Ziv Yaniv

Gradient-based 2-D/3-D rigid registration of fluoroscopic X-ray to CT

We present a gradient-based method for rigid registration of a patient preoperative computed tomography (CT) to its intraoperative situation with a few fluoroscopic X-ray images obtained with a tracked C-arm. The method is noninvasive, anatomy-based, requires simple user interaction, and includes validation. It is generic and easily customizable for a variety of routine clinical uses in orthopaedic surgery. Gradient-based registration consists of three steps: 1) initial pose estimation; 2) coarse geometry-based registration on bone contours, and; 3) fine gradient projection registration (GPR) on edge pixels. It optimizes speed, accuracy, and robustness. Its novelty resides in using volume gradients to eliminate outliers and foreign objects in the fluoroscopic X-ray images, in speeding up computation, and in achieving higher accuracy. It overcomes the drawbacks of intensity-based methods, which are slow and have a limited convergence range, and of geometry-based methods, which depend on the image segmentation quality. Our simulated, in vitro, and cadaver experiments on a human pelvis CT, dry vertebra, dry femur, fresh lamb hip, and human pelvis under realistic conditions show a mean 0.5-1.7 mm (0.5-2.6 mm maximum) target registration accuracy.

OpenIGTLink: an open network protocol for image-guided therapy environment

With increasing research on system integration for image‐guided therapy (IGT), there has been a strong demand for standardized communication among devices and software to share data such as target positions, images and device status.

FRACAS: A system for computer‐aided image‐guided long bone fracture surgery

This article describes FRACAS, a computer-integrated orthopedic system for assisting surgeons in performing closed medullary nailing of long bone fractures. FRACASs goal is to reduce the surgeons cumulative exposure to radiation and surgical complications associated with alignment and positioning errors of bone fragments, nail insertion, and distal screw locking. It replaces uncorrelated, static fluoroscopic images with a virtual reality display of three-dimensional bone models created from preoperative computed tomography and tracked intraoperatively in real time. Fluoroscopic images are used to register the bone models to the intraoperative situation and to verify that the registration is maintained. This article describes the system concept, software prototypes of preoperative modules (modeling, nail selection, and visualization), intraoperative modules (fluoroscopic image processing and tracking), and preliminary in vitro experimental results to date. Our experiments suggest that the modeling, nail selection, and visualization modules yield adequate results and that fluoroscopic image processing with submillimetric accuracy is practically feasible on clinical images.

Precision targeting of liver lesions using a novel electromagnetic navigation device in physiologic phantom and swine.

Radiofrequency ablation of primary and metastatic liver tumors is becoming a potential alternative to surgical resection. We propose a novel system that uses real-time electromagnetic position sensing of the needle tip to help with precision guidance into a liver tumor. The purpose of this study was to evaluate this technology in phantom and animal models. Using an electromagnetic navigation device, instrumented 18 g needles were advanced into radioopaque tumor targets in a respiratory liver phantom. The phantom featured a moving liver target that simulated cranio-caudal liver motion due to respiration. Skin-to-target path planning and real-time needle guidance were provided by a custom-designed software interface based on pre-operative 1 mm CT data slices. Needle probes were advanced using only the electromagnetic navigation device and software display. No conventional real-time imaging was used to assist in advancing the needle to the target. Two experienced operators (interventional radiologists) and two inexperienced ones (residents) used the system. The same protocol was then also used in two anesthetized 45 kg Yorkshire swine where radioopaque agar nodules were injected into the liver to serve as targets. A total of 76 tumor targeting attempts were performed in the liver phantom, and 32 attempts were done in the swine. The average time for path planning was 30 s in the phantom, and 63 s in the swine. The median time for the actual needle puncture to reach the desired target was 33 s in the phantom, and 42 s in the swine. The average registration error between the CT coordinate system and electromagnetic coordinate system was 1.4 mm (SD 0.3 mm) in the phantom, and 1.9 mm (SD 0.4 mm) in the swine. The median distance from the final needle tip position to the center of the tumor was 6.4 mm (SD 3.3 mm, n=76) in the phantom, and 8.3 mm (SD 3.7 mm, n=32) in the swine. There was no statistical difference in the planning time, procedure time, or accuracy of needle placement between experienced and inexperienced operators. The novel electromagnetic navigation system allows probe delivery into hepatic tumors of a physiologic phantom and live anesthetized swine. The system allows less experienced operators to perform equally well as experienced radiologists in terms of procedure time and accuracy of needle probe delivery.

Robust Automatic C-Arm Calibration for Fluoroscopy-Based Navigation: A Practical Approach

This paper presents a new on-line automatic X-ray fluoroscopic C-arm calibration method for intraoperative use. C-arm calibration is an essential prerequisite for accurate X-ray fluoroscopy-based navigation and image-based registration. Our method utilizes a custom-designed calibration ring with a two-plane pattern of fiducials that attaches to the C-arm image intensifier, and an on-line calibration algorithm. The algorithm is robust, fully automatic, and works with images containing anatomy and surgical instruments which cause fiducial occlusions. It consists of three steps: fiducial localization, distortion correction, and camera calibration. Our experimental results show submillimetric accuracy for calibration and tip localization with occluded fiducials.

Needle-Based Interventions With the Image-Guided Surgery Toolkit (IGSTK): From Phantoms to Clinical Trials

We present three image-guided navigation systems developed for needle-based interventional radiology procedures, using the open source image-guided surgery toolkit (IGSTK). The clinical procedures we address are vertebroplasty, RF ablation of large lung tumors, and lung biopsy. In vertebroplasty, our system replaces the use of fluoroscopy, reducing radiation exposure to patient and physician. We evaluate this system using a custom phantom and compare the results obtained by a medical student, an interventional radiology fellow, and an attending physician. In RF ablation of large lung tumors, our system provides an automated interventional plan that minimizes damage to healthy tissue and avoids critical structures, in addition to accurate guidance of multiple electrode insertions. We evaluate the systems performance using an animal model. Finally, in the lung biopsy procedure, our system replaces the use of computed tomographic (CT) fluoroscopy, reducing radiation exposure to patient and physician, while at the same time enabling oblique trajectories which are considered challenging under CT fluoroscopy. This system is currently being used in an ongoing clinical trial at Georgetown University Hospital and was used in three cases.

Long bone panoramas from fluoroscopic X-ray images

This paper presents a new method for creating a single panoramic image of a long bone from several individual fluoroscopic X-ray images. Panoramic images are useful preoperatively for diagnosis, and intraoperatively for long bone fragment alignment, for making anatomical measurements, and for documenting surgical outcomes. Our method composes individual overlapping images into an undistorted panoramic view that is the equivalent of a single X-ray image with a wide field of view. The correlations between the images are established from the graduations of a radiolucent ruler imaged alongside the long bone. Unlike existing methods, ours uses readily available hardware, requires a simple image acquisition protocol with minimal user input, and works with existing fluoroscopic C-arm units without modifications. It is robust and accurate, producing panoramas whose quality and spatial resolution is comparable to that of the individual images. The method has been successfully tested on in vitro and clinical cases.

Fluroscopic Image Processing for Computer-Aided Orthopaedic Surgery

This paper describes the fluoroscopic X-ray image processing techniques of Fracas, a computer-integrated orthopaedic system for bone fracture reduction. Fluoroscopic image processing consists of image dewarping, camera calibration, and bone contour extraction. Our approach focuses on bone imaging and emphasizes integration, full automation, simplicity, robustness, and practicality. We describe the experimental setup and report results quantifying the accuracy of our methods. We show that after dewarping and calibration, submillimetric spatial positioning accuracy is achievable with standard equipment. We present a new bone contour segmentation algorithm based on robust image region statistics computation which yields good results on clinical images.

A hardware and software protocol for the evaluation of electromagnetic tracker accuracy in the clinical environment: a multi-center study

This paper proposes an assessment protocol that incorporates both hardware and analysis methods for evaluation of electromagnetic tracker accuracy in different clinical environments. The susceptibility of electromagnetic tracker measurement accuracy is both highly dependent on nearby ferromagnetic interference sources and non-isotropic. These inherent limitations combined with the various hardware components and assessment techniques used within different studies makes the direct comparison of measurement accuracy between studies difficult. This paper presents a multicenter study to evaluate electromagnetic devices in different clinical environments using a common hardware phantom and assessment techniques so that results are directly comparable. Measurement accuracy has been shown to be in the range of 0.79-6.67mm within a 180mm3 sub-volume of the Aurora measurement space in five different clinical environments.

Treatment Planning and Image Guidance for Radiofrequency Ablation of Large Tumors

This article addresses the two key challenges in computer-assisted percutaneous tumor ablation: planning multiple overlapping ablations for large tumors while avoiding critical structures, and executing the prescribed plan. Toward semiautomatic treatment planning for image-guided surgical interventions, we develop a systematic approach to the needle-based ablation placement task, ranging from preoperative planning algorithms to an intraoperative execution platform. The planning system incorporates clinical constraints on ablations and trajectories using a multiple objective optimization formulation, which consists of optimal path selection and ablation coverage optimization based on integer programming. The system implementation is presented and validated in both phantom and animal studies. The presented system can potentially be further extended for other ablation techniques such as cryotherapy.