X-ray or gamma ray systems or devices – Electronic circuit – With display or signaling
Reexamination Certificate
1999-08-19
2001-05-08
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Electronic circuit
With display or signaling
C378S119000, C348S126000, C345S211000
Reexamination Certificate
active
06229875
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an X-ray examination apparatus which includes: an X-ray image means for providing an X-ray image composed of pixels, each having a grey value, and a brightness control system which is coupled to the X-ray image means in order to provide the X-ray image means with a brightness control signal of the X-ray image. The present invention also relates to a method for deriving a brightness control value from information contained in an X-ray image.
2. Description of Related Art
Such an apparatus and method are known from EP-A-0 629 105. This document discloses in particular an X-ray examination apparatus having an X-ray image means including an X-ray source, an X-ray image intensifier, a lens structure and a visible image processing device. An auxiliary light detection system of the apparatus forms a brightness control system and provides a brightness control signal which is fed back to the X-ray image means for X-ray image brightness control. In particular brightness and contrast of the X-ray image are being controlled by allowing only certain parts of the visible image to contribute to the brightness control. These parts are called measuring fields, which measuring fields are either selected manually, which is troublesome, or automatically. The prior art application discloses processor controlled automatic selection based on the brightness or grey values of parts in the visible image. The automatic selection raises additional problems in a situation wherein the image shows virtually unabsorbed, so called direct radiation and the object to be examined contains tissues having a low X-ray absorbing, for example lungs, such as in thorax (spine/lungs) images. Discrimination in such an image between parts of the body that may and parts that may not contribute to the brightness control in the X-ray examination apparatus is problematic, also because the position of the lungs in the image may vary.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide an apparatus and method providing an improved X-ray image quality and being capable of offering a physician additional possibilities for notably visual X-ray analyses of certain changes that appear in less absorbing body parts, such as in particular the lungs, without being bothered by negative influences of possible direct radiation in the image or other objects more absorbing than the lungs.
To this end, the apparatus according to the present invention is characterized in that the brightness control system comprises an image analyzing means for deriving the brightness control signal CS from a maximum over the number of times f(gr) that a grey value gr occurs in the image.
It has been found that the brightness control signal thus derived provides an advantageous, adequate indicator for discriminating between relevant sorts of information contained in the X-ray image when the aim is to derive brightness control information therefrom. Using either directly or indirectly the maximum of the number of times that a grey value occurs in the relevant visible image, the weak X-ray absorbing objects in the image can be given an optimum brightness despite their varying position in the image; this improves the image quality and makes these weak X-ray absorbing objects better discernable for medical examination purposes.
Moreover, said indicator indicates the transitional brightness area between the weak absorbing tissue of, for example, the lungs and said direct radiation. It is a further advantage of the apparatus according to the present invention that it is no longer necessary to manually specify a region of interest in the image since, given a tissue to be imaged, the apparatus provides optimized, automated brightness control information. Advantageously, the optimized brightness control signal can still be fine tuned in dependence on further particulars of the image or technical components or elements in the apparatus.
Accordingly, the method having easy and fast software implementation is characterized in that information wherefrom a brightness control value is derived includes data about a maximum in the frequency f(gr) of grey values gr occurring in the image.
One embodiment of the apparatus according to the invention, wherein the image analyzing means incorporate time averaging means for deriving the brightness control signal from a maximum over the time-averaged number of times that a grey value gr occurs in the X-ray image, provides the advantage that, despite a weak signal to noise ratio as well as jitter conditions in the available image signal, a stable brightness control signal can still be output.
With or without time averaging, in a further embodiment of the apparatus according to the invention the image analyzing means incorporate running averaging means for deriving the brightness control signal from a maximum over the running averaged number of times f(gr) that n possibly, but not necessarily, consecutive, either in time or in grey value, grey values gr occur in the image. This implementation also provides increased stability, because the noise is averaged by applying the running average operation across n generally digital grey values, wherein n is generally lower than about 15; in a practical, sufficiently reliable software implementation n equals 5.
In still a further embodiment of the apparatus according to the invention the image analyzing means comprises threshold means for deriving the brightness control signal from a percentage p of the maximum in the number of times a grey value occurs in the image. Advantageously the threshold means are arranged to allow the percentage p to be adjustable, preferably programmably adjustable, the percentage p being between 30% and 98%, preferably between 60% and 95%, and more preferably about 90% lower than said maximum number of times a grey value occurs in the image; the latter percentage has proven to be optimally suited for effective visualization of certain lung tissues.
The present invention mainly provides flexibility by being capable of empirically determining p and/or n in dependence on inter alia image parameters, such as image amplifier format or type, maximum number of available grey values, amount of or estimation of direct radiation present in the image, X-ray intensity (X-ray tube current), film type, X-ray frequency spectrum (X-ray tube high voltage) and/or object parameters such as expected absorption coefficients of imaged objects such as, for example lungs, brain etcetera. Preferably, well known Fuzzy Logic is used in order to provide a software implemented image brightness control based on Fuzzy Logic rules.
REFERENCES:
patent: 4236178 (1980-11-01), Tiemeijer
patent: 5461658 (1995-10-01), Joosten
patent: 5608453 (1997-03-01), Gerber et al.
patent: 5764225 (1998-06-01), Koshobu
patent: 0629105 (1994-12-01), None
patent: 0748148 (1996-12-01), None
patent: 0779770 (1997-06-01), None
Hobden Pamela R.
Kim Robert H.
U.S. Philips Corporation
Vodopia John F.
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