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The invention relates to an X-ray fluoroscopy device, comprising an X-ray
source, an image intensifier, a television camera tube, and a television
monitor for the display of an image of a part of an object.
A device of this kind is used, for example, for routine examinations,
catherisation, surgery, neuroradiography and so on, where it is important
to obtain a high-quality image of, for example, a comparatively small
radiation zone within a larger anatomic unit. In modern versions, an X-ray
image intensifier tube and a television camera tube are coupled to a
fibre-optical window, so that a very sensitive high-quality image
formation can be realized. Notably when use is made of an X-ray
intensifier having a comparatively small entrance detection screen, which
is attractive in order to obtain high resolution, a drawback consists in
that the radiologist requires a comparatively long period of time for
localizing the radiation image displayed within the anatomic unit. Not
only is a substantial amount of time thus lost, but the patient is also
exposed to radiation for a period of time which is longer than required
for the actual image formation. For example, it has been found in practice
that when use is made of a 5 cm image intensifier entrance screen 75 to
90% of the overall exposure time is used for locating the image. In X-ray
exposures made, for example, by Bucky techniques, similar drawbacks occur
in that the localizing of a sub-zone to be irradiated must be performed by
means of a light viewfinder.
The invention has for its object to provide an X-ray fluorescopy device in
which the localization time can be substantially reduced to, for example,
only 10% of the total fluoroscopy time, while optimum image formation is
maintained. To this end, an X-ray fluoroscopy device of the described kind
in accordance with the invention is characterized in that the device
comprises a second television camera for the display of a readily
recognizable optical image of the object which covers the area to be
irradiated.
Because an optical image of the object to be examined is displayed in an
X-ray examining device in accordance with the invention by means of the
second television chain which acts as a viewfinder, the location of the
zone to be irradiated therein can be simply observed.
In a preferred embodiment in accordance with the invention, both images are
simultaneously displayed on the same monitor, so that the irradiation
field is directly localized in the object.
A further preferred embodiment comprises a monitor for the irradiation
image as well as a monitor for the optical image of the environment. On
the latter monitor the irradiation image or the contours thereof are also
displayed. Complete freedom then exists for manipulation with the
irradiation image displayed on the first monitor.
Some preferred embodiments in accordance with the invention will be
described in detail hereinafter with reference to the accompanying
diagrammatic drawing.
The drawing diagrammatically shows an X-ray fluoroscopy device, comprising
an X-ray tube 1, an X-ray image intensifier/television camera system 2, a
television monitor 3, and a second television camera 4. The embodiment
shown comprises only a single television monitor on which both images are
displayed in a superposed manner, an image thus being formed of, for
example, a hand within which the irradiation field is localized. It is
alternatively possible to use a separate television monitor for each of
the television cameras, for example, the contours of the irradiation field
of the first camera then being displayed on the monitor for the optical
image. The advantage thereof consists in that the image on the two
monitors can be individually adjusted, so that no information of the
fluoroscopy image is lost or becomes difficult to observe, this is liable
to occur when the two images are combined. The magnification, the contrast
etc. of particularly the fluoroscopy image can thus be freely adjusted on
the appropriate monitor, while a fixed indication of the irradiation field
on the other monitor is maintained. A customary collimator 5 is associated
with the X-ray source 1. An X-ray beam 7 emerges from a target anode of
the X-ray tube 6 and after having passed through a part of an object 8 is
incident on an entrance detection screen 9 of an image intensifier tube
10. Preferably the beam 7 has an angle of divergence such that it exactly
covers the effective part of the entrance detection screen. The entrance
detection screen of the image intensifier tube has a diameter of, for
example, 5 cm and preferably contains CsI activated by, for example, Th as
the luminescent material. In the described preferred embodiment, the
luminescent material is provided on a fibre-optical screen 11 which is
coupled to a (preferably also fibre-optical) entrance screen 12 of the
image intensifier tube 10. On the inner side, the entrance window supports
a photocathode 13 which preferably has a concave geometry, viewed from the
inside. An electron beam emitted by the photocathode is displayed on an
output luminescent screen 14, in this case reduced in diameter by only a
factor 2. A light image thus transmitted is projected directly onto a
target 16 of a television camera tube 17, again by means of a
fibre-optical coupling 15. An image signal derived from the camera tube 17
is displayed on the monitor 3. A customary scattered radiation grid 18 may
be arranged between the object 8 and the entrance screen/detection screen
9. A scattered radiation grid of this kind contains, for example, a heavy
metal for absorbing scattered radiation in the X-ray beam as well as
ferromagnetic material for shielding against disturbing magnetic fields. A
surrounding sleeve 19 may have a shielding function against electrical and
magnetic stray fields in addition to a structural function.
In a preferred embodiment in accordance with the invention, a mirror 21 is
arranged in the X-ray beam 7. The mirror 21 should have a high
transmission and a comparatively low dispersion for the X-radiation to be
used. This can be achieved, for example, by utilizing a foil of a
comparatively light element which is as thin as possible but which is
sufficiently rigid, said foil being suitably optically reflective on the
side facing the object.
Light reflected from the object 8 is projected onto an entrance screen 22
of the television camera 4 by the mirror 21. When an entrance optical
system 23 of this television camera is panoramic, i.e. the camera has a
comparatively large angle of aperture, the entire object or at least a
readily recognizable part thereof can be intercepted and displayed, in
this case again on the monitor 3. Alternatively this optical image can be
displayed on a separate monitor on which geometrical data of the
irradiation field are also projected. When the entrance optical system 23
of the camera 4 has a fixed or permanently adjustable focus, a fixed
relationship with the angle of aperture of the X-ray beam can be assured
as a result of the fixed image angle, so that the irradiation field is
always displayed as a fixed contour, normally a circle, on the monitor for
the optical image. The associated large depth of focus of the entrance
optical system is a favourable side-effect for imaging. By the addition of
an adjusting mechanism, adaptation to variations in the distance between
the X-ray source 6 and the object 8 or the entrance detection screen 9 can
be realized.
In a further preferred embodiment in accordance with the invention, the
X-ray fluoroscopy device is designed for Bucky-examination methods. In
known Bucky devices, use is made of a light viewfinder for localizing the
part of the body to be irradiated; this viewfinder is comparatively
expensive and involves rather difficult adjustment and also necessitates
marking of the patient. When the viewfinder is replaced by a second
television camera in accordance with the invention, the optical image can
again be displayed on a monitor together with the radiation field in order
to achieve fast and accurate localizing. Whenever a second monitor was
mentioned in the foregoing, use could also be made of a monitor on which a
partial image can be displayed, for example, as denoted by a partial image
24.
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