Image Registered Gastroscopic Ultrasound (IRGUS)
Endoscopic ultrasound (EUS) has been shown to be beneficial in diagnosis, biopsy guidance, and interventional procedures in the thorax and abdomen. EUS offers imaging advantages by achieving close proximity to target organs thus producing high contrast and resolution. However, the traditional challenges of all ultrasonic imaging techniques (variable contrast, dependence on boundary-layer reflections, and occlusion by sonically opaque structures) are compounded in EUS by small fields of view, uncertainty in probe position and orientation, and difficulty in establishing target contact or a clear viewing window. These limitations result in a long learning curve and necessitate formal EUS fellowship training, thus limiting the adoption of EUS by practicing gastroenterologists.
Image Registered Gastroscopic UltraSound (IRGUS), is a real-time guidance system that uses two synthetic displays driven by the position of the ultrasonic probe to overcome these technical hurdles. One display is a 3D anatomic model that tracks scope position and the second display is an oblique CT scan slice in the exact plane and location of the EUS image. These displays provide contextual information that complement and reinforce both the positioning of the EUS transducer and the identification of features in the ultrasound image.
The IRGUS system provides the clinician with contemporaneous real-time displays that show the probe orientation within preoperative volumetric CT image. IRGUS uses established techniques for the visualization of probe position and image registration, but implements them in real-time using recent advances in miniaturized position tracking technology. These synthetic images have no perceptible lag when the probe is moved.
For our 2006 studies the volumetric data were collected using a Siemens Sensation 64 (slice) CT system. The Ascension Technologies tracking sensors are small (0.3mm dia,1.8mm length) and have been tested to meet EN 60601-01 standards. Such a sensor was attached to the tip of a curvilinear echoendoscope (Olympus EU-C60; Olympus America Inc., Melville, NY) and covered with medical-grade heat-shrink tubing for sterilization by conventional techniques. All components (tracker system, interfaces, personal computer with displays) are commercially available, with a total cost well under $10,000, depending on the size of the displays, and the software is written in the open-source 3D Slicer environment.
Results of our initial evaluation of the IRGUS approach point out the significant benefit provided by our display, as shown in the figure below. More details are given in the publications.
Publications
- Vosburgh, KG, N. Stylopoulos, R. San Jose Estepar, RE Ellis, E. Samset, CC Thompson. EUS and CT Improve Efficiency and Structure Identification over Conventional EUS. Gastrointest Endosc. 2007 May;65(6):866-70. PMID: 17466206.