X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
2002-09-26
2003-09-30
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Absorption
C378S004000
Reexamination Certificate
active
06628749
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to computed radiography (CR) imaging, and more particularly, to systems and methods for intensity correction of under-exposed regions within CR images using nonlinear enhancement and/or linear transformation techniques.
BACKGROUND
In computed radiography (CR), multiple cassettes containing storage phosphor plates may be positioned together with a certain amount of overlap between neighboring cassettes, so that anatomy larger than the size of a single plate can be imaged.
FIG. 1
illustrates a method for acquiring CR images using multiple cassettes. An object
10
(e.g. person's leg, as shown) to be imaged is positioned within a field of view between a x-ray source
11
and multiple image-recording cassettes
12
a
,
12
b
, and
12
c
. Each of the cassettes
12
a-c
are shorter than the length of the object
10
. The image recording cassettes overlap one another with each cassette acquiring a high resolution image of a portion of the object
10
to ensure the object
10
is entirely recorded. The CR images of each cassette are then combined into a mosaic image. Advantages of this kind of image acquisition, include, for example, no artifacts caused by body motion and a perfect alignment between successive images.
There are known methods for composing a mosaic image (i.e. seamlessly combining individual CR images). For instance, one method is based on cross-correlation techniques, as disclosed in U.S. Pat. No. 6,101,238, entitled “System for generating a compound x-ray image for diagnosis,” which issued August 2000. Another method is based on reference grid lines, as disclosed in U.S. Pat. No. 5,986,279, issued Nov. 16, 1999, entitled “Method of recording and reading a radiation image of an elongate body”. These conventional methods, however, generate artifacts in the CR mosaic image composition.
More specifically,
FIG. 2
illustrates how artifacts are generated in a mosaic CR image using conventional imaging methods. In
FIG. 2
, two overlapping cassettes
12
a
and
12
b
are shown, which cause an under-exposed region
15
within the image captured on cassette
12
b
. More specifically, since the two neighboring cassettes
12
a
and
12
b
are overlapped, with cassette
12
b
lying behind cassette
12
a
when viewed from the x-ray source, an under-exposed region
15
, or what is referred to herein as “white band” region, is formed in the image captured on cassette
12
b
. The overlapped region in the underlying cassette
12
b
is less exposed thereby generating an under-exposed region
15
(or white band) in the image of the cassette
12
b
. The white band
15
in the image is under-exposed and not as defined as a normal exposure region
17
.
In addition, due to the presence of a thick metal edge
16
of cassette
12
a
, the portion of the under-exposed region
15
of cassette
12
b
corresponding to the metal edge
16
of cassette
12
a
appears in the mosaic image
13
as an artifact
14
, or white strip.
The presence of under-exposed regions within a CR image not only cause visual disturbances for the examining physicians, but also may hide important diagnostic information. Thus, it is very desirable to provide a method to regulate the intensities of the under-exposed image regions so that the under-exposed regions may appear equally definite and clear as other parts of the image. Such a method would ensure that important anatomies in the under-exposed regions can be brought into better visibility for diagnosis.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an automatic method for correcting the image intensity of under-exposed regions (or “white band” regions) within a CR image, so that artifacts can be removed or reduced from CR images without introducing any additional distortion to the diagnostic information.
In one aspect of the invention, a method for generating a mosaic CR image comprises acquiring a set of CR images and processing each CR image to detect an under-exposed region (or “white band”) in the CR image. If an under-exposed region is detected, the CR image is separated into an under-exposed region and a normal exposure region. The image intensity of the under-exposed region is then adjusted to be substantially similar, or as close as possible, to the image intensity of the normal exposure region of the CR image using linear transformation techniques and/or nonlinear enhancement. The intensity corrected CR images are then combined in a mosaic image.
In another aspect of the invention, a method for adjusting the intensity of a computed radiography (CR) image comprises inputting a CR image and separating the CR image into a normal exposure region and an under-exposed region. The under-exposed region of the CR image is then enhanced. Preferably, the process of enhancing the under-exposed region comprises applying a non-linear transformation to the under-exposed region to increase the dynamic range of intensity variations of the under-exposed region. A set of intensity correction parameters is then determined using the enhanced under-exposed region and the normal exposure region. Preferably, the intensity correction parameters are determined by performing a linear regression on samples of equal size of the enhanced under-exposed region and the normal exposure region. The image intensity of the enhanced under-exposed region is then adjusted using the intensity correction parameters. Preferably, the image intensity adjustment process comprises applying a linear transformation to the enhanced under-exposed region using the determined intensity correction parameters.
In another aspect of the invention, a method for adjusting the image intensity of a computed radiography (CR) image comprises a process for automatically determining whether to enhance the under-exposed region, which prevents over-enhancement of the under-exposed region. The method comprises inputting a CR image and separating the CR image into a normal exposure region and an under-exposed region. The image intensity of the under-exposed region is enhanced, preferably using a non-linear transformation to increase the dynamic range of intensity variations of the under-exposed region. A first set of intensity correction parameters are determined using the enhanced under-exposed region and the normal exposure region, preferably by performing a linear regression of the enhanced under-exposed region and equal size sample of the normal exposure region. A second set of intensity correction parameters is further determined using the under-exposed region and the normal exposure region, preferably by performing a linear regression of equal size samples of the under-exposed region and of the normal exposure region. Then, the first and second set of intensity correction parameters are evaluated to select the set of intensity correction parameters that would provide optimal intensity correction. Preferably, the evaluation process comprises determining which set of parameters provide a minimum residual error, and then selecting the set of parameters for intensity correction which provides the minimal residual error. If the first set of intensity correction parameters is selected, the image intensity of the under-exposed region is adjusted preferably applying a linear transformation to the enhanced under-exposed region using the first set of intensity correction parameters. If the second set of intensity correction parameters is selected, the image intensity of the under-exposed region is adjusted preferably by applying a linear transformation to the under-exposed region using the second set of intensity correction parameters.
These and aspects, objects, features and advantages of the present invention will be described or become apparent from the following detailed description of the preferred embodiments, which is to be read in connection with the accompanying drawings.
REFERENCES:
patent: 5099505 (1992-03-01), Seppi et al.
patent: 5168532 (1992-12-01), Seppi et al.
patent: 5986279 (1999-11-01), Dewaele
patent: 6101238 (2000-08-0
Novak Carol
Qian Jianzhong
Schramm Helmuth
Wei Guo-Qing
Bruce David V.
F. Chau & Associates LLP
Paschburg Donald B.
Siemens Corporate Research Inc.
LandOfFree
Systems and methods for intensity correction in CR (computed... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Systems and methods for intensity correction in CR (computed..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Systems and methods for intensity correction in CR (computed... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3108974