@article{Thuerauf2018a, author = {Th{\"{u}}rauf, Sabine and Hornung, Oliver and K{\"{o}}rner, Mario and Vogt, Florian and Knoll, Alois and Nasseri, M. Ali}, title = {Model-Based Calibration of a Robotic C-Arm System Using X-Ray Imaging}, journal = {Journal of Medical Robotics Research}, year = {2018}, month = apr, abstract = {In interventional radiology or surgery, C-arm systems are typical imaging modalities. Apart from 2D X-ray images, C-arm systems are able to perform 2D/3D overlays. For this application, a previously recorded 3D volume is projected on a 2D X-ray image for providing additional information to the clinician. The required accuracy for this application is 1.5 mm. Such a spatial accuracy is only achievable with C-arms, if a calibration is performed. State-of-the-art approaches interpolate between values of lookup tables of a sampled Cartesian volume. However, due to the non-linear system behavior in Cartesian space, a trade-off between the calibration effort and the calibrated volume is necessary. This leads to the calibration of the most relevant subvolume and high calibration times. We discuss a new model-based calibration approach for C-arm systems which potentially leads to a smaller calibration effort and simultaneously to an increased calibrated volume. In this work, we demonstrate that it is possible to calibrate a robotic C-arm system using X-ray images and that a static model of the system is required to achieve the desired accuracy for 2D/3D overlays, if re-orientations of the system are performed.}, doi = {10.1142/S2424905X18410027}, keywords = {robotics, roboterr{\"{o}}ntgen}, } @inproceedings{Thuerauf2017a, author = {Th{\"{u}}rauf, Sabine and K{\"{o}}rner, Mario and Vogt, Florian and Hornung, Oliver and Nasseri, M. Ali and Knoll, Alois}, title = {Environment Effects at Phantom-Based {X}-Ray Pose Measurements}, booktitle = {Proceedings of the International Conference of the {IEEE} Engineering in Medicine and Biology Society ({EMBC})}, pages = {1836--1839}, year = {2017}, month = jul, address = {Seogwipo, South Korea}, abstract = {Image-based pose measurements relative to phantoms are used for various applications. Some examples are: tracking, registration or calibration. If highly precise measurements are needed, even changes of environment factors influence the measurements. This work evaluates how humidity and room temperature affect an image based pose measurements using a phantom. The pose measurement is used for the specific use case of an absolute accurate calibration of a C-arm X-ray system. However, the results are transferable to other applications, too. We describe the effects on different measurement parameters and experimentally evaluate the imprecisions caused by water absorption and thermal expansion of the phantom. The real world results show, that it is needed to monitor the environment effects if measurement precisions in the submillimeter scale are necessary.}, doi = {10.1109/EMBC.2017.8037203}, keywords = {robotics, roboterr{\"{o}}ntgen}, } @inproceedings{Thuerauf2017b, author = {Th{\"{u}}rauf, Sabine and Hornung, Oliver and K{\"{o}}rner, Mario and Vogt, Florian and Nasseri, M. Ali and Knoll, Alois}, title = {Absolute Accurate Calibration of a Robotic {C}-Arm System based on {X}-Ray Observations using a Kinematic Model}, booktitle = {Proceedings of the Workshop on Surgical Robots: Compliant, Continuum, Cognitive, and Collaborative, {IEEE} International Conference on Robotics and Automation ({ICRA})}, year = {2017}, month = jun, address = {Singapore, Singapore}, abstract = {C-arm X-ray systems are commonly used imaging modalities in surgery or interventional radiology. In addition to typical 2D X-ray images, 2D/3D overlays can be performed by these systems. For the 2D/3D overlay a high spatial accuracy of 1:5mm is needed. This accuracy is only achievable, if a spatial calibration of the system is performed. We introduce a new calibration technique for C-arm systems based on an absolute accurate robot calibration to speed up the calibration process and increase the calibrated working volume in future. This work is a proof of concept and shows that the accuracy needed for 2D/3D overlays is achievable with an absolute accurate robot calibration based on X-ray images. However, a deformation model is needed if the C-arm system is reorientated.}, keywords = {robotics, roboterr{\"{o}}ntgen}, } @inproceedings{Thuerauf2016a, author = {Th{\"{u}}rauf, Sabine and Vogt, Florian and Hornung, Oliver and K{\"{o}}rner, Mario and Nasseri, M. Ali and Knoll, Alois}, title = {Experimental Evaluation of the Accuracy at the {C}-Arm Pose Estimation with {X}-Ray Images}, booktitle = {Proceedings of the International Conference of the {IEEE} Engineering in Medicine and Biology Society ({EMBC})}, pages = {3859--3862}, year = {2016}, month = aug, address = {Orlando, FL, USA}, abstract = {C-arm X-ray systems need a high spatial accuracy for applications like cone beam computed tomography and 2D/3D overlay. One way to achieve the needed precision is a model-based calibration of the C-arm system. For such a calibration a kinematic and dynamic model of the system is constructed whose parameters are computed by pose measurements of the C-arm. Instead of common measurement systems used for a model-based calibration for robots like laser trackers, we use X-ray images of a calibration phantom to measure the C-arm pose. By the direct use of the imaging system, we overcome registration errors between the measurement device and the C-arm system. The C-arm pose measurement by X-ray imaging, the new measurement technique, has to be evaluated to check if the measurement accuracy is sufficient for the modelbased calibration regarding the two mentioned applications. The scope of this work is a real world evaluation of the C-arm pose measurement accuracy with X-ray images of a calibration phantom using relative phantom movements and a laser tracker as ground truth.}, doi = {10.1109/EMBC.2016.7591570}, keywords = {robotics, roboterr{\"{o}}ntgen}, } @inproceedings{Thuerauf2016b, author = {Th{\"{u}}rauf, Sabine and Wolf, Markus and K{\"{o}}rner, Mario and Vogt, Florian and Hornung, Oliver and Nasseri, M. Ali and Knoll, Alois}, title = {A Realistic {X}-Ray Simulation for {C}-Arm Geometry Calibration}, booktitle = {Proceedings of the {IEEE} International Conference on Biomedical Robotics and Biomechatronics ({B}io{R}ob)}, pages = {383--388}, year = {2016}, month = jun, address = {Singapore, Singapore}, abstract = {Applications like cone beam computed tomographies (CBCTs) or 2D-3D overlays need a high geometrical accuracy of the C-arm system. In order to achieve this, geometry calibrations are performed to increase the accuracy given by the kinematics of the system. Commonly X-ray images of a phantom with known geometry are taken for the calibration. The images, together with a 3D model of the phantom, serve as input for an optimizer, which estimates the pose of the C-arm relative to the phantom. Afterwards, the estimates are used to increase the geometrical accuracy of the system. Inaccuracies due to real world effects appear, e.g. manufacturing or assembly inaccuracies of the phantom, the position of the X-ray tube, or the pose of the detector. To evaluate these factors separately a simulation is helpful, which needs to be as realistic as possible. To achieve this we defined three requirements, which have to be fulfilled: realistic noise, realistic absolute errors and similar error distributions within the working volume. By means of these criteria we investigate if our simulation mirrors a real world C-arm pose measurement for C-arm geometry calibration sufficiently.}, doi = {10.1109/BIOROB.2016.7523656}, keywords = {robotics, roboterr{\"{o}}ntgen}, } @inproceedings{Thuerauf2015a, author = {Th{\"{u}}rauf, Sabine and Hornung, Oliver and K{\"{o}}rner, Mario and Vogt, Florian and Nasseri, M. Ali and Knoll, Alois}, title = {Evaluation of a 9{D}-Position Measurement Method of a {C}-Arm Based on {X}-Ray Projections}, booktitle = {Proceedings of the Workshop on Interventional Microscopy, International Conference on Medical Image Computing and Computer Assisted Intervention ({MICCAI})}, year = {2015}, month = oct, address = {Munich, Germany}, abstract = {For features like X-ray CTs (computed tomography) a high absolute pose accuracy of the C-arm system is needed. Therefore, an extensive calibration has to be performed to make the C-arm system sufficiently accurate. One new approach to calibrate the system is to perform an absolute robot calibration with end effector pose measurements as input. To measure the poses, X-ray images of a calibration phantom can be used. This work determines a lower bound for an X-raybased 9D-position measurement technique for a C-arm system (including the 3D-position of the tube, the 3D-position of the detector and the 3Dorientation of the detector) using a helical calibration phantom regarding its accuracy by a simulation.}, keywords = {robotics, roboterr{\"{o}}ntgen}, } @inproceedings{Thuerauf2015b, author = {Th{\"{u}}rauf, Sabine and Vogt, Florian and Hornung, Oliver and K{\"{o}}rner, Mario and Nasseri, M. Ali and Knoll, Alois}, title = {Tuning of {X}-Ray Parameters for Noise Reduction of an Image-Based Focus Position Measurement of a {C}-Arm {X}-Ray System}, booktitle = {Proceedings of the Workshop on Alternative Sensing for Robot Perception, {IEEE}/{RSJ} International Conference on Intelligent Robots and Systems ({IROS})}, year = {2015}, month = oct, address = {Hamburg, Germany}, abstract = {In surgery or interventional radiology 2D/3D overlays of X-rays combined with previously recorded 3D volumes support the physician with additional visual information. Typical X-ray systems in these fields are C-arm systems. First of all, the 3D volume and the 2D images need to be registered. Afterwards, if the system moves, errors between the real world pose and the nominal pose of the system appear. One possible way to overcome this problem is an absolute calibration of the system. With this approach the projection geometry can be defined accurately enough for a whole working volume. Therefore, measurements of the end effector pose serve as input. A potential method to determine the pose of the C-arm, is a pose estimation by X-ray observations of a calibration phantom. This work evaluates how the focal spot size, the pixel size and the dose affect the noise at the pose estimation of the C-arm by X-ray observations.}, keywords = {robotics, roboterr{\"{o}}ntgen}, }