Statistical shape models for 3D medical image segmentation: a review.

Computerized Image Registration approaches can offer automatic and accurate image alignments without extensive user involvement and provide tools for visualizing combined images. The aim of this survey is to present a review of publications related to Medical Image Registration. This paper paints a comprehensive picture of image registration methods and their applications. This paper is an introduction for those new to the ﬁeld, an overview for those working in the ﬁeld and a reference for those searching for literature on a speciﬁc application. Methods are classiﬁed according to the diﬀerent aspects of Medical Image Registration.

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Survey of Medical Image Registration

Object tracking is a key enabling technology in the context of computer-assisted medical interventions. Allowing the continuous localization of medical instruments and patient anatomy, it is a prerequisite for providing instrument guidance to subsurface anatomical structures. The only widely used technique that enables real-time tracking of small objects without line-of-sight restrictions is electromagnetic (EM) tracking. While EM tracking has been the subject of many research efforts, clinical applications have been slow to emerge. The aim of this review paper is therefore to provide insight into the future potential and limitations of EM tracking for medical use. We describe the basic working principles of EM tracking systems, list the main sources of error, and summarize the published studies on tracking accuracy, precision and robustness along with the corresponding validation protocols proposed. State-of-the-art approaches to error compensation are also reviewed in depth. Finally, an overview of the clinical applications addressed with EM tracking is given. Throughout the paper, we report not only on scientific progress, but also provide a review on commercial systems. Given the continuous debate on the applicability of EM tracking in medicine, this paper provides a timely overview of the state-of-the-art in the field.

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Electromagnetic tracking in medicine--a review of technology, validation, and applications.

Augmented reality during robot-assisted laparoscopic partial nephrectomy: toward real-time 3D-CT to stereoscopic video registration.

A LUS robotic surgical system is trainable by a surgeon to automatically move a LUS probe in a desired fashion upon command so that the surgeon does not have to do so manually during a minimally invasive surgical procedure. A sequence of 2D ultrasound image slices captured by the LUS probe according to stored instructions are processable into a 3D ultrasound computer model of an anatomic structure, which may be displayed as a 3D or 2D overlay to a camera view or in a PIP as selected by the surgeon or programmed to assist the surgeon in inspecting an anatomic structure for abnormalities. Virtual fixtures are definable so as to assist the surgeon in accurately guiding a tool to a target on the displayed ultrasound image.

Laparoscopic ultrasound robotic surgical system

Organ deformation between preoperative image data and the patient in the OR is the main obstacle for using surgical navigation systems in liver surgery. Our approach is to provide accurate navigation via intraoperative 3D ultrasound. These ultrasound data are augmented with preoperative anatomical models and planning data as an important additional orientation aid for the surgeon. We present an overview of the whole ultrasound navigation system as well as an approach for fast intraoperative non-rigid registration of the preoperative models to the ultrasound volume. The registration method is based on the vessel center lines and consists of a combination of the Iterative Closest Point algorithm and multilevel B-Splines. Quantitative results for three different patients are presented.

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Augmenting Intraoperative 3D Ultrasound with Preoperative Models for Navigation in Liver Surgery

Liver resection has become increasingly safe as a result of considerable progress in equipment, technology, perioperative management, and surgical technique.1 Intraoperative identification of the vascular tree, ie, hepatic and portal veins and the localization of the tumor remains essential for segment oriented surgical resection.

Preoperative 3-dimensional (3D) imaging techniques using computed tomography (CT) or magnetic resonance imaging (MRI) data offer perfect visualization of the anatomy.2 However, 3D simulation models are mainly used for preoperative planning. Anatomic information cannot be transferred to the intraoperative situation directly, due to organ shift and deformation of the liver during mobilization for resection.3

The most frequently used intraoperative imaging technique is ultrasound. It is generally available, and its diagnostic quality is continuously improving. The main objectives of intraoperative ultrasound during liver surgery are to determine tumor resectability, to localize nonpalpable tumors, and to guide surgical procedures.4 Intraoperative imaging is particularly useful for resection of malignant liver lesions,5 but at this time it is mainly used to detect additional metastases.

Two-dimensional ultrasound is mostly displayed on a monoscopic video monitor. Advanced 3D and four-dimensional visualization for guidance of interventional procedures has been only realized in tumor ablation and liver biopsy procedures.6,7 The spatial relationship of the needle and the target lesion was conceived more intuitively with 3D and four-dimensional ultrasonography and helped in adjusting the needle to an optimal position.

We have integrated 3D ultrasound and optoelectronic tracking into a strategy of navigated liver resection. Optoelectronic tracking was used for this study. Accuracy and precision of the system were first validated in a tumor model in an experimental setup. Then a clinical study was performed to evaluate feasibility, basic requirements of 3D ultrasound visualization, performance, and resection margins in relation to the surgical plan.

Feasibility of navigated resection of liver tumors using multiplanar visualization of intraoperative 3-dimensional ultrasound data.

Objective: Computer assisted planning of liver surgery based on preoperative computed tomography (CT) or magnetic resonance imaging (MRI) data can be an important aid to operability decisions and visualization of individual patients' 3D anatomy. A navigation system based on intraoperative 3D ultrasound may help the surgeon to precisely localize vessels, vascular territories or tumors. The preoperative planning must be transferred to the intraoperative ultrasound data and thus to the patient on the operating table. Due to deformations of the liver between planning and surgery, a fast non-rigid registration method is needed.Materials and Methods: A feature-based non-rigid registration approach based on the center-lines of the portal veins has been developed. The combination of an iterative closest point (ICP) approach and Multilevel B-Spline transformations offers a fast registration method. The vessels are segmented and their centerlines extracted from preoperative CT/MRI and intraoperative 3D Power-dopple...

Vessel-based non-rigid registration of MR/CT and 3D ultrasound for navigation in liver surgery.

BACKGROUND: Vessel-oriented surgery and tumour-free resection margins are essential for resection of liver metastases to preserve liver parenchyma and improve oncological outcome. Preoperative three-dimensional models reconstructed from imaging data could facilitate surgical planning with the use of navigation technology. METHODS: Thirty-three patients with central and/or impalpable liver metastases were scheduled for navigated hepatic resection. Intraoperative three-dimensional ultrasonography and an infrared-based optical tracking system were used for data registration and image-guided surgery. Postoperative three-dimensional data were compared with the preoperative virtual surgical plan to assess the accuracy of navigation, and clinical results were compared with those of a matched control group of 32 patients. RESULTS: Navigation was successful in 32 of 33 patients. Realization of the preoperative plan and R0 resection was achieved in 30 of these 32 patients. The median discrepancy between the planned and actual vascular dissection level was 6 (range 0-11) mm. There was a reduced rate of R1 resection in the navigated group compared with the control group (two versus four patients), and more parenchyma was preserved. CONCLUSION:: Three-dimensional ultrasound-based optoelectronic navigation technology improves intraoperative orientation and enables parenchyma-preserving surgery with high precision.

Image-guided surgery of liver metastases by three-dimensional ultrasound-based optoelectronic navigation.

The main problems of navigation in liver surgery are organ movement and deformation. With a combination of direct optical and indirect electromagnetic tracking technology, visualisation and positional control of surgical instruments within three-dimensional ultrasound data and registration of organ movements can be realised simultaneously. Surgical instruments for liver resection were localised with an infrared-based navigation system (Polaris®). Movements of the organ itself were registered using an electromagnetic navigation system (Aurora®). The combination of these two navigation techniques and a new surgical navigation procedure focussed on a circumscribed critical dissection area were applied for the first time in liver resections. This new technique was effectively implemented. The position of the surgical instrument was localised continuously. Repeated position control with observation of the navigation screen was not necessary. During surgical resection, a sonic warning signal was activated when the surgical instrument entered a “no touch” area—an area of reduced safety margin. Optical tracking of surgical instruments and simultaneous electromagnetic registration of organ position is feasible in liver resection.

Sebastian Eulenstein

Papers

Augmenting Intraoperative 3D Ultrasound with Preoperative Models for Navigation in Liver Surgery

Feasibility of navigated resection of liver tumors using multiplanar visualization of intraoperative 3-dimensional ultrasound data.

Vessel-based non-rigid registration of MR/CT and 3D ultrasound for navigation in liver surgery.

Image-guided surgery of liver metastases by three-dimensional ultrasound-based optoelectronic navigation.

Upgrade of an optical navigation system with a permanent electromagnetic position control: a first step towards "navigated control" for liver surgery.