ULTRASOUND PROBE CALIBRATION PHANTOM, ULTRASOUND PROBE CALIBRATION SYSTEM AND CALIBRATION METHOD THEREOF

Abstract

An ultrasound probe calibration system and method. The system comprises an ultrasound probe calibration phantom (100), and the ultrasound probe calibration phantom (100) is provided with a sunken recess (110) at a middle position of an upper surface thereof and with several conical holes on a side surface thereof. The sunken recess (110) is fixedly connected with a two dimensional ultrasound probe (220) therein. The conical hole is inserted with an NDI insertion stylus (230), and a tip of the NDI insertion stylus (230) can be acquired in ultrasound imaging. An ultrasound probe calibration system employing the above structure enables a midplane of an ultrasound plane to pass a midplane of an ultrasound probe calibration phantom (100) along a middle gap, such that a tip of an NDI insertion stylus (230) is used for the midplane of the ultrasound plane, thereby addressing the problem of misalignment of a point-type phantom or a two-dimensional plane-type phantom to the ultrasound plane.

Claims

1. A calibration phantom of an ultrasonic probe, wherein a concave groove is formed in middle of an upper surface of the calibration phantom of the ultrasonic probe, and a plurality of conical holes are formed on a side surface of the calibration phantom of the ultrasonic probe.

2. A calibration system of an ultrasonic probe, comprising: an ultrasonic water tank, which contains purified water; a calibration phantom of an ultrasonic probe, which is fixed in the ultrasonic water tank, wherein the purified water exactly submerges the calibration phantom of the ultrasonic probe; a concave groove is formed in the middle of the upper surface of the calibration phantom of the ultrasonic probe; and a plurality of conical holes are formed on the side surface of the calibration phantom of the ultrasonic probe; a two-dimensional ultrasonic probe, which is fixed in the concave groove, wherein a locating and tracking device is further fixed in the two-dimensional ultrasonic probe; and NDI puncture probes, which are inserted in the conical holes, so that tips of the NDI puncture probes are acquired through ultrasonic images.

3. The calibration system of an ultrasonic probe of claim 2, wherein the calibration phantom of the ultrasonic probe is made of organic glass.

4. A method of calibration of an ultrasonic probe, comprising following steps: fixing the calibration phantom of the ultrasonic probe in the ultrasonic water tank, and enabling the purified water in the ultrasonic water tank to exactly submerge the calibration phantom of the ultrasonic probe, wherein a concave groove is formed in the middle of the upper surface of the calibration phantom of the ultrasonic probe; and a plurality of conical holes are formed on the side surface of the calibration phantom of the ultrasonic probe; fixing the two-dimensional ultrasonic probe in the concave groove, and further fixing a locating and tracking device in the two-dimensional ultrasonic probe; inserting NDI puncture probes in the conical holes, and acquiring tips of the NID puncture probes through ultrasonic images; simultaneously acquiring position information of the tips and position information of the locating and tracking device in a world coordinate system through the NDI puncture probes, and respectively marking the position information of the tips and the position information of the locating and tracking device as y.sub.i and T.sub.S.fwdarw.W; recording the pixel position information of the tips on the ultrasonic image plane, and marking the pixel position information as x.sub.i, wherein y.sub.i=T.sub.S.fwdarw.W.Math.T.sub.P.fwdarw.S.Math.x.sub.i, and T.sub.P.fwdarw.S is a transformation matrix from an unknown ultrasonic imaging plane coordinate system P to an ultrasonic probe locating device coordinate system S; and solving the transformation matrix T.sub.P.fwdarw.S by an image registration algorithm based on an iterative closest point to synchronously acquire space calibration and time calibration.

5. The method of calibration of an ultrasonic probe of claim 4, further comprising following steps: changing the positions of the NDI puncture probes in the calibration phantom of the ultrasonic probe, acquiring a point set pair of positions of at least six tips, and marking the point set pair as Y={y.sub.i,iεm} and X={x.sub.i,iεn}, where m is not equal to n, and m and n are natural numbers; and solving an optimal transformation matrix T to enable the point set pair Y={y.sub.i,iεm} and X={x.sub.i,iεn} to be aligned with each other.

6. The method of calibration of an ultrasonic probe of claim 4, wherein solving the optimal transformation matrix T to enable the point set pair Y={y.sub.i,iεm} and X={x.sub.i,iεn} to be aligned with each other comprises: step 1: transforming every point x.sub.iεX of a set X by using a formula (1) through a transformation matrix T.sup.k, finding a point which is the closest to T.sup.k(x.sub.i) in a set Y, and marking the point as a corresponding point c.sub.i.sup.k of k.sup.th iteration to obtain a set (x.sub.i,c.sub.i.sup.k) of a corresponding point pair, wherein the formula (1) is as follows: $c_i^k=\underset{y_i\in Y}{\mathrm{argmin}}.Math.\underset{i=1}{\overset{m}{.Math.}}.Math.{.Math.T^k\left(x_i\right)-y_i.Math.}^2;$ and step 2: solving a transformation matrix T according to a set (x.sub.i,c.sub.i.sup.k) by using a formula (2) to obtain a direct transformation relation of a description point set pair Y={y.sub.i,iεm} and X={x.sub.i,iεn} wherein the formula (2) is as follows: $T^{k+1}=\underset{T}{\mathrm{argmin}}.Math.\stackrel{n}{\underset{i=1}{.Math.}}.Math.{.Math.T\left(x_i\right)-c_i^k.Math.}^2;$ and iteratively carrying out step 1 and step 2, and solving to obtain an optimal transformation matrix T to enable the point set pair Y={y.sub.i,iεm} and X={x.sub.i,iεn} to be aligned with each other.

7. The method of calibration of an ultrasonic probe of claim 4, wherein the calibration phantom of the ultrasonic probe is made of organic glass.

8. The method of calibration of an ultrasonic probe of claim 5, wherein the calibration phantom of the ultrasonic probe is made of organic glass.

9. The method of calibration of an ultrasonic probe of claim 6, wherein the calibration phantom of the ultrasonic probe is made of organic glass.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In FIG. 1, (a) is a structure diagram of a point phantom of a calibration phantom of an ultrasonic probe provided in the prior art;

[0035] in FIG. 1, (b) is a structure diagram of a single-intersection-line phantom of a calibration phantom of an ultrasonic probe provided in the prior art;

[0036] in FIG. 1, (c) is a structure diagram of a multi-intersection-line phantom of a calibration phantom of an ultrasonic probe provided in the prior art;

[0037] in FIG. 1, (d) is a structure diagram of a two-dimensional-shaped phantom of a calibration phantom of an ultrasonic probe provided in the prior art;

[0038] in FIG. 1, (e) is a structure diagram of a three-intersection-line phantom of a calibration phantom of an ultrasonic probe provided in the prior art;

[0039] in FIG. 1, (f) is a structure diagram of an N-shaped phantom of a calibration phantom of an ultrasonic probe provided in the prior art;

[0040] FIG. 2 is a structure diagram of a calibration phantom of an ultrasonic probe provided by an embodiment of the invention;

[0041] FIG. 3 is a structure diagram of a calibration system of an ultrasonic probe provided by an embodiment of the invention;

[0042] FIG. 4 is a flow diagram of steps of a method of calibration of an ultrasonic probe provided by an embodiment of the invention; and

[0043] FIG. 5 is an image of NDI puncture probes provided by an embodiment of the invention on an ultrasonic probe.

DETAILED DESCRIPTION

[0044] For understanding the invention conveniently, the invention will be described more comprehensively below with reference to the related drawings.

[0045] In the drawings, preferred embodiments of the invention are shown. The above description is only the preferred embodiments of the invention and does not limit the scope of the patent of invention; any equivalent structure or equivalent process modification used according to the contents of the specification and drawings in the invention, no matter whether it is directly or indirectly used in any other related technical fields, should be included within the protection scope of the patent of invention.

[0046] As shown in FIG. 2, an embodiment of the invention provides a calibration phantom 100 of an ultrasonic probe; a concave groove 110 is formed in the middle of the upper surface of the calibration phantom 100 of the ultrasonic probe; and a plurality of conical holes (not shown) are formed on the side surface of the calibration phantom 100 of the ultrasonic probe.

[0047] It may be appreciated that the calibration phantom 100 of the ultrasonic probe is made of a material with good ultrasonic wave permeability, and particularly, the calibration phantom 100 of the ultrasonic probe is made of organic glass.

[0048] As for the calibration phantom 100 of the ultrasonic probe provided by the invention, because the concave groove 110 is formed in the middle of the upper surface, several conical holes are formed on the side surface; because such structure of the calibration phantom of the ultrasonic probe makes the two-dimensional ultrasonic probe able to be fixed on the calibration phantom of the ultrasonic probe, accidental shake errors caused by the reason that the two-dimensional ultrasonic probe is grasped manually and the like are avoided, which greatly improves the practicability of the calibration system.

[0049] As shown in FIG. 3, an embodiment of the invention provides a calibration system of an ultrasonic probe, which comprises an ultrasonic water tank 210, a calibration phantom 100 of an ultrasonic probe, a two-dimensional ultrasonic probe 220 and NDI puncture probes 230.

[0050] Wherein, the ultrasonic water tank 210 contains purified water; the calibration phantom 100 of the ultrasonic probe is fixed in the ultrasonic water tank 210; the purified water exactly submerges the calibration phantom 100 of the ultrasonic probe; the two-dimensional ultrasonic probe 220 is fixed in the concave groove 110; a locating and tracking device (not shown) is further fixed in the two-dimensional ultrasonic probe 220; the NDI puncture probes 230 are fixedly inserted in the conical holes; and tips of the NDI puncture probes 230 can be acquired through ultrasonic images.

[0051] The calibration system 200 of the ultrasonic probe adopting the above structure in the invention can make the neutral surface of an ultrasonic plane exactly pass through a neutral surface of the calibration phantom of the ultrasonic probe along a gap in the middle, so that the neutral surface of the ultrasonic plane exactly adopts the tips of the NDI puncture probes, and therefore, the problem that a ‘point-shaped’ phantom and a two-dimensional ‘surface-shaped’ phantom cannot be aligned with the ultrasonic plane is solved well.

[0052] As shown in FIG. 4, the flow diagram of steps of a method of calibration of an ultrasonic probe provided in the embodiment of the invention comprises the following steps:

[0053] step S310: fixing the calibration phantom of the ultrasonic probe in the ultrasonic water tank, and enabling the purified water in the ultrasonic water tank to exactly submerge the calibration phantom of the ultrasonic probe;

[0054] step S320: fixing the two-dimensional ultrasonic probe in the concave groove, and further fixing a locating and tracking device in the two-dimensional ultrasonic probe;

[0055] step S330: inserting the NDI puncture probes in the conical holes, and acquiring the tips of the NDI puncture probes through the ultrasonic images, wherein it may be appreciated that an acquired tip image should be a point of intersection between another side wall in a gap and an ultrasonic plane theoretically, but because the actual ultrasonic plane has certain thickness, a quite small error exists, a dot A in a ring as shown in FIG. 5 can be obtained, an imaging effect shows that the imaging quality of feature points of the tips of the NDI puncture probes is excellent, and requirements of precision of manual and automatic separation can be met;

[0056] step S340: simultaneously acquiring position information of the tips and position information of the locating and tracking device in a world coordinate system through the NDI puncture probes, and respectively marking the position information of the tips and the position information of the locating and tracking device as y.sub.i and T.sub.S.fwdarw.W;

[0057] step S350: recording the pixel position information of the tips on the ultrasonic image plane, and marking the pixel position information as x.sub.i, wherein y.sub.i=T.sub.S.fwdarw.W.Math.T.sub.P.fwdarw.S.Math.x.sub.i, T.sub.P.fwdarw.S is a transformation matrix from an unknown ultrasonic imaging plane coordinate system P to an ultrasonic probe locating device coordinate system S; and it may be appreciated that x.sub.i and y.sub.i are different expressions of the same point in two different coordinate systems in space; and

[0058] step S360: solving the transformation matrix T.sub.P.fwdarw.S by the image registration algorithm based on the iterative closest point to synchronously acquire space calibration and time calibration.

[0059] It may be appreciated that the image registration algorithm based on the iterative closest point is used for solving a transformation matrix to be solved, which can simultaneously solve space calibration and time calibration, and greatly improve the precision of calibration.

[0060] Another embodiment further comprises the following steps:

[0061] step S370: changing the positions of the NDI puncture probes in the calibration phantom of the ultrasonic probe, acquiring a point set pair of positions of tips in some lines, and marking the point set pair as Y={y.sub.i,iεm} and X={x.sub.i,iεn}, where m is not equal to n, and m and n are natural numbers;

[0062] step S380: establishing the following formula according to the image registration algorithm based on the iterative closest point, wherein a process of iteratively solving the following formula can be regarded as a process of iteratively minimizing the following two equations:

[00002]$c_i^k=\underset{y_i\in Y}{\mathrm{argmin}}.Math.\underset{i=1}{\overset{m}{.Math.}}.Math.{.Math.T^k\left(x_i\right)-y_i.Math.}^2,T^{k+1}=\underset{T}{\mathrm{argmin}}.Math.\stackrel{n}{\underset{i=1}{.Math.}}.Math.{.Math.T\left(x_i\right)-c_i^k.Math.}^2;$

[0063] It may be appreciated that the most outstanding feature of the ICP algorithm is as follows: points in the point set X are not required to be in one-to-one correspondence to points in the point set Y completely. On the contrary, if the transformation matrix T corresponding to the two point sets are known, the one-to-one corresponding relation between the two point sets can be confirmed by ICP. In mathematics, the solving process of the ICP algorithm can be regarded as the process of iteratively minimizing the above two equations.

[0064] Step S390: transforming every point x.sub.iεX of the set X by a current transformation matrix T.sup.k, finding a point which is the closest to T.sup.k (x.sub.i) in the set Y, and marking the point as a corresponding point c.sub.i.sup.k of k.sup.th iteration, wherein the result of the step is a set (x.sub.i,c.sub.i.sup.k) of a corresponding point pair;

[0065] step S410: repeating the operation, and finding a transformation matrix T to enable a point set Y={y.sub.i,iεm} and a point set X={x.sub.i,iεn} to be aligned with each other.

[0066] The method of calibration of the ultrasonic probe provided by the invention adopts the image registration algorithm based on the iterative closest point, so that (i) a corresponding relation between two point sets (feature points on the calibration phantom of the ultrasonic probe and corresponding feature points on the ultrasonic imaging plane) can be found out automatically, and synchronization of the two point sets on time is not required; (ii) the set numbers of the two point sets are not required to be equal; and (iii) once the transformation matrix is solved and obtained, delayed time between image data and locating data in the calibration system can be solved reversely, and therefore, the problem of space calibration and time calibration of the ultrasonic probe can be solved well by the algorithm.

[0067] The above embodiments only express several embodiments of the invention, whose description is relatively specific and detailed, but it should not be construed as limiting the scope of the patent of invention. It should be noted that for those ordinary skilled in the art, various changes and modifications can further be carried out on the premise of not departing from the concept of the invention, and belong to the protection scope of the invention. Therefore, the protection scope of the patent of invention should be determined by the appended claims.