Tracking a Part of a Surface of a Patient's Body Using Thermographic Images

Abstract

A medical image processing method, performed by a computer, for measuring the spatial location of a point on the surface of a patient's body including: acquiring at least two two-dimensional image datasets, wherein each two-dimensional image dataset represents a two-dimensional image of at least a part of the surface which comprises the point, and wherein the two-dimensional images are taken from different and known viewing directions; determining the pixels in the two-dimensional image datasets which show the point on the surface of the body; and calculating the spatial location of the point from the locations of the determined pixels in the two-dimensional image datasets and the viewing directions of the two-dimensional images; wherein the two-dimensional images are thermographic images.

Claims

1. A system including memory and one or more processors operable to execute instructions stored in the memory, comprising instructions to: acquire a three-dimensional image dataset; acquire at least two two-dimensional image datasets, wherein each two-dimensional image dataset represents a two-dimensional thermographic image of at least a part of a surface of a patient's body which comprises a plurality of points and wherein the two-dimensional thermographic images are taken from different and known viewing directions; determine, for each point in the plurality of points, the pixels in the two-dimensional image datasets which show said point on the surface of the patient's body; and calculate, for each point in the plurality of points, a spatial location of the point from locations of the corresponding determined pixels in the two-dimensional image datasets and the viewing directions of the two-dimensional thermographic images; and calculate alignment information which represents a virtual relative position between the three-dimensional image dataset and the locations of the plurality of points, such that the measured locations of the plurality of points lie on a contour of the body as represented by the three-dimensional image dataset.

2. The system of claim 1, further comprising instructions to: calculate movement control data from the alignment information, and cause, based on the movement control data, the patient's body to be moved into a position that is identical to a position at a time the three-dimensional image dataset was created.

3. The system of claim 2, wherein the movement control data describes how the patient's body has to be moved for the surface of the patient's body to match the contour of the patient's body as represented by the three-dimensional image dataset

4. The system of claim 2, wherein the position at the time the three-dimensional image dataset was created is a predetermined position relative to an accelerator for radiotherapy.

5. The system of claim 1, wherein the three-dimensional image dataset is a CT or MR image dataset.

6. The system of claim 1, wherein the two-dimensional thermographic images represent wavelengths having a predefined wavelength range between 8 ?m and 14 ?m.

7. The system of claim 1, further comprising instructions to: filter the two-dimensional image datasets in order to discard pixels which represent wavelengths outside the predefined wavelength range.

8. A computer implemented method, comprising: acquiring a three-dimensional image dataset; acquiring at least two two-dimensional image datasets, wherein each two-dimensional image dataset represents a two-dimensional thermographic image of at least a part of a surface of a patient's body which comprises a plurality of points and wherein the two-dimensional thermographic images are taken from different and known viewing directions; determining, for each point in the plurality of points, the pixels in the two-dimensional image datasets which show said point on the surface of the patient's body; and calculating, for each point in the plurality of points, the a spatial location of the point from the locations of the corresponding determined pixels in the two-dimensional image datasets and the viewing directions of the two-dimensional thermographic images; and calculating alignment information which represents a virtual relative position between the three-dimensional image dataset and the locations of the plurality of points, such that the measured locations of the plurality of points lie on a contour of the body as represented by the three-dimensional image dataset.

9. The method of claim 8, further comprising: calculating movement control data from the alignment information, and causing, based on the movement control data, the patient's body to be moved into a position that is identical to a position at a time the three-dimensional image dataset was created.

10. The system of claim 9, wherein the movement control data describes how the patient's body has to be moved for the surface of the patient's body to match the contour of the patient's body as represented by the three-dimensional image dataset

11. The system of claim 9, wherein the position at the time the three-dimensional image dataset was created is a predetermined position relative to an accelerator for radiotherapy.

12. The system of claim 8, wherein the three-dimensional image dataset is a CT or MR image dataset.

13. The system of claim 8, wherein the two-dimensional thermographic images represent wavelengths having a predefined wavelength range between 8 ?m and 14 ?m.

14. The system of claim 8, further comprising: filtering the two-dimensional image datasets in order to discard pixels which represent wavelengths outside the predefined wavelength range.

15. A non-transitory computer-readable program storage medium comprising instructions which, when executed by at least one processor, causes the at least one processor to execute steps of: acquiring a three-dimensional image dataset; acquiring at least two two-dimensional image datasets, wherein each two-dimensional image dataset represents a two-dimensional thermographic image of at least a part of a surface of a patient's body which comprises a plurality of points and wherein the two-dimensional thermographic images are taken from different and known viewing directions; determining, for each point in the plurality of points, the pixels in the two-dimensional image datasets which show said point on the surface of the patient's body; calculating, for each point in the plurality of points, the a spatial location of the point from the locations of the corresponding determined pixels in the two-dimensional image datasets and the viewing directions of the two-dimensional thermographic images; and calculating alignment information which represents a virtual relative position between the three-dimensional image dataset and the locations of the plurality of points, such that the measured locations of the plurality of points lie on a contour of the body as represented by the three-dimensional image dataset.

16. The non-transitory computer-readable program storage medium of claim 15, further comprising instructions which, when executed by at least one processor, cause the at least one processor to execute further steps of: calculating movement control data from the alignment information; and causing, based on the movement control data, the patient's body to be moved into a position that is identical to a position at a time the three-dimensional image dataset was created.

17. The non-transitory computer-readable program storage medium of claim 16, wherein the movement control data describes how the patient's body has to be moved for the surface of the patient's body to match the contour of the patient's body as represented by the three-dimensional image dataset

18. The non-transitory computer-readable program storage medium of claim 16, wherein the position at the time the three-dimensional image dataset was created is a predetermined position relative to an accelerator for radiotherapy.

19. The non-transitory computer-readable program storage medium of claim 15, wherein the three-dimensional image dataset is a CT or MR image dataset.

20. The non-transitory computer-readable program storage medium of claim 15, wherein the two-dimensional thermographic images represent wavelengths between 8 ?m and 14 ?m.

Description

[0054] In the following, the invention is described with reference to the enclosed figures which represent preferred embodiments of the invention. The scope of the invention is not however limited to the specific features disclosed in the figures.

[0055] FIG. 1 schematically shows a system for measuring the spatial location of a point on the surface of a patient's body.

[0056] FIG. 2 schematically shows an example of virtually aligning a patient and a three-dimensional dataset.

[0057] FIG. 1 shows a system 1 for measuring the spatial location of a point on the surface of the body of a patient P. The system 1 essentially comprises a computer 2 and a stereoscopic thermographic camera 3. The computer 2 is connected to an input device 10, such as a keyboard or a mouse, and to an output device 11 such as a monitor.

[0058] The stereoscopic thermographic camera 3 comprises two thermographic imaging units 4a and 4b. The imaging unit 4a comprises a lens system 5a and a sensor 6a. The imaging unit 4b correspondingly comprises a lens system 5b and a sensor 6b. The lens systems 5a and 5b guide incident thermal radiation onto the sensors 6a and 6b, respectively, wherein each of the sensors 6a and 6b creates a two-dimensional thermographic image which preferably represents wavelengths of between 8 ?m and 14 ?m. The lens systems 5a and 5b have characteristic axes similar to the optical axis of a camera which captures an image in the visible spectrum. As can be seen from FIG. 1, the two imaging units 4a and 4b have different characteristic axes and therefore different viewing directions. The characteristic axes are shown as dashed lines in FIG. 1.

[0059] Thermal radiation emitted from a point on the body is guided onto corresponding pixels of the sensors 6a and 6b in accordance with the spatial location of the point on the surface of the patient's body and the characteristics of the lens systems 5a and 5b.

[0060] In the present example, the sensors 6a and 6b are two-dimensional arrays of sensor cells which convert incident thermal radiation into a voltage which corresponds to the temperature of the corresponding point on the surface of the patient's body. The temperature is typically derived from the wavelength of the maximum within the spectrum of the incident infrared radiation.

[0061] The computer 2 comprises a central processing unit 7, a memory unit 8 and an interface 9. The memory unit 8 stores program data and/or working data, such as the image datasets acquired from the stereoscopic camera 3. The computer is connected to the input device 10, the output device 11 and/or the stereoscopic camera 3 via an interface 9.

[0062] The computer 2 acquires the two two-dimensional image datasets, which were captured using the sensors 6a and 6b, from the stereoscopic camera 3. The computer 2 is provided with the properties of the stereoscopic camera 3, such that for each pixel in each of the two-dimensional thermographic image datasets, the computer 2 knows or is able to calculate the line on which points imaged by said pixel are located.

[0063] The computer 2 determines the pixels in the two two-dimensional thermal images which capture the thermal radiation emitted from the same point on the surface of the patient's body. The pixels are for example determined by means of a descriptor which describes the thermal signature of the point and the area surrounding this point, such that the descriptor is characteristic of this point.

[0064] For each of the two-dimensional cameras 4a and 4b, the computer 2 uses the position of the determined pixel in the two-dimensional thermographic image and the properties of the lens system 5a or 5b, respectively, to determine the line in space on which the point on the surface of the patient's body lies. These lines are shown as solid lines in FIG. 1. The computer 2 then calculates the point in space at which the two lines intersect each other. The location of this point is the location of the point on the surface of the patient's body.

[0065] If the computer 2 measures the spatial locations of a plurality of points on the surface of the patient's body, a set of points is obtained which represents the shape of the surface of the patient's body.

[0066] One advantage of using thermographic images rather than images in the visible spectrum is that the thermal signature of the body is independent of the optical characteristics of the surface of the patient's body and/or the characteristics of the light which is emitted onto the patient's body.

[0067] FIG. 2 shows the principle of aligning the patient P and a three-dimensional dataset which represents at least a part of a contour of the body of the patient P. In this embodiment, the three-dimensional dataset represents a medical three-dimensional image such as an MR or CT image. The three-dimensional dataset comprises a three-dimensional array of voxels. The contour of the patient's body can be derived from the values of the voxels.

[0068] FIG. 2 shows the body of the patient P in a reference co-ordinate system C.sub.R. The computer 2 then measures the spatial locations of a plurality of points on the surface of the patient's body in the reference co-ordinate system C.sub.R. The position of the stereoscopic camera 3 in the reference co-ordinate system C.sub.R is known, such that the computer 2 can measure the spatial locations of the points in this reference co-ordinate system C.sub.R.

[0069] In order to make the example easier to understand, FIG. 2 shows the surface of the body of the patient P rather than the points on the surface of the patient's body. FIG. 2 also shows the contour of the patient's body as represented by the three-dimensional dataset DS. A dataset co-ordinate system C.sub.DS is assigned to the three-dimensional dataset DS. The position of the contour as shown in FIG. 2 corresponds to the position of the patient's body when the three-dimensional dataset DS was captured.

[0070] The computer 2 calculates alignment information which represents a relative position between the three-dimensional dataset DS and the locations of the plurality of points on the surface of the patient's body, such that the locations of the plurality of points lie on the contour of the patient's body as represented by the three-dimensional dataset DS. The alignment information describes the position of the dataset co-ordinate system C.sub.DS in the reference co-ordinate system C.sub.R, such that the contour represented by the three-dimensional dataset DS matches the surface of the patient's body as represented by the measured spatial locations of the points on the surface of the patient's body. This position of the dataset co-ordinate system C.sub.DS is shown as the co-ordinate system C.sub.DS in FIG. 2.

[0071] If the dataset co-ordinate system C.sub.DS has a particular initial position in the reference co-ordinate system C.sub.R, for example if the three-dimensional dataset DS was created by a medical imaging device which was at a known position in the reference co-ordinate system C.sub.R, then a transformation T can be calculated in order to align the three-dimensional dataset DS with the actual position of the patient's body, i.e. to register the dataset DS to the patient P. Once the three-dimensional dataset DS is aligned with the patient's body, the three-dimensional dataset DS can be displayed on the display device 11, for example together with an image of a medical instrument which is tracked in the reference co-ordinate system C.sub.R, for example by a known medical tracking system.

[0072] Conversely, if the initial position of the dataset co-ordinate system C.sub.DS corresponds to a target position of the patient's body in the reference co-ordinate system C.sub.R, then the inverse of the transformation T describes how the actual position of the patient's body in the reference co-ordinate system C.sub.R needs to be changed so as to match the target position. One application of this is in order to move the patient P into the position which is equal to the position in which the three-dimensional dataset DS was created.