System and method for controlling scanning planes of imaging device

This application is a nationalization under 35 U.S.C. 371 of PCT/CN2010/000952, filed Jun. 25, 2010, and published as WO 2011/116509 A1, on Sep. 29, 2011, which claims priority to Chinese patent Application Serial No. 201010130676.4, filed Mar. 22, 2010, which applications and publications are incorporated herein by reference in their entirety.

1. Field of this Invention

This invention relates to a imaging technology, especially a system and a method for controlling scanning planes of imaging device.

2. Description of the Related Art

In some imaging devices (such as magnetic resonance, CT and PET-CT) with traditional scanning operation, in order to completely scan a target, the scan plane will need to pass that target accurately. Therefore, an general method comprises following steps: scanning one group or two groups of scout images so as to obtain part of the image of the target through the scout images; then defining the position and orientation data of target through part of the image (the position and orientation can be decomposed into three dimensions that are perpendicular to each other) in order to establish its necessary scan plane, which allows the scan plane to pass that target accurately, so as to accurately define the target. Taking a needle shaped device as an example, firstly, a group of planes that are at a certain angle with the needle shaped device to scan the device. (Referring to FIG. 1 ) to obtain a series of scout images. Each plane of the scout image obtained may appear as a cross section image of a needle shaped device in the form of a point. And then a scan plane 5 is established according to the points on the cross section image (referring to FIG. 2 ), after that the scan plane passes through those points, so that the image of the needle shaped device can be completely shown on one picture. IF the scout image 6 obtained can not well illustrate partial image of the target to be scanned, the operator may repeatedly scan the scout image until obtaining partial image of the target to be scanned which is recognizable, and then the operator scans the target to be scanned, however, the method may cause a low efficiency of scanning operation.

In view of the above-described problem, it is one object of the invention to provide a system and a method for controlling scanning planes of imaging device, which may scan a target to obtain its image with high efficiency and high precision at real time.

To achieve the above objective, in accordance with one embodiment of the invention provided is a system for controlling scanning planes of imaging device, comprising:

a tracer, on which a tracer coordinate system is built, fixed on a target which is to be scanned; a tracking device, on which a tracking device coordinate system is built, for obtaining the position and orientation of the tracer in said tracking device coordinate system and converting the known position and orientation of the target to be scanned from a coordinate system of said tracer to a coordinate system of said tracking device; and an imaging device, for scanning the position and orientation of the target to be scanned in said coordinate system of said imaging device to form images, on which an imaging device coordinate system is built; wherein, said tracking device or said imaging device has a conversion module preset therein, which is for converting the position and orientation of the target to be scanned from the tracking device coordinate system to the imaging device coordinate system; and when the conversion module is preset in the tracking device, the tracking device transfers the position and orientation of the target to be scanned in the tracking device coordinate system to the imaging device.

In a class of this embodiment, the expression of the conversion module C track scan that is mentioned above is presented as:

In a class of this embodiment, the tracer comprises a position/orientation sensor and a fixing support. The position/orientation sensor is fixed via the fixing support on the target to be scanned. The position and orientation of the position/orientation sensor is the same as the position and orientation of the tracer.

In a class of this embodiment, the expression of the position and orientation C tool track of the tracer in the tracking device coordinate system is presented as:

wherein, C tool track is a 4*4 matrix, R track scan is a 3*3 rotation matrix, and T track scan is a 3 dimensional translation vector.

The invention further provides a method for controlling scanning planes of imaging device comprise steps of:

step 1: building a systems comprising a tracer, a tracking device, and an imaging device; and then fixing the tracer a target which is to be scanned; and, presetting a conversion module between a tracking device coordinate system and an imaging device coordinate system in a tracking device or an imaging device; step 2: defining a plane through which the imaging device scans the target to be scanned as a scanning plane G, and the expression of the scanning plane G in the tracer coordinate system is presented as:

{right arrow over (n)} tool ·( X tool −S tool )=0

Wherein, X tool represents the coordinate of any point on the scanning plane G in the tracer coordinate system, which is a 3 dimensional vector; {right arrow over (n)} tool represents a normal vector for the scanning plane G in the tracer coordinate system, which is a normalized 3 dimensional vector; and S tool represents the coordinate of a known point on the scanning plane G in the tracer coordinate system, which is also a 3 dimensional vector; step 3: measuring a position and orientation C tool track of the tracer in the tracking device coordinate system ‘track’ with the tracking device; step 4: calculating a first plane equation of scanning plane G in the tracking device coordinate system with the tracking device using the position and orientation C tool track of step 3, the expression of which is presented as bellow:

{right arrow over (n)} track ·( X track −S track )=0

{right arrow over (n)} track =R tool track ·{right arrow over (n)} tool

S track =R tool track ·S tool +T tool track

wherein, {right arrow over (n)} track represents a normal vector of the scanning plane G in the tracking device coordinate system, which is a normalized 3 dimensional vector; X track represents a coordinate of any point on the scanning plane G in the tracking device coordinate system, which is a 3 dimensional vector; and S track represents a coordinate of a known point on the scanning plane G in the tracking device coordinate system, which is a 3 dimensional vector; step 5: calculating a second plane equation of the scanning plane G in the imaging device coordinate system in terms of a conversion module C track scan for conversion between the tracking device coordinate system and the imaging device coordinate system, wherein, an expression of the second plane equation is presented as bellow:

{right arrow over (n)} scan ·( X scan −S scan )=0

{right arrow over (n)} scan =R track scan ·{right arrow over (n)} track =R track scan ·R tool track ·{right arrow over (n)} tool

S scan =R track scan ·S track +T track scan =R track scan ·( R tool track ·S tool ·T tool track )+ T track tool

and {right arrow over (n)} scan represents a normal vector of the scanning plane G in the imaging device coordinate system, which is a normalized 3 dimensional vector; X scan represent a coordinate of any point on the scanning plane G in the imaging device coordinate system, which is a 3 dimensional vector; S scan represents a coordinate of a known point on the scanning plane G in the imaging device coordinate system, which is a 3 dimensional vector; and Step 6: scanning the target to be scanned with the imaging device 3 , in terms of second plane equation calculated in step 5. an expression of the conversion matrix C track scan in step 1 is

For step 5, the conversion module is preset in the tracking device, and the second plane equation of the scanning plane G in the imaging device coordinate system is calculated by the tracking device and then transferred to the imaging device.

For step 5, the conversion module is preset in the imaging device, and the second plane equation of the scanning plane G in the imaging device coordinate system is calculated by the imaging device.

This invention has the following advantages:

1) the system in this invention comprises a tracer, a tracking device and an imaging device and defines the coordinate systems of the tracer, the tracking device and the image device respectively as the coordinate systems built upon the tracer, the tracking device and the image device, and the tracer is fixed on a target to be scanned (such as instruments and focus etc), to allow the tracer to move with the target to be scanned, which allows the system of the invention to measure the precise position and orientation of the tracer at real time via the tracking device. It is also possible for the system of the invention to obtain the precise position and orientation of the target to be scanned in the tracking system at real time, in terms of the position and orientation of the tracer measured at real time, the known position and orientation of the target to be scanned in the tracer coordinate system, and the conversion relation between the tracking device coordinate system and the tracer coordinate system. And then it is further possible for the system of the invention to obtain the precise position and orientation of the target to be scanned in the imaging device coordinate system, in terms of the preset conversion relation between the tracking device coordinate system and the imaging device coordinate system, which may reduce error rate made due to manual operation such as manual setting of the position and orientation of the scout image. In addition, an instrument can be used as a scanning probe adapted for scanning what it points to, which may improve the operating flexibility. 2) Due to the fact that this system has preset a conversion module between the tracking device coordinate system and the imaging device coordinate system in the tracking device or the imaging device, the position and orientation of target can be converted from the tracking device coordinate system to the imaging device coordinate system at real time, so as to reduce operating time and improve imaging speed. Consequently, the system of the invention to be of high imaging speed and high imaging precision and may be applied to various imaging devices.

FIG. 1 shows a position image in the existing technology;

FIG. 2 shows the building of a scanning plane in the existing technology;

FIG. 3 shows the structure of the system of this invention;

FIG. 4 shows the use of the scanning plane of this invention;

Referring to FIG. 3 , the system of one embodiment of the invention comprises a tracer 1 , a tracking device 2 , and an imaging device 3 . For each device, a corresponding coordinate system is built thereon. Those coordinate systems can be presented as ‘tool’ for the tracer coordinate system, ‘track’ for the tracking device coordinate system, and ‘scan’ for the imaging device coordinate system.

The tracer 1 of one embodiment of this invention comprises a position/orientation sensor and a fixing support. The position/orientation sensor is fixed on the target (such as instruments and focus etc) which is to be scanned through the fixing support. In the tracer coordinate system ‘tool’, the position and orientation for the position/orientation sensor can be regarded as the position and orientation of the tracer 1 . The position/orientation sensor may comprise three plastic balls with phosphor powder coating on the external surface thereof, which are not arranged in line. Tracking device 2 comprises an optical camera based on binocular vision, a computer and software. Tracking device 2 can measure the position and orientation of a position/orientation sensor. Therefore, the tracking device 2 may obtain the position and orientation C tool track of the tracer 1 in the tracking device coordinate system ‘track’ by tracking and measuring the position and orientation of the position/orientation sensor of the tracer 1 , which is a conversion matrix for converting a coordinate to the tracking device coordinate system ‘track’ from the tracer coordinate system ‘tool’, and an expression of the conversion matrix is presented as:

For example, by using the formula below, a coordinate Q tool of any point Q in the tracer coordinate system can be converted into a coordinate Q track in the tracking device coordinate system track, wherein, for example, the coordinate Q tool can be 3 dimensional vector represented by a 3*1 matrix and the superscript ‘tool’ represents the coordinate is in the tracer coordinate system ‘tool’; and the coordinate Q track can be a 3 dimensional vector represented by a 3*1 matrix, and its superscript ‘track’ represents the coordinate is in the tracking coordinate system ‘track’, the expression of the formula is presented as bellow:

Q track =C tool track Q tool   (2)

A certain orientation {right arrow over (t)} in the tracer coordinate system ‘tool’ can be represented by a unit vector {right arrow over (t)} tool (which is a normalized 3 dimensional vector represented by a 3*1 matrix, and its superscript ‘tool’ represents the vector is in the tracer coordinate system ‘tool’), and the orientation is converted into a unit vector {right arrow over (t)} track in the tracking device coordinate system ‘track’, wherein, the unit vector {right arrow over (t)} track is a 3 dimensional vector represented by a 3*1 matrix, and its superscript ‘track’ represents the unit vector is in the tracking device coordinate system ‘track’, and the expression of formula for conversion is presented as bellow:

{right arrow over (t)} track =R tool track ·{right arrow over (t)} tool   (3)

In order to allow the imaging device 3 to use the position and orientation data in the tracking device

coordinate system ‘track’, it is required to convert the position and orientation data from the tracking device coordinate system ‘track’ to the imaging device coordinate system ‘scan’. And the conversion module C track scan for conversion between the tracking device coordinate system and the imaging device coordinate system is presented as bellow:

Q scan =C track scan Q track   (5)

wherein, the coordinate Q track is a 3 dimensional vector represented by a 3*1 matrix, and its superscript ‘track’ represents the coordinate is in the tracking device coordinate system ‘track’.

A certain orientation {right arrow over (t)} in the tracking coordinate system ‘track’ can be represented by a unit vector {right arrow over (t)} tool (which is a normalized 3 dimensional vector represented by a 3*1 matrix, and its superscript ‘tool’ represents that the vector is in the tracking coordinate system ‘track’, and in the imaging device coordinate system ‘scan’, the orientation is converted into a unit vector {right arrow over (t)} scan (which is a normalized 3 dimensional vector represented by a 3*1 matrix, and its superscript ‘scan’ represents the unit vector {right arrow over (t)} scan is in the imaging device coordinate system ‘scan’. The expression of the formula of the conversion is presented as bellow:

{right arrow over (t)} scan =R track scan ·{right arrow over (t)} track   (6)

Conversion module C track scan for conversion between the tracking device coordinate system and the imaging device coordinate system can be preset either in the tracking device 2 or the imaging device 3 . The conversion module C track scan is used to convert the position and orientation of the target to be scanned from the tracking device coordinate system ‘track’ to the imaging device coordinate system ‘scan’. When the conversion module C track scan is preset in the tracking device 2 , the tracking device 2 will transfer the position and orientation of the target to be scanned to the imaging device 3 , and then the imaging device 3 will convert the position and orientation from the tracking device coordinate system to the imaging device coordinate system. The imaging device may conduct scanning in terms of the position and orientation of the target to be scanned in its own coordinate system.

Conversion module C track scan for conversion between the tracking device coordinate system and the imaging device coordinate system can be obtained through other technical calibrations, such as the one disclosed in Chinese patent under no. ZL200710064900.2, titled ‘A navigating method and a navigation System for Supporting Multiple Modes’. In this patent, inverse matrix C scan track of conversion module C track scan for conversion between the tracking device coordinate system and the imaging device coordinate system is obtained, and the conversion module C track scan can be obtained through inversion, and the expression of formula of conversion module C track scan is presented as bellow:

C track scan =( C scan track ) −1   (7)

According to FIG. 4 , for a needle shaped device 4 , there are three types of ordinary scanning planes, for example, plane 7 and plane 8 pass the needle shaped device 4 and are perpendicular to each other, and plane 9 is perpendicular to plane 8 and 7 respectively. The information of the entire image can be quickly provided through observation of the combination of the three planes. In addition, the needle shaped device 4 can be used as a probe, for example, it may scan what it points to, so as to improve the flexibility of operation.

The methods for controlling scanning planes of imaging device comprise steps of:

step 1: building a system comprising a tracer 1 , a tracking device 2 , and an imaging device 3 ; and then fixing the tracer on a target to be scanned; and presetting a conversion module for conversion between a tracking device coordinate system and an imaging device coordinate system in a tracking device or an imaging device; step 2: defining a plane with a certain thickness as a scanning plane G of the imaging device, and an expression of formula of the scanning plane G in the tracer coordinate system is presented as:

{right arrow over (n)} tool ·( X tool −S tool )=0  (8)

wherein, X tool represents a coordinate of any point on plane G in the tracer coordinate system ‘tool’, which is an unknown 3*1 matrix, and is also an unknown 3D vector; {right arrow over (n)} tool represents the normal vector of plane G is in the tracer coordinate system, which is a 3*1 matrix and is also a normalized 3 dimensional vector. S tool represents a coordinate of a known point on plane G in the tracer coordinate system, which is a 3*1 matrix and is also a 3 dimensional vector. The superscript of X tool , {right arrow over (n)} tool and S tool represents these vectors are in the tracer coordinate system ‘tool’. {right arrow over (n)} tool and S tool are known vectors and can be obtained through mechanical design and calibration, during the process of designing a tracer 1 ; step 3: measuring a position and orientation C tool track of the tracer 1 in the tracking device coordinate system ‘track’ with the tracking device 2 , wherein, C tool track is a conversion matrix for conversion from the tracer coordinate system ‘tool’ to the tracking device coordinate system ‘track’, and an expression of formula 1 of the conversion matrix is presented as bellow:

{right arrow over (n)} track ·( X track −S track )=0  (9)

{right arrow over (n)} track =R tool track ·{right arrow over (n)} tool   (10)

S track =R tool track ·S tool +T tool track   (11)

wherein, a normal vector of the scanning plane G in the tracking device coordinate system ‘track’ is represented by {right arrow over (n)} track , which is a 3*1 matrix, and is also a normalized 3 dimensional vector. Its superscript ‘track’ represents that the vector is in the tracking device coordinate system ‘track’; X track represents the coordinate of any point on the scanning plane G in the tracking device coordinate system ‘track’, which is an unknown 3*1 matrix and is also an unknown 3 dimensional vector. Its superscript ‘track’ represents that its vector is in the tracking device coordinate system ‘track’; S track represents the coordinate of a known point on the scanning plane G in the tracking device coordinate system, which is a 3*1 matrix and is also a 3 dimensional vector, and its superscript ‘track’ represents the vector is in the tracking device coordinate system ‘track’;

step 5: calculating a second plane equation of scanning plane G in the imaging device coordinate system ‘scan’ with the tracking device 2 using the conversion module C track scan for conversion between the tracking device coordinate system and the imaging device coordinate system in formula 4 and with formula 5, 6, 9, 10, and 11, an expression of the second plane equation is presented as bellow:

{right arrow over (n)} scan ·( X scan −S scan )=0  (12)

{right arrow over (n)} scan =R track scan ·{right arrow over (n)} track =R track scan ·R tool track ·{right arrow over (n)} tool   (13)

S scan =R track scan ·S track +T track scan =R track scan ·( R tool track ·S tool +T tool track )+ T track scan   (14)

wherein, {right arrow over (n)} scan represents a normal vector of the scanning plane G in the imaging device coordinate system ‘scan’, which is a 3*1 matrix and is also a normalized 3 dimensional vector. Its superscript ‘scan’ represents the vector is in imaging device coordinate system ‘scan’; X scan represent a coordinate of any point on said scanning plane G in said imaging device coordinate system, which is a unknown 3*1 matrix and is also a unknown 3 dimensional vector and its superscript ‘scan’ represents the vector is in the imaging device coordinate system ‘scan’; S scan represents a coordinate of a known point on the scanning plane G in the imaging device coordinate system, which is a 3*1 matrix and is also a 3 dimensional vector; its superscript ‘scan’ represents its unit vector is in imaging device coordinate system ‘scan’. After the plane equations 12, 13, and 14 of the scanning plane G in the imaging device coordinate system ‘scan’ are calculated, tracking device ( 2 ) will transfer these equations to the imaging device 3 ;

step 6: scanning the target to be scanned with the imaging device 3 , in terms of the plane equations 12, 13 and 14 of the scanning plane G in the imaging device coordinate system ‘scan’.

Referring to the step 5 mentioned above, it is also possible to transfer the plane equations 9, 10, and 11 of the scanning plane G in the tracking device coordinate system from the tracking device 2 to the imaging device 3 , and then the imaging device 3 calculates plane equations 12, 13, and 14 of the scanning plane G in the imaging device coordinate system ‘scan’.