Precise Target Localization Research Articles

Tracking by Affine Kernel Transformations Using Color and Boundary Cues

Kernel-based trackers aggregate image features within the support of a kernel (a mask) regardless of their spatial structure. These trackers spatially fit the kernel (usually in location and in scale) such that a function of the aggregate is optimized. We propose a kernel-based visual tracker that exploits the constancy of color and the presence of color edges along the target boundary. The tracker estimates the best affinity of a spatially aligned pair of kernels, one of which is color-related and the other of which is object boundary-related. In a sense, this work extends previous kernel-based trackers by incorporating the object boundary cue into the tracking process and by allowing the kernels to be affinely transformed instead of only translated and isotropically scaled. These two extensions make for more precise target localization. A more accurately localized target also facilitates safer updating of its reference color model, further enhancing the tracker's robustness. The improved tracking is demonstrated for several challenging image sequences.

基于多线索集成的鲁棒视觉跟踪

Traditional color-based mean shift tracking algorithm is unable to accurately track the object. To address this problem, we present an improved tracking algorithm. The improved tracker integrates the color and motion cues which characterize the appearance and motion information of the object, respectively. These two visual cues can complement each other and make for more precise target localization. Experiments show that the proposed tracking algorithm has better performance than the traditional mean shift tracker.

Robotic and imaging in urological surgery

New imaging modalities and tissue navigation systems, which are adoptable to minimally invasive robotic urological surgical systems and prone to make the procedures more precise and easy, are reviewed. Image-guided surgery as the general name of combining information of imaging modalities with real-time surgery has already found a place in open and minimally invasive procedures. Soft tissue navigation is a complex type of computer-assisted surgery for soft tissue interventions. Robotic surgery has advantages of superior degrees of freedom and three-dimensional stereotactic user interface. A combination of surgical robotics with image-assisted surgery and soft tissue navigation may offer advantages of more precise anatomical target localization and dissection with minimal damage to the tissue. Solving the problem of organ shift and as a result, unpredictable changing of intraoperative anatomy soft tissue navigation has the potential to increase the precision of minimally invasive robotic surgery. Apart from less invasiveness, the concomitant use of minimal invasive robotic systems with soft tissue navigation enhances surgical precision. However, at present, abdominal navigation systems are in experimental use and not perfect enough for daily surgical routine.

High precision transponder localization using a novel electromagnetic positioning system in patients with localized prostate cancer

Background and purpose The Micropos 4DRT system is being developed to provide accurate, precise, objective, and continuous target localization during radiotherapy. This study involves the first in vivo use of the system, aiming to evaluate the localization accuracy of this electromagnetic positioning technique compared with radiographic localization and to assess its real-time tracking ability. Material and methods An active positioning marker was inserted in the prostatic urethra of 10 patients scheduled to receive radiotherapy for localized prostate cancer. A receiving sensor plate (antennae system) was placed at a known position in the treatment tabletop. Initial in vivo system calibrations were performed in three subjects. Ten additional patients were then enrolled in a study arm that compared radiographic transponder location to radiotransponder location simultaneously acquired by the Micropos 4DRT system. Frontal and side radiographs were taken with the radiopaque transponder located at three different positions within the prostatic urethra. Results The transponder insertions were all successful and without complications. Comparison of the transponder location as per the Micropos 4DRT system with the radiographic transponder localization showed an average (±SD) absolute and relative 3D difference of 2.7 ± 1.2 and 1.7 ± 1.0 mm, respectively. Continuous transponder tracking capability was also demonstrated. Conclusions Electromagnetic positioning using the Micropos transponder system is feasible in vivo. Evaluation of this novel non-ionizing localization system, in this study using a transponder positioned in the prostatic urethra, indicates transponder localization accuracy to isocenter comparable with X-ray localization of a radiopaque marker.

Quantifying Respiratory-induced Prostate Motion using Continuous Real-time Tracking Technology

Prostate positional variability can alter the effectiveness of radiation therapy when precise target location is unknown. Traditionally, PTV margins are designed to compensate for inter-fraction prostate setup variability. PTV margins may be reduced when using daily image-guidance. More recently, the dosimetric relevance of intra-fraction prostate motion has been recognized, and may be compensated for by continuous real-time adaptive radiation therapy afforded by the Calypso® 4D Localization System. As of today, sparse data is available regarding the magnitude and clinical relevance of highfrequency respiratory-induced prostate motion. The specific aim of this analysis was to quantify respiratory-induced prostate motion using electromagnetic continuous real-time tracking technology.

SU‐FF‐T‐167: Dose Perturbation From Head Frame at Gamma Knife Stereotactic Radiosurgery

Purpose: To investigate the possible dose perturbation from head frame which is attached to patient skull to provide precise location of target in brain and is not considered during dose calculation in Gamma Knife SRS. Method and Materials: An EGS4 based Monte Carlo simulation was applied to Gamma Knife SRS. In the simulation, the geometries of the stationary collimator and the helmet collimator were reconstructed exactly according to Gamma Knife Model C. The materials of the collimators were selected as close to the original materials as possible. All particles were traced through the stationary collimator and the helmet collimator until they pass the inner surface of the helmet or were absorbed. Patient's geometries were rebuilt from CT data. The dose was calculated using Monte Carlo simulation with and without presence of head frame using identical beam parameters. DVH was compared in a small volume around the iso‐center. Results: For patient's data, Monte Carlo results showed that although the 50% to 90% isodose lines remained almost the same with and without the presence of head frame, the maximum distance between two 10% isodose lines could be as far as 1.5 mm. The dose with head frame was about 1.3% lower than the dose without head frame. The dose difference varied from 1% to 2% among five patients. Conclusion: The head frame may have significant impact on peripheral dose distribution as well as absolute dose. Since Automatic Positioning System is applied on Gamma Knife unit, average shot number for each patient has been increased to produce a conformal dose distribution to match the irregular tumor volume. Regular position check can't exclude the possibility that some shots are affected by the head frame. The dose perturbation from head frame should be considered in dose calculation.

Automatic registration of megavoltage to kilovoltage CT images in helical tomotherapy: An evaluation of the setup verification process for the special case of a rigid head phantom

Precise daily target localization is necessary to achieve highly conformal radiation delivery. In helical tomotherapy, setup verification may be accomplished just prior to delivering each fraction by acquiring a megavoltage CT scan of the patient in the treatment position. This daily image set may be manually or automatically registered to the image set on which the treatment plan was calculated, in order to determine any needed adjustments. The system was tested by acquiring 104 MVCT scans of an anthropomorphic head phantom to which translational displacements had been introduced with respect to the planning image set. Registration results were compared against an independent, optically guided positioning system. The total experimental uncertainty was within approximately 1 mm. Although the registration of phantom images is not fully analogous to the registration of patient images, this study confirms that the system is capable of phantom localization with sub-voxel accuracy. In seven registration problems considered, expert human observers were able to perform manual registrations with comparable or inferior accuracy to automatic registration by mutual information. The time to compute an automatic registration is considerably shorter than the time required for manual registration. However, human evaluation of automatic results is necessary in order to identify occasional outliers, and to ensure that the registration is clinically acceptable, especially in the case of deformable patient anatomy.

2213: Tolerance, Stability and Reliability of Implanted Electromagnetic Transponders in the Prostate: A Multi-Center Analysis

Knowledge of the location of a target organ is critical during external beam radiation therapy (EBRT) to optimize therapy and minimize complications. The Calypso® 4D Localization System (Calypso Medical, Seattle, WA) is being developed to provide accurate, precise, objective and continuous target localization during EBRT. The study objectives were to evaluate implant experience and positional stability and reliability with the implanted transponders.

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.

Gated Radiotherapy for Lung Tumors Using Infrared Detectors, Stereoscopic X-rays, and Implanted Markers

Gated Radiotherapy for Lung Tumors Using Infrared Detectors, Stereoscopic X-rays, and Implanted Markers

Buried cable sensor with intruder location

A buried cable sensor has been added to the Intrepid family of outdoor perimeter intrusion sensors. The sensor with the trademarked name "MICROTRACK" is similar to the "MICROPOINT" fence sensor with precise detection location, sensitivity leveling, and free format zoning. Intruder location is accomplished with low-power ultra wideband frequency stepped radar driving the sensor cables. Target range resolution also allows the use of sensitivity leveling for each individual range bin. This will compensate for differences in soil conductivity along the length of the cable and for metal objects, which may be located in the near field radiation. The design of the MICROTRACK sensor was presented at the 2002 Carnahan Conference in Atlantic City. It has been described as FM-CW radar, however it differs from the generic form in that the frequency is stepped rather than continuously swept and phase code modulation is added to discriminate against interference. The wide bandwidth of the MICROTRACK sensor fills in the nulls typical of a single frequency radar and provides a more uniform field profile along the entire length of the sensor cables. This describes the testing that has been performed to characterize the system for different environmental conditions. Southwest Microwave, Inc. has procured an open field site of 31 acres of flat desert land for testing the buried cable. Another site in Canada is used for testing with an additional set of weather and soil conditions. Detection patterns, proximity to stationary objects, and various environmental factors will be discussed. Extensive measurements of both electric and magnetic fields along the length and perpendicular to the sensor cables show a detailed map of the multiple frequency surface wave. When the cables are buried, the uniformity of the field is degraded slightly but no deep nulls are observed. Site testing has confirmed major benefits of the MICROTRACK sensor: - Uniform Detection Zone - Elimination of Deep Nulls - Precise Target Location - Sensitivity Leveling.

Implant experience and positional stability of AC magnetic beacon™ transponders used to localize patients for external beam radiation therapy of the prostate

Implant experience and positional stability of AC magnetic beacon™ transponders used to localize patients for external beam radiation therapy of the prostate

Location selection in the visual domain

According to A.H.C. Van der Heijden (1992), attentional selection of visual stimuli can be considered as location selection. Depending on the type of task, location selection can be considered to be automatic (e.g., in case of abrupt onsets), directly controlled (e.g., in case of symbolic precues), or indirectly controlled (e.g., in case of visual search). In tasks with symbolic precues a contralateral enhancement of the P1 event‐related potential (ERP) component has been found, whereas in visual search tasks a contralateral enhancement of the N2 component has been found. We hypothesized that both lateralized effects reflect the influence of location selection, which differs only in its moment of activation. Linear arrays (a target among five distractors, presented at two eccentricities) requiring left or right responses, were preceded by cues indicating either the precise target location or the side of the target, or by bilateral cues that indicated all array positions. Array‐evoked ERPs, corrected for cue‐evoked and interactive effects, showed not only lateralized but also target location‐specific effects for both components, which supports the view that, depending on the type of task, either the P1 or the N2 component reflect the influence of location selection.

Simulation of the spinning concentric annular ring reticle seeker and an efficient counter-countermeasure

Reticle systems, which are widely used in infrared (IR) missile seekers, are considered to be the classical approach for estimating the position of a target in the field of view (FOV). A new simulation tool is proposed that gives tracking results of the concentric annular ring reticle seeker in various cases. Our simulation model is applicable to the devel- opment of the advanced seekers. When false targets such as flares are present in the FOV, simulation results show that the existing seeker cannot determine the precise target location. To decrease the suscepti- bility to countermeasures such as flares, we propose an efficient counter-countermeasure using signal prediction and correlation. In the simulation results, we ascertain that with our technique the reticle seeker can perform more effective target tracking than previous seekers. © 1997 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(97)03211-X) Subject terms: reticle seeker; simulation; countermeasure; counter- countermeasure; signal prediction; correlation.

The Effects of Cue Informativeness and Signal Amplitude on Auditory Spatial Facilitation of Visual Performance

Research with aurally-aided visual search has demonstrated that a spatial auditory cue facilitates detection of a visual target. By varying both the informativeness of the cue and the amplitude of the cue, this study sought to evaluate the underlying attentional mechanisms involved in this facilitation. In varying informativeness, the auditory cue was either located at the exact location of a target (valid) or at a random location on the opposite lateral side of the target (invalid); the percentage of valid cues (vs. invalid cues) varied at 5%, 25% and 95%. These percentages indicated precise target location (95%), general target location (5%) and minimal information regarding target location (25%). The amplitude of the auditory cue varied at 40dB and 70 dB. The results indicated that the observer can control the allocation of attention toward the target, and that cues indicating general locations are processed differently that cues indicating specific target locations.

Clinical Introduction of an Adjustable Rigid Instrument Holder for Frameless Stereotactic Interventions

Interactive image guidance is now in routine use for open neurosurgical procedures and has demonstrated patient benefits. However, freehand interactive guidance is not an appropriate replacement for the traditional frame-based stereotactic procedures of biopsy, electrode placement, and functional lesioning. These point-based procedures require precise target localization and direct instrument guidance to avoid collateral brain injury. To perform true frameless stereotactic procedures requires a guide that is also adjustable for positioning, lockable, and adaptable to multiple instruments. We describe such a device, which is employed for the guidance of biopsy needles, shunts, electrodes, and endoscopes during neuronavigation. The method of frameless stereotactic biopsy retrieval with an infrared-based neuronavigation system is described, clinical results are given, and further areas of application discussed.

Clinical introduction of an adjustable rigid instrument holder for frameless stereotactic interventions

Interactive image guidance is now in routine use for open neurosurgical procedures and has demonstrated patient benefits. However, freehand interactive guidance is not an appropriate replacement for the traditional frame-based stereotactic procedures of biopsy, electrode placement, and functional lesioning. These point-based procedures require precise target localization and direct instrument guidance to avoid collateral brain injury. To perform true frameless stereotactic procedures requires a guide that is also adjustable for positioning, lockable, and adaptable to multiple instruments. We describe such a device, which is employed for the guidance of biopsy needles, shunts, electrodes, and endoscopes during neuronavigation. The method of frameless stereotactic biopsy retrieval with an infrared-based neuronavigation system is described, clinical results are given, and further areas of application discussed.

VBH Head Holder to Improve Frameless Stereotactic Brachytherapy of Cranial Tumors

Precise target localization is essential for brachytherapy. We have adapted the VBH (Vogele-Bale-Hohner) head holder (Wellhoefer Dosimetry, Schwarzenbruck, Germany), originally developed at the University of Innsbruck, for frameless stereotactic surgery, for use in brachytherapy of cranial tumors. The VBH head holder allows for rigid, noninvasive head fixation by means of an individualized upper dental cast. Registration rods, rigidly attached to the dental cast, provide stable external points of reference. The dental cast is sucked against the upper palate by vacuum, and then the fixated patient is scanned. During simulation, the targeting device can be positioned with respect to the virtual patient using the ISG Viewing Wand. Following simulation, the real patient is repositioned under vacuum control, the targeting device repositioned as well, and the actual brachytherapy initiated.The VBH head holder is well tolerated by patients and simple to use, and various studies have confirmed submillimeter accuracy. The modified head holder in combination with a new targeting device allows for precise and well-planned insertion of hollow needles into a tumor using frameless stereotactic systems as well as being compatible for uses in other fields.

VBH head holder to improve frameless stereotactic brachytherapy of cranial tumors.

Precise target localization is essential for brachytherapy. We have adapted the VBH (Vogele-Bale-Hohner) head holder (Wellhoefer Dosimetry, Schwarzenbruck, Germany), originally developed at the University of Innsbruck, for frameless stereotactic surgery, for use in brachytherapy of cranial tumors. The VBH head holder allows for rigid, noninvasive head fixation by means of an individualized upper dental cast. Registration rods, rigidly attached to the dental cast, provide stable external points of reference. The dental cast is sucked against the upper palate by vacuum, and then the fixated patient is scanned. During simulation, the targeting device can be positioned with respect to the virtual patient using the ISG Viewing Wand. Following simulation, the real patient is repositioned under vacuum control, the targeting device repositioned as well, and the actual brachytherapy initiated. The VBH head holder is well tolerated by patients and simple to use, and various studies have confirmed submillimeter accuracy. The modified head holder in combination with a new targeting device allows for precise and well-planned insertion of hollow needles into a tumor using frameless stereotactic systems as well as being compatible for uses in other fields.

Use of a micro-ionization chamber and an anthropomorphic head phantom in a quality assurance program for stereotactic radiosurgery.

Quality assurance methods used in association with radiosurgery must include all aspects of the radiosurgery process: visualization and localization of the target, treatment and dose planning and dose delivery. Presented here is a quality assurance method that utilizes an anthromorphic head phantom and a micro-ionization chamber to demonstrate precise target localization and accurate dose delivery. This micro-ionization chamber method offers an immediate readout which is both accurate and reproducible. Additionally, this method allows unlimited repetition of the dose measurement process without repeated radiographic localization studies as is necessary with the conventional methods of TLD, film, and Fricke gels. The method and techniques presented can be used in the acceptance testing and routine quality assurance of both linac-based and Gamma Knife radiosurgery units.