Phase contrast imaging

Claim 2

A phase contrast imaging method of synthesizing an intensity pattern I(x',y') of an image, comprising the steps of pixellating the intensity pattern I(x',y') in accordance with the disposition of resolution elements (x,y) of a spatial phase mask (4, 23, 43) having a plurality of individual resolution elements (x,y), each resolution element (x,y) modulating the phase of electromagnetic radiation incident upon it with a predetermined phasor value e i φ(x,y), radiating electromagnetic radiation towards the spatial phase mask (4, 23, 43), Fourier or Fresnel transforming the modulated electromagnetic radiation, phase shifting in a region of spatial frequencies comprising DC in the Fourier or Fresnel plane, the modulated electromagnetic radiation by a predetermined phase shift value θ in relation to the remaining part of the electromagnetic radiation, and forming the intensity pattern by Fourier or Fresnel transforming, respectively, the phase shifted Fourier or Fresnel transformed modulated electromagnetic radiation, whereby each resolution element (x,y) of the phase mask (4, 23, 43) is imaged on a corresponding resolution element (x',y') of the image, calculating the phasor values e i φ(x,y) of the phase mask (4, 23, 43) and the phase shift value θ in accordance with I(x',y')=|e.sup.iφ(x',y') +α(e.sup.iθ -1)|.sup.2 for selected phase shift values θ, α being the average of the phasors e i φ(x,y) of the resolution elements of the phase mask (4, 23, 43), selecting, for each resolution element, one of two phasor values which represent a particular grey level, and supplying the selected phasor values e i φ(x,y) to the resolution elements (x,y) of the spatial phase mask (4, 23, 43).

Claim 3

A method according to claim 1, wherein the step of calculating the phasor values comprises setting the synthesized intensity of at least one resolution element (x o ',y o ') of the intensity pattern to zero, and calculating the phasor values e i φ(x,y) of the phase mask (4, 23, 43) in accordance with ##EQU42## for selected phase shift values θ, φ.sub.α being the phase of α.

Claim 4

A method according to claim 2, further comprising the step of selecting the phase shift θ=π, selecting |α|=1/2, and calculating the phasor values e i φ(x,y) of the phase mask (4, 23, 43) in accordance with ##EQU43## .

Claim 5

A method according to claim 1, further comprising the steps of moving the DC-part of the electromagnetic radiation to a second part of the Fourier or Fresnel plane, and phase shifting the Fourier or Fresnel transformed modulated electromagnetic radiation at the second part of the Fourier or Fresnel plane by θ in relation to the remaining part of the electromagnetic radiation.

Claim 6

A method according to claim 4, wherein the step of moving the DC-part of the electromagnetic radiation comprises utilization of an optical component, such as a grating, a prism, etc, with an appropriate carrier frequency.

Claim 7

A method according to claim 4, wherein the step of moving the DC-part of the electromagnetic radiation comprises encoding the function of an optical component, such as a grating, a prism, etc, with an appropriate carrier frequency, into the spatial phase mask (4, 23, 43).

Claim 8

A method according to claim 1, further comprising the step of adjusting the modulus of the Fourier transform of the phasors e i φ(x,y) at specific spatial frequencies in order to control the range of intensity levels of the synthesized intensity pattern.

Claim 9

A method according to claim 7, wherein the step of adjusting the modulus of the Fourier transform of the phasors e i φ(x,y) at specific spatial frequencies comprises at least one of the following measures: a) adjusting the individual phasors e i φ(x,y) of the resolution elements of the phase mask (4, 23, 43) maintaining prescribed relative intensity levels between intensities of resolution elements of the intensity pattern, b) adjusting the individual phasors e i φ(x,y) of the resolution elements of the phase mask (4, 23, 43) by histogram techniques, c) spatially scaling the phasor e i φ(x,y) pattern of the phase mask (4, 23, 43), and d) utilizing half tone coding techniques.

Claim 10

A method according to claim 1, further comprising the step of controlling power of the electromagnetic radiation in response to the intensity range of the intensity pattern.

Claim 11

A method according to claim 1, wherein each phasor e i φ(x,y) of the phase mask (4, 23, 43) is selected from a set of two determined phasors with complementary phasor values e i φ1(x,y) and e i φ2(x,y) in such a way that a specific spatial frequency distribution of the intensity of the electromagnetic radiation in the Fourier or Fresnel plane is attained.

Claim 12

A method according to claim 10, wherein the phase φ(x,y) of phasors e i φ(x,y) of adjacent resolution elements alternates between the two possible complementary phasor values e i φ1(x,y) and e i φ2(x,y).

Claim 13

A method according to claim 10, wherein the phasors e i φ1(x,y) and e i φ2(x,y) are complex conjugated.

Claim 14

A method according to claim 1, further comprising the step of phase shifting at selected spatial frequencies constituting a region that is shaped to match the spatial frequency content of the phasors e i φ(x,y) of the spatial phase mask (4, 23, 43).

Claim 15

A method according to claim 1, wherein modulus of the average value |α| of the phasors e i φ(x,y) ranges from 0.1 to 0.9.

Claim 16

A method according to claim 14, wherein modulus of the average value |α| of the phasors e i φ(x,y) ranges from 0.25 to 0.75.

Claim 17

A method according to claim 14, wherein modulus of the average value |α| of the phasors e i φ(x,y) ranges from 0.4 to 0.6.

Claim 18

A method according to claim 14, wherein modulus of the average value |α| of the phasors e i φ(x,y) is approximately 0.5.

Claim 19

A method according to claim 1 wherein the phase shift θ ranges from π/4 to 7π/4.

Claim 20

A method according to claim 1, wherein the phase shift θ ranges from π/2 to 3π/2.

Claim 21

A method according to claim 1, wherein the phase shift θ ranges from 3π/4 to 5π/4.

Claim 22

A method according to claim 1, wherein the phase shift θ is approximately π.

Claim 23

A method according to claim 1, further comprising the step of zooming the image for scaling of the intensity pattern.

Claim 24

A method according to claim 22, wherein zooming of the image is dynamically controllable.

Claim 25

A method according to claim 22, wherein zooming of the image is controllable in dependence of the scaling of the phase mask (4, 23, 43).

Claim 26

A method according to claim 22, further comprising the step of controlling power of the electromagnetic radiation in response to the spatial scaling of the pattern in the phase mask (4, 23, 43) and/or the zooming of the image.

Claim 27

A method according to claim 1, wherein the step of phase shifting comprises utilization of a spatial light modulator.

Claim 28

A method according to claim 1, further comprising the step of encoding the optical function of a Fourier-transforming lens into the phasors e i φ(x,y) of the phase mask (4, 23, 43).

Claim 29

A method according to claim 1, further comprising the step of encoding the optical function of an output lens into the phase filter (6, 27, 45).

Claim 30

A method according to claim 1, wherein the step of radiating electromagnetic radiation comprises radiation of electromagnetic radiation of different wavelengths corresponding to three different colours, such as red, green and blue, for generation of intensity patterns of arbitrary colours.

Claim 31

A phase contrast imaging system (1) for synthesizing an intensity pattern I(x',y') of an image, comprising a source (2, 21, 41) of electromagnetic radiation for emission of electromagnetic radiation, a spatial phase mask (4, 23, 43) for phase modulation of electromagnetic radiation and having a plurality of individual resolution elements (x,y), each resolution element (x,y) modulating the phase of electromagnetic radiation incident upon it with a predetermined phasor value e i φ(x,y), and being positioned on a propagation axis of the electromagnetic radiation, means (5, 26, 44) for Fourier or Fresnel transforming the phase modulated electromagnetic radiation positioned on a propagation axis of the phase modulated radiation, a spatial phase filter (6, 27, 45) for phase shifting in a region of spatial frequencies comprising DC in the Fourier or Fresnel plane, the transformed electromagnetic radiation by a predetermined phase shift value θ in relation to the remaining part of the transformed electromagnetic radiation, means (7, 10, 26, 30, 44, 47) for forming the intensity pattern by Fourier or Fresnel transforming, respectively, the phase shifted Fourier or Fresnel transformed modulated electromagnetic radiation, whereby each resolution element (x,y) of the phase mask (4, 23, 43) is imaged on a corresponding resolution element (x',y') of the image, the phasor values e i φ(x,y) of the phase mask (4, 23, 43) and the phase shift value θ substantially fulfilling that I(x',y')=|e.sup.iφ(x,y) +α(e.sup.iθ -1)|.sup.2 for selected phase shift values θ, α being the average of the phasors e i φ(x,y) of the resolution elements of the phase mask (4, 23, 43), subject to the proviso that if θ=π, the phase mask (4, 23, 43) is not divided into a matrix of rows and columns of resolution elements of the same size and shape, every fourth resolution element having the phasor value e i π and being distributed periodically and regularly across the area of the phase mask in such a way that every second row and every second column do not contain a resolution element with the phasor value e i π, the remaining resolution elements having the phasor value e i0 , or, if θ=π/2, the phase mask (4, 23, 43) is not divided into a matrix of rows or columns of the same size and shape, every second row or column having the phasor value e i π/2 and being interlaced with the remaining rows or columns having the phasor value e i0 .

Claim 32

A phase contrast imaging system (1) for synthesizing an intensity pattern I(x',y') of an image, comprising a source (2, 21, 41) of electromagnetic radiation for emission of electromagnetic radiation, a spatial phase mask (4, 23, 43) for phase modulation of electromagnetic radiation and having a plurality of individual resolution elements (x,y), each resolution element (x,y) modulating the phase of electromagnetic radiation incident upon it with a predetermined phasor value e i φ(x,y), and being positioned on a propagation axis of the electromagnetic radiation, means (5, 26, 44) for Fourier or Fresnel transforming the phase modulated electromagnetic radiation positioned on a propagation axis of the phase modulated radiation, a spatial phase filter (6, 27, 45) for phase shifting in a region of spatial frequencies comprising DC in the Fourier or Fresnel plane, the transformed electromagnetic radiation by a predetermined phase shift value θ in relation to the remaining part of the transformed electromagnetic radiation, means (7, 10, 26, 30, 44, 47) for forming the intensity pattern by Fourier or Fresnel transforming, respectively, the phase shifted Fourier or Fresnel transformed modulated electromagnetic radiation, whereby each resolution element (x,y) of the phase mask (4, 23, 43) is imaged on a corresponding resolution element (x',y') of the image, the phasor values e i φ(x,y) of the phase mask (4, 23, 43) and the phase shift value θ substantially fulfilling that I(x',y')=|e.sup.iφ(x,y) +α(e.sup.iθ -1)|.sup.2 for selected phase shift values θ, α being the average of the phasors e i φ(x,y) of the resolution elements of the phase mask (4, 23, 43), subject to the proviso that if θ=π, the phase mask (4, 23, 43) is not divided into a matrix of rows and columns of resolution elements of the same size and shape, every fourth resolution element having the phasor value e i π and being distributed periodically and regularly across the area of the phase mask in such a way that every second row and every second column do not contain a resolution element with the phasor value e i π, the remaining resolution elements having the phasor value e i0 , or, if θ=π/2, the phase mask (4, 23, 43) is not divided into a matrix of rows or columns of the same size and shape, every second row or column having the phasor value e i π/2 and being interlaced with the remaining rows or columns having the phasor value e i0 .

Claim 33

A system (1) according to claim 30, further comprising means for pixellation of the intensity pattern I(x',y') in accordance with the elements (x,y) of the spatial phase mask (4, 23, 43), means for calculating the phasor values e i φ(x,y) of the phase mask (4, 23, 43) and the phase shift value θ in accordance with equation I(x',y')=|e.sup.iφ(x',y') +α(e.sup.iθ -1)|.sup.2, means for selecting, for each resolution element, one of two phasor values which represent a particular grey level, and means for supplying the calculated phasor values e i φ(x,y) to the elements (x,y) of the phase mask (4, 23, 43).

Claim 34

A system (1) according to claim 30, wherein the intensity is zero for at least one resolution element (x o ',y o ') of the intensity pattern, and wherein the phasor values e i φ(x,y) of the phase mask (4, 23, 43) substantially fulfil that ##EQU44## for selected phase shift values θ, φ.sub.α being the phase of α.

Claim 35

A system (1) according to claim 31, wherein the means for calculating the phasor values is adapted to calculate the phasor values e i φ(x,y) of the phase mask (4, 23, 43) in accordance with ##EQU45## for selected phase shift values θ, φ.sub.α being the phase of α.

Claim 36

A system (1) according to claim 32, wherein the phase shift θ is substantially equal to π and α is substantially equal to 1/2, and the phases φ(x,y) substantially fulfil that ##EQU46## .

Claim 37

A system (1) according to claim 33, wherein the means for calculating the phasor values is adapted to calculate the phasor values e i φ(x,y) of the phase mask (4, 23, 43) in accordance with ##EQU47## .

Claim 38

A system (1) according to claim 30, further comprising means for moving the region of spatial frequencies comprising DC to a second part of the Fourier or Fresnel plane, and wherein the phase filter (6, 27, 45) is positioned at the second part of the Fourier or Fresnel plane for phase shifting of the transformed modulated electromagnetic radiation at the second part of the Fourier or Fresnel plane by θ in relation to the remaining part of the electromagnetic radiation.

Claim 39

A system (1) according to claim 36, wherein the means for moving the region of spatial frequencies comprising DC to a second part of the Fourier or Fresnel plane comprises an optical component, such as a grating, a prism, etc, with an appropriate carrier frequency.

Claim 40

A system (1) according to claim 36, wherein the means for moving the region of spatial frequencies comprising DC to a second part of the Fourier or Fresnel plane comprises the phase mask (4, 23, 43) in which the function of an optical component, such as a grating, a prism, etc, with an appropriate carrier frequency, has been encoded.

Claim 41

A system (1) according to claim 30, wherein the modulus of the Fourier transform of the phasors e i φ(x,y) at specific spatial frequencies have been adjusted to keep the intensity levels of the synthesized intensity pattern within a desired range.

Claim 42

A system (1) according to claim 39, wherein the modulus of the Fourier transform of the phasors e i φ(x,y) at specific spatial frequencies have been adjusted according to at least one of the following measures: a) adjusting the individual phasors e i φ(x,y) of the resolution elements of the phase mask (4, 23, 43) maintaining prescribed relative intensity levels between intensities of resolution elements of the intensity pattern, b) adjusting the individual phasors e i φ(x,y) of the resolution elements of the phase mask (4, 23, 43) by histogram techniques, c) spatially scaling the phasor e i φ(x,y) pattern of the phase mask (4, 23, 43), and d) utilizing half tone coding techniques.

Claim 43

A system (1) according to claim 30, further comprising means for controlling power of the electromagnetic radiation in response to the intensity range of the intensity pattern.

Claim 44

A system (1) according to claim 30, wherein each phasor e i φ(x,y) of the phase mask (4, 23, 43) is substantially equal to a selected phasor that has been selected from a set of two phasors with complementary phase values e i φ1(x,y) and e i φ2(x,y) in such a way that a specific spatial frequency distribution of the intensity of the electromagnetic radiation in the Fourier or Fresnel plane is attained.

Claim 45

A system (1) according to claim 42, wherein the phase φ(x,y) of phasors e i φ(x,y) of adjacent resolution elements alternates between the two possible complementary phasor values e i φ1(x,y) and e i φ2(x,y).

Claim 46

A system (1) according to claim 30, wherein the phase filter (6, 27, 45) is shaped to match the spatial frequency content of the phasors e i φ(x,y) of the spatial phase mask (4, 23, 43).

Claim 47

A system (1) according to claim 30, wherein modulus of the average value |α| of the phasors e i φ(x,y) ranges from 0.1 to 0.9.

Claim 48

A system (1) according to claim 45, wherein modulus of the average value |α| of the phasors e i φ(x,y) ranges from 0.25 to 0.75.

Claim 49

A system (1) according to claim 45, wherein modulus of the average value |α| of the phasors e i φ(x,y) ranges from 0.4 to 0.6.

Claim 50

A system (1) according to claim 45, wherein modulus of the average value |α| of the phasors e i φ(x,y) is approximately 0.5.

Claim 51

A system (1) according to claim 45, wherein the phase shift θ ranges from π/4 to 7π/4.

Claim 52

A system (1) according to claim 45, wherein the phase shift θ ranges from π/2 to 3π/2.

Claim 53

A system (1) according to claim 45, wherein the phase shift θ ranges from 3π/4 to 5π/4.

Claim 54

A system (1) according to claim 30, wherein the phase shift θ is approximately π.

Claim 55

A system (1) according to claim 30, further comprising zooming means (10, 30, 47) for scaling of the intensity pattern.

Claim 56

A system (1) according Lo claim 30, wherein the phase filter (6, 27, 45) comprises a spatial light modulator.

Claim 57

A system (1) according to claim 30, wherein the phase mask (4, 23, 43) is adapted to perform the optical function of a Fourier-transforming lens by appropriate encoding of the phasors e i φ(x,y) of the phase mask (4, 23, 43).

Claim 58

A system (1) according to claim 30, wherein the spatial phase filter (6, 27, 45) is adapted to perform the optical function of an output lens by appropriate encoding of the phase filter (6, 27, 45).

Claim 59

A system (1) according to claim 30, wherein the source (2, 21, 41) of electromagnetic radiation is adapted to radiate electromagnetic radiation of different wavelengths corresponding to three different colours, such as red, green and blue, for generation of intensity patterns of arbitrary colours.

Claim 60

A system (1) according to claim 30, further comprising a first and a second Fourier transforming lens (5, 7), the spatial phase mask (4, 23, 43) being positioned in the front focal plane of the first lens (5), the spatial phase filter (6, 27, 45) being positioned at the back focal plane of the first lens (5), and the second lens (7) being positioned so that its front focal plane is positioned at the position of the back focal plane of the first lens (5).

Claim 61

A system (1) according to claim 30, further comprising one Fourier transforming lens (44), the spatial phase filter (45) being positioned at the back focal plane of the lens (44).

Claim 62

A system (1) according to claim 30, further comprising one imaging lens, the spatial phase filter (6, 27, 45) being positioned in the back focal plane of the lens.

Claim 63

A system (1) according to claim 30, further comprising a polarizing beam splitter (24) and a quarter wave plate (25) and/or a phase filter (27) reflecting electromagnetic radiation incident upon it.

Claim 64

A system (1) according to claim 30, wherein the spatial phase filter (6, 27, 45) changes the phase of the radiation in the region of spatial frequencies comprising DC and leaves the phase of the remaining part of the radiation unchanged.

Claim 65

A system (1) according to claim 30, wherein the spatial phase filter (6, 27, 45) do not change the phase of the radiation in the region of spatial frequencies comprising DC and changes the phase of the remaining part of the radiation.

Claim 66

A system (1) according to claim 30, wherein the spatial phase filter (6, 27, 45) blocks the radiation at the region of spatial frequencies comprising DC and leaves the remaining part of the radiation unchanged.

Claim 67

A system (1) according to claim 30, wherein the source (2, 21, 41) of electromagnetic radiation is a Laser (2, 21, 41).