Rolf Linde

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.

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.

Simplified production of spatial inverse filters

A logarithmic nonlinearity in the transmittance-versus-exposure curve of a photographic material can greatly simplify holographic fabrication of inverse filters. We present here two filter-production methods utilizing this non-linearity, which produce relatively high-dynamic-range inverse filters. Confirming computer simulations and coherent-optical experiments are presented.

Digital Flashing Tomosynthesis (DFTS) — A technique for three-dimensional coronary angiography

Digital Flashing Tomosynthesis (DFTS) represents a technique for three-dimensional (3D) coronary angiography. Four ECG-gated simultaneously flashed X-ray tubes generate a multiperspective digital substraction image as DFTS multiangiogram for 3D reconstruction and visualization. Computerized morphologic and morphometric quantitative analysis can be performed including videodensitometry.Postmortem coronary angiography of 30 human hearts with suspected coronary artery disease was performed by 35-mm cine technique and by DFTS. The results of angiographic measurements in 50 stenotic arterial segments were compared with the histologic reference and show excellent regression results with correlation coefficients of more than 0.95 (p≲-0.0001). No significant differences in standard errors of estimates between the techniques were found. DFTS yields an accuracy in depiction of the coronary arteries and angiographic estimation of arterial lumen equivalent to 35-mm cineangiography. DFTS images can be directly used for visual interpretation and for computerized morphologic and morphometric quantitative analysis. DFTS technology reduces the amount of radiation exposure, the amount of contrast medium, and the time of the procedure. DFTS offers the possibility to obtain 3D images of the coronary artery tree.

Real-Time Distortion Correction Of Digital X-Ray II/TV Systems: An Application Example

In X-ray image intensifier (II)/TV-camera systems geometric distortions occur, e.g. due to the curved input screen of the II. For methods which are based on a pixelwise comparison of images, e.g. digital angiotomosynthesis, an accurate correction of these geometric distortions is absolutely necessary. For the application of tomosynthesis to coronary angiography the correction in addition has to be done in real-time, because the recon-struction of the three dimensional structure of the blood vessels has to be done while the patient is undergoing catheterization. This paper describes a digital correction unit which allows a large variety of geome-tric distortions to be corrected. It consists of an input memory for storing the distorted image, an output memory for storing the corrected image and a special address memory which will serve as an address table during the correction step. For each element of the output image the location of the corresponding element of the distorted input image is determined in a preprocessing step and stored in the address memory. The actual correction of an image is then done while the image is copied from the input into the output memory. In this way 512x512 images can be corrected in real-time by a 32-bit 68020-based micro-processor system.

Three-Dimensional Angiography With Digital Flashing Tomosynthesis

Tomosynthesis presents a simple procedure for 3D angiography, because the recording step requires only one injection of contrast medium. Digital flashing tomosynthesis is based on a new nonlinear reconstruction producing less artifacts than conventional backprojection techniques. In addition to reconstructed slices synthetic projections can be calculated, which can be used in combination with the original projections for stereo views. The object structures can be analysed by a stereo cursor controlled by a 3D joystick. This may be an important adjunct to diagnostic and interventional angiographic procedures.

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.

3D Reconstruction of Vascular Structures from few X-Ray Projections

A number of techniques for the reconstruction of slice images from a set of projections taken under different angles have been proposed. The most frequently used ‘backprojection’ method produces artefacts in the reconstructed slices, caused by the neighboring ‘out-offocus’ planes. These artefacts cannot be avoided, but they can be blurred, if a large number (n=50) of projections are available. We have developed new non-linear algorithms applicable for the reconstruction of DSA images showing significantly less artefacts than backprojecdon. The number of projections can be drastically reduced. Applying the simple extreme-value algorithm, we have obtained slice reconstructions of satisfactory quality from coronary arteries using only 4 simultaneously acquired projection images. However, the image quality and thus the diagnostic information can be improved by increasing the number of projections. In the case of cerebral vessels the extreme-value algorithm generates more artefacts, because of the higher complexity of the vascular system of the brain. Thus we improved the extreme-value decoding scheme by incorporating a priori knowledge about the global structure of blood vessels. The new global-coincidence algorithm was tested on a wire phantom representing the main branches of cerebral arteries to be reconstructed from 3 sequentially recorded projections.

X-ray Coded-aperture Image Reconstruction Using an Array of Kinoforms

Radiograms which retain three-dimensional information about an object can be recorded using coded apertures. Recovering this information as slice images necessitates a decoding step. We describe here an improved lensmatrix decoding method. For this method the coded radiogram is (incoherently) imaged simultaneously by several compound imaging elements composed of lens-kinoform pairs. The lenses provide shifting and focusing for the decoding, while the kinoforms provide spatial filtering to suppress images of undesired slices.