Computed tomography scout images with depth information

This application claims the benefit of U.S. Provisional Application No. 60/114,334, filed Dec. 31, 1998, which is hereby incorporated by reference in its entirety.

This invention relates generally to computed tomography (CT) imaging and more particularly, to generating depth information scout 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.

In at least one known imaging system, a single scout image is generated by fixing the position of the x-ray source and translating the object in a z-axis direction. As a result, the scout image is similar to a plain radiography image. Using the scout image, an operator may identify anatomical landmarks so that proper techniques may be selected for different areas of the object. However, as a result of generating the scout image from a single projection angle, no depth information regarding the object anatomy is provided.

It is therefore seen to be desirable to provide a CT system which provides scout images having depth information of the object. It is also desirable to generate a shaded 3D image of the scanned object.

There is therefore provided, in one embodiment of the present invention, a method for generating depth information images of an object using a computed tomography system by performing multiple scout scans of the object, generating a scout image for each scout scan, and displaying the scout images from each scout scan at least once.

The above described embodiment and others described herein generate scout images having depth information of anatomical objects. In addition, 3D images are rapidly generated without increasing the cost of the system.

FIG. 1 is a pictorial view of a C-T imaging system.

FIG. 2 is a block schematic diagram of the system illustrated in FIG. 1 .

FIG. 3 is pictorial view of location information based on the intersection of two scout scans.

FIG. 4 is a flow chart illustrating a method for generating depth information from multiple scout images of an object acquired by a CT scanner according to the invention.

Referring to FIGS. 1 and 2, a computed tomograph (CT) imaging system 10 is shown as including a gantry 12 representative of a “third generation” CT scanner. Gantry 12 has an x-ray source 14 that projects a beam of x-rays 16 toward a detector array 18 on the opposite side of gantry 12 . Detector array 18 is formed by detector elements 20 which together sense the projected x-rays that pass through a medical patient 22 . Detector array 18 may be fabricated in a single slice or multi-slice configuration. Each detector element 20 produces an electrical signal that represents the intensity of an impinging x-ray beam and hence the attenuation of the beam as it passes through patient 22 . During a scan to acquire x-ray projection data, gantry 12 and the components mounted thereon rotate about a center of rotation 24 .

Rotation of gantry 12 and the operation of x-ray source 14 are governed by a control mechanism 26 of CT system 10 . Control mechanism 26 includes an x-ray controller 28 that provides power and timing signals to x-ray source 14 and a gantry motor controller 30 that controls the rotational speed and position of gantry 12 . A data acquisition system (DAS) 32 in control mechanism 26 samples analog data from detector elements 20 and converts the data to digital signals for subsequent processing. An image reconstructor 34 receives sampled and digitized x-ray data from DAS 32 and performs high speed image reconstruction. The reconstructed image is applied as an input to a computer 36 which stores the image in a mass storage device 38 .

Computer 36 also receives commands and scanning parameters from an operator via console 40 that has a keyboard. An associated cathode ray tube display 42 allows the operator to observe the reconstructed image and other data from computer 36 . The operator supplied commands and parameters are used by computer 36 to provide control signals and information to DAS 32 , x-ray controller 28 and gantry motor controller 30 . In addition, computer 36 operates a table motor controller 44 , which controls a motorized table 46 to position patient 22 in gantry 12 . Particularly, table 46 moves portions of patient 22 through gantry opening 48 .

In one embodiment of the present invention, system 10 performs a plurality of scout scans to generate depth information scout images of an object. More specifically, in order to generate at least one depth information scout image, system 10 performs each scout scan at a different projection angle with respect to the scanned object, i.e., patient 22 . Particularly, after patient 22 is positioned on table 46 , the position of gantry 12 is adjusted so that source 14 and detector array 18 are aligned along a first projection angle, or scout angle, with respect to patient 22 . As patient 22 is translated along a z-axis at a constant speed, x-ray beams 16 are emitted from the fixed position source 14 so that first scout, or projection, data is collected, or generated, from detector array 18 . At least a second scout scan is then performed by adjusting the position of x-ray source 14 with respect to patient 22 . Particularly, the position of gantry 12 is adjusted so that source 14 and detector array 18 are aligned along a second projection angle, or scout angle, with respect to patient 22 . As patient 22 is translated along the z-axis at a constant speed, x-ray beams 16 are emitted from source 14 so that second scout, or projection, data is collected from detector array 18 .

The obtained scout scan data is then processed to generate at least one scout image. More specifically and in one embodiment, first projection data is processed, in a manner known in the art, to generate a first scout image. Scout images for each additional scout scan are then generated from the respective scout scan data. Each scout scan image is displayed to provide depth information regarding the anatomy of patient 22 . Specifically, each scout scan is sequentially displayed, for example on display 42 , at least once. In one embodiment, where two scout images are generated, the first scout image is displayed and then the second image is displayed. To generate a 3D effect image, system 10 rapidly alternates between the two scout images. For example, each scout image may be displayed in a rapid cine sequence, i.e., display of first image, second image, first image, second image, etc. on display 42 so that a 3D visual effect is generated. In addition, where more than two scout images are generated, each image may be sequentially displayed on display 42 , or at least any two selected scan images may be displayed so that the 3D visual effect is generated.

As a result of alternating between each scout image, the scanned object will appear to rock, or shift, back and forth. As the scout images are displayed on display 42 , integration by the eyes of the operator provide relative spatial location information of different anatomical parts. This spatial location information represents the 3D visual effect image.

In one embodiment, to generate at least one depth information scout image, system 10 performs two scout scans. Specifically, a first scout scan is performed at a first projection angle and a second scout scan is performed at a second projection angle, wherein the first projection angle is not equal to the second projection angle. For example, by performing the first scout scan at a 70 degree projection angle and the second scout scan at a 90 degree projection angle, a depth information scout image may be generated. After processing the scan data to generate a first scout image and a second scout image, the scout images may be alternatingly displayed on display 42 . In one embodiment, the projection angles of each scout scan may be adjusted, or altered, so that the best visual effects are obtained. In addition, where more than two scout images are generated, each image may be sequentially displayed on display 42 , or at least any two selected scan images may be displayed.

In another embodiment, the scout scan data is processed to produce at least one depth dependent shading, or intensity, scout image. More specifically and as shown in FIG. 3, a 3D shaded image is generated using the data from the intersection of at least two scout scans. Particularly, using known bi-plane reconstruction algorithms, the shading of the 3D image is determined by the attenuation of the intersection of the scout scans. As a result, the 3D images may be used to identify the specific location of highly attenuating objects within the scanned object.

In another embodiment, stereo-pair views are used to communicate depth information. For example, two scout images generated after processing scan data taken at two different angles are placed side by side as a stereo-pair view (e.g. 7.5 centimeters apart). An experienced viewer looks straight ahead and allows the brain to fuse the two images without optical aids. This is often called stereoscopy.

In another embodiment, two scout images generated after processing the scan data taken at two different angles are overlaid and displayed simultaneously using different colors, for example, red and green or red and blue, for each image. To view the combined image and perceive depth information, the viewer uses glasses with, for example, a red filter in front of one eye and a green or blue filter in front of the other eye so that each eye sees only one of the scout images. The human brain sorts out the depth information.

In yet another embodiment, an algorithm performs the fusion of at least two .scout scans into one viewable scout image instead of the human brain. The algorithm identifies the same features in the different scans and estimates depth information from the parallax in the scout scans.

The above described system generates depth information scout images of anatomical objects. In addition, shaded 3D images are rapidly generated without increasing the cost of the system.

Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is intended by way of illustration and example only and is not to be taken by way of limitation. In addition, the CT system described herein is a “third generation” system in which both the x-ray source and detector rotate with the gantry. Many other CT systems including “fourth generation” systems wherein the detector is a full-ring stationary detector and only the x-ray source rotates with the gantry, may be used. Accordingly, the spirit and scope of the invention are to be limited only by the terms of the appended claims.