CT systems with oblique image planes

Details CT systems with oblique image planes CT systems with oblique image planes

1999-10-18

2001-01-23

Bruce, David V. (Department: 2876)

X-ray or gamma ray systems or devices

Specific application

Computerized tomography

C378S015000, C378S017000, C378S094000

Reexamination Certificate

active

06178220

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to computerized tomographic (CT) imaging, and specifically to methods of reconstructing CT images along oblique image planes.
BACKGROUND OF THE INVENTION
CT scanners known in the art typically produce a plurality of parallel, planar image slices. The slice planes are generally defined by the plane of revolution of an X-ray tube, which is mounted on an annular gantry, so as to revolve about a subject being imaged. The subject lies on a bed, which is translated through the gantry along a scan axis. An array of X-ray detectors on the opposite side of the subject from the X-ray tube receives radiation transmitted through the subject. Each of the detectors generates signals proportional to the attenuated X-ray flux incident thereon. These signals are pre-processed to produce attenuation data, which are filtered and back-projected to determine CT values, representing image data, at a plurality of points in each of the plurality of planar image slices. These slices, which are located at a corresponding plurality of mutually-spaced axial positions, are taken together to provide a three-dimensional image of all or a part of the subject's body.
Usually the scan axis is approximately parallel to the long axis of the subject's body and perpendicular to the plane of revolution of the tube, so that the image slices represent a series of axial cross-sections through the body. Such slices are known as “axial slices.” Axial slices commonly have a relatively high image resolution, for example 1 mm or less, within the plane of each slice, but a poorer resolution in the axial dimension, for example about 5 mm. This axial resolution is known as the slice “thickness.” Typically the spacing between one axial slice and the next is set to be approximately equal to the slice thickness.
In some cases, however, a physician examining the subject wishes to observe oblique. rather than axial, image slices, intersecting the body along planes that are angled with respect to the body's long axis. Several methods are known in the art for enabling such oblique slices to be viewed.
In some CT scanners, oblique image slice data are captured by angling the bed relative to the plane of revolution of the tube, by swiveling the bed and/or by tilting the tube's plane of revolution. The mechanisms required to implement and control the tilt and swivel capabilities, however, add substantially to the cost of the CT scanner. Furthermore, mechanical and other practical considerations limit the tilt and swivel angles to no more than about 30°, so that more oblique image slices, such as sagittal or coronal slices through the subject's body, cannot be directly produced.
Alternatively, an oblique image slice may be reconstructed by interpolation of the CT values in the original axial image slices. Such interpolative methods are well known in the art. as described, for example, in U.S. Pat. No. 4,674,046, to Ozeki et al., which is incorporated herein by reference. To view an oblique image slice according to this method, a user of a CT system, such as a physician, must generally operate the system first to acquire and display a full series of axial images, covering all or at least a substantial portion of the subject's body. Only afterwards may the user input to the system the position and orientation of the desired oblique slice.
Each oblique slice to be reconstructed in this manner intersects a number of the axial slices. For each of a plurality of points in the oblique slice, an interpolated CT value is found by taking a weighted sum of the CT values at a group of neighboring points in one or more of the original axial image slices. When using this method, typically only the CT values are stored in computer memory, while the attenuation data that were used to derive the CT values are deleted in order to conserve memory space.
Derivation of oblique slices by interpolation of axial images has several serious drawbacks. Interpolation of the CT values inevitably leads to a loss of resolution in the oblique image slice, since the axial resolution of the data is low. The interpolated oblique image slices generally appear to have poorer image quality, particularly higher noise level, and may exhibit artifacts, such as stair-step effects. Furthermore, the interpolation operation is computation-intensive and, consequently, time-consuming, and requires a very large computer memory.
SUMMARY OF THE INVENTION
It is an object of the present-invention to provide methods for reconstructing oblique CT image slices rapidly and with improved image quality.
It is another object of the present invention to provide methods for reconstructing oblique CT image slices at substantially any desired slice angle, without the necessity of introducing swivel or tilt into the CT system.
In one aspect of the present invention, CT images are directly reconstructed along sagittal and coronal planes, for example, along sagittal and coronal cuts through the spinal cord.
In another aspect of the present invention, CT images are reconstructed along non-planar cuts through the body of a subject, for example, along cuts that follow anatomical features, such as the spinal cord or major blood vessels.
In yet another aspect of the present invention, the thickness of each image slice, i.e., the resolution of the slice in a direction perpendicular to the slice plane, is set to substantially any desired value, within geometrical limits of the CT scanner used to acquire the attenuation data.
In still another aspect of the present invention, multiple oblique slices are reconstructed having differing slice thickness, for example, to provide a CT image of the head of a subject including multiple slices of varying resolution from a single scan.
It is yet a further object of some aspects of the present invention to provide methods for reconstruction of oblique CT image slices directly from X-ray attenuation data, without first back-projecting the data to obtain CT values in full axial image slices, thus reducing the computing time needed and the consumption of film involved in obtaining desired oblique slice images.
Still another object of some aspects of the present invention is to allow a user of a CT system to specify one or more desired oblique image slices before scanning the body of a subject, whereupon acquisition and processing of X-ray attenuation data by the system are optimized to produce the oblique slice with suitable resolution while minimizing radiation dosage to the subject and scanning and computing time.
In one aspect of the present invention, the user may specify, a non-planar cut through the body, for example, a cut that follows the spinal cord.
In another aspect of the present invention, the user may specify a plurality of non-parallel oblique slices, for example, so as to image one or more disc spaces between the subject's vertebrae. One or several of the plurality of slices pass through or are adjacent to each of the one or more disc spaces. The slices are oriented so that the plane of each slice is substantially perpendicular to the axis of the subject's spine at the disc space where the slice is located.
It is an additional object of some aspects of the present invention to provide methods for reconstructing oblique slices directly from X-ray attenuation data acquired by a spiral-scan CT system.
In preferred embodiments of the present invention, a spiral-scan CT scanner comprises an X-ray tube, mounted to revolve on an annular gantry about a bed on which a subject lies. and a detector array. The bed is advanced through the gantry along a translation axis that is generally parallel to the long axis of the subject's body. The X-ray tube thus describes a (generally helical trajectory about the subject's body and irradiates the subject from multiple positions, or “views,” along this trajectory. Preferably, the translation axis is substantially perpendicular to a plane of revolution of the X-ray tube, although it will be appreciated that the princi

Affiliated with

Also associated with

Rating

CT systems with oblique image planes does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with CT systems with oblique image planes, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and CT systems with oblique image planes will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2454941