X-RAY RING MARKERS FOR X-RAY CALIBRATION

Abstract

Various embodiments of the present disclosure include a C-arm registration system employing a controller (70) for registering a C-arm (60) to a X-ray ring marker (20). The X-ray ring marker (20) includes a coaxial construction of a chirp ring (40) and a centric ring (50) on an annular base (30). In operation, the controller (70) acquires a baseline X-ray image illustrative of the X-ray ring marker (20) within a baseline X-ray projection by the C-arm (60) at a baseline imaging pose, derives baseline position parameters of the X-ray ring marker (20) within the baseline X-ray projection as a function of an illustration of the centric ring (50) within the baseline X-ray image, and derives a baseline twist parameter of the X-ray ring marker (20) within the baseline X-ray projection as a function of the baseline position parameters and of an illustration of the chirp ring (40) within the baseline X-ray image.

Claims

1. A C-arm registration system, comprising: a X-ray ring marker including a coaxial construction of a chirp ring and a centric ring on an annular base; and a C-arm registration controller for registering a C-arm to the X-ray ring marker, wherein the C-arm registration controller-(is configured to: acquire a baseline X-ray image illustrative of the X-ray ring marker within a baseline X-ray projection by the C-arm at a baseline imaging pose; derive baseline position parameters of the X-ray ring marker as a function of an illustration of the centric ring within the baseline X-ray image, the baseline position parameters being definitive of a position of the X-ray ring marker within the baseline X-ray projection; and derive a baseline twist parameter of the X-ray ring marker as a function of the baseline position parameters and of an illustration of the chirp ring within the baseline X-ray image, the baseline twist parameter being definitive of a twist of the X-ray ring marker within the baseline X-ray projection.

2. The C-arm registration system as claimed in claim 1, wherein the C-arm registration controller being configured to derive the baseline position parameters of the X-ray ring marker includes the C-arm registration controller further configured to: delineate the centric ring within the baseline X-ray image; and parameterize the position of the X-ray ring marker within the baseline X-ray projection as a function of a delineation of the centric ring within the baseline X-ray image.

3. The C-arm registration system as claimed in claim 2, wherein the C-arm registration controller being configured to derive the baseline position parameters of the X-ray ring marker includes the C-arm registration controller further configured to: construct a cost function as a function of a parameterization of the position of the X-ray ring marker within the baseline X-ray projection.

4. The C-arm registration system as claimed in claim 3, wherein the C-arm registration controller being configured to derive the baseline position parameters of the X-ray ring marker includes the C-arm registration controller further configured to: apply a non-linear least square technique to the cost function.

5. The C-arm registration system as claimed in claim 1, wherein the C-arm registration controller being configured derive the baseline twist parameter includes the C-arm registration controller further configured to: project points of the X-ray ring marker onto the X-ray detector of the C-arm based on the baseline position parameters; and parametrize a normalized cross-correlation of a sweep frequency of the chirp ring and image intensity values of the points of the X-ray ring marker projected onto the X-ray detector of the C-arm.

6. The C-arm registration system as claimed in claim 1, wherein the C-arm registration controller is further configured to: derive a registration error as a function of a location of the centric ring on the X-ray ring marker and a location of the centric ring within the baseline X-ray image.

7. The C-arm registration system as claimed in claim 1, wherein the C-arm registration controller is further configured to: acquire a target X-ray image illustrative of the X-ray ring marker within a target X-ray projection by the C-arm at a target imaging pose; derive target position parameters of the X-ray ring marker as a function of an illustration of the centric ring within the baseline X-ray image, the target position parameters being definitive of a position of the X-ray ring marker within the target X-ray projection; and derive a target twist parameter of the X-ray ring marker as a function of the target position parameters and of an illustration of the chirp ring within the target X-ray image, the target twist parameter being definitive of a twist of the X-ray ring marker within the target X-ray projection.

8. The C-arm registration system as claimed in claim 7, wherein the C-arm registration controller is further configured to: implement an intervention step based on a landmark as illustrated in the baseline X-ray image and the target X-ray image as a function of the baseline position parameters, the baseline twist parameter, the target position parameters and the target twist parameter.

9. A C-arm registration controller for registering a C-arm to a X-ray ring marker, the X-ray ring marker including a coaxial construction of a chirp ring and a centric ring on an annular base, the C-arm registration controller comprising: a non-transitory machine-readable storage medium encoded with instructions for execution by at least one processor of a registration of the C-arm to X-ray ring marker, the non-transitory machine-readable storage medium comprising instructions to: acquire a baseline X-ray image illustrative of the X-ray ring marker within a baseline X-ray projection by the C-marker at a baseline imaging pose; derive baseline position parameters of the X-ray ring marker as a function of an illustration of the centric ring within the baseline X-ray image, the baseline position parameters being definitive of a position of the X-ray ring marker within the baseline X-ray projection; and derive a baseline twist parameter of the X-ray ring marker as a function of the baseline position parameters and of an illustration of the chirp ring within the baseline X-ray image, the baseline twist parameter being definitive of a twist of the X-ray ring marker within the baseline X-ray projection.

10. The C-arm registration controller as claimed in claim 9, wherein the instructions to derive the baseline position parameters of the X-ray ring marker includes instructions to: parameterize the position of the X-ray ring marker within the baseline X-ray projection as a function of a delineation of the centric ring within the baseline X-ray image.

11. The C-arm registration controller as claimed in claim 10, wherein the instructions to derive the baseline position parameters of the X-ray ring marker further includes instructions to: construct a cost function based on a parameterization of the position of the X-ray ring marker within the baseline X-ray projection.

12. The C-arm registration controller as claimed in claim 9, wherein the instructions to derive the baseline twist parameter of the X-ray ring marker includes instructions to: project points of the X-ray ring marker onto the X-ray detector of the C-arm based on the baseline position parameters; and parametrize a normalized cross-correlation of a sweep frequency of the chirp ring and image intensity values of the points of the X-ray ring marker projected onto the X-ray detector of the C-arm.

13. The C-arm registration controller as claimed in claim 9, wherein the non-transitory machine-readable storage medium further comprises instructions to: derive a registration error as a function of a location of the centric ring on the X-ray ring marker and a location of the centric ring within the baseline X-ray image.

14. The C-arm registration controller as claimed in claim 9, wherein the non-transitory machine-readable storage medium further comprises instructions to: acquire a target X-ray image illustrative of the X-ray ring marker within a target X-ray projection by the C-arm at a target imaging pose; derive target position parameters of the X-ray ring marker as a function of an illustration of the centric ring within the baseline X-ray image, the target position parameters being definitive of a position of the X-ray ring marker within the target X-ray projection; and derive a target twist parameter of the X-ray ring marker as a function of the target position parameters and of an illustration of the chirp ring within the target X-ray image, the target twist parameter being definitive of a twist of the X-ray ring marker within the target X-ray projection.

15. The C-arm registration controller as claimed in claim 14, wherein the non-transitory machine-readable storage medium further comprises instructions to: implement an intervention step based on a landmark as illustrated in the baseline X-ray image and the target X-ray image as a function of the baseline position parameters, the baseline twist parameter, the target position parameters and the target twist parameter.

16. A C-arm registration method executable by a C-arm registration controller for registering a C-arm to a X-ray ring marker, the X-ray ring marker including a coaxial construction of a chirp ring and a centric ring on an annular base, the C-arm registration method comprising: acquiring, via the C-arm registration controller, a baseline X-ray image illustrative of the X-ray ring marker within a baseline X-ray projection by the C-arm at a baseline imaging pose; deriving, via the C-arm registration controller, baseline position parameters of the X-ray ring marker as a function of an illustration of the centric ring within the baseline X-ray image, the baseline position parameters being definitive of a position of the X-ray ring marker within the baseline X-ray projection; and deriving, via the C-arm registration controller, a baseline twist parameter definitive of the X-ray ring marker as a function of the baseline position parameters and of an illustration of the chirp ring within the baseline X-ray image, the baseline twist parameter being definitive of a twist of the X-ray ring marker within the baseline X-ray projection.

17. The C-arm registration method as claimed in claim 16, wherein deriving, via the C-arm registration controller, the baseline position parameters of the X-ray ring marker includes: parameterizing, via the C-arm registration controller, the position of the X-ray ring marker within the baseline X-ray projection as a function of a delineation of the centric ring within the baseline X-ray image; and constructing, via the C-arm registration controller, a cost function as a function of a parameterization of the position of the X-ray ring marker within the baseline X-ray projection.

18. The C-arm registration method as claimed in claim 17, deriving, via the C-arm registration controller, the baseline twist parameter of the X-ray ring marker includes instructions to: projecting, via the C-arm registration controller, points of the X-ray ring marker onto the X-ray detector of the C-arm based on the baseline position parameters; and parametrizing, via the C-arm registration controller, a normalized cross-correlation of a sweep frequency of the chirp ring and image intensity values of the points of the X-ray ring marker projected onto the X-ray detector of the C-arm.

19. The C-arm registration method as claimed in claim 16, further comprising: acquiring, via the C-arm registration controller, a target X-ray image illustrative of the X-ray ring marker within a target X-ray projection by the C-arm at target imaging pose; deriving, via the C-arm registration controller, target position parameters of the X-ray ring marker as a function of an illustration of the centric ring within the target X-ray image, the target position parameters being definitive of a position of the X-ray ring marker within the target X-ray projection; and deriving, via the C-arm registration controller, a target twist parameter definitive of the X-ray ring marker as a function of the target position parameters and of an illustration of the chirp ring within the target X-ray image, the target twist parameter being definitive of a twist of the X-ray ring marker within the target X-ray projection.

20. The C-arm registration method as claimed in claim 19, further comprising: implementing, via the C-arm registration controller, an intervention step based on a landmark as illustrated in the baseline X-ray image and the target X-ray image as a function of the baseline position parameters, the baseline twist parameter, the target position parameters and the target twist parameter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 illustrates an exemplary embodiment of a X-ray ring marker in accordance with various aspects of the present disclosure.

[0032] FIG. 2 illustrates an exemplary embodiment of a dual X-ray ring marker in accordance with various aspects of the present disclosure.

[0033] FIGS. 3A and 3B illustrate a first exemplary embodiment of the X-ray ring marker of FIG. 1 in accordance with various aspects of the present disclosure.

[0034] FIG. 4 illustrates a first exemplary embodiment of the dual X-ray ring marker of FIG. 2 in accordance with various aspects of the present disclosure.

[0035] FIGS. 5A and 5B illustrate a second exemplary embodiment of the X-ray ring marker of FIG. 1 in accordance with various aspects of the present disclosure.

[0036] FIG. 6 illustrates a second exemplary embodiment of the dual X-ray ring marker of FIG. 2 in accordance with various aspects of the present disclosure.

[0037] FIG. 7 illustrates a third exemplary embodiment of the X-ray ring marker of FIG. 1 in accordance with various aspects of the present disclosure.

[0038] FIG. 8 illustrates a third exemplary embodiment of the dual X-ray ring marker of FIG. 2 in accordance with various aspects of the present disclosure.

[0039] FIG. 9 illustrates a fourth exemplary embodiment of the X-ray ring marker of FIG. 1 in accordance with various aspects of the present disclosure.

[0040] FIG. 10 illustrates a fourth exemplary embodiment of the dual X-ray ring marker of FIG. 2 in accordance with various aspects of the present disclosure.

[0041] FIG. 11A illustrates an exemplary embodiment of a baseline phase of a C-Arm.fwdarw.X-ray ring marker registration in accordance with various aspects of the present disclosure.

[0042] FIG. 11B illustrates an exemplary embodiment of a target phase of a C-Arm.fwdarw.X-ray ring marker registration in accordance with various aspects of the present disclosure.

[0043] FIG. 12 illustrates a flowchart representative of an exemplary embodiment of a C-Arm X-ray ring marker registration method in accordance with various aspects of the present disclosure.

[0044] FIG. 13 illustrates a flowchart representative of an exemplary embodiment of a registration parameter computation method in accordance with various aspects of the present disclosure.

[0045] FIG. 14A illustrates an exemplary baseline imaging pose of a C-Arm in accordance with the various aspects of the present disclosure.

[0046] FIG. 14B illustrates an exemplary target imaging pose of a C-Arm in accordance with the various aspects of the present disclosure.

[0047] FIG. 15 illustrates an exemplary baseline X-ray image in accordance with the various aspects of the present disclosure.

[0048] FIG. 16 illustrates a flowchart representative of an exemplary embodiment of a intervention step implementation method in accordance with various aspects of the present disclosure.

[0049] FIG. 17 illustrates a flowchart representative of an exemplary embodiment of a intervention computation method in accordance with various aspects of the present disclosure.

[0050] FIG. 18 illustrates an exemplary computation of landmark image delineation of in accordance with various aspects of the present disclosure.

[0051] FIG. 19 illustrates an exemplary embodiment of a C-Arm registration controller in accordance with various aspects of the present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] To facilitate an understanding of various aspects of the present disclosure, the following description of FIGS. 1-10 teaches embodiments of a X-ray ring marker of the present disclosure. From this description, those having ordinary skill in the art will appreciate how to apply the various aspects of the present disclosure for making and using additional embodiments of X-ray ring markers of the present disclosure.

[0053] Referring to FIG. 1, a X-ray ring marker 20 of the present disclosure employs a coaxial construction of a chirp ring 40 and a centric ring 50 onto an annular base 30.

[0054] In practice, annular base 30 may have any annular shape suitable for a registration of C-arm to X-ray ring marker 30 including, but not limited to a circular shape and an elliptical shape.

[0055] Also in practice, annular base 30 may be constructed from material that is partially or entirely X-ray imageable.

[0056] Chirp ring 40 is a X-ray imageable annular structure embodying a chirp signal symbolically shown as a varying frequency waveform encircling annular base 30.

[0057] In one embodiment of chirp ring 40, the chirp signal is embodied as a varying spatial annular arrangement of protrusions formed in annular base 30.

[0058] In a second embodiment of chirp ring 40, the chirp signal is embodied as a varying spatial annular arrangement of indentations formed in annular base 30.

[0059] In a third embodiment of chirp ring 40, the chirp signal is embodied as a varying spatial annular arrangement of X-ray imageable objects disposed permanently or transiently onto/into annular base 30 (e.g., cooper balls, brass balls, etc.).

[0060] In practice, the chirp signal may have any amplitude, starting frequency and frequency shift suitable for an encoding of a twist of X-ray ring marker 20 around a Z-axis (not shown) of a C-Arm coordinate system as will be further described in the present disclosure.

[0061] Still referring to FIG. 1, centric ring 50 is a X-ray imageable annular spatial structure embodying center intersection points as symbolically shown as a dashed ring encircling annular base 30. The center intersection points define a center point 21 of X-ray ring marker 20 as symbolically shown by the dashed lines extending from centric ring 50 to center point 21.

[0062] In one embodiment of centric ring 50, the center intersection points are embodied as a symmetrical annular spatial arrangement of protrusions formed in annular base 30.

[0063] In a second embodiment of centric ring 50, the center intersection points are embodied as a symmetrical annular spatial arrangement of indentations formed in annular base 30.

[0064] In a third embodiment of a centric ring 50, the center intersection points are embodied as a symmetrical annular spatial arrangement of X-ray imageable objects disposed permanently or transiently disposed onto/into annular base 30 (e.g., cooper balls, brass balls, etc.).

[0065] In practice, centers of the chirp ring 40 and centric ring 50 are concentrically or eccentrically co-axially aligned along the Z-axis (not shown) of a coordinate system X.sub.20-Y.sub.20-Z.sub.20 of X-ray ring marker 20 with center point 21 serving as on origin of coordinate system X.sub.20-Y.sub.20-Z.sub.20.

[0066] FIG. 2 illustrates a dual X-ray ring marker 22 of the present disclosure employing a pair of X-ray ring markers 20 of FIG. 1 of the present disclosure connected via a bridge 23. In practice, bridge 23 may be any shape suitable for a C-Arm.fwdarw.X-ray ring maker 20 registration involving a movement of C-arm from a baseline imaging pose to a target imaging pose as will be further described in the present disclosure, such as, for example, a prismatic shape of bridge 23 for establishing a co-planar alignment of the pair of X-ray ring markers 20 as shown in FIG. 2.

[0067] FIG. 3A illustrates an embodiment 20a of X-ray ring marker 20 of FIG. 1 of the present disclosure. X-ray ring marker 20a employs an annular base 30a having a chirp ring embodied as an annular spatial arrangement of indentations 40a formed in annular base 30a as exemplary shown in FIG. 3B. The dimensions of the indentations 40a vary along a 360° traversal of annular base 30a to define a chirp signal.

[0068] Still referring to FIG. 3A, centric ring 50 as shown in FIG. 1 of the present disclosure is embodied by an outer circle of uniformly spaced objects 50a (e.g., cooper balls, brass balls, etc.) affixed adjacent an outer perimeter of annular base 30a, and an inner circle of uniformly spaced objects 50b (e.g., cooper balls, brass balls, etc.) affixed adjacent an inner perimeter of annular base 30a. Each object 50a of the outer circle is paired with a corresponding object 50b of the inner circle to define an intersection line of a center point 21a of X-ray ring marker 20a serving as an origin of a coordinate system X.sub.20a-Y.sub.20a-Z.sub.20a of X-ray ring marker 20a (Z-axis not shown).

[0069] FIG. 4 illustrates a dual X-ray ring marker 22a of the present disclosure employing a pair of X-ray ring markers 20a of FIG. 3A of the present disclosure connected via a bridge 23a. In practice, bridge 23a may be any shape suitable for a C-Arm.fwdarw.X-ray ring maker 20a registration involving a movement of C-arm from a baseline imaging pose to a target imaging pose as will be further described in the present disclosure, such as, for example, a prismatic shape of bridge 23a for establishing a co-planar alignment of the pair of X-ray ring markers 20a as shown in FIG. 4.

[0070] FIG. 5A illustrates an embodiment 20b of X-ray ring marker 20 of FIG. 1 of the present disclosure. X-ray ring marker 20b employs an annular base 30b having a chirp ring embodied as an annular spatial arrangement of protrusions 40b formed in annular base 30b as exemplary shown in FIG. 5B. The dimensions of protrusions 40b vary along a 360° traversal of annular base 30b to define a chirp signal.

[0071] Still referring to FIG. 5A, centric ring 50 as shown in FIG. 1 of the present disclosure is again embodied by an outer circle of uniformly spaced objects 50a (e.g., cooper balls, brass balls, etc.) affixed adjacent an outer perimeter of annular base 30b, and an inner circle of uniformly spaced objects 50b (e.g., cooper balls, brass balls, etc.) affixed adjacent an inner perimeter of annular base 30b. Each object 50a of the outer circle is paired with a corresponding object 50b of the inner circle to define an intersection line of a center point 21b of X-ray ring marker 20b serving as an origin of a coordinate system X.sub.20b-Y.sub.20b-Z.sub.20b of X-ray ring marker 20b (Z-axis not shown).

[0072] FIG. 6 illustrates a dual X-ray ring marker 22b of the present disclosure employing a pair of X-ray ring markers 20b of FIG. 5A of the present disclosure connected via a bridge 23b. In practice, bridge 23b may be any shape suitable for a C-Arm.fwdarw.X-ray ring maker 20 registration involving a movement of C-arm from a baseline imaging pose to a target imaging pose as will be further described in the present disclosure, such as, for example, a prismatic shape of bridge 23b for establishing a co-planar alignment of the pair of X-ray ring markers 20b as shown in FIG. 6.

[0073] FIG. 7 illustrates an embodiment 20c of X-ray ring marker 20 of FIG. 1 of the present disclosure. X-ray ring marker 20c employs an annular base 30c having a chirp ring embodied by an outer circle of varyingly spaced objects 40c (e.g., cooper balls, brass balls, etc.) affixed adjacent an outer perimeter of annular base 30c, and an inner circle of varyingly spaced objects 40d (e.g., cooper balls, brass balls, etc.) affixed adjacent an inner perimeter of annular base 30c. The spacing of the objects 40c and 40d vary along a 360° traversal of annular base 30c to define a chirp signal.

[0074] Still referring to FIG. 7, X-ray ring marker 20c further employs a centric ring embodied as uniformly spaced protrusions 50c formed into annular base 30c. Each protrusion 50c is paired with a corresponding 180° protrusion 50c to define intersection lines of a center point 21c of X-ray ring marker 20c serving as an origin of a coordinate system X.sub.20c-Y.sub.20c-Z.sub.20c of X-ray ring marker 20c (Z-axis not shown).

[0075] In an alternative embodiment, centric ring may be embodied as uniformly spaced indentations formed into annular base 30c. Each indentations would be paired with a corresponding 180° indentation to define intersection lines of center point 21c of X-ray ring marker 20c.

[0076] FIG. 8 illustrates a dual X-ray ring marker 22c of the present disclosure employing a pair of X-ray ring markers 20c of FIG. 7 of the present disclosure connected via a bridge 23c. In practice, bridge 23c may be any shape suitable for a C-Arm.fwdarw.X-ray ring maker 20 registration involving a movement of C-arm from a baseline imaging pose to a target imaging pose as will be further described in the present disclosure, such as, for example, a prismatic shape of bridge 23c for establishing a co-planar alignment of the pair of X-ray ring markers 20c as shown in FIG. 8.

[0077] FIG. 9 illustrates an embodiment 20d of X-ray ring marker 20 of FIG. 1 of the present disclosure. X-ray ring marker 20d employs an annular base 30d having a chirp ring embodied by an outer circle of varyingly spaced objects 40e (e.g., cooper balls, brass balls, etc.) affixed adjacent an outer perimeter of annular base 30d. The spacing of the objects 40e vary along a 360° traversal of annular base 30d to define a chirp signal.

[0078] Still referring to FIG. 9, X-ray ring marker 20d further employs a centric ring embodied an inner circle of varyingly spaced objects 50d (e.g., cooper balls, brass balls, etc.) affixed adjacent an inner perimeter of annular base 30d. Each object 50d is paired with a corresponding 180° object 50d to define intersection lines of a center point 21d of X-ray ring marker 20d serving as an origin of a coordinate system X.sub.20d-Y.sub.20d-Z.sub.20d of X-ray ring marker 20d (Z-axis not shown).

[0079] FIG. 10 illustrates a dual X-ray ring marker 22d of the present disclosure employing a pair of X-ray ring markers 20d of FIG. 7 of the present disclosure connected via a bridge 23d. In practice, bridge 23d may be any shape suitable for a C-Arm.fwdarw.X-ray ring maker 20 registration involving a movement of C-arm from a baseline imaging pose to a target imaging pose as will be further described in the present disclosure, such as, for example, a prismatic shape of bridge 23d for establishing a co-planar alignment of the pair of X-ray ring markers 20d as shown in FIG. 10.

[0080] To further facilitate an understanding of various aspects of the present disclosure, the following description of FIGS. 11-18 teaches embodiments of a C-Arm Arm.fwdarw.X-ray ring maker registration of the present disclosure. From this description, those having ordinary skill in the art will appreciate how to apply various aspects of the present disclosure for making and using additional embodiments of C-Arm.fwdarw.X-ray ring maker registration of the present disclosure.

[0081] In practice, a C-Arm.fwdarw.X-ray ring maker registration of the present disclosure may be implemented in a baseline phase and a target phase for generating registration parameters to facilitate a wide range of C-Arm intervention technologies including, but not limited to, robot three-dimensional measurements, anatomical/implant tracking, image stitching, pre-operative image overlay and first-time-right C-Arm positioning.

[0082] Referring to FIG. 11A, generally in the baseline phase, an embodiment of X-ray ring marker 20 as shown in FIG. 1 of the present disclosure or an embodiment of dual X-ray ring marker 22 shown in FIG. 2 of the present disclosure has a fixed position within an intervention space (e.g., an attachment to an operating table, a rail, a drape, or an intervention robot) and a body part of interest of a patient PBP is positioned above and adjacent X-ray ring marker 20 or dual X-ray ring marker 22.

[0083] A X-ray source 61 and a X-ray detector 62 of a C-Arm 60 are positioned in a baseline imaging pose to generate a baseline X-ray image 63 illustrating an image of X-ray ring marker 20i below an image of patient body part PBPi.

[0084] A C-Arm registration controller 70 acquires data of baseline X-ray image 63 and executes a C-Arm.fwdarw.X-ray ring marker registration 71 of the present disclosure to derive baseline position parameters 72 and a baseline twist parameter 73 as a first subset of the registration parameters as will be further described in the present disclosure.

[0085] Referring to FIG. 11B, generally in the target phase, X-ray source 61 and X-ray detector 62 of C-Arm 60 are moved from the baseline imaging pose to a target imaging pose, such as, for example, a rotation of C-arm 60 from the baseline imaging pose of FIG. 11A of the present disclosure to a target imaging pose of FIG. 11B. At the target imaging pose, X-ray source 61 and X-ray detector 62 of C-Arm 60 are positioned to generate a target X-ray image 64 illustrating an image of X-ray ring marker 20i below an image of patient body part PBPi.

[0086] C-Arm registration controller 70 acquires target X-ray image 64 and executes C-Arm.fwdarw.X-ray ring marker registration 71 of the present disclosure to derive target position parameters 74 and a target twist parameter 75 as a second final subset of the registration parameters as will be further described in the present disclosure.

[0087] C-Arm registration controller 70 may further execute C-Arm.fwdarw.X-ray ring marker registration 71 to implement of one or more intervention steps to generate intervention data 76 based on the registration parameters.

[0088] In practice, any imaging pose of a C-arm may serve as a baseline imaging pose for one C-Arm.fwdarw.X-ray ring marker registration during an intervention/diagnostic/imaging procedure, and may serve as a target imaging pose for another C-Arm.fwdarw.X-ray ring marker registration during the same or different intervention/diagnostic/imaging procedure.

[0089] FIG. 12 illustrates a flowchart 80 representative of an embodiment of C-Arm.fwdarw.X-ray ring marker registration 71. To facilitate an understanding of flowchart 80, FIG. 12 will be described in reference to FIGS. 11A, 11B, 14A and 14B. From this description, those having ordinary skill in the art will appreciate how to apply flowchart 80 to numerous and various additional embodiments of C-Arm.fwdarw.X-ray ring marker registration 71.

[0090] Referring to FIGS. 11A and 12, a stage S82 of flowchart 80 encompasses an acquisition by controller 70 of baseline X-ray image 63 from C-arm 60 as known in the art of the present disclosure. More particularly during the baseline phase, as shown in FIG. 14A, the C-Arm.fwdarw.X-ray ring marker registration 71 involves registering a position and a twist of X-ray ring marker 20 of the present disclosure within a X-ray projection 68B originating from a focal spot 67 of X-ray source 61 to X-ray detector 62.

[0091] In practice, a X.sub.62-Y.sub.62-Z.sub.62 coordinate system of C-Arm 60 may be defined on X-ray detector 62 whereby the X-axis and the Y-axis of the coordinate system of C-Arm 60 may be aligned with a coordinate system of the baseline X-ray image, such as, for example a X.sub.65a-Y.sub.65a coordinate system of baseline X-ray image 63 shown in FIG. 11A. An origin 69 of X.sub.62-Y.sub.62-Z.sub.62 coordinate system of C-Arm 60 may be delineated whereby X-ray source 62 is on a positive range of a Z.sub.62 axis of X.sub.62-Y.sub.62-Z.sub.62 coordinate system of C-Arm 60 whereby focal spot 67 of X-ray source 61 has a (0, 0, +Z.sub.62) coordinate within X.sub.62-Y.sub.62-Z.sub.62 coordinate system of C-Arm 60.

[0092] Referring back to FIGS. 11A and 12, a stage S84 of flowchart 80 encompasses controller 70 deriving baseline position parameters t.sub.x.sup.B, t.sub.y.sup.B, t.sub.z.sup.B, θ.sub.z1.sup.B and θ.sub.x.sup.B of X-ray ring marker 20 as a function of an illustration of the centric ring within the baseline X-ray image 63. The baseline position parameters t.sub.x.sup.B, t.sub.y.sup.B, t.sub.z.sup.B, θ.sub.z1.sup.B and θ.sub.x.sup.B are definitive of a position of X-ray ring marker 20 within the baseline X-ray projection 68B.

[0093] Stage S84 of flowchart 80 further encompasses controller 70 deriving a baseline twist parameter θ.sub.z2.sup.B of X-ray ring marker 20 as a function of the baseline position parameters t.sub.x.sup.B, t.sub.y.sup.B, t.sub.z.sup.B, θ.sub.z1.sup.B and θ.sub.x.sup.B of an illustration of the chirp ring within the baseline X-ray image 63. The baseline twist parameter θ.sub.z2.sup.B is definitive of a twist of the X-ray ring marker 20 within the baseline X-ray projection 68B.

[0094] In one embodiment of stage S84, controller 70 executes a registration parameter computation method of the present disclosure represented by a flowchart 90 of FIG. 13.

[0095] Referring to FIGS. 13 and 14A, a stage S92 of flowchart 90 encompasses a computation of a center point 21 of X-ray ring marker 20 on X-ray detector 62.

[0096] In one embodiment of stage S92 with spherical objects (e.g., cooper balls or brass balls. etc.), an identification of the spherical objects as illustrated within baseline X-ray image 63 starts with an adaptive thresholding technique as known in the art of the present disclosure to identify imaging blobs within the baseline X-ray image 63 followed by a series of morphological operations to eliminate blobs having a smaller size relative to the size of the spherical objects.

[0097] From the remaining image blobs within the baseline X-ray image, image blobs having an aspect ratio close to round and areas between certain thresholds are selected as candidate spherical objects radial pairs whereby blob pairs with a distance therebetween within a certain range are selected as radial pairs whereby an intersection of all lines defined by radial pairs are computed using a least square approach providing a residual. A robustness of identification of the spherical objects as illustrated within a baseline X-ray image 63 is improved by iteratively eliminating candidate spherical objects that lead to large residual values.

[0098] The result of stage S92 is a following listing of an M number of paired objects in the C-Arm coordinate system: {[(X.sub.1.sup.1, Y.sub.1.sup.1), (X.sub.1.sup.2, Y.sub.1.sup.2)] . . . [(X.sub.M.sup.1, Y.sub.M.sup.1), (X.sub.M.sup.2, Y.sub.M.sup.2)]}, M≥2.

[0099] Still referring to FIGS. 13 and 14A, stage S92 further encompasses controller 70 delineating intersection lines between paired objects {[(X.sub.1.sup.1, Y.sub.1.sup.1), (X.sub.1.sup.2, Y.sub.1.sup.2)] . . . [(X.sub.M.sup.1, Y.sub.M.sup.1), (X.sub.M.sup.2, Y.sub.M.sup.2)]}, M≥2, within the baseline X-ray image 63 to compute a projection (X.sub.C, Y.sub.C) of a center of the X-ray ring marker 20 on the X-ray detector 62.

[0100] Referring back to FIGS. 13 and 14A, a stage S94 of flowchart 90 encompasses controller 70 utilizing the projection (X.sub.C, Y.sub.C) of a center point 21 of the X-ray ring marker 20 on the X-ray detector 62 during stage S92 to compute baseline position parameters t.sub.x.sup.B, t.sub.y.sup.B, t.sub.z.sup.B, θ.sub.z1.sup.B and θ.sub.x.sup.B.

[0101] In one embodiment of stage S94, based on the projection (X.sub.C, Y.sub.C) of a center point 21 of the X-ray ring marker 20 on the X-ray detector 62, the projection ray defining the center point 21 of the X-ray ring marker 20 extend from source point (0, 0, S.sub.d.sup.B) to detector point (X.sub.C, Y.sub.C, 0). This means that the center point 21 of the X-ray ring marker 20 may be parameterized by the following equation [1]:

[00001]$\begin{array}{cc}\left(\begin{array}{c}{t}_x^B\\ t_y^B\\ t_z^B\end{array}\right)=\left(\begin{array}{cc}{X}_c^B& \frac{S_d^B-t_z^B}{S_d^B}\\ Y_c^B& \frac{S_d^B-t_z^B}{S_d^B}\\ t_z^B& \end{array}\right);t_z^B\in \left(0,S_d^B\right)& \left[1\right]\end{array}$

[0102] Assuming the listed object points {[(X.sub.1.sup.1, Y.sub.1.sup.1), (X.sub.1.sup.2, Y.sub.1.sup.2)] . . . [(X.sub.M.sup.1, Y.sub.M.sup.1), (X.sub.M.sup.2, Y.sub.M.sup.2)]} is such that the first point belongs to inner centering circle of a radius R.sub.I and the belongs to an the outer centering circle of a radius R.sub.O, a cost function may be defined with parameters t.sub.z.sup.B, θ.sub.z1.sup.B and θ.sub.x.sup.B as a measure of how well the object points fit X-ray ring marker 20 placed at a location (t.sub.x.sup.B, t.sub.y.sup.B, t.sub.z.sup.B).sup.T and angulation θ.sub.z1.sup.B and θ.sub.x.sup.B.

[0103] In one embodiment, the cost function is constructed as follows.

[0104] First, a cost CF is initialized at a value of zero (0).

[0105] Second, for each landmark pair {[(X.sub.i.sup.1, Y.sub.i.sup.1), (X.sub.i.sup.2, Y.sub.i.sup.2)]: [0106] a. a computation of an intersection between segment {[(X.sub.i.sup.1, Y.sub.i.sup.1, 0), (0, 0, S.sub.d.sup.B).sub.] and marker XY plane assuming that the X-ray ring marker 20 is at a location (t.sub.x.sup.B, t.sub.y.sup.B, t.sub.z.sup.B).sup.T and angulation θ.sub.z1.sup.B and θ.sub.x.sup.B. This point is (Xsol.sub.1, Ysol.sub.1, 0) in the marker coordinate system; [0107] b. a closest point on the circle to (Xsol.sub.1, Ysol.sub.1, 0) is (Xr.sub.1, Yr.sub.1, 0)=(R.sub.1 cos(ϕ.sub.1), R.sub.1 sin(ϕ.sub.1), 0), where ϕ.sub.1−atan 2(Ysol.sub.1, Xsol.sub.1); [0108] c. the square distance between the two points is dsq.sub.1−(Xsol.sub.1−xr.sub.1).sup.2+(Ysol.sub.1−yr.sub.1).sup.2 [0109] d. update cost function CF+=dsq.sub.1; [0110] e. a computation of an intersection between segment {[(X.sub.i.sup.2, Y.sub.i.sup.2, 0), (0, 0, S.sub.d.sup.B)] and marker XY plane assuming that the X-ray ring marker 20 is at a location (t.sub.x.sup.B, t.sub.y.sup.B, t.sub.z.sup.B).sup.T and angulation θ.sub.z1.sub.B and θ.sub.x.sub.B. This point is (xsol.sub.2, ysol.sub.2, 0) in the marker coordinate system; [0111] f. a closest point on the circle to (Xsol.sub.2, Ysol.sub.2, 0) is (Xr.sub.2, Yr.sub.2, 0)=(R.sub.2 cos(ϕ.sub.2), R.sub.1 sin(ϕ.sub.2), 0), where ϕ.sub.2−atan 2(Ysol.sub.2, Xsol.sub.2); [0112] g. the square distance between the two points is dsq.sub.2−(Xsol.sub.2−Xr.sub.2).sup.2+(Ysol.sub.2−Yr.sub.2).sup.2 [0113] h. update cost function CF+=dsq.sub.2;

[0114] This is repeated for all M points and minimized using a Levenberg-Marquardt routine as known in the art of the present disclosure to find the optical values of position parameters t.sub.z.sup.B, θ.sub.z1.sup.B and θ.sub.x.sup.B, and provide position parameters t.sub.x.sup.B and t.sub.y.sup.B.

[0115] Still referring to FIGS. 13 and 14A, a stage S96 of flowchart 90 encompasses controller 70 utilizes baseline position parameters t.sub.x.sup.B, t.sub.y.sup.B, t.sub.z.sup.B, θ.sub.z1.sup.B and θ.sub.x.sup.B and the chirp signal to compute baseline twist parameter θ.sub.z2.sup.B.

[0116] In one embodiment of stage S96, points on a rim of X-ray ring marker 20 may be parameterized in accordance with the following three equations [2]-[4]:

[00002]$\begin{array}{cc}p\left(t\right)=R_z^B\left({\theta }_{z1}^B\right)R_x^B\left({\theta }_x^B\right)R_z^B\left({\theta }_{z2}^B\right)\left(\begin{array}{c}\frac{R_i+R_0}{2}\cos \left(t\right)\\ \frac{R_i+R_0}{2}\sin \left(t\right)\\ 0\end{array}\right)+\left(\begin{array}{c}{t}_x^B\\ t_y^B\\ t_z^B\end{array}\right);t\in \left[0,2\pi \right]& \left(2\right)\\ p\left(t\right)=R_z^B\left({\theta }_{z1}^B\right)R_x^B\left({\theta }_x^B\right)R_z^B\left({\theta }_{z2}^B+t\right)\left(\begin{array}{c}\frac{R_i+R_0}{2}\\ 0\\ 0\end{array}\right)+\left(\begin{array}{c}{t}_x^B\\ t_y^B\\ t_z^B\end{array}\right);t\in \left[0,2\pi \right]& \left(3\right)\\ p\left(t_1\right)=R_z^B\left({\theta }_{z1}^B\right)R_x^B\left({\theta }_x^B\right)R_z^B\left(t_1\right)\left(\begin{array}{c}\frac{R_i+R_0}{2}\\ 0\\ 0\end{array}\right)+\left(\begin{array}{c}{t}_x^B\\ t_y^B\\ t_z^B\end{array}\right);t_1\in \left[0,2\pi \right]& \left(4\right)\end{array}$

[0117] Thus, p(t.sub.1) is projected onto the X-ray detector 62 through a perspective transformation with known parameters and the pixel values are retrieved I(t.sub.1) as exemplary shown in FIG. 14A. The chip ring has a model in accordance with the following equation [5]:

c(t)=Ae.sup.jf.sup.s.sup.t(1+tf.sup.sh.sup.);t∈[0,2π]  (5)

[0118] where f.sub.S is the start frequency (e.g., 40 Hz) and f.sub.sh is the frequency shift (e.g., 1/2π).

[0119] Then, an offset t.sub.0 is computed to maximize a normalized cross correlation between signals I(t.sub.1) and c(t.sub.1+t.sub.0). Since the intensity signal embeds the twist θ.sub.z2.sup.B through t.sub.1 whereas c(t) doesn't, then t.sub.0≡θ.sub.z2.sup.B.

[0120] Referring back to FIGS. 11A and 13, a stage S98 of flowchart 90 encompasses controller 70 optimizing baseline position parameters t.sub.x.sup.B, t.sub.y.sup.B, t.sub.z.sup.B, θ.sub.z1.sup.B and θ.sub.x.sup.B and baseline twist parameter θ.sub.z2.sup.B.

[0121] In one embodiment of stage S98, a final optimization matches the locations of the object points from the model of the X-ray ring marker 20 with the locations of the object points in the baseline X-ray image 63. This final optimization provides a measure of the Marker Registration Error (MRE) as a squared sum of the distances between the object points projected using the model of the X-ray ring marker 20 and the baseline parameters t.sub.x.sup.B, t.sub.y.sup.B, t.sub.z.sup.B, θ.sub.z1.sup.B, θ.sub.x.sup.B and θ.sub.z2.sup.B the object point projections retrieved from the baseline X-ray image 63. An MRE of less than 1 pixel squared, where a pixel edge length is fixed (e.g., 0.64 mm of a source-detector distance and zoom remained constant across all images), is an indication of an accurate C-Arm.fwdarw.X-ray ring marker registration.

[0122] Referring to FIGS. 11B and 12, a stage S86 of flowchart 80 encompasses an acquisition by controller 70 of target X-ray image 64 from C-arm 60 as known in the art of the present disclosure. More particularly, as shown in FIG. 14B, during the target phase the C-Arm.fwdarw.X-ray ring marker registration 71 involves registering a position and a twist of X-ray ring marker 20 of the present disclosure within a target X-ray projection 68T originating from a focal spot 67 of X-ray source 61 to X-ray detector 62.

[0123] In practice, a X.sub.62-Y.sub.62-Z.sub.62 coordinate system of C-Arm 60 may be defined on X-ray detector 62 whereby the X-axis and the Y-axis of the coordinate system of C-Arm 60 may be aligned with a coordinate system of the target X-ray image, such as, for example a X.sub.65a-Y.sub.65a coordinate system of target X-ray image 64 shown in FIG. 11B. An origin 69 of X.sub.62-Y.sub.62-Z.sub.62 coordinate system of C-Arm 60 may be delineated whereby X-ray source 62 is on a positive range of a Z.sub.62 axis of X.sub.62-Y.sub.62-Z.sub.62 coordinate system of C-Arm 60 whereby focal spot 67 of X-ray source 61 has a (0, 0, +Z.sub.62) coordinate within X.sub.62-Y.sub.62-Z.sub.62 coordinate system of C-Arm 60. Referring back to FIGS. 11B and 12, stage S88 of flowchart 80 encompasses controller 70 deriving target position parameters t.sub.x.sup.T, t.sub.y.sup.T, t.sub.z.sup.T, θ.sub.z1.sup.T and θ.sub.x.sup.T of X-ray ring marker 20 as a function of an illustration of the centric ring within the target X-ray image 64. The target position parameters t.sub.x.sup.T, t.sub.y.sup.T, t.sub.z.sup.T, θ.sub.z1.sup.T and θ.sub.x.sup.T are definitive of a position of X-ray ring marker 20 within the target X-ray projection 68B.

[0124] Stage S88 of flowchart 80 further encompasses controller 70 deriving a target twist parameter θ.sub.z2.sup.T of X-ray ring marker 20 as a function of the target position parameters t.sub.x.sup.T, t.sub.y.sup.T, t.sub.z.sup.T, θ.sub.z1.sup.T and θ.sub.x.sup.T and of an illustration of the chirp ring within the target X-ray image 64. The target twist parameter θ.sub.z2.sup.T is definitive of a twist of the X-ray ring marker 20 within the target X-ray projection 68T.

[0125] In one embodiment of stage S88, controller 70 executes registration parameter computation method of the present disclosure as represented by flowchart 90 of FIG. 13.

[0126] Referring to FIGS. 13 and 14B, stage S92 of flowchart 90 encompasses a computation of a center point 21 of X-ray ring marker 20 on X-ray detector 62.

[0127] In one embodiment of stage S92 with spherical objects (e.g., cooper balls or brass balls. etc.), an identification of the spherical objects as illustrated within target X-ray image 64 starts with an adaptive thresholding technique as known in the art of the present disclosure to identify imaging blobs within the target X-ray image 64 followed by a series of morphological operations to eliminate blobs having a smaller size relative to the size of the spherical objects.

[0128] From the remaining image blobs within the target X-ray image, image blobs having an aspect ratio close to round and areas between certain thresholds are selected as candidate spherical objects radial pairs whereby blob pairs with a distance therebetween within a certain range are selected as radial pairs whereby an intersection of all lines defined by radial pairs are computed using a least square approach providing a residual. A robustness of identification of the spherical objects as illustrated within a target X-ray image 64 is improved by iteratively eliminating candidate spherical objects that lead to large residual values.

[0129] The result of stage S88 is a following listing of an M number of paired objects in the C-Arm coordinate system: {[(X.sub.1.sup.1, Y.sub.1.sup.1), (X.sub.1.sup.2, Y.sub.1.sup.2)] . . . [(X.sub.M.sup.1, Y.sub.M.sup.1), (X.sub.M.sup.2, Y.sub.M.sup.2)]}, M≥2.

[0130] Still referring to FIGS. 13 and 14B, stage S92 further encompasses controller 70 delineating intersection lines between paired objects {[(X.sub.1.sup.1, Y.sub.1.sup.1), (X.sub.1.sup.2, Y.sub.1.sup.2)] . . . [(X.sub.M.sup.1, Y.sub.M.sup.1), (X.sub.M.sup.2, Y.sub.M.sup.2)] }, M≥2, within the target X-ray image 64 to compute a projection (X.sub.C, Y.sub.C) of a center of the X-ray ring marker 20 on the X-ray detector 62.

[0131] Referring back to FIGS. 13 and 14B, stage S94 of flowchart 90 encompasses controller 70 utilizing the projection (X.sub.C, Y.sub.C) of a center point 21 of the X-ray ring marker 20 on the X-ray detector 62 during stage S92 to compute target position parameters t.sub.x.sup.T, t.sub.y.sup.T, t.sub.z.sup.T, θ.sub.z1.sup.T and θ.sub.x.sup.T.

[0132] In one embodiment of stage S94, based on the projection (X.sub.C, Y.sub.C) of a center point 21 of the X-ray ring marker 20 on the X-ray detector 62, the projection ray defining the center point 21 of the X-ray ring marker 20 extend from source point (0, 0, S.sub.d.sup.T) to detector point (X.sub.C, Y.sub.C, 0). This means that the center point 21 of the X-ray ring marker 20 may be parameterized by the following equation [6]:

[00003]$\begin{array}{cc}\left(\begin{array}{c}{t}_x^T\\ t_y^T\\ t_z^T\end{array}\right)=\left(\begin{array}{cc}{X}_c^T& \frac{S_d^T-t_z^T}{S_d^B}\\ Y_c^T& \frac{S_d^T-t_z^T}{S_d^T}\\ t_z^T& \end{array}\right);t_z^T\in \left(0,S_d^T\right)& \left[6\right]\end{array}$

[0133] Assuming the listed landmark points {[(X.sub.1.sup.1, Y.sub.1.sup.1), (X.sub.1.sup.2, Y.sub.1.sup.2)] . . . [(X.sub.M.sup.1, Y.sub.M.sup.1), (X.sub.M.sup.2, Y.sub.M.sup.2)]} is such that the first point belongs to inner centering circle of a radius R.sub.I and the belongs to an the outer centering circle of a radius R.sub.O, a cost function may be defined with parameters t.sub.z.sup.T, θ.sub.z1.sup.T and θ.sub.x.sup.T as a measure of how well the object points fit X-ray ring marker 20 placed at a location (t.sub.x.sup.T, t.sub.y.sup.T, t.sub.z.sup.T).sup.T and angulation θ.sub.z1.sup.T and θ.sub.x.sup.T.

[0134] In one embodiment, the cost function is constructed as follows.

[0135] First, a cost CF is initialized at a value of zero (0).

[0136] Second, for each landmark pair {[(X.sub.i.sup.1, Y.sub.i.sup.1), (X.sub.i.sup.2, Y.sub.i.sup.2)]: [0137] a. a computation of an intersection between segment {[(X.sub.i.sup.1, X.sub.i.sup.1, 0), (0, 0, S.sub.d)] and marker XY plane assuming that the X-ray ring marker 20 is at a location (t.sub.x.sup.T, t.sub.y.sup.T, t.sub.z.sup.T).sup.T and angulation θ.sub.z1.sup.T and θ.sub.x.sup.T This point is (Xsol.sub.1, Ysol.sub.1, 0) in the marker coordinate system; [0138] b. a closest point on the circle to (xsol.sub.1, ysol.sub.1, 0) is (Xr.sub.1, Yr.sub.1, 0)=(R.sub.1 cos(ϕ.sub.1), R.sub.1 sin(ϕ.sub.1), 0), where ϕ.sub.1−atan 2(Ysol.sub.1, Xsol.sub.1); [0139] c. the square distance between the two points is dsq.sub.1−(Xsol.sub.1-Xr.sub.1).sup.2+(Ysol.sub.1−Yr.sub.1).sup.2 [0140] d. update cost function CF+=dsq.sub.1; [0141] e. a computation of an intersection between segment {[(X.sub.i.sup.2, y.sub.i.sup.2, 0), (0, 0, S.sub.d)] and marker XY plane assuming that the X-ray ring marker 20 is at a location (t.sub.x.sup.T, t.sub.y.sup.T, t.sub.z.sup.T).sup.T and angulation θ.sub.z1.sup.T and θ.sub.x.sup.T. This point is (Xsol.sub.2, Ysol.sub.2, 0) in the marker coordinate system; [0142] f. a closest point on the circle to (Xsol.sub.2, Ysol.sub.2, 0) is (Xr.sub.2, Yr.sub.2, 0)=(R.sub.2 cos(ϕ.sub.2), R.sub.1 sin(ϕ.sub.2), 0), where ϕ.sub.2−atan 2(Ysol.sub.2, Xsol.sub.2); [0143] g. the square distance between the two points is dsq.sub.2−(Xsol.sub.2−Xr.sub.2).sup.2+(Ysol.sub.2−Yr.sub.2).sup.2 [0144] h. update cost function CF+=dsq.sub.2;

[0145] This is repeated for all M points and minimized using a Levenberg-Marquardt routine as known in the art of the present disclosure to find the optical values of position parameters t.sub.z.sup.T, θ.sub.z1.sup.T and θ.sub.x.sup.T, and provide position parameters t.sub.x.sup.T and t.sub.y.sup.T.

[0146] Still referring to FIGS. 13 and 14B, a stage S96 of flowchart 90 encompasses controller 70 utilizes target position parameters t.sub.x.sup.T, t.sub.y.sup.T, t.sub.z.sup.T, θ.sub.z1.sup.T and θ.sub.x.sup.T and the chirp signal to compute target twist parameter θ.sub.z2.sup.T.

[0147] In one embodiment of stage S96, points on a rim of X-ray ring marker 20 may be parameterized in accordance with the following three equations [7]-[9]:

[00004]$\begin{array}{cc}p\left(t\right)=R_z^T\left({\theta }_{z1}^T\right)R_x^T\left({\theta }_x^T\right)R_z^T\left({\theta }_{z2}^T\right)\left(\begin{array}{c}\frac{R_i+R_0}{2}\cos \left(t\right)\\ \frac{R_i+R_0}{2}\sin \left(t\right)\\ 0\end{array}\right)+\left(\begin{array}{c}{t}_x^T\\ t_y^T\\ t_z^T\end{array}\right);t\in \left[0,2\pi \right]& \left(7\right)\\ p\left(t\right)=R_z^T\left({\theta }_{z1}^T\right)R_x^T\left({\theta }_x^T\right)R_z^T\left({\theta }_{z2}^T+t\right)\left(\begin{array}{c}\frac{R_i+R_0}{2}\cos \left(t\right)\\ \frac{R_i+R_0}{2}\sin \left(t\right)\\ 0\end{array}\right)+\left(\begin{array}{c}{t}_x^T\\ t_y^T\\ t_z^T\end{array}\right);t\in \left[0,2\pi \right]& \left(8\right)\\ p\left(t_1\right)=R_z^T\left({\theta }_{z1}^T\right)R_x^T\left({\theta }_x^T\right)R_z^T\left(t_1\right)\left(\begin{array}{c}\frac{R_i+R_0}{2}\cos \left(t\right)\\ \frac{R_i+R_0}{2}\sin \left(t\right)\\ 0\end{array}\right)+\left(\begin{array}{c}{t}_x^T\\ t_y^T\\ t_z^T\end{array}\right);t\in \left[0,2\pi \right]& \left(9\right)\end{array}$

[0148] Thus, p(t.sub.1) is projected onto the X-ray detector 62 through a perspective transformation with known parameters and the pixel values are retrieved I(t.sub.1) as exemplary shown in FIG. 14B. The chip ring has a model in accordance with the following equation [10]:

c(t)=Ae.sup.jf.sup.s.sup.t(1+tf.sup.sh.sup.);t∈[0,2π]  [10]

[0149] where f.sub.S is the start frequency (e.g., 40 Hz) and f.sub.sh is the frequency shift (e.g., 1/2π).

[0150] Then, an offset t.sub.0 is computed to maximize a normalized cross correlation between signals I(t.sub.1) and c(t.sub.1+t.sub.0). Since the intensity signal embeds the twist θ.sub.z2.sup.T through t.sub.1 whereas c(t) doesn't, then t.sub.0≡θ.sub.z2.sup.T.

[0151] Referring back to FIGS. 11B and 13, stage S98 of flowchart 90 encompasses controller 70 optimizing target position parameters t.sub.x.sup.T, t.sub.y.sup.T, t.sub.z.sup.T, θ.sub.z1.sup.T and θ.sub.x.sup.T and target twist parameter θ.sub.z2.sup.T.

[0152] In one embodiment of stage S98, a final optimization matches the locations of the object points from the model of the X-ray ring marker 20 with the locations of the object points in the target X-ray image 64. This final optimization provides a measure of the Marker Registration Error (MRE) as a squared sum of the distances between the object points projected using the model of the X-ray ring marker 20 and the target parameters t.sub.x.sup.T, t.sub.y.sup.T, t.sub.z.sup.T, θ.sub.z1.sup.T, θ.sub.x.sup.T and θ.sub.z2.sup.T and the object point projections retrieved from the target X-ray image 64. An MRE of less than 1 pixel squared, where a pixel edge length is fixed (e.g., 0.64 mm of a source-detector distance and zoom remained constant across all images), is an indication of an accurate C-Arm.fwdarw.X-ray ring marker registration.

[0153] Referring back to FIG. 12, the generation of the registration parameters via flowchart 100 facilitates an implementation of a wide range of C-Arm intervention technologies including, but not limited to, robot three-dimensional measurements, anatomical/implant tracking, image stitching, pre-operative image overlay and first-time-right C-Arm positioning.

[0154] Referring to FIG. 16, a flowchart 100 is representative of an intervention step implementation method of the present disclosure in support of such C-Arm intervention technologies.

[0155] A stage S102 of flowchart 100 encompasses controller 70 controlling a delineation of a landmark in both the baseline X-ray image and the target X-ray image. For example, as shown in FIG. 18, a point 120B can be placed on a landmark of a baseline X-ray image 63B via and a projection 122 of this point 120.sub.B may then be overlaid a target X-ray image 64T. The same landmark 120.sub.T can be identified in target X-ray image 64B by sliding the point 120.sub.T along the projection line 122.

[0156] Once the same landmark is defined in both images 63B and 64T, controller 70 proceeds to a stage S104 of flowchart 100 to implement an intervention computation, such as, for example, a distance measurement between landmarks in the baseline/target images, a computation of three-dimensional angles between lines in the baseline/target images and three-dimensional reconstruction of linear or tree-like structures from the baseline/target images.

[0157] FIG. 17 illustrates a flowchart 110 as one embodiment of stage S104. Flowchart 110 uses the following TABLE 1 of previously computed registration parameters:

TABLE-US-00001 TABLE 1 CArm Registration Parameters Detector Projection Position t.sub.x t.sub.y t.sub.z θ.sub.z1 θ.sub.x θ.sub.z2 X Y Baseline t.sub.x.sup.B t.sub.y.sup.B t.sub.z.sup.B θ.sub.z1.sup.B θ.sub.x.sup.B θ.sub.z2.sup.B X.sup.B Y.sup.B Target t.sub.x.sup.T t.sub.y.sup.T t.sub.z.sup.T θ.sub.z1.sup.T θ.sub.x.sup.T θ.sub.z2.sup.T X.sup.T Y.sup.T

[0158] From TABLE 1, homogenous transformations may be computed from marker space to C-Arm space in accordance with the following equations [11] and [12]:

[00005]$\begin{array}{cc}{H}^B=\left(\begin{array}{cc}{R}_z^B\left({\theta }_{z1}^B\right)R_x^B\left({\theta }_x^B\right)R_z^B\left({\theta }_{z2}^B\right)& \begin{array}{c}{t}_x^B\\ t_y^B\\ t_z^B\end{array}\\ 0_{1\times 3}& 1\end{array}\right)& \left[11\right]\\ H^T=\left(\begin{array}{cc}{R}_z^T\left({\theta }_{z1}^T\right)R_x^T\left({\theta }_x^T\right)R_z^T\left({\theta }_{z2}^T\right)& \begin{array}{c}{t}_x^T\\ t_y^T\\ t_z^T\end{array}\\ 0_{1\times 3}& 1\end{array}\right)& \left[12\right]\end{array}$

[0159] where Rz(.) and Rx(.) are 3D rotations around the Z-axis and the A-axis, respectively.

[0160] For the baseline imaging pose, landmark 121 is on ray 69B as shown in FIG. 15 that is defined by points in accordance with the following equations [13] and [14]:

[00006]$\begin{array}{cc}{S}^B={\left(H^B\right)}^{-1}\left(\begin{array}{c}0\\ 0\\ S_d^B\\ 1\end{array}\right)& \left[13\right]\\ p^B={\left(H^B\right)}^{-1}\left(\begin{array}{c}{x}^B\\ y^B\\ 0\\ 1\end{array}\right)& \left[14\right]\end{array}$

[0161] For the target imaging pose, landmark 121 is on ray 69T as shown in FIG. 15 that is defined by points in accordance with the following equations [15] and [16]:

[00007]$\begin{array}{cc}{S}^T={\left(H^T\right)}^{-1}\left(\begin{array}{c}0\\ 0\\ S_d^B\\ 1\end{array}\right)& \left[15\right]\\ p^T={\left(H^T\right)}^{-1}\left(\begin{array}{c}{x}^T\\ y^T\\ 0\\ 1\end{array}\right)& \left[16\right]\end{array}$

[0162] Thus, the 3D position L of the landmark in the marker coordinates is computed by finding the intersection between the S.sup.Bp.sup.B and S.sup.T p.sup.BT. This embodiment may be extended to multiple points providing 3D landmark positions in marker space. With these it is easy to compute true distances between landmark, 3D angle between lines or to build approximate 3D reconstructions of linear or tree-like structures.

[0163] With the two images of the marker in the same position, the controller 70 may perform additional error checking by comparing the distances between known marker landmarks computed from the two views against the ones retrieved from the model.

[0164] To facilitate a further understanding of the various inventions of the present disclosure, the following description of FIG. 20 teaches an exemplary embodiment of a C-Arm registration controller of the present disclosure. From this description, those having ordinary skill in the art will appreciate how to apply various aspects of the present disclosure for making and using additional embodiments of C-Arm registration controller of the present disclosure.

[0165] Referring to FIG. 20, a C-Arm registration controller 210 includes one or more processor(s) 211, memory 212, a user interface 213, a network interface 214, and a storage 215 interconnected via one or more system buses 216.

[0166] Each processor 211 may be any hardware device, as known in the art of the present disclosure or hereinafter conceived, capable of executing instructions stored in memory 212 or storage or otherwise processing data. In a non-limiting example, the processor(s) 211 may include a microprocessor, field programmable gate array (FPGA), application-specific integrated circuit (ASIC), or other similar devices.

[0167] The memory 212 may include various memories, as known in the art of the present disclosure or hereinafter conceived, including, but not limited to, L1, L2, or L3 cache or system memory. In a non-limiting example, the memory 212 may include static random access memory (SRAM), dynamic RAM (DRAM), flash memory, read only memory (ROM), or other similar memory devices.

[0168] The user interface 213 may include one or more devices, as known in the art of the present disclosure or hereinafter conceived, for enabling communication with a user such as an administrator. In a non-limiting example, the user interface may include a command line interface or graphical user interface that may be presented to a remote terminal via the network interface 214.

[0169] The network interface 214 may include one or more devices, as known in the art of the present disclosure or hereinafter conceived, for enabling communication with other hardware devices. In a non-limiting example, the network interface 214 may include a network interface card (NIC) configured to communicate according to the Ethernet protocol. Additionally, the network interface 214 may implement a TCP/IP stack for communication according to the TCP/IP protocols. Various alternative or additional hardware or configurations for the network interface 214 will be apparent.

[0170] The storage 215 may include one or more machine-readable storage media, as known in the art of the present disclosure or hereinafter conceived, including, but not limited to, read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash-memory devices, or similar storage media. In various non-limiting embodiments, the storage 215 may store instructions for execution by the processor(s) 211 or data upon with the processor(s) 211 may operate. For example, the storage 215 may store a base operating system for controlling various basic operations of the hardware. The storage 215 also stores application modules in the form of executable software/firmware for implementing the various functions of the controller 210 as previously described in the present disclosure including, but not limited to, a C-Arm.fwdarw.X-ray ring marker registration module 218 as an embodiment of C-Arm.fwdarw.X-ray ring marker registration 71 as previously described in the present disclosure, and a ring marker removal module 219 as known in the art of the present disclosure for removing X-ray ring marker from an X-ray image being displayed.

[0171] In practice, controller 210 may be installed within a X-ray imaging system 200, an intervention system 201 (e.g., an intervention robot system), or a stand-alone workstation 202 in communication with X-ray imaging 200 system and/or intervention system 201 (e.g., a client workstation or a mobile device like a tablet). Alternatively, components of controller 210 may be distributed among X-ray imaging system 200, intervention system 201 and/or stand-alone workstation 202.

[0172] Referring to FIGS. 1-19, those having ordinary skill in the art of the present disclosure will appreciate numerous benefits of the inventions of the present disclosure including, but not limited to, a X-ray ring marker facilitating an accurate and reliable C-Arm Registration, particularly for mobile C-Arms.

[0173] Further, as one having ordinary skill in the art will appreciate in view of the teachings provided herein, structures, elements, components, etc. described in the present disclosure/specification and/or depicted in the Figures may be implemented in various combinations of hardware and software, and provide functions which may be combined in a single element or multiple elements. For example, the functions of the various structures, elements, components, etc. shown/illustrated/depicted in the Figures can be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software for added functionality. When provided by a processor, the functions can be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which can be shared and/or multiplexed. Moreover, explicit use of the term “processor” or “controller” should not be construed to refer exclusively to hardware capable of executing software, and can implicitly include, without limitation, digital signal processor (“DSP”) hardware, memory (e.g., read only memory (“ROM”) for storing software, random access memory (“RAM”), non-volatile storage, etc.) and virtually any means and/or machine (including hardware, software, firmware, combinations thereof, etc.) which is capable of (and/or configurable) to perform and/or control a process.

[0174] Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (e.g., any elements developed that can perform the same or substantially similar function, regardless of structure). Thus, for example, it will be appreciated by one having ordinary skill in the art in view of the teachings provided herein that any block diagrams presented herein can represent conceptual views of illustrative system components and/or circuitry embodying the principles of the invention. Similarly, one having ordinary skill in the art should appreciate in view of the teachings provided herein that any flow charts, flow diagrams and the like can represent various processes which can be substantially represented in computer readable storage media and so executed by a computer, processor or other device with processing capabilities, whether or not such computer or processor is explicitly shown.

[0175] Having described preferred and exemplary embodiments of the various and numerous inventions of the present disclosure (which embodiments are intended to be illustrative and not limiting), it is noted that modifications and variations can be made by persons skilled in the art in light of the teachings provided herein, including the Figures. It is therefore to be understood that changes can be made in/to the preferred and exemplary embodiments of the present disclosure which are within the scope of the embodiments disclosed herein.

[0176] Moreover, it is contemplated that corresponding and/or related systems incorporating and/or implementing the device/system or such as may be used/implemented in/with a device in accordance with the present disclosure are also contemplated and considered to be within the scope of the present disclosure. Further, corresponding and/or related method for manufacturing and/or using a device and/or system in accordance with the present disclosure are also contemplated and considered to be within the scope of the present disclosure.