Localization Tracking Research Articles

SU‐GG‐J‐176: The Accuracy and Stability of the Calypso System for Prostate Localization and Motion Tracking

Purpose: To investigate the long‐term accuracy and stability of a real‐time electromagnetic tracking system (“Calypso System” Calypso Medical Tech. Inc, Seattle, WA) that has been used for localization and motion monitoring for prostate IMRT. Method and Materials: Two Calypso Systems have been installed in our center and were calibrated bimonthly. A quality‐assurance (QA) phantom provided by the manufacture has been used to check the localization accuracy every day. The phantom was set up under the guidance of the room laser and checked with the beam crosshair. The measured isocenter offsets in three directions were recorded for different calibration periods (the time period between two calibrations). The mean value and the standard deviation of the offset for every calibration period were analyzed statistically. The systematic error and the random error for prostate localization were calculated and compared with the acceptance tests when the systems were first installed. Results: Phantom localization data for 9 calibration periods in one year were used for the calculation of the localization accuracy and stability. The mean offsets in lateral, longitudinal and vertical directions are 0.08mm towards right, 0.24mm toward inferior and 0.71mm toward posterior. The standard deviations in these three directions are 0.34mm, 0.49mm and 0.47mm for the systematic error and 0.67mm, 0.9mm and 1.29mm for the random error, respectively. The results agreed with the acceptance tests in which the average setup and tracking accuracy was 0.95mm and the maximum error was 1.5mm when only two transponders were used. Conclusion: The localization uncertainty using the Calypso System is less than 1mm based on the phantom measurements and it was confirmed through the acceptance tests. The system is accurate and stable for prostate patient localization and motion tracking based on long term phantom calibration measurements.

SU‐GG‐J‐172: Static and Dynamic Tracking Accuracy of a Novel Radioactive Tracking Technology for Target Localization and Real Time Tracking in Radiation Therapy

Purpose: In radiation therapy there is a need to accurately know the location of the target in real time. A novel radioactive tracking technology is being developed to answer this need. The technology consists of a radioactive non‐migrating implanted fiducial marker and a linac mounted tracking device. This study measured the static and dynamic accuracy of the new tracking technology in a clinical radiation therapy environment. Method and Materials: The tracking device was installed on an Elekta Synergy® linac gantry. The radioactive marker was located in a tissue equivalent phantom. Actual marker location was measured using a Microscribe G2 coordinate measuring machine (CMM) arm (certified spatial accuracy of 0.38 mm). The marker was attached to the tip of the CMM arm and its location was measured simultaneously by the CMM and the tracking system. Static accuracy was measured at multiple locations covering a 12cm cube centered at the linac iso‐center. The measurements were repeated at multiple gantry angles. Dynamic accuracy was measured with the marker located inside a breathing phantom. Results: The mean localization error for the static source was less than 0.7mm throughout the tested region at all measured gantry angles. The mean real time tracking error for the dynamic source within the breathing phantom was less than 1mm. Conclusion: The novel radioactive tracking technology has the potential to be useful in accurate target localization and real time monitoring for radiation therapy. Conflict of Interest: Research sponsored by Navotek Medical Ltd.

SU-GG-T-373: Real-Time Tracking of Inter Marker Distances to Assess Maker Stability, Organ Deformation in Prostate Cancer

Purpose: The use of intraprostatic fiducials as surrogates for prostate gland position assumes that the markers are rigidly positioned within the prostate. To test this assumption, the intermarker distances (IMD) of implanted Calypso® beacon transponders were monitored during radiation therapy to determine marker stability within the prostate gland. Method and Materials: The analysis is performed on 4 patients treated with intensity‐modulated radiotherapy. A total of 12 markers (3 transponders per patient) were implanted. Each of the three transponder locations are continuously measured using the Calypso® 3D Localization and Real Time Tracking system at a rate of 10 Hz. A total of 110,265 sampling points were available for analysis. Each sampling point allows the computation of the 3 IMDs. To study variations in marker position, daily IMDs were compared with the IMD that was observed during the first alignment. We defined the variation in the IMD as the important measure of intrinsic marker position variation. The standard deviation (SD) of IMD variations was studied as a measure of the extent of marker position variation. Results: The maximum deformation as measured by analysis of IMDs with a 95% confidence interval was +/− 2.8 mm across all 4 patients with the minimum deformation of +/− 0.28 mm. The average deformation with a 95% confidence interval was +/− 2 mm. The maximum relative variation of all the IMDs was 7.7% in the worse case scenario and represents at least a 92.7% confidence in the data. Conclusion: IMDs varied minimally, which indicated relatively little deformation of the gland as well as the absence of significant marker migration. Intraprostatic implanted Calypso ® beacon transponders in the prostate allow for a reliable localization of the prostate gland.

Clinical Experience on Localization and Real-Time Tracking of the Prostate During External Radiotherapy using Calypso® 4D Localization System

Clinical Experience on Localization and Real-Time Tracking of the Prostate During External Radiotherapy using Calypso® 4D Localization System

2P1-N04 Robot as mobile sensor in Intelligent Space : Analysis of cooperative sensing using onboard and static sensors

This paper deals with the problem of robot localization and object tracking inside a space with distributed sensors - Intelligent Space. In addition to static sensors distributed in the space, a mobile robot is used as a mobile sensor to gather additional information and improve the estimation. We discuss the characteristics of such a tracking system, which uses both robot onboard and static sensors. In the implementation laser range finders were used.

A reactive agent-based problem-solving model

For two decades, multi-agent systems have been an attractive approach for problem solving and have been applied to a wide range of applications. Despite the lack of generic methodology, the reactive approach is interesting considering the properties it provides. This article presents a problem-solving model based on a swarm approach where agents interact using physics-inspired mechanisms. The initial problem and its constraints are represented through agents' environment, the dynamics of which is part of the problem-solving process. This model is then applied to localization and target tracking. Experiments assess our approach and compare it to widely-used classical algorithms.

Target localization and real-time tracking using the Calypso 4D localization system in patients with localized prostate cancer

The Calypso 4D Localization System is being developed to provide accurate, precise, objective, and continuous target localization during radiotherapy. This study involves the first human use of the system, to evaluate the localization accuracy of this technique compared with radiographic localization and to assess its ability to obtain real-time prostate-motion information. Three transponders were implanted in each of 20 patients. Eleven eligible patients of the 20 patients participated in a study arm that compared radiographic triangulated transponder locations to electromagnetically recorded transponder locations. Transponders were tracked for 8-min periods. The implantations were all successful, with no major complications. Intertransponder distances were largely stable. Comparison of the patient localization on the basis of transponder locations as per the Calypso system with the radiographic transponder localization showed an average (+/-SD) 3D difference of 1.5 +/- 0.9 mm. Upon tracking during 8 min, 2 of the 11 patients showed significant organ motion (>1 cm), with some motion lasting longer that 1 min. Calypso transponders can be used as magnetic intraprostatic fiducials. Clinical evaluation of this novel 4D nonionizing electromagnetic localization system with transponders indicates a comparable localization accuracy to isocenter, (within 2 mm) compared with X-ray localization.

Clinical Experience with the Calypso® 4D Localization System in Prostate Cancer Patients: Implantation, Tolerance, Migration, Localization and Real Time Tracking

Purpose/Objective: To study the implantation and long-term tolerance of Beacon® transponders, and localization and tracking in patients with localized prostate cancer. Materials/Methods: Calypso 4D Localization System (“Calypso System”, Calypso Medical, Seattle, WA) is an investigational patient positioning device including markers (transponders: 8.5 × 1.85 mm, glass-encapsulated electrical circuits used for permanent implantation), and external electronics that continuously localize the transponders using electromagnetic signals at a 10 Hz rate. Three transponders were implanted with 14G needles at the apex, left and right base under transrectal ultrasound guidance in 20 patients. Adverse event checks were conducted at Day 0 (day of implant), 4, 7, 10, 14 (simulation); Fraction 4, 10, 15, 20; and 1, 6, and 12 months post- RT. CTs or pair of kV X-rays were acquired at Day 0, 4, 7, 10, 14; at Fractions 1, 2, 3, 4, 10, 15, 20; and 1 month post-RT to document transponder geometry and compute inter-transponder distance, a migration indicator. Results: The implantation procedures completed without any major complications. Of 60 transponders, one was presumably implanted in the urethra and subsequently voided (patient was asymptomatic) and one migrated cephalad approx. 3 cm from the apex prior to Day 4 presumably within the venous plexus (the transponder subsequently remained stable). In 2 cases, there was a minimal change in urinary status (IPSS scores) prior to RT. All acute bleeding (hematuria, hematospermia, and/or hematochezia) resolved by Day 10 (n=7). To date, 5/20 subjects have completed the 12-month post-RT follow-up. Dysuria was reported in 11 patients after RT. One case of prostatitis was reported at 6 months, and one patient with a very large prostate gland had urinary obstruction requiring surgical intervention at 8 months post-RT that was considered unrelated to the transponders. Analysis of inter-transponder distances indicated stable geometry in 15/20 patients by Day 4, and in all patients by Day 14. Distances at 4-week post-RT again showed stable geometry. In 11/20 patients, localization and tracking were performed (1 patient not localizable and 8 not evaluated). Comparison of the Calypso System coordinates with transponder locations on X-rays showed average (±+SD) 3D difference between the two systems was 1.5 ± 0.9 mm. Finally, during tracking, 2/11 patients showed significant organ motion (>1 cm) over 8 minutes. Longitudinal and vertical motion followed the same pattern of change, with no significant motion in the lateral direction. The excursions persisted for over one minute. Conclusions: Transrectal implantation of transponders for use with the Calypso System has an acceptable adverse event profile that appears consistent with gold marker implantation. Care should be taken to implant transponders within the prostate gland, off mid-line, to avoid migration. Real-time target position monitoring is possible for the first time without requiring X-rays for imaging. Tracking the prostate showed significant motion over time periods of interest in radiation therapy in some patients. Real-time tracking of organ motion will play an important role in modern external beam radiotherapy.

시각장애인 유도 로봇의 자기 위치 추적 시스템 및 사용자 인터페이스 개발

시각 장애인용 유도 로봇을 안전하게 유도하기 위해서는 경로를 검색하기 위해 사용되는 전자지도가 섬세해야 하며 위험한 위치에 대한 정보를 가지고 있어야 한다. 또한 GPS와 INS에 의해 획득한 위치정보를 통하여 안전하면서도 빠른 최단 경로를 검색해야 한다. 본 논문에서는 시각 장애인의 인식 능력의 차이에 따라 시각 장애인에게 경로의 안내 및 위치정보만을 제공하는 이동경로 생성 및 확인을 위한 자기 위치 추적 시스템과 주변 환경정보인식 및 GPS 오차보정기능을 가진 유도로봇과 통합된 시각장애인용 전역항법시스템을 구현하였다. 이 시스템을 통하여 시각 장애인이 비교적 짧은 거리를 이동하고자 할 때 활용할 수 있으며, 실외 환경에서는 GPS의 보조 항법 시스템으로 위치의 보정을 할 수 있음을 알 수 있었다. To guide the guiding robot for the visually impaired carefully, the digital map to be used to search a path must be detailed and has some information about dangerous spots. It also has to search not only safe but also short path through the position data by GPS and INS sensors. In this paper, as the difference of the ability that the visually unpaired can recognize, we have developed the localization tracking system so that it can make a movement path and verify position information, and the global navigation system for the visually impaired using the GPS and INS. This system can be used when the visually impaired move short path relatively. We had also verified that the system was able to correct the position as the assistant navigation system of the GPS on the outside.

Space-time Coordinated Distributed Sensing Algorithms for Resource Efficient Narrowband Target Localization and Tracking

Distributed sensing has been used for enhancing signal to noise ratios for space-time localization and tracking of remote objects using phased array antennas, sonar, and radio signals. The use of these technologies in identifying mobile targets in a field, emitting acoustic signals, using a network of low-cost narrow band acoustic micro-sensing devices randomly dispersed over the region of interest, presents unique challenges. The effects of wind, turbulence, and temperature gradients and other environmental effects can decrease the signal to noise ratio by introducing random errors that cannot be removed through calibration. This paper presents methods for dynamic distributed signal processing to detect, identify, and track targets in noisy environments with limited resources. Specifically, it evaluates the noise tolerance of adaptive beamforming and compares it to other distributed sensing approaches. Many source localization and direction-of-arrival (DOA) estimation methods based on beamforming using acoustic sensor array have been proposed. We use the approximate maximum likelihood parameter estimation method to perform DOA estimation of the source in the frequency domain. Generally, sensing radii are large and data from the nodes are transmitted over the network to a centralized location where beamforming is done. These methods therefore depict low tolerance to environmental noise. Knowledge based localized distributed processing methods have also been developed for distributed in-situ localization and target tracking in these environments. These methods, due to their reliance only on local sensing, are not significantly affected by spatial perturbations and are robust in tracking targets in low SNR environments. Specifically, Dynamic Space-time Clustering (DSTC)-based localization and tracking algorithm has demonstrated orders of magnitude improvement in noise tolerance with nominal impact on performance. We also propose hybrid algorithms for energy efficient robust performance in very noisy environments. This paper compares the performance of hybrid algorithms with sparse beamforming nodes supported by randomly dispersed DSTC nodes to that of beamforming and DSTC algorithms. Hybrid algorithms achieve relative high accuracy in noisy environments with low energy consumption. Sensor data from a field test in the Marine base at 29 Palms, CA, were analyzed for validating the results in this paper. The results were compared to “ground truth” data obtained from GPS receivers on the vehicles.

Cooperative Localization and Tracking in Distributed Robot-Sensor Networks

This paper addresses the problem of real-time position and orientation estimation of networked mobile robots in two-dimensional Euclidean space with simultaneous tracking of a rigid unknown object based on exteroceptive sensory information extracted from distributed vision systems. The sufficient and necessary conditions for team localization are proposed. A localization and object tracking approach based on statistical operators and graph searching algorithms is presented for a team of robots localized with heterogeneous sensors. The approach was implemented in an experimental platform consisting of car-like mobile robots equipped with omnidirectional video cameras and IEEE 802.11b wireless networking. The experimental results validate the approach.

Computer-assisted LISS plate osteosynthesis of proximal tibia fractures: Feasibility study and first clinical results

Fluoroscopy is the most common tool for the intraoperative control of long-bone fracture reduction. Limitations of this technology include high radiation exposure for the patient and the surgical team, limited visual field, distorted images, and cumbersome verification of image updating. Fluoroscopy-based navigation systems partially address these limitations by allowing fluoroscopic images to be used for real-time surgical localization and instrument tracking. Existing fluoroscopy-based navigation systems are still limited as far as the virtual representation of true surgical reality is concerned. This article, for the first time, presents a reality-enhanced virtual fluoroscopy with radiation-free updates of in situ surgical fluoroscopic images to control metaphyseal fracture reduction. A virtual fluoroscopy is created using the projection properties of the fluoroscope; it allows the display of detailed three-dimensional (3D) geometric models of surgical tools and implants superimposed on the X-ray images. Starting from multiple registered fluoroscopy images, a virtual 3D cylinder model for each principal bone fragment is constructed. This spatial cylinder model not only supplies a 3D image of the fracture, but also allows effective fragment projection recovery from the fluoroscopic images and enables radiation-free updates of in situ surgical fluoroscopic images by non-linear interpolation and warping algorithms. Initial clinical experience was gained during four tibia fracture fixations that were treated by LISS (Less Invasive Stabilization System) osteosynthesis. In the cases operated on, after primary image acquisition, the image intensifier was replaced by the virtual reality system. In all cases, the procedure including fracture reduction and LISS osteosynthesis was performed entirely in virtual reality. A significant disadvantage was the unfamiliar operation of this prototype software and the need for an additional operator for the navigation system.

A new system to perform continuous target tracking for radiation and surgery using non-ionizing alternating current electromagnetics

A new technology based on alternating current (AC) nonionizing electromagnetic fields has been developed to enable precise localization and continuous tracking of mobile soft tissue targets or tumors during radiation therapy and surgery. The technology utilizes miniature, permanently implanted, wireless transponders (Beacon™ Transponders) and a novel array to enable objective localization and continuous tracking of targets in three-dimensional space. The characteristics of this system include use of safe, nonionizing electromagnetic fields; negligible tissue interaction, delivery of inherently objective three-dimensional data, continuous operation during external beam radiation therapy or surgery. Feasibility testing has shown the system was capable of locating and continuously tracking transponders with submillimeter accuracy at tracking rates of up to 10 Hz and was unaffected by operational linear accelerator. Preclinical animal studies have shown the transponders to be suitable for permanent implantation and early human clinical studies have demonstrated the feasibility of inserting transponders into the prostate. This system will enable accurate initial patient setup and provide real-time target tracking demanded by today's highly conformal radiation techniques and has significant potential as a surgical navigation platform.

Computer aided long bone fracture treatment

Intraoperative fluoroscopy is the tool for intraoperative control of long bone fracture reduction and osteosynthesis. Limitations of this technology include: High radiation exposure to the patient and the surgical team, limited field of view, image distortion, limitation to 2-D representations, and cumbersome updating of verification images. Fluoroscopy based navigation systems partially address these limitations by allowing fluoroscopic images to be used for real-time surgical localization and instrument tracking. In a clinical study on computer guidance by virtual fluoroscopy for distal locking, the capability to provide online guidance with significantly reduced fluoroscopy times is demonstrated. Virtual fluoroscopy applied for guidewire placement in a laboratory setup demonstrated the potential of the method to reduce procedure times, and the potential to increase precision of implant placement with decreased fluoroscopy times. By using virtual reality enhancement, starting from multiple registered fluoroscopy images, a virtual 3-D cylinder model for each principal bone fragment is reconstructed. This spatial cylinder model is not only used to supply a 3-D image of the fracture, but also allows effective fragment projection extraction from the fluoroscopic images and further achieves radiation-free updates of in-situ surgical fluoroscopic images through a non-linear interpolation and warping algorithm. After primary image acquisition, the image intensifier was replaced by the virtual reality system. It was shown that all the steps of the procedure, including fracture reduction and LISS osteosynthesis can be performed completely in virtual reality.

Biocompatibility of a wireless electromagnetic transponder permanent implant for accurate localization and continuous tracking of tumor targets

Purpose/Objective: The purpose of this study was to examine biocompatibility of permanently implantable electromagnetic transponders in animal models. A new technology using non-ionizing, electromagnetic fields for accurate localization and continuous tracking of tumor targets during radiation therapy has been developed (Calypso Medical Technologies, Seattle, WA). The technology utilizes miniature, permanently implanted, wireless electromagnetic transponders (Beacon|TM| Transponders) and a means for objective localization and continuous tracking in 3-D space. The transponders are temporarily excited and induce resonant response signals. Each excited transponder briefly emits a magnetic field at a unique frequency. Sensors measure the emitted magnetic field strength to determine the coordinates. Electromagnetic fields exhibit negligible interaction with tissue in the human body.

Demonstration of accurate localization and continuous tracking of implantable wireless electromagnetic transponders

Demonstration of accurate localization and continuous tracking of implantable wireless electromagnetic transponders

Feature-based multi-hypothesis localization and tracking using geometric constraints

Mobile robot localization deals with uncertain sensory information as well as uncertain data association. In this paper we present a probabilistic feature-based approach to global localization and pose tracking which explicitly addresses both problems. Location hypotheses are represented as Gaussian distributions. Hypotheses are found by a search in the tree of possible local-to-global feature associations, given a local map of observed features and a global map of the environment. During tree traversal, several types of geometric constraints are used to determine statistically feasible associations. As soon as hypotheses are available, they are tracked using the same constraint-based technique. Track splitting is performed when location ambiguity arises from uncertainties and sensing. This yields a very robust localization technique which can deal with significant errors from odometry, collisions and kidnapping. Experiments in simulation and with a real robot demonstrate these properties at low computational costs.

Mobile robot self-localisation using occupancy histograms and a mixture of Gaussian location hypotheses

The topic of mobile robot self-localisation is often divided into the sub-problems of global localisation and position tracking. Both are now well understood individually, but few mobile robots can deal simultaneously with the two problems in large, complex environments. In this paper, we present a unified approach to global localisation and position tracking which is based on a topological map augmented with metric information. This method combines a new scan matching technique, using histograms extracted from local occupancy grids, with an efficient algorithm for tracking multiple location hypotheses over time. The method was validated with experiments in a series of real world environments, including its integration into a complete navigating robot. The results show that the robot can localise itself reliably in large, indoor environments using minimal computational resources.

Virtual fluoroscopy

Fluoroscopy is a useful and familiar technology to all orthopedic surgeons. Its limitations include radiation exposure to the patient and surgical team and the need to reposition the fluoroscope repeatedly to obtain surgical guidance in multiple planes. Virtual fluoroscopy, which uses image-guided computer technology to enhance a standard C-arm fluoroscope, addresses these limitations by allowing preacquired fluoroscopic images to be used for real-time surgical localization and instrument tracking. In addition, it enables a single C-arm fluoroscope to provide real-time, multiplanar surgical guidance. In this article, we report the technical requirements for a virtual fluoroscopy system and illustrate some of the applications for this system in spinal surgery.

Nonlinear data observability and information

For the deterministic system observability, two conditions, connectedness and univalence, are introduced and used. Depending on how the conditions are satisfied, observability is classified in three categories: observability in the strict sense, observability in the wide sense and the unobservable case. An underwater acoustical localization tracking example, the bearing-only information problem described in three different coordinates, and an array SONAR problem described in terms of a small number of sensors and various measurement policies are analyzed. For stochastic process observability, an information theoretic approach is introduced. Computed here, is the mutual information between the state and the observation. Since this quantity is expressed as an entropy difference between a prior and a posteriori processes, two densities are required for computation. Due to the difficulty in solving the density equation, an estimated second-moment approximation is considered. Then, mutual information is used as a criterion to determine the “degree of observability”. Sensitivity with respect to various coordinate systems for an array SONAR, a combination of relative delay and Doppler measurements for up to three sensors are compared. Due to complexity of the computations, the tracking results, presented here, rely heavily on simulation.