Abstract

The current fiber-based illumination systems of laparoscopes are unable to uniformly illuminate a large enough area in abdomen due to the limited numerical aperture (NA) of the fiber bundle. Most energy is concentrated in a small region at the center of the illumination area. This limitation becomes problematic in laparoscopes which require capturing a wide field of view. In this paper, we propose an aspherical lens array which is used to direct the outgoing rays from the fiber bundle of laparoscope to produce a more uniformly illuminated, substantially larger field coverage than standalone fiber source. An intensity feedback method is developed to design the aspherical lens unit for extended non-Lambertian sources, which is the key to the design of this lens array. By this method, the lens unit is obtained after only one iteration, and the lens array is constructed by Boolean operation. Then, the ray-tracing technique is used to verify the design. Further, the lens array is fabricated and experimental tests are performed. The results clearly show that the well-illuminated area is increased to about 0.107m2 from 0.02m2 (about 5x larger than a standard fiber illumination source). More details of the internal organs can be clearly observed under this improved illumination condition, which also reflects the significant improvement in the optical performance of the laparoscope.

© 2016 Optical Society of America

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References

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2015 (2)

2014 (2)

2013 (4)

2010 (3)

2008 (1)

2007 (1)

J. Bortz and N. Shatz, “Iterative generalized functional method of nonimaging optical design,” Proc. SPIE 6670, 66700A (2007).
[Crossref]

2002 (1)

1998 (1)

Bäuerle, A.

Benítez, P.

Berens, M.

Bortz, J.

J. Bortz and N. Shatz, “Iterative generalized functional method of nonimaging optical design,” Proc. SPIE 6670, 66700A (2007).
[Crossref]

Bruneton, A.

Cassarly, W. J.

W. J. Cassarly, “Iterative reflector design using a cumulative flux compensation approach,” Proc. SPIE 7652, 76522L (2010).
[Crossref]

F. R. Fournier, W. J. Cassarly, and J. P. Rolland, “Fast freeform reflector generation usingsource-target maps,” Opt. Express 18(5), 5295–5304 (2010).
[Crossref] [PubMed]

Ding, Y.

Feng, Z.

Fournier, F. R.

Gordon, J. M.

Gu, P. F.

Han, Y.

Hua, H.

Li, H.

Liu, P.

Liu, X.

Loosen, P.

Luo, Y.

Meuret, Y.

Miñano, J. C.

Müller, G.

Muschaweck, J.

Nguyen, M.

Qin, Y.

Rabl, A.

Ries, H.

Rolland, J. P.

Shatz, N.

J. Bortz and N. Shatz, “Iterative generalized functional method of nonimaging optical design,” Proc. SPIE 6670, 66700A (2007).
[Crossref]

Stollenwerk, J.

Völl, A.

Wang, K.

Wester, R.

Wu, R.

Xu, L.

Zhang, Y.

Zheng, Z.

Zheng, Z. R.

Appl. Opt. (1)

Biomed. Opt. Express (1)

J. Opt. Soc. Am. A (1)

Opt. Express (6)

Opt. Lett. (4)

Proc. SPIE (2)

J. Bortz and N. Shatz, “Iterative generalized functional method of nonimaging optical design,” Proc. SPIE 6670, 66700A (2007).
[Crossref]

W. J. Cassarly, “Iterative reflector design using a cumulative flux compensation approach,” Proc. SPIE 7652, 76522L (2010).
[Crossref]

Other (1)

R. Liang, Optical Design for Biomedical Imaging (SPIE, 2010).

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Figures (9)

Fig. 1
Fig. 1 Examples of the illumination patterns produced by the current laparoscopes: (a) three laparoscopes with fiber-based illumination systems and three illumination patterns produced by (b) laparoscope 1, (c) laparoscope 2 and (d) laparoscope 3, respectively. The illumination patterns are recorded on an acrylic sheet with the size of 500mm × 500mm at a lighting distance of 150mm. The Stryker X-6000 Xenon Light Source is used here.
Fig. 2
Fig. 2 (a) The normalized intensity distribution of the outgoing beam from the laparoscope 1. The blue dash line represents the measured intensity distribution and the red solid line represents the one obtained from data fitting, which will be used in the lens unit design. (b) Design strategy: an aspherical lens array is placed adjacent to the end surface of the laparoscope to produce a uniform illumination. The dimensions of the end surface of the laparoscope just indicate the limited degree of design freedom left for the subsequent lens design.
Fig. 3
Fig. 3 A feedback method for extended non-Lambertian sources in 3D rotational geometry.
Fig. 4
Fig. 4 (a) Due to the limitation of one single aspherical surface and the Monte Carlo raytracing, there will be a region of abrupt intensity change near βC. (b) γmax represents the maximum direction angle of the ray from point S1 after the refraction of the entrance surface (That is, γmax satisfies nsinγmax = sinθmax.) and βm is the direction angle of ray 6. The direction angle of ray 5 also equals βm. Due to the limitation of one single aspherical surface, we have the fact that γjmax, and βm<βmax. Plus, an arbitrary ray emitted from S2 with a direction angle between γj<θmax will take a resulting direction angle between βm<β<βk (βk is the direction angle of the ray 7. Usually, βk>βmax) [14].
Fig. 5
Fig. 5 (a) Normalized intensity distribution. (b) The target intensity distribution used in the initial design and the 1st iteration. (c) The illumination pattern obtained from Monte Carlo ray-tracing. (d) The illuminance distribution along the line y = 0mm. (e) The profile of the lens unit which is a spline curve passing through a set of discrete data points and (f) the Boolean operation. 15 lens units are used here.
Fig. 6
Fig. 6 The illuminance distributions along the line y = 0 mm on the target plane at a lighting distance of 150 mm produced by the lens array, the diffuser element and the annular lens, respectively.
Fig. 7
Fig. 7 Misalignment and tolerancing analyses. (a) The influence of misalignment between the aperture and the lens unit on the performance of the illumination system. (b) The influence of fabrication errors of the aperture array on the performance of the illumination system. (c) The fitting deviation is used to simulate the fabrication errors which may be present in fabricating the lens array. (d) The influence of fabrication errors of the lens unit on the performance of the illumination system.
Fig. 8
Fig. 8 (a) The fabricated lens, and (b) the illumination pattern produced by the updated illumination system on an acrylic sheet at a lighting distance of 150mm. (c) The normalized illuminance distribution and (d) the normalized intensity distribution produced by the updated illumination system.
Fig. 9
Fig. 9 Comparisons between the optical performance of the initial laparoscope and that of the updated laparoscope. (a) The normalized illuminance distribution and (b) the normalized intensity distribution. (c) The organ model cannot be well illuminated by the initial illumination system, and most part of the organ model cannot be clearly observed, especially at the center and the edge of the model. (d) The organ model is well illuminated by the updated illumination system, and the whole model can be clearly observed.

Tables (1)

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Table 1 Design parameters.

Equations (4)

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η i ( β )= I t ( β ) / I i ( β ), 0β β C
I t( i+1 ) ( β )= I t ( β )× j=0 i η j ( β ), 0β β C
I t( i+1 ) ( β )= a 2 β 4 + a 1 β 2 + a 0 , 0β β max
RMS= 1 N k1=1 N ( I ak1 I tk1 I tk1 ) 2

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