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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a medical examination system including
means for generating an internal image of a patient, and means for
generating an image of the external surface of the patient, and in
particular to such a system wherein signals from the latter means are used
to control selected components in the former means.
2. Description of the Prior Art
Medical examination systems are known wherein internal images of a patient
are produced using an x-ray diagnostics installation for positioning the
patient, even if the examination system is not itself used to generate an
x-ray image. Such systems include those for generating conventional x-ray
shadow images, computer tomography, magnetic resonance imaging, and
ultrasound imaging. The diagnosis made from an image assumes that a
precise and accurate positioning of the patient has been undertaken prior
to creating the image.
It is also known to produce x-ray transillumination images and surface
images of an examination subject using two video cameras.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a medical examination
system having means for generating an internal image of a patient, and
means for generating an external, surface image of the patient, wherein
the signals obtained from the surface scan of the patient are used to
control the positioning of selected components in the means for generating
the internal image.
The above and other objects are achieved in accordance with the principles
of the present invention in a medical examination system wherein the means
for generating an internal image has a memory to which the surface images
of the patient are supplied, obtained from the surface scan. The means for
generating an internal image also includes a comparator. The comparator
generates an output signal for driving an adjustable component, such as
the primary radiation diaphragm and/or the patient support. The output of
the comparator is dependent upon the difference between the stored image
of the patient, and a current patient image.
In addition to being used to obtain information about the patient for the
examining personnel to complete the internal image of the patient, the
surface image can also be used as a three-dimensional mask for
re-positioning the patient in routine follow-up examinations. In medical
technology, especially in radiology, such follow-up examinations are often
necessary, which require that the patient be placed in precisely the same
position as in a preceding examination. The surface image can be used to
adjust the patient and the components, such as the patient support, to
achieve such position repetition.
Precise reproduction of the same patient position as was used in a
preceding exposure is required, for example, in subsequent exposures which
are taken for the purpose of measuring the calcium content of bone
substance in osteoporosis. This is because the percentage change of
calcium content over time, i.e., over successive examinations, is on the
order of magnitude of the reproduction precision of the measuring
position. Although computer tomography x-ray images have been used as a
positioning aid for this purpose, the use of a surface image in accordance
with the principles of the present invention makes further improvement
possible.
Another problem in the generation of internal patient images is that of
blooming. Blooming occurs when the radiation is not properly gated onto
the subject. This has two disadvantages. The first disadvantage is that
the patient is exposed to higher than necessary radiation levels, due to
scattered radiation. The second disadvantage is a loss in image quality.
The surface image generated in accordance with the principals of the
present invention can be used to control the positioning of the primary
radiation diaphragm to achieve an exact gating of the x-ray beam, thereby
avoiding blooming.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block diagram of a medical examination system
constructed in accordance with the principles of the present invention.
FIG. 2 is a schematic block diagram of another embodiment of a medical
examination system constructed in accordance with the principles of the
present invention.
FIG. 3 is a schematic block diagram of a further embodiment of a medical
examination system constructed in accordance with the principles of the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in FIG. 1, a medical examination system constructed in accordance
with the principles of the present invention includes an x-ray source 1
which generates an x-ray beam which transirradiates a patient 2 (shown in
cross-section) through a primary radiation diaphragm 3. The patient 2 lies
on a patient support 4. Radiation attenuated by the patient 2 is incident
on the input screen of an x-ray image intensifier 5, having an output
screen connected to a video chain 6 in a known manner for producing x-ray
shadow images.
A patient surface scanner 7, which may be a laser scanner, is disposed
facing the patient 2 for producing a geometrical or topological scan of
the surface of the patient 2. Various types of surface scanners suitable
for use as the scanner 7 are known in the art. Electrical signals
corresponding to the shape of the surface of the patient are formed from
information identifying the scan direction and the scan angle.
A surface image generated by the scanner 7 is stored in a memory 8 of a
computer 9. The computer 9 includes a further memory 10, which receives
and stores the x-ray image from the video chain 6, via an
analog-to-digital converter 11. An image computer 12 produces a contour
image from the surface image in the memory 8, and supplies electrical
signals corresponding to this contour image to a comparator 13. The
comparator 13 also receives signals corresponding to the contours of the
x-ray image stored in the memory 10. The comparator 13 generates a
superposition image at its output 14. This superposition image permits a
better diagnosis than is possible only on the basis of the x-ray shadow
image from the video chain 6.
The video chain 6 generates an internal image of the patient. Such an image
may also be acquired using another type of image-generating system, for
example, a computer tomography system, a magnetic resonance imaging
system, or an ultrasound imaging system. The scanner 7, instead of being a
laser scanner, may be any suitable type of means for scanning the surface
of the patient, for example, a system which produces such a surface image
by acoustic emission.
A further embodiment of the system is shown in FIG. 2, wherein components
identical to those already described in FIG. 1 are provided with the same
reference symbols. In this embodiment, the memory 8 is contained in a
computer 9a, which also contains a memory 10a for a three-dimensional
surface image of the patient 2, obtained in an earlier examination. A
comparator 13a compares the current surface image in the memory 8 to the
earlier surface image in the memory 10a. The output of the comparator 13a
controls a motor 15 via an amplifier 6, which adjusts the position of the
patient support 4 until the two surface images coincide. At this point,
the patient 2 is positioned as he or she was positioned in the earlier
examination. Additionally, the computer 9a controls the size of the
opening of the primary radiation diaphragm 3 via an amplifier 17 so that
the x-ray beam from the x-ray source 1 is gated to be as small as possible
without degrading the resulting image, i.e., the boundary or size of the
radiation field is optimally approximated (matched) to the examined region
of the patient 2. Blooming is substantially prevented by such control.
In addition to controlling the position of the patient 2 on the basis of
the comparison of the current image in the memory 8 and the earlier image
in the memory 10a, the position of the patient 2 via the motor 15 can also
be undertaken by comparing the current image in the memory 8 with the
current image from the output of the analog-to-digital converter 11. In
this case, the motor 15 then adjusts the patient support 4 until the
current surface image in the memory 8 substantially coincides with the
earlier surface image in the memory 10a and, with respect to the contour
of the patient 2, substantially coincides with the current image from the
analog-to-digital converter 11.
It is also possible to combine the comparison of the surface images (old
and current) with the comparison of the x-ray images (old and current), as
is done in the embodiment of FIG. 3. In this embodiment, a further memory
10b is provided in a computer 9b for the earlier x-ray image. The outputs
of both of the comparators are supplied to an evaluation stage 20 which
supplies a positioning signal for the patient support 4 via the amplifier
16 and the motor 15, and a positioning signal for the primary radiation
diaphragm 3 via the amplifier 17. The evaluation stage 20 can provide a
drive signal based on various evaluation criteria. For example, it can be
determined in the evaluation circuit 20 which of the two comparisons has
resulted in a higher correlation value, and that comparison signal is then
assigned priority and is used exclusively, or primarily, to generate the
positioning signal. Another possibility is to use the mean value of both
comparison results. It is also possible to use different sets of criteria
for generating the respective drive signals, i.e., one set for generating
the patient support drive signal and another set for generating the
primary radiation diaphragm drive signal. Gating of the x-ray beam is
usually set on the basis of a desired x-ray attenuation value of the
tissue being examined. Control of the opening of the primary radiation
diaphragm 3 in the manner described above, can be undertaken by adjusting
the extent to which the contour of the patient is overlapped by the
radiation shadow of the primary radiation diaphragm 3.
As in the embodiment of FIG. 1, the embodiments shown in FIGS. 2 and 3 may
use other image generating systems, such as a magnetic resonance imaging
system or an ultrasound imaging system to generate the internal image of
the patient. Any suitable type of surface scanner can be used as the
surface scanner 7 in the embodiments of FIGS. 2 and 3 as well. In all of
the above embodiments, the computer 9, 9a or 9b receives electrical
signals at an input 18 which correspond to the apparatus geometry, which
are generated in a known manner, to assist in the exact positioning of the
patient 2.
The output signal from the computer 9, 9a or 9b may also be used to drive
an ink printer 19 for applying markings on the patient to identify a
field. Coordinates for setting the ink printer can be acquired from the
image from the analog-to-digital converter 11, and from the current
surface image in the image memory 8.
In addition to portraying a surface image, it is also possible in the
embodiment of FIG. 1 to portray the contour of the patient 2 in a defined
sectional plane or slice, for example, the section A--A shown in FIG. 1.
Both the three-dimensional surface image and the contour image can be
acquired by turning the surface scanner 7 relative to the patient 2.
In the embodiment of FIG. 1, the superposition of the surface image in the
memory 8 with the image of the memory 10 ensues with reference to the
contours of the patient 2. It is also possible to apply a suitable
reference member to the patient, for example, a lead block, which is
visible in both images. When superimposing the images, this reference
member is then brought into coincidence in the images.
A suitable system and technique for generating the surface images, which
can be used in the subject matter of the present application, is
described, for example, in the periodical "Automatisierungstechnische
Praxis," Vol. 2, 1988, at page 99.
Although modifications and changes may be suggested by those skilled in the
art, it is the intention of the inventors to embody within the patent
warranted hereon all changes and modifications as reasonably and properly
come within the scope of their contribution to the art.
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