Patent Description:
X-ray C-arm systems are frequently used in minimally invasive surgical procedures (e.g., orthopedic procedures, vascular interventions, etc.) for enabling surgeons to see inside a patient body by taking X-ray images from arbitrary directions. More particularly, a mobile C-arm usually has wheels to provide mobility around the room and once positioned, the mobile C-arm allows the user to adjust the position of the C-arm in five (<NUM>) directions. While this provides flexibility in the execution of minimally invasive surgical procedures, the exact position and angle of the X-ray projection is not known. This precludes the user from employing advanced tools including making true three-dimensional ("3D") measurements, large field of view imaging, dynamic overlay of pre-operative or intraoperative information, and target localization for image guided intervention. Thus, after a positioning of the mobile C-arm with respect to the patient body, there has been a need to compute a pose of the X-ray projection with respect to a fixed coordinate system, which is conventionally called C-arm Registration. Specifically, a mobile C-arm position is computed with respect to a fixed coordinate system and described by a homogeneous transformation composed of a translation vector (t ∈ R<NUM>) and a rotation matrix (R ∈ SO(<NUM>)). Therefore, the task has been to compute the pair (t, R) that accurately describes the position of the mobile C-arm with respect to the fixed coordinate system.

One historic approach for solving the C-arm Registration required an installation of hardware on the C-arm (e.g., optical tracking markers, inertial markers, etc.). This approach requires the addition of multiple components to the room and often negatively impacts the workflow for the procedure.

A current practice for C-Arm Registration is to provide a marker having a fixed position in the operating space (e.g., a marker attached to a robot or an operating table), and to generate an X-ray image of features of the marker to perform the C-arm Registration (e.g., steel balls or features of a known geometry). For such markers, there are cost-benefit tradeoffs with respect to a required registration accuracy, the number of opaque features on the marker, size of the marker, impact to the workflow, and impact to the x-ray image.

The article "<NPL>, presents a method for estimating the pose of a C-arm fluoroscopy device during interventions such as bronchoscopy. A specially designed marker pattern - composed of small steel spheres and radial sticks arranged on an acrylic plate - is placed on the patient table.

While known C-arm Registration methods have proven to be beneficial, there remains a need for improved techniques for providing accurate and reliable C-arm Registration, particularly for mobile C-arms. The present disclosure teaches a X-ray ripple marker that creates one or more X-ray imaged wave(s) with characteristics that are a function of a pose of an X-ray projection by the C-arm with respect to the X-ray ripple marker. In some implementations, X-ray ripple marker employs additional features (e.g., copper or steel balls) that improve registration algorithm robustness.

The invention is an C-arm registration system as defined in claim <NUM>.

The identification of the ripple pattern within the X-ray image is characteristic of a pose of the X-ray projection by the C-arm relative to the X-ray rippler marker, and the transformation parameter(s) is(are) definitive the pose of the X-ray projection by the C-arm relative to the X-ray rippler marker.

The pose of the X-ray projection by the C-arm relative to the X-ray ripple marker encompasses a location and/or an orientation of the X-ray projection by the C-arm within a coordinate system associated with the X-ray ripple marker (e.g., a coordinate system having the fixed point of the X-ray ripple marker as the origin or a coordinate system of an intervention device such as an intervention robot system having the X-ray ripple marker attached thereto).

In the invention, the C-arm registration controller is defined in claim <NUM>.

The invention also concerns an C-arm registration method as defined in claim <NUM>.

For various embodiments of the present disclosure, the ripple pattern includes a plurality of concentric circular ripples, a first series of concentric arc ripples, and/or a second series of concentric arc ripples dissimilar to the first series of concentric arc ripples in frequency, phase and/or amplitude.

For various embodiments of the present disclosure, the X-ray ripple marker further includes a chirp pattern and/or a landmark pattern axially aligned with the ripple pattern.

For purposes of the description and claims of the present disclosure:.

The foregoing embodiments and other embodiments of the inventions of the present disclosure as well as various structures and advantages of the inventions of the present disclosure will become further apparent from the following detailed description of various embodiments of the inventions of the present disclosure read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the inventions of the present disclosure rather than limiting, the scope of the inventions of the present disclosure being defined by the appended claims.

To facilitate an understanding of various aspects of the present disclosure, the following description of <FIG> teaches embodiments of an X-ray ripple 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 ripple markers of the present disclosure.

Referring to <FIG>, an X-ray ripple marker <NUM> of the present disclosure employs one or more radial ripples <NUM> integrated within a platform <NUM> and radially extending from a fixed point <NUM> of platform <NUM> (e.g., a center point of platform <NUM>).

In practice, platform <NUM> may have any size and shape that facilitates an X-ray imaging of radial ripple(s) <NUM> radially extending from fixed point <NUM> of platform <NUM>. For example, platform <NUM> may have a disc shape or a cuboid shape with radial ripple(s) <NUM> integrated onto a same side surface of the disc or the cuboid, and radially extending from any fixed point on that side surface of the disc or the cuboid (e.g., a center of the disc or the cuboid). The size of the disc and cuboid is not limited by the X-ray imaging space of one or particular types of X-ray imaging systems or generic to all X-ray imaging systems.

Also in practice, a radial ripple <NUM> may have any shape and dimensions that partially or fully encircles the fixed point. For example, <FIG> shows a radial ripple 30a as a circle fully encircling a fixed point <NUM> of platform <NUM>, <FIG> shows a radial ripple 30b as a <NUM>° arc partially encircling the fixed point <NUM> of platform <NUM>, <FIG> shows a radial ripple 30c as a <NUM>° arc partially encircling the fixed point <NUM> of platform <NUM> and <FIG> shows a radial ripple 30d as a <NUM>° arc partially encircling the fixed point <NUM> of platform <NUM>.

Further in practice, a radial ripple <NUM> may be integrated into platform <NUM> in any manner than facilitates an X-ray imaging of X-ray ripple marker <NUM> that distinguishes the radial ripple(s) <NUM> from the platform <NUM> within the X-ray image. For example, <FIG> shows a cross-section of a platform 40a having a plurality of radial ripples <NUM> as protrusions <NUM> upwardly extending from a top surface of platform 40a relative to a fixed point 41a, and <FIG> shows a cross-section of a platform 40b having a plurality of radial ripples as grooves <NUM> downwardly extending into a top surface of platform 40b relative to a fixed point 41b. Also by example, an X-ray ripple marker <NUM> may employ one or more radial ripples <NUM> as protrusions and one or more additional radial ripples <NUM> as grooves.

Referring back to <FIG>, for C-arm registration purposes, radial ripple(s) <NUM> are integrated onto platform <NUM> to form a ripple pattern that create(s) X-ray imaged wave(s) with characteristics that are a function of a position of an X-ray projection of a C-arm with respect to the X-ray ripple marker <NUM> as will be further described in the present disclosure with the C-arm registration description of <FIG>.

For example, <FIG> illustrates a radial pattern <NUM> of radial ripple(s) <NUM> being integrable onto a surface of a disc 40c or a platform 40b for creating X-ray imaged wave(s) as symbolically shown by waves 21a and 21b.

In practice, a frequency, a phase and/or an amplitude of an X-ray imaged wave may be the characteristic(s) that is(are) a function of a position of an X-ray projection of a C-arm with respect to the X-ray ripple marker <NUM>.

Further in practice, relative frequencies, relative phases and/or relative amplitudes of two or more X-ray imaged wave(s) may be the characteristics that is(are) a function of a position of an X-ray projection of a C-arm with respect to the X-ray ripple marker <NUM>.

In one embodiment of ripple pattern <NUM> as shown in <FIG>, a ripple pattern 50a of twenty (<NUM>) concentric circular radial ripples as integrated on disc 40c or cuboid 40d, which provides a five (<NUM>) degree of freedom transformation of an X-ray projection of a C-arm to the coordinate system associated with the marker using a single X-ray image.

In a second embodiment of ripple pattern <NUM> as shown in <FIG>, a ripple pattern 50b includes a series 51a of nine (<NUM>) concentric <NUM>° arc radial ripples, a series 51b of seventeen (<NUM>) concentric <NUM>° arc radial ripples, a series 51c of nine (<NUM>) concentric <NUM>° arc radial ripples and a series 51d of seventeen (<NUM>) concentric <NUM>° arc radial ripples. Ripple pattern 50b also provides a five (<NUM>) degree of freedom transformation of an X-ray projection of a C-arm to the coordinate system associated with the marker using a single X-ray image.

Still referring to <FIG>, in practice of a ripple pattern <NUM> having a plurality of arc series, an arc series may be identical to one or more other arc series in terms of frequency, phase and amplitude, or the arc series may be dissimilar to or more other arc series in terms of frequency, phase and/or amplitude.

Arc series 51a and arc series 51c are identical to each other in terms of frequency, phase and amplitude. Arc series 51a and arc series 51c are identical to arc series 51b and 51d in terms of phase, but dissimilar to arc series 51b and arc series in terms of 51d in frequency and amplitude.

For any embodiment of ripple pattern <NUM> (e.g., ripple pattern 50a of <FIG> and ripple pattern 50b of <FIG>), a chirp pattern of chirps (e.g., protrusions and/or grooves) may be axially aligned with a ripple pattern <NUM> to provide a sixth degree of freedom transformation of an X-ray projection of a C-arm to the coordinate system associated with the marker using a single X-ray image. For example, <FIG> shows a circular chirp pattern <NUM> of forty (<NUM>) chirps encircling a perimeter of ripple pattern <NUM>.

In practice, a chirp may be disposed on the same side surface of the platform as ripple pattern <NUM>, and/or a chirp may be disposed on a side surface of the platform opposing the ripple pattern <NUM>.

For any embodiment of ripple pattern <NUM> (e.g., ripple pattern 50a of <FIG> and ripple pattern 50b of <FIG>), a landmark pattern (e.g., a pattern of copper balls) may be axially aligned with the ripple pattern <NUM> to facilitate a finding of the fixed point of the platform and/or for C-arm registration computations including, but not limited to, a final optimization and registration error estimation. For example, <FIG> shows a landmark pattern of a series of sixteen (<NUM>) pairings of copper balls <NUM> encircling a perimeter of ripple pattern <NUM>.

In practice, the landmark pattern may be disposed on the same side surface of the platform as ripple pattern <NUM>, and/or the landmark pattern may be disposed on a side surface of the platform opposing the ripple pattern <NUM>.

From the description of <FIG>, those having ordinary skill in the art will appreciate the broad scope of embodiments of X-ray ripple markers of the present disclosure.

For example, <FIG> shows an exemplary X-ray ripple marker 20a incorporating a protrusion embodiment <NUM> of ripple pattern 50a (<FIG>) integrated on disc 40c, a protrusion embodiment 52a of circular chirp pattern <NUM> (<FIG>) disposed on a same side surface or an opposite side surface of disc 40c as ripple pattern 50a, and the landmark pattern of copper balls <NUM> of <FIG> encircling a perimeter of ripple pattern <NUM>.

By additional example, <FIG> shows an exemplary X-ray ripple marker 20b incorporating a protrusion embodiment <NUM> of ripple pattern 50a (<FIG>) integrated on disc 40c, and a progressive spacing protrusion embodiment 52b of circular chirp pattern <NUM> (<FIG>) disposed on the same side surface or the opposite side surface of disc 40c as ripple pattern 50a.

By further example, <FIG> shows an exemplary X-ray ripple marker 20c incorporating a protrusion embodiment 50d of ripple pattern 50b (<FIG>) integrated on cuboid 40d.

To further facilitate an understanding of various aspects of the present disclosure, the following description of <FIG> teaches embodiments of a C-arm 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 registration of the present disclosure.

While X-ray ripple marker 20a of <FIG> and X-ray ripple marker 20b of <FIG> will be utilized for purposes of describing embodiments of a C-arm registration of the present disclosure, those having ordinary skill in the art will appreciate how to apply various aspects of the present disclosure for executing a C-arm registration of the present disclosure using any embodiment of an X-ray ripple marker of the present disclosure.

Referring to <FIG>, a C-arm registration of the present disclosure is implemented in a patient-less mode and a patient mode.

Generally in the patient-less mode, an X-ray ripple marker <NUM> (e.g., X-ray ripple marker 20a of <FIG> or X-ray ripple marker 20b of <FIG> as shown) has a fixed position within an intervention space (e.g., an attachment to an operating table, a rail, a drape, or an intervention robot). An X-ray source <NUM> and an X-ray detector <NUM> of a C-arm <NUM> are translated and/or rotated to a position to generate an X-ray image <NUM> of a ripple pattern <NUM> of X-ray ripple marker <NUM>. A C-arm registration controller <NUM> acquires X-ray image <NUM> and executes a C-arm to marker registration <NUM> of the present disclosure delineating a position of an X-ray projection by C-arm <NUM> with respect to the X-ray ripple marker <NUM> as will be further described in the present disclosure. Subsequently, X-ray ripple marker <NUM> is removed from an imaging space of C-arm <NUM> whereby a patient may be positioned within the imaging space of C-arm <NUM> to thereby perform an intervention based on the C-arm registration involving a generation of X-ray image(s) <NUM>.

Generally in the patient mode, an X-ray ripple marker <NUM> (e.g., X-ray ripple marker 20a of <FIG> or X-ray ripple marker 20b of <FIG> as shown) has a fixed position within an intervention space (e.g., an attachment to an operating table or an intervention robot) and a body part of interest of a patient is positioned above and adjacent X-ray ripple marker <NUM> (body part not shown for clarity of the marker). The X-ray source <NUM> and the X-ray detector <NUM> of C-arm <NUM> are translated and/or rotated to a position to generate an X-ray image <NUM> of a ripple pattern <NUM> of X-ray ripple marker <NUM>. A C-arm registration controller <NUM> acquires X-ray image 65a and executes a C-arm to marker registration <NUM> of the present disclosure delineating a position of an X-ray projection by C-arm <NUM> with respect to the X-ray ripple marker <NUM> as will be further described in the present disclosure. C-arm registration controller <NUM> may additionally executes a ripple marker removal <NUM> of the present disclosure removing X-ray ripple marker <NUM> (or at least the ripple pattern <NUM>) from X-ray image 65a to render an X-ray image 65b for display during an intervention based on the C-arm registration of the present disclosure.

More particularly to both the patient-less mode and the patient mode, as shown in <FIG>, the C-arm to marker registration <NUM> involves registering a position of an X-ray projection relative to an X-ray ripple marker <NUM> of the present disclosure within a 3D coordinate system <NUM> or 3D a coordinate system <NUM> (only the Y-axis and the X-axis are shown, the Z-axis is not shown).

In practice, the X-ray projection may originate at any point of the X-ray source <NUM>, such as, for example, a focal spot <NUM> as shown in <FIG>.

In practice, X-ray ripple marker <NUM> may establish coordinate system <NUM> having a fixed point of the X-ray ripple marker <NUM> as the origin of coordinate system <NUM>, or alternatively, X-ray ripple marker <NUM> may be calibrated with a coordinate system <NUM> of an intervention device (e.g., an intervention robot system having the X-ray ripple marker <NUM> attached thereto).

Referring to <FIG>, a stage S82 of flowchart <NUM> encompasses controller <NUM> identifying a signature and a ripple pattern <NUM> of X-ray ripple marker <NUM> in the X-ray image <NUM> in the patient-less mode of <FIG> or in the X-ray image 65a of the patient mode of <FIG>. The identification of ripple pattern <NUM> within the X-ray image is characteristic of a position of the X-ray projection by the C-arm <NUM> (e.g., focal spot <NUM>) relative to the X-ray ripple marker <NUM>, meaning a location and/or an orientation the X-ray projection within coordinate system <NUM> or coordinate system <NUM> is characterized by ripple pattern <NUM> as illustrated within the X-ray image.

In practice, knowing the geometry of X-ray ripple marker <NUM> may serve as a basis for identifying X-ray maker <NUM> within the X-ray image when an entirety of X-ray ripple marker <NUM> is illustrated within the X-ray image, or the utilization of a landmark pattern (e.g., landmark pattern of copper balls <NUM>) may serve as a basis for identifying X-ray maker <NUM> within the X-ray image when a portion of X-ray ripple marker <NUM> is illustrated within the X-ray image.

For example, in the patient-less mode, X-ray ripple marker <NUM> may be aligned between focal spot <NUM> and X-ray detector <NUM> whereby an entirety of X-ray ripple marker <NUM> may be illustrated within X-ray image <NUM> (<FIG>).

By further example, in the patient mode, a landmark pattern of copper balls <NUM> (<FIG>) may be utilized to find the fixed point of X-ray ripple marker <NUM> (e.g., the center point), particularly when a portion of the X-ray ripple marker <NUM> is illustrated within X-ray image 65a (<FIG>).

A stage S84 of flowchart <NUM> involves a derivation of transformation parameter(s) from the ripple pattern <NUM> identified in stage S82 to thereby register X-ray ripple marker <NUM> and X-ray C-arm <NUM> during a stage S86 of flowchart <NUM>.

In practice, stage S84 involves a generation of transformation signal(s) from frequency(ies), phase(s) and/or amplitude(s) of the radial ripples of ripple pattern <NUM> identified in stage <NUM>. The transformation signal(s) may be analyzed during stage S84 to derive transformation parameter(s) that define the position of the X-ray projection by the C-arm <NUM> (e.g., focal spot <NUM>) relative to the X-ray ripple marker <NUM>, meaning a location and/or an orientation of the X-ray projection within coordinate system <NUM> or coordinate system <NUM> may now be determined from the transformation parameter(s) during stage S86.

In one embodiment of stages <NUM> and <NUM>, particularly for embodiments of ripple pattern <NUM> having an arrangement of radial ripples of the same frequency, phase and amplitude, a pose of X-ray ripple marker <NUM> in the C-arm space is described by a rigid body transformation composed of a rotation R and a translation t. The rotation is parameterized using ZXZ Euler angles as in accordance with the following equation [<NUM>]: <MAT> where RZ (θ) is a rotation around z axis with angle θ.

The translation vector t is composed of elementary displace-ments along axes as shown in the following equation [<NUM>]: <MAT>.

Any point pMarker ∈ R<NUM> in marker space <NUM> or <NUM> may be converted in C-arm space (e.g., having focal spot <NUM> as an origin) in accordance with the following equation [<NUM>]: <MAT>.

Similarly, a position of any point in C-arm space - pC-arm - can be translated in marker space <NUM> or <NUM> in accordance with the following equation [<NUM>]: <MAT>.

In a second embodiment of stages <NUM> and <NUM>, particularly for embodiments of ripple pattern <NUM> having an arrangement of a first series radial ripples and a second series of radial ripples having a frequency, a phase and/or an amplitude dissimilar from the first series of radial ripples, a distance from the focal spot <NUM> to the fixed point of the X-ray ripple marker <NUM> may be determined from the dissimilar frequencies, dissimilar phases and/or dissimilar amplitudes as will be exemplary described in the present disclosure with the description of <FIG>.

Still referring to <FIG>, for the patient mode only, a stage S88 of flowchart <NUM> involves a removal of X-ray ripple marker <NUM> from X-ray image 65a (<FIG>) to render X-ray image 65b (<FIG>). In practice, any technique may be used to remove the X-ray ripple marker <NUM> in a manner that minimizes, if not impedes, an induce artifacts and/or affect the illustrates of the patient body part in a same spatial frequency ranges as X-ray ripple marker <NUM>.

In one embodiment, a frequency-based filtering technique may be utilized during stage S88.

In a second embodiment, image subtraction technique may be utilized involving a transformation of a model of X-ray ripple marker <NUM> to an actual location and orientation of X-ray ripple marker in the X-ray image 65a to thereby subtract the X-ray ripple marker in the X-ray image 65a with minimal effect on image quality as will be exemplary described in the present disclosure with the description of <FIG>.

The following is a description of one embodiment of a patient mode of C-arm registration controller <NUM> (<FIG>) in the context of an X-ray image 63a of an X-ray ripple marker 20a being held by an arm <NUM> (e.g., a robot extension or C-arm extension) as shown in <FIG>. In practice, where the ripple pattern <NUM> of X-ray ripple marker 20a is passed through a perspective transformation, the pattern <NUM> will change into a chirp signal whereby the following equation [<NUM>] will become the following equation [<NUM>] whereby wave projection parameters c<NUM> and c<NUM> are a function of the perspective transformation parameters: <MAT> <MAT> where s(r) is the model sinusoidal pattern, A is the amplitude, fm is the frequency, and sp(s) is the projective geometry transformed pattern of s(r).

<FIG> shows the transformation of the sinusoidal signal of X-ray ripple marker <NUM> through a perspective projection. If the marker <NUM> is parallel with X-ray detector <NUM> and at a midpoint of an X-ray projection 120a as shown, then an original sinusoidal signal <NUM> of marker <NUM> is stretched into sinusoidal signal 122a whereby c<NUM> = <NUM> and c<NUM> = <NUM>. If the marker <NUM> is tilted with respect to X-ray detector <NUM> and at a midpoint of an X-ray projection 120b as shown, the c<NUM> > <NUM>, resulting in a chirp signal 122b (e.g., c<NUM> = <NUM> and c<NUM> = <NUM>). Thus, the signal along each diagonal of the marker is transformed through the perspective transformation into wave projection parameters c1 and c2.

<FIG> illustrates a flowchart <NUM> representative of a transformation generation method for X-ray ripple marker 20a shown in <FIG>.

Referring to <FIG>, a stage S92 of flowchart <NUM> encompasses controller <NUM> processing an acquired X-ray image 63a and a stored marker geometry <NUM> to compute (xbbi(k), ybbi(k)) coordinates <NUM> for each ball bearing landmark of X-ray ripple marker 20a to thereby find (xci, yci) coordinates <NUM> for the center point of X-ray ripple marker 20a during a stage S94 of flowchart <NUM>.

A stage S96 of flowchart <NUM> encompasses controller <NUM> processing acquired X-ray image 63a and computed center point (xci, yci) coordinates <NUM> to compute wave projection parameters c<NUM> and c<NUM>.

A stage S98 of flowchart <NUM> encompasses controller <NUM> processing acquired X-ray image 63a, wave projection parameters c<NUM> and c<NUM> and stored marker geometry <NUM> and C-arm geometry to obtain an initial approximation of transformation parameters (tx<NUM>, ty<NUM>, tz<NUM>, Θx<NUM>, Θy<NUM>, Θz<NUM>) <NUM>.

A stage S100 of flowchart <NUM> encompasses controller <NUM> processing transformation parameters (tx<NUM>, ty<NUM>, tz<NUM>, Θx<NUM>, Θy<NUM>, Θz<NUM>) <NUM>, (xbbi(k), ybbi(k)) coordinates <NUM> for each ball bearing landmark and stored marker geometry <NUM> and C-arm geometry to obtain a refinement/least square optimization of transformation parameters (tx, ty, tz, Θx, Θy, Θz) <NUM>, bearing projection <NUM> and error/rms <NUM>.

More particularly, in one embodiment of stages S92 and S94, a marker geometry <NUM> is such that a connection of the closet two (<NUM>) ball bearings defines lines that will intersect in the marker center as shown in <FIG>. Therefore, the projection of center of X-ray ripple marker 20a is identified by segmenting the BBs in the image 63a and grouping them to define rays as shown in <FIG>. The intersection of these rays defines the center of X-ray ripple marker 20a in image space.

The center of the ball bearings is computed using simple thresholding or more advanced algorithms, such as, for example, adaptive thresholding or Otsu thresholding. The ball bearing pairs are formed by simple clustering since the radial neighbor which is of interest is much closer than the lateral ones. After segmentation, blobs that are too small or too large are filtered out. Then, the intersection of the rays is computed using a linear least squares approach.

In one embodiment of stage S96, <FIG> illustrates a plot 123a of wave projection parameter c<NUM> and <FIG> illustrates a plot 123b of wave projection parameter c<NUM> for two marker positions for X-ray ripple marker 20a being parallel with X-ray detector <NUM> and at a midpoint of an X-ray projection 120a as shown in <FIG>. <FIG> illustrates a plot 123c of wave projection parameter c<NUM> and <FIG> illustrates a plot 123d of wave projection parameter c<NUM> for X-ray ripple marker 20a is tilted with respect to X-ray detector <NUM> and at a midpoint of an X-ray projection 120b as shown in <FIG>. The computation of wave projection parameters c<NUM> and c<NUM> for a diagonal is performed by maximizing the convolution of the image signal along that diagonal with the chirp signal windowed with a Gaussian function.

In one embodiment of stage S98, c<NUM>, c2, and a range ofy values are then used to compute the position of X-ray ripple marker 20a down to the twist around the axis of the marker 20a. An initial approximation of the marker position in the image space comprises five (<NUM>) degrees of freedom computed from wave projection parameters c<NUM> and c<NUM> and (<NUM>) degree of freedom which is twisted around z axis angle Θz2. The angle Θz2 is the one that maximizes the normalized cross correlation between the image signal retrieved at the coordinates corresponding to the projection of the rim chirp using the 5DOF initial position approximation and γ twist angle and the model chirp pattern in accordance with the following equation [<NUM>]: <MAT>.

<FIG> shows a registration verification after an initial approximation whereby a computed position 124a of marker 20a is very close to a true position 125b of marker 20a due to an error in the twist.

In one embodiment of stage S100, the computed position is optimized using a least squares approach. For each ball bearing identified in the image, bi ; i = <NUM>. n, a model corresponding to position bm i ; i = <NUM>. n is computed and subsequently, using the approximate parameters tx, ty, tz, θz1, θx, θz2 and C-arm geometry <NUM>, virtual projections are computed in accordance with the following equations [<NUM>] and [<NUM>]: <MAT> <MAT> where (xs, ys, zs)T is the position of the source <NUM> with respect to the detector <NUM> coordinate system, and pszx and pszy are the pixel sizes in x and y directions. It is assumed that the detector coordinate system coincides with the image coordinate system with only a difference in pixel size.

A cost function may then represented in accordance with the following equation [<NUM>]: <MAT>.

The cost function is minimized using a "Nelder-Mead" algorithm.

<FIG> shows a registration verification after final optimization whereby a computed position 124c of marker 20a corresponds to true position 125b of marker 20a.

Referring to <FIG>, a subtraction embodiment of stage S88 for a patient image 65a of X-ripple marker 20a as shown in <FIG> utilizes a pre-acquired image 126a of X-ray image marker 20a alone in the field of view as shown in <FIG>, which will be referred to as the marker model. Additional nterventional images can then be acquired that contain all or part of the marker at a variety of orientations. The marker model 20a is matched toan interventional image (e.g., interventional image 65a) using a point-to-point homographic transform based on the location of the ball bearings (for example, in OpenCV: cv2. findHomography((Pt smodel ),(Pt simage ))). Ball bearings were used for the point-to-point transform in this case because ball bearings are clear fiducials in each image, although any other points on the marker could be used instead of the ball bearings. In order to match the correct corresponding pairs of ball bearings in the marker model 126a with those in the interventional image 65a, the ball bearings are detected in order radially starting from the x-axis of the marker model 126b as shown in <FIG>.

Once the point-to-point homographic transform has been applied to the marker model 126b to provide a rough registration 65c of <FIG> to the interventional marker in image space, the model alignment is fine-tuned using an enhanced correlation coefficient (ECC) optimization routine (e.g., iOpenCV: cv2. findTransformECCU). Once optimal alignment between the marker model 126b and the image has been achieved, the aligned marker model 126c as shown in <FIG> is subtracted from the image to render image 65d of <FIG>, where the gray level of the subtracted model is optimized based on minimizing the power of the main frequency of the marker in the image. A uniform offset representing the mean gray level of the subtracted marker is added back into the image in the marker region.

The following Table I outlines the subtraction techniques.

<FIG> illustrates a flowchart <NUM> representative of a transformation generation method for X-ray ripple marker 20b shown in <FIG>.

More particularly to both the patient-less mode and the patient mode, as shown in <FIG>, the C-arm to marker registration <NUM> involves projecting one period projecting through the perspective transformation of a distance <NUM> of an X-ray source <NUM> to an X-ray detector <NUM> into a distance <NUM> of X-ray source <NUM> to an X-ray ripple marker <NUM> in accordance with the following equation [11a]: <MAT> where SM is the distance <NUM> from X-ray source <NUM> to X-ray ripple marker <NUM>, SD is the distance from X-ray source <NUM> to X-ray detector <NUM> (which is known from calibration or DICOM data), TM is the time period of the ripple pattern and TI is image period (computed from image). Converting equation [11A] to frequencies yields the following equation [11b]: <MAT> fM is the frequency of the known ripple pattern and fI is image frequency (computed from image).

Equation [11b] is for looking in one direction of the image. The following equation [11c] is for two directions suitable for X-ripple marker 20b (<FIG>): <MAT> where <MAT> is the highest frequency of the known ripple pattern,
<MAT> is the highest frequency of the known ripple pattern, <MAT> is highest image frequency (computed from image) and <MAT> is lowest image frequency (computed from image).

In practice, more than two directions may be utilized. Also in practice, a simplest approach is by using fast Fourier transform (FFT) along lines going through the center of X-ray ripple marker 20b of <FIG>.

Referring to <FIG>, a stage S142 of flowchart <NUM> encompasses controller <NUM> plotting an intensity of each direction through the ripple pattern of X-ray ripple marker 20b, and a stage S144 of flowchart <NUM> encompasses controller <NUM> deriving transformation parameter(s) from a FFT analysis of the intensity plot(s).

For example, <FIG> illustrates a scenario where the ripple pattern of X-ray ripple marker 20b is parallel with the X-ray detector at a first parallel position <NUM> with a line <NUM> traversing through low frequency radial ripple series 51a and low frequency radial ripple series 51c, and a line <NUM> traversing through high frequency radial ripple series 51b and high frequency radial ripple series 51d.

By further example, <FIG> illustrates a scenario where the ripple pattern of X-ray ripple marker 20b is parallel with the X-ray detector at a second parallel position <NUM> with a line <NUM> traversing through low frequency radial ripple series 51a and low frequency radial ripple series 51c, and a line <NUM> traversing through high frequency radial ripple series 51b and high frequency radial ripple series 51d.

For the first parallel position <NUM> (<FIG>) during stage S142, <FIG> shows an intensity plot <NUM> for low frequency radial ripple series 51a and low frequency radial ripple series 51c at the first position <NUM>, and intensity plot <NUM> for high frequency radial ripple series 51b and high frequency radial ripple series 51d.

For the second parallel position <NUM> (<FIG>) during stage S142, <FIG> shows an intensity plot <NUM> for low frequency radial ripple series 51a and low frequency radial ripple series 51c at the first position <NUM>, and intensity plot <NUM> for high frequency radial ripple series 51b and high frequency radial ripple series 51d.

<FIG> shows a FFT analysis 157a of intensity plot <NUM>, a FFT analysis 157b of intensity plot <NUM>, a FFT analysis 157c of intensity plot <NUM> and a FFT analysis 157c of intensity plot <NUM>.

For the first position <NUM> of <FIG>, a peak of FFT analysis 157a is the lowest image frequency <MAT> of equation [11c] and a peak of FFT analysis 157b is the highest image frequency <MAT> of equation [11c].

For the second position <NUM> of <FIG>, a peak of FFT analysis 157c is the lowest image frequency <MAT> of equation [11c] and a peak of FFT analysis 157d is the highest image frequency <MAT> of equation [11c].

Referring back to <FIG>, a stage S140 of flowchart S146 encompasses controller <NUM> registering X-ray ripple marker 20b and the X-ray C-arm.

In one embodiment of stage S140, xcd and ycd represent the center of the X-ray ripple marker 20b in detector coordinate system whereby the compute the translation of X-ray ripple marker 20b is computed in accordance with the following equations [12a]-[12c]: <MAT> <MAT> <MAT>.

By additional example illustrates a scenario where the ripple pattern of X-ray ripple marker 20b is titled with respect to the X-ray detector at a position <NUM> with a line <NUM> traversing through low frequency radial ripple series 51a and low frequency radial ripple series 51c, and a line <NUM> traversing through high frequency radial ripple series 51b and high frequency radial ripple series 51d.

<FIG> shows a FFT analysis 159a of an intensity plot for line <NUM> and a FFT analysis 159b of an intensity plot for line <NUM>. The rotation axis of FFT analysis 159a is sharp as the rotation of the ripple pattern due to the tilt will not change the frequency of low frequency radial ripple series 51a and low frequency radial ripple series 51c, while the rotation axis of FFT analysis 159b is spread out as the rotation of the ripple pattern due to the tilt will change the frequency of high frequency radial ripple series 51b and high frequency radial ripple series 51d.

To facilitate a further understanding of the various inventions of the present disclosure, the following description of <FIG> 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.

Referring to <FIG>, a C-arm registration controller <NUM> includes one or more processor(s) <NUM>, memory <NUM>, a user interface <NUM>, a network interface <NUM>, and a storage <NUM> interconnected via one or more system buses <NUM>.

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

The memory <NUM> 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 <NUM> may include static random access memory (SRAM), dynamic RAM (DRAM), flash memory, read only memory (ROM), or other similar memory devices.

The user interface <NUM> 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 <NUM>.

The network interface <NUM> 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 <NUM> may include a network interface card (NIC) configured to communicate according to the Ethernet protocol. Additionally, the network interface <NUM> 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 <NUM> will be apparent.

The storage <NUM> 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 <NUM> may store instructions for execution by the processor(s) <NUM> or data upon with the processor(s) <NUM> may operate. For example, the storage <NUM> may store a base operating system for controlling various basic operations of the hardware. The storage <NUM> also stores application modules in the form of executable software/firmware for implementing the various functions of the controller 170a as previously described in the present disclosure including, but not limited to, a C-arm to marker registration module <NUM> and a ripple marker removal module <NUM> as previously described in the present disclosure.

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

Referring to <FIG>, 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, an X-ray ripple marker facilitating an accurate and reliable C-arm Registration, particularly for mobile C-arms.

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.

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.

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 appended claims.

Claim 1:
A C-arm registration system, comprising:
an X-ray ripple marker (<NUM>) including a ripple pattern (<NUM>) radially extending from and partially or fully encircles a fixed point (<NUM>) of the X-ray ripple marker (<NUM>), whereby a frequency, a phase and/or an amplitude of the circular/arc ripple(s) of the ripple pattern serve to create X-ray imaged wave(s); and
a C-arm registration controller (<NUM>) configured to:
identify the ripple pattern (<NUM>) within an X-ray image generated from an X-ray projection by a C-arm (<NUM>) and illustrative of at least a portion of the ripple pattern (<NUM>),
wherein an identification of the ripple pattern (<NUM>) within the X-ray image is characteristic of a pose of the X-ray projection by the C-arm (<NUM>) relative to the X-ray rippler marker (<NUM>);
analyze the ripple pattern (<NUM>) within the X-ray image to derive at least one transformation parameter definitive of the pose of the X-ray projection by the C-arm (<NUM>) relative to the X-ray ripple marker (<NUM>); and
register the C-arm (<NUM>) to the X-ray ripple marker (<NUM>) based on the at least one transformation parameter.