Reiner Koppe

Performance of image intensifier-equipped X-ray systems for three-dimensional imaging

Abstract The performance of image intensifier (II)-equipped C-arm systems for three-dimensional (3D) imaging was investigated. The three-dimensional image quality was evaluated in terms of spatial resolution (modulation transfer function, MTF), contrast resolution, geometrical accuracy and homogeneity depending on the image intensifier format, focal spot size, number of projections and the angular span covered during the data acquisition. Experiments have been performed on a vascular C-arm system equipped with a 38-cm image intensifier. Several objects, including CT performance, MTF and pelvis phantoms, were scanned under various conditions. It was shown that for reasonable acquisition parameters, a contrast resolution below 100 HU could be obtained with standard acquisition strategies. Focusing on the spatial resolution, an almost isotropic three-dimensional resolution of up to 22 lp/cm at 10% modulation could be obtained when a 17-cm II was used. The homogeneity in the resulting images was limited by the remaining scatter and truncations. The resulting geometrical accuracy was in the order of the voxel size.

Image quality of flat-panel cone beam CT

We present results on 3D image quality in terms of spatial resolution (MTF) and low contrast detectability, obtained on a flat dynamic X-ray detector (FD) based cone-beam CT (CB-CT) setup. Experiments have been performed on a high precision bench-top system with rotating object table, fixed X-ray tube and 176 x 176 mm2 active detector area (Trixell Pixium 4800). Several objects, including CT performance-, MTF- and pelvis phantoms, have been scanned under various conditions, including a high dose setup in order to explore the 3D performance limits. Under these optimal conditions, the system is capable of resolving less than 1% (~10 HU) contrast in a water background. Within a pelvis phantom, even inserts of muscle and fat equivalent are clearly distinguishable. This also holds for fast acquisitions of up to 40 fps. Focusing on the spatial resolution, we obtain an almost isotropic three-dimensional resolution of up to 30 lp/cm at 10% modulation.

Die 3-D-Rotationsangiographie (3-D-RA) in der Neuroradiologie

ZusammenfassungDie 3-D-Rotationsangiographie (3-D-RA) ist eine neue 3-D-Technik, die hauptsächlich in der Neuroradiologie ihre Anwendungen hat. Die 3-D-Rekonstruktion geschieht anhand von 100 Projektionsbildern, die mit einem Integris BN5000 (Philips Medical Systems Best, Niederlande) mittels Rotationsangiographie aufgenommen werden. Der C-Bogen rotiert in 8 Sekunden über einen Winkel von 180°. Geometrische Verzerrungen der Bildverstärker/Fernsehkette und geometrische Abweichungen des C-Bogens von der Kreisbahn werden gemessen und bei der 3-D-Rekonstruktion berücksichtigt. Die Rekonstruktionszeit für die 1283-Voxel-Matrix liegt bei ca. 2 Minuten, sodass die 3-D-Bilder auch während einer interventionellen Behandlung erzeugt werden können. Die 3-D-Visualisierung geschieht vorwiegend mittels Volume-Rendering-Technik, kann aber auch stereoskopisch erfolgen. Neben der Diagnostik wurde die Methode hauptsächlich zur Planung endovaskulärer Behandlungen benutzt. Die freie Wahl der Richtung bei der Visualisierung ermöglicht eine schnelle und genaue Analyse der Aneurysmaanatomie einschließlich der Beziehung des Aneurysmahalses zu seinem Trägergefäß. Außerdem kann eine geeignete Projektionsrichtung für eine endovaskuläre Behandlung bestimmt werden. Die 3-D-RA stellt einen wichtigen Fortschritt zur Planung einer endovaskulären Behandlung zerebraler Aneurysmen dar. Die diagnostische Aussagekraft der 3-D-RA ist höher als bei der konventionellen Angiographie. Strahlendosis und Kontrastmittel können eingespart werden. Die 3-D-RA kann auch bei AV-Malformationen und Karotisstenosen von Nutzen sein.Abstract3-D-rotational angiography is a new angiographic 3-D-imaging technique mainly used for neuroradiology. The 3-D reconstruction is performed on the basis of 100 projections acquired with an Integris BN5000 (Philips Medical Systems, Best, Netherlands) using rotational angiography. The C-arm rotates in 8 seconds about an angle of 180°. The geometrical distortions of the image intensifier/TV-chain and the geometrical deviations of the C-arm from the circular trajectory are measured and taken into account during the 3-D reconstruction. The time for reconstruction for a 1283 voxel matrix is about 2 minutes, so that the 3-D images are also produced during the endovascular treatment. 3-D visualization is typically performed with volume rendering and can also make use of a stereoscopic presentation. In addition to the diagnosis, 3-D-RA was mainly used for planning an endovascular treatment. The free choice of arbitrary viewing directions allows a fast and accurate analysis of the anatomy of an aneurysm including the aneurysm neck and its relationship to the carrier vessel. 3-D-RA also helps to determine the most favorable projection direction for the endovascular treatment. 3-D-RA represents a major breakthrough in the endovascular treatment of aneurysms. The diagnostic value is significantly improved in comparison to conventional angiography. The X-ray dose and the amount of contrast medium can be reduced. 3-D-RA can also be of significant value with AV-malformations and carotid stenoses.

Automatische Abbildung eines planaren Graphen in einen ebenen Streckengraphen

ZusammenfassungEs wird ein automatischer Zeichenalgorithmus beschrieben, der es gestattet, jeden planaren Graphen geradlinig in die Ebene abzubilden, wenn die zyklische Reihenfolge der Nachbarknoten nach einem topologischen Planarisierungsalgorithmus für jeden Knoten des Graphen bekannt ist.In diesem Zusammenhang wird auch eine hinreichende Bedingung dafür angegeben, daß die oben erwähnte zyklische Reihenfolge in einer kreuzungsfreien Zeichung des Graphen durch diesen eindeutig bestimmt ist.AbstractThe paper describes an automatic drawing algorithm permitting every planar graph to be displayed with straight lines in the plane, if the cyclic order of the adjacent vertices for every vertex of the graph is found out by a topological algorithm for planarity.In this connection also a sufficient condition is proved for the uniqueness of the above mentioned cyclic order in every drawing without crossings.

Automatische Abbildung eines planaren Graphen in die Ebene mit beliebig vorgebbaren Örtern der Knotenbilder

ZusammenfassungEs wird ein automatischer Zeichenalgorithmus beschrieben, der es gestattet, jeden planaren Graphen kreuzungsfrei so in die Ebene abzubilden, daß die Knoten in beliebig vorgegebene Örter abgebildet werden. Voraussetzung ist, daß die zyklische Reihenfolge der Nachbarknoten nach einem topologischen Planarisierungsalgorithmus für jeden Knoten des Graphen bekannt ist.AbstractThe paper describes an automatic drawing algorithm permitting every planar graph to be displayed without cross overs in the plane with optionally predetermined geometric locations of the vertices. Requirement is, that the cyclic order of the adjacent vertices for every vertex of the graph is found out by a topological algorithm for planarity.

3D X-ray imaging of human bones using a mobile C-arm

Motorized high-end C-arm systems can be used for 3D imaging of high contrast objects such as bones [1]. Based on cone-beam data acquisition, careful calibration and conebeam reconstruction, volume data sets can be obtained that enable an improved insight into 3D structures of bones in order to analyse complex joint fractures or to position prostheses. New developments offer this functionality on hand-moved low-end C-arm systems too.

Improved visualization of 3D data sets on the example of 3D-rotational angiography

3D-Rotational Angiography (3D-RA) is a new 3D imaging method based on the standard X-ray technique. Since the analysis of the clinically relevant information is often difficult, we have developed tools for improving the 3D visualization.

Three-dimensional imaging using low-end C-arm systems

During the last years, three-dimensional X-ray imaging has become a well-established imaging modality, setting the golden standard for spatial resolution in three-dimensional X-ray imaging. Firstly introduced on a motorized C-arm system, it gained benefit from the high spatial resolution of the image intensifier. Using cone-beam reconstruction, it provided fast access to truly three-dimensional imaging with isotropic voxel dimensions. However, the non-rigid mechanics and the image distortion in the image intensifier required dedicated calibration processes and obligated the developers to use the most stable and reliable system in the C-arm device family. The need for system calibration also required the system to be able to reproducibly adjust the C-arm to the pre-calibrated positions, which seemed only possible with the motorized movement of a high-end system. On mobile, non-motorized C-arm systems, which are often used for guiding surgical procedures, however, 3D application has not been feasible due to the non-reproducibility of the mechanical movement. In this paper, first results regarding the feasibility of this approach are presented. The data were acquired on a Philips BV 26 surgical C-arm. This device is fully movable. The C arc is adjusted manually.