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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 16 — Aug. 12, 2013
  • pp: 19187–19187
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Gradient field microscopy of unstained specimens: comment

José A. Ferrari and Gastón A. Ayubi  »View Author Affiliations


Optics Express, Vol. 21, Issue 16, pp. 19187-19187 (2013)
http://dx.doi.org/10.1364/OE.21.019187


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Abstract

We comment on a recent paper by Kim et al. [Opt. Exp. 20(6) 6737-6745 (2012)], in which the authors claimed to present a new method for first-order differentiation of phase objects called gradient field microscopy (GFM). We consider that the method does not substantially differ from well-known Fourier methods discussed in textbooks. Also, we discuss some deficiencies of the paper.

© 2013 OSA

In a recent paper, Kim et al. [1

1. T. Kim, S. Sridharan, and G. Popescu, “Gradient field microscopy of unstained specimens,” Opt. Express 20(6), 6737–6745 (2012). [CrossRef] [PubMed]

] presented a method for first-order differentiation of phase objects called gradient field microscopy (GFM). Our purpose in the present Comment is not to discuss the applicability of the GFM for the study of biological cells, with what we agree.

The point we like to remark is the following: The authors of [1

1. T. Kim, S. Sridharan, and G. Popescu, “Gradient field microscopy of unstained specimens,” Opt. Express 20(6), 6737–6745 (2012). [CrossRef] [PubMed]

] claim to use a sine-function in the y-direction of the spatial frequency domain, H(kx,ky)=A[1+sin(aky)]. This filter function gives the convolution [δ(x,y)+δ(x,ya)δ(x,y+a)2i]*U(x,y) across the image plane. The important issue is that the approximation used in Eq. (1) of [1

1. T. Kim, S. Sridharan, and G. Popescu, “Gradient field microscopy of unstained specimens,” Opt. Express 20(6), 6737–6745 (2012). [CrossRef] [PubMed]

], [δ(x,ya)δ(x,y+a)2i]*U(x,y)iaU(x,y)y, is only valid in the limit a0.

The limit a0 means that the period of sin(aky) must be larger than the spatial frequencies involved in U(kx,ky). In other words, they are not using a sine function at all, but only a small portion of the spatial filter around the origin of the y-coordinate in the Fourier plane, in which sin(aky)aky. Thus, actually they are using a linear function (i.e., a ramp) for performing the spatial filtering instead of a sine-function as claimed. In fact, it could be absolutely equivalent to use any other function (F(aky)) with the behavior F(aky)aky in the limit a0, since the appearance of a first derivative is actually granted by the formula FT[kyU(kx,ky)]=iU(x,y)y.

We like to mention that the proposed method does not substantially differ from well-known Fourier methods discussed in several old papers and textbooks. For example, the “gradient field” as result of spatial filtering is discussed in references [2

2. S. K. Yao and S. H. Lee, “Spatial differentiation and integration by coherent optical-correlation method,” J. Opt. Soc. 61(4), 474–477 (1971). [CrossRef]

,3

3. J.K.T. Eu, C.Y.C. Liu, and A.W. Lohmann, “Spatial filters for differentiation,” Opt. Comm . 9(2), 168-171 (1973).

], and a review (also improvements to the method described by the authors of [1

1. T. Kim, S. Sridharan, and G. Popescu, “Gradient field microscopy of unstained specimens,” Opt. Express 20(6), 6737–6745 (2012). [CrossRef] [PubMed]

]) is presented in [4

4. G. O. Reynolds, J. B. DeVelis, G. B. Parrent, Jr., and B. J. Thompson, eds., The New Physical Optics Notebook: Tutorials in Fourier Optics (SPIE, 1989), Chap. 32.

].

References and links

1.

T. Kim, S. Sridharan, and G. Popescu, “Gradient field microscopy of unstained specimens,” Opt. Express 20(6), 6737–6745 (2012). [CrossRef] [PubMed]

2.

S. K. Yao and S. H. Lee, “Spatial differentiation and integration by coherent optical-correlation method,” J. Opt. Soc. 61(4), 474–477 (1971). [CrossRef]

3.

J.K.T. Eu, C.Y.C. Liu, and A.W. Lohmann, “Spatial filters for differentiation,” Opt. Comm . 9(2), 168-171 (1973).

4.

G. O. Reynolds, J. B. DeVelis, G. B. Parrent, Jr., and B. J. Thompson, eds., The New Physical Optics Notebook: Tutorials in Fourier Optics (SPIE, 1989), Chap. 32.

OCIS Codes
(170.0180) Medical optics and biotechnology : Microscopy
(170.1650) Medical optics and biotechnology : Coherence imaging

ToC Category:
Medical Optics and Biotechnology

History
Original Manuscript: November 21, 2012
Revised Manuscript: February 7, 2013
Manuscript Accepted: April 25, 2013
Published: August 5, 2013

Virtual Issues
Vol. 8, Iss. 9 Virtual Journal for Biomedical Optics

Citation
José A. Ferrari and Gastón A. Ayubi, "Gradient field microscopy of unstained specimens: comment," Opt. Express 21, 19187-19187 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-16-19187


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References

  1. T. Kim, S. Sridharan, and G. Popescu, “Gradient field microscopy of unstained specimens,” Opt. Express20(6), 6737–6745 (2012). [CrossRef] [PubMed]
  2. S. K. Yao and S. H. Lee, “Spatial differentiation and integration by coherent optical-correlation method,” J. Opt. Soc.61(4), 474–477 (1971). [CrossRef]
  3. J.K.T. Eu, C.Y.C. Liu, and A.W. Lohmann, “Spatial filters for differentiation,” Opt. Comm. 9(2), 168-171 (1973).
  4. G. O. Reynolds, J. B. DeVelis, G. B. Parrent, Jr., and B. J. Thompson, eds., The New Physical Optics Notebook: Tutorials in Fourier Optics (SPIE, 1989), Chap. 32.

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