Resolution and Contrast Enhancement for Lensless Digital Holographic Microscopy and Its Application in Biomedicine

Round 1

Reviewer 1 Report

The manuscript written by Chen et. al contains a good review about lensles digital holographic microscopy and its application in biomedicine. The paper is well written and it contains a deep and useful review of this topic. I recommend publish this paper in this editorial.

 

I have some minor comments or smalller mistakes, typos which could be revised:

-Line 58: Is it refered a volume hologram in the whole paper? Please, consider that plane holograms are characterized by more than two diffraction orders.

-Eq. 1: Size and format.

-Line 94: Please, revise format of the amplitude distribution and phase in the line text.

-Line 375: "cell classification using multiple parallel channels [107,108].combining with deep"

-Line 452: Format of reference 25.

-Line 458: Format of reference 28.

-Line 470: Format of reference 35.

 

Author Response

Please see the attachment. Thanks.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript of Duofang Chen et al. ‘Resolution enhancement for lensless digital holographic microscopy and its application in biomedicine’ being a review of the recent developments in the field of contrast and resolution enhancement in digital holographic microscopy and its application in biomedicine is an interesting article, however, before acceptance for publication, some explanation should be provided and some corrections have to be made:

Major Comments:

1. In the Introduction section the authors should highlight that in comparison with classical optical microscopy the digital holography provides complex,  quantitative amplitude and phase information about the object. Moreover, in optical microscopy there is no such counterpart as phase patterns obtained by digital holography. Moreover, in context of the in-line digital holography it should be pointed out that the transparent and semi-transparent can generally be imaged.
2. I don’t understand the authors’ statement (lines 50-56), that the optical system based on the Mach-Zehnder interferometer (fig.1b) is an example of the in-line or off-axis digital holographic system, because this is confusing? If the off-axis setup has to be applied in this system, the M1 mirror have to be rotated (respectively to the M1 mirror). Orientation of the two mirrors M1/M2 at 45 degree will  not provide the angular separation of the object and reference beam needed for off-axis setup.
3. Fig. 2 In my opinion, this figure should include also the initial processing of the digital hologram in the part related to the numerical reconstruction of the digital hologram, since before we obtain the reconstructed image the hologram processing is necessary such as DC suppression or spatial filtration of the Fourier spectrum.
4. Authors indicate two main algorithms for digital holograms reconstruction: Fresnel and angular spectrum method. However, they did not indicate any main constraint of these algorithms (advantages or disadvantages of both algorithms). For example, the Fresnel method fails for short distances between the object and the CCD camera even with hologram up-sampling prior reconstruction.
5. In sections devoted to resolution enhancement, the authors of each section should indicate the possible ranges of achieved (enhanced) resolutions defined in um and not only in ‘times’. They should also consider including them in table1 or add new one with the comparison of the main requirements, complexity,  advantages and disadvantages of the described method of resolution enhancement.  This significantly improves the quality of this review.
6. Taking into account the main purposes of review, the concepts of the resolution enhancement should be directly indicated, because in many cases it can be hard to understand for the reader based description of some discussed methods without direct familiarization with the cited references.  For examples in case of the structured illumination (Section 3.2.6) in lines: 283-284 it was stated that structured illumination can improve the resolution in a similar way as in conventional microscopy. Then in lines:284-289 the authors described how illumination patterns are projected on the object, how the intermediate image is formed and how the digital holograms is formed. But there is no direct explanation how the structured illumination leads to the resolution increase. This is common also in the case of some other methods described in this section.
7. In Section 3.2.2 the authors are briefly describing the synthetic aperture approach. This should explain the need to use of band-pass filters and SLM in this context of “SA system where NA can be enlarged by an arbitrary factor”. It should also be noted that this technique can be used for incoherent illumination.  Moreover, the figure Fig.7(b) did not explain or visualize in a clear way the concept of three times larger NA as Fig.1 in [52] I recommend the modification of this figure. I also suggest including additional references as: https://doi.org/10.1364/OE.26.012620 or https://doi.org/10.1364/AO.55.000A43
8. Line 224: What do you mean as “spectral regions of the samples’ in line 225?
9. Line 224: What do you mean as “spectral regions of the samples’ in line 225?
10. In Section 3.2.5 the authors should explain Fig. 10 in more detailed manner.
11. In my opinion, in the section devoted to the use of the DHM in biomedical application, the authors should consider including more applications (see examples bellow):

https://doi.org/10.1371/journal.pone.0030912,

https://doi.org/10.1364/DH.2011.DTuC25

https://doi.org/10.3390/cells11040755

https://doi.org/10.1371/journal.pone.0150449

https://doi.org/10.1364/OE.26.008923

 10.1109/RAST.2019.8767842

https://doi.org/10.1016/j.optcom.2020.126300

https://doi.org/10.1093/jmicro/dfaa077

 https://doi.org/10.3390/app8071027

https://doi.org/10.3390/cells11040644

https://doi.org/10.3390/microorganisms10020391

12. Moreover, the author did not discussed the recent advances in digital holographic tomography, where the adaptation of the tomographic approach enable the reconstruction of the 3D refractive index distribution rather than integrated phase distribution.

Minor comments

1. In general, the title should be changed as follows: “Resolution and contrast enhancement for lensless digital holographic microscopy and its application in biomedicine”
2. Fig.1: So many dots are necessary in one figure caption? It should be: ‘Figure 1.’ Lensless digital holographic microscopy schematic: (a) in-line holographic system, (b) off-axis holographic system. ‘
3. Eq.1: The font size in this equation is appropriate according to the Journal requirements?
4. Line 64: ‘W is the highest spatial frequencies” – spatial frequency of what? This should be clearly indicated to avoid confusion among the readers.
5. The resolution of Fig. 9, particularly Fig.9c, should be improved.
6. Correct all typo errors in manuscript as ‘fisrt’ on line 134 or “ligth source arry’ on line 211.
7. Lines 211-212: ‘Illuminating each source sequentially in a light source arry is an equivalent way to 211 realize the source shifting, which is illustrated in Fig.5(c)’ Do you mean : illuminating object sequentially by each source of the source array is an equivalent way to?
8. Line 223: “ The synthetic  aperture is a combination of multi-angle tilted beam illumination samples” it should not be: (….) illumination of samples?
9. Line 224: What do you mean as “spectral regions of the samples’ in line 225?
10. Line 228: “The system in 7(b)” : in Fig.7(b)?

Author Response

Please see the attachment. Thanks a lot.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Thank you for incorporating the amendments. As it stands, the manuscript is much improved and, in my opinion, suitable for publication after minor revision.

I read a redlines version, and there a lot of fragments were lack of "space" i evident. Particularly in the sections were the corrections were made. This should be corrected before publication.

In the suggested references there were many more publications related to lensless digital holographic microscopy than those listed by the authors, which somewhat narrows the field of application eg. 4,5, but I leave it to the editors' and Authors judgement whether a review paper should be more or less comprehensive.

I would like to thank Author for their work.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf