## Theoretical analysis of spectrally encoded endoscopy

Optics Express, Vol. 17, Issue 26, pp. 24045-24059 (2009)

http://dx.doi.org/10.1364/OE.17.024045

Acrobat PDF (1225 KB)

### Abstract

Using a single optical fiber and miniature distal optics, spectrally-encoded endoscopy (SEE) has been demonstrated as a promising, three-dimensional endoscopic imaging method with a large number of resolvable points and high frame rates. We present a detailed theoretical study of the SEE prototype system and probe. Several key imaging parameters of SEE are thoroughly derived and formulated, including the three-dimensional point-spread function and field of view, as well as the system’s optical aberrations and fundamental limits. We find that the point-spread function of the SEE system maintains a unique relation between its transverse and axial shapes, discuss the asymmetry of the volumetric field of view, determine that the number of lateral resolvable points is nearly twice than what was previously accepted, and derive an expression for the upper limit for the total number of resolvable points in the cross-sectional image plane.

© 2009 OSA

## 1. Introduction

1. C. M. Brown, P. G. Reinhall, S. Karasawa, and E. J. Seibel, “Optomechanical design and fabrication of resonant microscanners for a scanning fiber endoscope,” Opt. Eng. **45**, 043001-043010 (2006). [CrossRef]

4. Y. C. Wu, Y. X. Leng, J. F. Xi, and X. D. Li, “Scanning all-fiber-optic endomicroscopy system for 3D nonlinear optical imaging of biological tissues,” Opt. Express **17**(10), 7907–7915 (2009). [CrossRef] [PubMed]

5. G. J. Tearney, M. Shishkov, and B. E. Bouma, “Spectrally encoded miniature endoscopy,” Opt. Lett. **27**(6), 412–414 (2002). [CrossRef] [PubMed]

6. D. Yelin, I. Rizvi, W. M. White, J. T. Motz, T. Hasan, B. E. Bouma, and G. J. Tearney, “Three-dimensional miniature endoscopy,” Nature **443**(7113), 765 (2006). [CrossRef] [PubMed]

7. D. Yelin, S. H. Yun, B. E. Bouma, and G. J. Tearney, “Three-dimensional imaging using spectral encoding heterodyne interferometry,” Opt. Lett. **30**(14), 1794–1796 (2005). [CrossRef] [PubMed]

8. L. Froehly, S. N. Martin, T. Lasser, C. Depeursinge, and F. Lang, “Multiplexed 3D imaging using wavelength encoded spectral interferometry: a proof of principle,” Opt. Commun. **222**, 127–136 (2003). [CrossRef]

9. D. Yelin, W. M. White, J. T. Motz, S. H. Yun, B. E. Bouma, and G. J. Tearney, “Spectral-domain spectrally-encoded endoscopy,” Opt. Express **15**(5), 2432–2444 (2007). [CrossRef] [PubMed]

10. M. A. Choma, M. V. Sarunic, C. H. Yang, and J. A. Izatt, “Sensitivity advantage of swept source and Fourier domain optical coherence tomography,” Opt. Express **11**(18), 2183–2189 (2003). [CrossRef] [PubMed]

12. R. Leitgeb, C. Hitzenberger, and A. Fercher, “Performance of fourier domain vs. time domain optical coherence tomography,” Opt. Express **11**(8), 889–894 (2003). [CrossRef] [PubMed]

8. L. Froehly, S. N. Martin, T. Lasser, C. Depeursinge, and F. Lang, “Multiplexed 3D imaging using wavelength encoded spectral interferometry: a proof of principle,” Opt. Commun. **222**, 127–136 (2003). [CrossRef]

9. D. Yelin, W. M. White, J. T. Motz, S. H. Yun, B. E. Bouma, and G. J. Tearney, “Spectral-domain spectrally-encoded endoscopy,” Opt. Express **15**(5), 2432–2444 (2007). [CrossRef] [PubMed]

13. D. Yelin, B. E. Bouma, N. Iftimia, and G. J. Tearney, “Three-dimensional spectrally encoded imaging,” Opt. Lett. **28**(23), 2321–2323 (2003). [CrossRef] [PubMed]

14. D. Yelin, B. E. Bouma, and G. J. Tearney, “Volumetric sub-surface imaging using spectrally encoded endoscopy,” Opt. Express **16**(3), 1748–1757 (2008). [CrossRef] [PubMed]

15. D. Yelin, B. E. Bouma, J. J. Rosowsky, and G. J. Tearney, “Doppler imaging using spectrally-encoded endoscopy,” Opt. Express **16**(19), 14836–14844 (2008). [CrossRef] [PubMed]

*et al.*[8

8. L. Froehly, S. N. Martin, T. Lasser, C. Depeursinge, and F. Lang, “Multiplexed 3D imaging using wavelength encoded spectral interferometry: a proof of principle,” Opt. Commun. **222**, 127–136 (2003). [CrossRef]

5. G. J. Tearney, M. Shishkov, and B. E. Bouma, “Spectrally encoded miniature endoscopy,” Opt. Lett. **27**(6), 412–414 (2002). [CrossRef] [PubMed]

9. D. Yelin, W. M. White, J. T. Motz, S. H. Yun, B. E. Bouma, and G. J. Tearney, “Spectral-domain spectrally-encoded endoscopy,” Opt. Express **15**(5), 2432–2444 (2007). [CrossRef] [PubMed]

6. D. Yelin, I. Rizvi, W. M. White, J. T. Motz, T. Hasan, B. E. Bouma, and G. J. Tearney, “Three-dimensional miniature endoscopy,” Nature **443**(7113), 765 (2006). [CrossRef] [PubMed]

## 2. The SEE system

6. D. Yelin, I. Rizvi, W. M. White, J. T. Motz, T. Hasan, B. E. Bouma, and G. J. Tearney, “Three-dimensional miniature endoscopy,” Nature **443**(7113), 765 (2006). [CrossRef] [PubMed]

**15**(5), 2432–2444 (2007). [CrossRef] [PubMed]

13. D. Yelin, B. E. Bouma, N. Iftimia, and G. J. Tearney, “Three-dimensional spectrally encoded imaging,” Opt. Lett. **28**(23), 2321–2323 (2003). [CrossRef] [PubMed]

15. D. Yelin, B. E. Bouma, J. J. Rosowsky, and G. J. Tearney, “Doppler imaging using spectrally-encoded endoscopy,” Opt. Express **16**(19), 14836–14844 (2008). [CrossRef] [PubMed]

**443**(7113), 765 (2006). [CrossRef] [PubMed]

14. D. Yelin, B. E. Bouma, and G. J. Tearney, “Volumetric sub-surface imaging using spectrally encoded endoscopy,” Opt. Express **16**(3), 1748–1757 (2008). [CrossRef] [PubMed]

*n*and

_{p}*n*denote the refractive indices of the grating substrate and the medium surrounding the probe, respectively,

_{m}*θ*are the incidence and the diffraction angles, respectively,

*m*denotes the diffraction order,

*λ*denotes the wavelength and

*G*denotes the grating groove density. Note that Eq. (1) slightly differs from commonly used grating equations to account for the light transition between two different media having different refractive indices. To achieve high angular dispersion, SEE often uses high groove density gratings designed to have high diffraction efficiency only in the first (

*m*= 1) diffraction order, which, for simplicity, will be considered throughout this work.

*O*) at the center of the diffraction grating, where the positive

*z*axis is pointed at the direction of the diffracted center wavelength

*n*= 1) and substituting

_{m}*y*axis) is accomplished by scanning the angle

*φ*(see Fig. 1), rotating the SEE probe around its optical axis. In recent works a galvanometric scanner (Cambridge Technology, Inc., not shown in Fig. 1) was used for probe rotation, which was limited to a maximum mechanical scanning angle of 20° [6

**443**(7113), 765 (2006). [CrossRef] [PubMed]

**15**(5), 2432–2444 (2007). [CrossRef] [PubMed]

## 3. SEE prototype analysis

### 3.1 Probe structure and components

**443**(7113), 765 (2006). [CrossRef] [PubMed]

14. D. Yelin, B. E. Bouma, and G. J. Tearney, “Volumetric sub-surface imaging using spectrally encoded endoscopy,” Opt. Express **16**(3), 1748–1757 (2008). [CrossRef] [PubMed]

15. D. Yelin, B. E. Bouma, J. J. Rosowsky, and G. J. Tearney, “Doppler imaging using spectrally-encoded endoscopy,” Opt. Express **16**(19), 14836–14844 (2008). [CrossRef] [PubMed]

*θ*

_{0}= 19°, chosen as the Littrow’s angle for the central wavelength

*n*= 1]. The different components are held together using optical grade glue. A photograph of the probe is shown in Fig. 2(b) for reference.

_{m}### 3.2 Point-spread function

5. G. J. Tearney, M. Shishkov, and B. E. Bouma, “Spectrally encoded miniature endoscopy,” Opt. Lett. **27**(6), 412–414 (2002). [CrossRef] [PubMed]

*D*and is deflected by a grating, as schematically depicted in Fig. 3 . According to Fresnel diffraction theory, the field distribution

*E*at the focal plane

_{M}*z*

_{0}of the SEE probe for

*monochromatic illumination*of angular wavenumber

*k*, is given by:where

_{m}*C*denotes a scaling constant containing uniform spectral attenuations in the optical system,

*E*

_{0}denotes the source field amplitude, and

*x*denotes the location of the first diffraction order for

_{m}*k*(Fig. 3, red solid lines). For simplicity, we will consider the field at

_{m}*y*coordinate from the following equations.

*r*

_{0}located at

*x*:

_{s}*δ*denotes the Dirac delta function. When the illumination field contains a continuum of wavelengths with a total bandwidth

*x*is obtained by integrating over all angular wavenumbers:

_{s}*x*for any wavenumber

_{s}*k*is given by:where

*x*denotes the location of the first diffraction order, corresponding to the angular wavenumber

_{k}*k*(Fig. 3, blue dashed lines). The field

*k*and a collection channel

_{m}*k*:

*confocal*optical arrangement in which both the illumination and the collection optical paths overlap in space, i.e.

*k*is the wavenumber whose first diffraction order is located at the scatterer location

_{s}*x*, and where we have assumed that

_{s}*y*axis:

**443**(7113), 765 (2006). [CrossRef] [PubMed]

*λ*

_{0}= 800 nm (black solid line and black dashed line, respectively). These Airy patterns are the result of the circular aperture of the diffraction grating, and would have different geometries for different probe shapes and illuminating wavefronts. For example, some feasible SEE probe designs require the use of gratings with rectangular shapes, which could be easier to manufacture compared with circular or oval gratings. Such rectangular gratings produce different intensity PSF and transfer function curves, as illustrated by red markers in Fig. 4(a) for a square probe aperture, showing somewhat broader central spot and slightly more pronounced side lobes.

*E*

_{C}(

*k*) collected from the sample can be expressed as the coherent summation of all scatterers with reflectivities

*r*(

_{S}*x,z*) within the illuminated

*x-z*cross section, given by:where DOF denotes the depth of focus (FWHM of the confocal axial PSF). We assume here that the transfer function

*h*, previously calculated for the focal plane at

*z*

_{0}, remains approximately unchanged within DOF. The distance

*z*

_{0}is given by

*z*and

_{m}*z*denote the propagation distances in the medium and in the sample, respectively. For simplicity, we assumed that the probe optics have a total length that is much smaller than its working distance

_{s}*z*

_{0}, thus we can neglect phase accumulation inside the probe. This assumption is justified by realizing that the 1.5 mm separation between the lens and the grating (Fig. 2) is a result of the specific manufacturing process, and could be made much smaller in future versions of the probe. The weighted refractive index is given by

*n*and

_{m}*n*denote the refractive indices of the medium and the sample, respectively.

_{s}*r*is given by:where

_{R}*z*denotes the distance between the fiber exit and the reference mirror (Fig. 1). Constant attenuations in both arms were neglected for clarity. In order to calculate the interferometric axial PSF, we consider the spectral interference between the returning reference and sample signals, captured by the spectrometer line camera, which can be expressed as the coherent summation of the fields from the reference (Eq. (11)) and sample (Eq. (10)) arms:

_{R}*G =*0 in Eq. (7) (meaning essentially no diffraction grating in the probe) we obtain from Eq. (12) an expression for the spectral interference in spectral domain OCT (SD-OCT) [16] (neglecting constant attenuation factors):where the sample reflectivity

*r*(

_{S}*z*) is a function of the

*z*coordinate only. OCT could be therefore viewed as private case of SEE, in the limit where the number of transverse resolvable points in SEE equals 1. A comparison between SD-OCT and SD-SEE has been previously described in Ref [14

**16**(3), 1748–1757 (2008). [CrossRef] [PubMed]

*x-z*plane:

**15**(5), 2432–2444 (2007). [CrossRef] [PubMed]

**16**(3), 1748–1757 (2008). [CrossRef] [PubMed]

17. M. Wojtkowski, A. Kowalczyk, R. Leitgeb, and A. F. Fercher, “Full range complex spectral optical coherence tomography technique in eye imaging,” Opt. Lett. **27**(16), 1415–1417 (2002). [CrossRef] [PubMed]

**16**(3), 1748–1757 (2008). [CrossRef] [PubMed]

**443**(7113), 765 (2006). [CrossRef] [PubMed]

### 3.3 Field of view

*θ*is linear with

*λ*across the entire source spectrum

*y*axis, the field of view depends on the scanning angle of the galvanometric scanner (see Ref [9

**15**(5), 2432–2444 (2007). [CrossRef] [PubMed]

*y*axis is given by:where

*ζ*in Section 3.2). The total imaging range in the

*z*axis is then derived from the Nyquist sampling limit and is given by:

**15**(5), 2432–2444 (2007). [CrossRef] [PubMed]

### 3.4 Resolvable points

*x*axis, the number of resolvable points can be approximated by calculating the ratio between the field of view and the spatial resolution:

*y*axis, the number of resolvable points is given by:

**27**(6), 412–414 (2002). [CrossRef] [PubMed]

**222**, 127–136 (2003). [CrossRef]

**15**(5), 2432–2444 (2007). [CrossRef] [PubMed]

*confocal*lateral PSF. Overall, we find a total of

*axial*resolvable points in SEE is limited by the number of resolvable spectral modulation frequencies (

*ζ*), which is equal to the number of resolvable elements

**443**(7113), 765 (2006). [CrossRef] [PubMed]

*x-y*plane is

**15**(5), 2432–2444 (2007). [CrossRef] [PubMed]

**16**(3), 1748–1757 (2008). [CrossRef] [PubMed]

*x-z*plane) resolvable points:

*x-z*plane is

*independent of the optical parameters of the probe*, only on the source and spectrometer properties. Therefore, Eq. (24) represents a fundamental upper limit of the spectral encoding technique, implying that the spectral content of the SEE system eventually limits its imaging performance, operating as an ‘information resource’ for the system.

### 3.5 Optical aberrations

*x*-

*z*plane as a result of chromatic aberrations only.

*λ*(Eq. (8)) illuminating each sample location, and may help in reducing the cost and complexity of future miniature lenses [18

18. K. B. Sung, C. N. Liang, M. Descour, T. Collier, M. Follen, and R. Richards-Kortum, “Fiber-optic confocal reflectance microscope with miniature objective for in vivo imaging of human tissues,” IEEE Trans. Biomed. Eng. **49**(10), 1168–1172 (2002). [CrossRef] [PubMed]

*x*and

*y*axes cause the beam to focus at different axial locations. To study the effect of astigmatism, we have simulated the transverse intensity profile of the beam for different axial locations and for several wavelengths, 25 nm apart within the source bandwidth. A plot of the focal shifts of the two foci in the

*x*axis (green circles) and in the

*y*axis (blue rectangles) as a function of wavelength is shown in Fig. 7(a) , with the axial locations corresponding to maximum lateral circular symmetry (red triangles). The effect of chromatic aberrations is also evident in Fig. 7(a) through the focal tilt on

*y*axis, where astigmatism is negligible. Also evident is the focal line curvature with radius of approximately

*z*

_{0}, which results from the grating angular dispersion, and could be perceived as the equivalent of the Petzval curvature of lenses and objectives.

*z*

_{0}is replaced by

*x-*axis [approximately 1.5 times wider than the

*y*axis PSF, Fig. 8(b)]. Combined with the chromatic aberrations of the GRIN lens, which result in different beam curvatures for different wavelengths, this effect is also wavelength-dependant, and is more pronounced for long wavelengths which have shorter focal lengths. The PSF FWHM is plotted in the

*x*and

*y*axes as a function of the working distance in Fig. 8(c), showing that this aberration becomes significant for short working distances, below 1.5 mm. Consequently, there is a limit to the maximum possible spatial resolution obtained with the distal-grating SEE configuration. High resolution spectrally encoded imaging is most suitable using confocal arrangement in which the imaging lens is the most distal element in the probe [19

19. C. Boudoux, S. Yun, W. Oh, W. White, N. Iftimia, M. Shishkov, B. Bouma, and G. Tearney, “Rapid wavelength-swept spectrally encoded confocal microscopy,” Opt. Express **13**(20), 8214–8221 (2005). [CrossRef] [PubMed]

20. D. Yelin, C. Boudoux, B. E. Bouma, and G. J. Tearney, “Large area confocal microscopy,” Opt. Lett. **32**(9), 1102–1104 (2007). [CrossRef] [PubMed]

*x*-

*z*plane is summarized in Fig. 9 , showing that the resulting focal plane (red dashed line) is tilted by approximately 25° (on average) from the aberration-free focal plane (solid green line) due to the combined effect of chromatic aberrations (8.5° tilt, dotted blue line) and astigmatism.

### 3.6 Three-dimensional field of view

*x*,

*y*, and

*z*axes, respectively, and incorporate our optical aberrations analysis to account for focal plane angle and curvature. The total effect of the unique optical configuration and optical aberration of SEE on the volumetric FOV is summarized in Fig. 10(a) for

*x*axis) and probe rotation (

*y*axis). In an

*x-z*section [Fig. 10(c)], the strong tilt of the field due to chromatic aberrations and astigmatism is clearly visible, as well as the asymmetry in image depth due to the longer encoding wavelengths. Volumetric rendering of the FOV for a full probe rotation (

## 4. Discussion

21. D. Yelin, B. E. Bouma, S. H. Yun, and G. J. Tearney, “Double-clad fiber for endoscopy,” Opt. Lett. **29**(20), 2408–2410 (2004). [CrossRef] [PubMed]

**27**(6), 412–414 (2002). [CrossRef] [PubMed]

**15**(5), 2432–2444 (2007). [CrossRef] [PubMed]

**443**(7113), 765 (2006). [CrossRef] [PubMed]

**16**(3), 1748–1757 (2008). [CrossRef] [PubMed]

*h*(

*k*), including its far-extending side-lobes, which spans over the entire source bandwidth. Triangular PSF would potentially improve the effective axial resolution of interferometric SEE in specific high SNR imaging applications. The coupling between the lateral and axial dimensions also results with a fundamental limit on the number of resolvable points in the cross sectional (

*x-*z) plane: since the total bandwidth

*decode*the image (

*h*(

*k*) [Eq. (7)].

19. C. Boudoux, S. Yun, W. Oh, W. White, N. Iftimia, M. Shishkov, B. Bouma, and G. Tearney, “Rapid wavelength-swept spectrally encoded confocal microscopy,” Opt. Express **13**(20), 8214–8221 (2005). [CrossRef] [PubMed]

20. D. Yelin, C. Boudoux, B. E. Bouma, and G. J. Tearney, “Large area confocal microscopy,” Opt. Lett. **32**(9), 1102–1104 (2007). [CrossRef] [PubMed]

## References and Links

1. | C. M. Brown, P. G. Reinhall, S. Karasawa, and E. J. Seibel, “Optomechanical design and fabrication of resonant microscanners for a scanning fiber endoscope,” Opt. Eng. |

2. | D. L. Dickensheets and G. S. Kino, “Silicon-micromachined scanning confocal optical microscope,” J. Microelectromech. Syst. |

3. | A. L. Polglase, W. J. McLaren, S. A. Skinner, R. Kiesslich, M. F. Neurath, and P. M. Delaney, “A fluorescence confocal endomicroscope for in vivo microscopy of the upper- and the lower-GI tract,” in |

4. | Y. C. Wu, Y. X. Leng, J. F. Xi, and X. D. Li, “Scanning all-fiber-optic endomicroscopy system for 3D nonlinear optical imaging of biological tissues,” Opt. Express |

5. | G. J. Tearney, M. Shishkov, and B. E. Bouma, “Spectrally encoded miniature endoscopy,” Opt. Lett. |

6. | D. Yelin, I. Rizvi, W. M. White, J. T. Motz, T. Hasan, B. E. Bouma, and G. J. Tearney, “Three-dimensional miniature endoscopy,” Nature |

7. | D. Yelin, S. H. Yun, B. E. Bouma, and G. J. Tearney, “Three-dimensional imaging using spectral encoding heterodyne interferometry,” Opt. Lett. |

8. | L. Froehly, S. N. Martin, T. Lasser, C. Depeursinge, and F. Lang, “Multiplexed 3D imaging using wavelength encoded spectral interferometry: a proof of principle,” Opt. Commun. |

9. | D. Yelin, W. M. White, J. T. Motz, S. H. Yun, B. E. Bouma, and G. J. Tearney, “Spectral-domain spectrally-encoded endoscopy,” Opt. Express |

10. | M. A. Choma, M. V. Sarunic, C. H. Yang, and J. A. Izatt, “Sensitivity advantage of swept source and Fourier domain optical coherence tomography,” Opt. Express |

11. | J. F. de Boer, B. Cense, B. H. Park, M. C. Pierce, G. J. Tearney, and B. E. Bouma, “Improved signal-to-noise ratio in spectral-domain compared with time-domain optical coherence tomography,” Opt. Lett. |

12. | R. Leitgeb, C. Hitzenberger, and A. Fercher, “Performance of fourier domain vs. time domain optical coherence tomography,” Opt. Express |

13. | D. Yelin, B. E. Bouma, N. Iftimia, and G. J. Tearney, “Three-dimensional spectrally encoded imaging,” Opt. Lett. |

14. | D. Yelin, B. E. Bouma, and G. J. Tearney, “Volumetric sub-surface imaging using spectrally encoded endoscopy,” Opt. Express |

15. | D. Yelin, B. E. Bouma, J. J. Rosowsky, and G. J. Tearney, “Doppler imaging using spectrally-encoded endoscopy,” Opt. Express |

16. | B. E. Bouma, and G. J. Tearney, eds., |

17. | M. Wojtkowski, A. Kowalczyk, R. Leitgeb, and A. F. Fercher, “Full range complex spectral optical coherence tomography technique in eye imaging,” Opt. Lett. |

18. | K. B. Sung, C. N. Liang, M. Descour, T. Collier, M. Follen, and R. Richards-Kortum, “Fiber-optic confocal reflectance microscope with miniature objective for in vivo imaging of human tissues,” IEEE Trans. Biomed. Eng. |

19. | C. Boudoux, S. Yun, W. Oh, W. White, N. Iftimia, M. Shishkov, B. Bouma, and G. Tearney, “Rapid wavelength-swept spectrally encoded confocal microscopy,” Opt. Express |

20. | D. Yelin, C. Boudoux, B. E. Bouma, and G. J. Tearney, “Large area confocal microscopy,” Opt. Lett. |

21. | D. Yelin, B. E. Bouma, S. H. Yun, and G. J. Tearney, “Double-clad fiber for endoscopy,” Opt. Lett. |

**OCIS Codes**

(110.2350) Imaging systems : Fiber optics imaging

(110.2990) Imaging systems : Image formation theory

(110.4850) Imaging systems : Optical transfer functions

(170.2150) Medical optics and biotechnology : Endoscopic imaging

**ToC Category:**

Medical Optics and Biotechnology

**History**

Original Manuscript: August 17, 2009

Revised Manuscript: October 28, 2009

Manuscript Accepted: October 29, 2009

Published: December 17, 2009

**Virtual Issues**

Vol. 5, Iss. 1 *Virtual Journal for Biomedical Optics*

**Citation**

Michal Merman, Avraham Abramov, and Dvir Yelin, "Theoretical analysis of spectrally encoded endoscopy," Opt. Express **17**, 24045-24059 (2009)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-26-24045

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### References

- C. M. Brown, P. G. Reinhall, S. Karasawa, and E. J. Seibel, “Optomechanical design and fabrication of resonant microscanners for a scanning fiber endoscope,” Opt. Eng. 45, 043001-043010 (2006). [CrossRef]
- D. L. Dickensheets and G. S. Kino, “Silicon-micromachined scanning confocal optical microscope,” J. Microelectromech. Syst. 7, 38–47 (1998). [CrossRef]
- A. L. Polglase, W. J. McLaren, S. A. Skinner, R. Kiesslich, M. F. Neurath, and P. M. Delaney, “A fluorescence confocal endomicroscope for in vivo microscopy of the upper- and the lower-GI tract,” in Digestive Disease Week/105th Annual Meeting of the American-Gastroenterological-Association (New Orleans, LA, 2004), pp. 686–695.
- Y. C. Wu, Y. X. Leng, J. F. Xi, and X. D. Li, “Scanning all-fiber-optic endomicroscopy system for 3D nonlinear optical imaging of biological tissues,” Opt. Express 17(10), 7907–7915 (2009). [CrossRef] [PubMed]
- G. J. Tearney, M. Shishkov, and B. E. Bouma, “Spectrally encoded miniature endoscopy,” Opt. Lett. 27(6), 412–414 (2002). [CrossRef] [PubMed]
- D. Yelin, I. Rizvi, W. M. White, J. T. Motz, T. Hasan, B. E. Bouma, and G. J. Tearney, “Three-dimensional miniature endoscopy,” Nature 443(7113), 765 (2006). [CrossRef] [PubMed]
- D. Yelin, S. H. Yun, B. E. Bouma, and G. J. Tearney, “Three-dimensional imaging using spectral encoding heterodyne interferometry,” Opt. Lett. 30(14), 1794–1796 (2005). [CrossRef] [PubMed]
- L. Froehly, S. N. Martin, T. Lasser, C. Depeursinge, and F. Lang, “Multiplexed 3D imaging using wavelength encoded spectral interferometry: a proof of principle,” Opt. Commun. 222, 127–136 (2003). [CrossRef]
- D. Yelin, W. M. White, J. T. Motz, S. H. Yun, B. E. Bouma, and G. J. Tearney, “Spectral-domain spectrally-encoded endoscopy,” Opt. Express 15(5), 2432–2444 (2007). [CrossRef] [PubMed]
- M. A. Choma, M. V. Sarunic, C. H. Yang, and J. A. Izatt, “Sensitivity advantage of swept source and Fourier domain optical coherence tomography,” Opt. Express 11(18), 2183–2189 (2003). [CrossRef] [PubMed]
- J. F. de Boer, B. Cense, B. H. Park, M. C. Pierce, G. J. Tearney, and B. E. Bouma, “Improved signal-to-noise ratio in spectral-domain compared with time-domain optical coherence tomography,” Opt. Lett. 28(21), 2067–2069 (2003). [CrossRef] [PubMed]
- R. Leitgeb, C. Hitzenberger, and A. Fercher, “Performance of fourier domain vs. time domain optical coherence tomography,” Opt. Express 11(8), 889–894 (2003). [CrossRef] [PubMed]
- D. Yelin, B. E. Bouma, N. Iftimia, and G. J. Tearney, “Three-dimensional spectrally encoded imaging,” Opt. Lett. 28(23), 2321–2323 (2003). [CrossRef] [PubMed]
- D. Yelin, B. E. Bouma, and G. J. Tearney, “Volumetric sub-surface imaging using spectrally encoded endoscopy,” Opt. Express 16(3), 1748–1757 (2008). [CrossRef] [PubMed]
- D. Yelin, B. E. Bouma, J. J. Rosowsky, and G. J. Tearney, “Doppler imaging using spectrally-encoded endoscopy,” Opt. Express 16(19), 14836–14844 (2008). [CrossRef] [PubMed]
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