Divider for directing an X-ray light beam into two or three directions, which beam emerges from the screen of an X-ray image intensifier in diagnostic X-ray arrangements. The divider is disposed at 45.degree. with respect to the optical axis, and consists essentially of a slit mirror which has a non-transparent metallization with one or two non-metallized, transparent areas or gaps therein, these areas corresponding to the required divisional ratios, there being similarly non-transparent mirrors or reflecting prisms behind the gaps.

X-ray light divider for equipment provided with image intensifiers, 
comprising a partially light-transmitting split mirror behind the usual 
collimator optics, the mirror being at about 45.degree. with respect to 
the optical axis. 
In the two main territories of diagnostic X-ray technology, namely in 
transillumination and in making exposures, it is most important to be able 
to divide the light of the nowadays indispensable X-ray image intensifier 
in at least two directions, with an appropriate, controllable ratio, so as 
to attend to the transillumination and to make an exposure at the same 
time. 
In X-ray equipment fitted with an intensifier, transillumination is usually 
carried out by way of a TV camera adapted to a first light channel, 
usually in the form of a monitor. Exposures are made through a second or a 
third channel, by adapting thereto a moving film camera or a so-called 
spot film camera. 
It is well known that such equipment should be operated with only a minimum 
X-ray exposure to the patient, regardless of the applied operational mode 
(transillumination, single-frame exposure, moving film sequence). It is 
also a requirement that a specific amount of light or intensity be 
available for each mode, as needed by the particular sensitivity of the TV 
or film camera and the like sensing unit. It is also necessary to allow 
observation of the image on a TV screen, simultaneously with the actual 
making of an exposure. 
It has been established that it is best, in consideration of the present 
degree of development of the presently used units, to convey about 90% of 
the available useful light quantity to the camera, whle 10% are sufficient 
for the TV camera or for visual observation. It should be clear that this 
ratio might be subject to changes when technology develops further in this 
area. When only transillumination is carried out, an optimally high 
proportion of the available light should be directed to the TV camera. 
The known two- and three-channel light dividers solve these tasks in two 
different ways. In one, image transmission is ensured with tandem optics, 
a partly transparent and partly non-transparent mirror being disposed 
between the optical elements so that the transmission path remains 
rectilinear while the reflected path makes for a beam diversion in a 
perpendicular direction. The mirror can be removed. 
In the other solution, mainly applied for three-channel dividers, there is 
a special (non-transparent) mirror behind a primary light-transmitting 
mirror disposed at 45 degrees, the special mirror being perpendicular to 
the light beam so as to reflect the beam back onto the primary mirror, 
whereby that beam is projected in a direction perpendicular to that of the 
original impinging beam. 
In both cases there are collimator optics behind the X-ray image 
intensifier, providing non-linear light distribution, so that the parallel 
beam of rays has a higher intensity near the edges than along the optical 
axis. 
A characteristic feature of the known arangements is the partly transparent 
dividing mirror. The latter is usually formed by a thin metal layer 
applied by vaporization under vacuum to a glass plate. The application of 
partly transparent mirrors brings about difficulties in regard to 
efficiency, performance and technology. In order to achieve the desirable 
90% - 10% divisional ratio, the reflection of the dividing mirror, for 
example with the second solution, cannot be higher than 70% on account of 
the absorption of the metal film or layer. Assuming an absorption of 18%, 
about 12% can pass the dividing mirror, of which the special or auxiliary 
mirror (assuming one of very good quality) reflects 11%: of the latter, 
about 70% is allowed to pass to the TV camera by the dividing mirror, 
which is a mere 7.7%. Assuming a similar degree of absorption for the 
first known solution, only about 12% would reach the TV camera. 
Compared to the ideal situation, it would become necessary to subject the 
patient to a 20% dose increase on account of the mirror having 70% 
reflection. For constructional reasons it is difficult to control the 
ratio of the reflection and the transmission of partly transparent 
mirrors. One of the reasons is that the rather complex refractive index 
that determines the reflection, the absorption and the transmission of the 
metal layer changes for unexplained reasons with the thickness of that 
layer; and furthermore it also depends on the purity of the evaporated 
material and on the vaporizing speed. For technological and economical 
reasons it is difficult to strictly observe the experimentally established 
evaporating conditions. It would also become necessary to apply optically 
planar machining to both surfaces of the dividing mirror. 
The mirror systems of the dividers always determine the positions where the 
camera(s) can be attached, in which respect the following considerations 
apply. 
In the first known solution mentioned earlier, the TV camera is applied to 
the first channel in the optical axis of the system, thereby extending its 
longitudinal dimension; the spot or film camera would be disposed in a 
perpendicular direction, in the second channel. The length of such an 
arrangement is such that it cannot be accommodated within the conditions 
of movement provided for X-ray examinations, and rooms would have to be 
chosen that are much higher than average hospital wards and the like rooms 
where such examinations are made. Room heights of 3.2 meters have been 
internationally accepted, whereagainst the requirement of such 
arrangements would be at least 3.4 meters, an increase of 20 centimeters 
(or almost 8 inches) which would seriously handicap the applicability of 
the X-ray equipment in question. When constructing new facilities it would 
thus become necessary to reckon with such room height increases, causing 
serious economic and architectural problems. 
In the second earlier-mentioned solution the cameras, namely the TV, spot 
and film cameras, are all disposed perpendicular to the optical axis of 
the arrangement. 
The total light emission or projection into the channels can be tabulated 
in the following in accordance with the requirements of X-ray diagnostic 
procedures. 
______________________________________ 
Total Luminous Output 
Light Channel 
Transillumination 
Exposure Camera 
______________________________________ 
First Known Solution 
I. 100% -- TV 
II. 12% 70% Spot or Film 
Second Known Solution 
I. 70% -- TV 
II. 7.7% 70% Spot or Film 
or: 
I. 70% -- TV 
II. -- 70% Spot 
III. 7.7% 70% Film 
______________________________________ 
As can be seen from the preceding Table, it is only with channel II. that 
an exposure can be made which is checked by a simultaneous 
transillumination. Depending on the kind of X-ray examination to be 
performed, it is therefore necessary with the known solutions to 
interchange the cameras between the second and third channels when making 
serial spot exposures. 
In the first known solution, 100% light transmission is possible with the 
mirror; however when the mirror is removed the optical axis of channel I. 
is shifted, in a parallel direction, by about 3 millimeters, owing to the 
absence of light refraction by the glass plate which is usually 8 to 12 
millimeters thick. On account of the non-linear light distribution of 
collimator optics this results in a rather unfavorable light distribution 
and brings about a deterioration of sharpness. The known arrangement 
attempts to keep the quality deterioration within acceptable limits by 
adjusting a median axis shift, both with and without the mirror, in that, 
for example, a 3 millimeter change in the optical axis is broken up into 
.+-. 1.5 mm shift values, as a result of which, it will however be clear, 
optimum light distribution cannot be attained in any one of the 
operational modes, neither on the image area, nor in terms of picture 
sharpness. 
For further reference, it appears simpler to relate the characteristics of 
the known equipment solutions as follows, based on the preceding Table: 
(a) as a first mode of operation, transillumination will be considered, 
usually through a "first channel"; (b) second, moving film exposures 
should be feasible, simultaneously with mode (a); and finally (c) spot 
exposures are also required, the modes (b) and (c) being performed through 
second and third channels of such light dividers -- the "third channel" 
being optional and not necessarily provided. 
It is the object of the present invention to eliminate the drawbacks and 
inconveniences of known arrangements and devices, namely primarily the 
applicability disadvantages resulting from the poor efficiency of partly 
transparent mirrors, and the so far unavoidable shift of the optical axis. 
According to important features of the invention, the mirror is provided in 
the form of a non-transparent slit mirror on which a light-transmitting 
gap is provided for each of the additional channels, an additional mirror 
or prism being disposed behind the gaps, having a respective reflecting 
surface that is perpendicular to the slit mirror. 
According to an optional inventive feature, a symmetrical or asymmetrical 
light gate may be provided behind one or both gaps to limit the light beam 
passing therethrough. 
It is one of the novel features of the invention that the slit mirror can 
be pivoted or rotated about an axis that is substantially parallel to the 
lengthwise optical axis of the system, including of course the collimator 
optics therein. 
The X-ray light divider according to the invention can be built with modest 
expenditures, much lower than those that were hitherto required, yet the 
efficiency is greatly increased as compared to the hitherto used fully 
transparent mirrors. There is no optical axis shift when changing from one 
operational mode to the other, all the more because the mirror does not 
have to be removed or even changed in its position. 
The inventive exemplary light dividers allow excellent light distribution 
conditions to be achieved, satisfying all diagnostic requirements, by 
themselves and among the light channels. As an added advantage, a 
three-channel division is possible without turning the mirror.

Although the exemplary embodiment of FIGS. 3 and 4 is simpler, and can be 
expanded by the addition of parts to become that of FIGS. 1 and 2 (two and 
three channels, respectively, in the two exemplary embodiments), the 
three-channel embodiment will be described first. A head portion 1 of a 
conventional image intensifier used in such arrangements is shown in FIG. 
1, with an exit screen 2 therein, followed by collimator optics 3 in the 
direction in which the entering light beam proceeds, which is identified 
in FIG. 2 by numeral 11. The X-ray divider has an outer housing portion 4 
into which all parts can be assembled for proper support and protection. 
The divider is arranged at 45.degree., approximately, with respect to and 
centered onto the optical axis of the system (parts 2, 3 and beam 11). 
As was explained in the introduction, a three-channel divider of this kind 
has to be suitable for three kinds of operations: (a) transillumination, 
for example with a TV screen; (b) film exposures; and (c) spot exposures, 
the latter mode being the one in which the exemplary device is illustrated 
in FIG. 1. It will be seen later that the simpler of the two disclosed 
embodiments, of FIGS. 3 and 4, combines the possibility of the operations 
(b) and (c) in one channel, thereby presenting an even more versatile but 
two-channel X-ray light divider arrangement. 
It will be understood that the beam 11 of the optics 3, constituting a 
first element of the optical system of the divider, is properly focused 
onto the exit screen 2 of the image intensifier. Subsequent elements of 
the optical system are designed according to the invention, as will be 
described hereinafter. 
The divider has three light image channels, identified by numerals 5, 6 and 
7, which can be seen in FIG. 1 as being on the left-hand side, toward the 
viewer, and on the right-hand side, respectively, and which allow the 
above-explained operational modes (a), (b) and (c) to be respectively 
practiced. FIG. 2 shows that these channels are displaced by 90.degree. 
each with respect to each other; they respectively lead to a TV camera 8, 
a film camera 9, and to a spot camera 10 (only broken-away, schematic 
parts of these conventional units are shown in FIG. 1). The inventive 
divider provides for the angular adjustment of the units 8, 9 and 10 (not 
shown in detail). 
It can be seen in FIG. 1 that TV camera 8 (for operation (a)) has optics 18 
in channel 5, film camera 9 (for (b)) has optics 21, schematically shown 
at channel 6, and that spot camera 10 (for operation (c)) has optics 13. 
In accordance with the invention, the light divider 4 includes a slit 
mirror 12 (substituting the earlier described mirrors of the known 
arrangements), which mirror has additional optical features as will be 
explained. 
When operating according to (c), the entire luminous intensity of the beam 
11 from the exit screen 2 impinges upon the mirror 12 through the optics 
3. As shown, the mirror has substantially circular or oval-shaped 
non-reflecting, transparent areas 15 and 22, constituting gaps for the 
passage of beams that serve for the channels 5 and 6, respectively (modes 
(a) and (b)). 
On the side of the mirror 12 that is opposite the impinging beam 11, the 
invention furthermore provides a small mirror or prism 17, for purposes to 
be described hereafter. A pivotable socket or support 19 is preferably 
disposed in the divider 4 for holding the mirrors 12, 17 and possibly 
other parts of the inventive device, such as the light gates to be 
described later. 
For transilluminations according to (a), the area 15 of slit mirror 12 
allows about 10% of the beam to proceed, in the form of a beam 16, being 
diverted by a surface of mirror or prism 17 that is perpendicular to the 
main surface of the slit mirror 12, as can be seen just to the left of the 
top center of FIG. 1. 
When using the divider for mode (b), namely for film exposures, the support 
19 can be pivoted about 90.degree., with the mirrors 12, 17 thereon, about 
an axis 20 that is parallel to the earlier-mentioned optical axis of the 
parts 2, 3. The area 22 of slit mirror 12 allows about 80% of the light 
beam to proceed toward channel 6, as a further beam 23 (passing in a 
direction perpendicular to the plane of the drawing). 
Finally, when operating per (c), the underside of the slit mirror 12 
reflects and rotates about 80% of the beam 11 (see the bottom part of FIG. 
2) toward the optics 13 of the spot camera 10, constituting a light beam 
14 passing to channel 7 (right-hand side of FIG. 1). 
An optional feature is also provided according to the invention to 
eliminate or to throttle disturbing light-beam portions that might impinge 
upon the optics 18 and 21 (channels (a) and (b), respectively). This is 
accomplished by providing one or both of light gates 24, 25 (see FIG. 2), 
which can be pivoted together with the mirror system 12, 17 (and the 
support 19), namely in the beam paths 16, 23, respectively. Uniform light 
distribution can be ensured by the intercalation of these gates which 
allow only the desirable amounts and portions of the beams to pass to the 
channels 5 and 6. 
When switching to mode (a) from the illustrated position, pivoting or 
rotation of the mirrors 12, 17 by 90.degree. brings approx. 80% of the 
beam 11 to the optics 18 of the TV camera 8. It might be added at this 
point that the described beams 11, 14, 16 and 23 necessarily also contain 
non-psrallel components although the drawings were made with parallel 
hatchings for the sake of simpler illustrations. 
By way of summary it will assist the understanding of the described 
exemplary, three-channel light divider embodiment to recapitulate that: 
parts and beams 1, 2, 3, 11, 12 and 19 relate to all three operational 
modes; 5, 8, 15 to 18 and 24 to mode (a); 6, 9, 20 to 23 and 25 to (b); 
and 7, 10, 13 and 14 to mode (c). 
We are now coming to the description of the two-channel embodiment of FIGS. 
3 and 4. Differences in details are now being described for this 
simplified light divider. This device can be used for transillumination, 
operational mode (a), and also for film as well as spot exposures, 
provided by way of a combined second channel that is capable of performing 
the exposure modes (b) and (c), as will be seen. 
In FIG. 3 it can be seen that the channel 6 takes the place of channel 7 of 
FIG. 1 (while the perpendicular channel 6 of FIG. 1 is not used here). The 
first exit beam 16, for channel 5, is the same as in the first embodiment; 
but the second beam 14 now serves either a film camera or a spot camera, 
as shown by the use of both numerals 9 and 10 at the optics 13. FIG. 3 is 
simpler than FIG. 1 owing to the omission of the omitted parts 7, 21, 22, 
23 and 25 (of the first embodiment). The slit mirror 12 has only one 
non-reflecting area, 15, the mirror or prism 17 performing the beam 
diversion with its surface perpendicular to the main surface of the slit 
mirror 12. 
It will be understood from the foregoing that in FIGS. 3, 4 the two 
channels 5, 6 are displaced by 180.degree. degrees with respect to each 
other (as against the 90.degree. arrangement of the three channels in 
FIGS. 1, 2). Owing to the somewhat different optical conditions, the 
exposure mode (b), (c) allows more light to pass toward channel 6 than in 
the three-channel embodiment, namely about 90% (as against 80%), well 
suitable for either film or spot exposures to be taken by the aid of the 
inventive X-ray light divider. 
The optional light gate 24 (there being no need for a second such gate), 
pivotable together with the mirror system 12, 17, again eliminates 
undesirable portions of the beam 16, as was described earlier. 
The system can be pivoted by 180.degree. about the axis 20, out of the 
illustrated position, to bring the optics in a condition required for 
operational mode (a), in which 90% of the light is available (as against 
80% of the first embodiment), in a manner similar to that just described 
for the combined mode (b), (c). 
It is characteristic for both exemplary light dividers that a slit-type 
special mirror system is provided, with two or three light channels, the 
system being disposed at 45.degree. with respect to the longitudinal 
optical axis, the slit mirror having a non-transparent metallization with 
one or two non-metallized areas or gaps therein, with areas that 
correspond to the required divisional aratios, there being similarly 
non-transparent mirrors or reflecting prisms behind the gaps. Depending on 
the embodiment, the system can be pivoted by 90 or 180 degrees about a 
suitable axis. 
There is preferably one gap for each additional channel and mirror, in 
association with the basic slit mirror, with optional light gates for 
limiting the light beams and throttling undesirable areas thereof. 
The present invention is more efficient than other solutions where light 
division is accomplished with light-transmitting mirrors and the like. and 
also ensures the divisional ratio to be accomplished without any 
limitation. In each of the operational modes, it is still possible to 
observe the exposure by the aid of conventional transillumination. 
The described characteristics of the inventive dividers can be applied and 
used independently of other particulars, for example mechanical, 
electrical or pneumatic controls and movements of the divider are equally 
possible. 
Any image advancement can be used for purposes of image pick-up or 
freezing. The ratio of the image division can be chosen at will, without 
any limitations, and the light gates which pivot together with the mirror 
system ensure uniform light distribution over the entire image areas. 
Either of the exposure modes can be accompanied by transillumination, on 
any one of the light channels. The rotational axis of the mirror system, 
substantially in the area of the longitudinal optical axis of the 
arrangement, makes for a reasonable space exploitation since the attached 
cameras do not increase the length of the arrangement. 
The inventive slit mirror that has a non-transparent metallization thereon 
offers substantial advantages in quality, structure, technology as well as 
economy. 
It is nowadays possible to achieve reflections exceeding 90% when using 
modern metallized mirrors; the divisional ratio is easily calculated; such 
mirrors are cheaper and more economical to manufacture than partly 
transparent mirrors of the earlier types. Optics are nowadays designed by 
computerized procedures, which also allows the locations of the 
non-reflecting, transparent areas to be ideally determined within wide 
ranges, thereby dispensing with the need for dividing the entire extent of 
the light beam. 
Those skilled in the prior art will understand that various departures 
from, modifications in and/or additions to the disclosed two exemplary 
light divider embodiments are possible within the spirit and scope of the 
present invention.