High-frequency anti-scatter grid movement profile for line cancellation

Abstract

A process for deploying an anti-scattering grid in a mammograph is provided. The mammograph comprises a radiation source configured to emit radiation for taking mammographic images of a patient, a radiation detector comprising a network of sensors arranged periodically with a first pitch, and an anti-scattering grid arranged between the source and the detector, the anti-scattering grid comprising radiation adsorbing strips arranged parallel to each other and distributed periodically with a second pitch. The process comprises: displacing the anti-scattering grid relative to the detector or displacing the detector relative to the anti-scattering grid during emission of radiation; adapting the second pitch to the first pitch, wherein displacement is perpendicular to the direction of the strips of the anti-scattering grid, the strips being arranged parallel to a side of the anti-scattering grid positioned against the patient, and altering the positions of the return points between successive periods of the displacement motion.

Claims

1. A mammograph comprising: a radiation source configured to emit radiation for taking mammographic images of a patient; a radiation detector comprising a network of sensors arranged periodically with a first pitch; an anti-scattering grid arranged between the source and the detector, the anti-scattering grid comprising radiation adsorbing strips arranged parallel to each other and distributed periodically with a second pitch; and at least one actuator configured to displace the anti-scattering grid relative to the detector or displace the detector relative to the anti-scattering grid during emission of radiation, wherein displacement is perpendicular to the direction of the strips of the anti-scattering grid, the strips being arranged parallel to a side of the anti-scattering grid positioned against the patient, and the locations of the return points are changed between successive cycles of the displacement motion.

2. The mammograph of claim 1, wherein the at least one actuator is configured to displace at least one of the anti-scattering grid and the detector in a manner derived from a periodic pattern where the velocity just before and just after the return point is higher than for an oscillation of same amplitude and frequency.

3. The mammograph of claim 1, wherein the at least one actuator comprises at least one of a stepper motor, electromagnet, voice coil, linear actuator, and piezoelectric motor.

4. The mammograph of claim 1 wherein the combined movements of both the anti-scattering grid and the detector relative to each other alter the perceived relative return point of the grid as viewed by the detector.

5. The mammograph of claim 1 comprising two actuators, wherein the two actuators comprise motors operating at speeds different to each other.

6. The mammograph of claim 1, wherein the at least one actuator is arranged on a side of the anti-scattering grid opposite the side of the grid positioned against the patient.

7. The mammograph of claim 1, wherein the second pitch is at least one of a multiple of the first pitch, and a multiple of the Nyquist frequency of the detector.

8. The mammograph of claim 1, further comprising a control and processing unit configured to control the source and the detector and configured to control acquisition and processing of images.

9. A process for deploying an anti-scattering grid in a mammograph comprising a radiation source configured to emit radiation for taking mammographic images of a patient, a radiation detector comprising a network of sensors arranged periodically with a first pitch, and an anti-scattering grid arranged between the source and the detector, the anti-scattering grid comprising radiation-adsorbing strips arranged parallel to each other and distributed periodically with a second pitch, the process comprising: displacing at least one of the anti-scattering grid relative to the detector and displacing the detector relative to the anti-scattering grid during emission of radiation; wherein displacement is perpendicular to the direction of the strips of the anti-scattering grid, the strips being arranged parallel to a side of the anti-scattering grid positioned against the patient, and the locations of the return points are changed between successive cycles of the displacement motion.

10. The process of claim 9, wherein the displacement motion is derived from a periodic pattern where the velocity just before and just after the return point is higher than for an oscillation of same amplitude and frequency.

11. The process of claim 9, wherein the periodic pattern is a triangular wave.

12. The process of claim 9, wherein the amplitude of the grid displacement is longer than 5 periods of the strips of the anti-scattering grids.

13. The process of claim 9, wherein the return time is smaller than 5% of the grid movement period.

14. The process of claim 9, wherein the amplitude of the displacement motion period to period is changed by at least one of a, random number generator, pseudo-random equation, and a complex periodic movement.

15. The process of claim 14, wherein the amplitude of the displacement motion period to period is altered in relation to exposure time.

16. The process of claim 9, wherein at least one of an electromagnet, linear motor, and voice coil are used to drive the displacement motion.

17. The process of claim 9, wherein the displacement motion profile is tailored to reduce the required acceleration of the anti-scattering grid for a given radiation emission duration.

18. The process of claim 9, wherein the displacement occurs in a space of 2 mm or less.

19. The process of claim 9, further comprising moving the source relative to the detector to acquire three-dimensional mammographic images.

20. The process of claim 9, wherein the first pitch of the detector is adapted to the second pitch of the scattering grid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other characteristics, aims and advantages of the present invention will emerge from the following detailed description, with respect to the attached figures given by way of non-limiting examples and in which:

(2) FIG. 1 illustrates a process for deploying an anti-scattering grid according to the prior art;

(3) FIG. 2A illustrates a traditional mammography device using an anti-scattering grid;

(4) FIG. 2B illustrates a tomosynthesis device deploying an anti-scattering grid;

(5) FIG. 3 illustrates a configuration of an anti-scattering grid on a radiation detector;

(6) FIG. 4 schematically illustrates creation of a mammograph according to an embodiment of the present invention;

(7) FIG. 5A illustrates an example for deploying relative movement according to an embodiment of the present invention;

(8) FIG. 5B illustrates, in plan view, an example for deploying relative movement according to an embodiment of the present invention; and

(9) FIG. 6 schematically illustrates a mammograph according to an embodiment of the present invention.

(10) FIG. 7 represents an illustration of a displacement motion profile for an embodiment whereby displacement motion amplitude is derived from a randomized triangular periodic wave pattern, resulting in altered return point positions. Wherein X(t) is grid position as a function of time (t), with grid movement period 1/f, amplitude A, and a zone wherein the amplitude can vary A. The response time, t.sub.R, is also highlighted, and defined, as above, as the time centered on the return point in which grid movement slows down, stops, and resumes in the opposite direction with a comparable speed.

DETAILED DESCRIPTION OF THE INVENTION

(11) In reference to FIG. 4, a mammograph is illustrated comprising a radiation source 1, for example of X-ray type, emitting radiation 10 designed to illuminate the breast of a patient P of whom images are to be taken during a pause time T. The radiation transmitted then reaches a detector 3 made up of a network of sensors 31 (Shown in FIG. 3) distributed periodically with a pitch p.sub.d of the detector, of the order of 20 to 200 m.

(12) An anti-scattering grid 2 is interposed between the source 1 and the detector 3, more precisely between the breast of the patient P and the detector 3, so as to stop radiation scattered by the breast of the patient P not coming directly from the source 1.

(13) This anti-scattering grid 2 is placed immediately above the detector 3, and is protected by means of a cover 4. This cover also forms a support for the breast of the patient to be examined.

(14) The grid 2 comprises alternating radio-opaque strips 21, for example constituted by metal, and radio-transparent strips 21, which can be cavities in the grid, the strips 21 being parallel and distributed periodically with a pitch p.sub.g between two radio-opaque strips,

(15) This pitch p.sub.g is for example adapted to that of the detector, that is, it can be a multiple of the pitch p.sub.d of the detector 3, for example equal to the pitch p.sub.d of the detector 3, or even be a multiple of the Nyquist frequency of the detector 3. For example, a pitch of the grid p.sub.g may be about 100 m. The grid 2 may have a thickness of the order of about 1 mm to 3 mm, and sides of a length of the order of about 1824 to 2430 cm. In an example embodiment, the ratio of the detector pitch to the grid pitch is 1.5.

(16) The strips 21 of the grid are oriented according to a direction parallel to one side 22 of the grid 2 against which the patient P can be positioned. As such, the source 1 is capable of pivoting about an axis, Y-Y, thus enabling the capture successive frames to construct 3D images.

(17) The mammograph also comprises one or more actuators 5, whereof two are illustrated by way of non-limiting example in FIG. 4. This actuator or these actuators 5 permit relative movement between the grid 2 and the detector 3 explained herein below, by shifting the grid 2 relative to the detector 3 or alternatively by shifting the detector 3 relative to the grid 2, or simultaneously shifting both relative each other, over a time T corresponding at least to the exposure time of the patient P.

(18) The actuator or the actuators 5 can be located on the same side of the grid 2, and located under, as it is, under the cover 4 which holds the grid and the detector.

(19) Given the abovementioned spread of less than 2 mm between the edge of the grid 2 and the internal edge of the cover 4 at the side 21 against which the patient P can be positioned, the actuator or the actuators 5 can be located to the side opposite the patient chest wall. This also reduces added bulk caused by addition of this actuator or these actuators 5.

(20) In reference to FIG. 6, the source 1, the actuator or the actuators 5 and the detector 3 are connected to a control and processing unit 6 which manages both the source 1 and the actuator or the actuators 5 and also ensures acquisition and processing of images, if needed.

(21) Relative movement between the grid 2 and the detector 3 eliminates the moir on the detector 3 by varying the phase of the latter during the exposure time T. For this, it comprises at least one component according to a direction perpendicular to the direction in which the strips 21 of the grid 2 extend. In addition, the amplitude of the movement of the grid 2 or of the detector 3 according to this component, irrespective of its nature, should be at least one grid pitch p.sub.g in every sensor 31 of the detector 3 throughout exposure time T.

(22) According to a first embodiment of relative displacement between the grid 2 and the detector 3, the actuator or the actuators 5 can be piezoelectric motors. In this case, they shift the grid 2 or the detector 3 according to a translation movement along an axis perpendicular to the direction of the strips 21, that is, perpendicularly to the side 21 of the grid 2 against which the patient P can be positioned.

(23) In a variant illustrated in FIG. 5B, the mammograph comprises just one motor 5 connected to a reducer and a cam for executing angular displacement, in its plane, of the grid 2 or of the detector 3 about an axis X-X illustrated in the figure, by means of rotation whereof the centre is located outside the grid 2, respectively the detector 3. This variant has the advantage of using just one motor, reducing usage costs of such a mammograph.

(24) In this case, the amplitude of rotation corresponding to the amplitude of displacement is adapted as a function of the distance between the grid 2 (or the detector 3), and the centre of rotation. This embodiment modifies the moir phase non-uniformly during the exposure time T, another way of deleting the moir figures.

(25) As per another variant illustrated in FIG. 5B, the mammograph comprises at least two motors 5, actuating the grid 2respectively the detector 3at different speeds and preferably non-multiple integers such that they are desynchronised, which also modifies the moir phase non-uniformly during the exposure time T.

(26) In another embodiment, the motor or motors 5, displacing the grid 2 or the detector 3 can be stepper motors, electromagnets, voice coils, linear motors, and the like. In this case, one or more of these either singly or in multiple combinations thereof provide the displacement motion for grid 2.

(27) In the case of more than one motor arranged in series or parallel, different types of technologies can be combined, such as a stepper motor for the main periodic movement and, in the transmission between this motor and the grid, an additional piezeoelectric actuator generates the random variation of the return point.

(28) The movement of the grid 2respectively of the detector 3whereof especially some components such as its displacement speed and its amplitude, is dependent of the exposure time or pause time T.

(29) The total amplitude of the movement of the grid 2respectively of the detector 3can thus be equal to k times the pitch of the grid p.sub.g, k being an integer or a semi-integer between 1 and 50, depending on the pitch p.sub.g of the grid.

(30) In the case of a grid pitch equal to 100 microns, k can be between 1 and 20 inclusive, corresponding to displacement of the grid 2respectively of the detector 3by amplitude between around 100 m and 2 mm.

(31) Thus, displacement of minimal amplitude can be done in the abovementioned small space (of the order of 2 mm) between the cover 4 and the grid 2.

(32) This movement, in conjunction with adaptation of the pitch of the grid p.sub.g to the pitch of the detector p.sub.d, eliminates the image of the grid on the detector, as well as the residual moir effects. Movement of only the grid 2respectively of the detector 3by likewise minimal amplitude would not eliminate the image of the grid 2. Further enhancing the movement by also altering the return points of the grid motion results in increased image contrast and clarity as shadows from the return points are removed from the image.

(33) The speed v of the grid 2respectively of the detector 3enabling this displacement during the exposure time T can be constant and equal to v=x/T where x is the total amplitude of the displacement of the grid.

(34) Alternatively, the grid 2or the detector 3, if requiredcan be animated by oscillatory movement which can be periodical or not.

(35) In the case of periodical movement, the speed v of the grid 2respectively of the detector 3can be constant throughout each half period.

(36) The amplitude of the movement of the grid 2respectively of the detector 3on oscillation can be equal to k times the pitch of the grid, k being an integer or a semi-integer between 1 and 50, depending on the pitch p.sub.g of the grid.

(37) In the case of a grid pitch equal to 100 microns, k can be between 1 and 20 inclusive, corresponding to displacement of the grid 2 by amplitude between around 100 m and 2 mm.

(38) Because of this mammograph and the process for deploying the grid which is executed, neither the image of the grid on the detector, shadows from return points, nor does any moir effect appear on the images obtained.

(39) Finally, in reference to FIG. 7, in accordance with an embodiment of the invention, the profile of the amplitude of the displacement motion is displayed. In this instance the motion is derived from a triangular periodic pattern, although other patterns are possible and contemplated. Return point 1 of period 1 is altered with respect to return point 2 of period 2.

(40) The written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.

(41) As used herein, an element or step recited in the singular and proceeded with the word a or an should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to one embodiment of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments comprising, including, or having an element or a plurality of elements having a particular property may include additional such elements not having that property.

(42) Since certain changes may be made in the above-described invention, without departing from the spirit and scope of the invention herein involved, it is intended that all of the subject matter of the above description shown in the accompanying drawings shall be interpreted merely as examples illustrating the inventive concept herein and shall not be construed as limiting the invention.