Quantitative phase microscopy imaging based on fractional spiral phase plate

Quantitative phase imaging (QPI), which combines phase imaging with optical microscopy technology, provides a marker-free, fast, non-destructive, and high-resolution imaging method for observing transparent biological samples. It is widely used in life science, biomedicine, etc. As an emerging QPI technology, spiral phase contrast microscopy (SPCM) uses a spiral phase filter to achieve edge enhancement of amplitude or phase objects. Using the multi-step phase-shifting technology, a complex sample can be measured quantitatively, which has the advantages of high stability, high sensitivity and high precision. However, the SPCM requires at least three-step phase-shifted spiral phase filtered images to achieve the quantitative reconstruction of the amplitude and phase of a sample, and the image acquisition process and the reconstruction process are relatively complicated, which require high stability of system, and the SPCM has low temporal resolution. In order to further improve the performance of SPCM and increase the system stability, sensitivity and temporal resolution, in this paper a quantitative phase imaging method and system based on a fractional spiral phase plate is proposed. Through a sample intensity image filtered by a fractional spiral phase plate, the modified Gerchberg-Saxton iterative phase retrieval algorithm is used to quantitatively reconstruct the phase of a pure phase sample, which simplifies the experimental process and phase reconstruction steps of spiral phase contrast microsocopy. In the computer simulation experiments, the phase imaging process and the reconstruction process of spiral phase plates based on different topological charges are studied, the feasibility of which is analyzed. Finally, through imaging and phase reconstruction of the phase grating and biological cell sample, it is verified that the phase contrast microscopy method based on the fractional spiral phase plate can effectively improve the contrast of spiral phase contrast microscopy and can obtain a quantitative reconstruciton of a weak phase object. The phase information of a sample has significance in research and application for developing the spiral phase contrast microscopy.


Abstract
Quantitative phase imaging (QPI), which combines phase imaging with optical microscopy technology, provides a marker-free, fast, non-destructive, and high-resolution imaging method for observing transparent biological samples.It is widely used in life science, biomedicine, etc.As an emerging QPI technology, spiral phase contrast microscopy (SPCM) uses a spiral phase filter to achieve edge enhancement of amplitude or phase objects.Using the multi-step phase-shifting technology, a complex sample can be measured quantitatively, which has the advantages of high stability, high sensitivity and high precision.However, the SPCM requires at least three-step phase-shifted spiral phase filtered images to achieve the quantitative reconstruction of the amplitude and phase of a sample, and the image acquisition process and the reconstruction process are relatively complicated, which require high stability of system, and the SPCM has low temporal resolution.In order to further improve the performance of SPCM and increase the system stability, sensitivity and temporal resolution, in this paper a quantitative phase imaging method and system based on a fractional spiral phase plate is proposed.Through a sample intensity image filtered by a fractional spiral phase plate, the modified Gerchberg-Saxton iterative phase retrieval algorithm is used to quantitatively reconstruct the phase of a pure phase sample, which simplifies the experimental process and phase reconstruction steps of spiral phase contrast microsocopy.In the computer simulation experiments, the phase imaging process and the reconstruction process of spiral phase plates based on different topological charges are studied, the feasibility of which is analyzed.Finally, through imaging and phase reconstruction of the phase grating and biological cell sample, it is verified that the phase contrast microscopy method based on the fractional spiral phase plate can effectively improve the contrast of spiral phase contrast microscopy and can obtain a quantitative reconstruciton of a weak phase object.The phase information of a sample has significance in research and application for developing the spiral phase contrast microscopy.

Fig. 4 .
Fig. 4. MSE error between the recovered phase image and ground truth phase image vs. the number of iterations.

图 5
Fig. 5. Comparisons of the recorded images and the recovered results: (a) The ground truth phase sample image; (b) the recorded image via traditional integer order spiral phase plate filtering; (c) the recovered phase sample image using SGSA for panel (b); (d) the recorded image via fractional spiral phase plate filtering; (e) the recovered phase sample image using SGSA for panel (d).

图Fig. 10 .Fig. 11 .
Fig. 10.Imaging of a custom phase gratinig: (a) The unfiltered bright field image of the phase grating; (b) the recorded integer-order spiral phase filtered edge enhancement image; (c) the recovered phase image; (d) the recovered depth image, the abscissa and ordinate values are pixel values, each pixel represents 0.325 µm, and the total length is 332.8 µm.

图Fig. 12 .Fig. 13 .图Fig. 14 .Fig. 15 .
Fig. 12. Imaging of a custom phase grating: (a) The unfiltered phase grating bright field image; (b) the fractional spiral phase plate filtered image when the topological charge l is 0.1; (c) the recovered phase image; (d) the recovered depth image (the coordinates are the same as Fig. 10.(d)).

Table 1 .
The SSIM between the recovered phase image and the ground truth phase image for three fractional topological values.