JP-7856326-B2 - Digital holographic imaging technology using double image cancellation

JP7856326B2JP 7856326 B2JP7856326 B2JP 7856326B2JP-7856326-B2

Inventors

セダガート，ゾーレ
ジョッソ，クエンティン
ロール，ファビアン

Assignees

ビオメリュー
ビオアステル

Dates

Publication Date: 20260511
Application Date: 20211019
Priority Date: 20201020

Claims (10)

A digital holographic imaging method: 1) A step (S01) to obtain a hologram by holography, wherein the hologram represents the spatial intensity distribution of interference caused by the interaction between the illumination beam and the object to be imaged, which is placed at object coordinates (z o ) on the imaging axis (6), in the hologram plane at hologram coordinates (z h ); 2) A stage in which multiple iterative processes are carried out (S03), each iterative process being the following steps: 2.a) A step (S03a) Determining an object field including the spatial absorption distribution and spatial phase shift distribution of the imaged object by backpropagating the hologram field, which has a spatial amplitude distribution and a spatial phase distribution corresponding to the spatial intensity distribution of the hologram, to the object coordinates. 2.b) A step in which the values of the spatial absorption distribution and the spatial phase shift distribution of the object to be imaged are thresholded by reducing the value of the spatial absorption distribution below an absorption threshold and reducing the value of the spatial phase shift distribution below a phase shift threshold, wherein the absorption threshold and the phase shift threshold are reduced in each iteration step (S03b), 2.c) A step of determining a modified hologram field including a modified spatial amplitude distribution and a modified spatial phase distribution by repropagating the object field to the hologram coordinates (S03c), 2.d) A step (S03d) in which the spatial phase distribution of the hologram field is replaced with the modified spatial phase distribution, wherein the spatial amplitude distribution of the hologram field is preserved; 3) A step of determining the spatial phase shift distribution and the spatial absorption distribution of the imaged object as those of the object field in the final iteration step, method.
The method according to claim 1, wherein during thresholding, the values of the spatial absorption distribution below the absorption threshold and the values of the spatial phase shift distribution below the phase shift threshold are set to 0.
The method according to claim 1 or 2, wherein the absorption threshold depends on the maximum value of the spatial absorption distribution, and the phase shift threshold depends on the maximum value of the spatial phase shift distribution included in the object field.
The method according to any one of claims 1 to 3, wherein in the first iteration step, the absorption threshold and/or the phase shift threshold correspond to a range of 40% to 15% of the maximum value of the spatial absorption distribution or the spatial phase shift distribution, respectively.
The method according to any one of claims 1 to 4, wherein in each iterative step, the absorption threshold and/or the phase shift threshold is reduced by 1% to 6% of the maximum value of the spatial absorption distribution or spatial phase shift distribution.
The method according to any one of claims 1 to 5, wherein in the final iteration step, the absorption threshold and the phase shift threshold are set to 0.
The method according to any one of claims 1 to 6, wherein, during sequential iterations, the values of the spatial absorption and phase shift distributions are kept positive or zero during thresholding.
The method according to any one of claims 1 to 7, wherein, prior to sequential iteration, the hologram field is normalized by dividing the value of the spatial intensity distribution by the background image value corresponding to the intensity of the illumination beam in the hologram coordinates.
The method according to any one of claims 1 to 8, wherein the thresholding process includes smoothing the modified spatial absorption distribution and the modified spatial phase shift distribution.
The method according to any one of claims 1 to 9, wherein the hologram field and/or the object field have increasing spatial resolution with each iterative step.

Description

This invention relates to the field of digital holography, and more precisely, to a method for removing double images in digital holographic imaging. Digital holography is a method of recording a hologram using a sensor, representing the phase and amplitude of waves diffracted by an object. The hologram records the spatial intensity distribution of the interference pattern generated by the illumination beam and the light diffracted by the object being imaged. The hologram allows for the computational reconstruction of the object's image using digital reconstruction algorithms. More precisely, the phase and absorption characteristics of the imaged object are obtained through backpropagation from the hologram. Backpropagation is calculated, for example, using propagation algorithms based on Rayleigh-Sommerfeld diffraction theory. Digital holography is used particularly in biological imaging, especially in digital holographic microscopy, due to its ability to image transparent objects such as biological cells and organisms. Specifically, in contrast to other imaging methods, digital holography does not require the injection of dyes to visualize transparent objects or the use of high-energy radiation (such as X-rays) that could damage the biological object being imaged. Holographic imaging aims to find the spatial phase shift and absorption distribution of the object being imaged. Specifically, these properties of the imaged object allow for precise characterization of the object, and therefore, for example, identification. Among various holographic techniques, inline holography exhibits high phase sensitivity, making it the most suitable method for imaging low-phase biological objects. However, inline holography has a major drawback: the existence of twin images or orthoscopic images, which result from the hologram recording only intensity and losing phase information within the hologram. Twin images are artifacts in a hologram that appear to result from an additional imaged object positioned symmetrically with respect to the imaged object with respect to the holographic plane. Because twin images are out of focus, the shape of the imaged object is distorted during the reconstruction of phase and absorption images, which can hinder the usability of these images. Other features, purposes, and advantages of the present invention will become apparent from the following description. This description is purely illustrative and non-limiting and should be read with reference to the accompanying drawings. This shows the main steps of a method according to one possible embodiment of the present invention. A schematic example of a holographic imaging system used to obtain a hologram according to one possible embodiment of the present invention is shown. A hologram of a bacterial cluster is shown as a first example of an implementation of a method according to one possible embodiment of the present invention. In a first example of implementing a method according to one possible embodiment of the present invention, the initial spatial phase shift distribution determined from the hologram in Figure 3 is shown. In a first example of implementing a method according to one possible embodiment of the present invention, the initial spatial absorption distribution determined from the hologram in Figure 3 is shown. Figure 4a shows the bacterial phase shift profile. Figure 4b shows the bacterial absorption profile. In a first example of implementing a method according to one possible embodiment of the present invention, the spatial phase shift distribution after the first iteration is shown. In a first example of implementing a method according to one possible embodiment of the present invention, the spatial absorption distribution after the first iteration is shown. Figure 5a shows the bacterial phase shift profile. Figure 5b shows the bacterial absorption profile. In a first example of an implementation of a method according to one possible embodiment of the present invention, the spatial phase shift distribution after the fifth iteration is shown. In a first example of implementing a method according to one possible embodiment of the present invention, the spatial absorption distribution after the fifth iteration is shown. Figure 6a shows the bacterial phase shift profile. Figure 6b shows the bacterial absorption profile. In a first example of implementing a method according to one possible embodiment of the present invention, the spatial phase shift distribution after the 20th iteration is shown. In a first example of implementing a method according to one possible embodiment of the present invention, the spatial absorption distribution after the 20th iteration is shown. Figure 7a shows the bacterial phase shift profile. Figure 7b shows the bacterial absorption profile. In a second example of implementing a method according to one possible embodiment of the present invention, a hologram of polystyrene beads acquired by an imag