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Franz Wegner,1 Thomas Friedrich,2 Maximilian Wattenberg,2 Justin Ackers,2 Malte Maria Sieren,1,3 Roman Kloeckner,1 Joerg Barkhausen,3 Thorsten M Buzug,2,4 Matthias Graeser,2,4 Anselm von Gladiss5 1Institute for Interventional Radiology, University of Luebeck, Luebeck, Germany; 2Fraunhofer Research Institution for Individualized and Cell-Based Medical Engineering IMTE, Luebeck, Germany; 3Department of Radiology and Nuclear Medicine, University of Luebeck, Luebeck, Germany; 4Institute of Medical Engineering, University of Lubeck, Luebeck, Germany; 5Institute for Computer Science, University of Koblenz, Koblenz, GermanyCorrespondence: Franz Wegner, University of Luebeck, Institute for Interventional Radiology, Ratzeburger Allee 160, Luebeck, 23538, Germany, Tel +4945150072388, Fax +4945150017004, Email franz.wegner@uksh.dePurpose: Magnetic particle imaging (MPI) is an emerging medical imaging modality that is on the verge of clinical use. In recent years, cardiovascular applications have shown huge potential like, e.g., intraprocedural imaging guidance of stent placement through MPI. Due to the lack of signal generation, nano-modifications have been necessary to visualize commercial medical instruments until now. In this work, it is investigated if commercial interventional devices can be tracked with MPI without any nano-modification.Material and Methods: Potential MPI signal generation of nine endovascular metal stents was tested in a commercial MPI scanner. Two of the stents revealed sufficient MPI signal. Because one of the two stents showed relevant heating, the imaging experiments were carried out with a single stent model (Boston Scientific/Wallstent-Uni Endoprothesis, diameter: 16 mm, length: 60 mm). The nitinol stent and its delivery system were investigated in seven different scenarios. Therefore, the samples were placed at 49 defined spatial positions by a robot in a meandering pattern during MPI scans. Image reconstruction was performed, and the mean absolute errors (MAE) between the signals’ centers of mass (COM) and ground truth positions were calculated. The stent material was investigated by magnetic particle spectroscopy (MPS) and vibrating sample magnetometry (VSM). To detect metallic components within the delivery system, nondestructive testing via computed tomography was performed.Results: The tracking of the stent and its delivery system was possible without any nano-modification. The MAE of the COM were 1.49 mm for the stent mounted on the delivery system, 3.70 mm for the expanded stent and 1.46 mm for the delivery system without the stent. The results of the MPS and VSM measurements indicate that besides material properties eddy currents seem to be responsible for signal generation.Conclusion: It is possible to image medical instruments with dedicated designs without modifications by means of MPI. This enables a variety of applications without compromising the mechanical and biocompatible properties of the instruments.Keywords: magnetic particle imaging, instrument tracking, interventional instruments, stent, medical imaging

In endovascular aneurysm repair (EVAR) procedures, the stent graft navigation and implantation is currently performed under a two-dimensional (2D) imaging based guidance requiring X-rays and contrast agent. In this work, a novel 3D stent graft guidance approach based on tracking systems is introduced. A calibration method and the visualization of the stent graft guidance are described. The tracking based stent graft guidance is evaluated by conducting an EVAR procedure on a torso phantom using a stent graft system equipped with an optical fiber and three EM sensors. The physicians were able to navigate the stent graft to the landing zone, and to place and implant it as intended using the introduced guidance. This showed that the application of the stent graft guidance is feasible in a clinical environment and promising for the reduction of radiation and contrast agent.

Franz Wegner,1,* Anselm von Gladiss,2,* Julian Haegele,1,3 Ulrike Grzyska,1 Malte Maria Sieren,1 Erik Stahlberg,1 Thekla Helene Oechtering,1 Kerstin Lüdtke-Buzug,2 Joerg Barkhausen,1 Thorsten M Buzug,2,4 Thomas Friedrich2,4 1Department of Radiology and Nuclear Medicine, University of Lübeck, Lübeck, Germany; 2Institute of Medical Engineering, University of Lübeck, Lübeck, Germany; 3Zentrum für Radiologie und Nuklearmedizin Rheinland, Dormagen, Germany; 4Fraunhofer Research Institution for Individualized and Cell-Based Medical Engineering, Lübeck, Germany*These authors contributed equally to this workCorrespondence: Franz WegnerUniversity Hospital Schleswig-Holstein, Campus Lübeck, Department of Radiology and Nuclear Medicine, Ratzeburger Allee 160, Lübeck 23538, GermanyTel +004945150017001Fax +004945150017004Email franz.wegner@uksh.dePurpose: Endovascular stents are medical devices, which are implanted in stenosed blood vessels to ensure sufficient blood flow. Due to a high rate of in-stent re-stenoses, there is the need of a noninvasive imaging method for the early detection of stent occlusion. The evaluation of the stent lumen with computed tomography (CT) and magnetic resonance imaging (MRI) is limited by material-induced artifacts. The purpose of this work is to investigate the potential of the tracer-based modality magnetic particle imaging (MPI) for stent lumen visualization and quantification.Methods: In this in vitro study, 21 endovascular stents were investigated in a preclinical MPI scanner. Therefore, the stents were implanted in vessel phantoms. For the signal analysis, the phantoms were scanned without tracer material, and the signal-to-noise-ratio was analyzed. For the evaluation of potential artifacts and the lumen quantification, the phantoms were filled with diluted tracer agent. To calculate the stent lumen diameter a calibrated threshold value was applied.Results: We can show that it is possible to visualize the lumen of a variety of endovascular stents without material induced artifacts, as the stents do not generate sufficient signals in MPI. The stent lumen quantification showed a direct correlation between the calculated and nominal diameter (r = 0.98).Conclusion: In contrast to MRI and CT, MPI is able to visualize and quantify stent lumina very accurately.Keywords: magnetic particle imaging, endovascular stents, artifacts, superparamagnetic iron oxide nanoparticles, lumen quantification

Previous research reported catheter pose-dependent virtual angioscopy images for endovascular aortic repair (EVAR) (phantom studies) without any validation with video images. The goal of our study focused on conducting this validation using a video graphics array (VGA) camera. The spatial relationship between the coordinate system of the virtual camera and the VGA camera was computed with a Hand-Eye calibration so that both cameras produced similar images. A re-projection error of 3.18 pixels for the virtual camera and 2.14 pixels for the VGA camera was obtained with a designed three-dimensional (3D) printed chessboard. Similar images of the vessel (3D printed aorta) were acquired with both cameras except for the different depth. Virtual angioscopy images provide information from inside the vessel that may facilitate the understanding of the tip position of the endovascular tools while performing EVAR.

C-arms are medical devices widely used for image-guided minimally invasive endovascular procedures. This technology requires considerable experience for the physicians to position the C-arm to obtain X-ray images of the endovascular tools. In addition, this image-guided therapy is based on two-dimensional images which lack depth information. The purpose of this study was to develop a system that controls the C-arm movements based on the previous position of the tip of a guide wire and the vessel information, and also displays the estimated tip position (specifically, the virtual line that would join the X-ray source and the projected tip in the flat-panel detector) on an augmented reality device (HoloLens). A phantom study was conducted to evaluate the system using intraoperative cone-beam computed tomography scans to obtain the reference tip position. The mean distance between the tip position (ground truth) and the virtual three-dimensional line was 1.18 mm. The proposed system was able to control the C-arm movements based on the position of the tip of the guide wire. The visualization on HoloLens also allowed a more intuitive understanding of the position of the endovascular tool related to the patient’s anatomy during the intervention.