Configuration Of Control Points Research Articles

Interventional Tool Tracking Using Discrete Optimization

This work presents a novel scheme for tracking of motion and deformation of interventional tools such as guide-wires and catheters in fluoroscopic X-ray sequences. Being able to track and thus to estimate the correct positions of these tools is crucial in order to offer guidance enhancement during interventions. The task of estimating the apparent motion is particularly challenging due to the low signal-to-noise ratio (SNR) of fluoroscopic images and due to combined motion components originating from patient breathing and tool interactions performed by the physician. The presented approach is based on modeling interventional tools with B-splines whose optimal configuration of control points is determined through efficient discrete optimization. Each control point corresponds to a discrete random variable in a Markov random field (MRF) formulation where a set of labels represents the deformation space. In this context, the optimal curve corresponds to the maximum a posteriori (MAP) estimate of the MRF energy. The main motivation for employing a discrete approach is the possibility to incorporate a multi-directional search space which is robust to local minima. This is of particular interest for curve tracking under large deformation. This work analyzes feasibility of employing efficient first-order MRFs for tracking. In particular it shows how to achieve a good compromise between energy approximations and computational efficiency. Experimental results suggest to define both the external and internal energy in terms of pairwise potential functions. The method was successfully applied to the tracking of guide-wires in fluoroscopic X-ray sequences of several hundred frames which requires extremely robust techniques. Comparisons with state-of-the-art guide-wire tracking algorithms confirm the effectiveness of the proposed method.

DGPF-Project: Evaluation of Digital Photogrammetric Camera Systems Geometric Performance

The geometric performance of digital airborne cameras also including the impact of direct sensor orientation has been evaluated by a test of the German Society of Photogrammetry, Remote Sensing and Geoinformation (DGPF). This test includes following airborne photogrammetric cameras: the large format frame cameras Z/I Imaging DMC, Vexcel Imaging UltraCamX and the line scanning camera system Leica Geosystems ADS40 (2 generation) and Jena Optronik JAS-150 as well as the mid-format camera Rolleimetric AIC-x1 and the combination of four mid-format cameras Quattro-DigiCAM. The results presented in this paper were achieved by a group of researchers from different institutions, working independently from each other and with different programs for data acquisition and bundle block adjustment. Moreover, different adjustment configurations (i.e. with/without use of perspective centre coordinates and/or attitude information from GPS/inertial systems), and also different control point configurations have been used in the test; this results in a wide range of solutions and accuracy results which are not easy to compare, on the other hand this just shows the spectrum of possible solutions in operational applications.

Control point based exact description of a class of closed curves and surfaces

Based on cyclic curves/surfaces introduced in Róth et al. (2009), we specify control point configurations that result an exact description of those closed curves and surfaces the coordinate functions of which are (separable) trigonometric polynomials of finite degree. This class of curves/surfaces comprises several famous closed curves like ellipses, epi- and hypocycloids, Lissajous curves, torus knots, foliums; and surfaces such as sphere, torus and other surfaces of revolution, and even special surfaces like the non-orientable Roman surface of Steiner. Moreover, we show that higher order (mixed partial) derivatives of cyclic curves/surfaces are also cyclic curves/surfaces, and we describe the connection between the cyclic and Fourier bases of the vector space of trigonometric polynomials of finite degree.

Accuracy assessment of aerial photographs acquired using lighter‐than‐air blimps: low‐cost tools for mapping river corridors

AbstractMonitoring river systems with repeat aerial photography is a powerful tool although the temporal resolution of surveys is rarely performed at anything better than annual time‐scales. In recent years, a variety of low‐cost aerial platforms for acquiring aerial photography have emerged. While these economical options may facilitate more frequent repeat surveys, the accuracy of imagery needs further consideration.The accuracy of imagery obtained from a Lighter‐Than‐Air Blimp is investigated through two simple experiments. The first looks at the geospatial error of aerial photographs derived using five geometric transformation models, and the sensitivity of the photo registration quality to various ground control point (GCP) configurations and densities. At high GCP densities, higher order polynomial transformation models provide the highest quality registrations. However, at more modest GCP densities (i.e. 19–28 GCPs Ha−1), simple aerotriangulation and 2nd order polynomial transformation models perform modestly, resulting in registration errors at standards equal to or better than obtained with conventional aerial photography (e.g. 0.5–1 m). The quality of image registration is highly dependent on the configuration of GCPs. In a second experiment, the practical utility of producing a mosaic of blimp acquired imagery is explored over a kilometre long braided reach. Even at relatively low GCPs densities (e.g. 9 GCPs Ha−1), a mosaiced aerial of the entire reach can be produced of adequate quality to support bar‐scale mapping of patch‐scale features. The survey required less than a single day of field work and laboratory processing, and presents a cost‐effective alternative to traditionally commissioned flights. Copyright © 2008 John Wiley & Sons, Ltd.

SU‐GG‐J‐114: Intrafraction Set‐Up Variability in SBRT Patients Monitored by IR Optical Localizer and KV X‐Ray Images

Purpose: To investigate intrafraction setup variability in high precision stereotactic body radiotherapy (SBRT) by means of integrated infra‐red optical localization and stereoscopic kV X‐ray imaging. Method and Materials: We analyzed data coming from 24 patients treated with SBRT. Patient setup was realized through the ExacTrac X‐ray 6D system (BrainLAB, Germany), consisting of 2 infra‐red TV cameras for external fiducial localization and 2 couples of X‐ray source‐detectors for image registration. Before irradiation, patients were pre‐aligned relying on optical marker localization. Subsequently, patient position was refined through the automatic matching of X‐ray images to digitally reconstructed radiographs (DRR, 3 mm CT slice thickeness), providing 6 corrective parameters that were automatically applied using a robotic couch. The 3D position of the external configuration of control points was detected and stored before (PREmk) and after (POSTmk) the irradiation fraction. A final set of stereoscopic images was acquired and registered to DRR at the end of the treatment, relying on bony anatomy, thus obtaining 6 verification parameters (VP_post). Patient intrafraction motion was evaluated by comparing PREmk with POSTmk (optical measurement). Moreover VP_post parameters were applied to POSTmk thus defining a new configuration of control points (POSTmk‐Xray) that was compared to PREmk (X‐ray measurement). Results: According to the optical measurement, intrafraction motion measured on external fiducials was 0.61±0.53 mm (median±quartile). The X‐ray measurement overestimated intrafraction motion up to 2.05±1.8 mm. The latero‐lateral direction resulted more sensitive to residual errors in X‐ray measurement (0.34±2.88 mm, mean±std). Conclusion: Intrafraction motion, as monitored by the optical system, is not significant. When relying on X‐ray imaging registration, larger motion may be measured because of inherent limitations in DRR cranio‐caudal resolution and digital X‐ray image noise. Such results lead to further questions in assessing the accuracy of X‐ray based setup when integration with optical patient localization is not taken into account.

Patient set-up verification by infrared optical localization and body surface sensing in breast radiation therapy

Background and purpose The aim of the study was to investigate the clinical application of a technique for patient set-up verification in breast cancer radiotherapy, based on the 3D localization of a hybrid configuration of surface control points. Materials and methods An infrared optical tracker provided the 3D position of two passive markers and 10 laser spots placed around and within the irradiation field on nine patients. A fast iterative constrained minimization procedure was applied to detect and compensate patient set-up errors, through the control points registration with reference data coming from treatment plan (markers reference position, CT-based surface model). Results The application of the corrective spatial transformation estimated by the registration procedure led to significant improvement of patient set-up. Median value of 3D errors affecting three additional verification markers within the irradiation field decreased from 5.7 to 3.5 mm. Errors variability (25–75%) decreased from 3.2 to 2.1 mm. Laser spots registration on the reference surface model was documented to contribute substantially to set-up errors compensation. Conclusions Patient set-up verification through a hybrid set of control points and constrained surface minimization algorithm was confirmed to be feasible in clinical practice and to provide valuable information for the improvement of the quality of patient set-up, with minimal requirement of operator-dependant procedures. The technique combines conveniently the advantages of passive markers based methods and surface registration techniques, by featuring immediate and robust estimation of the set-up accuracy from a redundant dataset.

Constrained anatomical surface registration for patient positioning in breast cancer radiotherapy

Constrained anatomical surface registration for patient positioning in breast cancer radiotherapy

Three-dimensional point localisation in low-dose X-ray images using stereo-photogrammetry.

A stereo-photogrammetric method for three-dimensional reconstruction of points in low-dose digital X-ray images obtained using a scanner with similar imaging geometry to that of computed tomography scan projection radiography, was analysed. A calibration frame containing 25 radio-opaque markers with known three-dimensional locations was scanned, and the accuracy of reconstruction of the marker positions under varying control point configurations and separation angles was assessed. Errors of less than 1 mm were obtained when nine test points were reconstructed, with 16, 11 and 7 control points at a 90 degrees separation angle, and with 16 and 11 control points at 75 degrees and 60 degrees separation angles. The optimum reconstruction, with a resultant error of 0.68 mm, was found to occur at a separation angle of 90 degrees, with the largest number of control points (16) used to calculate the parameters of the transformation. Extrapolation in the scanning direction beyond the space defined by the control points gave errors of less than 2 mm. This method should be suitable for three-dimensional point reconstruction in applications such as cephalometry, brachytherapy planning and assessment of spinal shape.

Validation of the Pi-SAR Data for Land Cover Mapping

In this paper, we analyzed the accuracy of orbit modeling with various control point configurations and adjustment unknown parameter sets. We used 152 GCP points acquired from GPS surveying, which were distributed from Choon-chun to Nha-ju along 420km in distance. For orbit modeling, seven adjustment parameter sets were chosen to include parameters for satellite position, velocity and attitude angles at different degree of freedom. Firstly we determined the location of model point in seven configurations. Secondly we estimated model parameters for each parameter set and for each GCP configurations. Finally we applied the model to reference check points and analyzed its accuracy. We were able to find the unknown parameter set that produce best orbit modeling performance regardless of the configuration of model points.

トンネルの変形計測のためのデジタル写真測量法の研究

Because deformations are important indicators of the degree of stability during construction of rock structures, monitoring of deformation is a key element of observational method in tunnels. Monitoring can also help determine the depth of the loosened zone, movements on discontinuities, in-situ modulus, and other items that may be dealt with in design. We have studied the applicability of digital photogrammetry for monitoring of surface displacements in civil engineering. Digital Photogrammetry is the technique obtaining three dimensional coordinates of an object by means of digital photography. This photogrammetry has the advantage of measuring deformation of an object by some photos with easy measurements and excellent cost performance. Because the linearized equation to analyze the coordinates of object points has some rank defects due to no control points in tunnel, we present constrained least square estimation to measure the displacements without the incorporation of control point configuration. The results of experiments demonstrated that this measurement system could yield high accurate three dimensional coordinates of target points situated on an object. It is also shown that this digital photogrammetry can monitor the displacements of the tunnel accurately along with a capability of real-time measurement because of removal of human skills in measurement tasks.

Managing the shape of planar splines by their control polygons

A practical formulation of the shape-preservation theorem is presented. It states how the control points should be positioned to obtain a prescribed curve shape and avoid shape anomalies. The concept of hyperconvex polygons is introduced. These polygons can be intersected by straight lines at three points, and are therefore not covered by previous versions of the theorem. The extended theorem addresses all the possible control-point configurations, and is proved for important classes of planar B-splines and beta2-splines.

Accuracy assessment and control point configuration when using the DLT for photogrammetry

The direct linear transformation (DLT) is a common technique used to calibrate cameras and subsequently reconstruct points filmed with two or more cameras in a three-dimensional object space. The assessment of the accuracy of this technique, and of the influence of the distribution of control points on accuracy were examined. It was concluded that to obtain a true estimation of reconstruction accuracy, an independent assessment criterion is required, and that the use of control points distributed around the outside, rather than within the space to be calibrated, is preferred.