Patent Application
20070100234
This invention relates generally to computed tomography (CT) imaging and more particularly, to tracking instruments during interventional CT Fluoroscopy.
In at least one known CT 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 display device.
To reduce the total scan time, a “helical” scan may be performed. To perform a “helical” scan, the patient is moved while the data for the prescribed number of slices is acquired. Such a system generates a single helix from a one fan beam helical scan. The helix mapped out by the fan beam yields projection data from which images in each prescribed slice may be reconstructed.
Reconstruction algorithms for helical scanning typically use helical weighting (“HW”) algorithms which weight the collected data as a function of view angle and detector channel index. Specifically, prior to filtered back projection, the data is weighted according to a helical weighting factor, which is a function of both the view angle and detector angle. As with underscan weighting, in a HW algorithm, projection data is filtered, weighted, and backprojected to generate each image.
In multi-slice CT fluoroscopy, a fan beam of x-rays is projected toward a detector that includes a plurality of rows of detector elements in the z-axis direction. Each row of detector elements is used to reconstruct an image of a target lying between the source of the x-ray beam and the detector. Any number of images may be combined to generate a volumetric image of the target and/or sequential frames of images to help, for example, in guiding a needle to a desired location within a patient. A frame, like a view, corresponds to a two dimensional slice taken through the imaged object. Particularly, projection data is processed at a frame rate to construct an image frame of the object.
In CT Fluoro systems, it is generally advantageous to increase the frame rate while minimizing image degradation. Increasing the frame rate provides advantages including, for example, that an operator physician is provided with more timely (or more up to date) information regarding the location of, for example, a biopsy needle. However, increasing the frame rate generally adversely affects minimizing image degradation. For example, an increase in the frequency that projection data is filtered, weighted and backprojected, tends to slow the frame rate. The frame rate is thus limited to the computational capabilities of the CT Fluoro system. As the number of acquired slices per gantry rotation offered in multi-slice CT systems increases, the user is unable to use all the information available. More specifically, in interventional CT procedures the user is challenged when attempting to monitor multi-slice scanners which are capable of presenting multiple images at frame rates often exceeding approximately 10 frames per second. With multi-slice CT Fluoro systems, one to three thick-slice summations of the available thinner axial slices can be presented as summed images, however, such a summation foregoes the potential resolution enhancement afforded by thin slice imaging. As a result, such summation may not provide the possible improved needle placement accuracy afforded by multi-slice scanners.
Additionally, the trajectory of the needle insertion during the interventional procedure (biopsy, drainage etc.) may be different from the axial plane such that in conventional CT single-slice interventional procedures, the needle insertion is generally limited to the image plane only and any Z direction needle position change requires patient table movement in the appropriate direction. The decision regarding the correct magnitude and direction of this movement requires experience and frequently involves a “trial and error” approach. Moreover, there is an added risk of moving the patient table and patient In and Out of the gantry aperture during the procedure while the needle remains inserted in the patient's body.
In one embodiment, an imaging system for displaying an instrument in a region of interest is provided. The imaging system includes a multi-slice detector, a processor coupled to the multi-slice detector, and a display configured to display reconstructed images. The processor is configured to receive a plurality of multi-slice scan data, identify at least a portion of an instrument in at least one slice of the plurality of multi-slice scan data, and display the identified instrument portion with an indicator associated with the at least one slice.
In another embodiment, a computer system is provided. The computer system is configured to receive a plurality of multi-slice scan data, and identify at least a portion of a needle-like instrument positioned in at least one slice of the multi-slice scan data with an indicator associated with the slice.
In yet another embodiment, a method of displaying an instrument in a region of interest is provided. The method includes associating an indicator including at least one of a color, a shading, and a pattern with each slice of a multi-slice image of a region of interest, identifying at least a portion of an instrument in at least one slice, and applying the indicator associated with the slice, to the identified instrument portion in that slice.
In still another embodiment, an imaging scanner is provided. The imaging scanner includes a data acquisition apparatus configured to acquire imaging data from a subject, a monitor configured to display images reconstructed from the acquired imaging data and a computer programmed to acquire multiple slices of imaging data from the subject having an intracorporeal device positioned therein, reconstruct a multi-slice image from the multiple slices of imaging data, and cause the monitor to display the multi-slice image at a real-time frame rate while preserving information of a position of the intracorporeal device contained in the multiple slices of imaging data for observation by a human observer.
In another embodiment, a method of tracking an invasive instrument relative to a target using an imaging system that includes a movable patient table and a multi-slice detector array to automatically move the scan plane of the imaging system within the Z coverage area of the multi-slice detector array is provided. The method includes determining an intracorporeal trajectory of the instrument, displaying a tip of the instrument in at least one of a plurality of adjacent slices, and translating a patient table when the tip reaches a substantial extent of the Z coverage area.
As used herein, an element or step recited in the singular and preceded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.
Also as used herein, the phrase, “reconstructing an image” is not intended to exclude embodiments of the present invention in which data representing an image is generated but a viewable image is not. Therefore, as used herein the term, “Image,” broadly refers to both viewable images and data representing a viewable image. However, many embodiments generate (or are configured to generate) at least one viewable image. Additionally, although described in detail in a CT medical setting, it is contemplated that the benefits accrue to all imaging modalities including, for example, ultrasound, Magnetic Resonance Imaging, (MRI), Electron Beam CT (EBCT), Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT), and in both medical settings and non-medical settings such as an industrial setting or a transportation setting, such as, for example, but not limited to, a baggage scanning CT system for an airport or other transportation center.
Detector array 18 is formed by a plurality of detector rows (not shown) including a plurality of detector elements 20 which together sense the projected X-ray beams that pass through an object, such as a medical patient 22. Each detector element 20 produces an electrical signal that represents the intensity of an impinging radiation beam and hence the attenuation of the beam as it passes through object or patient 22. An imaging system 10 having a multi-slice detector 18 is capable of providing a plurality of images representative of a volume of object 22. Each image of the plurality of images corresponds to a separate “slice” of the volume. The “thickness” or aperture of the slice is dependent upon the thickness of the detector rows.
During a scan to acquire radiation projection data, gantry 12, and the components mounted thereon rotate about a center of rotation 24.
Rotation of gantry 12 and the operation of radiation source 14 are governed by a control mechanism 26 of CT system 10. Control mechanism 26 includes a radiation controller 28 that provides power and timing signals to radiation 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 radiation 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 display 42, for example, a monitor, 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, radiation 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, computer 36 includes a device 50, for example, a floppy disk drive or CD-ROM drive, for reading instructions and/or data from a computer-readable medium 52, such as a floppy disk or CD-ROM. In another embodiment, computer 36 executes instructions stored in firmware (not shown). Generally, a processor in at least one of DAS 32, reconstructor 34, and computer 36 shown in
In the exemplary embodiment, each thin slice of an n-slice multi-slice scanner is designated a specific indicator, such as a color, a shade, a pattern, or a texture that is chosen such that a natural continuum of n colors corresponds to the n detector rows. The selected continuum could be, for example, a heat spectrum, a rainbow, or other progression of colors. Similarly, a continuum of shading, patterns or textures may be associated with each detector row. Associating elements of the continuum is performed on a slice by slice basis, where segments or portions of the instrument that appear in the slice are assigned the appropriate element for the selected continuum. In one embodiment, for example, a rainbow spectrum is selected as the continuum for a color indicator for a biopsy needle instrument. In a rainbow spectrum the colors transition from red, orange, yellow, green, blue, indigo and violet. The colors are not discrete bands of color, rather the colors transition continually from violet to red. In the case where six slices are used to reconstruct the image of the region of interest, each slice is assigned a color based on the selected continuum. In the example of the rainbow spectrum, a first slice at one end of the region of interest is assigned red, an adjacent slice is assigned the color orange, the next adjacent slice is assigned the color yellow, and so on to the other end of the region of interest. A portion of the biopsy needle that is located in each slice is colorized the same color as the color assigned to the slice. Accordingly, a color, shade, pattern, or texture is associated 306 with each portion of the instrument and the slice in which the portion was positioned.
In the exemplary embodiment, an image of the region of interest is reconstructed using a plurality of the image slices from the multi-slice scan data. An image of the instrument, colorized in colors associated with each slice where the portion of the instrument was located is reconstructed. A combined image of multiple slices of the region of interest and the portions of the instrument associated with the slices is then displayed 308.
An image 428, reconstructed from the scan data associated with slice 406 includes an image portion 430 of needle 404. Portion 430 is colorized red, the color associated with the slice in which it is positioned. An image 432, reconstructed from the scan data associated with slice 410 includes an image portion 434 of needle 404. Portion 434 is colorized red-orange, the color associated with the slice in which it is positioned. Images 436 through 444 are likewise reconstructed from the scan data associated with scan data for slices of region of interest 402. Each of images 436 through 444 only includes a portion of needle 404 that is positioned within that slice. For example, image 436 includes an image portion 437 of needle 404 and image 438 includes an image portion 439 that illustrates tip 418 of needle 404. If needle 404 is not positioned such that any portion of needle 404 is located within a slice, the image corresponding to that slice will not include a portion of needle 404 in the image. For example, images 440, 442, 444 do not include a corresponding portion illustrating a position of needle 404 because needle 404 is not positioned such that a portion of needle 404 is located within the slice corresponding to images 440, 442, 444.
Image 444, reconstructed from the scan data associated with slice 424 includes an image portion 502 of needle 404. Portion 502 is colorized blue, the color associated with the slice in which it is positioned. Image 442, reconstructed from the scan data associated with slice 422 includes an image portion 504 of needle 404. Portion 504 is colorized green, the color associated with the slice in which it is positioned. Images 428 through 440 are likewise reconstructed from the scan data associated with scan data for slices of region of interest 402. Each of images 428 through 440 only includes a portion of needle 404 that is positioned within that slice. For example, image 440 includes an image portion 506 of needle 404 and image 438 includes image portion 508 that illustrates tip 418 of needle 404. If needle 404 is not positioned such that any portion needle 404 is located within a slice, the image corresponding to that slice will not include a portion of needle 404 in the image. Accordingly, images 436, 432, and 428 do not include a corresponding portion illustrating a position of needle 404 because needle 404 is not positioned within the slice corresponding to images 436, 432, and 428.
The viewer is presented a first viewing area 606 including single composite thick slice image 602 that is comprised of a combination, such as a summation, of the acquired n thin slices and overlayed with the multi-color composite needle segments. In the exemplary embodiment, this single composite slice is updated at high frame rates for observer viewing.
Improved placement information may be obtained by displaying a second viewing area 608 that includes a thin-slice image, for example, image 438 showing the needle tip, alongside combined thick slice image 602. Second viewing area 608 provides the viewer with a detailed, thin-slice, high-resolution image for confirmation of needle tip positioning. Automatic needle-tip identification and tracking may be accomplished in a similar fashion to the techniques described above.
In another embodiment, a third viewing area (not shown) displays a second thin-slice image, selected to lie in the plane of the target anatomy. This allows the observer to further confirm that needle 404 has reached the target.
A legend 610 indicates relative positions of the slices associated with each color, texture, or pattern used in composite thick slice image 602. Another legend 612, displayed with the thin slice image selected in second viewing area 608 illustrates the relative position of the portion of needle 404 associated with the slice selected and displays the needle portion in the color, texture, or pattern associated with that slice to facilitate confirmation of the position of needle 404 in any portion of region of interest 402.
Based on a previously performed volume scan, the user locates 802 a display cursor on each of a needle tip entry point and a target. These two points may be located at different table positions (images) to determine the planned needle trajectory.
The system moves 804 the patient table such that the needle tip appears on an image, for example, an image 918 using a calculation based on the display cursor locations. In the exemplary embodiment, the initial entry direction (3D angle) of the needle is adjusted by the user using a guide (i.e. laser, calipers, lights, etc.). In an alternative embodiment, tuning of the initial entry angle is based on acquiring continuous or “tap” scanning with very low dose of the needle out of the patient just prior to insertion into the patient. The calculation is based on at least two images wherein the images are based on data acquired by more than one detector row.
The XY angle of the needle is continuously verified 806 based on the information from image 920. The angle relative to the Z-axis is continuously verified based on the information from image 918 and image 920.
The needle movement direction is calculated 808 on image 918 by continuously subtracting the actual (current) and previous images 918. If the needle movement is slow, and the frame rate is fast, then the subtraction is performed on images 918 with longer time gaps.
Based on the initial entry direction (3D angle), calculated needle movement direction and slice thickness, the expected needle tip appearance area 924 on image 922 is predicted 810. If the needle is completely included in only one image, each adjacent image, for example, image 920 and image 922 are both monitored 812 in their predicted areas. These areas will be located adjacent to the needle tip position on image 918.
The area corresponding to the predicted appearance point on an image 922 is continuously verified 814 by subtracting the actual (current) image 922 from reference images 922 acquired previously. Verification that the needle tip has reached image 922 is confirmed by observing a dramatic density change within the predicted appearance area and/or confirmation of the density change for several consecutive reconstructed images. In the specific case where the needle is rigid, straight and has a relatively small angle (relative to z axis), the two adjacent images 920 and 922 may be sufficient for monitoring the needle positioning and predicted areas 918. For curved interventional tools the calculation can be done using thinner slice thicknesses and enlarging the predicted appearance areas 918.
After the confirmation, the system generates 816 images from rows 907, 908, 909, and 910 instead of rows 906, 907, 908, and 909 and the needle tip will remain in the displayed image 907 as before and the upper beam collimator translates 818 in the Z-direction a corresponding amount and direction.
The system verifies 820, in real-time, on-line, that the needle is traveling along the predetermined trajectory. If the needle deviates substantially from the predetermined trajectory by exceeding a selectable position threshold, a warning is indicated to the user. Such a warning is advantageous for procedures where the needle trajectory and the target area are not in the same imaged plane.
When the needle tip reaches 822 a limit of the Z coverage of the multi-slice detector array, for example, by exiting the last slice of the array, the user is warned that movement of the patient table, either manually or automatically, is necessary to maintain the needle tip within the viewing capability of the system.
Because the needle is able cross more than one slice plane (i.e. the needle is skewed to the scanner's axial plane), a significant dose saving to the user may be achieved by, for example, tilting the gantry. The system is programmed to determine 824 a recommended optimum gantry tilt angle for the specific interventional procedure used.
The above-described embodiments of an imaging system provide a cost-effective and reliable means for displaying wide scan coverage imaging while maintaining thin-slice detailed imaging for medical instrument insertion accuracy. More specifically, the needle color-coding provides a single thick-slice image while still showing thin-slice needle positioning to facilitate simultaneously benefiting from both aspects of multi-slice CT. As a result, the described embodiments of the present invention facilitate imaging a patient in a cost-effective and reliable manner.
Exemplary embodiments of imaging system methods and apparatus are described above in detail. The imaging system components illustrated are not limited to the specific embodiments described herein, but rather, components of each imaging system may be utilized independently and separately from other components described herein. For example, the imaging system components described above may also be used in combination with different imaging systems. A technical effect of the various embodiments of the systems and methods described herein include at least one of facilitating imaging a patient with images wherein instrument placement accuracy is enhanced.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
