Depth-resolved analytical model and correction algorithm for photothermal optical coherence tomography

Abstract

Photothermal OCT (PT-OCT) is an emerging molecular imaging technique that occupies a spatial imaging regime between microscopy and whole body imaging. PT-OCT would benefit from a theoretical model to optimize imaging parameters and test image processing algorithms. We propose the first analytical PT-OCT model to replicate an experimental Ascan in homogeneous and layered samples. We also propose the PT-CLEAN algorithm to reduce phase-accumulation and shadowing, two artifacts found in PT-OCT images, and demonstrate it on phantoms and in vivo mouse tumors.

Imaging Melanin Distribution in the Zebrafish Retina Using Photothermal Optical Coherence Tomography

“…More comparative anatomy is needed before findings from the zebrafish can be generalized to humans. Additionally, shadowing and phase accumulation are two artifacts present in the PT-OCT signal 40 , 41 that will affect the signal intensity as a function of depth. For this reason, it is difficult to precisely quantify the distribution of melanin as a function of depth, and artifacts can be seen on some images (such as Fig.…”

In vivo photothermal optical coherence tomography of endogenous and exogenous contrast agents in the eye

“…During a PT-OCT scan, an additional laser is tuned to the absorption peak of the contrast agent or endogenous absorber, amplitude-modulated over time, and focused onto the sample. The light from the photothermal laser is then absorbed by the contrast agent or endogenous absorber and transformed into heat, which creates a local temperature variation (~1–3 °C) 35 . The temporary increase in temperature causes an elastic expansion of the sample and a local change in index of refraction.…”

Stimulated Raman scattering spectroscopic optical coherence tomography

“…Unfortunately, label-free molecular imaging with SOCT has been limited to a couple of molecules (namely, hemoglobin and melanin). Other variant OCT methods that provide molecular information (e.g., photothermal OCT) rely on exogenous agents (e.g., nanoparticles) [5–8]. Exceptions include pump–probe OCT [9] and second-harmonic OCT [10], which have shown the ability to image melanin and collagen, respectively.…”

“…This process is similar to pump–probe OCT, which has been used to measure amplitude changes from long-lived transient states in melanin and methylene blue [6,22]. This is also similar to photothermal OCT, which looks at phase changes resulting from heating (typically using exogenous agents, such as nanoparticles) [5]. …”

“…It is also important to highlight that because SRS-SOCT relies on coherence gating for imaging, the method possesses the same limitations as most other molecular OCT methods, namely that the information is path-length integrated. However, methods do exists to potentially prevent the accumulation of the molecular signals as a function of the depth [5], which can be explored in the future.…”