Image analysis – Applications – Biomedical applications
Reexamination Certificate
1998-06-24
2001-07-17
Mancuso, Joseph (Department: 2621)
Image analysis
Applications
Biomedical applications
C382S217000, C250S334000
Reexamination Certificate
active
06263097
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an image processing method to find the symmetry line and orientation angle of a radiation image, such as a medical radiation image.
BACKGROUND OF THE INVENTION
One of the basic properties of shapes and objects is symmetry. The human body shows symmetry along an axis oriented from top to bottom.
Medical images originating from image acquisition modalities such as computed projection radiography show symmetry to a large extent for examination types of body parts which are essentially symmetric. Examples of such examination types are e.g. frontal skull, frontal spine, frontal thorax, frontal abdomen, frontal pelvis.
In U.S. Pat. No. 5,533,143 a method is disclosed for determining whether an image is symmetric or asymmetric. Image processing conditions are based on the judgment that the image is a frontal (symmetric) object image or a lateral (asymmetric) image.
The disclosed method is based on the assumption that the hypothetical symmetry axis is always fixed and coincides with a vertical center line passing through the center of the image. The method does not discriminate between vertical or horizontal symmetry.
By studying a large mixture of all symmetric examination types, it is observed that (1) the symmetry line in most cases does not coincide with the center line of the image, nor is its angle with respect to a perfectly vertical (or perfectly horizontal) line equal to zero and (2) horizontal symmetry occurs equally well as vertical symmetry.
The above-mentioned observations limit the accuracy and applicability of the prior art method disclosed in the above-mentioned patent.
In U.S. Pat. No. 4,903,310 and U.S. Pat. No. 4,951,201 various histogram based methods are proposed to discriminate between a frontal and a lateral body posture.
It is however not possible to decide by applying these methods whether the object is symmetrical and whether the object is positioned horizontally or vertically.
The above methods are thus not adequate.
Experience has learnt that radiologists prefer to examine radiographic images in standard viewing conditions, i.e. with the image displayed so that a symmetry axis in the image is substantially horizontally or vertically oriented.
OBJECT OF THE INVENTION
It is an object of the invention to provide a method of determining a symmetry line of a radiation image.
It is a further object of the invention to provide a method of determining an orientation angle associated with such a symmetry line.
It is still a further object to provide a method by means of which images can be provided having a symmetry axis directed in a predetermined orientation.
Further objects of the present will become apparent from the description hereafter.
SUMMARY OF THE INVENTION
The objects of the present invention are achieved by a method of determining a symmetry line in a radiation image represented by a raster of pixel values comprising the steps of
(i) calculating a symmetry point for each column (row) of said image,
(ii) interconnecting symmetry points calculated for each column (row).
The way in which (a) symmetry point(s) is calculated, is described further on.
The method of the present invention can be applied to a digital signal representation of a radiation image such as a medical X-ray image. But it can also be applied to other kinds of radiation images such as images originating from non-destructive testing (NDT) of objects by irradiation of these objects.
Collimation and direct exposure areas in the image need to be excluded from consideration since they are not necessarily present in the image in a symmetrical way. In European patent application 97201683.6 an ensemble of methods is disclosed to perform a raw segmentation of a radiation image into collimation areas (foreground), direct exposure areas (background) and diagnostic areas (body parts).
The method of the present invention can also be applied to each of the sub-images of a multiply exposed image.
The method of the present invention permits to compute a symmetry index for a horizontal and vertical direction in the image, and to classify the image as either horizontally or vertically oriented based on the horizontal and vertical symmetry index referred to further on.
The matrix of pixel values representing a radiation image can be obtained by means of a wide variety of image acquisition techniques.
In one example of an image acquisition technique, a radiation image which is temporarily stored in a photostimulable phosphor screen is read out by scanning the screen with stimulating radiation, detecting light emitted by the screen upon radiation and converting detected light into a digital signal representation.
However, other acquisition techniques may be envisaged.
REFERENCES:
patent: 4720870 (1988-01-01), Billiotte
patent: 4951201 (1990-08-01), Tanka
patent: 5421331 (1995-06-01), Devito
patent: 5502561 (1996-03-01), Hutchins et al.
patent: 5533143 (1996-07-01), Takeo
patent: 5790700 (1998-08-01), Saito
patent: 5818458 (1998-10-01), Sito
patent: 5877774 (1999-03-01), Saito
patent: 6019485 (2000-02-01), Winston et al.
“Symmetry-Based Recognition of Vechicle Rears” by A. Kuehnle; Pattern Recognition Letters, vol. 12, No. 4, Apr. 1, 1991. pp. 249-258, XP000206854.
AGFA-GEVAERT
Baker & Botts L.L.P.
Mancuso Joseph
Tabatabai A
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