ABSTRACT
Institute for Biological and Medical Imaging and Chair for Biological Imaging, Helmholtz Zentrum
M
¨
unchen and Technische Unversit
¨
at M
¨
unchen, Ingolst
¨
adter Landstr. 1, Neuherberg, Germany
12.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
12.2 Optoacoustic Signal Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450
12.3 Optoacoustic Wave Propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
12.4 Instrumentation and Implementations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
12.5 Image Reconstruction and Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455
12.6 Sources of Contrast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459
12.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 468
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470
Key words: molecular imaging, optical imaging, optoacoustic imaging, photoacoustic imaging
Optical imaging at tissue depths of several millimeters to centimeters becomes feasible by operat-
ing in the far-red and near-infrared (NIR) wavelength range, i.e., 630 nm-900 nm. In the NIR, light
absorption by tissue is much lower than in the visible spectrum, as evident by the red appearance of
light seen penetrating tissue after illumination with a white light source [1]. While simple tissue epi-
illumination and transillumination results in an image blurred in appearance due to strong photon
scattering in tissue, optical tomography methods have demonstrated the abilility to quantitatively
resolve fluorescent molecules delivered in vivo in tissues [2, 3] or intrinsic tissue chromophores,
such as hemoglobin concentration [4]. However, optical imaging, even in tomographic mode, is
limited by the scattering of light by tissue cellular interfaces and organelles, resulting in reduced
scattering coefficients of tissue in the range of µ
∼ 10 cm
in the NIR [5]. As a result of photon
scattering, light coming from a collimated laser beam incident on tissue becomes completely diffu-
sive within 1 mm of photon propagation. Tomographic methods only partially resolve the loss in
imaging resolution that derives as a result of photon diffusion in tissue. For example, fluorescence
molecular tomography (FMT), a modality based on detection at several projections of diffuse light
that has propagated several millimeters to centimeters in tissues, achieves spatial resolutions in the
order of 1 mm at depths of approximately 1-2 cm.
