膠囊內視鏡之成像鏡頭設計

Design of imaging lens in capsule endoscope

陳永霖(Yung-Lin Chen)

指導教授 ： 歐陽盟

國立中央大學/理學院/光電科學研究所/碩士(2006年)

摘要

近年來，使用膠囊內視鏡來檢視消化到病變，是醫學工程上的一大突破，然而膠囊內視鏡普遍面臨到兩個問題，第一為視場角不夠大，第二為成像品質不夠好，這兩個問題可能使醫生無法明確的檢測出病徵，為了解決此問題，所以在本論文中，作者提出了兩種設計，以達到擁有廣視角、並且有良好成像品質的微小型膠囊鏡頭之要求。
設計一為雙片式膠囊鏡頭組，此鏡頭組由一片塑膠非球面鏡片和一片玻璃鏡片所組成，使用256 256 pixel，pixel大小10 m的CMOS感測器，視場角可達到86o，然而卻存在畸變過大的缺點，致使影像變形，有鑑於此，因此作者提出了設計二，以解決此問題。
設計二為三片式膠囊鏡頭組，因為膠囊大小有其限制，所以如果要增加鏡片來達到降低畸變的效果，則膠囊可能因此變大，又因光學保護罩為一幾乎沒有折光的功能的薄殼，而光學保護罩到雙片鏡頭組之間還有約7mm的空間，如果能把光學保護罩做成一片透鏡，不僅不會增加膠囊大小，又可增加透鏡設計的自由度。除此之外，原本雙片式膠囊鏡頭設計，把物面假想為一平面，然而膠囊在腸道內是靠小腸蠕動往前前進，因此物面非一理想平面，而是一曲面，所以此三片式膠囊內視鏡鏡頭的設計，把物面設計為一曲面，更能接近真實的情況。此鏡頭組視場角依然維持86o，但可適用於512 512 pixel數，pixel大小5 m的CMOS感測器，所以不僅成像解析度可以提昇，畸變問題也獲得很大改善。

關鍵字

光學保護罩 ； 膠囊內視鏡 ； 成像鏡頭 ； 畸變 ； 廣視場角

並列摘要

In recent years, using the capsule endoscope to inspect the pathological change of digestive system and intestine had a great break-through on the medical engineering. However, there still existed two main problems in the capsule endoscopes. One is that, the field of view was not wide enough, and the other is that the image quality was not enough well. The drawbacks made medical professionals to examine digestive diseases unclearly and ambiguously. In order to solve these problems, the paper designed two kinds of novel miniature lenses which has a wide angle of field of view and a good quality of imaging.
First design is the lenses employed in the capsule endoscope simply consisted of a piece of plastic aspherical lens and a piece of glass lens and compacted in the 9.8mm (W) X9.8mm (L) X10.7mm (H) size. Taking the white LED light source and the10 umX10um pixel size of CMOS sensor under considerations, the field of view of the lenses could be achieved to 86 degrees, and the MTF to 41% at 50lp/mm of space frequency. And the specification of the designed capsule lens includes effective focal length, back focal length, f-number, total length, image circle, distortion, relative illumination at 1 field, are equal to 1.98mm, 1.52mm, 2.8, 3.49mm, 3.32mm, -26.6%, 48.5%.
Second design is a distortion improvement design with a dome lens, distortion exists in the present capsule endoscope image resulting from the confined space and the wide-angle requirement. Based on the previous two lens works, the optimal design had obtained that the field of view was about 86 degrees , and MTF was about 18% at 100 lp/mm, but distortion would go to -26%. It’s difficult to add another lens on the 7mm optical path between the dome and imaging lenses for improving distortion. In order to overcome this problem, we intend to design the optical dome as another optical lens. The original dome is transparent and has an equal thickness, namely without refracting light almost. Our objective in this paper is to design the inner curvature of the dome and associate two aspheric imaging lenses in front of the CMOS sensors to advance the distortion with maintaining field of view and MTF under the same capsule volume. Furthermore, the paper proposes the real object plane of intestine is nearly a curved surface rather than an ideal flat surface. Taking those reasons under consideration, we design three imaging lenses with curved object plane and obtain the field of view is about 86 degrees , MTF is about 26% at 100 lp/mm, and the distortion improve to -7.5%. Adding the dome lens is not only to enhance the image quality, but also to maintain the tiny volume requirement.

並列關鍵字

Dome lens ； capsule endoscope ； distortion ； MTF ； field of view

參考文獻

[1-3]廖榮聖，”無線膠囊內視鏡影像資訊系統之設計”，中原大學醫學工程研究所碩士論文，民國九十二年

[2-1] Virendra N.Mahajan，”Optical imaging and aberrations ”，SPIE，(1998)

[2-4]許哲源，”手機相機模組之光學設計”，元智大學電機工程研究所碩士論文，民國九十三年

[3-2]王啟雄，”手機取像模組之設計研究”， 元智大學光電工程研究所碩士論文，民國九十四年

[3-3] C-S CHEN，S-G SHIUE and M-H Lu，” Method of solving