US 6,011,874 AGranted

Phase contrast imaging

AssigneeForskningscenter Riso (Danish national laboratory)

InventorJesper Gluckstad

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Abstract

An improved method based on a simple imaging operation with a simple one-to-one mapping between resolution elements of a spatial phase modulator and resolution elements of the generated intensity pattern is provided. According to the invention a method is provided for synthesizing an intensity pattern with low loss of electromagnetic energy, spatial modulation of electromagnetic radiation with a spatial phase mask for modulation of the phase of the incident electromagnetic radiation by phasor values of individual resolution elements of the spatial phase mask, each phasor value being determined in such a way that the values of the Fourier transformed phasors attain predetermined values for predetermined spatial frequencies, and the phasor value of the specific resolution element of the spatial phasor mask corresponds to a distinct intensity level of the image of the resolution element in the intensity pattern, and a spatial phase filter for phase shifting of a part of the electromagnetic radiation, in combination with an imaging system for generation of the intensity pattern by interference in the image plane of the imaging system between the part of the electromagnetic radiation that has been phase shifted by the phase filter and the remaining part of the electromagnetic radiation.

Claims65

Dependent claims

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.sup.i.phi.(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 .theta. 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.sup.i.phi.(x,y) of the phase mask (4, 23, 43) and the phase shift value .theta. in accordance with
I(x',y')=.vertline.e.sup.i.phi.(x',y') +.alpha.(e.sup.i.theta. -1).vertline..sup.2
for selected phase shift values .theta., .alpha. being the average of the phasors e.sup.i.phi.(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.sup.i.phi.(x,y) to the resolution elements (x,y) of the spatial phase mask (4, 23, 43).

8 more elements

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.sup.i.phi.(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 .theta. 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.sup.i.phi.(x,y) of the phase mask (4, 23, 43) and the phase shift value .theta. substantially fulfilling that
I(x',y')=.vertline.e.sup.i.phi.(x,y) +.alpha.(e.sup.i.theta. -1).vertline..sup.2
for selected phase shift values .theta., .alpha. being the average of the phasors e.sup.i.phi.(x,y) of the resolution elements of the phase mask (4, 23, 43),
subject to the proviso that
if .theta.=.pi., 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.sup.i.pi. 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.sup.i.pi., the remaining resolution elements having the phasor value e.sup.i0, or,
if .theta.=.pi./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.sup.i.pi./2 and being interlaced with the remaining rows or columns having the phasor value e.sup.i0.

10 more elements

Dependencies are inferred from the claim text.