Natural Orifice Transluminal Endoscopic Surgery (NOTES)
For centuries, the peritoneal cavity has been approached through large incisions of the anterior abdominal wall. In the past two decades, the laparoscopic approach has gained wide acceptance because it offers a safe and less invasive alternative: pain and the complications associated to large abdominal incisions are minimized. To further reduce the invasiveness of peritoneal access, the next logical step is to eliminate the incision through the abdominal wall altogether. Rather, natural orifices may provide the entry points for surgical interventions. Recently, several research groups have been able to access the peritoneal cavity through peroral- transgastric (i.e. through a small incision in the gastric wall) and also peranal-transcolonic approaches to perform organ resections in an animal model. This new approach has the potential to replace or augment laparoscopic techniques currently used to treat many diseases. It may be especially beneficial to obese patients or those who have undergone multiple procedures and thus are at risk for adhesions.
Minimally invasive peroral-transgastric and peranal-transcolonic surgery is in its infancy. Before widespread use of these techniques is possible, several technical barriers must be overcome. These include providing the physician with adequate visual feedback, clear indicators of instrument location and orientation and support in the recognition of anatomic structures (see stomach anatomy figure). The appearance of the abdominal structures through the transgastric approach is totally different than in an open or laparoscopic approach. The unique angle of view, limited light, and the need to insert all instruments through a narrow channel are critical technical challenges. The introduction of the instruments in the peritoneal cavity (e.g through a gastrotomy) should be performed in a way that precludes damage to surrounding organs and vasculature.
One relatively simple approach to augment the endocopic/laparoscopic view is to use ultrasound (US). Laparoscopic US (LUS) and endoscopic US (EUS) are often used to guide biopsies and interventional procedures. However, the vast majority of physicians are not comfortable with performing invasive procedures under ultrasound guidance because of the inherent problems of image interpretation.
The navigation of a flexible endoscopic device inside the abdomen brings similar challenges as in traditional laparoscopy, but new complexities are added:
- The flexibility of the endoscope tip makes the understanding of its distal orientation difficult. Unlike laparoscopic procedures, there is no direct observation of the endoscope tip. Because of the lack of a global reference of the tip with respect to the patient body, successful navigation inside the stomach and in the abdomen cavity generally requires the expertise of a highly trained gastroenterologist (up to two years subspecialization) (see curved scope figure).
- A majority of the structures that are accessible through a transgastric access lie in a retrograde position with respect to the incision in the stomach wall. Access to such locations requires detailed knowledge of the place of the tip with respect to adjacent structures, particularly vessel.
- Understanding the position and orientation of the ultrasound B-scan plane is a ubiquitous problem even for experienced sonographers.
- An inherent problem to any ultrasound based system is the difficulty in interpreting the images because of low contrast, reduced field of view and acoustic windows constrains, despite the close proximity of the US probe to the target organs.
Several groups have attempted to address the orientation and interpretation problem by using preoperative data jointly with the intraoperative US data. Lindseth et al. have shown that the fusion of intraoperative US images and preoperative MRI enhance the perception by extending the overview of the operating field. Ellsmere et al. showed that a 3D display with the main vascular structures and the probe positioning improved the spatial orientation of the CT and the operator, thus reducing the time to locate the organ of interest and increasing the operator's certainty. The MeVis group has also fused ultrasound and instument position for open liver resection procedures.
We present here a system that addresses those challenges and makes intra-cavitary interventional techniques easier to master and use in practice, and thus more likely to be widely adopted. Our system relies on providing context information about the interpretation of the US image based on preoperative data (CT or MRI). The system is based on tracking the endoscope tip and US plane with an electromagnetic tracker and established the correspondence of the real time positioning of the instrument tip with respect to preoperative data. The preoperative data is also used to generate 3D models of reference anatomical structure. Those structures are displayed with respect to the position of the probe in real time. An enhance interpretation of the US image is achieved by oblique reformatting the preoperative dataset according to the US plane.
Publications
- Kirby Vosburgh, Raul San Jose Estepar. Natural Orifice Transluminal Endoscopic Surgery (NOTES): An Opportunity for Augmented Reality Guidance. Stud Health Technol Inform. 2007;125:485-90.
- Raul San Jose Estepar, Nicholas Stylopoulos, Randy Ellis, Eigil Samset, Carl-Fredrik Westin, Christopher Thompson, Kirby Vosburgh. Towards Scarless Surgery: An Endoscopic-Ultrasound Navigation System for Transgastric Access Procedures. Comput Aided Surg. 2007;12(6):311-24.