The disclosure is related to methods for performing percutaneous procedures, and more particularly to improved guidance methods for percutaneous procedures utilizing movable arm fluoroscopic devices.
Percutaneous procedures, such as needle biopsies, drainages, radiofrequency ablations, and other medical interventional procedures, are often performed using X-ray fluoroscopy devices. In an attempt to reduce procedure times as well as radiation exposure to both the user and the patient, while improving targeting accuracy, the use of laser pointer devices has been proposed. The laser pointer may be mounted on the C-arm and aligned with a pair of points, one on the skin entry position and another on a targeted site within the patient. The needle or other instrument is aligned with the laser beam and inserted along the line defined by the laser.
When using laser pointers, however, unless the laser beam (or a laser cross formed by two laser fan beams) can be flexibly steered, the use of a fixed laser guide device requires moving the patient table to align the needle trajectory with the direction of the laser. A popular choice is to align the laser with the central ray of the C-arm system passing through the C-arm iso-center. As noted, however, such alignment of the needle trajectory with this fixed laser guide direction may require shifting the patient table. This can be cumbersome and may even put some patients (e.g., large patients) on a collision course with the C-arm as the system elements are moved around the patient to provide the different image views (e.g., Bull's Eye view, progression view, C-arm CT image acquisition (e.g., DynaVision) runs) that are often acquired during the alignment and insertion procedures.
A further issue relating to requiring table movement as part of a procedure is that it may result in registration errors between the live fluoroscopic image and the volumetric data set used to visualize the target within the patient. Since the needle trajectory is often planned using such a volumetric data set (created using the C-arm system itself or registered to a C-arm CT volume), if the table is moved after such C-arm CT imaging, accurate table tracking is required in order to shift the virtual plan with the patient. If there are significant table tracking errors, the planned needle trajectory may deviate unacceptably from its actual position relative to the patient. These potential disadvantage—cumbersome table alignment and collision after table motion, as well as the risk of table tracking errors—have prompted the development of an alternative guidance method for percutaneous procedures involving C-arm fluoroscopic devices, including those that involve table motion.
A method for planning a percutaneous procedure is disclosed. The method may be for use in a system comprising an imaging system having a movable arm, an x-ray source and an x-ray detector and a display and a system controller connected to and in communication with the imaging system and display. The method may comprise (a) providing a three-dimensional image data set of a patient tissue region; (b) obtaining an x-ray image of the patient tissue region using the x-ray source and the x-ray detector; (c) co-registering the three-dimensional image data set to an x-ray image acquired using the imaging system; (d) obtaining target point data representative of a target object within the patient tissue region, and obtaining skin entry point data representative of a skin entry point, wherein the target point data and skin entry point data are obtained from one of: (i) the co-registered three dimensional image data set, and (ii) two x-ray views taken under different view orientations using a triangulation technique; (e) generating a line on the display, where the line intersects the target point and the skin entry point and defines a planned instrument trajectory; and (f) adjusting the movable arm to a position at which an x-ray image taken using the x-ray source and x-ray detector results in the target point and the skin entry point being superimposed on each other. Alignment of an instrument positioned between the x-ray source and the skin entry point may be verified as an acceptable position with respect to the planned instrument trajectory when the instrument appears on the display as a point overlying the target point and the skin entry point in a verification x-ray image taken using the x-ray source and x-ray detector.
A system for planning a percutaneous procedure is also disclosed. The system may comprise an imaging system having a movable arm, an x-ray source and an x-ray detector and a display and a system controller connected to and in communication with the imaging system and display, and a machine-readable storage medium encoded with a computer program code such that, when the computer program code is executed by a processor, the processor performs a method. The method performed by the processor may comprise: (a) obtaining a three-dimensional image data set of a patient tissue region; (b) obtaining an x-ray image of the patient tissue region using the x-ray source and the x-ray detector; (c) co-registering the three-dimensional image data set to an x-ray image acquired using the imaging system; (d) obtaining target point data representative of a target object within the patient tissue region, and obtaining skin entry point data representative of a skin entry point, wherein the target point data and skin entry point data are obtained from one of: (i) the co-registered three dimensional image data set, and (ii) two x-ray views taken under different view orientations using a triangulation technique; (e) generating a line on the display of the combined image, where the line intersects the target point and the skin entry point and defines a planned instrument trajectory; and (f) adjusting the movable arm to a position at which an x-ray image taken using the x-ray source and x-ray detector results in the target point and the skin entry point being superimposed on each other. Alignment of an instrument positioned between the x-ray source and the skin entry point may be verified as an acceptable position with respect to the planned instrument trajectory when the instrument appears on the display as a point overlying the target point and the skin entry point in a verification x-ray image taken using the x-ray source and x-ray detector.
A method for planning a percutaneous procedure is further disclosed. The method may be used in a system comprising an imaging system having a movable arm, an x-ray source and an x-ray detector and a display and a system controller connected to and in communication with the imaging system and display. The method may comprise: (a) obtaining a three-dimensional image data set of a patient tissue region; (b) obtaining an x-ray image of the patient tissue region using the x-ray source and the x-ray detector and displaying the x-ray image on a first portion of the display; (c) obtaining a multi-planar reformatting (MPR) view generated from the three-dimensional image data set and displaying the MPR view on a second portion of the display; (d) co-registering the three-dimensional image data set to the x-ray image and displaying the combined image on a third portion of the display; (e) displaying a three-dimensional rendering of the three-dimensional data set on a fourth portion of the display; (f) obtaining target point data from the combined image, the target point data representative of a target object within the patient tissue region; (g) obtaining skin entry point data from the combined image; (h) displaying the target point, the skin entry point, and a line connecting the two points on each of the x-ray image, the MPR view, the combined image, and the three-dimensional rendering on the display, where the line connecting the two points represents a planned instrument trajectory; and adjusting the movable arm to a position at which an x-ray image taken using the x-ray source and x-ray detector results in the target point and the skin entry point being superimposed on each other on at least one of the x-ray image, the MPR view, the combined image and the three-dimensional rendering on the display. Alignment of an instrument positioned between the x-ray source and the skin entry point may be verified as an acceptable position with respect to the planned instrument trajectory when the instrument appears on the display as a point overlying the target point and the skin entry point in a verification x-ray image taken using the x-ray source and x-ray detector.
The accompanying drawings illustrate preferred embodiments of the disclosed method so far devised for the practical application of the principles thereof, and in which:
An “imaging system” is a system that includes at least a movable arm, an x-ray source, an x-ray detector, a display and a system controller. A “patient 3-dimensional image data set” is a three dimensional numerical array whose elements hold the values of specific physical properties at points in space inside the patient's body. A “multiplanar reformation image (MPR)” is a planar cross-section of the patient 3-dimensional image data set generated by cutting through the three-dimensional data set at some orientation (e.g., axial, coronal, sagittal, or oblique). A “fluoroscopic image” is a two-dimensional x-ray projection image showing internal tissues of a region of the body. A “live fluoroscopic image” is a sequence of x-ray images taken successively showing live movement of internal tissues of a region of the body. A “combined image” is an image in which an x-ray image is combined with an MPR or three-dimensional rendering of a three-dimensional data set. “Co-registering” means aligning an x-ray image with a patient 3-dimensional image data set such that associated features within the x-ray image and a two-dimensional overlay image generated from the patient 3-dimensional image data set appear at the same location on a display in which the x-ray image and the overlay image are shown together. Co-registration can be point-based or gray-level based. In point-based co-registration, a transform is applied to the 3-dimensional image data set such that points in the resulting overlay image line up with their counterparts in the x-ray image as closely as possible. Gray-level based co-registration techniques determine the transform not by minimizing the distance between associated points in the overlay image and x-ray image, but by minimizing an error metric based on the resulting overlay image's gray levels and the x-ray image's gray levels. “Instrument” refers to any object which may pierce tissue of a patient, a non-limiting listing of which include needles and other biopsy devices, screws, implants, cannula, endoscopes, and anything else that can be inserted into a patient's body either percutaneously or intravascularly. A “skin entry point” is the position on a patient's skin at which an instrument is inserted. “Skin entry point data” is data representative of the skin entry point within the patient 3-dimensional image data set or within two x-ray views taken under different view orientations using a triangulation technique. A “target” or “target point” is a point within the body of a patient that is the subject of a percutaneous procedure. “Target point data” is data representative of the skin entry point within the patient 3-dimensional image data set or within two x-ray views taken under different view orientations using a triangulation technique. A “planned path” is a line generated between the skin entry point and the target point. “Instrument trajectory” is a desired trajectory of the instrument defined by the planned path. A “Bull's Eye View” is an x-ray view under which a target point and another point along the instrument trajectory are projected onto each other. The other point along the instrument trajectory may be the skin entry point. The movable arm view direction can be visualized using a graphical overlay in which the target point and skin entry point, forward-projected from 3-dimensions to 2-dimensions, are displayed as individual circles. If the Bull's Eye View has been reached, these two circles are projected at the same 2-dimensional position (i.e., they appear concentrically aligned). A “progression view” is an x-ray image taken at an oblique angle with respect to a line joining the skin entry point and the target. movable arm tomographic reconstruction refers to a technique in which multiple x-ray images taken along a partial circle scan of the movable arm system are used to construct a patient 3-dimensional image data set.
A system and method are disclosed for providing a user with enhanced information regarding instrument positioning and guidance to a target within a patient's body as part of a percutaneous procedure. Using a patient 3-dimensional image data set (referred to hereinafter as a “3D volume”) the system and method enable the user to select a skin entry point and a target point within the patient. A line is generated between the skin entry point and the target point which is used to align the movable arm to achieve a “Bull's Eye View,” in which the two points are superimposed to show only a single point to the user. The instrument is placed at the skin entry point and aligned using the Bull's Eye View to orient the instrument along a desired instrument trajectory (i.e., one that hits both points). Initial alignment is verified using a fluoroscopic image of the oriented instrument. After the initial alignment is verified, the user inserts the instrument a short distance into the patient. One or more progression x-ray views are used to verify that the instrument is on the planned path between the skin entry point and the target point. The user may employ an iterative approach of inserting the instrument a small distance followed by a verification of the instrument's position using progression x-ray views to guide the instrument to the target. When the instrument reaches the target, a desired additional procedure may be performed, such as a biopsy, a drainage procedure, a radiofrequency ablation, or other medical interventional procedure.
Referring to
In the illustrated embodiment, a patient 18 is shown on patient-support table 20 such that an X-ray beam 6 generated by the X-ray source passes through him/her onto a detector 22. In one embodiment the detector 22 is a flat panel detector that acquires digital image frames directly, which are transferred to an image processor 24. A display/record device 26 records and/displays the processed image(s). The display/record device 26 may include a display for displaying the displayed image output, as well as a separate device for archiving. The image is arranged for storage in an archive such as a network storage device. The X-ray source 2 is controlled by the system controller 10 via exposure controller 8 and X-ray generator 28. The position of the X-ray source 2 may be adjusted via a drive system associated with the movable arm 4. The movable arm 4, X-ray source 2, X-ray detector 22, display 26 and system controller 10 may together be referred to as an imaging system.
Workflow Steps
Referring to
At step 300, an x-ray image of the patient tissue region is obtained using the X-ray source 2 and X-ray detector 22. In one embodiment, shown at step 310 in
At step 500, the system obtains target point data representative of a target object within the patient tissue region. The system also obtains skin entry point data representative of a skin entry point. The target point data and the skin entry point data are obtained from one of (a) the co-registered three dimensional image data set, and (b) two x-ray views of the patient tissue region taken under different view orientations using triangulation. In one embodiment, shown at step 510 in
Referring again to
At step 800, alignment of an instrument positioned between the x-ray source 2 and the skin entry point is verified as an acceptable position with respect to the planned instrument trajectory when the instrument appears on the display as a point overlying the target point and the skin entry point in a verification x-ray image taken using the x-ray source and detector. In one embodiment, acceptable position with respect to the planned instrument trajectory is verified by taking multiple x-ray images using the x-ray source 2 and detector 22 at movable arm positions oblique to the position of the movable arm 4 used to obtain the verification x-ray image.
In further steps, the user may insert the instrument into the patient at the skin entry point. One or more progression x-ray views may be taken to ensure that the instrument remains aligned with the projected instrument path. It will be appreciated that the user may also return to the Bull's Eye View to gain additional insights regarding instrument orientation. The user may press the instrument further into the patient toward the target while making adjustments to ensure the instrument remains aligned with the projected instrument path. The pressing and progression x-ray steps may be repeated as desired by the user to guide the instrument in an incremental manner to intersect the target.
An exemplary embodiment of the disclosed system and method will now be described in relation to a series of graphical screen displays which show the detailed implementation of the system.
Initially, it will be appreciated that the x-ray views (fluoroscopic images) obtained using the movable arm, source 2 and detector 22, needs to be appropriately “registered” with the MPR images derived from the 3-dimensional data set of the region of interest of the patient. Data registration may be performed manually, automatically or semi-automatically (i.e., computer assisted).
In one exemplary embodiment of a manual registration technique, movable arm x-ray views may be set up to aid in the registration of the movable arm x-rays with 3-dimensional data sets that have been previously obtained. Thus, the user may initially place the movable arm into an oblique or lateral view with respect to the patient 18 before taking an x-ray. Referring to
If the user detects mis-registration between the x-ray images and the respective overlay image, manual registration of the 3-dimensional data set with 2-dimensional x-ray images can be performed. To this end, shift and rotation may be adjusted. An intuitive way to arrive at the rotation involves the use of a “pivot point,” which is a point around which the 3-dimensional data set can be rotated either before, or preferably after, shifting the 3-dimensional data set to align the associated 2-dimensional overlay image with the fluoroscopic image in the x-ray views (display quadrants 8A and 8B). In one exemplary embodiment, a “pivot point” may be a landmark, such as a bone, visible vessel, or other visually distinctive point of reference within the 3-dimensional patient data set (including MPRs obtained by putting cut-planes through the patient data set) and the x-ray images. Once such a pivot point has been identified, the 2-dimensional overlay image (computed by forward projecting of the 3-dimensional data rendered in display quadrant 8D along the movable arm view direction) may be manually shifted in one or more directions to align the pivot points. This shifting can be performed using a key-stroke, track-ball, mouse input, or other input device. If rotational misalignment exists between the two data sets, it can be eliminated by rotating the 3-dimensional data set around the pivot point while displaying the resulting 2-dimensional overlay views over the 2-dimensional x-ray views. Again, this may be performed using one of the manual input devices discussed.
The manual registration process may be started by pressing an appropriate soft key 8C in the “Registration” pop-up tab card. In
It will be appreciated that the aforementioned manual registration technique is only one method for registering the 3-dimensional data set to the live x-ray image(s), and others may also be used. Further, if the 3-dimensional data set is obtained using movable arm CT image acquisition just prior to performance of the percutaneous procedure, a registration step may not be required, since it is possible to keep the patient from moving in the time period between the CT-image acquisition procedure and the percutaneous procedure.
Once the 3-dimensional data set is appropriately registered to the 2-dimensional x-ray geometry, the instrument trajectory may be planned. To this end, the user may select a target point, xt, and a skin entry point, xe within the overlay images by visualizing the areas within a particular MPR and clicking on the point(s) using a selector such as a mouse button.
As shown in
Based on where the click points are made in the MPR view, the system obtains data representative of the target and skin entry points using data from the 3-dimensional patient data set. Using the target point data and skin entry point data, the system generates a graphical overlay showing a line which represents the planned instrument trajectory. Such a graphical overlay is applied to each of the images shown on the user display (as seen as line 11F in
As an alternative to visualizing and selecting target and skin entry points using a particular MPR view, the user may instead obtain the location of the target point and skin entry point using x-ray images that have been successively obtained using mono-plane or bi-plane x-ray devices shooting at multiple oblique angles. The selection of target point xt and skin entry point xe is selected in a similar manner to the way these points are selected in the MPR view(s) as previously described. The user employs a mouse or other selection device to “click” on each selected point in the two x-ray images (i.e., one from each direction). The system obtains data representative of the target and skin entry points as described previously. Based on the target and skin entry point data the system generates a graphical overlay consisting of the three-dimensional target point xt, the skin entry point xe (as well as the connecting vector “n”) at their precise locations in the corresponding MPR view and/or three-dimensional rendering view.
In one embodiment, a needle guidance device 30 (e.g., a SeeStar device, manufactured by Radi Medical Devices, Uppsala, Sweden) may be used to aid in planning an instrument insertion trajectory. The SeeStar device (see
As an alternative to a SeeStar device, the user may instead employ an elongated metal marker that shows up in an x-ray image to allow the user to verify the trajectory as acceptable using either 3-dimensional image rendering or by using two angularly offset X-ray views. Defining a skin entry point by localizing an instrument guidance device such as the SeeStar 30 may be particularly beneficial when using bi-plane x-ray devices in which both offset x-ray views are acquired simultaneously. In such a case, on-line re-planning can be performed to allow the user to adjust the instrument trajectory. The re-adjusted position may be quickly verified in the two bi-plane x-ray views.
If using an instrument guidance device other than a SeeStar 30, the guidance device can be oriented under a Bull's Eye View orientation such that the guidance device is projected directly onto the skin entry point and the target point. Once a desired position is achieved, the guidance device can be clamped into the Bull's Eye View position to guide the instrument into the soft tissue below.
As shown in the four display quadrants 11A, 11B, 11C and 11D of
Once the skin entry point and target point have been selected, a verification step may be performed to ensure that the planned instrument trajectory is achievable (i.e., that the movable arm can be physically positioned in the planned Bull's Eye View position). Additionally, the system performs a check to ensure that the movable arm does not interfere with the patient table 20, the patient 18, or the user. These checks can be implemented by providing the system with a pre-determined range of impermissible positions, and verifying that the selected position (corresponding with the planned procedure path), is not within that range.
Thus, the system determines whether the movable arm 4 can be mechanically driven into the Bull's Eye View position (i.e., the position in which the instrument trajectory projects onto the display 22 as a single point rather than a line) and that the instrument trajectory can be seen on the detector 22 using the x-ray source 2. In the illustrated case, the Bull's eye view position requires that the source be located such that xt and xe are projected onto the same detector (pixel) position.
In addition, the system may also perform a verification step to ensure that the projections of xt and xe are captured by the active field of view of the detector 22. For a quick check on the feasibility of the x-ray source 2 position under the planned Bull's Eye View orientation, the intersection point, xs, of the needle trajectory and the “source sphere” can be computed. The “source sphere” is the set of possible X-ray source locations that are a particular distance away from the iso-center of the movable arm. Some variations in the “source sphere” can be taken into consideration by resorting to mechanical and image calibration information. The intersection of the path vector “n” with the source sphere determines two potential X-ray source positions under which the
Bull's eye view is obtained. The preferred location is the one that puts the X-ray source underneath the patient table to minimize radiation exposure to the eyes of the patient and user.
Thus, with the source located at xs, an ideal projection matrix may be computed taking the source-to-image distance (SID) and zoom factor into account. This is possible since both intrinsic and extrinsic source/detector parameters are known. Using this projection matrix, the locations at which xe and xt project onto the detector 22 are determined. If the instrument path connecting xe and xt projects outside of the detector area (or if the source 2 cannot be driven into this position xs), the system may provide a warning to prompt the user to change the instrument trajectory.
Once the aforementioned verification steps are performed and an acceptable instrument trajectory has been planned, the movable arm may be moved into the Bull's Eye View position. As previously noted, the Bull's Eye View orientation is one in which the skin entry point and the target point (xe and xt) overlie each other on the same detector positions xe′ and xt′, respectively. Adjustment of the movable arm 4 to achieve this positioning can either be performed manually or automatically.
For manual movable arm adjustment, the user may be graphically guided (using the display) to drive the system into a position at which xe and xt are projected onto each other, i.e., where xt′=xe′. During manual adjustment of the movable arm, a graphical overlay (
As shown in
In lieu of manual movable arm positioning, the system may perform an automatic Bull's Eye View positioning of the movable arm 4. In the automatic mode, the intersection of instrument trajectory with the source hemisphere may be determined by the system before the x-ray source 2 is automatically driven to that location, as previously discussed. To this end, the system may include a feedback-loop in which the movable arm 4 is driven automatically while continually comparing the locations of the detector points xt′ and xe′ of the target point and skin entry point, respectively. In this manner, the system may move the movable arm in a direction that minimizes the distance between xt′ and xe′, with the result being that the movable arm is driven to a position in which the detector points overlap (xt′=xe′). Once the Bull's Eye View position is achieved, the instrument may be positioned on the skin entry point xe.
In practice, positioning an instrument at the skin entry point xe may be a difficult task, and thus a positioning aide may be used. If the user has access to a CT scanner equipped with a laser, a biopsy grid 32 (
Alternatively, where simple fluoroscopic (x-ray) equipment is being used to guide the percutaneous procedure, a radio-opaque biopsy mesh 34 (
The biopsy mesh 34 may be made out of a thin adhesive support material with embedded radio-opaque markers to facilitate easy cell identification. In one embodiment, radio-opaque numbers may be placed at the center of each “cell” center such as “(2,2)” to designate the second cell in the second row. In this way, the mesh may be easily visualized under collimated conditions.
Once the appropriate instrument positioning has been achieved, collimation may be set around the Bull's Eye View to limit radiation exposure to the user and patient. In one embodiment, “auto collimation” may be performed in which an asymmetric collimator is set to block radiation outside a rectangle that has xt′ and xe′ as center points (for a Bull's Eye View positioning). Collimated views are shown in display quadrant 15A in
The Bull's Eye View may be isolated and enlarged, as shown in
As can be seen, the zoomed view of
As previously noted, in lieu of a SeeStar device, the user could instead use a hollow instrument guide to verify instrument placement. The hollow instrument guide may be configured so that it shows up as a point under fluoroscopy in the Bull's Eye View when a desired alignment is achieved. The hollow instrument guide may be clamped in position during fluoroscopy to limit radiation to the user, and its position may be adjusted and verified in a manner similar to that described in relation to the SeeStar device.
Once the desired instrument alignment is achieved, the instrument is pushed forward by a small amount into the patient tissue to stabilize the instrument's orientation. This insertion is performed under the Bull's Eye View. As shown in
Instrument alignment may again be verified at this early stage of insertion. Such verification can be performed using x-ray “progression views,” which are oblique x-ray views (i.e., non-Bull's Eye Views) obtained using the source 2 and detector 22. It will be appreciated that the user may also return to the Bull's Eye View at any time during the procedure to obtain additional information regarding instrument alignment. If a bi-plane x-ray device is available with the B-plane providing a progression, it is possible to check if the instrument remains aligned with the associated graphical overlay (shown as line 44 in
The movable arm 4 may be rotated back and forth between two different progression views, one which is collimated around the instrument path, and a second in which a lateral view shows the instrument moving toward the target. It will be appreciated that the user may return to the Bull's Eye View for additional orientation information. In one embodiment, a first progression view (
During the procedure, the movable arm 4 may be moved between the first and second progression views to enable the user to control the actual instrument movement from two oblique angles until the instrument has reached the target. When the target has been almost reached in one progression view, the user can return to the other progression view to confirm that the instrument has indeed been placed correctly before making the final push or releasing a spring-loaded biopsy device if one is used. The user can also return to the Bull's Eye View to obtain additional orientation information.
Under each progression view, as well as under the Bull's Eye View, collimators may be placed to both sides of the instrument path before x-rays are released. Collimator placement may be controlled manually or automatically (“auto-collimation”). If auto-collimation is used, it may be performed such that xt′ and xe′ shown in the progression views reside at the corner points of an inner rectangle (see, e.g.,
Referring again to
Referring to
From experiments performed on static phantoms, the inventors estimate that the size of a spherical static target 48 that can be successfully engaged under double-oblique conditions (the aforementioned progression views) is about 1 centimeter.
In practice, an asymmetric collimator is preferable to limit radiation to a minimum by establishing a tight collimation around the instrument path. If, however, only a symmetric collimator is available that blocks x-rays symmetrically around the central ray of the x-ray cone, table motion may be required to enable a tight collimation around the instrument trajectory. In such a case, the disclosed method still provides the benefit in that it does not require an exact alignment of the central ray of the source 2 and the instrument 46 trajectory.
The method described herein may be automated by, for example, tangibly embodying a program of instructions upon a computer readable storage media capable of being read by machine capable of executing the instructions. A general purpose computer is one example of such a machine. A non-limiting exemplary list of appropriate storage media well known in the art would include such devices as a readable or writeable CD, flash memory chips (e.g., thumb drives), various magnetic storage media, and the like.
The features of the method have been disclosed, and further variations will be apparent to persons skilled in the art. All such variations are considered to be within the scope of the appended claims. Reference should be made to the appended claims, rather than the foregoing specification, as indicating the true scope of the disclosed method.
The functions and process steps herein may be performed automatically or wholly or partially in response to user command. An activity (including a step) performed automatically is performed in response to executable instruction or device operation without user direct initiation of the activity.
The systems and processes of
This is a non-provisional application of pending U.S. provisional patent application Ser. No. 60/992,830, filed Dec. 6, 2007 by Strobel et al., the entirety of which application is incorporated by reference herein.
Number | Date | Country | |
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60992830 | Dec 2007 | US |