FR2485790A1 - Prim. filter for radiology - where geometric profile of filter can be modulated by remote control to alter contrast of image on viewing screen - Google Patents

Abstract

A patient or a mechanical workpiece is located between a radiation source and a receiver which includes data- and image- processors. The source is provided with a prim. filter with a geometric shape which can be modulated by motors operated by remote control. The pref. filter consists of a rectangular frame contg. two gps. of filter blades. Each gp. of blades is located on a flexible cable which is spring-loaded; and each gp. can be moved by a row of rods which worms are fixed. The worms are rotated by electric motors fed by a controller. The result is that the blades form a hole of adjustable size and shape in the filter. Used for equalising the contrast in radiological images, e.g. in the radiography of a cardiac region masked by lungs with reduced density.

Description

 The present invention relates to a primary filtration system with a modular effect remotely. It allows in particular to equalize the contrasts of an image acquired by an X-ray machine.

 The practice of examining material bodies by means of images obtained using beams of radiation comes up against the problem of contrasts. Indeed, when in a body examined there are located # two organs with very different absorption densities, it may happen that one of the organs is masked by the other. This is for example the case of the radiography of the cardiac region masked by the lungs of reduced density.

 Two solutions to this problem are known in the prior art. First of all, it has been proposed the use of receivers of the radiological image whose sensitivity curve as a function of the exposures reduces the difference between the traces left by the two neighboring organs of too different densities. This solution results in a compression of the image dynamics and therefore in a loss of information.

Primary filtration systems have also been proposed, of which the present invention is an improvement. Such a system is interposed between the source of the high energy rays and the body under examination. It reduces the dpse of rays sent around the periphery of the emission beam. This system is described in the journal "Radiology", Vol 99 no 3, June 1971 in an article by MM. EDHOLM and
JACOBSON entitled "Primary X-Ray dodging". This device has the disadvantage of being passive and therefore not adjustable and moreover of requiring the intervention of an operator near the irradiation source.

 Another system, described in Swedish patent no. image to filter.

 The invention provides a remedy to these drawbacks of the prior art. In fact, the invention relates to a primary filtration system with a modular effect at a distance, cooperating with a chain of acquisition of the radiological image comprising at least one source of radiation, a organ for receiving radiation after examination of a body and a display member and is characterized by the fact that it comprises at least one filter, the profile of which is adjustable in geometric shape and in absorption by motor means controlled remotely by means of adjustment from the display member.

 The different elements of the invention will now be described with the aid of exemplary embodiments illustrated by the figures which are - FIG. 1: a diagram of the radiological chain, - FIG. 2: a filter diagram according to the invention, - Figure 3: a detail of the previous figure.

The primary filtration system according to the invention therefore mainly comprises two distinct parts - a filter proper placed on the path of the primary beam, therefore interposed between the source of the radiation and the body examined, - a set of adjustment means placed on the 'display unit.

This set allows the geometry of the filter to be fully adjustable in one plane, from complete opacification (to within a transmission factor) to transparency to radiation (in neutral position). Being connected by an electrical connection to the filter itself, this assembly can be distant from the source and therefore effectively protect the operator against additional irradiation.

In addition, being located on the display console, the installation of filtering is almost instantaneous. This characteristic is particularly advantageous in Surgery for example.

 Finally, the filter itself is built to adapt to different geometric shapes, to different filter contours. The invention is therefore also characterized by great flexibility of use.

FIG. 1 shows a complete chain of acquisition of the radiological image, comprising a filtering system of the first type according to the invention.

The channel comprises a radiological source A and a receiver of the radiological image B placed on either side of a body C to be examined. This body C can be a patient in Medical Radiology or a mechanical structure in Industrial Control. The radiological source A comprises a radiation source 1, a primary collimation-filtration chamber 2 and a filter holder box 3. The receiver of the radiological image comprises a detector 4, a member for processing the radiological data 5, a visualization console ó and a graphics computer 7.

An X-ray beam 8 coming from the focal point 9 of the radiation source 1 crosses the members 2 and 3, the body C examined and strikes the detector 4.

Depending on the case, the processing chain may include digital processing, the radiological image being divided into image elements (picture el # ement
PIXEL in Anglo-Saxon literature). The radiological data processing unit 5 then controls, for example, a display by cathode ray tube. The brightness is then adjusted according to a grayscale scale and the deviations are determined by the address of each picture element. The processing unit 5 can also perform color processing or other image processing in conjunction with the graphics computer 7.

The processing chain may include a direct display on the display console, for example by means of photonic transducers and a charge transfer device or any other conventional means of display in Radiology.

 The filter 3 is shown in FIG. 2. It comprises a frame 17 and means 18 for holding the movable parts of the filter in the plane of the filter.

Two mobile groups were represented face to face.

Each group is composed of a plurality of blades 19, narrow in width. One of them was drawn in Figure 3. It is in the form of a non-rectangular parallelepiped. The lateral faces, like the face 20, are inclined at a given angle to the main direction of the beam. This inclination of the lateral races makes it possible to erase the traces of the blades, if an X-ray could cross their interstice.

On the other hand, each blade 19 may have a front face 21, directed towards the center of the filter 3, machined so as to have a decreasing ray absorption coefficient as one reaches the central region. of the filter not attenuated.

 Each blade 19 is pierced towards its rear face with a hole 22 intended to receive means for returning the blade 19 into the chassis 17 outside the field of the beam. In Figure 2, such means have been shown. They comprise for each group of the filter 3, a cable 23 which joins all the blades 19 of the same group. Each end of a cable 23 is fixed elastically to the chassis 17 by means of a spring 24 blocked by a washer 25 on a stop 26 secured to the end of the cable.

The blades are operated by means of electric motors like 29. These, by translation rotation transformers, like the worm system 28, repel blades 19 of each group by rods 27.

 The end of each rod 27 is secured to a particular blade 19, which it drives.

The movement of each particular blade, actuated by one of the rods 27 is transmitted and averaged via the cable 23 or 39. A profile like 40 can thus be produced; Its shape is largely flexible.

 When the filter is ordered in neutral position, that is to say when it is not put into action, the rays of the beam directly strike the body examined. The display unit can include, for example, a television screen. On this one, you can activate on each right and left edge of the image a light index. A given light index corresponds to the position of a particular blade 19 of the filter. Such a blade is in fact in direct engagement with a motor as has been described above.

The operator, thanks to a series of potentiometers with cursor or button can move each index so as to define the outline of the organ to be selected.

Each potentiometer acts on the one hand on the luminous index which corresponds to it on the screen, on the other hand on the supply circuit of the electric motor which moves the blade 19 identified by the luminous index.

The connection between the display member 6 and the filter is represented by line 10 in FIG. 1.

 The chain of acquisition of the radiological image must make it possible to obtain stable images on the display screen. This can be done for example with a memory tube, the image being obtained in a single exposure. The operator then places the light indices which effect the modulation of the filter, then relaunches a second exposure which erases the first. This second acquisition provides the corrected radiological image.

The display screen can only be of the afterglow type. The image must then be continuously refreshed, for example by a series of exposures defining the same image. For example, we could send an X-ray beam every second for two hundred milliseconds. The equalization of the contrasts of the image is visible during the modulation of the profile of the filter by the manipulation of the luminous indexes.

 Other modes of acquisition of the radiological image can make it possible to implement the filtering system according to the invention.

 To allow proper filtering, the filter blades must have characteristics determined according to the absorbtions presented by the body itself. The operator must therefore have a certain number of interchangeable filters, acting alone or in combination, which he selects in according to the needs of the exam. Thus for an X-ray of the notch or for a chest X-ray the operator will have in each case a specialized filter.

 Selection can be manual. The frame containing the filter is then introduced into a housing of the filter holder box.

Selection can be automatic. In this case, a mechanical device will select the appropriate filter, position it and introduce it into the filter holder box.
The selection can be remote controlled. The filter holder has several complete filters, only one of which is selected at a time, the others being locked in the neutral position. The dimensions of the blades, the gear ratios of the motors are dimensioned as a function of the distance of the filter considered from the focus of the tube. On the display console, the operator selects a particular filter corresponding to the desired examination by means of a switch comprising as many positions as the box includes filters.

The operation of this switch selects the filters and blocks the others in the neutral position. The operator then modulates the shape of the filter as desired.

 The filter can also have more than two groups of blades facing each other. These blades are gathered in groups distributed uniformly or not around the periphery of the chassis. Increasing the number of blade groups can reduce the angular points of the filter profile at intersections between groups.

 The invention is advantageously associated with a chain of acquisition of computerized radiological data. In particular, the display screen 6 can be managed by a graphic computer 7.

He can therefore use the different resources of interactive infographics. In particular, the drawing of the geometric profile of the filter can be carried out using a photostyle or a graphic ball. The choice of absorption profile can also be made by means of a stored program.

Claims (14)

 1. Primary filtration system with a modular effect at a distance, cooperating with a radiological channel comprising a source (1) of radiation, an organ (4) receiving radiation from an examined body and a visualization organ (6), characterized by the fact that it comprises at least one filter (3) whose profile is adjustable in geometric shape by motor means controlled remotely by adjustment means from the display member (6).  2. Filtration system according to claim 1, characterized in that the filter (3) comprises a plurality of blades (19) of approximately parallelepiped shape and a frame (17) in which said blades (19) slide along of their major axis in a plane perpendicular to the central axis of the radiation beam.  3. filtration system according to claim 2, characterized in that the blades (19) slide one on the other by inclined faces (20) of an angle i on the direction of the central axis of the radiation beam so as to erase the edges of the blades on the display member (6r.  4. filtration system according to claim 3, characterized in that each blade (19) has an upper or lower face, perpendicular to the central axis of the beam, which is profiled towards the center of the filter so as to achieve a variable absorption in the filter plane.  5. filtration system according to claim 2, characterized in that the blades (19) are divided into at least two groups. 6. filtration system according to claim 5, characterized in that the blades (19), divided into two groups, are arranged face to face in the frame.  7. filtration system according to claim 2, characterized in that elastic return means of the blades (19) in the neutral position are located in the chassis.  8. Filtration system according to claims 6 and 7, characterized in that the elastic return means consist of two cables (23), each passing through bores (22) of each blade (19) of a group, and fixed to the frame by spiral springs (24) with heads (26), at their two ends.  9. filtration system according to claims 2 and 6, characterized in that the motor means are composed of a series of micromotors associated with each group of blades. 10. Filtration system according to claim 9, characterized in that each micromotor consists of an axis (27) pressing on a blade (19) specific to a group, of a rotation-translation transformer (28), a motor (29) and an adjustable power supply (30).  11. Filtration system according to claims 1, 2 and 10, characterized in that the means for adjusting the motor means consist of potentiometers (30) adjustable by sliders which moreover move light indices on a display screen ( 6) to locate the area of the filtered image.  12. Filtration system according to claim 1, characterized in that the adjustment means comprise means for tracing the filtering profile in geometry and in absorption on the display member (6), managed by a graphic computer (7) associated with the display member (6).  13. Filtration system according to any one of the preceding claims, characterized in that it comprises several filters according to claim 2 distributed in planes. perpendicular to the central axis of the beam, successively from the diaphragm (2), so as to propose different filtering characteristics, at different focal distances and in that selection means make it possible to select any one of these filters, from the display member (6).  14. X-ray apparatus comprising a filtration system according to one of the preceding claims.