In vivo spectroscopic photoacoustic tomography imaging of a far red fluorescent protein expressed in the exocrine pancreas of adult zebrafish

Abstract

Fluorescent proteins brought a revolution in life sciences and biological research in that they make a powerful tool for researchers to study not only the structural and morphological information, but also dynamic and functional information in living cells and organisms. While green fluorescent proteins (GFP) have become a common labeling tool, red-shifted or even near infrared fluorescent proteins are becoming the research focus due to the fact that longer excitation wavelengths are more suitable for deep tissue imaging. In this study, E2-Crimson, a far red fluorescent protein whose excitation wavelength is 611 nm, was genetically expressed in the exocrine pancreas of adult zebrafish. Using spectroscopic all optical detection photoacoustic tomography, we mapped the distribution of E2-Crimson in 3D after imaging the transgenic zebrafish in vivo using two different wavelengths. With complementary morphological information provided by imaging the same fish using a spectral domain optical coherence tomography system, the E2-Crimson distribution acquired from spectroscopic photoacoustic tomography was confirmed in 2D by epifluorescence microscopy and in 3D by histology. To the authors' knowledge, this is the first time a far red fluorescent protein is imaged in vivo by spectroscopic photoacoustic tomography. Due to the regeneration feature of zebrafish pancreas, this work preludes the longitudinal studies of animal models of diseases such as pancreatitis by spectroscopic photoacoustic tomography. Since the effective penetration depth of photoacoustic tomography is beyond the transport mean free path length, other E2-Crimson labeled inner organs will also be able to be studied dynamically using spectroscopic photoacoustic tomography.

Optical coherence tomography today: speed, contrast, and multimodality

“…AO, analog output; AI, analog input; OPO, optical parametric oscillator; FPI, Fabry-Perot interferometer; Ref, reference arm; DBD, dual-balanced detector; PD, photodiode; Ct, counter; DM, dichroic mirror. 223 …”

Quantitative reconstructions in multi-modal photoacoustic and optical coherence tomography imaging

“…where m = e ω 2 θ3 2 m, using that |ϑ| = 1 and ϑ 1 = 0. The term ω s can be analysed using the inverse explicit expression (23)…”

“…In this work we consider the multi-modal PAT/OCT system, developed for imaging biological tissues, see [10,21,22,23,31]. We show that with such a system, in contrast to the single modality setups, we obtain sufficient measurements which allow us to extract quantitative information on the electric susceptibility and the Grüneisen parameter of the sample.…”

Inverse problems of combined photoacoustic and optical coherence tomography

“…Only recently there have been developed experimental setups that can perform photoacoustic and optical coherence tomography experiments in parallel, see [52] and further developments in [33,34]. Combined setups can be used for imaging biological tissue up to a depth of approximately 5 mm.…”