X-ray or gamma ray systems or devices – Specific application – Tomography
Patent
1988-07-27
1990-07-03
Fields, Carolyn E.
X-ray or gamma ray systems or devices
Specific application
Tomography
378 62, 378 99, 358111, H05G 164
Patent
active
049397583
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an apparatus for the generation of tomographic X-ray images having enhanced contrast properties. The radiation of an X-ray source is received by a receiver after having passed the object and is converted by an image converter into electrical image signals original images correspond element-by-element to the X-ray radiation. Signals are conducted by an electronic circuit to an image display device, for example, a monitor. Mechanical means produce a tomographic relative movement between the receiver and the X-ray source during the radiation.
As it is well known, single body layers can be displayed by tomographic methods of X-ray images, the depth and thickness of each body layer being selectable all other body layers are displayed out of focus. Usually, layers parallel to the longitudinal axis of the body (object) are recorded. It is of disadvantage within the known recording processes that the interference of contrasts by shadows of other layers cannot be fully avoided. In other words, layers not belonging to the recordal plane, if the diameter of these shadows is bigger than the movment range of the mechanical system used for the tomographic movement are displayed. Even smaller disturbing shadows are displayed in the form of smudges distorting the real picture, if any part of the contour of the shadow presents a curve similar to that of the tomographic movement. Therefore, the contrast and the resolution of the images produced by the known apparatus are not satisfactory. There have been attempts to avoid these disadvantages by complicated tomographic movements, but the desired success has not been reached. In addition, the known methods suffer from the disadvantage that the X-ray doses is comparatively high. This occurs because, when recording, radiographic radiation rates must be used. These disadvantages also result for the known method of computer tomography, particularly, if a longitudinal section is calculated from a plurality of cross sections by means of computers. A common disadvantage of the computer tomograhpy systems is the relatively high cost. The method of the so-called "indirect tomography" uses images amplifiers in combination with usual tomographic systems in order to amplify the photo intensity of the signals before integration of the images on a film of reduced format. It has been shown that this affords no improvement of the image quality.
U.S. Pat. No. 4,079,417 and the document IEEE TRANSACTIONS ON BIOMEDICAL ENTINEERING (volume BME-26, No. 5, May 1979, pages 253-262) disclose a method for increasing the contrast between image elements laying between a selectable grey value range or, respectively, for contrast increase by flattening of the grey value histogramm. However, these methods are not satisfactory.
SUMMARY OF THE INVENTION
It is the object of the invention to avoid these disadvantages of known tomographic mehtods. It is a further object apparatus and to provide an apparatus for producing tomographic images with improved contrast properties with comparatively little effort, only small radiation amounts are required when recording the images. The present invention is an improvement which solves the above problems an electronic circuit includes an analyzing circuit for contrast comparision of a plurality of original images between image elements neighbouring each other and for statistic interception of the single contrast comparisons. The probability of occurence of contrasts of a certain sign between image elements neighbouring each other is determined in the analyzing circuit by this statistical interception a transformation circuit is provided for correction of original image signals dependent upon the signals obtained from the analyzing circuit. In a circuit image element pairs are selected for further contrast rise. The image element compares the signs of the contrasts corresponding to the signs of maximum probability. The output of this transformation circuit is connected to the image display device. It is, thus, poss
REFERENCES:
patent: 4079417 (1978-03-01), Scudder, III
patent: 4379329 (1983-04-01), Lemay
patent: 4516261 (1985-05-01), Harding et al.
"Image Enhancement of Conventional Transverse-Axial Tomagrams", IEEE Transactions on Biomedical Engineering, Strohbehn et al., vol. BME-26, No. 5, May 1979, pp. 253-262.
Art Bickford & Co.
Fields Carolyn E.
Porta David P.
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