X-ray or gamma ray systems or devices – Photographic detector support – For plural films or plates
Reexamination Certificate
2002-10-10
2004-09-21
Bruce, David V (Department: 2882)
X-ray or gamma ray systems or devices
Photographic detector support
For plural films or plates
C378S062000
Reexamination Certificate
active
06793390
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to digital radiography, and in particular to the imaging of a long human body part, such as the spine or legs, using a storage phosphor-based computed radiography system.
BACKGROUND OF THE INVENTION
When a long segment of the human body is imaged using the conventional screen-film technique, special cassettes and films of extended length are used, such as 14″×36″ and 14″×51″. As medical institutions are migrating from analog screen-film systems to digital modalities, such as computed radiography (CR), these types of exams impose a significant challenge. This is because the size of digital detector is limited. For example, the largest CR storage phosphor cassette from several major CR vendors is limited to 14″×17″, which can only image a portion of the long body part at a time.
Several methods have been proposed to extend the CR imaging coverage by stacking several existing standard CR cassettes. European Patent Application 0919856A1 (also U.S. Pat. No. 6,273,606B1) discloses a way of overlapping several storage phosphor cassettes
101
adjacently. The cassettes can be in the alternating (FIG.
1
A), staircase-wise (FIG.
1
B), or oblique (
FIG. 1C
) arrangement. During the x-ray exposure, all the partially overlapping cassettes are exposed simultaneously, therefore each storage phosphor screen
102
that resides inside the corresponding cassette records a part of the image of the long body part. Similar approach is disclosed by Japanese Patent Application 2000250153A. European Patent Application 0866342A1 (also U.S. Pat. No. 5,986,279A) presents a method that is based on partially overlapping a plurality of storage phosphor screens for extended imaging coverage. The screens
102
can also be configured in the alternating (FIG.
1
D), staircase-wise (FIG.
1
E), or oblique (
FIG. 1F
) overlapping arrangement in a single elongated cassette
103
. Similar approaches are proposed in Japanese Patent Application 2000267210A and 2000241920A. Further, cassettes and screens can be used together in alternating arrangement as shown in
FIG. 1G
, the cassettes
101
and storage phosphor screens
102
are placed in a partially overlapping and alternating arrangement with the screens
102
always positioned in front of the cassettes
101
. This method eliminates the cassette shadow from the acquired images, and reduces the number of storage phosphor screens that need to be removed out of and to be replaced back into cassettes.
Because the phosphor screens are the fundamental imaging recording devices, no matter whether the screens are packaged within the individual cassette or not, the term “storage phosphor screen”, “phosphor screen”, or “screen” is used hereinafter to represent either the phosphor screen itself or the phosphor screen that is conveyed inside a cassette. Therefore the different scenarios in
FIG. 1
are reduced to alternating, staircase-wise, and oblique arrangements of overlapping phosphor screens, with the exception that the distance between the screen planes can vary for each scenario depending on if the screen(s) is conveyed inside the cassette or not.
A schematic view of how a patient radiographic image is acquired is shown in FIG.
2
. The patient (element
203
) is positioned between the x-ray source (element
201
) and a plurality of screens (element
205
). Any of the screen arrangement methods shown in
FIGS. 1A-1G
can be used for imaging. An optional anti-scatter grid (element
204
) can be placed between the patient and the screens. The grid can be either a stationary type or reciprocating type. During x-ray exposure, the x-rays can be collimated to minimize the radiation to the nondiagnostically relevant patient anatomy. After the x-ray generator is fired and the cassette is exposed, the image of the patient is recorded by the plurality of screens as latent radiographic signals. Each screen captures only a portion of the image of the patient. The screens are fed into a CR reader and the latent radiographic signals are converted to electronic images. The electronic image acquired from an individual screen will be referred to as a sub-image.
The sub-images acquired by the individual storage phosphor screens must be stitched together to create a composite full image. Information about the spatial order, orientation, and overlap arrangement of the phosphor screens used during x-ray exposure is required in order to stitch together the composite image. After x-ray exposure, the phosphor screens may be scanned in an arbitrary order in the CR reader. It is therefore necessary to rearrange the sequence of the scanned sub-images into the order corresponding to the physical setup used for image acquisition. It is also required that the overlap arrangement between consecutive screens be known exactly. For example, screens can overlap either on the top or on the bottom in cases of staircase-wise and oblique screen arrangements, and in the case of alternating screen arrangement, screens closer to the x-ray source overlap differently from those further away. A screen may be equivalently positioned for image capture in the landscape (horizontal) orientation with either of the two long dimensions facing up. Consequently, a scanned sub-image may be rotated 180° from an adjacent sub-image. Detection of sub-image rotation is therefore necessary.
U.S. Pat. Nos. 4,613,983 and 5,833,607 each disclose methods to reconstruct a composite radiographic image from a set of sub-images. The former method is predicated on all sub-images being sequentially acquired and scanned in a predetermined spatial position and orientation. The latter method relies on a hardware position sensor to determine the relative position of each sub-image during acquisition. Neither of these two methods can be applied to the situation when the scanned sub-image sequence does not match the sequence used during acquisition. European Patent Application 0919858A1 (also U.S. Pat. No. 6,269,177B1) proposes a stitching method that utilizes a pattern of reference markers for the alignment of sub-images. However, this patent does not teach how the sub-images are ordered and requires that the sub-images are properly oriented prior to the stitching operation. Another stitching method was proposed by Wei et al. (“A new fully automatic method for CR image composition by white band detection and consistency rechecking,” Guo-Qing Wei, et al., Proceedings of SPIE Medical Imaging, 2001, vol. 4322, pp 1570-1573), to automatically stitch sub-images read from phosphor sheets in staircase-wise arrangement. However, this method assumes the sub-images are already pair-wise sequentially arranged before stitching.
Japanese Patent Application 2000258861A discloses a method that depends upon two different identification labels attached on every phosphor screen as auxiliary information for determining the orientation and location of the corresponding screen. Japanese Patent Application 2000232976A further teaches how the auxiliary information can be used in the stitching process. However, it is desirable not to use auxiliary information at all because doing so usually means either the standard cassette needs to be modified or the standard phosphor screen IDs need to be replaced, both of which may cause the cassette or screen incompatible for other general purposes.
It is therefore desirable to develop an automatic method to determine the spatial order, orientation, and overlap arrangement of the phosphor screens used in the x-ray exposure directly based on the acquired sub-images.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a solution to the problems discussed above.
According to a feature of the present invention, there is provided a method of a method for automatic arrangement determination of partial radiation images for reconstructing a stitched full image comprising: acquiring at least two radiation sub-images of an elongated object by means of corresponding overlapped radiation recording me
Foos David H.
Wang Xiao-hui
Bruce David V
Eastman Kodak Company
Noval William F.
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