OPTICAL DETECTION OF FOREIGN METAL OBJECTS ON SUBJECTS BEFORE UNDERGOING MAGNETIC RESONANCE IMAGING

Abstract

Provided is an optical metal detector device (10) for preparing magnetic resonance imaging, MRI, comprising: a light (11) configured to emit light to illuminate a subject (S), a camera (12) configured to be positioned in multiple different positions relative to the subject, to capture a series of images of the illuminated subject and to provide assigned image signals, a linear polarizer (13) configured to be arranged in at least a first angular position and a second angular position relative to the subject, the first angular position and the second angular position are different to each other, and to polarize the light emitted by the light source or to polarize the image captured by the camera, and a data processing means (14) configured to obtain at least the image signals from the camera, wherein the data processing means is further configured to combine the image signals associated with the first angular position and the second angular position of the linear polarizer and the image signals associated with one or more of the multiple different positions of the camera to obtain a combined signal and to compare the combined signal with a threshold indicating a quantity of foreign metal objects on the subject. Thereby, combining the image signals with each other comprises a convolution operation.

Claims

1. An optical metal detector device comprising: a light source configured to emit light to illuminate a subject (S), a camera configured to be positioned in multiple different positions relative to the subject, to capture a series of images of the illuminated subject and to provide assigned image signals, a linear polarizer configured to be arranged in at least a first angular position and a second angular position relative to the subject, the first angular position and the second angular position are different to each other, and to polarize the light emitted by the light source or to polarize the image captured by the camera, and a data processing unit configured to obtain at least the image signals from the camera, wherein the data processing unit is further configured to combine the image signals associated with the first angular position and the second angular position of the linear polarizer and the image signals associated with one or more of the multiple different positions of the camera to obtain a combined signal and to compare the combined signal with a threshold indicating a quantity of foreign metal objects on the subject, and wherein combining the image signals with each other comprises a convolution operation of image signals associated with the first angular position and the second angular position of the linear polarizer with each other.

2. The optical metal detector device of claim 1, wherein the combined signal represents one or more portions of the subject in which light-reflecting metal objects are present.

3. The optical metal detector device of claim 1, wherein the data processing unit is further configured to generate an alarm signal if the threshold is violated.

4. The optical metal detector device of claim 1, wherein the data processing unit is further configured to assign various thresholds for foreign metal objects specifically to various body portions of the subject.

5. The optical metal detector device of claim 1, wherein the light source is configured to be positioned in multiple different positions relative to the subject, and the data processing unit is further configured to combine image signals obtained for one or more of the different positions of the light source.

6. The optical metal detector device of claim 1, wherein the linear polarizer is arranged in a light beam path between light source and subject or between subject and camera.

7. The optical metal detector device of claim 1, wherein a wavelength of the light emitted by the light source is from near-infrared to ultraviolet.

8. The optical metal detector device of claim 1, wherein a band-pass filter having a passband that transmits the light emitted by the light source and that at least partially blocks ambient light is applied to the camera.

9. A method of detecting foreign metal objects on or in a subject (S), the method comprising: illuminating (S1), by a light source, the subject with light, moving (S2) a linear polarizer from at least a first angular position to a second angular position relative to the subject (S), moving (S3) a camera from at least a first position to a second position relative to the subject (S), capturing (S4), by the camera, a series of images of the illuminated subject, at least a first image of the series associated with the first position of the linear polarizer, a second image of the series associated with the second position of the linear polarizer, a third image of the series associated with the first position of the camera and a fourth image of the series associated with the second position of the camera, and combining (S5), by a data processing unit, the images obtained by the camera to obtain a combined signal, wherein combining the image signals with each other comprises a convolution operation of image signals associated with the first angular position and the second angular position of the linear polarizer with each other, and comparing (S6) the combined signal with a threshold indicating a quantity of the foreign metal objects on the subject.

10. The method of claim 9, wherein the metal objects to be detected are present as particles or dust.

11. The method of claim 9, wherein the threshold is set based on at least one anatomical feature of the subject.

12. The method of claim 1, wherein a wavelength of the light emitted by the light source is selected as a function of a detection depth of the foreign metal objects with reference to an outer surface of the subject, the metal objects to be detected being on the skin, partially stuck in the skin, or being enclosed in the skin or underlying tissue.

13. A computer program product for detecting metal objects on a subject, the computer program product including instructions stored on a non-transitory computer readable medium which, when executed by a causes the processor of an optical medical detector to: illuminate, by a light source of the optical medical detector, the subject with light, move a linear polarizer of the optical medical detector from at least a first angular position to a second angular position relative to the subject (S), move a camera of the optical medical detector from at least a first position to a second position relative to the subject (S), capture, by the camera, a series of images of the illuminated subject, at least a first image of the series associated with the first position of the camera linear polarizer, a second image of the series associated with the second position of the linear polarizer, a third image of the series associated with the first position of the camera and a fourth image of the series associated with the second position of the camera, and combine, by the processor, the images obtained by the camera to obtain a combined signal, wherein combining the image signals with each other comprises a convolution operation of image signals associated with the first angular position and the second angular position of the linear polarizer with each other, and compare the combined signal with a threshold indicating a quantity of the foreign metal objects on the subject.

14. A non-transitory computer readable medium or data carrier comprising or carrying the computer program product of claim 13.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Exemplary embodiments of the invention will be described in the following drawings.

[0061] FIG. 1 shows in a schematic perspective overview an MRI system comprising an MRI device and an optical metal detector device according to an exemplary embodiment of the invention.

[0062] FIG. 2 shows in a schematic side view an optical metal detector device according to an exemplary embodiment of the invention separate from an MRI device.

[0063] FIG. 3 shows different angular positions of a linear polarizer and resulting images of a foreign metal object taken at the different angular positions of the linear polarizer by use of a camera of an optical metal detector device according to an exemplary embodiment of the invention.

[0064] FIG. 4 shows exemplary cropped parts of an image signal of a metal object taken at the different angular positions of the linear polarizer by use of a camera of an optical metal detector device according to an exemplary embodiment of the invention.

[0065] FIG. 5 shows a flow chart of a method of detecting foreign metal objects in or on a subject.

DETAILED DESCRIPTION OF EMBODIMENTS

[0066] FIG. 1 shows in a schematic perspective overview a magnetic resonance imaging, MRI, system 100 comprising a magnetic resonance imaging, MRI, device 110 and an optical metal detector device 10 according to an exemplary embodiment. The MRI device 110 and the optical metal detector device 10 are operatively connected to each other, so as to control the MRI device 110 based on output control data of the optical metal detector device 10. In particular, the MRI device 110 may be configured to be started or to be switched off on basis of output control data of the optical metal detector device 10. Accordingly, in this exemplarily embodiment as shown in FIG. 1, the MRI device 110 and the optical metal detector device 10 are located within the same room which exemplarily is a scanning room. A patient or subject S is to be examined for undesired metal objects by using the optical metal detector device 10 before the MRI is performed. By way of example, the subject S may have metal objects to be detected which are present as particles or dust.

[0067] The MRI device 110 comprises a magnetic unit 111 that defines a bore 112 into which the patient or subject S can be moved by means of a subject supporting couch 113. For better illustration, in FIG. 1, the subject S is placed on the couch 113.

[0068] The optical metal detector device 10 comprises at least one light source 11 configured to emit light in a defined and/or predetermined and/or adjustable wavelength to illuminate the subject S. For example, the light source 11 may be configured to emit light from near-infrared to ultraviolet, wherein the wavelength may be varied to provide different penetration depths of the emitted light with respect to a surface or skin of the subject S, which penetration depths depend on the wavelength used. Preferably, the wavelength used is different to a wavelength of an ambient light in the surroundings of the optical metal detector device 10. The light source 11 may be configured to be positioned in multiple different positions relative to the subject S, which different positions of the light source 11 are indicated in FIG. 1 by showing the light source 11 in solid lines in a first position and in dashed lines in a second position. It is understood that the second position may be achieved from the first position by moving, pivoting etc., wherein to perform the movement, the optical metal detector device 10 may have one or more actuators that may be controlled electronically. Thus, the subject S may be illuminated from different positions and/or at different angles, so that the reflection intensity of illuminated metal objects changes.

[0069] Further, the optical metal detector device 10 comprises at least one camera 12 which may be adapted to acquire multiple images of the subject S. In operation of the optical metal detector device 10, the camera 12 is configured to capture images of the subject S being illuminated by the light of the light source 11. The camera 12 may be configured to be positioned in multiple different positions relative to the subject S, to capture a series of images of the illuminated subject S and to provide assigned image data and/or signals. The multiple different positions of the camera 12 are indicated in FIG. 1 by showing the camera 12 in solid lines in a first position and in dashed lines in a second position. It is understood that the second position may be achieved from the first position by moving, pivoting etc., wherein to perform the movement, the optical metal detector device 10 may comprise one or more actuators that may be controlled electronically. Thus, the subject S may be detected from different positions and/or at different angles, so that the reflection intensity of illuminated metal objects changes.

[0070] Further, the optical metal detector device 10 comprises at least one linear polarizer 13, which may be rotatable with respect to the camera 12 and/or the light source 11, in particular around an axis of view of the camera 12 and/or around an axis corresponding to a light beam of the light source 11. In particular, the linear polarizer 13 is configured to be arranged in at least a first angular position and a second angular position, relative to the subject S, wherein the first angular position and the second angular position are different to each other. Further, the linear polarizer 13 may be configured to polarize the light emitted by the light source 11 or to polarize the image captured by the camera 12. By way of example, in FIG. 1, the linear polarizer 13 is arranged in the front of the camera 12, so as to be located between the camera 12 and the subject S. In at least some embodiments, however, the linear polarizer 13 may additionally or alternatively be arranged in a light beam path between the light source 11 and the subject S. It is understood that the different may be achieved from the first position by rotating the linear polarizer 13, wherein to perform the movement, the optical metal detector device 10 may comprise one or more actuators that may be controlled electronically.

[0071] Further, the optical metal detector device 10 comprises a data processing means 14 configured to obtain at least the image signals from the camera 12. It may be provided as a processor, a computing means etc. The data processing means 14 may be operatively connected to the camera 12, and may be further operatively connected to light source 11 and/or the linear polarizer 13, for providing control signals for movement and/or for obtaining feedback signals regarding a current position or alignment. The data processing means 14 may be further configured to combine the image signals associated with the first angular position and the second angular position of the linear polarizer 13 and the image signals associated with one or more of the multiple different positions of the camera 12 to obtain a combined signal and to compare the combined signal with a threshold indicating a quantity of foreign metal objects on the subject S. The threshold may be assigned to a specific body portion of the subject S, and may be set based on at least one anatomical feature of the subject S, wherein the threshold may be higher for less sensitive tissue and lower for more sensitive tissue. By way of example, an eye region may be regarded as a more sensitive tissue, whereas an arm, a leg or the like may be regarded as less sensitive tissue. The threshold may indicate a quantity or density of e.g. metal dust, with optional consideration of the type of tissue and/or metal object, the penetration depth, duration of the planned MRI scan, magnet field intensity etc. The data processing means 14 is further configured to assign various thresholds for foreign metal objects specifically to various body portions of the subject S. Further, the data processing means 14 may be configured to generate an alarm signal if the one or more thresholds are violated. Also, the data processing means 14 may be configured to combine the images obtained by the camera 12 to obtain a combined image signal. Further, the data processing means 14 may be configured to compare the combined image signal with the one or more thresholds above.

[0072] FIG. 2 shows a schematic side overview of the optical metal detector device 10 according to an exemplary embodiment, where it is separate from the MRI device 110. In this embodiment, the optical metal detector device 10 may be located in a separate preparation room instead of the MR scanning room. However, the functionality of this embodiment is preferably the same as described above with regard to FIG. 1. It shows, however, that the optical metal detector device 10 does not necessarily depends on the presence of the MRI device 110. As denoted by reference signs 15, in at least some embodiments, a band-pass filter having a passband that transmits the light emitted by the light source and that at least partially blocks ambient light may applied to the camera 12.

[0073] FIG. 3 shows different angular positions of the linear polarizer 13 and resulting captured images I.sub.N of the optical metal detector device 10 according to an exemplary embodiment of the invention. FIG. 3 comprises three rows, whereby in a first row, here upper row, seven different images I.sub.1 to I.sub.6 taken by the camera 12 are contained, which images are assigned in each case to an angular position of the linear polarizer 13. In the first row of FIG. 3, black ovals of varying intensity indicate that the detectable intensity of reflection caused by the illumination of the metal object, which is denoted by M, or subject S by the light source 11 changes with the angular position of the linear polarizer 13. In a second, middle row the linear polarizer 13 is shown in the seven different angular positions, namely at 0° as start position, at 15°, 30°, 45°, 60°, 75° as intermediate positions and at 90° as end position. As can be seen in FIG. 3, by way of example, at 0° the intensity may be maximum, wherein in the intermediate position the intensity decreases. The intermediate positions are reached by turning the linear polarizer 13 by e.g. 30°, wherein other angular steps are possible. The third, lowest row of FIG. 3 designates the seven different angular positions of the linear polarizer 13 with 0° as start position, and 15°, 30°, 45°, 60°, 75° as intermediate positions and 90° as end position. As will be described below, the sequence of images I.sub.N when convoluted will highlight the portions with metal dust with preferably a Gaussian enhancement (see e.g. FIG. 5). The largest reflecting surface of each metal object M may contribute to a maximum intensity at a particular linear polarizer angle, whereas the skin pigments maintain a nearly uniform reflective property across all polarization angles. These intensity histograms may be convoluted with each other to generate an image devoid of e.g. facial features.

[0074] FIG. 4 shows exemplary cropped parts of an image signal of a metal object M taken at the different angular positions of the linear polarizer 13 by use of the camera 12 of the optical metal detector device 10 according to an exemplary embodiment of the invention. On the left are the several different images I.sub.N known from FIG. 3. In the middle the combining operation, which may be a convolution operation, of these images I.sub.N is indicated by an arrow. The combining operation may be performed by use of the data processing means 14. On the right the resulting combined, e.g. convoluted signal, is shown. The convolution of images taken at multiple polarizer angles increases the Signal to Noise Ratio. The highest peaks representing the brightest refection points at a particular pixel in the rotationally combined images. The scattered and/or absorbed components are subjected to a very minimal value post convolution. A reconstruction of the original image from the convoluted signals would have to be thresholded to filter out any other objects other than highest reflecting points.

[0075] FIG. 5 shows a flow chart of a method of detecting foreign metal objects on a subject S. In a step S1, the subject S is illuminated with light by the light source 11.

[0076] In a step S2, the linear polarizer 13 is moved from at least a first angular position to a second angular position relative to the subject S.

[0077] In a step S3, the camera 12 is moved from at least a first position to a second position relative to the subject (S). It is noted that steps S2 and S3 may also be performed in any different order.

[0078] In a step S4, a series of images of the illuminated subject S is captured by the camera 12, wherein at least a first image of the series associated with the first position of the linear polarizer 13 and a second image of the series associated with the second position of the linear polarizer 13, a third image of the series associated with the first position of the camera 12 and a fourth image of the series associated with the second position of the camera 12. It is noted that the first to fourth images may be obtained in any different order.

[0079] In a step S5, the images obtained by the camera 12 are combined by the data processing means 14 to obtain a combined signal. The combining operation may comprise a convolution operation.

[0080] In a step S6, the combined signal is compared with a threshold indicating a quantity of the foreign metal objects m in or on the subject S. The comparison step may be performed by the data processing means 14.

[0081] It has to be noted that embodiments of the invention are described with reference to different subject matter. In particular, some embodiments are described with reference to method type claims whereas other embodiments are described with reference to the device type claims. However, a person skilled in the art will gather from the above and the following description that, unless otherwise notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters is considered to be disclosed with this application. However, all features can be combined providing synergetic effects that are more than the simple summation of the features.

[0082] 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 a claimed invention, from a study of the drawings, the disclosure, and the dependent claims.

[0083] 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. A single processor or other unit may fulfill the functions of several items re-cited in the claims. The mere fact that certain measures are re-cited 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.

LIST OF REFERENCE SIGNS

[0084] 100 MRI system [0085] 110 MRI device [0086] 111 magnetic unit [0087] 112 bore [0088] 113 support table [0089] 10 optical metal detector device [0090] 11 light source [0091] 12 camera [0092] 13 linear polarizer [0093] 14 data processing means [0094] 15 band-pass filter [0095] M metal object (e.g. particle, dust etc.) [0096] S subject