Emmanuel Wilson

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.

Stereoscopic augmented reality for laparoscopic surgery

BackgroundConventional laparoscopes provide a flat representation of the three-dimensional (3D) operating field and are incapable of visualizing internal structures located beneath visible organ surfaces. Computed tomography (CT) and magnetic resonance (MR) images are difficult to fuse in real time with laparoscopic views due to the deformable nature of soft-tissue organs. Utilizing emerging camera technology, we have developed a real-time stereoscopic augmented-reality (AR) system for laparoscopic surgery by merging live laparoscopic ultrasound (LUS) with stereoscopic video. The system creates two new visual cues: (1) perception of true depth with improved understanding of 3D spatial relationships among anatomical structures, and (2) visualization of critical internal structures along with a more comprehensive visualization of the operating field.MethodsThe stereoscopic AR system has been designed for near-term clinical translation with seamless integration into the existing surgical workflow. It is composed of a stereoscopic vision system, a LUS system, and an optical tracker. Specialized software processes streams of imaging data from the tracked devices and registers those in real time. The resulting two ultrasound-augmented video streams (one for the left and one for the right eye) give a live stereoscopic AR view of the operating field. The team conducted a series of stereoscopic AR interrogations of the liver, gallbladder, biliary tree, and kidneys in two swine.ResultsThe preclinical studies demonstrated the feasibility of the stereoscopic AR system during in vivo procedures. Major internal structures could be easily identified. The system exhibited unobservable latency with acceptable image-to-video registration accuracy.ConclusionsWe presented the first in vivo use of a complete system with stereoscopic AR visualization capability. This new capability introduces new visual cues and enhances visualization of the surgical anatomy. The system shows promise to improve the precision and expand the capacity of minimally invasive laparoscopic surgeries.

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.

Needle Biopsy of Anatomically Unfavorable Liver Lesions with an Electromagnetic Navigation Assist Device in a Computed Tomography Environment

PURPOSE Emerging interventional radiology assistance systems that incorporate electromagnetic navigation (EMN) can help the operator guide a needle or other instrument toward a target along preplanned oblique trajectories while avoiding critical structures. A proof-of-concept study was conducted to assess the use of EMN, and EMN was compared with the standard computed tomographic (CT) fluoroscopy guidance technique. MATERIALS AND METHODS A total of 14 needle passes, seven each with EMN and CT fluoroscopy guidance, were performed into an artificially created liver lesion of a single swine. The accuracy of needle placement for each pass was verified with a confirmatory CT scan. The total radiation dose and time of procedure was compared between the EMN and conventional CT fluoroscopy methods. RESULTS All needle passes were successful, and all passes conducted with EMN were completed with a single insertion, whereas multiple passes (mean, 2.9) with needle repositioning were required with CT fluoroscopic guidance. Statistically significant reduction in procedure time and overall radiation dose for EMN punctures was shown. Accuracy of needle placement was statistically equivalent for the two methods. CONCLUSIONS This proof-of-concept study shows that EMN guidance has equivalent accuracy of needle placement to conventional CT fluoroscopy-guided methods in swine. EMN is also associated with favorable radiation-dose and time-of-procedure profiles for biopsy of liver lesions. Clinical studies are needed to evaluate the safety and efficacy of this technology in the biopsy of lesions in anatomically challenging locations that require steep angles of needle insertion.

Radiofrequency ablation of lung tumors in swine assisted by a navigation device with preprocedural volumetric planning.

PURPOSE To develop an image guidance system that incorporates volumetric planning of spherical ablations and electromagnetic tracking of radiofrequency (RF) electrodes during insertion. MATERIALS AND METHODS Simulated tumors were created in three live swine by percutaneously injecting agar nodules into the lung. A treatment plan was devised for each tumor with optimization software to solve the planning problem. The desired output was the minimum number of overlapping ablation spheres necessary to ablate each tumor and the margin. The insertion plan was executed with use of the electromagnetic tracking system that guided the insertion of the probe into precomputed locations. After a 72-hour survival period, animals were killed and histopathologic sections of the tissue were examined for cell viability and burn pattern analysis. RESULTS A planning algorithm to spherically cover the tumors and the margin was computed. Electromagnetic tracking allowed successful insertion of the instrument, and impedance roll-off was reached in all ablations. Depending on their size, the tumors and the tumor margins were successfully covered with two to four ablation spheres. The image registration error was 1.0 mm +/- 0.64. The overall error of probe insertion was 9.4 mm +/- 3.0 (N = 8). Analysis of histopathologic sections confirmed successful ablations of the tissue. CONCLUSIONS Computer-assisted RF ablation planning and electromagnetically tracked probe insertion were successful in three swine, validating the feasibility of electromagnetic tracking-assisted tumor targeting. Image misregistration caused by respiratory motion and tissue deformation contributed to the overall error of probe insertion.

Medical needle steering for lung biopsy: Experimental results in tissue phantoms using a robotic needle driver

Needle steering is a commonly used technique in the medical field as it enables physicians to more precisely reach the target tissue. In this paper we describe our interest in needle steering for lung biopsy and the significance of this technique. There has been much interest in modeling needle steering in recent years and this paper builds upon that work. We describe our Matlab implementation and present simulation results. We also show our experimental results based on a robotic needle driver and X-Ray imaging in the interventional suite. The experimental results showed good agreement with the simulation results.

Robot-assisted ultrasound imaging: Overview and development of a parallel telerobotic system

Abstract Ultrasound imaging is frequently used in medicine. The quality of ultrasound images is often dependent on the skill of the sonographer. Several researchers have proposed robotic systems to aid in ultrasound image acquisition. In this paper we first provide a short overview of robot-assisted ultrasound imaging (US). We categorize robot-assisted US imaging systems into three approaches: autonomous US imaging, teleoperated US imaging, and human-robot cooperation. For each approach several systems are introduced and briefly discussed. We then describe a compact six degree of freedom parallel mechanism telerobotic system for ultrasound imaging developed by our research team. The long-term goal of this work is to enable remote ultrasound scanning through teleoperation. This parallel mechanism allows for both translation and rotation of an ultrasound probe mounted on the top plate along with force control. Our experimental results confirmed good mechanical system performance with a positioning error of < 1 mm. Phantom experiments by a radiologist showed promising results with good image quality.

A Buyer's Guide to Electromagnetic Tracking Systems for Clinical Applications

When choosing an Electromagnetic Tracking System (EMTS) for image-guided procedures, it is desirable for the system to be usable for different procedures and environments. Several factors influence this choice. To date, the only factors that have been studied extensively, are the accuracy and the susceptibility of electromagnetic tracking systems to distortions caused by ferromagnetic materials. In this paper we provide a holistic overview of the factors that should be taken into account when choosing an EMTS. These factors include: the systems refresh rate, the number of sensors that need to be tracked, the size of the navigated region, system interaction with the environment, can the sensors be embedded into the tools and provide the desired transformation data, and tracking accuracy and robustness. We evaluate the Aurora EMTS (Northern Digital Inc., Waterloo, Ontario, Canada) and the 3D Guidance EMTS with the flat-panel and the short-range field generators (Ascension Technology Corp., Burlington, Vermont, USA) in three clinical environments. We show that these systems are applicable to specific procedures or in specific environments, but that, no single system is currently optimal for all environments and procedures we evaluated.

A Computer-Controlled Pump and Realistic, Anthropomorphic Respiratory Phantom for Validating Image-Guided Systems

The development of image-guided interventions requires validation studies to evaluate new protocols. So far, these validation studies have been limited to animal models and to software and physical phantoms that simulate respiratory motion but cannot accommodate needle punctures in a realistic manner. We have built a computer-controlled pump that drives an anthropomorphic respiratory phantom for simulating natural breathing patterns. This pump consists of a power supply, a motion controller with servo amplifier, linear actuator, and custom fabricated pump assembly. By generating several sample waveforms, we were able to simulate typical breathing patterns. Using this pump, we were able to produce chest wall movements similar to typical chest wall movements observed in humans. This system has potential applications for evaluating new respiratory compensation algorithms and may facilitate improved testing of image-guided protocols under realistic interventional conditions.

Quantitative CT for volumetric analysis of medical images: initial results for liver tumors

Quantitative CT for volumetric analysis of medical images is increasingly being proposed for monitoring patient response during chemotherapy trials. An integrated MATLAB GUI has been developed for an oncology trial at Georgetown University Hospital. This GUI allows for the calculation and visualization of the volume of a lesion. The GUI provides an estimate of the volume of the tumor using a semi-automatic segmentation technique. This software package features a fixed parameter adaptive filter from the ITK toolkit and a tumor segmentation algorithm to reduce inter-user variability and to facilitate rapid volume measurements. The system also displays a 3D rendering of the segmented tumor, allowing the end user to have not only a quantitative measure of the tumor volume, but a qualitative view as well. As an initial validation test, several clinical cases were hand-segmented, and then compared against the results from the tool, showing good agreement.