Eric M. Friets

System for laparoscopic tissue tracking

This paper describes the development of a laparoscopic tissue tracking system for use during minimally-invasive, image-guided abdominal surgery. The system is designed to measure organ position and shape to permit coregistration of preoperative, volumetric image data with the actual anatomy encountered during surgery. The laparoscopic tissue tracking system relies on projection of a scanned laser beam through a conventional laparoscope. The projected laser is then imaged using a second laparoscope oriented obliquely to the projecting laparoscope. Knowledge of the optical characteristics of the laparoscopes, along with their relative positions in space, allows determination of the three-dimensional coordinates of the illuminated point. Rapid localization permits tracking of tissue motion due to respiration or surgical manipulation. This paper provides a brief overview of the system, discusses system accuracy measured during laboratory testing, and shows data obtained from use of the system during surgery on an experimental animal

Tissue localization using endoscopic laser projection for image-guided surgery

Image-guided surgery has led to more accurate lesion targeting and improved outcomes in neurosurgery. However, adaptation of the technology to other forms of surgery has been slow largely due to difficulties in determining the position of anatomic landmarks within the surgical field. The ability to localize anatomic landmarks and provide real-time tracking of tissue motion without placing additional demands on the surgeon will facilitate image-guided surgery in a variety of clinical disciplines. Even approximate localization of anatomic landmarks would benefit many forms of surgery. For example, liver surgeons could visualize intraoperative locations on preoperative CT or MR scans to assist them in navigating through the complex hepatic vascular network. This paper describes the initial stages of development of an endoscopic localization system for use during minimally-invasive, image-guided abdominal surgery. The system projects a scanned laser beam through a conventional endoscope. The projected laser spot is then observed using a second endoscope orientated obliquely to the projecting endoscope. Knowledge of the optical geometry of the endoscopes, along with their relative positions in space, allows determination of the three-dimensional coordinates of the illuminated point. The ultimate accuracy of the system is dependent on the geometric relationship between the endoscopes, the ability to accurately measure the position of each endoscope, and careful calibration of the optics used to project the laser beam. We report a system design intended to support automated operation, methods and initial results of measurement of target points, and preliminary data characterizing the performance of the system.

Effects of uncertainty in camera geometry on three-dimensional catheter reconstruction from biplane fluoroscopic images

Clinical procedures that rely on biplane x-ray images for three-dimensional (3-D) information may be enhanced by three-dimensional reconstructions. However, the accuracy of reconstructed images is dependent on the uncertainty associated with the parameters that define the geometry of the camera system. In this paper, we use a numerical simulation to examine the effect of these uncertainties and to determine the limits required for adequate three-dimensional reconstruction. We then test our conclusions with images of a calibration phantom recorded using a clinical system. A set of reconstruction routines, developed for a cardiac mapping system, were used in this evaluation. The routines include procedures for correcting image distortion and for automatically locating catheter electrodes. Test images were created using a numerical simulation of a biplane x-ray projection system. The reconstruction routines were then applied using accurate and perturbed camera geometries and error maps were produced. Our results indicate that useful catheter reconstructions are possible with reasonable bounds on the uncertainty of camera geometry provided the locations of the camera isocenters are accurate. The results of this study provide a guide for the specification of camera geometry display systems and for researchers evaluating possible methodologies for determining camera geometry.

Endoscopic laser range scanner for minimally invasive, image guided kidney surgery

Image guided surgery (IGS) has led to significant advances in surgical procedures and outcomes. Endoscopic IGS is hindered, however, by the lack of suitable intraoperative scanning technology for registration with preoperative tomographic image data. This paper describes implementation of an endoscopic laser range scanner (eLRS) system for accurate, intraoperative mapping of the kidney surface, registration of the measured kidney surface with preoperative tomographic images, and interactive image-based surgical guidance for subsurface lesion targeting. The eLRS comprises a standard stereo endoscope coupled to a steerable laser, which scans a laser fan beam across the kidney surface, and a high-speed color camera, which records the laser-illuminated pixel locations on the kidney. Through calibrated triangulation, a dense set of 3-D surface coordinates are determined. At maximum resolution, the eLRS acquires over 300,000 surface points in less than 15 seconds. Lower resolution scans of 27,500 points are acquired in one second. Measurement accuracy of the eLRS, determined through scanning of reference planar and spherical phantoms, is estimated to be 0.38 ± 0.27 mm at a range of 2 to 6 cm. Registration of the scanned kidney surface with preoperative image data is achieved using a modified iterative closest point algorithm. Surgical guidance is provided through graphical overlay of the boundaries of subsurface lesions, vasculature, ducts, and other renal structures labeled in the CT or MR images, onto the eLRS camera image. Depth to these subsurface targets is also displayed. Proof of clinical feasibility has been established in an explanted perfused porcine kidney experiment.

Image-guided ex-vivo targeting accuracy using a laparoscopic tissue localization system

In image-guided surgery, discrete fiducials are used to determine a spatial registration between the location of surgical tools in the operating theater and the location of targeted subsurface lesions and critical anatomic features depicted in preoperative tomographic image data. However, the lack of readily localized anatomic landmarks has greatly hindered the use of image-guided surgery in minimally invasive abdominal procedures. To address these needs, we have previously described a laser-based system for localization of internal surface anatomy using conventional laparoscopes. During a procedure, this system generates a digitized, three-dimensional representation of visible anatomic surfaces in the abdominal cavity. This paper presents the results of an experiment utilizing an ex-vivo bovine liver to assess subsurface targeting accuracy achieved using our system. During the experiment, several radiopaque targets were inserted into the liver parenchyma. The location of each target was recorded using an optically-tracked insertion probe. The liver surface was digitized using our system, and registered with the liver surface extracted from post-procedure CT images. This surface-based registration was then used to transform the position of the inserted targets into the CT image volume. The target registration error (TRE) achieved using our surface-based registration (given a suitable registration algorithm initialization) was 2.4 mm ± 1.0 mm. A comparable TRE (2.6 mm ± 1.7 mm) was obtained using a registration based on traditional fiducial markers placed on the surface of the same liver. These results indicate the potential of fiducial-free, surface-to-surface registration for image-guided lesion targeting in minimally invasive abdominal surgery.