Molecular imaging true-colour spectroscopic optical coherence tomography

Abstract

Molecular imaging holds a pivotal role in medicine due to its ability to provide invaluable insight into disease mechanisms at molecular and cellular levels. To this end, various techniques have been developed for molecular imaging, each with its own advantages and disadvantages1–4. For example, fluorescence imaging achieves micrometre-scale resolution, but has low penetration depths and is mostly limited to exogenous agents. Here, we demonstrate molecular imaging of endogenous and exogenous chromophores using a novel form of spectroscopic optical coherence tomography. Our approach consists of using a wide spectral bandwidth laser source centred in the visible spectrum, thereby allowing facile assessment of haemoglobin oxygen levels, providing contrast from readily available absorbers, and enabling true-colour representation of samples. This approach provides high spectral fidelity while imaging at the micrometre scale in three dimensions. Molecular imaging true-colour spectroscopic optical coherence tomography (METRiCS OCT) has significant implications for many biomedical applications including ophthalmology, early cancer detection, and understanding fundamental disease mechanisms such as hypoxia and angiogenesis.

Nano-sensitive optical coherence tomography

“…Light scattering spectroscopy (LSS) was incorporated in OCT for depth resolved nuclear morphology measurements 11,12 . Spectroscopic information was extracted from OCT data 13 , angular resolved low coherence interferometry was demonstrated for the assessment of subcellular features 14 , and molecular imaging was realized 15 . Interferometric synthetic aperture microscopy (ISAM) has been developed to improve the out of focal plane resolution 16 .…”

Nanosensitive optical coherence tomography for the study of changes in static and dynamic structures

“…Light scattering spectroscopy has been used in OCT to study the three-dimensional morphology of the cell nuclei [17,18]. Spectral characteristics of the objects were derived from OCT [19], and the authors of [20] studied molecules. A correlation method for imaging the vascular system has been recently developed at our laboratory [21].…”

Pump-probe nonlinear phase dispersion spectroscopy

“…Recently, a method named nonlinear phase dispersion spectroscopy (NLDS), an extension of spectroscopic OCT [17,18] and spectral-domain phase microscopy [19], has demonstrated the ability to independently assess the real and imaginary parts of the linear refractive index (RI), thus separating the scattering and absorption coefficients [20], and providing a more sensitive measure of absorption in biological samples [21]. In this work, NLDS is extended to assess a sample's nonlinear, real and imaginary, wavelength-dependent optical response to a pump beam (hereafter termed PP-NLDS).…”

“…Equation (18) gives the familiar form of a spectral shift, as previously described in Ref [8], along with a quadratic phase change with respect to frequency. Equation (18) can be further simplified to yield a solution of the resulting probe field that fits the form of Eq. (2).…”