Diagnostic radiology installation

In an exemplary embodiment, there is provided a patient support, a radiation measuring arrangement including a radiation source which generates at least one fan-shaped radiation beam, penetrating the radiography subject, and a radiation receiver which has an array of detectors which are connected to a signal processing circuit, and means for generating relative movement between the patient support and the radiation measuring arrangement in a longitudinal direction of the support, for the generation of a shadow image several radiation directions are generated so that a plurality of intersection points of the radiation paths result within an image exposure region. The signal processing circuit determines the radiation transparency in the patient for every intersection point of a plane parallel to the patient support.

BACKGROUND OF THE INVENTION 
The invention relates to a diagnostic radiology installation, comprising a 
patient support, a radiation measuring arrangement comprised of a 
radiation source, which generates at one least fan-shaped radiation beam 
penetrating the radiography subject, and disposed transversely to the 
patient support, and comprised of a radiation receiver which is formed by 
an array of detectors which are connected to a signal processing circuit, 
and means for effecting a relative movement between the patient support 
and the radiation measuring arrangement in the longitudinal direction of 
the support for generation of a shadow image from the detector output 
signals by means of the signal processing circuit. 
A diagnostic radiology installation of this type is described in the German 
O.S. No. 26 13 809 (U.S. Pat. No. 4,174,481). The known diagnostic 
radiology installation relates to a computer tomograph which is 
supplemented with means which permit the preparation of a shadow image of 
a specific region of a patient. For the preparation of the computer 
tomogram, the measuring arrangement is rotated about the longitudinal axis 
of the support or about an axis which is parallel thereto. From the output 
signals of the detectors, a computer calculates the attenuation values of 
image points arranged in a matrix, which can then be reproduced as an 
image of the examined transverse layer of the patient. For the generation 
of a shadow image, the measuring arrangement is locked against rotation 
and a relative movement between the patient support and the measuring 
arrangement in the longitudinal direction of the support takes place. A 
shadow image thus contains, in superimposed form, all details of the 
irradiated radiography region. Since these details are superimposed on one 
another, (for example, in the case of observation of the chest, a 
superposition of the front and rear rib sections takes place), the image 
is of little significance in terms of information-content. 
In order to improve x-ray shadow images, it is already known to form a 
sharp image of only one layer of the patient, parallel to the patient 
support, by fixedly coupling with one another the x-ray tube and an x-ray 
film cassette and pivoting this unit about a pivot axis lying in the 
desired layer. In this case, sharp images are produced on the x-ray film 
only of the details of the selected layer, whereas the remaining details 
are imaged in a blurry fashion. It is disadvantageous here that the 
secondary radiation grid, which must be aligned to the focus of the x-ray 
tube, on account of the necessary movement of the radiographic unit 
comprised of the x-ray tube and the x-ray film cassette, can exhibit only 
lamellae or leaves which extend in the direction of movement. There 
consequently results only incomplete stray radiation suppression. 
SUMMARY OF THE INVENTION 
The object underlying the invention resides in creating a diagnostic 
radiology apparatus of the type initially cited with which it is possible 
to prepare radiographs of desired layers of the patient, said layers being 
disposed parallel to the patient support whereby the effect of the stray 
radiation on the image quality is kept as low as possible. 
In accordance with the invention, this object is achieved by virtue of the 
fact that means are present for generating several radiation directions, 
such that a plurality of intersection points of the radiation paths result 
within an image exposure region, and that the signal processing circuit is 
so designed that, for every intersection point of a plane parallel to the 
patient support, it determines the radiation transparency in the patient. 
In the case of the inventive diagnostic radiation installation, the stray 
radiation can be well suppressed by means of a collimator arranged in 
front of the radiation receiver. An x-ray shadow image of a layer parallel 
to the patient support can, in a simple fashion, be calculated by the 
signal processing circuit and reproduced on a video unit. 
One embodiment of the invention is one wherein a radiation source is 
rigidly connected with the radiation receiver formed of a single detector 
array, and wherein the detector array is pivotable about the focus of the 
radiation source. In this case, the scanning of the image exposure region 
can proceed in such a fashion that, first a pivoting of the radiation 
measuring arrangement through a predetermined angle takes place, then a 
relative longitudinal movement between the radiation measuring arrangement 
and the patient support through a predetermined step takes place, then 
again a pivoting takes place, then again a relative movement, etc., takes 
place. Another variant is one wherein the radiation source emits several 
ray fans in different directions, each of which is received by a detector 
array, and that the radiation source and all detector arrays are 
stationarily arranged in the apparatus. In each case, a movement of the 
patient support suffices for the purpose of scanning the image exposure 
region. 
The invention shall be explained in greater detail below on the basis of 
the accompanying drawing sheets; and other objects, features and 
advantages will be apparent from this detailed disclosure and from the 
appended claims.

DETAILED DESCRIPTION 
In FIG. 1, the focus 1 of an x-ray tube is illustrated which emits a 
fan-shaped x-ray beam 2 which is defined by means of a collimator or 
primary radiation diaphragm 3. The x-ray beam 2 is received by a detector 
array 4 which, for example, can be designed as an arcuate segment with a 
center of curvature at the focus 1. The detector array 4 can comprise 512 
individual detectors. The measuring arrangement 1, 4, serves the purpose 
of scanning a patient 5 resting on a support 6 which is movable in its 
longitudinal direction. 
The scanning of the image exposure region of the patient 5 proceeds in such 
a manner that, in the illustrated position I of the focus, the x-ray tube 
and the radiation receiver 4 are pivoted about the focus 1 through the 
angle .alpha.. During the pivoting, in predetermined angular positions, 
the output signals of the individual detectors of the radiation receiver 4 
are interrogated (or sampled). In FIG. 1, seven radiation paths are 
illustrated in which interrogation (or sampling) takes place. In practice, 
naturally, there will be substantially more radiation paths. Following the 
pivotal movement, a longitudinal movement of the x-ray tube and of the 
radiation receiver 4, which is rigidly connected therewith, takes place 
until the focus lies in the position II. In this position, a pivoting 
through the angle .alpha. and an interrogation (or sampling) corresponding 
to the previously described instance again takes place. Subsequently, the 
x-ray tube with the radiation receiver 4 is so moved that the focus 
occupies the position III. In this position, again a pivoting and a signal 
interrogation (or sampling), etc., takes place. The angle .alpha. can, for 
example, amount to 40.degree.. 
From FIG. 1 it is apparent that the individual radiation paths of the 
radiation beam 2, running transversely to the patient support 6, have a 
plurality of intersection points in the image exposure region of the 
patient 5, which intersection points result from the different radiation 
directions. By means of a signal processing circuit, which contains a 
computer, it is possible to determine and reproduce, as an image, the 
radiation transparency in the patient 5 for the intersection points lying 
in a plane S running parallel to the patient support 6. In this manner, 
one obtains an x-ray shadow image of a longitudinal layer of the patient. 
The computer thus processes the output signals of the individual detectors 
of the radiation receiver 4, which are designed as radiation-electric 
transducers. 
In a second embodiment for effecting the described scanning procedure of 
FIG. 1, it is possible to dispense with the longitudinal movement of the 
radiation measuring arrangement 1, 4, if it is replaced by a longitudinal 
movement of the patient support 6 with the patient 5. In this case, it 
suffices if the measuring arrangement 1, 4, is pivotably mounted about the 
focus 1. 
In the exemplary embodiment according to FIG. 2, a collimator (or primary 
radiation diaphragm) 7 is present which defines two fan-shaped x-ray beams 
8, 9, which penetrate the patient 5 from different directions. Every 
radiation beam 8, 9, is received by one radiation receiver 10, 11, 
respectively, which again is comprised of a series of individual 
detectors, for example 512 individual detectors. In this case, the x-ray 
tube as well as the radiation receiver 10, 11, can be stationarily 
arranged in the apparatus. The scanning of the image exposure region can 
proceed by virtue of the fact that the patient support 6 with the patient 
5 is moved a predetermined extent in its longitudinal direction. In this 
manner, as is illustrated in FIG. 2, one likewise obtains a plurality of 
intersection points which, in the described manner, form the basis for 
image production. 
In the example according to FIG. 2, it is possible to control the apertures 
7a and 7b in such a fashion that they are only then opened when the 
radiation generates the signals which also actually are usable for the 
purpose of image production. Thus, for example, the scanning operation can 
proceed from the illustrated position in such a manner that first only the 
x-ray beam 9 is present, and only when intersection points result in the 
patient 5, is the x-ray beam 8 established. At the end of the advance, the 
aperture 7b then first closes, and only thereafter does the aperture 7a 
close. The radiation exposure of the patient 5 can thereby be kept small. 
In FIG. 2, the intersection points of the radiation paths are illustrated 
in that the focus 1 is illustrated as traveling and the patient support 6 
is illustrated as stationary. This is indeed a possibility for scanning 
the image exposure region; however, as described above, in the example, 
the relative movement takes place in longitudinal direction of the support 
by virtue of the fact that only the patient support 6 is moved. Nothing is 
changed thereby regarding the position of the intersection points. 
In FIGS. 3 and 4, orthogonal views of a diagnostic radiology installation 
according to the invention are illustrated by means of which the scanning 
movement, described as a second embodiment in conjunction with FIG. 1, can 
take place. On an apparatus frame 12, an x-ray tube 13 is pivotably 
mounted about a horizontal axis 14. The x-ray tube 13 is fixedly connected 
via an arm 15 with the radiation receiver 4. From FIG. 4 it is apparent 
that the radiation receiver is comprised of an array 4a of individual 
detectors in front of which a collimator 4b is arranged aligned with the 
focus 1. 
Via a crank mechanism 16, which is driven by a motor 17, FIG. 4, the x-ray 
tube 13 is pivotal about the axis 14, which passes through the focus 1, 
through the angle .alpha. illustrated in FIG. 3. The radiation receiver 4 
participates in this pivotal movement, and can thus be pivoted into the 
positions illustrated by dot dash lines in FIG. 3. The longitudinal 
movement of the support proceeds by means of a motor 18 which engages in a 
toothed rack 19 on the lower side of the patient support 6. In addition, a 
computer 20 is present which is connected to the radiation receiver 4 and 
computes the respective x-ray shadow image of the selected layer and 
effects its reproduction on a video unit 21. In FIG. 1, such a possible 
layer is, for example, illustrated and referenced with S. For the 
computation of the image of this layer, the intersection points are 
utilized which are heavily marked in FIG. 1. 
In the example according to FIG. 1, it is also possible to rigidly connect 
only the collimator (or primary radiation diaphragm) 3 with the radiation 
receiver 4, comprised of a single detector array, and to arrange it 
pivotably about the focus 1 of the stationary x-ray tube. 
It will be apparent that many modifications and variations may be effected 
without departing from the scope of the novel concepts and teachings of 
the present invention.