X-ray or gamma ray systems or devices – Electronic circuit – X-ray source power supply
Reexamination Certificate
1999-10-19
2001-09-25
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Electronic circuit
X-ray source power supply
C378S098700
Reexamination Certificate
active
06295336
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an x-ray examination apparatus comprising
an x-ray source for generating an x-ray image and
an image analysis system
for deriving brightness variations from the x-ray image, and
for deriving a dose control signal dependent on said brightness variations in order to control the x-ray source
2. Description of Related Art
Such an x-ray examination apparatus is known from German Offenlegungsschrift DE 43 28 784.
The image processor of the known x-ray examination apparatus is a temporal recursive filter which derives the processed image as a temporally filtered image from the x-ray image. The known x-ray examination apparatus comprises an image analysis system with a motion detection module for deriving brightness variations in the processed image which are due to motion in the processed image. In particular the motion detection module calculates these brightness variations as differences between brightness values at successive instants in time and in the same spatial position in the processed image. An amount of motion in the x-ray image is estimated from such differences between brightness values with the help of fuzzy logic rules. The motion in the processed image is motion in the temporally filtered image. The x-ray source of the known x-ray examination apparatus is adjusted on the basis of the amount of motion as estimated from the differences between brightness values. Notably, the x-ray source is adjusted to generate a high x-ray dose when the amount of motion is large and to generate a low-x-ray dose when the amount of motion is small.
The known x-ray examination apparatus employs a rather crude estimate of the amount of motion. As a consequence the x-ray source, in the known x-ray examination apparatus os adjusted rather inaccurately.
Citation of a reference herein, or throught this specification, is not to construed as an admission that such reference is prior art to the Applicants invention of the invention subsequently claimed.
An object of the invention is to provide an x-ray examination apparatus which can achieve more accurate adjustment of the x-ray source. A particular object of the invention is to provide an x-ray examination apparatus which can achieve accurate adjustment of the x-ray source which takes into account the amount of motion in the x-ray image more accurately for the adjustment of the x-ray source.
This object is achieved by an x-ray examination apparatus according to the invention which is characterized in that the image analysis system is arranged to
derive a distribution of said brightness variations and
derive the dose control signal from the distribution of brightness variations.
According to the invention, on the basis of the distribution of brightness variations it is determined to what extent the x-ray image is affected by noise and motion in the x-ray image. Local information, such as local brightness variations, is aggregated into a dose control signal that is an accurate and global i.e. a comprehensive representation of the amount of motion in the x-ray image. It has been found that brightness variations due to local image corruptions and brightness variations due to changes in significant areas of the x-ray image cause different distributions of brightness variations. The distribution of brightness variations notably allows corruptions of the x-ray image which do not substantially affect the diagnostic quality to be distinguished from image corruptions which deteriorate the diagnostic quality of the x-ray image. The diagnostic quality of the image is high when small details of little contrast are clearly visible in the image.
The dose control signal controls the x-ray source, in particular the dose control signal controls a high voltage supply for the x-ray source. On the basis of the dose control signal, the x-ray source is adjusted in such a manner that the x-ray dose is kept low when only insignificant image corruptions occur and the x-ray dose is set to a higher value when significant portions of the x-ray image are affected. The insignificant corruptions hardly affect the diagnostic quality of the x-ray image while significant corruptions seriously deteriorate the diagnostic quality. Notably when in the case of a low x-ray dose it appears that only insignificant image corruptions occur in the x-ray image, such isolated image corruptions are preferably reduced by filtering the x-ray image. Such isolated image corruptions, due to x-ray quantum noise, are preferably reduced by filtering rather than to avoid them by employing a higher x-ray dose. Insignificant image corruptions are, for example, caused by spurious isolated brightness variations or by small brightness variations. Significant image changes are caused, for example, by motion in the x-ray image, such motion may be due to a moving catheter, the beating of the patient's heart or the patient's respiratory motion. In areas where such a significant change occurs image corruptions due to, for example x-ray quantum noise cannot be removed by recursive filtering. This is because when if recursive filtering is applied to portions of the x-ray image containing a significant amount of motion, a series of after-images of the moving portion is generated. Such a series of after-images gives the impression of the moving portion having a tail of after-images.
The x-ray dose can be adjusted by adjusting the energy and/or the intensity of the x-rays emitted by the x-ray source.
These and other aspects of the invention will be elucidated with reference to the embodiments defined in the dependent Claims.
In a preferred embodiment of an x-ray examination apparatus according to the invention, the distribution of brightness variations is derived from a processed image rather than directly from the x-ray image itself. The image processing may involve recursive temporal filtering or spatial filtering of the brightness values of the x-ray image. In particular, the image processing involves adaptive recursive temporal filtering which is adjusted in dependence on an amount of motion in the x-ray image. The x-ray dose is controlled on the basis of the processed image, because the dose control signal is derived from a distribution of brightness variations in the processed image. Thus it is achieved that variations or changes in the image quality due to the processing are taken into account for the adjustment of the x-ray dose. Accurate adjustment of the x-ray dose is achieved; the x-ray dose is notably suitable for realizing a processed image with a high diagnostic quality, and a comparatively low x-ray dose is used. The processed image is displayed and used as a technical aid for making a diagnosis.
In a further preferred embodiment of the x-ray examination apparatus according to the invention, the brightness variations are derived from a comparison between previous brightness values of the processed image and present brightness values of the x-ray image. Differences between corresponding previous brightness values of the processed, i.e. filtered, image and present brightness values of the x-ray image notably represent mainly changes in the x-ray image due to motion when such differences are of large magnitude. Differences of small magnitude, however, are substantially due to small variations caused by x-ray quantum noise. Notably, motion in the image usually extends over a rather large number of pixels and hence results in brightness variations of about the same magnitude in many pixels, whereas isolated brightness variations are likely to be due to noise.
In a further preferred embodiment of an x-ray examination apparatus according to the invention, the distribution of brightness variations is formed on the basis of a motion quantity which is a function of the brightness variations. Thus the distribution is in fact formed from values of the motion quantity. The motion quantity is a decreasing function of the brightness variations. Preferably, the motion quantity has a gradual threshold in that for relatively large
Aach Til
Kunz Dietmar W.
Kiknadze Irakli
Kim Robert H.
U.S. Philips Corporation
Vodopia John F.
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