Atrial fibrillation (AF) is the most common arrhythmia and results in
an increased risk of ischemic stroke. Recently, a european consortium
has developed a new minimally invasive device for surgical AF
treatment. It consists of a micro-robot holding an end-effector called
"umbrella" containing 22 radiofrequency powered electrodes. Surgery
using this new device can only be performed having an appropriate
navigation technique. Therefore, we have developed an image-based
navigation workflow and a prototypic navigation application. First, a navigation workflow including an appropriate intra-operative
image-modality was defined. Intraoperative ultrasound became the
imaging modality of choice. Once the umbrella is unfolded inside the
left atrium, data is acquired and segmented. Using a reliable
communication protocol, mobility values are transferred from the
control software to the navigation system. A deformation model
predicts the behavior of the umbrella during repositioning. Prior to surgery, desired ablation lines can be interactively planned and actually made ablation lines are visualized during surgery. Several in-vitro tests were performed. The navigation prototype has been integrated and tested within the overall system successfully. Image acquisitions of the umbrella showed the feasibility of the navigation procedure. More in-vitro and in-vivo tests are currently performed to make the new device and the described navigation procedure ready for clinical use.
KEYWORDS: Visualization, Optical spheres, Medical imaging, 3D displays, Arteries, 3D visualizations, Image visualization, Spherical lenses, 3D image processing, Imaging systems
Modern systems for visualization, image guided procedures and display allow not only one type of visualization, but a variety of different visualization options. Only a combination of two-dimensional image display and three-dimensional rendering provides enough information for many tasks. Multiplanar orthogonal and oblique reformations of image data are standard features of medical imaging software packages today. Additionally, curved reformations are useful. For example, diagnosis of stenotic vessels can be supported by curved reformations along the centerline of the vessel, showing the complete vessel in one two-dimensional view. In this paper, we present how the open-source Medical Imaging Interaction Toolkit (MITK, www.mitk.org), which is based on the Insight Toolkit (ITK) and the Visualization Toolkit (VTK), can be used to rapidly build interactive systems that provide curved reformations. MITK supports curved reformations not only for images, but also for other data types (e.g., surfaces). Besides visualizations of curved reformations, which can be combined and are kept consistent with other two- and three-dimensional views of the data, interactions on such non-planar manifolds are supported. The developer only has to define the curved manifold, everything else is dealt with by the toolkit. We demonstrate these capabilities by means of a tool for mapping of coronary vessel trees.
KEYWORDS: Visualization, Medical imaging, Image segmentation, Surgery, 3D vision, Data acquisition, 3D image processing, Image processing, Image processing algorithms and systems, Data processing
The aim of the Medical Imaging Interaction Toolkit (MITK) is to facilitate the creation of clinically usable
image-based software. Clinically usable software for image-guided procedures and image analysis require a high
degree of interaction to verify and, if necessary, correct results from (semi-)automatic algorithms. MITK is
a class library basing on and extending the Insight Toolkit (ITK) and the Visualization Toolkit (VTK). ITK
provides leading-edge registration and segmentation algorithms and forms the algorithmic basis. VTK has
powerful visualization capabilities, but only low-level support for interaction (like picking methods, rotation,
movement and scaling of objects). MITK adds support for high level interactions with data like, for example, the
interactive construction and modification of data objects. This includes concepts for interactions with multiple
states as well as undo-capabilities. Furthermore, VTK is designed to create one kind of view on the data
(either one 2D visualization or a 3D visualization). MITK facilitates the realization of multiple, different views
on the same data (like multiple, multiplanar reconstructions and a 3D rendering). Hierarchically structured
combinations of any number and type of data objects (image, surface, vessels, etc.) are possible. MITK can
handle 3D+t data, which are required for several important medical applications, whereas VTK alone supports
only 2D and 3D data. The benefit of MITK is that it supplements those features to ITK and VTK that are
required for convenient to use, interactive and by that clinically usable image-based software, and that are
outside the scope of both. MITK will be made open-source (http://www.mitk.org).
Background: Three-dimensional (3D) ultrasound has a great potential in medical diagnostics. However, there are also some limitations of 3D ultrasound, e.g., in some situations morphology cannot be imaged accurately due to acoustical shadows. Acquiring 3D datasets from multiple positions can overcome some of these limitations. Prior to that a calibration of the ultrasound probe is necessary. Most calibration methods descibed rely on two-dimensional data. We describe a calibration method that uses 3D data. Methods: We have developed a 3D calibration method based on single-point cross-wire calibration using registration techniques for automatic detection of cross centers. For the calibration a cross consisting of three orthogonal wires is imaged. A model-to-image registration method is used to determine the cross center. Results: Due to the use of 3D data less acquisitions and no special protocols are necessary. The influence of noise is reduced. By means of the registration method
the time-consuming steps of image plane alignment and manual cross
center determination becomes dispensable. Conclusion: A 3D
calibration method for ultrasound transducers is described. The
calibration method is the base to extend state-of-the-art 3D
ultrasound devices, i.e., to acquire multiple 3D, either morphological or functional (Doppler), datasets.
This contribution presents a novel method for image-guided navigation in oncological liver surgery. It enables the perpetuation of the registration for deeply located intrahepatic structures during the resection. For this purpose, navigation aids localizable by an electro-magnetic tracking system are anchored within the liver. Position and orientation data gained from the navigation aids are used to parameterize a real-time deformation model. This approach enables for the first time the real-time monitoring of target structures also in the depth of the intraoperatively deformed liver. The dynamic behavior of the deformation model has been evaluated with a silicon phantom. First experiments have been carried out with pig livers ex vivo.
Most cardiac diseases, like coronary artery disease or valve defects, are related to wall motion malfunctions. Much research has been done in the estimation of cardiac movement using magnetic resonance (MR) techniques, like MR tagging or phase contrast MR. But echocardiography (cardiac ultrasound) is still the method of choice in clinical routine. Besides visual, subjective wall motion scoring using gray-scale data, myocardial velocities can be obtained using tissue Doppler techniques. A major limitation of Doppler techniques is the one-dimensional estimation of velocities: only the component towards transducer position is measured. Assessing the true velocity field will lead to a more objective measurement. In this paper we describe a method for reconstructing velocity fields using a-priori information about the solution. The feasibility is quantitatively evaluated using simulated data of typical velocity patterns. Translation, contraction and shear movement can be reconstructed well. The proposed method can also be used for the reconstruction of blood flow velocities using color Doppler.
Repair of a defect heart valve is of great advantage for the patient in comparison to replacement with a prosthesis. The applicability and the success of heart valve repair can be improved by an exact diagnosis of the valve's pathological modification. The best way for imaging heart valve insufficiencies is echocardiography, since it is fast, relatively cheap, can be used intraoperatively and provides information about morphology as well as blood flow. Three-dimensional echocardiography has been proven to be superior to conventional echocardiographic techniques. Although the overall structures are much better displayed by three-dimensional visualization methods, it is sometimes difficult to comprehend the orientation of the scene, since anatomical landmarks like the aortic outflow tract may be hidden by other structures. Also, such anatomical landmarks often are only partly contained in the acquired data set so that they are clearly visible in a few slices only, making them difficult to find in a three-dimensional visualization. The knowledge of the absolute orientation is of essential value for the surgeon to mentally transfer the preoperatively acquired data to the intraoperative situs. Therefore, it is desirable to have additional hints for orientation in the three-dimensional scene. We present methods that enable better and easier orientation and therefore improve the usability of three-dimensional echocardiography.
The knowledge about the complex three-dimensional (3D) heart wall motion pattern, particular in the left ventricle, provides valuable information about potential malfunctions, e.g., myocardial ischemia. Nowadays, echocardiography (cardiac ultrasound) is the predominant technique for evaluation of cardiac function. Beside morphology, tissue velocities can be obtained by Doppler techniques (tissue Doppler imaging, TDI). Strain rate imaging (SRI) is a new technique to diagnose heart vitality. It provides information about the contraction ability of the myocardium. Two-dimensional color Doppler echocardiography is still the most important clinical method for estimation of morphology and function. Two-dimensional methods leads to a lack of information due to the three-dimensional overall nature of the heart movement. Due to this complex three-dimensional motion pattern of the heart, the knowledge about velocity and strain rate distribution over the whole ventricle can provide more valuable diagnostic information about motion disorders. For the assessment of intracardiac blood flow three-dimensional color Doppler has already shown its clinical utility. We have developed methods to produce strain rate images by means of 3D tissue Doppler echocardiography. The tissue Doppler and strain rate images can be visualized and quantified by different methods. The methods are integrated into an interactively usable software environment, making them available in clinical everyday life. Our software provides the physician with a valuable tool for diagnosis of heart wall motion.
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