ARRANGEMENT AND METHOD FOR DETERMINING THE POSITION OF AN INVASIVE DEVICE

Abstract

For the field of determining the position of an invasive device (1) a solution for improving the localization of the invasive device (1) is specified. This is achieved by an arrangement and a method for determining the position of an invasive device (1), wherein an optical shape sensing system for sensing a position and/or shape of the invasive device (1) is provided, wherein the system is arranged to localize at least one point P.sub.i on the invasive device (1) at a position x.sub.i, y.sub.i, z.sub.i, with some en-or margin (2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i) in a region of interest (3), localizing and reconstructing at least one point P.sub.i on the invasive device (1) at a position x.sub.i, y.sub.i, z.sub.i, with some error margin (2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i) in a region of interest (3) by the optical shape sensing system. An MRI system is also provided for measuring the position x.sub.i, y.sub.i, z.sub.i of the point P.sub.i on the invasive device (1) within the error margin in the region of interest at least in one spatial direction by the MRI system, wherein a signal of the magnetization in the error margin (2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i) is read out by the MRI system and a position of the invasive device (1) is determined based on the signal. The position x.sub.i, y.sub.i, z.sub.i, of the point P.sub.i on the invasive device (1) in the region of interest (3) determined by the optical shape sensing system is corrected with the x.sub.i, y.sub.i, z.sub.i, of the point P.sub.i on the invasive device (1) in the region of interest (3) determined by the MRI system by a calculating system to an actual position of the point P.sub.i on the invasive device (1).

Claims

1. An arrangement for determining the position of an invasive device, the arrangement comprising: at least one invasive device, at least one optical shape sensing system, wherein the optical shape sensing system is configured for determining at least one of a position or shape of the invasive device, the optical shape sensing system further being arranged to localize and reconstruct at least one point P.sub.i on the invasive device at a position x.sub.i, y.sub.i, z.sub.i with some error margin (2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i) in a region of interest, a diagnostic imaging system, wherein the diagnostic imaging system is configured to measure the position x.sub.i, y.sub.i, z.sub.i of the point P.sub.i on the invasive device within the error margin (2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i) in the region of interest at least in one spatial direction (x, y, z), at least one calculating system wherein the calculating system is configured to correct the position x.sub.i, y.sub.i, z.sub.i of the point P.sub.i on the invasive device determined by the optical shape sensing system by the position x.sub.i, y.sub.i, z.sub.i, of the point P.sub.i on the invasive device determined by the diagnostic imaging system to an actual position of the invasive device.

2. The arrangement as claimed in claim 1, wherein the diagnostic imaging system is at least one selected from a group consisting of: a magnetic resonance imaging system, a computed tomography imaging system or an X-ray imaging system.

3. The arrangement according to claim 1, wherein the diagnostic imaging system is a magnetic resonance imaging (MRI) system and is further configured to excite a magnetization in the error margin (2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i) in the region of interest at least in one spatial direction (x, y, z) by exciting at least one of a z-slice, y-slice, or an x-slice centered at the point P.sub.i at the position x.sub.i, y.sub.i, z.sub.i and perpendicular to a direction vector (n.sub.i) with the MRI system, the MRI system being arranged to read out a signal of the excited z-slice, y-slice, or x-slice with a readout gradient along the x-direction (x) and/or along the y-direction (y) and/or along the z-direction (z), the MRI system further being arranged to to find a signal suppression in the signal of the excited z-slice, y-slice, x slice to determine a position x.sub.i, y.sub.i, z.sub.i of the point P.sub.i on the invasive device based on the signal.

4. The arrangement according to claim 1, wherein the diagnostic imaging system is a magnetic resonance imaging system and the invasive device comprises at least one MR marker along the extension of the invasive device.

5. The arrangement according to claim 4, wherein the MR marker is at least one selected from the list consisting of: paramagnetic agents, ferromagnetic agents, ferrimagnetic agents, antiferromagnetic agents, resonant pickup radiofrequency (RF) coils, or inductively coupled RF coils.

6. A method for determining the position of an invasive device the method comprising the following steps: providing an invasive device providing a diagnostic imaging) system, providing an optical shape sensing system for sensing a position and/or shape of the invasive device, the system being arranged that to localize at least one point P.sub.i on the invasive device at a position x.sub.i, y.sub.i, z.sub.i with some error margin (2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i) in a region of interest, localizing and reconstructing at least one point P.sub.i on the invasive device at a position x.sub.i, y.sub.i, z.sub.i in the region of interest by the optical shape sensing system, measuring the position x.sub.i, y.sub.i, z.sub.i of the point P.sub.i on the invasive device within the error margin (2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i) in the region of interest at least in one spatial direction (x, y, z) by the MRI system, correcting the position x.sub.i, y.sub.i, z.sub.i of the point P.sub.i on the invasive device in the region of interest determined by the optical shape sensing system with the position x.sub.i, y.sub.i, z.sub.i of the point P.sub.i on the invasive device in the region of interest determined by the MRI system by the calculating system to an actual position of the invasive device.

7. The method according to claim 6, wherein the diagnostic imaging system is a magnetic resonance imaging system and the step of measuring the position x.sub.i, y.sub.i, z.sub.i of the point P.sub.i on the invasive device within the error margin (2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i) in the region of interest comprises the steps of exciting at least one of a z-slice, a y-slice or an x-slice centered at the position x.sub.i, y.sub.i, z.sub.i of the point P.sub.i and perpendicular to a direction vector (n.sub.i) of the invasive device with the diagnostic imaging system, reading out a signal of the excited z-slice, yslice, x-slice within the error margin (2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i) by the diagnostic imaging system, determining a position of the invasive device based on the signal.

8. The method according to claim 7, wherein the step of reading out a signal of the magnetization in the error margin (2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i), comprises the step of reading out a signal of the excited z-slice, y-slice, or x-slice with a readout gradient along at least one of the x-direction and/or along, the y-direction and/or, along the z-direction.

9. The method according to claim 7, wherein the step of determining a position of the invasive device based on the signal comprises the step of performing a scheme for signal suppression of the signal of the excited z-slice and/or a y-slice and/or a x-slice outside a region x.sub.i−Δx.sub.i to x.sub.i+Δx.sub.i and/or y.sub.i−Δy.sub.i to y.sub.i+Δy.sub.i and/or z.sub.i−Δz.sub.i to z.sub.i+Δz.sub.i based on the localizing and reconstructing of the at least one point P.sub.i on the invasive device at the position x.sub.i, y.sub.i, z.sub.i by the optical shape sensing system.

10. The method according to claim 9, wherein the step of performing a scheme for signal suppression of the signal of the excited z-slice, y-slice, a x-slice is performed by a spin echo scheme comprising the following steps: selective exciting a z-slice and/or y-slice and/or x-slice, performing a selective y-slice refocusing pulse with a slice center at y.sub.i and a slice thickness of 2Δy.sub.i and/or performing a selective x-slice refocusing pulse with a slice center at x.sub.i and a slice thickness of 2Δx.sub.i and/or performing a selective z-slice refocusing pulse with a slice center at z.sub.i and a slice thickness of 2Δz.sub.i reading out the signal along the x-direction (x), and/or z-direction (z) and/or y-direction (y).

11. The method according to claim 9, wherein the step of performing a scheme for signal suppression of the signal of the excited z-slice, y-slice, or x-slice is performed by a saturation scheme comprising the following steps: exciting and spoiling a signal in a region outside y.sub.i−Δy.sub.i to y.sub.i+Δy.sub.i and/or x.sub.i−Δx.sub.i to x.sub.i+Δx.sub.i and/or z.sub.i−Δz.sub.i to z.sub.i+Δz.sub.i, selective exciting at least one of the z-slice , y-slice, or x-slice, reading out the signal along at least one of the x-direction (x), z-direction (z), or y-direction (y).

12. The method according to claim 9, wherein the step of performing a scheme for signal suppression of the signal of the excited z-slice and/or a y-slice and/or a x-slice is performed by a 2d-excitation scheme comprising the following steps: exciting a column of a signal along at least one of the x-direction (x), y-direction (y), or z-direction (z) by a 2d-pulse centered at the point P.sub.i at the position x.sub.i, y.sub.i, z.sub.i.

13. The method according to claim 6, wherein the step of localizing and reconstructing at least one point P.sub.i on the invasive device at a position x.sub.i, y.sub.i, z.sub.i by the optical shape sensing system, comprises: localizing and reconstructing at least one point P.sub.i on the invasive device, wherein the invasive device comprises at least one MR marker along the extension of the invasive device.

14. The method according to claim 6 wherein the step of localizing and reconstructing at least one point P.sub.i on the invasive device at a position x.sub.i, y.sub.i, z.sub.i, by the optical shape sensing system comprises the step of localizing and at least one of reconstructing a point P.sub.i at the tip point of the invasive device or at least at one point P.sub.i along a shaft of the invasive device.

15. The method according to claim 5, wherein when the step of exciting a magnetization in the error margin (2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i) in the region of interest has been performed in a first spatial direction (x, y, z) by the MRI system the method comprises the step of exciting a magnetization in the error margin (2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i) in the region of interest in at least another spatial direction (x, y, z).

16. A computer program product comprising instructions stored on non-transitory computer readable medium which, when the program is executed by a computer comprising a calculating system, cause the computer to carry out a method of: sensing a position by a an optical shape sensing system and/or shape of an invasive device, the system being arranged that to localize at least one point P.sub.i on the invasive device at a position x.sub.i, y.sub.i, z.sub.i with some error margin (2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i) in a region of interest, localizing and reconstructing at least one point P.sub.i on the invasive device at a position x.sub.i, y.sub.i, z.sub.i in the region of interest by the optical shape sensing system, measuring by a diagnostic imaging system the position x.sub.i, y.sub.i, z.sub.i of the point P.sub.i on the invasive device within the error margin (2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i) in the region of interest at least in one spatial direction (x, y, z), and correcting, by the calculating system, the position x.sub.i, y.sub.i, z.sub.i of the point P.sub.i on the invasive device in the region of interest determined by the optical shape sensing system with the position x.sub.i, y.sub.i, z.sub.i of the point P.sub.i on the invasive device in the region of interest determined by diagnostic imaging system to an actual position of the invasive device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0052] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. Such an embodiment does not necessarily represent the full scope of the invention, however, and reference is made therefore to the claims and herein for interpreting the scope of the invention.

[0053] In the drawings:

[0054] FIG. 1 schematically depicts a sketch of an invasive device with point P.sub.i at a position x.sub.i, y.sub.i, z.sub.i localized by an optical shape sensing system and an excited z-slice in accordance with an embodiment of the invention,

[0055] FIG. 2 shows a flowchart of a method for determining the position of an invasive device in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0056] FIG. 1 schematically depicts a sketch of an invasive device 1 with point P.sub.i at a position x.sub.i, y.sub.i, z.sub.ilocalized by an optical shape sensing system and an excited z-slice 2 in accordance with an embodiment of the invention. A point P.sub.i is localized by FORS on the invasive device 1 to be at the position x.sub.i, y.sub.i, z.sub.ibut due to limited accuracy the true location may be contained in an error margin 2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i centered at x.sub.i, y.sub.i, z.sub.i, wherein the size of this error margin 2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i may vary per point and is therefore indexed and without further prior knowledge the size will generally increase towards the tip of the invasive device 1. The FORS reconstruction also provides the direction vector n.sub.i of the invasive device 1 at point P.sub.i. In order to improve the accuracy of localization of P.sub.i in x-direction x the MR scanner measures the position x.sub.i, y.sub.i, z.sub.i of the point P.sub.i on the invasive device 1. In an embodiment of the invention, it may in particular be provided that the MR scanner excites a slice 2 of about two to three times the thickness of the invasive device 1 centered at x.sub.i, y.sub.i, z.sub.i and perpendicular to the direction vector n.sub.i as sketched in FIG. 1. A readout of signal of that slice 2 with a readout gradient along the x-direction x provides a projection of all signal in that slice 2 integrated along the y-direction y. Due to the absence of water in the invasive device 1 a small signal reduction is expected in this projection at the true position x.sub.ti of the device. However, the heterogeneity of the signal from body tissue in the entire slice 2 will also provide signal variations so that the small signal reduction by the invasive device 1 will likely be obscured. Therefore, the signal from the slice 2 outside the region y.sub.i−Δy.sub.i to y.sub.i+Δy.sub.i is proposed to be suppressed before signal readout. As a result, the projection contains only signal integrated along y in that small region. The absence of signal in the device will now result in a significant signal reduction in the projection. The position of this signal dip corresponds to the true position x.sub.ti of the device. The search for this signal dip only needs to be performed in a region x.sub.i−Δx.sub.i to x.sub.i+Δx.sub.i due to the prior knowledge from the FORS measurement. The signal suppression can be performed by various schemes.

[0057] In an embodiment of the invention the signal suppression is performed by a spin echo-scheme. After a z-slice-selective excitation a y-slice-selective refocusing pulse is performed with slice center at y.sub.i, and slice thickness of 2Δy.sub.i. The following readout in x-direction x will only acquire signal from the cross section of the excitation z-slice 2 and the refocusing y-slice. In another embodiment the signal suppression is performed by a saturation-scheme, wherein a signal in regions outside y.sub.i−Δy.sub.i to y.sub.i+Δy.sub.i is excited and spoiled, followed by the z-slice 2 selective excitation and readout along x-direction x.

[0058] In a further embodiment of the invention the signal suppression is performed by a 2d-excitation scheme. A 2d-pulse is used to excite only a column of signal along x, centered at x.sub.i, y.sub.i, z.sub.i and with width y.sub.i, z.sub.i. For illustration and ease of annotation, the invasive device 1 has been oriented along the z-axis z in FIG. 1. The approximate orientation of the invasive device 1 at point P.sub.i can be derived from the FORS data to orient the selection slice 2 perpendicular to the invasive device 1. This results in minimal partial volume effects caused by the finite width of slice 2 and pixels in the projection read-out.

[0059] The above embodiment of the invention describes the acquisition of MR projection data to improve the localization of P.sub.i in x-direction x. To improve the localization also in y- and z-direction y, z in an embodiment of the invention analog steps can be performed in at least another spatial direction x, y, z.

[0060] The direction along the invasive device 1, in the embodiment shown in FIG. 1 the z-direction z, represents a slightly different problem because the invasive device 1 a priori does not provide structures that can be visualized in MR. However, points P.sub.i may be chosen to coincide with structures of the invasive device 1 that already provide some MR contrast. In another embodiment of the invention points P.sub.i may be equipped with passive MR markers known in the art to provide sufficient MR contrast. Passive MR markers are paramagnetic, ferromagnetic, ferrimagnetic and antiferromagnetic metals, metal alloys and metal compounds. They are preferably embedded as particles in a plastic matrix. In addition, active markers like resonant pickup radiofrequency (RF) coils or semi-active inductively coupled RF coils can be provided. Even with only the x.sub.i and y.sub.i co-ordinates of point P.sub.i the localization of FORS is improved. As a result of the MR measurements, the true positions of points P.sub.i are available at a high accuracy. Therefore, the FORS reconstruction can be done segment per segment and just must solve for the shapes between those points. Initially, MR localization of the tip of the invasive device 1 results in the largest gain of information with respect to the FORS reconstruction. In an embodiment it is may be intended to firstly localize the tip point of the invasive device 1 with MR and to continue with a point at half the length of the invasive device 1, then at quarter length and so forth as in a half-interval search.

[0061] FIG. 2 shows a flowchart of a method for determining the position of an invasive device 1 in accordance with an embodiment of the invention. The method starts with step 200 by providing at least one invasive device 1, a magnetic resonance imaging (MRI) system and an optical shape sensing system. The optical shape sensing system is configured for determining a position and/or shape of the invasive device 1. Optical shape sensing or fiber-optical shape sensing allows sensing the shape of a flexible compound optical fiber in 3D with high temporal and spatial resolution. It is based on optical sensing of the strain of individual optical cores along the compound fiber, either by fiber Bragg gratings or by Rayleigh scattering. The known relative configuration of the cores allows reconstruction the shape of the compound fiber from the strain data.

[0062] In step 210 at least one point P.sub.i on the invasive device 1 at a position x.sub.i, y.sub.i, z.sub.i, is localized and reconstructed by the optical shape sensing system with some error margin 2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i in a region of interest 3.

[0063] In step 220 a magnetization is excited in the error margin 2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i in the region of interest 3 at least in one spatial direction x, y, z by the MRI system. In an embodiment of the invention the magnetization can be excited as a z-slice and/or a y-slice and/or a x-slice 2 centered at the point P.sub.i at a position x.sub.i, y.sub.i, z.sub.i and perpendicular to a direction vector n.sub.i of the invasive device 1 with the MRI system. In order to improve the accuracy of localization of P.sub.i e.g. in x-direction x the MR scanner excites a slice 2 of about two to three times the thickness of the invasive device 1 centered at x.sub.i, y.sub.i, z.sub.i and perpendicular to the direction vector n.sub.i. Therefore, in an embodiment of the invention it can be foreseen to derive the approximate orientation of the invasive device 1 at point P from the FORS data and to orient the selection slice 2 perpendicular to the invasive device 1. This results in minimal partial volume effects caused by the finite width of slice and pixels in the projection read-out.

[0064] In step 230 a signal of the magnetization in the error margin 2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i is read out by the MRI system. In an embodiment of the invention the signal of the excited z-slice and/or a y-slice and/or a x-slice 2 with a readout gradient along the x-direction x and/or along the y-direction y and/or along the z-direction z is read out by the MRI system. For example a readout of signal of a slice 2 with a readout gradient along the x-direction x provides a projection of all signal in that slice 2 integrated along the y-direction y. Due to the absence of water in the device a small signal reduction is expected in this projection at the true position of the device x.sub.ti. However, the heterogeneity of the signal from body tissue in the entire slice will also provide signal variations so that the small signal reduction by the device will likely be obscured. Therefore, the signal from the slice 2 outside the region y.sub.i−Δy.sub.i to y.sub.i+Δy.sub.i is proposed to be suppressed before signal readout. As a result, the projection contains only signal integrated along y in that small region. The absence of signal in the device will now result in a significant signal reduction in the projection. The position of this signal dip corresponds to the true position x.sub.ti of the invasive device 1. The search for this signal dip only needs to be performed in a region x.sub.i−Δx.sub.i to x.sub.i+Δx.sub.i due to the prior knowledge from the FORS measurement. Therefore, in a further embodiment of the invention the step of determining a position of the invasive device 1 based on the signal comprises the step of performing a scheme for signal suppression of the signal of the excited z-slice and/or a y-slice and/or a x-slice 2 outside a region x.sub.i−Δx.sub.i to x.sub.i+Δx.sub.i and/or y.sub.i−Δy.sub.i to y.sub.i+Δy.sub.i and/or z.sub.i−Δz.sub.i to z.sub.i+Δz.sub.i based on the localizing and reconstructing of the at least one point P.sub.i on the invasive device 1 at the position x.sub.i, y.sub.i, z.sub.i by the optical shape sensing system.

[0065] The signal suppression can be performed by various schemes. For example, the step of performing a scheme for signal suppression of the signal of the excited z-slice and/or a y-slice and/or a x-slice 2 is performed by a spin echo scheme comprising the following steps:

[0066] selective exciting a z-slice and/or y-slice and/or x-slice 2,

[0067] performing a selective y-slice refocusing pulse with a slice center at y.sub.i and a slice thickness of 2Δy.sub.i and/or performing a selective x-slice refocusing pulse with a slice center at x.sub.i and a slice thickness of 2Δx.sub.i and/or performing a selective z-slice refocusing pulse with a slice center at z.sub.i and a slice thickness of 2Δz.sub.i

[0068] reading out the signal along the x-direction x, and/or z-direction z and/or y-direction y.

[0069] In another embodiment of the invention the step of performing a scheme for signal suppression of the signal of the excited z-slice and/or a y-slice and/or a x-slice 2 is performed by a saturation scheme comprising the following steps:

[0070] exciting and spoiling a signal in a region outside y.sub.i−Δy.sub.i to y.sub.i+Δy.sub.i and/or x.sub.i−Δx.sub.i to x.sub.i+Δx.sub.i and/or z.sub.i−Δz.sub.i to z.sub.i+Δz.sub.i,

[0071] selective exciting a z-slice and/or y-slice and/or x-slice 2,

[0072] reading out the signal along the x-direction x and/or z-direction z and/or y-direction y.

[0073] In a further embodiment of the invention the step of performing a scheme for signal suppression of the signal of the excited z-slice and/or a y-slice and/or a x-slice 2 is performed by a 2d-excitation scheme comprising the following steps:

[0074] exciting a column of a signal along x-direction x and/or y-direction y and/or z-direction z by a 2d-pulse centered at the point P.sub.i at the position x.sub.i, y.sub.i, z.sub.i.

[0075] The measured data obtained in this way are then used for determining a position of the invasive device 1 based on the signal.

[0076] In step 240 the position x.sub.i, y.sub.i, z.sub.i, of the point P.sub.i on the invasive device 1 in the region of interest 3 determined by the optical shape sensing system is corrected with the position x.sub.i, y.sub.i, .sub.i, of the point P.sub.i on the invasive device 1 in the region of interest 3 determined by the MRI system by the calculating system to an actual position of the invasive device 1.

[0077] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope. Further, for the sake of clearness, not all elements in the drawings may have been supplied with reference signs.

REFERENCE SYMBOL LIST

[0078] invasive device 1 [0079] excited slice by the MRI system 2 [0080] region of interest 3 [0081] point P.sub.i at position x.sub.i, y.sub.i, z.sub.i P.sub.i [0082] direction vector of the invasive device n.sub.i [0083] spatial direction x, y, z [0084] error margin around point P.sub.i 2Δx.sub.i, 2Δy.sub.i, 2Δz.sub.i