Fabian Stopp

Overlay visualization in endoscopic ENT surgery.

PurposeIn endoscopic ENT surgery, the identification and localization of target structures is challenging—depth information is missing, relevant tissues could be hidden behind opaque material and image distortion affects the instrument handling. In this paper, a novel overlay visualization is presented that supports the surgeon by superimposing planning and navigation information on the endoscopic image.MethodTarget regions, which have been identified in preoperative CT data, are superimposed on the endoscopic image, allowing the use of guiding lines for distance visualization. To match the overlay information with the geometrically distorted endoscopic images, a new intraoperative calibration procedure has been developed.ResultsThe accuracy of this new method has been verified by cadaver studies. Clinical evaluation in three paranasal sinus interventions was performed to show the intraoperative assistance and practicability with promising results.ConclusionThe new techniques safely support the surgeon in locating target structures in the paranasal sinuses with little change in the actual workflow.

Misalignment correction in open cone-beam CT

Cone-beam computed tomography (CBCT) is an established standard for both, medical and industrial volumetric imaging. To compute a 3D volume, multiple 2D x-ray projection images of an object of interest are acquired from different directions. Using the geometric information about the acquisition geometry of each image, the volume is reconstructed. Incorrect geometric information (misalignments) leads to blurring and other artifacts in the resulting reconstruction. The exact acquisition geometry is commonly calculated by the analysis of a scan of a dedicated calibration body (off-line calibration). Such approach requires high repeat accuracy of the scanner mechanics and cannot account for non-systematic deviations. Current methods allowing for misalignment correction without a dedicated phantom, e.g. by iteratively adapting the geometry to minimize the arising artifacts, were developed to work with planar trajectories. It poses a problem for open CBCT systems driving complex trajectories. Therefore, we propose an enhanced method allowing for misalignment correction for general trajectories. We developed a new quality function and a flexible modeling for misalignments. We successfully applied our method to real datasets acquired along planar and non-planar trajectories. The correction with our approach substantially increases the resulting volume quality.

Simulation of Clinical Applications for Intraoperative CBCT System Concepts

Intraoperative cone-beam computed tomography (CBCT) is an essential method to verify the placement of implants and the repositioning of bone fractures during surgery. New concepts of open intraoperative CBCT systems attempt to ensure free access to the patient. In this paper we present simulation studies of different intraoperative CBCT system concepts and identify addressable clinical applications. Based on volume reconstructions we compare the reachable image quality and occurring artifacts.

Simulative Assessment of Radiation Exposure for Freely Definable CBCT X-ray Source Trajectories

In cone-beam computed tomography (CBCT) x-ray source and image detector rotate around the patient on a circular path. However, this imaging technique leads to cone-beam artifacts within the reconstructed volume. To avoid or reduce these artifacts the x-ray source trajectory should not be restricted to one plane. An expansion of the x-ray source movement to a three-dimensional (e.g. sinusoidal) trajectory can improve the reconstruction quality. But such an expansion can affect the radiation exposure to the patient. For this reason we developed a simulation method to estimate the radiation exposure for freely definable x-ray source trajectories, which allows us to evaluate and compare different trajectories for CBCT.

Quality Evaluation of Image Recording Strategies for Limited Angle Tomography

Abstract In this paper we propose a new method for evaluating image recording strategies for limited angle tomography. In limited angle tomography exact three-dimensional (3-D) reconstruction is not achievable. With this method a metric for the reachable reconstruction quality by defined X-ray source trajectories is calculated. The result of our method is independent of reconstruction algorithms. Our approach is based on the gradients of the scanned volume and their grade of determinability. Compared to simulated reconstruction accuracy with simultaneous algebraic reconstruction techniques, the method of evaluation shows the same dependencies on X-ray source trajectories. By using the proposed method different source trajectories for a limited angle range are comparable with respect to the reachable reconstruction quality.