Xinyang Liu, Timothy D Kane, Raj Shekhar. Children’s National Health System
Objective: Computer-assisted surgery (CAS) is increasingly an integral part of modern patient care. To enable CAS, it is important to localize imaging devices and surgical tools with respect to one another and the patient. This localization in the 3D space, referred to as tracking, is a key component of CAS. For computer-assisted laparoscopic surgery, tracking of the laparoscopic ultrasound (LUS) probe is one of the first steps. Laparoscopic ultrasound is indeed a commonly used imaging tool to visualize anatomic structures and surgical targets internal to organs. The purpose of this project was to perform the necessary engineering to track the articulating imaging tip of the LUS probe for CAS applications.
Methods: Our solution is based on electromagnetic (EM) tracking, a real-time tracking method which reports the location and angulation of a small (~1-mm diameter) wired sensor inside a 3D working volume with a magnetic field created by a field generator. Unlike optical tracking which has the line-of-sight requirement, EM tracking is suitable for tracking the flexible imaging tip of the LUS probe. A trivial way to apply EM tracking to the LUS probe is to affix the sensor externally on the imaging tip. However, this solution will inevitably create many challenges for clinical use. The GPS LUS, our unique innovation, features a small EM sensor embedded inside the imaging tip, as illustrated in the figure. To achieve this, we disassembled an LUS probe, carefully ran the sensor wire from the handle to the imaging tip, and permanently fixed the sensor on the tip. The probe was then re-assembled and sealed. The imaging tip of the integrated probe may be flexed normally and the complete transducer may be sterilized by autoclave.
Results: As a preliminary evaluation of tracking accuracy, we attached a second sensor externally on the imaging tip of the GPS LUS probe. If the readings of the two sensors are correct, we should expect a constant offset between the two sensors. We recorded the readings of the sensors at various probe positions with various articulations of the tip. The standard deviations of the measured offsets between the two sensors were 0.05 mm for location and 0.12° for angulation, which are sufficiently small.
Conclusion: By equipping the LUS probe with an integrated spatial sensor, we have developed a GPS-like technology for enabling laparoscopic CAS applications that use LUS. For example, by tracking the LUS probe and the laparoscope, the ultrasound image may be overlaid on the laparoscopic video in real time, creating augmented reality visualization to see both inside and around structures to be dissected. As another example, the GPS LUS probe may be used for intraoperative 3D ultrasound imaging. Piecing together ultrasound image slices and tracking data at various time points makes creating a 3D ultrasound image of the surgical anatomy possible. More thorough evaluations of the tracking accuracy of the GPS LUS probe will be conducted in the future.
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Presented at the SAGES 2017 Annual Meeting in Houston, TX.
Abstract ID: 84435
Program Number: ET007
Presentation Session: Emerging Technology Session
Presentation Type: Podium