許多重要疾病如腫瘤的研究，皆與血管有著密切的關係。光聲造影為一種基於光聲效應之新穎生醫造影技術，對於微細血管造影來說，此技術最大優點為不需標定的高光學吸收對比且為非侵入式的成像技術，同時可進行血液相關重要參數如血紅素濃度及血氧飽和濃度的功能性造影。在本研究中，我們基於非聚焦式超音波換能器，建立一套可用於微細血管脈絡造影廣視野之光學式掃描光學解析度光聲顯微鏡。傳統的光學解析度光聲顯微鏡，使用機械式掃描及聚焦式超音波換能器來提升系統之訊雜比，但此架構會增加系統成像時間，本研究採光學式掃描來解決此問題。然傳統系統使用的光學物鏡與聚焦式超音波換能器會限制系統之視野，本系統選用非聚焦式超音波換能器增加系統之視野。目前本系統使用超音波換能器的中心頻率10-MHz時，軸向解析度為120um，橫向解析度為4um，視野至少可達2x2 mm2，並可用於活體小鼠耳中微細血管脈絡造影，於活體實驗穿透深度估計可達0.8 mm。未來工作重點將放在系統成像速度提升至即時影像、空間解析度的改進及多波長功能性血管造影上。

Blood vessels play an important role in many significant disease researches such as cancer study. Photoacoustic imaging is a novel bio-imaging modality based on the photoacoustic effect. For micro-vasculature imaging, it owns the advantages of label free high optical absorption contrast and can be performed non-invasively. It also
can provide blood-related functional imaging capability for the measure of total hemoglobin concentration and hemoglobin oxygen saturation. In this thesis, we developed an unfocused ultrasound transducer based laser
scanning optical resolution photoacoustic microscope (OR-PAM) for
extended large field of view (FOV) in vivo micro-vasculature imaging of
small animals. Conventional OR-PAM employs a focused ultrasound
transducer to improve the signal-to-noise ratio and performs mechanical
scanning for imaging. However, mechanical scanning is time-consuming.
Such a problem is solved by optical scanning in this study while the
optical objective lens and focused ultrasound transducer limit the FOV
instead. In our design, the FOV is improved by using an unfocused
ultrasound transducer plus laser scanning. The experimental results
showed that the developed OR-PAM is with axial resolution of 120m
and lateral resolution of 4m when using a 10-MHz unfocused
transducer. The achievable FOV is at least 2x2 mm2. The resolving
power of the system was also demonstrated by imaging the in vivo
micro-vasculature of a mouse ear. The estimated noise-equivalent
penetration depth is 0.8 mm in vivo. Future work will focus on the
improvement of the imaging frame rate and spatial resolution and the
development of multi-wavelength functional micro-vascular imaging.

1 A. G. Bell, “On the Production and Reproduction of Sound by Light,”
American Journal of Science 20, 305-324 (Oct. 1880).
2 M. Xu and L. V. Wang, “Photoacoustic imaging in biomedicine,”
Review of Scientific Instruments 77, 041101 (Apr. 2006).
3 K. Maslov, G. Stoica, and L. V. Wang, “In vivo dark-field
reflection-mode photoacoustic microscopy,” Optics Letters 30, 625–627
(2005).
4 H. F. Zhang, K. Maslov, M. L. Li, G. Stoica, and L. V. Wang, “In vivo
volumetric imaging of subcutaneous microvasculature by photoacoustic
microscopy,” Optics Express 14, 9317–9323 (2006).
5 H. F. Zhang, K. Maslov, G. Stoica, and L. V. Wang, “Imaging acute
thermal burns by photoacoustic microscopy,” Journal of Biomedical
Optics 11, 054033 (2006).
6 J. T. Oh, M. L. Li, H. F. Zhang, K. Maslov, G. Stoica, and L. V. Wang,
“Three-dimensional imaging of skin melanoma in vivo by
dual-wavelength photoacoustic microscopy,” Journal of Biomedical
Optics 11, 034032 (2006).
7 H. F. Zhang, K. Maslov, G. Stoica, and L. V. Wang, “Functional
photoacoustic microscopy for high-resolution and noninvasive in vivo
imaging,” Nat. Biotechnol. 24(7), 848–851 (2006).
8 K. Maslov, H. F. Zhang, S. Hu, and L. V. Wang, “Optical-resolution
photoacoustic microscopy for in vivo imaging of single capillaries,”
Optics Letters 33, 929–931 (2008).
9 S. Hu, K. Maslov, and L. V. Wang, “In vivo functional chronic imaging
of a small animal model using optical-resolution photoacoustic
microscopy,” Medical Physics, 36(6), 2320–2323 (2009).
10 S. Hu, K. Maslov, and L. V. Wang, “Noninvasive label-free imaging of
microhemodynamics by optical-resolution photoacoustic microscopy,”
Optics Express 17(9), 7688-7693 (2009).
11 B. Rao, L. Li, K. Maslov, and L. V. Wang, “Hybrid-scanning
optical-resolution photoacoustic microscopy system for in vivo
vasculature imaging,” Optics Letters 35 (10), 1521–1523 (2010).
12 C. Zhang, K. Maslov, and L. V. Wang, “Subwavelength-resolution
label-free photoacoustic microscopy of optical absorption in vivo”,
Optics Letters 35, 3195–3197 (2010).
13 L. Song, K. Maslov, and L. V. Wang, “Multifocal optical-resolution
photoacoustic microscopy in vivo,” Optics Letters 36(7), 1236–1238
(2011).
14 B. Rao, K. Maslov, A. Danielli, R. Chen, K. K. Shung, Q. Zhou, and L.
V. Wang, “Real-time four-dimensional optical-resolution photoacoustic
microscopy with Au nanoparticle-assisted subdiffraction-limit resolution,”
Optics Letters 36, 1137-1139 (2011).
15 S. Hu, K. Maslov, and L. V. Wang, “Second-generation
optical-resolution photoacoustic microscopy with improved sensitivity
and speed,” Optics Letters 36(7), 1134–1136 (2011).
16 L. V. Wang and S. Hu, “Photoacoustic tomography: in vivo imaging
from organelles to organs,” Science 335, 1458–1462 (2012).
17 G. J. Diebold, T. Sun, and M. I. Khan, “Photoacoustic monopole
radiation in one, two, and three dimensions,” Physical Review Letters 67,
3384-3387 (Dec. 1991).
18 Zhixing Xie, Shuliang Jiao, Hao F. Zhang,1 and Carmen A. Puliafito,
“Laser-scanning optical-resolution photoacoustic microscopy”, Optics
Letters, 34(12): 1771-1773, (2009)
19 Shi, W., Kerr, S., Utkin, I., Ranasinghesagara, J. C., Pan, L., Godwal,
Y., Zemp, R. J. and Fedosejevs, R.,"Optical Resolution Photoacoustic
Microscopy Using Novel High-Repetition-Rate Passively Q-switched
Microchip and Fiber Lasers", J. Biomed. Opt. 15, 056017 (2010)
20 B. Piwakowski, and B. Delannoy, "Method for computing spatial pulse
response: Time-domain approach," J. Acoust. Soc. Am. 86(6), 2422–2432
(1989).
21 M. Xu, and L. V. Wang, "Analytic explanation of spatial resolution
related to bandwidth and detector aperture size in thermoacoustic or
photoacoustic reconstruction", Phys. Rev. E Stat. Nonlin. Soft Matter
Phys. 67(5), 056605 (2003)
22 M. L. Li, Y. C. Tseng, and C. C. Cheng, "Model-based correction of
finite aperture effect in photoacoustic tomography", Optical Express,
18(25) 26285-26292 (2010).
23 ANSI_Z136.1. American national standard for the safe use of lasers.
ANSIZ136.1-2007. Washington, DC: American National Standards
Institute; 2007.
24 D. A. Nedosekin, M. Sarimollaoglu, J. H. Ye, E. I. Galanzha, and V. P.
Zharov, “In vivo ultra-fast photoacoustic flow cytometry of circulating
human melanoma cells using near-infrared high-pulse rate lasers,”
Cytometry Part A 79A(10), 825–833 (2011).
25 Y. N. Billeh, M. Liu, and T. Buma, “Spectroscopic photoacoustic
microscopy using a photonic crystal fiber supercontinuum source,” Opt.
Express 18(18), 18519–18524 (2010).
26 D. Koeplinger, L. Mengyang, and T. Buma, “Photoacoustic
microscopy with a pulsed multi-color source based on stimulated Raman
scattering,” Ultrasonics Symposium (IUS), 2011 IEEE International,
296 – 299, (2011).
27 A. Loya, J. P. Dumas, and T. Buma, “Photoacoustic microscopy with a
tunable source based on cascaded stimulated Raman scattering in a
large-mode area photonic crystal fiber,” in Proceedings of IEEE
Ultrasonics Symposium,(2012 IEEE International), pp.1208–1211.