Erhard Klotz

Coherent Optical Generation and Inspection of Two-dimensional Periodic Structures

Three spatial filtering projects using periodic structures are presented. The aim of the first two methods is to produce from one object (or from a few identical objects, side by side) many identical images, side by side. In the third project irregularities of periodic objects are detected.

Three-dimensional reconstruction of high contrast objects using C-arm image intensifier projection data.

The reconstruction of three-dimensional (3D) objects from 2D X-ray cone-beam projections using a circular source path is most commonly done with an algorithm according to Feldkamp et al. [Feldkamp LA, Davis LC, Kress JW. Practical cone-beam algorithms. J Opt Soc Am A 1984;6:612-619]. An adaptation of this so-called Feldkamp method to cone-beam projections acquired with a C-arm system is presented here. In a phantom study, reconstruction results obtained along real source-detector trajectories of a C-arm system are compared to reconstruction results obtained from projections acquired from a full-circular trajectory and from one consisting of two full orthogonal circles, which fulfills Tuys sufficiency condition. The straightforward application of Feldkamps method adapted to projection data obtained with a C-arm system illustrates the 3D imaging potential of image intensifier based cone-beam computed tomography. Reconstruction results from projection data of different patients acquired with a motorized C-arm system such as vessel structures filled with contrast agent and bones are presented.

Coded Aperture Imaging with X-rays (Flashing Tomosynthesis)

So far, three-dimensional X-ray imaging methods like tomography, etc. require exposure times of a few seconds or more. Hence, moving objects like the pulsating heart cannot be observed. This obstacle can be overcome by using an array of synchronously flashed X-ray sources. The source array acts as the coded aperture. The X-ray photograph is decoded optically, showing arbitrary layers of the object. We present four new versions of ‘flashing tomosynthesis’, as this approach is called. The obtainable image qualities and other practical features of these four new methods will be compared.

Three-dimensional coded aperture imaging using nonredundant point distributions

Abstract A nonredundant distribution of ten point sources is used for coded aperture imaging. The coded image of a three-dimensional X-ray object is decoded by means of an incoherent projection system in all its layers. This decoding process avoids all the adjustment problems of coherent processing systems.

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.

A new method for deconvoluting coded aperture images of three dimensional X-ray objects

Abstract Three-dimensional objects are coded using a non-redundant distribution of X-ray sources. The deconvolution of the image is performed by means of an incoherent optical processing system using a zoom-lens and a point-hologram. The method is capable of decoding the layers of the original object starting with a self-luminous image generated for example by an X-ray image intensifier tube.

Flashing tomosynthesis--a new tomographic method.

SummaryA new tomographic method called tomosynthesis and its first clinical results are presented. The method is based on classical tomography. All information necessary for the tomography of an object is obtained in one procedure without moving the X-ray tube, the film, or the object. Thus the investigation requires only a few seconds.

Deconvolution systems for coded aperture images of three-dimensional x-ray objects

Abstract A non-redundant distribution of ten point sources is used for coded aperture imaging. The coded image of a simple three-dimensional x-ray object is deconvoluted by means of three different decoding systems: by an optical projection system using spatially incoherent light, by an on-line optical set-up with information input using an electro-optic relay tube, and by a quasi-on-line electronic system using an electronic storage-tube. The three methods are compared with respect to signal-to-noise ratio, resolution, and convenience of handling.

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.