Image analysis – Applications – Biomedical applications
Reexamination Certificate
1994-12-14
2002-11-12
Chang, Jon (Department: 2623)
Image analysis
Applications
Biomedical applications
C382S240000, C382S299000
Reexamination Certificate
active
06480619
ABSTRACT:
FIELD OF THE INVENTION
The present invention is in the field of digital radiography. The invention more specifically relates to processing and display of radiographic images on a work station.
BACKGROUND OF THE INVENTION
In the field of digital radiography a wide variety of image acquisition techniques have been developed such as computerised tomography, nuclear magnetic resonance, ultrasound, detection of a radiation image by means of a CCD sensor or a video camera, radiographic film scanning etc.
In still another technique a radiation image, for example an image of x-rays transmitted by an object, is stored in a screen comprising a photostimulable phosphor such as one of the phosphors described in European patent publication 503 702 published on Sep. 9, 1992 and U.S. Ser. No. 07/842,603 filed Feb. 27, 1992, now U.S. Pat. No. 5,340,661 The technique for reading out the stored radiation image consists of scanning the screen with stimulating radiation, such as laser light of the appropriate wavelength, detecting the light emitted upon stimulation and converting the emitted light into an electric representation for example by means of a photomultiplier and digitizing the signal.
The digital images obtained by one of the acquisition techniques described hereinbefore can be transmitted to a graphic workstation for off-line processing or reprocessing and display on a CRT screen or the like.
The number of pixels in the digital radiographic image is commonly far greater than the!number of pixels that can be displayed on the display screen of the workstation.
For example, in case of a digital radiographic image obtained by read out of an exposed photostimulable phosphor screen, the number of pixels in the digital image representation typically amounts to 2000 times 2500 pixels or even more whereas commercially available display screens, for example CRT screens, can only display about 1000 by 1200 pixels. The number of pixels in the digital image representation is only indicative since the number of pixels in the pixel matrix may depend for example on the dimensions of the photostimulable phosphor screen and may for some dimensions exceed this number.
In any case, if a radiographic image is represented by a greater number of pixels than the number of pixels that can be displayed on the display device, the operator has to decide either to display only part of an image at a high resolution or to extract a low resolution representation of the entire image and to display said low resolution image representation.
The latter method is satisfactory in case an operator or radiologist only requires a first impression of the general outlook or content of an image and is not interested in every last detail.
However, when an image evaluation is to be performed on a displayed image, the operator will not be satisfied with a low resolution image representation.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide a method of displaying a radiographic image or at least part thereof on a display screen that can only display a smaller number of pixels than the number of pixels representing the radiographic image.
It is a further object or the invention to provide such a method that is fast and computationally inexpensive.
It is still a further object of the present invention to provide such a method for application on a digital representation of a radiographic image obtained by reading an image stored in a photo stimulable phosphor screen.
Still further objects will become apparent from the description hereinafter.
STATEMENT OF THE INVENTION
The objects of the present invention are achieved by a method of displaying on a display device a radiographic image represented by a digital signal representation comprising the steps of
1)—transforming said image into a pyramidal multiresolution representation which represents localised image detail at multiple scales,
2)—storing said multiresolution representation into a memory,
3)—defining an area of interest part of said radiographic image,
4)—retrieving the multiresolution representation at least of said area of interest from said memory,
5)—reconstructing said image area by applying the inverse of said transform to the retrieved multiresolution representation,
6)—displaying said reconstructed image area.
The method of the present invention provides that in case an image cannot be displayed in its entirety at full resolution on a display device because the resolution of the display device is not adequate, that in this case at least part of the image can be displayed at the resolution of the original image representation or even at higher resolution.
In the statement of the invention and the description hereinbelow interactions performed on an image or on a so-called detail image are to be interpreted as referring to interactions performed on the digital signal representation thereof.
In the context of the present application reference is often made to the monitor screen, being the area serving for visual display of an image.
It is known to the man skilled in the art that in case one of the nowadays frequently applied graphical user interfaces is used, the area on the screen available for image display is not the entire screen area because part of this screen area is occupied by icons, menus's and other indications that are used in selecting commands, operational modes etc.
So, when in this application reference is made to the monitor screen, this is meant to be interpreted as referring to the area of the monitor screen that is available for image display unless otherwise specified.
The first step of the method of the present invention is the decomposition of an image into a multiresolution pyramidal representation.
This kind of decomposition has been described extensively in our copending European application 91202079.9 filed on Aug. 14, 1991 and in U.S. Ser. No. 07/924,095 filed Aug. 5, 1992, now U.S. Pat. No. 5,350,914
In one embodiment the multi resolution representation is obtained as a sequence of detail images at multiple resolution levels and a residual image at a resolution level lower than the minimum of said multiple resolution levels.
The detail image at the finest resolution level is preferably obtained as the pixel wise difference between the original image and an image obtained by low pass filtering the original image. Successive coarser resolution level detail images are obtained by taking the pixelwise difference between two low pass filtered versions of the original image, the second having a smaller bandwidth than the former.
So, the detail images at successive coarser resolution levels are obtained as a result of K iterations of the following steps:
a) computing an approximation image at a next coarser level by applying a low pass filter to the approximation image corresponding to the current iteration, and subsampling the result in proportion to the reduction in spatial frequency bandwidth, using the original image as input to said low pass filter in the course of the first iteration;
b) computing a detail image as the pixelwise difference between the approximation image corresponding to the current iteration and the approximation image at a next coarser resolution level computed according to the method sub
4
a
; both images being brought into register by proper interpolation of the latter image,
The residual image is equal to the approximation image produced by the last iteration.
A preferred subsampling factor is 2, and preferably said low-pass filter has preferably an impulse response which approximates a two-dimensional gaussian distribution.
After decomposition the detail images and the residual image are stored in a storage device so that they can be used repeatedly without the need of repeating the image decomposition which is a processing step that demands a lot of computational effort.
After image decomposition the present invention comprises the definition of an area of interest part of the radiographic image.
An area of interest part of a radiographic image can be defined in several ways. It c
Buytaert Tom Guido
Vuylsteke Pieter Paul
Agfa-Gevaert
Chang Jon
Hoffman, Warnick & D'Alessandro LLC
Merecki John A.
LandOfFree
Method of displaying part of a radiographic image does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of displaying part of a radiographic image, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of displaying part of a radiographic image will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2988584