beating heart surgery. A system has been designed and tested that uses real-time instrument and target tracking for robot control.