X-ray or gamma ray systems or devices – Auxiliary data acquisition or recording – Distance or dimension marker
Reexamination Certificate
1999-04-28
2001-08-21
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Auxiliary data acquisition or recording
Distance or dimension marker
C382S131000
Reexamination Certificate
active
06278767
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to computed tomography (CT) imaging and more particularly, to measuring curved distances of an object of interest utilizing maximum intensity projection (MIP) images.
In at least one known computed tomography (CT) imaging system configuration, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as the “imaging plane”. The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
In known third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. A group of x-ray attenuation measurements, i.e., projection data, from the detector array at one gantry angle is referred to as a “view”. A “scan” of the object comprises a set of views made at different gantry angles, or view angles, during one revolution of the x-ray source and detector. In an axial scan, the projection data is processed to construct an image that corresponds to a two dimensional slice taken through the object. One method for reconstructing an image from a set of projection data is referred to in the art as the filtered back projection technique. This process converts the attenuation measurements from a scan into integers called “CT numbers” or “Hounsfield units”, which are used to control the brightness of a corresponding pixel on a cathode ray tube display.
At least one known CT imaging system is configured to perform CT angiograghy (CTA). Compared to a conventional x-ray angiogram, the CTA system is advantageous as result of being non-invasive and more cost effective. In performing a CTA procedure, a set of CT images are first acquired and a Maximum Intensity Projection (MIP) image is generated to mimic the appearance of an x-ray angiogram. To measure the length of a section, or segment, of a vessel, several points are identified in the MIP image. A set of straight line distances between two points are then measured. For straight vessels that are perpendicular to the direction of projection, such a procedure yields satisfactory results. However, known CTA systems are unable to accurately measure a distance of a vessel segment being curved in a direction non-parallel to a MIP projection plane. As a result, known CTA systems typically underestimate the length of the vessel.
At least one known x-ray angiography system overcomes the difficultly of measuring curved vessels by placing a specially designed catheter inside the vessel. The catheter includes a series of uniformly spaced beads to provide distance markers on the angiography images. The distance between two points is determined by counting the number of beads in the x-ray image. However, as described above, such x-ray systems are invasive and very costly.
It would be desirable to provide an system which facilitates accurate measurement of vessel segment. It would also be desirable to provide such a system which facilitates retrospective selection of any vessel segment.
BRIEF SUMMARY OF THE INVENTION
These and other objects may be attained in a system which, in one embodiment, includes a measurement algorithm that accurately determines a length of at least a segment of a object of interest. Particularly and in one embodiment, the object of interest is a blood vessel having a curvature in a direction orthogonal to a projection plane.
Specifically, and in accordance with one embodiment of the present invention, a plurality of Maximum Intensity Projection (MIP) images are generated from reconstructed computed tomography (CT) images generated from projection data acquired in a scan. After identifying the object of interest, boundaries are determined for the object of interest utilizing a first CT image. Boundaries of the object of interest in neighboring CT images are then determined using the first image boundaries. Specifically and in one embodiment, the boundaries are determined as a location where the intensity of the image is within a pre-determined percentage of the difference between an object of interest intensity and a background intensity and the region determined by the boundaries is connected with the region from a previous slice. Utilizing the boundaries, a center of the object of interest is determined for each CT image.
Utilizing the determined center and boundaries for each image, a length of the object of interest is determined. Specifically, the length of the object of interest is determined by determining a distance between each adjacent image and then summing the resulting values. Particularly and in one embodiment, utilizing the determined center and boundaries in the adjacent images, the length of a segment of the object of interest is determined in accordance with:
&Dgr;={square root over (&Dgr;
x
2
+L +&Dgr;
y
2
+L +&Dgr;
z
2
+L )},
where:
&Dgr;x=a difference between centers of the object of interest in adjacent images in the x-direction;
&Dgr;y=a difference between centers of the object of interest in adjacent images in the y-direction; and
&Dgr;z=an interval, or spacing, between adjacent images in the z-direction.
In one embodiment, the system displays a plurality of distance indicators along with the image of the object of interest so that an operator is able to determine the length of the object of interest. Particularly, each distance indicator represents a pre-determined distance so that by counting the number of distance indicators the total length of the object of interest is quickly determined by the operator. In one embodiment, the intensity level of the distance indicators may be altered so the intensity of the indicators is greater than or less than the intensity of the object of interest.
The above described system facilitates accurate measurement of an object of interest. More specifically and in one embodiment, the above described system includes a measurement algorithm for determining the length of at least a segment of a blood vessel. In addition, such algorithm facilitates the retrospective selection of any object of interest by the operator.
REFERENCES:
patent: 4099880 (1978-07-01), Kano
patent: 5825908 (1998-10-01), Pieper et al.
Armstrong Teasdale LLP
Cabou Christian G.
General Electric Company
Kiknadze Irakli
Kim Robert H.
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