Enhanced Ultrasound Visualization for Procedure Guidance

author:Laura Brattain
adviser:Robert D. Howe
degree: Ph.D.
institution: Harvard University

Intra-cardiac procedures often involve fast-moving anatomic structures with large spatial extent and high geometrical complexity. Real-time visualization of the moving structures and instrument-tissue contact is crucial to the success of these procedures. Real-time 3D ultrasound is a promising modality for procedure guidance as it offers improved spatial orientation information relative to 2D ultrasound. Imaging rates at 30 fps enable good visualization of instrument-tissue interactions, far faster than the volumetric imaging alternatives (MR/CT). Unlike fluoroscopy, 3D ultrasound also allows better contrast of soft tissues, and avoids the use of ionizing radiation.

The current key challenges in increasing the clinical adoption of 3D ultrasound include limited field of view, signal dropout, low resolution and poor rendering. A cardiac gated 3D mosaicing and visualization system is developed with an aim to address the limitations above. The system integrates electromagnetic position tracking with cardiac gating and leverages parallel computing for real-time instrument tip tracking in mosaiced 3D ultrasound volumes. User studies in clinical tasks show a 46% reduction in task completion time.

To further improve the mosaicing results, a novel 3D ultrasound compounding method based on structure tensors and weighted by ultrasound incident angles is developed. This method addresses the challenge in integrating multiview US images where the intensity values at overlapping regions could be significantly different due to differences in local structure orientations with regards to ultrasound beam propagation directions. Water tank and in vivo studies show 20% improvement in contrast to noise ratio when compared to the commonly used intensity averaging.

In clinical settings, a system that offers ease of use is essential. A robotic control and visualization system is built to facilitate the use of automated ultrasound catheter imaging for procedure guidance. The system creates 3D panorama by controlled sweep while keeping the catheter tip at a fixed and safe location. Instrument tracking and tip identification techniques are also developed, both require complex joint coordination thus are difficult for manual control. We are able to achieve an overall accuracy of 2.2mm RMS in position and 0.8deg in tracking. Such system has a great potential in improving the overall clinical work flow.

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