METHOD OF MAKING PLANIGRAMS OF A
THREE-DIMENSIONAL OBJECT
The invention relates to a method of and a device for 5 making planigrams of a three-dimensional object which is irradiated by a large number of radiation sources which are arranged in one plane in order to form a superposition image which is composed of separate primary perspective images, said superposition image i0 subsequently being imaged by means of an optical imaging matrix whose imaging elements are distributed in accordance with the distribution of the radiation sources, the imaging elements being positioned with respect to the primary perspective images so that cen- 15 tral rays of radiation beams which transmit the primary perspective images via the associated imaging elements intersect behind the imaging matrix in a point situated on an optical axis which is directed perpendicularly to the imaging matrix, in the superposition zone of the 20 radiation beams there being formed a real image of the object wherefrom planigrams can be formed by means of a record carrier.
A method of this kind is described in German Patent Application No. P 27 46 035. According to this method, 25 an object is simultaneously irradiated from different directions by means of a source matrix which consists of a plurality of radiation sources which are arranged in one plane, separate perspective images forming a superposition image on, for example, a film plate. During a 30 subsequent decoding step, reconstruction takes place by means of the superposition image in order to form separate planigrams of the three-dimensional object.
The decoding can be illustrated as follows: in order to make an image of a given, arbitrary flat slice of the 35 object, the superposition image is shifted and summed a number of times which equals the number of sources used for the irradiation of the object. The superposition image is then shifted so that all associated primary perspective images are made to register in order to obtain 40 a planigram (German Offenlegungsschrift No. 24 31 700).
A decoding step of this kind can be performed, for example, by means of an imaging matrix which is arranged in front of a superposition image which is illumi- 45 nated from the rear, the distribution of the imaging elements of the imaging matrix corresponding to the distribution of the separate radiation sources of the source matrix. Each separate primary perspective image is then transmitted by an associated imaging ele- 50 ment so that the central rays of the radiation beams which transmit the primary perspective images via the associated imaging elements intersect behind the imaging matrix in a point on an optical axis which extends perpendicularly through the imaging matrix, in the 55 superposition zone of the radiation beams there being formed a real image of the object wherefrom layer images can be derived by means of, for example, a ground glass plate. The central rays are to be understood to mean the rays which extend through the cen- 60 tres of the primary perspective images as well as through the centres of the imaging elements. However, primary perspective images are not only transmitted by means of the associated imaging elements, but also at the same time by inappropriate imaging elements, so 65 that these primary perspective images are imaged as artefact images together with the desired layer image, in an image plane in the superposition zone.
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Therefore, the invention has for its object to provide a method which enables the formation of arbitrary planigrams of a three-dimensional object which are artefact-poor (that is, which have few artefacts), at least at their center.
This object is achieved in accordance with the invention in that, in order to obtain planigrams which are artefact-poor at least in their centre, artefact images which are caused by transmission of primary perspective images by inappropriate imaging elements are suppressed by means of additional elements in that on each artefact image a correction perspective image derived from a primary perspective image is superposed, via an additional imaging element so that the artefact image is compensated for.
The correction perspective images derived from the primary perspective images are superposed on the artefact images by means of additional imaging elements which are included in the imaging matrix and which are arranged each time in the beam path between an artefact image to be compensated for and a suitable primary perspective image. Obviously, these imagetransmitting imaging elements also transmit correction perspective images to locations where there are no artefact images to be compensated for. At these areas new artefact images are formed which are compensated for by means of imaging elements, to be included in the imaging matrix, and primary perspective images which serve as correction perspective images. The magnitude of the area in which the artefact images in the reconstructed layer image can be compensated for can be chosen at random and is dependent only of the magnitude of the imaging matrix or of the structure and the number of imaging elements of the imaging matrix.
In a preferred embodiment in accordance with the invention, lenses are used for the imaging elements and a lens matrix is used as the imaging matrix, a first filter being arranged in the beam path of the lenses used for transmitting the primary perspective images, a second filter which differs from the first filter being arranged in the beam path of the lenses used for transmitting the correction perspective images, the radiation passing through the filters being detected by image pick-up tubes, a first input filter which corresponds to the first filter being arranged in front of the one tube, and a second input filter which corresponds to the second filter being arranged in front of the other tube. The video signals of the image pick-up tubes are subtracted from each other in order to obtain layer images.
The different filters in the relevant beam paths ensure that only a single superposition image consisting of primary perspective images has to be made. The formation of a superposition image consisting of correction perspective images can thus be dispensed with. When the superposition image is irradiated from the rear, for example, by means of white light, two different colour filters can be used, for example, a red filter and a blue filter. The red filters are then arranged, for example, in the beam path of the lenses transmitting the primary perspective images, whilst the blue filters are arranged in the beam path of the lenses which serve to superpose the correction perspective images on the artefact images. The image pick-up tubes, comprising corresponding input filters, each time detect only one colour in order to make corresponding colour images which are electronically subtracted from each other in order to form artefact-free layer images.
Said filters and input filters, however, may also be other filters, for example, polarization filters.
Embodiments in accordance with the invention will be described in detail hereinafter with reference to the accompanying diagrammatic drawing. 5
FIG. 1 shows the recording of a superposition image consisting of primary perspective images,
FIG. 2 shows the reconstruction of a layer image from the superposition image by means of a lens matrix and the compensation of artefact images, 10
FIGS. 3a-g illustrate a recording code consisting of two points and the step-wise building up of a compensation distribution which is correlated to the recording code,
FIGS. 4a-/ show a recording code consisting of three 15 points and the step-wise building up of a further compensation distribution which is correlated to the recording code,
FIG. 5 shows a three-point recording code which is correlated to a distribution which corresponds to the 20 recording code,
FIG. 6 shows a device for making layer images which are artefact-free at least in their centre,
FIG. 7 shows a further device for making layer images with separate optical and electronic channels, 25
FIG. 8 shows a device comprising separate optical channels and a common electronic channel,
FIG. 9 shows a device for making artefact-free layer images by way of holography, and
FIG. 10 shows a table of characteristic numbers. 30
The foregoing description, and also the following description, is given with reference to X-ray super-position images. However, images of particle radiation normal optical and electronic images can also be processed according to this method without restriction. Artificial 35 images calculated by a computer can also be processed by the method in accordance with the invention.
FIGS. 1 and 2 serve to illustrate the principle of the method in accordance with the invention. FIG. 1 shows a multiple radiation source 1 which comprises, for ex- 40 ample, three separate radiation sources 2, 3 and 4 which are arranged in a plane la. A so-termed point-image function indicates the positions of the separate radiation sources in the plane la.
The separate radiation sources 2, 3 and 4, which can 45 be simultaneously flashed, emit X-ray beams 6, 7, 8 which are stopped by apertures 5 and which intersect on an optical axis 10 (which extends perpendicular to the plane of the radiation sources) in order to irradiate an object 11 to be examined. The object 11 is thus re- 50 corded in a coded manner in that three separate primary perspective images 12, 13, 14 are imaged, for example, on a single film 15.
FIG. 2 shows the decoding step. The separate primary perspective images 12, 13, 14 on the film 15 are 55 irradiated by means of a light box 16, which comprises, for example, a flat ground glass plate 17 at its front, and are imaged by means of a lens matrix 18 so that the central rays 12b, 13b, 146 of the radiation beams transmitting the primary images 12, 13, 14 intersect each 60 other behind the lens matrix 8 in a point on an optical axis 18a which extends perpendicularly through the lens matrix 18. The radiation beams are superposed in a zone 19. The primary perspective images 12, 13, 14 are thus imaged by means of the associated lenses 12a, 13a, 65 14a. In the superposition zone 19 there may also be arranged a scatter disc 21, or a similar device, which can be arbitrarily positioned in order to make the layer
images 21 of the object 11 visible; oblique layers of the object 11 can thus also be reproduced.
An artefact image in the imaging plane 20 is formed because the separate primary perspective images 12, 13, 14, for example, being positive, are also transmitted by the inappropriate lenses. For example, the primary perspective image 12 is also transmitted, via the lens 13a, by way of a beam 22, so that in the imaging plane 20 an artefact image 23 is produced which corresponds to the primary perspective image 12. In order to compensate for this artefact image 23, an additional lens 24 is included in the imaging matrix 18. Via this additional lens 24, a correction perspective image 25 (negative), derived from the primary perspective image 14; is transmitted by way of a beam 26; and is superposed on the artefact image 23, so that they cancel each other. The correction perspective image 25 can be obtained from the primary perspective image 14 or from the total superposition image 15.
The additional lens 24 also transmits further correction perspective images 27 which are situated in the imaging plane 20, for example, via a beam 28, and which are produced in conjunction with the compensation of the artefact image 23 by the correction perspective image 25. This is because the correction perspective image 25 was obtained from the superposition image 15, thus from the primary perspective image 13.
The correction perspective image 27 (for example, a negative image) itself is then compensated for by means of a further lens 29 introduced into the lens matrix 18, so that, via a beam 29a, the primary perspective image 14 (positive) is superposed, via the lens 28, on the correction perspective image 27, so that the two images 14 and 27 cancel each other. Obviously, the primary perspective images and the correction perspective images are not transmitted in succession. For example, during a first step all primary perspective images 12, 13, 14 can be simultaneously transmitted via the lenses 12a, 13a, 14a and 29, whilst the correction perspective images 25 and 27 are transmitted, by way of the beams 26 and 28 during a second step, via the lens 24. Both transmissions can also be simultaneously performed; this will be elaborated hereinafter.
Using the method in accordance with the invention, therefore, within a layer image representing a given object layer the artefact images are compensated for which were produced during the reconstruction by transmission of primary perspective images from the corresponding object layer.
FIGS. 3a~g and 4a-;' illustrate how the positions of the lenses 24 and 29 in FIG. 2 are determined.
As has already been stated, the lenses 12a, 13a, 14a, are arranged in the plane la in accordance with the distribution of the radiation sources 2, 3 and 4 i.e. distributed in accordance with the point-image functions of the recording geometry (radiation source array) in the lens matrix 18.
FIG. 3a shows a so-termed recording code S' wherefrom a compensating code K' (FIG. 3/) can be derived which contains the recording code S', the compensating code K' being correlated to the recording code A' in order to obtain layer images which are artefact-poor at least in their centre (FIG. 3g).
To enable a clear illustration of the situation, it is assumed that the object 11 consists only of a point p' (not shown) and that two X-ray sources (not shown) having the same intensity are used for irradiating the object 11. Obviously, the object 11 may alternatively
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