Imaging the electro-kinetic response of biological tissues with optical coherence tomography

Abstract

We demonstrate the feasibility of using optical coherence tomography (OCT) to detect and image an electro-kinetic response: electric-field induced optical changes (EIOC) in soft biological tissues. A low-frequency electric field was applied to ex vivo samples of porcine heart tissues, while OCT signals were acquired continuously. Experimental results show that the amplitude of the OCT signal change is proportional to the amplitude and inversely proportional to the frequency of the applied electric field. We show that the nonconductive component of the sample was eliminated in the normalized EIOC image. To the best our knowledge, this is the first time a two-dimensional image related to the electro-kinetic response of soft tissues is obtained with depth resolution. Since electro-kinetic properties can change during cancerogenesis, EIOC imaging can potentially be used for cancer detection.

Imaging the electro-kinetic response of biological tissues with phase-resolved optical coherence tomography

“…Averaging of many frames simply filters out much of the useful signal phase which becomes close to zero ( Figure 6B). However, phase images obtained after angular de-trending procedure ( Figure 6C) and carrying the information about the local phase variations, reflect the local structural features of tissue (somewhat analogous to the amplitude image demonstrated in [13]). A 1-mm diameter dielectric (i.e., electrically insulating) optical fiber, seen in the middle of the sample in Figure 6C, was inserted at an arbitrary angle to represent a negative control in order to verify the ability of the technique to image the electro-kinetic properties of tissue.…”

“…The five points smoothing range was selected such as not to exceed [-π; π] range of the resulting angular detrended phase. The rest of the signal processing algorithm shown in Figure 3 to obtain the EIOC phase image (steps 5-8) was similar to our previous work on OCT signal amplitude analysis [13]. Briefly, for each pixel's angular de-trended phase in time, the temporal de-trending procedure was applied to eliminate the slow trend in the signal, and thus filter out the spurious frequencies in the spectrum obtained in the following step.…”

“…The detected signal oscillations were likely caused by the field-shifted tissue interstitial fluids, which may change light scattering and absorbance by affecting the mutual alignment of collagen fibrils [12]. Further investigations [13] revealed that the amplitude of the OCT signal change varied with the magnitude of the applied field and was inversely proportional to its frequency. More recently, Peña et al [14] used OCT amplitude images to visualize the propagation of low-frequency electric field in tissue samples ex vivo, invoking the mechanism of electrically induced optical changes (EIOC) related to the electrokinetic properties of tissue [14].…”

Monitoring of interaction of low-frequency electric field with biological tissues upon optical clearing with optical coherence tomography

“…13 In the current paper, we present the results of further OCT studies of the electro-kinetic response of biological tissues influenced by a low-frequency electric field at normal conditions and upon the topical application of optical clearing agents (OCAs). [19][20][21][22][23] Therefore, following the results of recent studies of the interaction of lowfrequency electric fields with biological tissues by OCT, 13,24 we apply a 50% glycerol solution in water as an OCA to enhance the image contrast and possibly observe the spatial distribution of the electric field within the tissues. Topical application of OCAs enhances light penetration depth and significantly increases the OCT image contrast.…”

Lorentz force optical coherence elastography

“…Since the pulse duration was only 1.5 ms, Joule heating should be negligible. 23 However, the interaction between an electric field and tissue is a complicated process, which has been previously investigated using OCT. 24,25 The electrical field change may cause various electro-kinetic responses such as electric field-induced mechanical changes, especially in vivo. Due the relatively weak and short duration of the electric field, these changes are typically confined locally to the excitation position, but this deserves further investigation.…”