Joern Borgert

Navigation with Electromagnetic Tracking for Interventional Radiology Procedures: A Feasibility Study

PURPOSE To assess the feasibility of the use of preprocedural imaging for guide wire, catheter, and needle navigation with electromagnetic tracking in phantom and animal models. MATERIALS AND METHODS An image-guided intervention software system was developed based on open-source software components. Catheters, needles, and guide wires were constructed with small position and orientation sensors in the tips. A tetrahedral-shaped weak electromagnetic field generator was placed in proximity to an abdominal vascular phantom or three pigs on the angiography table. Preprocedural computed tomographic (CT) images of the phantom or pig were loaded into custom-developed tracking, registration, navigation, and rendering software. Devices were manipulated within the phantom or pig with guidance from the previously acquired CT scan and simultaneous real-time angiography. Navigation within positron emission tomography (PET) and magnetic resonance (MR) volumetric datasets was also performed. External and endovascular fiducials were used for registration in the phantom, and registration error and tracking error were estimated. RESULTS The CT scan position of the devices within phantoms and pigs was accurately determined during angiography and biopsy procedures, with manageable error for some applications. Preprocedural CT depicted the anatomy in the region of the devices with real-time position updating and minimal registration error and tracking error (<5 mm). PET can also be used with this system to guide percutaneous biopsies to the most metabolically active region of a tumor. CONCLUSIONS Previously acquired CT, MR, or PET data can be accurately codisplayed during procedures with reconstructed imaging based on the position and orientation of catheters, guide wires, or needles. Multimodality interventions are feasible by allowing the real-time updated display of previously acquired functional or morphologic imaging during angiography, biopsy, and ablation.

Single-sided device for magnetic particle imaging

Recently, a new imaging modality called magnetic particle imaging (MPI) was introduced. The method is capable of imaging the distribution of superparamagnetic nanoparticles at high sensitivity, high resolution and high imaging speed by exploiting their non-linear magnetization curve. Up to now, all published simulation as well as experimental work uses a scanner setup, where the field of view (FOV) lies in between a symmetric coil configuration. This, however, poses a size limitation for the specimens. In this paper, we present a feasibility study of a new, so-called single-sided scanner, which is applied to the object of interest merely from one side. Thus, the problem of the specimen fitting into the scanner no longer exists, which denotes a major step for MPI. To date, the FOV of the single-sided device is limited to one dimension. First experimental results on imaging phantoms containing a superparamagnetic fluid show a resolution of up to 1 mm and are indeed promising.

Magnetic particle imaging using a field free line

This paper presents a simulation study on the use of a field free line in magnetic particle imaging. A major improvement in the image quality is demonstrated. The reason for this image quality improvement is discussed, and routes for the technical implementation of the effect are sketched.

Trajectory analysis for magnetic particle imaging

Recently a new imaging technique called magnetic particle imaging was proposed. The method uses the nonlinear response of magnetic nanoparticles when a time varying magnetic field is applied. Spatial encoding is achieved by moving a field-free point through an object of interest while the field strength in the vicinity of the point is high. A resolution in the submillimeter range is provided even for fast data acquisition sequences. In this paper, a simulation study is performed on different trajectories moving the field-free point through the field of view. The purpose is to provide mandatory information for the design of a magnetic particle imaging scanner. Trajectories are compared with respect to density, speed and image quality when applied in data acquisition. Since simulation of the involved physics is a time demanding task, moreover, an efficient implementation is presented utilizing caching techniques.

Motion compensated coronary interventional navigation by means of diaphragm tracking and elastic motion models

Current catheter tracking in the x-ray catheter laboratory during coronary interventions is performed using 2D fluoroscopy. Although this features real-time navigation on high-resolution images, drawbacks such as overlap and foreshortening exist and hamper the diagnosis and treatment process. An alternative to fluoroscopy-based tracking is device tracking by means of a magnetic tracking system (MTS). Having measured the 3D location of the interventional device, its position can be reconstructed on 3D images or virtual roadmaps of the organ or vessel structure under examination. In this paper, a method is presented which compensates the interventional device location measured by the MTS for organ motion and thus registers it dynamically to a 3D virtual roadmap. The motion compensation is accomplished by using an elastic motion model which is driven by the ECG signal and a respiratory sensor signal derived from ultrasonic diaphragm tracking. The model is updated during the intervention itself, thus allowing for a local refinement in regions which bear a complex geometric structure, such as stenoses and bifurcations. The evaluation is done by means of a phantom-based study using a dynamic heart-phantom. The mean displacement caused by the overall motion of the heart is improved from 10.4+/-4.8 mm in the uncompensated case to 2.1+/-1.2 mm in the motion compensated case.

Motion compensation for interventional navigation on 3D static roadmaps based on an affine model and gating

Current cardiac interventions are performed under 2D fluoroscopy, which comes along with well-known burdens to patients and physicians, such as x-ray exposure and the use of contrast agent. Furthermore, the navigation on complex structures such as the coronaries is complicated by the use of 2D images in which the catheter position is only visible while the contrast agent is introduced. In this work, a new method is presented, which circumvents these drawbacks and enables the cardiac interventional navigation on motion-compensated 3D static roadmaps. For this, the catheter position is continuously reconstructed within a previously acquired 3D roadmap of the coronaries. The motion compensation makes use of an affine motion model for compensating the respiratory motion and compensates the motion due to cardiac contraction by gating the catheter position. In this process, only those positions which have been acquired during the rest phase of the heart are used for the reconstruction. The method necessitates the measurement of the catheter position, which is done by using a magnetic tracking system. Nevertheless, other techniques, such as image-based catheter tracking, can be applied. This motion compensation has been tested on a dynamic heart phantom. The evaluation shows that the algorithm can reconstruct the catheter position on the 3D static roadmap precisely with a residual motion of 1.0 mm and less.

A Spectrometer for Magnetic Particle Imaging

Recently, a new tomographic imaging technique called magnetic particle imaging was proposed. It allows for the high resolution measurement of the spatial distribution of magnetic nanoparticles. The method is based on the non-linear response of magnetic nanoparticles (e.g. superparamagnetic iron oxide particles, SPIOs).

Magnetic particle imaging (MPI)

Magnetic particle imaging (MPI) displays the spatial distribution and concentration of superparamagnetic iron oxides (SPIOs). It is a quantitative, tomographic imaging method with high temporal and spatial resolution and allows work with high sensitivity yet without ionizing radiation. Thus, it may be a very promising tool for medical imaging. In this review, we describe the physical and technical basics and various concepts for clinical scanners. Furthermore, clinical applications such as cardiovascular imaging, interventional procedures, imaging and therapy of malignancies as well as molecular imaging are presented.

Interactive Magnetic Catheter Steering With 3-D Real-Time Feedback Using Multi-Color Magnetic Particle Imaging

Magnetic particle imaging (MPI) is an emerging tomographic method that enables sensitive and fast imaging. It does not require ionizing radiation and thus may be a safe alternative for tracking of devices in the catheterization laboratory. The 3-D real-time imaging capabilities of MPI have been demonstrated in vivo and recent improvements in fast online image reconstruction enable almost real-time data reconstruction and visualization. Moreover, based on the use of different magnetic particle types for catheter visualization and blood pool imaging, multi-color MPI enables reconstruction of separate images for the catheter and the vessels from simultaneously measured data. While these are important assets for interventional imaging, MPI field generators can furthermore apply strong forces on a magnetic catheter tip. It is the aim of this paper to give a first demonstration of the combination of real-time multi-color MPI with online reconstruction and interactive field control for the application of forces on a magnetic catheter model in a phantom experiment.

Ultrasonic diaphragm tracking for cardiac interventional navigation on 3D motion compensated static roadmaps

In this paper, a novel approach to cardiac interventional navigation on 3D motion-compensated static roadmaps is presented. Current coronary interventions, e.g. percutaneous transluminal coronary angioplasties, are performed using 2D X-ray fluoroscopy. This comes along with well-known drawbacks like radiation exposure, use of contrast agent, and limited visualization, e.g. overlap and foreshortening, due to projection imaging. In the presented approach, the interventional device, i.e. the catheter, is tracked using an electromagnetic tracking system (MTS). Therefore, the catheters position is mapped into a static 3D image of the volume of interest (VOI) by means of an affine registration. In order to compensate for respiratory motion of the catheter with respect to the static image, a parameterized affine motion model is used which is driven by a respiratory sensor signal. This signal is derived from ultrasonic diaphragm tracking. The motion compensation for the heartbeat is done using ECG-gating. The methods are validated using a heart- and diaphragm-phantom. The mean displacement of the catheter due to the simulated organ motion decreases from approximately 9 mm to 1.3 mm. This result indicates that the proposed method is able to reconstruct the catheter position within the VOI accurately and that it can help to overcome drawbacks of current interventional procedures.