US3086123A - Apparatus for radiology, in particular for local densigraphic examination - Google Patents

Description

April 16, 1963 H. M. MARCHAL 3,086,123 APPARATUS PoR RADIoLoCY, IN PARTICULAR FCR LOCAL nENsICRAPHIC EXAMINATION Filed April 27, 1959 /NVENTOR 26 "95 MAURICE IIARCHAL BY 4.1@ 37A ATTORNEYv United States Patent O 3,086,123 APPARATUS FOR RADIOLGY, IN PARTICULAR FOR LOCAL DENSIGRAPHIC EXAMLNATIN Henri Maurice Marchal, 12 Rue Jacques Bingen, Paris, France Filed Apr. 27, 1959, Ser. No. 809,181 Claims priority, application France Apr. 30, 1958 1 Claim. (Cl. Z50- 227) The present invention relates to apparatus used in radiology and especially in local densiography, following the technique of which the variations are recorded in the luminosity of a small liuorescent screen on to which falls a beam of rays, X-rays or other, after having passed through an obstacle a small zone of which it is desired to study, the said variations being a function of the variations of opacity and therefore of the density of the said zone. Since it is in these cases that its application would appear to oifer the greatest advantage, the invention is more particularly concerned, amongst this type of apparatus, with those used in medical radiology for the purposes of diagnosis, and in particular for the local examination of small zones of organs or of small organs, of which the variations of transparence and/or the movements are relatively rapid, for example for the examination of members subjected to pulsations of the blood, such as the arterioles which irrigate the lungs of a patient (this technique being sometimes known by the name of cine densiography) It has especially for its object to make these apparatus better adapted than they have been up to the present time, to the various requirements of practice, especially in that they enable the small region studied to be positioned and located with a greater degree of precision.

According to the invention, an apparatus for derisiographic examination enabling the variations of intensity of a main radiation flux (X, gamma or other rays) to be observed and recorded after its passage through an obstacle of variable opacity to be examined, comprising essentially a surface element of small dimensions irradiated by a portion of the said flux and a device adapted to convert the variations of intensity of the radiation emitted by Ithe said element to variations of a readily usable electrical parameter, in which the said surface element is disposed at the edge of said device and preferably at a certain distance from said edge, said distance being considered at right angles to the general direction of the main flux of rays, at least a part of the immediate vicinity of said surface element being composed only of material which is transparent to said main radiation, whereby, on the radioscopic image formed by said radiation beyond said surface element, the image formed by said element is not submerged in the shadow cast by the said device, but is disengaged, at least in part, from said shadow.

In addition to this principal arrangement, the apparatus of the invention comprises certain other arrangements which are preferably employed at the same time (but which could however be used separately, when so required) and which will be described in greater detail below, in particular:

A second device having two main features, the first of ICC modied at will, in particular by the insertion in the utilization circuit of one, two or three filters of the double T type connected in series for the calibration of cine-densiographic recordings relating respectively to an examination of the heart, to an examination of arterioles of the lung or of the arterioles of the liver.

The invention is more particularly directed to a certain method of application (that for which it is applic-d to radiological examination) and also to certain forms of embodiment of the said arrangements; it is also directed still more particularly, by way of new industrial products, to apparatus of the kind referred to embodying the applications of these same arrangements, together with the special elements and tools adapted to -their preparation, and the assembled units, especially radiological installa# tions, which are equipped with such apparatus.

The invention will be understood more clearly by reference to the descriptive text which follows below, together with the accompanying drawings, it being understood that this description and these drawings are only given by way of indication and without any implied limitation.

FIG. 1 of the drawings shows diagrammatically in plan view, an essential part of an apparatus for localized medical densiography, constructed in accordance with the invention.

FIGS. 2 and 3 are views on a l-arger scale of one of the members of the same apparatus, with portions broken away, the views being respectively in elevation and endview.

FIG. 4 shows a portion of the image observed on the large radioscopic screen of this apparatus.

FIGS. 5 and 6 show respectively, in horizontal crosssection along the line V-V of FIG. 6, and in vertical cross-section along the line VI-VI of FIG. 5, an essen- Vtial part of an alternative form of an apparatus for localized medical densiography in accordance with the present invention.

FIG. 7 shows diagrammatically `an essential part of a further alternative form of an apparatus of the same kind similarly constructed.

FIGS. 8 and 9 show in detail two elements of the device illustrated in FIGS. 2 and 3.

And nally, FIG/10 shows the form of the calibrated recorded curves in accordance with a preferred method of application of the invention.A

In accordance with the invention, and more especially in accordance with that of its methods of application and the methods of construction of its various parts to which preference should apparently be given, use is made of a source of radiation l, the radiation produced by this source being passed through the subject 2 with the object for example of studying the variations of opacity of a region of this subject, the said region being of small dimensions in the `direction at right angles to the iiux of X-rays.

It should first of all be stated that the recording of such variations is already known: to this end, a small iuorescent screen is placed in the field of the X-rays after they have passed through the subject, this screen being arranged to face a photo-electric cell (or other similar device such as a photo-multiplier) which is capable of transforming the luminosity of this Screen to an electric current.

In order to locate the position of this small screen with respect to the subject, there is arranged beyond the cell on the path of the X-rays, a normal radioscopic screen constituted for example by a lead glass having its face which is turned towards the subject covered by a layer of plastic material coated with a product which gives a visible iiuorescence to X-rays (examples of such products being calcium tungstate or zinc sulphide).

Unfortunately, with this arrangement, since the cell is opaque to X-rays it casts a substantial shadow on the screen: the portion of this shadow which corresponds to the small screen is thus badly defined; in addition, this shadow hides the immediate vicinity of the zone to be studied, and this cannot therefore be located with precision, especially `by radiography.

ln order to overcome these drawbacks, in accordance with the present invention at least one portion of the immediate vicinity of the small screen is made transparent to X-rays.

In the form of embodiment shown in FIGS. l to 3, the source 11 is arranged behind the patient 2, the latter being placed behind a frame 3 which supports a radioscopic screen 4 at right angles to the axis of the beam of X-rays.

The frame 3 carries known means enabling a photomultiplier cell 5 to be displaced in any desired manner. These means may be constituted by small remote-com trolled motors, independent of each other and adapted to control respectively the vertical and horizontal displacements and the angular movements of the cell in its vertical plane; or alternatively the frame may be articulated about a horizontal shaft 6 on a support 7 which can be moved vertically along a column S which can be displaced horizontally along two slides 9 by causing it to rotate about its axis, two cables 10 stretched horizontally between the two =uprights of the frame 3 ybeing each wound several times round this column.

Instead of arranging the small uorescent screen exactly facing the aperture of the cell and directing this aperture towards the subject as in the known types of apparatus, this small screen 11 is mounted on the edge of the cell, in the immediate proximity of its aperture 12, or preferably at a certain distance from this aperture, considered parallel to the screen 4, and the arrangement is such that the shadow which it casts on the screen 4 does not coincide with a portion of the shadow cast by the cell.

Fluorescent screens are generally formed with a support which is opaque or translucent but not transparent, this support being coated with the fluorescent substance.

It is an advantage to use a screen having a tluorescence which can be utilized on both its faces.

To this end, for example, the small screen 11 is formed in the following manner:

The iluorescent substance is coated on a support 13 (FIG. 3) which is transparent to visible light and which may or may not be rigid. The support may for example be made of methyl poly-methacrylate (a material known by the commercial name of Plexiglas), or a flexible plastic material.

In addition, the liuorescent coating 29 (FIG. 8)- whieh may be composed of a number of separate coatings transmitting their activation from one to the otheris preferably covered by a second plate 3d* for the purposes of protection, this plate being either rigid or flexible and transparent to light and to X-rays.

The support 13 is arranged parallel to the screen 4 at a few millimeters or a few centimeters above the aperture 12 of the lead-protected cell, the photo-cathode of which is shown diagrammatically at 14. Mirrors 1S, which may be plane or otherwise, are arranged on each side of the small screen 11 so as to reflect towards the aperture 12 the light which it emits under the impact of the X-r-ays.

The assembly formed by the mirrors 15 and the supporting means for these mirrors and of the support l13 (means which form a kind of `closed box 16 entirely opaque to light and coupled in a light-tight manner to the protective casing of the cell, which is itself opaque to X-rays and to light) is composed of materials transparent to X-rays such as aluminium, glass coated with aluminium or silver, etc.

The image then formed on the radioscopic screen 4 is composed on the one hand of shadows 17 (FIG. 4) which are more or less dark, corresponding to the organs of the subject traversed by the X-rays, and on the other hand, two dark shadows, one 18 corresponding to the shadow of the cell 5 andthe other 19 of the small screen 11. This latter shadow may be framed at least partially by an opaque line 29 which is the image formed by a wire of lead or other material opaque to Y-rays, surrounding the screen 11 when the said screen is transparent to X-rays, which is the preferred case of utilization. In this case in fact, it is possible to examine and to define, either by radioscopy or by radiography, the exact part of the member which corresponds to the densiographic recording.

A protective screen 21 (FiG. l) for example of wood or other material transparent to Xsrays, may be interposed between the patient and the cell 5.

In the form of embodiment which has just been described, the shadow 1S is considerable and may still be a source of diiculty in certain examinations.

This drawback can be removed by employing the alternative form of apparatus illustrated in FIGS. 5 and 6, in accordance with which the cell 5 is mounted outside the ilux of X-rays, on the uprights of the frame 3.

The screen 11 is housed between two strips 22 (FIGS. 5 and 6) of a substance such as quartz which is transparent to X-rays and capable of transmitting in an almost complete manner, the light which it receives.

These strips are sufliciently rigid to support the screen 11, the luminosity of which is transmitted through them to the photo-cathode 14.

In order to avoid all loss of light, it is advisable to surround them by a sheath 23 which is opaque to light but transparent to X-rays, for example of aluminium, the inner face of this sheath being preferably reflecting.

It will be understood that any suitable means may be provided for displacing the cell and the Strips.

It may ybe an advantage to articulate the strips on the cell.

The use of these strips enables the thickness between the protective plate 21 and the screen 4 to be considerably reduced, `and in particular it enables the latter to be completely disengaged so that, apart from the shadows corresponding to the organs to Ibe examined, there appears only that corresponding to the small screen 11 (and/or to its `frame).

By way of indication, it may be stated that the strips 22 can have a straight semi-cylindrical form having a diameter of the order of l centimeter and a length of about 2O` centimeters.

They may also be elbowed.

In accordance with an alternative form of embodiment, a ilexible light-guide may be formed over at least a part of the distance between the screen and the cell, by placing pieces of quartz 24 (FIG. 7) separated from each other in a deformable sheath of a material transparent to Xrays, the spaces between two successive pieces 24 being filled with a liquid 26 which is transparent to light and has the same index of refraction as quartz.

Means such as those shown diagrammatically at 27 enable the free extremity of this flexible tube, which carries the screen 11, to be moved with respect to the cell 5.

The light sent to the cell 5 must be modulated in a strictly stable manner, and in certain cases the use of the town mains supply or of X-radiation produced by the usual types of generator is not satisfactory for the respective reasons of the indifferent stability of the mains supply and of the parasites inherent with the said generators.

In accordance with an advantageous arrangement of the invention, a continuous beam of Xrays is first generated following the usual method, for example by the adjunction of an assembly of condensers which can be shunted to earth when so required, after ywhich an opaque screen is periodically interposed on the path of this beam close to its source, for example by causing the peripheral zone of a perforated disc to pass in a continuous manner across the beam at regular intervals, the disc being rotated at a well-defined constant speed about its axis, or by the use of a screen oscillating at a constant frequency, for example in front of a slot.

The X-radiation is then modulated in a stable manner (for example at 420 cycles per second) which removes the drawbacks inherently due to parasitic or irregular frequencies during the amplification which is necessary to use the data received by the cell.

In accordance with a particularly advantageous form of this arrangement, the periodic interruption is not applied to the X-radiation, but to the light radiation transmitted according to the invention, Whether by reflection or by refraction, from the small screen 11 to the aperture 12, as is shown diagrammatically by the disc 28 represented in chain-dotted lines on FIG. 5.

The'said periodic interruption may -be effected with advantage b-y means of a rotating disc 31 (FIGS. 3 and 9) provided with ra-dial or other perforations, rotating in front of a diaphragm 33, fixed or not fixed, provided with corresponding perforations and mounted at the input of the cell.

In the form of embodiment shown in FIGS. l to 3, it may be an advantage to arrange the oscillating screen or the perforated disc in the interior of the box 16, in order to reduce the overall size of the unit.

The modulation of the beam which has just been described is particularly well adapted to the form of embodiment in which the source of Iradiation is not a more or less continuous source of X-rays, but is a source of gamma rays. This is the case of radioactive thulium 170, the half-life of which is of the order of 4 months and which emits a perfectly stabilised gamma radiation, the energy of ywhich (of the order of 85 kev.) is compatible with the means of protection generally provided in the equipment of radiology installations. It will of course be understood that in the case of use of a source of this kind, it would be necessary to replace the uorescent screen yby a suitable detector such as a scintillator crystal of Sodium iodide activatedby thallium.

In order to apply the results recorded on the cinedensiographic curves under the best conditions, it is an advantage to be able to calibrate the curves obtained in an independent manner, especially independently of the amplifying chain employed and of the radiological density of the organ examined.

To this end, it has already been proposed to record on the same negative the variations of intensity of the light radiation employed due on the one hand to the modulation of -this radiation at a relatively high uniform frequency (for example of 100 cycles) and on the other hand to the more or less considera-ble interception of the said radiation by the organ studied by reason of the pulsations of the blood at a relatively low frequency, to which this organ is subjected.

The amplitude of the tirst oscillations is represented by a in FIG. l0, and that of the second by b in the same figure.

Experience has shown that the radio b/a of these amplitudes does not depend, for a given source of X-radiation, either on the gain of the amplifieror on the radiological density of the organ traversed, but only on the amplitude of the variations of that density. This ratio, which is sometimes known as the index of pulsatility, is thus a faithful image of the pulsatility of the said organ.

Up to the present time, a double T filter was used, which could either be put out of circuit, corresponding to the recording of a portion of curve similar to that shown at 34 in FIG. l0 (beginning of the recording),

or be put into circuit, which corresponded to the portion 35 of the said curve (end of recording).

A circuit arrangement of this kind does not enable the absolute value of the reference a to be modified as a function of the pulsatility of the organ studied, which can vary to a very considerable extent from one organ to another.

In order to overcome this drawback, according to an advantageous arrangement of the invention, a number of successive filters, preferably of the double T type, are connected in the amplifying chain in such manner that it is possible to use at will one of these filters only, or two, or more, depending on the pulsatility of the organ examined. These lilters are connected either in series or in parallel, and can be put into service at will by means of at least one change-over switch.

For example, if a series of three filters is available:

One only is used for the examination of a shadow corresponding to a very high pulsatility, such as the cardiac shadow, which has a large depth of modulation and only requires a low gain before recording: if the filtering system were too extensive, the residual amplitude corresponding to the rapid modulation cycles) wouldbe too small to be measured with accuracy, and would be for example of the order of 2 mm. only;

For the examination of shadows corresponding to the arterials of the lungs, which have a low pulsatility, the gain should be increased and two of the iilters are employed, connected in series;

An-d for the examination of shadows corresponding to the arterioles of the liver, the pulsatility of which is very small, the gain of the amplifying chain must be considerable and the filtering must be more powerful than in the preceding cases. In this case therefore the whole of the three available filters will be employed.

The quotient of the quantities b and a can be effected in any desired manner, and especially in an automatic manner, for example by means of electronic apparatus equipped with quotient-meters in known manner, which would kbe mounted in parallel to the amplifying chain.

In addition, means such as an oscillograph adapted for recording are preferably provided for recording the value of the ratio b/a or index thus calculated, while at the same time the densiographic record is made and preferably also an electro-cardiogram.

It should be noted -that for the -calibration referred to above, it is of particular advantage to effect a rapid and uniform modulation of the radiation employed by a periodic interruption of the light or X-radiation effected by the movement of opaque screens in the manner described above, for example a-t 420 cycles; the curve corresponding to this rapid modulation is in fact much more accurate and faithful than that obtained by modulating mains supply current at 100 cycles.

It will be understood that any filtering means may be provided in order to elimina-te oscillations of stray or parasitic frequencies.

In the result, and whatever form of embodiment may `be adopted, there is finally available an apparatus for radiological examination enabling densiography to be utilized, and having Va large number of advantages as compared with those existing up to the present time, in particular, having an increased accuracy in respect of the positioning and the location of the small zone studied, on the one hand, and on the other hand the iidelity of the result collected at the output of the device which converts the variations of density of the organ studied to variations of electric current.

llt will of course be understood, and this follows furthermore from the foregoing description, the invention is not in any Way limited to its forms of application described, nor is it limited to the forms of embodiment of its various parts which have been more particularly dealt with; on the contrary, it includes all the alternative forms, especially:

Those in which the apparatus is equipped with a number of small screens 11 associated with the same number 0f cells, in order to permit a more convenient scanning of ti e whole of the organs irradiated;

Those in which the stabilization of the flux of X-rays and/or a variable calibration is employed for densiographic studies, independently of the disengagement of the image corresponding to the small screen 11;

Those in which the device which delivers an electric current as a function of the intensity of the beam of X-rays which has passed through the subject, is directly sensitive to that intensity (Geiger counter, ionization chamber, etc.) instead of being indirectly affected through the intermediary ot the small screens 11;

Those in which the small screen 11 is essentially constituted, not by a substance which becomes fluorescent under the impact of X-rays, but by a scintillator crystal capable of transforming to light the radiant energy which it receives (produced by X-rays or other radiations), the light emitted by this crystal being capable of being transmitted to the cell by quartz strips such as those described above, with an excellent efficiency which may attain 80% for strips of 1 metre in length.

What I claim is:

`Densiography apparatus for use with radioscopic apparatus including means for generating a ilux of X-rays, means for directing a beam of said rays through an object of examination, and means beyond said object for observing a radioscopic image formed by said beam after passing through said object, a surface element of relatively small area which emits light in response to X-rays, said element being disposed in a plane intersecting said beam between said object and said observation means, means for positioning said element in said plane to intersect a small section of said beam at any desired point, a cell sensitive to light disposed with respect to said element and said beam for receiving light as directed from said element and to avoid simultaneously intersecting that section of the beam intersected at any time by said element, a flexible sheath forming a duct extending between said element and said cell, said sheath being made of a material transparent to X-rays, a plurality of quartz pieces located in said sheath and a liquid transparent to light and having the same index of refraction as quartz filling the spaces in said sheath between said quartz pieces,

whereby light is directed from said element to said cell.

References Cited in the tile of this patent UNITED STATES PATENTS 2,695,964 Schepker Nov. 30, 1954 2,750,514 Armistead June 12, 1956 2,768,308 Schultz Oct. 23, 1956 2,796,528 Ball et al June 18, 1957 2,798,164 Untermyer July 2, 1957 2,810,078 Ball et al. Oct. 15, 1957 2,813,204 Lee N'ov. 12, 1957 2,840,716 Godbarsen June 24, 1958 2,849,621 Clark Aug. 26, 1958 2,901,632 Stava et al Aug. 25, 1959 FOREIGN PATENTS 1,053,108 Germany Aug. 13, 1956

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