X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
2002-05-01
2004-01-27
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S094000
Reexamination Certificate
active
06683933
ABSTRACT:
The present invention relates to a three-dimensional image display device for displaying the spatial distribution of the physical matter of a specimen in the form of a three-dimensional image.
BACKGROUND OF THE INVENTION
Since the advent of the potential for producing precision tomogram data showing the physical matter of a body using x-ray CT devices, it has become possible to render three-dimensional images using multiple sets of tomogram data captured from different cross-section positions. In particular, it has become possible to reconstitute three-dimensional images with even greater precision due to the recent use of helical scan x-ray CT devices and multi-beam x-ray CT devices.
In order to construct a precise three-dimensional image, it is desirable to make the cross-section images and cross-section image spacing as narrow as possible in terms of the cross-sections that are used in constructing the three-dimensional image. With recently implemented multi-beam x-ray CT devices, x-ray detectors are divided along the body axis of the specimen perpendicular to the cross-sections, and by this means, more narrow cross-section image spacing (slice gap) and thinner cross-section images (slice width) have been achieved relative to conventional x-ray CT devices.
When using image data having narrow cross section gaps and cross section thicknesses captured using multi-beam x-ray CT devices, it is possible to produce three-dimensional images that are more detailed than those obtained using image data captured with a conventional x-ray CT device. For this reason, the range of diagnostic use of three-dimensional images produced using x-ray CT image data is greatly increased, and the technology is being used towards a wider variety of ends.
With multi-beam x-ray CT devices, it is possible to capture image data with thin cross-sections and narrow cross-section image gaps more rapidly than with conventional x-ray CT devices. However, the clinical requirement in terms of length along the axis of a body is the same as in the past, so the number of image data slices or image data volume is greatly increased.
With conventional x-ray CT devices, the number of image data slices captured in a single investigation is in the range of a few tens of slices. In general, the image is imaged on film using a multiformat camera, and this film is then generally used for observation or reading. However, with multi-beam x-ray CT devices, hundreds of cross-sectional images taken in a single investigation are used in the reproduction of an image, and so imaging these on film with a multiformat camera, and selecting them and observing or reading them is problematic. In light of these considerations, the necessity of constructing a three-dimensional image, and then observing or reading this image is additionally increased.
Thus, multi-beam x-ray CT devices are revolutionary in that they allow the collection of image data having a thin cross-section and cross-section image gap in a shorter period of time than with conventional x-ray CT devices. However, because the number of slices of reconstructed images that are obtained is greatly increased, the load on a network that is transmitting this data is greatly increased, leading to the necessity of high-speed networks. Moreover, picture archival and communication systems (PACS) must also have increased capacity and speed in order to deal with the increase in data. Linked three-dimensional image display devices can receive large quantities of data in a short period of time, and so the necessity has developed for a high-performance system that performs image processing on large quantities of data in a short period of time.
In terms of three-dimensional display methods used with medical images, there are surface rendering techniques whereby the shape of the domain surface is displayed after extracting the domain surface of the object that constitutes the specimen, and volume rendering techniques that treat the specimen as a three-dimensional array of voxels having values corresponding to physical properties.
The surface rendering method creates a three-dimensional image of the object to be displayed by means of the following processes carried out on each of numerous x-ray CT images. 1) extraction of a domain containing an object by threshold value processing that designates an upper and lower limit for CT values held by an object, 2) extraction of the domain of a display object by means of eliminating domains not related to the display object from this domain, 3) extraction of the contour of this domain, 4) production of a solid using the respective contours obtained from multiple slices of the x-ray CT image, and 5) final shadowing and projection processing on the solid, thereby displaying the object to be displayed as a three-dimensional image.
Volume rendering techniques handle voxels possessing opacity and color data corresponding to the physical properties of a specimen as a three-dimensional array, and by carrying out shadowing and projection processing, referred to as ray casting, on this array, the physical properties of a specimen are displayed as a three-dimensional image. Because each voxel possesses color and opacity levels corresponding to the CT values thereof, it is possible to display domains having different CT values as different colors and opacities.
With volume rendering techniques, 1) a three-dimensional voxel array is constructed using x-ray CT image data from multiple slices, 2) the color and opacity are set for a range of CT values possessed by the object of interest, and 3) shadowing and imaging processing known as ray casting are carried out, thereby displaying the object of interest as a three-dimensional image. By setting different colors and opacities for different CT value ranges, it is possible to display domains having different CT values as different colors and opacities.
Although it is necessary to carry out domain extraction for each of the multiple x-ray CT image slices when using the surface rendering technique, a domain extraction operation is not necessary with the volume rendering technique. With the human body, there are many cases where CT values vary continuously in a boundary domain having two anatomical structures, and so the effect of eliminating the domain extraction work is significant. In addition, in comparison to surface rendering techniques, a more natural and smooth shading can be obtained for edges having boundaries that change abruptly.
With volume rendering techniques, three-dimensional voxel arrays constructed using x-ray CT image data are classified based on the object, and the anatomical structural elements of the specimen are classified based on CT values. Consequently, spatial domains having different CT values can be handled as different objects, but spatial domains having the same CT value, for example, are handled as a single object, even with objects that are in physically distinct locations. This is inconvenient for cases in which spatial domains having the same CT values are to be handled as two or more objects.
Thus, with volume rendering techniques, spatial domains having different CT values can be handled as different objects, but spatial domains having the same CT values are handled as a single object, even when the spatial domains having the same CT values are in physically distinct locations. Consequently, as with operation simulations, for example, when a spatial domain having the same physical properties is to be separated and handled as two or more objects, it is necessary to carry out image processing or manipulations in order to separate spatial domains.
FIG. 1
is a block diagram showing a conventional three-dimensional image display device and its network environment. The x-ray CT device
101
collects x-ray CT data from multiple cross-sections of a specimen, reconstructs them, and produces image data for the multiple cross-sections. The PACS server
102
is an image storage and supply system whereby data is collected and reconstructed image data is stored for multiple modalities includi
Saito Motoaki
Simha Vikram
Takahashi Kazuo
Zhao Tiecheng
Bruce David V.
TeraRecon, Inc.
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