Flipping stereoscopic radiographs

Details Flipping stereoscopic radiographs Flipping stereoscopic radiographs

2000-10-05

2004-07-06

Boudreau, Leo (Department: 2621)

Image analysis

Applications

Biomedical applications

C382S154000, C378S041000

Reexamination Certificate

active

06760469

ABSTRACT:

BACKGROUND
1. Field of the Invention
This invention pertains in general to three-dimensional imaging and analysis. More specifically, the invention pertains to performing image processing on stereoscopic radiographs.
2. Background Art
Stereoscopic radiography is an effective method for obtaining three-dimensional (3-D) spatial information from two-dimensional (2-D) projection X-ray images without the need for tomographic reconstruction. In stereoscopic radiography, pairs of X-ray images of a subject exposed from slightly different positions are viewed as a 3-D image. The images can be viewed in 3-D by, for example, combining the pair of images into an anaglyph image or by rapidly alternating display of the images on a computer screen. To these ends, U.S. patent application Ser. No. 09/428,867, filed Oct. 27, 1999, now U.S. Pat. No. 6,317,481, entitled “Stereo X-ray Image Processing,” describes a technique for converting pairs of 2-D X-ray images into 3-D stereoscopic radiographs. Similarly, U.S. patent application Ser. No. 09/610,579, filed Jul. 5, 2000, now U.S. Pat. No. 6,317,481, entitled “Computer Assisted 2D Adjustment of Stereo X-Ray Images,” describes a technique for adjusting stereoscopic radiographs to correct for some vertical and/or horizontal distortions.
Alternatives to stereo radiography include magnetic resonance imaging (MRI), computed tomography (CT), and tomosynthetic reconstruction (TR). The first two of these techniques require expensive equipment and are very time consuming. The third technique produces images containing many artifacts, requires multiple images, and is also time consuming. Therefore, these alternatives are not as desirable as stereo radiography.
In chest radiography, radiologists, or other persons studying a radiographic image, strongly prefer to observe an image with the heart located at the right side of the image (i.e., as if the radiologist is looking at the subject from the front). This preference holds true even if the radiograph was taken from the back of the subject. A radiologist can easily manipulate a 2-D radiograph with the heart on the wrong side, such as a radiograph taken from the back of the subject, into the desired orientation by flipping the radiograph about its vertical axis.
However, such manipulations cannot be performed easily on stereoscopic radiographs. Simply flipping the original left and right images of the stereo pair distorts the 3-D effect by changing the apparent depth of the objects in the resulting stereoscopic image. Thus, the flipped 3-D image is generally unusable by a radiologist.
Therefore, there is a need in the art for a way to manipulate stereoscopic radiographs so that the radiographs can be placed in a desired orientation. The solution to this need will preferably allow a stereoscopic radiograph to be flipped about its vertical axis without introducing undesired distortions.
DISCLOSURE OF INVENTION
The above needs are met by a method, computer-readable medium, and graphics engine (
130
) for manipulating stereoscopic radiographs. A radiographic imaging system (
100
), such as an X-ray system, comprises an X-ray tube (
110
) (also referred to as a “camera”), a sensor plate (
120
), and a graphics engine (
130
). The tube (
110
) and the sensor plate (
120
) preferably rotate synchronously about the patient (or another subject or object being X-rayed).
In use, the sensor plate (
120
) and tube (
110
) are placed in the desired alignment relative to the patient. Then, at least two radiographic images of the patient are exposed from slightly different positions on the arc formed by rotating the sensor plate (
120
) and tube (
110
) system about the patient, or from other positions if the geometry of the system is different. The exposed images are either transmitted directly to the graphics engine (
130
), if a digital sensor plate is used, or converted into a digital format and then transmitted to the graphics engine.
The graphics engine (
130
) determines (
312
) the geometry of the radiographic system (
100
). In many instances, the geometry of the system (
100
) is known. If the geometry of the radiographic system (
100
) is unknown, however, the graphics engine (
130
) preferably recovers the geometry from the images. One embodiment of the present invention uses physical pointers, such as steel balls, placed around or inside the patient when the radiographic images are initially exposed in order to enable the graphics engine (
130
) to recover the system (
100
) geometry from the images.
If (
314
) the radiographic system has a C-arm (
140
) configuration, then the images in the stereoscopic pair are toed-in relative to each other. The toed-in nature of the images results in a curvature of the depth plane when the images are used as a stereo pair. Accordingly, the graphics engine (
130
) preferably converts (
316
) the toed-in images into a parallel geometry. This conversion places the images in the same plane, which is parallel to a base line between the two locations used to capture the image. The graphics engine (
130
) also preferably processes (
320
) the images to eliminate keystone distortion and moves (
321
) the images together in virtual space to define a screen parallax for the image. The “screen parallax” is the distance between two homologous points when the image is displayed on a screen. The amount of screen parallax determines the amount of depth in the 3-D image.
Assume that a radiologist desires to flip a stereoscopic image about its vertical axis. Simply flipping the images in the stereo pair distorts the depth of the objects in the resulting stereoscopic image. Instead of simply flipping the images, it is desirable to “go behind” the screen (
412
A) and look at the image from the back. In order to produce a stereoscopic image having this viewpoint, the graphics engine (
130
) preferably flips (
322
) the constituent images about the vertical axes and adjusts (
324
) the screen parallax of the resulting stereoscopic image. The graphics engine (
130
) preferably determines the proper screen parallax for the flipped image from the geometry of the radiographic system (
100
). An alternative embodiment of the present invention determines an area of interest in the unflipped stereoscopic image and adjusts (
324
) the screen parallax so that the area of interest is displayed at the level of the screen (
312
A) when the images are flipped.


REFERENCES:
patent: 5321447 (1994-06-01), Sander et al.
patent: 6108005 (2000-08-01), Starks et al.
patent: 6181768 (2001-01-01), Berliner
patent: 6381302 (2002-04-01), Berestov
patent: 6496598 (2002-12-01), Harman
Talukdar, A. et al., Modeling and Optimization of Rotational C-Arm Stereoscopic X-Ray Angiography,IEEE Transactions on Medical Imaging, vol. 18, No. 7, pp. 604-616 (Jul. 1999).
Woods, A. et al., Image Distortions in Stereoscopic Video Systems,SPIE, vol. 1915 Stereoscopic Displays and Applications IV, pp. 36-48 (1993).

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