Continuous Target Tracking Research Articles

The perception of depth vs. frontoparallel motion assessed by continuous target tracking

The perception of depth vs. frontoparallel motion assessed by continuous target tracking

Continuous Psychophysics: measuring visual sensitivity by dynamic target tracking

We introduce a novel framework for estimating visual sensitivity using a continuous target-tracking task in concert with a dynamic internal model of human visual performance. In our main experiment, observers used a mouse cursor to track the center of a 2D Gaussian luminance target as it moved in a Brownian walk in a field of dynamic Gaussian luminance noise. To estimate visual sensitivity, we fit a Kalman filter to the tracking data assuming that humans behave roughly as Bayesian ideal observers. Such observers optimally combine prior information with noisy observations to produce an estimate of target location at each point in time. We found that estimates of human sensory noise obtained from the Kalman filter model were highly correlated with traditional psychophysical measures of human sensitivity (R2 > 0.97). Because data can be collected at the display frame rate, the amount of time required to measure sensitivity is greatly reduced relative to traditional psychophysics. While our modeling framework provides principled estimates of sensitivity that are directly comparable with those from traditional psychophysics, easily-computed summary statistics based on cross-correlograms of the tracking data also accurately predict relative sensitivity, and are thus good empirical substitutes for the more computationally-intensive Kalman filter fitting. As a second example, we show contrast sensitivity functions quickly determined using target tracking. Finally, we show that psychophysical reverse-correlation can also be quickly done via tracking. We conclude that dynamic target tracking is a viable and faster alternative to traditional psychophysical methods in many situations. Meeting abstract presented at VSS 2015

Continuous psychophysics: Target-tracking to measure visual sensitivity.

We introduce a novel framework for estimating visual sensitivity using a continuous target-tracking task in concert with a dynamic internal model of human visual performance. Observers used a mouse cursor to track the center of a two-dimensional Gaussian luminance blob as it moved in a random walk in a field of dynamic additive Gaussian luminance noise. To estimate visual sensitivity, we fit a Kalman filter model to the human tracking data under the assumption that humans behave as Bayesian ideal observers. Such observers optimally combine prior information with noisy observations to produce an estimate of target position at each time step. We found that estimates of human sensory noise obtained from the Kalman filter fit were highly correlated with traditional psychophysical measures of human sensitivity (R2 > 97%). Because each frame of the tracking task is effectively a "minitrial," this technique reduces the amount of time required to assess sensitivity compared with traditional psychophysics. Furthermore, because the task is fast, easy, and fun, it could be used to assess children, certain clinical patients, and other populations that may get impatient with traditional psychophysics. Importantly, the modeling framework provides estimates of decision variable variance that are directly comparable with those obtained from traditional psychophysics. Further, we show that easily computed summary statistics of the tracking data can also accurately predict relative sensitivity (i.e., traditional sensitivity to within a scale factor).

К задаче управления маломерным свободнолетающим космическим роботом

Рассматривается возможность использования принципа обратной связи в решении задачи управления свободнолетающим космическим роботом в режиме манипуляционного функционирования. В рамках данного подхода вводится математическая модель космического манипуляционного робота (КМР), содержащая в явном виде координаты отклонения схвата от цели в инерциальном пространстве. Предлагается алгоритм вычисления оценок указанных координат при наличии информации о направлении на цель и расстоянии до нее, получаемой с помощью размещенной на корпусе КМР видеокамеры со встроенным дальномером. Решается задача формирования алгоритма управления манипуляционным захватом цели в инерциальном пространстве. Приводится пример компьютерного моделирования динамики космического робота, подтверждающий работоспособность предложенного алгоритма.

Calypso® 4D Localization System: a review

AbstractPurposeCalypso® 4D Localization System is a system based on electromagnetic transponders detection enabling precise 3D localisation and continuous tracking of tumour target. This review intended to provide information in order to (1) show how Calypso® 4D Localization System works, (2) to present advantages and disadvantages of this system, (3) to gather information from several clinical studies and, finally, (4) to refer Calypso® System as a tool in dynamic multileaf collimator studies for target motion compensation.MethodsA structured search was carried out on B-On platform. The key words used in this research were ‘Calypso’, ‘Transponder’, ‘Electromagnetic Localization’, ‘Electromagnetic Tracking’, ‘Target Localization’, ‘Intrafraction Motion’ and ‘DMLC’.ReviewTreatment the implanted transponders are excited by an electromagnetic field and resonate back. These frequencies are detected and Calypso® software calculates the position of the transponders. If the movement detected is larger than the limits previously defined, irradiation can be stopped. The system has been proven to be submillimetre accurate.DiscussionCalypso® System has been presented as an accurate tool in prostate radiotherapy treatments. The application of this system to other clinical sites is being developed.ConclusionThe Calypso® System allows real-time localisation and monitoring of the target, without additional ionising radiation administration. It has been a very useful tool in prostate cancer treatment.

A wavelet-based method for extracting intermittent discontinuities observed in human motor behavior

Human motor behavior often shows intermittent discontinuities even when people try to follow a continuously moving target. Although most previous studies revealed common characteristics of this “motor intermittency” using frequency analysis, this technique is not always appropriate because the nature of the intermittency is not stationary, i.e., the temporal intervals between the discontinuities may vary irregularly. In the present paper, we propose a novel method for extracting intermittent discontinuities using a continuous wavelet transform (CWT). This method is equivalent to the detection of peak of the jerk profile in principle, but it successfully and stably detects discontinuities using the amplitude and phase information of the complex wavelet transform. More specifically, the singularity point on the time-scale plane plays a key role in detecting the discontinuities. Another important feature is that the proposed method does not require parameter tuning because it is based on the nature of hand movement. In addition, this method does not contain any optimization process, which avoids explosive increase in computational cost for long time-series data. The performance of the proposed method was examined using an artificial trajectory composed of several primitive movements, and an actual hand trajectory in a continuous target-tracking task. The functional rationale of the proposed method is discussed.

Biological effect of dose distortion by fiducial markers in spot‐scanning proton therapy with a limited number of fields: A simulation study

In accurate proton spot-scanning therapy, continuous target tracking by fluoroscopic x ray during irradiation is beneficial not only for respiratory moving tumors of lung and liver but also for relatively stationary tumors of prostate. Implanted gold markers have been used with great effect for positioning the target volume by a fluoroscopy, especially for the cases of liver and prostate with the targets surrounded by water-equivalent tissues. However, recent studies have revealed that gold markers can cause a significant underdose in proton therapy. This paper focuses on prostate cancer and explores the possibility that multiple-field irradiation improves the underdose effect by markers on tumor-control probability (TCP). A Monte Carlo simulation was performed to evaluate the dose distortion effect. A spherical gold marker was placed at several characteristic points in a water phantom. The markers were with two different diameters of 2 and 1.5 mm, both visible on fluoroscopy. Three beam arrangements of single-field uniform dose (SFUD) were examined: one lateral field, two opposite lateral fields, and three fields (two opposite lateral fields + anterior field). The relative biological effectiveness (RBE) was set to 1.1 and a dose of 74 Gy (RBE) was delivered to the target of a typical prostate size in 37 fractions. The ratios of TCP to that without the marker (TCP(r)) were compared with the parameters of the marker sizes, number of fields, and marker positions. To take into account the dependence of biological parameters in TCP model, α∕β values of 1.5, 3, and 10 Gy (RBE) were considered. It was found that the marker of 1.5 mm diameter does not affect the TCPs with all α∕β values when two or more fields are used. On the other hand, if the marker diameter is 2 mm, more than two irradiation fields are required to suppress the decrease in TCP from TCP(r) by less than 3%. This is especially true when multiple (two or three) markers are used for alignment of a patient. It is recommended that 1.5-mm markers be used to avoid the reduction of TCP as well as to spare the surrounding critical organs, as long as the markers are visible on x-ray fluoroscopy. When 2-mm markers are implanted, more than two fields should be used and the markers should not be placed close to the distal edge of any of the beams.

A novel line of sight control system for a robot vision tracking system, using vision feedback and motion-disturbance feedforward compensation

SUMMARYThis paper presents a novel line of sight control system for a robot vision tracking system, which uses a position feedforward controller to preposition a camera, and a vision feedback controller to compensate for the positioning error. Continuous target tracking is an important function for service robots, surveillance robots, and cooperating robot systems. However, it is difficult to track a specific target using only vision information, while a robot is in motion. This is especially true when a robot is moving fast or rotating fast. The proposed system controls the camera line of sight, using a feedforward controller based on estimated robot position and motion information. Specifically, the camera is rotated in the direction opposite to the motion of the robot. To implement the system, a disturbance compensator is developed to determine the current position of the robot, even when the robot wheels slip. The disturbance compensator is comprised of two extended Kalman filters (EKFs) and a slip detector. The inputs of the disturbance compensator are data from an accelerometer, a gyroscope, and two wheel-encoders. The vision feedback information, which is the targeting error, is used as the measurement update for the two EKFs. Using output of the disturbance compensator, an actuation module pans the camera to locate a target at the center of an image plane. This line of sight control methodology improves the recognition performance of the vision tracking system, by keeping a target image at the center of an image frame. The proposed system is implemented on a two-wheeled robot. Experiments are performed for various robot motion scenarios in dynamic situations to evaluate the tracking and recognition performance. Experimental results showed the proposed system achieves high tracking and recognition performances with a small targeting error.

Continuous target tracking based on multiple cameras

Continuous target tracking based on multiple cameras

Bronchoscopic Implantation of a Novel Wireless Electromagnetic Transponder in the Canine Lung: A Feasibility Study

The success of targeted radiation therapy for lung cancer treatment is limited by tumor motion during breathing. A real-time, objective, nonionizing, electromagnetic localization system using implanted electromagnetic transponders has been developed (Beacon electromagnetic transponder, Calypso Medical Technologies, Inc., Seattle, WA). We evaluated the feasibility and fixation of electromagnetic transponders bronchoscopically implanted in small airways of canine lungs and compared to results using gold markers. After approval of the Animal Studies Committee, five mongrel dogs were anesthetized, intubated, and ventilated. Three transponders were inserted into the tip of a plastic catheter, passed through the working channel of a flexible bronchoscope, and implanted into small airways of a single lobe using fluoroscopic guidance. This procedure was repeated for three spherical gold markers in the opposite lung. One, 7, 14, 28, and 60 days postimplantation imaging was used to assess implant fixation. Successful bronchoscopic implantation was possible for 15 of 15 transponders and 12 of 15 gold markers; 3 markers were deposited in the pleural space. Fixation at 1 day was 15 of 15 for transponders and 12 of 12 for gold markers. Fixation at 60 days was 6 of 15 for transponders and 7 of 12 for gold markers, p value = 0.45. Bronchoscopic implantation of both transponders and gold markers into the canine lung is feasible, but fixation rates are low. If fixation rates can be improved, implantable electromagnetic transponders may allow improved radiation therapy for lung cancer by providing real-time continuous target tracking. Developmental work is under way to improve the fixation rates and to reduce sensitivity to implantation technique.

SU‐FF‐T‐107: Assessment of Dental Amalgam Backscatter with a Beacon Transponder Embedded Mouthpiece for Real‐Time Tracking During Head and Neck IMRT

Purpose: A mouthpiece embedded with Beacon® transponders (Calypso Medical) for continuous localization and tracking during IMRT head and neck irradiation was evaluated for backscatter to the oral mucosa. Dental amalgam can generate excessive backscatter dose to the oral mucosa during treatment. Study objectives were to measure backscatter dose from amalgams, transponders and mouthpiece relative to the oral mucosa. Method and Materials: A dental phantom having 16 of 28 teeth containing amalgam, and a prototype acrylic mouthpiece embedded with 3 transponders (1mm depth) were fabricated. To simulate overlying oral mucosa, a 1.5cm bolus was placed over the dental phantom and mouthpiece for baseline measurements. A TN502RD MOSFET dosimeter and TLD chips (3×3×1mm) with a 6 MV photon beam 10×10 cm2 field (Elekta Precise) with and without mouthpiece were used for measurements. Backscatter was measured with and without the mouthpiece at a source‐to‐detector distance of 100 cm in a single field. To assess dosimetric effects of amalgam in the presence of the mouthpiece, a parallel‐opposed field beam setup was used. Results: Standard amalgam causes dose increases of 24–29% at the tissue interface; however, backscatter decreases rapidly to 7–8% at 0.8mm depth. MOSFET and TLD measurements show the mouthpiece reduced backscatter dose by 15% (at 0.4 mm) for single beam and 6–8% for parallel‐opposed beams. The transponders (1.8mm × 8.5mm) in the mouthpiece do not generate measurable additional backscatter. Conclusion: A mouthpiece when used for continuous target localization and tracking, can effectively reduce backscatter dose caused by amalgams, potentially decreasing mucositis. Embedded transponders do not generate measurable backscatter dose. Conflict of Interest: Mate and Zeller have a financial interest in Calyspo Medical.

Influence of intrafraction motion on margins for prostate radiotherapy

To assess the impact of intrafraction intervention on margins for prostate radiotherapy. Eleven supine prostate patients with three implanted transponders were studied. The relative transponder positions were monitored for 8 min and combined with previously measured data on prostate position relative to skin marks. Margins were determined for situations of (1) skin-based positioning, and (2) pretreatment transponder positioning. Intratreatment intervention was simulated assuming conditions of (1) continuous tracking, and (2) a 3-mm threshold for position correction. For skin-based setup without and with inclusion of intrafraction motion, prostate treatments would have required average margins of 8.0, 7.3, and 10.0 mm and 8.2, 10.2, and 12.5 mm, about the left-right, anterior-posterior, and cranial-caudal directions, respectively. Positioning by prostate markers at the start of the treatment fraction reduced these values to 1.8, 5.8, and 7.1 mm, respectively. Interbeam adjustment further reduced margins to an average of 1.4, 2.3, and 1.8 mm. Intrabeam adjustment yielded margins of 1.3, 1.5, and 1.5 mm, respectively. Significant reductions in margins might be achieved by repositioning the patient before each beam, either radiographically or electromagnetically. However, 2 of the 11 patients would have benefited from continuous target tracking and threshold-based intervention.

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.