X-ray or gamma ray systems or devices – Electronic circuit – With display or signaling
Reexamination Certificate
1999-12-22
2001-12-11
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Electronic circuit
With display or signaling
C378S096000, C378S097000, C378S108000, C378S175000
Reexamination Certificate
active
06330302
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of forming an image of an exposed object.
The present invention also relates to a device for forming an image of an object, which device includes a source and an imaging device which is coupled to the source so as to produce the image.
A method and a device of this kind are known from EP-A-0 629 105. The cited document describes a device which includes a source, i.e. an X-ray source with an exposure control input, and an imaging device which includes an output which is connected to the exposure control input so as to form an image of the object. The image can be displayed on a display screen or monitor, for example, for medical examination purposes. During such examinations images can be formed of, for example, parts of the body or artificial parts (such as plates, screws, joints); the degree of radiation absorption then varies strongly within one and the same image. If in such cases the dynamic range of the imaging device is less than the intensity range of the image, the image quality will suffer, notably the contrast, in the parts of the image in which the radiation absorption is low or high. In addition to the local loss of quality in the image which is caused by a comparatively high noise level in parts with a high radiation absorption, the quality of the image as a whole is also degraded.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the invention to provide a method and a device in which the described image quality problems are mitigated by taking comparatively simple steps.
To this end, the method according to the invention is characterized in that images of at least a part of the object are formed with different exposure levels, the differently exposed images being combined so as to form the single image; the device according to the invention is characterized in that the imaging device is arranged to form images of at least a part of the object with different exposure levels, and that the imaging device is provided with an image processor in which the differently exposed images are combined so as to form the single image.
It is to be noted that EP-A-0 655 861 discloses an image composition method and device in which substantially circular and spatially shifted images of an elongate object are merged so as to form an assembled image of the object. However, the cited document concerns neither the formation of images with different exposure levels nor the combination of such differently exposed images so as to form a single image.
The advantage of the method and the device according to the invention resides in the fact that, using a minimum of investments in hardware, software or control operations, high quality, high-contrast detail information with a large dynamic range can be achieved in a combined image by means of a device which has a limited dynamic range only. The detail information thus obtained has a brightness quality and a detail contrast which are comparable to those of an image obtained by means of a device which has a much larger dynamic range and hence is more complex and expensive than the device according to the invention. Moreover, the perception of the image is enhanced because highly exposed regions, commonly occurring in prior images and extending to less exposed regions, no longer have a disturbing effect. Because of the absence of previously present saturation phenomena, due to highly absorbing, dark regions in the image, moreover, the signal-to-noise ratio in these regions is enhanced. Because the dynamic range of the combined image as a whole is also limited, the amplification in the video processor can be increased without adversely affecting the regions of low or high absorption in the images. This additionally leads to detail contrast enhancement upon display of the combined image.
A simple version of the method according to the invention which yields a significant improvement of the quality of the ultimate image is characterized in that the various exposure levels of the images are chosen in such a manner that they are compatible with the degrees of absorption of regions of the object to be imaged. This offers the advantage that the regions having a different radiation absorptivity, can be exposed, using correspondingly adapted different exposure levels of the images, in such a manner that an optimum quality in terms of detail contrast of the various regions is achieved in the ultimate combined image.
A further version of the method according to the invention is characterized in that the exposure levels of the images differ in that the periods of time during which the object is exposed by a source are different. The exposure times may overlap partly or not and may possibly commence at the same instant.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
An embodiment of the device according to the invention is characterized in that the imaging device includes an image pick-up device which is connected to the image processor, the image processor being provided with storage means for the storage of the respective differently exposed images. The advantage of this embodiment resides in the fact that the images stored in the storage means need not be processed in real time but can be processed at any convenient later instant.
A further embodiment of the device according to the invention is characterized in that the storage means are arranged to store two (dual-exposure) or more (multi-exposure) types of images. The storage means are arranged notably to store two types of images, that is to say a first type of “low-light” image, having pixel values between approximately ⅙ of the mean pixel value and this mean pixel value, and a second type of “high-light” image which has pixel values between this mean pixel value and approximately eight times this mean pixel value. Diagnostically relevant information is thus contained in the images, on the one hand information concerning shutters and wedges being excluded whereas on the other hand mainly direct radiation is excluded beyond 8 times the mean pixel value.
Another embodiment of the device according to the invention, which offers advantages in terms of signal-to-noise ratio and reproducibility because no system errors are introduced is characterized in that the image processor includes summing/stacking means for combining the respective images so as to form the single image by the summing/stacking of their pixels.
A further embodiment of the device according to the invention is characterized in that the source includes an exposure input which is connected to the exposure control circuit in order to realize pulsed control of the source. Pulsed operation of the source not only limits the radiation dose applied to the object but, in cases where a CCD camera is used in the image pick-up device, it also prevents an image read out after the pulse from being affected by the known smearing effect.
These and other aspects of the invention are apparent from and will be elucidated, by way of example, with reference to the embodiment described hereinafter and the accompanying diagrammatic drawing.
REFERENCES:
patent: 3854049 (1974-12-01), Mistretta et al.
patent: 3904874 (1975-09-01), Amtmann et al.
patent: 3974386 (1976-08-01), Mistretta et al.
patent: 4479231 (1984-10-01), Haendle et al.
patent: 5436952 (1995-07-01), Haendle et al.
patent: 5710801 (1998-01-01), Dillen et al.
patent: 0806175A2 (1997-11-01), None
Kim Robert H.
Thomas Courtney
U.S. Philips Corporation
Vodopia John F.
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