Zoom lens design using liquid lens for laparoscope

doi:10.1364/OE.21.001751

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Zoom lens design using liquid lens for laparoscope

Seungwan Lee, Minseog Choi, Eunsung Lee, Kyu-Dong Jung, Jong-hyeon Chang, and Woonbae Kim »View Author Affiliations

Optics Express, Vol. 21, Issue 2, pp. 1751-1761 (2013)
http://dx.doi.org/10.1364/OE.21.001751

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Abstract

Traditional laparoscopic optical systems consisting of about 30 lenses have low optical magnification. To magnify tissue during surgical operations, one must change from one laparoscope to another or use a magnifying adapter between the laparoscope and the sensor. Our work focuses on how to change the sag of a liquid lens while zooming from 1 × zoom, to 2 × , and 4 × in an optical design for a laparoscope. The design includes several lenses and two liquid lenses with variable focal lengths. A pair of laparoscopes for 3-D stereoscopy is placed within a tube 11 mm in diameter. The predicted depth resolution of tissue is 0.5 mm without interpolation at 4 × zoom.

1. Introduction

Traditional laparoscopes used in minimally invasive surgery consist of many lenses and have limited visual properties, such as a fixed field of view, low magnification of 1 × –1.5 × , and high F-number at high zoom. High-definition (HD) image quality and 3-D imaging have recently become necessary in laparoscopes. A conventional surgical laparoscope consisting of more than 30 lenses is 30–40 cm long and 5–11 mm in diameter. The magnification is limited in optical systems using a zoom adaptor between the lens and the sensor. A zoom of 4 × was reported in a laparoscope using liquid lenses, called bio-inspired fluidic lenses [1

F. S. Tsai, D. Johnson, C. S. Francis, S. H. Cho, W. Qiao, A. Arianpour, Y. Mintz, S. Horgan, M. Talamini, and Y.-H. Lo, “Fluidic lens laparoscopic zoom camera for minimally invasive surgery,” J. Biomed. Opt. 15(3), 030504 (2010). [CrossRef] [PubMed]

]. In this paper, a laparoscope offering high zoom and 3-D stereoscopy by using a fluidic lens is proposed. The aim of this work is to determine how to change the sag of liquid lenses from 1 × zoom to 2 × and 4 × with no moving parts. It has been shown experimentally that stereoscopes, which provide 3-D vision, improve the precision and speed of endoscopic surgery [2

N. Taffinder, S. G. T. Smith, J. Huber, R. C. G. Russell, and A. Darzi, “The effect of a second-generation 3D endoscope on the laparoscopic precision of novices and experienced surgeons,” Surg. Endosc. 13(11), 1087–1092 (1999). [CrossRef] [PubMed]

, 3

W. B. Verwey, S. Stroomer, R. Lammens, S. N. Schulz, and W. H. Ehrenstein, “Comparing endoscopic systems on two simulated tasks,” Ergonomics 48(3), 270–287 (2005). [CrossRef] [PubMed]

]. The transverse resolution depends mostly on the size of the lens, wavelength of the light, and CCD [4

C. Pitris, M. E. Brezinski, B. E. Bouma, G. J. Tearney, J. F. Southern, and J. G. Fujimoto, “High resolution imaging of the upper respiratory tract with optical coherence tomography: a feasibility study,” Am. J. Respir. Crit. Care Med. 157(5 Pt 1), 1640–1644 (1998). [PubMed]

]. The depth of resolution in stereoscopy, δz (also referred to as the axial resolution) is expressed as follows [5

J. P. O. Evens, M. Robinson, S. X. Godber, and R. S. Petty, “The development of 3-D (stereoscopic) imaging systems for security applications,” in International Carnahan Conference on Security Technology (Sanderstead, England, 1995), 505–511.

δ z = \frac{Z^{2} δ P_{1}}{B f}

(1)

where Z is the distance from the tissue at the point of interest in object space to the CMOS sensor, δP₁ is the minimum detectable disparity in the image sensor plane (resolution in the x–y plane), P₁ = P(L) - P(R), B is the camera lens separation, and f is the focal length of the camera lenses. According to Eq. (1), the depth of resolution of 3-D stereoscope will be small at long focal lengths. The depth of resolution of 3-D stereoscope in zoom 4 × is 4 times smaller than zoom 1 × .

2. Tunable focal length by varying the curvature of a liquid lens for zooming

A simplified conceptual model of the zoom system consists of two tunable liquid lenses which works together to adjust the total zoom as shown Fig. 1. Variable focal length in a lens can be achieved by changing its shape. Both liquid lenses are enclosed in a thin, transparent elastomer membrane. The curvature of the liquid-filled lenses at either end of the membrane is changed under pneumatic control. The effective focal length f of the two variable liquid lenses can be expressed as

\frac{1}{f} = (n_{1} - 1) (n_{2} - 1) (\frac{1}{R_{1} (n_{2} - 1)} - \frac{1}{R_{2} (n_{1} - 1)} + (\frac{d_{1}}{n_{1}} + \frac{d_{2}}{n_{2}}) \frac{1}{R_{1} R_{2}})

(2)

where n₁ and n₂ are the refractive index of liquids 1 and 2, respectively, and d₁ and d₂ are their lengths; R₁ and R₂ are the curvatures of lenses 1 and 2, respectively. If we use liquids having n₁ = n₂, then Eq. (2) can be expressed as follows.

Fig. 1 Optical lens configuration using two liquids.

\frac{1}{f} = (n_{1} - 1) (\frac{1}{R_{1}} - \frac{1}{R_{2}} + \frac{(d_{1} + d_{2}) (n_{1} - 1)}{R_{1} R_{2} n_{1}})

(3)

The general lens shape can be expressed by Eq. (4), where c is the vertex curvature of the lens, r is the radius of the lens aperture, k is a conic constant, and A₂, A₄, etc., are the coefficients of the polynomial.

z (r) = (\frac{c r^{2}}{1 + {(1 - (1 + k) c^{_{2}} r^{_{2}})}^{0.5}}) + A_{2} r^{4} + A_{4} r^{6} + A {}_{8}r^{8} ......

(4)

In a liquid lens having large sag, the spherical lens profile z(r) is given by Eq. (5), where k = A₂ = A₄ = … = 0. The radius of curvature of the lens, R₁, is related to the lens sag z(b₁) and aperture b₁ as shown in Eq. (6).

z (r) = (\frac{c r^{2}}{1 + {(1 - c^{_{2}} r^{_{2}})}^{0.5}})

(5)

R_{1} = (\frac{(b_{1}^{2} + z {(b_{1})}^{2})}{2 z (b_{1})})

(6)

The effective focal length versus the lens sag z(b₁) of lens 1 and the sag z(b₂) can be obtained using Eqs. (2) and (6). Figure 2 illustrates how the focal length changes with the lens sag. This fluidic lens design has the advantage of being convertible between a convex and a concave shape.

Fig. 2 (a) Effective focal length as a function of changes in the sag of two liquid lenses, (b) ray tracing of liquid lens.

3. Lens design conditions

The effective focal length of a lens system depends on the refractive index and Abbe number of the lenses. The refractive index and Abbe number of liquid lenses can be modified by making a salt solution, as shown in Fig. 3, that can have a refractive index ranging from n = 1.32 to n = 1.46. The refractive index of oil ranges widely from n = 1.3 to n = 2.3. But it is not easy to keep oil from permeating through polydimethylsiloxane (PDMS). It is known that PDMS can block water, which has a surface energy density of 72.8 mJ/m², and the surface energy of a liquid increases as the salt concentration increases [6

W. Yao, H. Bjurstroem, and F. Setterwall, “Surface tension of lithium bromide solutions with heat-transfer additives,” J. Chem. Eng. Data 36(1), 96–98 (1991). [CrossRef]

]. In this paper, the optical lenses are designed to use a liquid based on deionized water instead of oil. The liquid lens is enclosed by a transparent PDMS membrane (Sylgard 186, Dow Corning). PDMS has several excellent characteristics and is widely used for micro fabrication of various lab-on-a-chip devices because it is inexpensive, biocompatible, self-sealable, and highly elastic; further, it has excellent optical transparency and allows for easy device fabrication [7

J. C. McDonald, D. C. Duffy, J. R. Anderson, D. T. Chiu, H. Wu, O. J. A. Schueller, and G. M. Whitesides, “Fabrication of microfluidic systems in poly(dimethylsiloxane),” Electrophoresis 21(1), 27–40 (2000). [CrossRef] [PubMed]

, 8

J. M. K. Ng, I. Gitlin, A. D. Stroock, and G. M. Whitesides, “Components for integrated poly(dimethylsiloxane) microfluidic systems,” Electrophoresis 23(20), 3461–3473 (2002). [CrossRef] [PubMed]

]. The refractive index and Abbe number of LiCl solution increases 0.002 and 0.1377 times the salt concentration, respectively, as shown in Fig. 3. The design boundary conditions and goals for the 3-D laparoscope are given in Table 1. The maximum lens radius must be less 2.5 mm in order to insert two lens systems.

Fig. 3 (a) Refractive index vs. salt concentration; (b) Abbe number vs. salt concentration.

Table 1 Design conditions and goals for optical lens

parameters	wide angle 1 ×	medium angle 2 ×	tele angle 4 ×	remarks
Sensor grade	2M pixel	2M pixel	2M pixel	CMOS
Depth resolution	2 mm		0.5 mm	pixel size 1.75 μm
Distance lens to tissue	110 mm	110 mm	110 mm
The distance from last lens to image sensor	>3.5 mm	>3.5 mm	>3.5 mm
Overall length	20 mm	20 mm	20 mm
Max. radius of lens	2.5 mm.	2.5 mm	2.5 mm

4. Lens design results

The optical lens module consists of six glass lenses, one polymer lens, one iris with diffraction optical element (DOE), and two liquid lenses. The lens module was designed in Code V using a two-mega pixel CMOS sensor having a pixel size of 1.75 μm. Figure 4(a) shows the zoom lens configuration, and Fig. 4(b) shows the structure of iris. Figure 4(c) illustrates how to change the lens curvature for different focal lengths. It was designed using the CODE V software from the Optical Solutions Group at Synopsys. In Fig. 4(a), a liquid iris is adapted because it can be made thin and in pairs. The blocking fluid of the iris is moved by the electrowetting force [9

J.-H. Chang, K.-D. Jung, E. Lee, M. Choi, and S. Lee, “Microelectrofluidic iris for variable aperture,” Proc. SPIE 8252, 82520O, 82520O-6 (2012). [CrossRef]

] and can absorb visible light using black ink [10

P. Muller, N. Spengler, H. Zappe, and W. Monch, “An optofluidic concept for a tunable micro-iris,” J. Microelectromech. Syst. 19(6), 1477–1484 (2010). [CrossRef]

]. Figure 5 illustrates how the two sags of the lens module vary with the focal length. The relation between the effective focal length and the sag of the second lens can be expressed as y = −0.0937 Sag + 0.7357, but the relationship between the focal length and the sag of the first liquid lens is expressed by a curve marked with diamonds, as shown in Fig. 5. Figure 6 shows that the image resolution is changed by iris aperture due to zoom ratio. The F-number can be fixed by control the iris aperture. There is 4 mm gap from the stop to next lens. We designed the F-number 4.9–6.4 by using the slim liquid iris, 2 mm thickness like Fig. 4(b).

Fig. 4 (a) Schematic of lens module; (b) structure of IRIS; (c) Ray tracing and liquid lens shape at wide angle, middle angle, and tele angle.

Fig. 5 Change in lens sag vs. focal length.

Fig. 6 The image resolution by the IRIS aperture diameter.

To reduce the chromatic aberration of the optical module, a DOE lens is applied to the iris cover surface using PDMS. The DOE is described in Code V by a continuous profile. The profile can be a function of x and y, φ(x, y), or rotationally symmetric, φ(r). The form of the phase profile is determined by the command HCT (Polynomial Grating Type). In a rotationally symmetric model, φ(r) is described by Eq. (7), where C₁ = −0.000183, and C₂ = −0.000445. The height and focal length of the DOE can be calculated by Eqs. (8) and (9), respectively, where λ₀ is the design wavelength of light; n₁(λ₀) and n₂(λ₀) are the refractive index of the DOE lens and the surrounding refractive material, respectively. Figure 7 shows the phase function of the DOE. The number of DOE rings obtained using Eqs. (7) and (8) is 2.

Fig. 7 Phase profile of DOE.

φ (r) = \frac{2 π}{λ_{o}} \sum_{n = 1}^{10} C_{n} r^{2 n}

(7)

h e i g h t = \frac{λ_{o}}{n_{2} (λ_{o}) - n_{1} (λ_{o})} = \frac{0.572 μ m}{1.4923 - 1} = 1.17 μ m

(8)

f = \frac{- 0.5}{Q u d r a t i c_P h a s e_C o e f f i c i e n t} = \frac{- 0.5}{C {}_{1}} = 2735.6

(9)

5. Lens design characterizations

The modulation transfer function (MTF) is an important parameter for evaluating the optical performance. Figures 8(a)–8(f) illustrate the MTF value and the optical distortion is shown in Fig. 9 in wide-angle, medium-angle, and tele-angle mode. The optical performances are summarized in Table 2. Figure 10 is the result of 2D image simulation using USAF 1951 chart by CODE V utility.

Fig. 8 Design result; MTF (a),(b) Wide angle mode 1 × , (left 0–0.5F, right 0.6F–1.0F). (c),(d) Middle angle zoom 2 × ; (c), (d) Tele angle, zoom 4 ×.

Fig. 9 Design result; Optical distortion.

Table 2 Summary of design result

optical parameters	wide angle mode 1 ×	medium angle 2 ×	tele angle mode 4 ×	remarks (3 × )
focal length	3.241 mm	6.40 mm	12.945 mm	9.84 mm
field of view	66°	32°	13.8°	19.8°
F number	4.9	5.28	6.04	5.86
iris diameter	1.6 mm	2 mm	2.4 mm	2.2 mm
overall length	19.27 mm	19.27 mm	19.27 mm	19.27 mm
MTF 140 lp/mm @ 0.7F	35%	45%	30%	18%
MTF 70 lp/mm @ 0.7F	63%	70%	65%	46%
optical distortion	16%	5.16%	2.98%	6.48%
maximum lens dia.	2.08 mm	2.08 mm	2.08 mm	2.08 mm
total module length	23.26 mm	23.26 mm	23.26 mm	23.26 mm

Fig. 10 Image simulation result using USAF1951 chart; (a) zoom 1 × , (b) zoom 2 × ,(c) zoom 4 ×.

Table 3 Optical lens parameters

surface	lens shape	curvature	thickness	material	remark
object	spherical	infinite	110
1	spherical	infinite	0
2	spherical	7.11862489	0.5	FD60_HOYA
3	spherical	3.47998469	0.7
4	spherical	infinite	0.31136		refer to Table 4
5	spherical	−5.3586634	−0.31136	420000.461	refer to Table 4
6	spherical	infinite	0.5	420000.461	liquid
7	spherical	infinite	0.5	517000.642
8	spherical	infinite	0.1
9	spherical	10.1033247	0.8	LAC14_HOYA
10	spherical	infinite	0.5	FD60_HOYA
11	spherical	5.24058305	3.69149
12	spherical	10.7549464	0.9	FD60_HOYA
13	spherical	−10.087711	0.25479
14	spherical	infinite	0.3	517000.642
15	spherical	infinite	0.2
16	spherical	infinite	0.5	517000.642
IRIS	spherical	infinite	0.1		refer to Table 4
18	spherical	infinite	0.45	517000.642
19	spherical	infinite	0.05	492280.526
20	spherical	infinite	3.10094
21	spherical	3.35446332	1.3	BACD16_HOYA
22	spherical	−3.4788878	0.5	FD60_HOYA
23	spherical	3.7029371	0.3
24	spherical	infinite	0.5	517000.642
25	spherical	infinite	0.6	420000.461
26	spherical	infinite	0.4227	420000.461	refer to Table 4
27	spherical	−3.2395301	−0.4227		refer to Table 4
28	spherical	infinite	0.9227
29	aspheric	−18.236305	0.5	'E48R25'	refer to Table 5
30	aspheric	13.5350694	0.39574		refer to Table 5
31	aspheric	3.70327883	1.1	'E48R25'	refer to Table 5
32	aspheric	29.5887853	3.99000		refer to Table 5
image	spherical	infinite	0

Table 4 Lens parameters of liquid lens and iris

surface	parameters	zoom 1 ×	zoom 2 ×	zoom 3 ×	zoom 4 ×
4	thickness (sag)	0.31136	−0.141008	−0.341284	−0.460644
5	thickness (sag)	−0.31136	0.141008	0.341284	0.460644
5	curvature	−5.35866	11.55918	4.916687	3.747138
Stop	aperture radius	0.8	1.0	1.1	1.2
26	curvature	−3.23953	−9.48152	8.289928	2.823565
26	thickness (sag)	0.422696	0.135974	−0.15587	−0.49708
27	thickness (sag)	−0.422696	−0.135974	0.15587	0.49708

Table 5 Lens parameters of aspheric polymer lens

Surface	$k$	A₂	A₄	A₆	A₈
29	−9.8	−0.0127542	0.004246	−0.00027	−0.00018
30	−9.5	−0.0121767	0.003687	−0.00047	−8E-05
31	−1.4220	−0.0045646	−0.00189	−8E-05	−7.7E-05
32	9.5	−0.0063361	−0.0018	−0.00029	1.81E-05

6. Conclusion

Using two tunable liquid lenses, several lenses, a DOE, and one iris, we designed a variable zoom system that can achieve 1 × , 2 × , and 4 × zoom for a laparoscope with no moving parts. The trace of the sag of the liquid lens from 1 × zoom to 4 × zoom was optimized in the liquid lens module. The total length of the module is 23.26 mm. Its diameter is less than 4.1 mm, so two modules can be placed in a laparoscope 11 mm in diameter. The effective focal lengths of the wide-angle zoom, medium-angle zoom, and zoom-in modes are 3.24 mm, 6.4 mm, and 12.94 mm, respectively. The MTFs in the zoom-out and zoom-in modes are 35% and 30% at a frequency of 140 lp/mm. The fluidic zoom at lower F-number (4.9–6.04) is brighter than that of a conventional solid laparoscope. The optical distortions in the zoom-out and zoom-in modes are 16% and 3%, respectively The z-direction depth resolutions of this 3-D laparoscope are expected to be <0.5 mm and <2 mm in zoom-in and zoom-out modes, respectively, without interpolation.

References and links

1.	F. S. Tsai, D. Johnson, C. S. Francis, S. H. Cho, W. Qiao, A. Arianpour, Y. Mintz, S. Horgan, M. Talamini, and Y.-H. Lo, “Fluidic lens laparoscopic zoom camera for minimally invasive surgery,” J. Biomed. Opt. 15(3), 030504 (2010). [CrossRef] [PubMed]
2.	N. Taffinder, S. G. T. Smith, J. Huber, R. C. G. Russell, and A. Darzi, “The effect of a second-generation 3D endoscope on the laparoscopic precision of novices and experienced surgeons,” Surg. Endosc. 13(11), 1087–1092 (1999). [CrossRef] [PubMed]
3.	W. B. Verwey, S. Stroomer, R. Lammens, S. N. Schulz, and W. H. Ehrenstein, “Comparing endoscopic systems on two simulated tasks,” Ergonomics 48(3), 270–287 (2005). [CrossRef] [PubMed]
4.	C. Pitris, M. E. Brezinski, B. E. Bouma, G. J. Tearney, J. F. Southern, and J. G. Fujimoto, “High resolution imaging of the upper respiratory tract with optical coherence tomography: a feasibility study,” Am. J. Respir. Crit. Care Med. 157(5 Pt 1), 1640–1644 (1998). [PubMed]
5.	J. P. O. Evens, M. Robinson, S. X. Godber, and R. S. Petty, “The development of 3-D (stereoscopic) imaging systems for security applications,” in International Carnahan Conference on Security Technology (Sanderstead, England, 1995), 505–511.
6.	W. Yao, H. Bjurstroem, and F. Setterwall, “Surface tension of lithium bromide solutions with heat-transfer additives,” J. Chem. Eng. Data 36(1), 96–98 (1991). [CrossRef]
7.	J. C. McDonald, D. C. Duffy, J. R. Anderson, D. T. Chiu, H. Wu, O. J. A. Schueller, and G. M. Whitesides, “Fabrication of microfluidic systems in poly(dimethylsiloxane),” Electrophoresis 21(1), 27–40 (2000). [CrossRef] [PubMed]
8.	J. M. K. Ng, I. Gitlin, A. D. Stroock, and G. M. Whitesides, “Components for integrated poly(dimethylsiloxane) microfluidic systems,” Electrophoresis 23(20), 3461–3473 (2002). [CrossRef] [PubMed]
9.	J.-H. Chang, K.-D. Jung, E. Lee, M. Choi, and S. Lee, “Microelectrofluidic iris for variable aperture,” Proc. SPIE 8252, 82520O, 82520O-6 (2012). [CrossRef]
10.	P. Muller, N. Spengler, H. Zappe, and W. Monch, “An optofluidic concept for a tunable micro-iris,” J. Microelectromech. Syst. 19(6), 1477–1484 (2010). [CrossRef]

OCIS Codes
(170.0170) Medical optics and biotechnology : Medical optics and biotechnology
(220.3620) Optical design and fabrication : Lens system design

ToC Category:
Medical Optics and Biotechnology

History
Original Manuscript: October 19, 2012
Revised Manuscript: December 9, 2012
Manuscript Accepted: December 12, 2012
Published: January 16, 2013

Virtual Issues
Vol. 8, Iss. 2 Virtual Journal for Biomedical Optics

Citation
Seungwan Lee, Minseog Choi, Eunsung Lee, Kyu-Dong Jung, Jong-hyeon Chang, and Woonbae Kim, "Zoom lens design using liquid lens for laparoscope," Opt. Express 21, 1751-1761 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-2-1751

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References

F. S. Tsai, D. Johnson, C. S. Francis, S. H. Cho, W. Qiao, A. Arianpour, Y. Mintz, S. Horgan, M. Talamini, and Y.-H. Lo, “Fluidic lens laparoscopic zoom camera for minimally invasive surgery,” J. Biomed. Opt.15(3), 030504 (2010). [CrossRef] [PubMed]
N. Taffinder, S. G. T. Smith, J. Huber, R. C. G. Russell, and A. Darzi, “The effect of a second-generation 3D endoscope on the laparoscopic precision of novices and experienced surgeons,” Surg. Endosc.13(11), 1087–1092 (1999). [CrossRef] [PubMed]
W. B. Verwey, S. Stroomer, R. Lammens, S. N. Schulz, and W. H. Ehrenstein, “Comparing endoscopic systems on two simulated tasks,” Ergonomics48(3), 270–287 (2005). [CrossRef] [PubMed]
C. Pitris, M. E. Brezinski, B. E. Bouma, G. J. Tearney, J. F. Southern, and J. G. Fujimoto, “High resolution imaging of the upper respiratory tract with optical coherence tomography: a feasibility study,” Am. J. Respir. Crit. Care Med.157(5 Pt 1), 1640–1644 (1998). [PubMed]
J. P. O. Evens, M. Robinson, S. X. Godber, and R. S. Petty, “The development of 3-D (stereoscopic) imaging systems for security applications,” in International Carnahan Conference on Security Technology (Sanderstead, England, 1995), 505–511.
W. Yao, H. Bjurstroem, and F. Setterwall, “Surface tension of lithium bromide solutions with heat-transfer additives,” J. Chem. Eng. Data36(1), 96–98 (1991). [CrossRef]
J. C. McDonald, D. C. Duffy, J. R. Anderson, D. T. Chiu, H. Wu, O. J. A. Schueller, and G. M. Whitesides, “Fabrication of microfluidic systems in poly(dimethylsiloxane),” Electrophoresis21(1), 27–40 (2000). [CrossRef] [PubMed]
J. M. K. Ng, I. Gitlin, A. D. Stroock, and G. M. Whitesides, “Components for integrated poly(dimethylsiloxane) microfluidic systems,” Electrophoresis23(20), 3461–3473 (2002). [CrossRef] [PubMed]
J.-H. Chang, K.-D. Jung, E. Lee, M. Choi, and S. Lee, “Microelectrofluidic iris for variable aperture,” Proc. SPIE8252, 82520O, 82520O-6 (2012). [CrossRef]
P. Muller, N. Spengler, H. Zappe, and W. Monch, “An optofluidic concept for a tunable micro-iris,” J. Microelectromech. Syst.19(6), 1477–1484 (2010). [CrossRef]

Anderson, J. R.
Arianpour, A.
Bjurstroem, H.
Bouma, B. E.
Brezinski, M. E.
Chang, J.-H.
Chiu, D. T.
Cho, S. H.
Choi, M.
Darzi, A.
Duffy, D. C.
Ehrenstein, W. H.
Francis, C. S.
Fujimoto, J. G.
Gitlin, I.
Horgan, S.
Huber, J.
Johnson, D.
Jung, K.-D.
Lammens, R.
Lee, E.
Lee, S.
Lo, Y.-H.
McDonald, J. C.
Mintz, Y.
Monch, W.
Muller, P.
Ng, J. M. K.
Pitris, C.
Qiao, W.
Russell, R. C. G.
Schueller, O. J. A.
Schulz, S. N.
Setterwall, F.
Smith, S. G. T.
Southern, J. F.
Spengler, N.
Stroock, A. D.
Stroomer, S.
Taffinder, N.
Talamini, M.
Tearney, G. J.
Tsai, F. S.
Verwey, W. B.
Whitesides, G. M.
Wu, H.
Yao, W.
Zappe, H.

Am. J. Respir. Crit. Care Med.

C. Pitris, M. E. Brezinski, B. E. Bouma, G. J. Tearney, J. F. Southern, and J. G. Fujimoto, “High resolution imaging of the upper respiratory tract with optical coherence tomography: a feasibility study,” Am. J. Respir. Crit. Care Med.157(5 Pt 1), 1640–1644 (1998). [PubMed]

Electrophoresis

J. C. McDonald, D. C. Duffy, J. R. Anderson, D. T. Chiu, H. Wu, O. J. A. Schueller, and G. M. Whitesides, “Fabrication of microfluidic systems in poly(dimethylsiloxane),” Electrophoresis21(1), 27–40 (2000). [CrossRef] [PubMed]
J. M. K. Ng, I. Gitlin, A. D. Stroock, and G. M. Whitesides, “Components for integrated poly(dimethylsiloxane) microfluidic systems,” Electrophoresis23(20), 3461–3473 (2002). [CrossRef] [PubMed]

Ergonomics

W. B. Verwey, S. Stroomer, R. Lammens, S. N. Schulz, and W. H. Ehrenstein, “Comparing endoscopic systems on two simulated tasks,” Ergonomics48(3), 270–287 (2005). [CrossRef] [PubMed]

J. Biomed. Opt.

F. S. Tsai, D. Johnson, C. S. Francis, S. H. Cho, W. Qiao, A. Arianpour, Y. Mintz, S. Horgan, M. Talamini, and Y.-H. Lo, “Fluidic lens laparoscopic zoom camera for minimally invasive surgery,” J. Biomed. Opt.15(3), 030504 (2010). [CrossRef] [PubMed]

J. Chem. Eng. Data

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