Optical coherence tomography: a new strategy to image planarian regeneration

In Vivo Imaging of Newt Lens Regeneration: Novel Insights Into the Regeneration Process

Purpose

To establish optical coherence tomography (OCT) as an in vivo imaging modality for investigating the process of newt lens regeneration.

Methods

Spectral-domain OCT was employed for in vivo imaging of the newt lens regeneration process. A total of 37 newts were lentectomized and followed by OCT imaging over the course of 60 to 80 days. Histological images were obtained at several time points to compare with the corresponding OCT images. Volume measurements were also acquired.

Results

OCT can identify the key features observed in corresponding histological images based on the scattering differences from various eye tissues, such as the cornea, intact and regenerated lens, and the iris. Lens volume measurements from three-dimensional OCT images showed that the regenerating lens size increased linearly until 60 days post-lentectomy.

Conclusions

Using OCT imaging, we were able to track the entire process of newt lens regeneration in vivo for the first time. Three-dimensional OCT images allowed us to volumetrically quantify and visualize the dynamic spatial relationships between tissues during the regeneration process. Our results establish OCT as anin vivo imaging modality to track/analyze the entire lens regeneration process from the same animal.

Translational Relevance

Lens regeneration in newts represents a unique example of vertebrate tissue plasticity. Investigating the cellular and morphological events that govern this extraordinary process in vivo will advance our understanding and shed light on developing new therapies to treat blinding disorders in higher vertebrates.

Time-resolved monitoring of biofouling development on a flat sheet membrane using optical coherence tomography

Biofouling on a membrane leads to significant performance decrease in filtration processes. In this study, an optical coherence tomography (OCT) was used to perform a time-resolved analysis of dynamic biofouling development on a submerged membrane under continuous operation. A real-time change in the biofouling morphology was calculated through the image analysis of OCT scans. Three videos were generated through the acquisition of serial static images. This is the first study that displays the dynamic biofouling formation process as a video. The acquisition of OCT cross-sectional scans of the biofouling allowed to evaluate the time-lapsed evolution for three different time periods (early stage, double layers and long-term). Firstly, at the early filtration stage, membrane coverage and average biofouling layer thickness were found to be linearly correlated with the permeate flux pattern. Secondly, after 3 d of operation, an anomalous morphology was observed, constituted by a double-layered biofouling structure: denser on the bottom and looser on the top. In a long-term operation, the biofouling structure underwent a dynamic evolution over time, resulting in a multi-layered structure. The biofouling formation information was closely associated with filtration performance (i.e. flux) indicating the suitability of OCT as real-time and in-situ biofouling monitoring technique.

Diagnosis of subglottic stenosis in a rabbit model using long-range optical coherence tomography

OBJECTIVES/HYPOTHESIS

Current imaging modalities lack the necessary resolution to diagnose subglottic stenosis. The aim of this study was to use optical coherence tomography (OCT) to evaluate nascent subglottic mucosal injury and characterize mucosal thickness and structural changes using texture analysis in a simulated intubation rabbit model.

STUDY DESIGN

Prospective animal study in rabbits.

METHODS

Three-centimeter-long sections of endotracheal tubes (ETT) were endoscopically placed in the subglottis and proximal trachea of New Zealand White rabbits (n = 10) and secured via suture. OCT imaging and conventional endoscopic video was performed just prior to ETT segment placement (day 0), immediately after tube removal (day 7), and 1 week later (day 14). OCT images were analyzed for airway wall thickness and textural properties.

RESULTS

Endoscopy and histology of intubated rabbits showed a range of normal to edematous tissue, which correlated with OCT images. The mean airway mucosal wall thickness measured using OCT was 336.4 μm (day 0), 391.3 μm (day 7), and 420.4 μm (day 14), with significant differences between day 0 and day 14 (P = .002). Significance was found for correlation and homogeneity texture features across all time points (P < .05).

CONCLUSIONS

OCT is a minimally invasive endoscopic imaging modality capable of monitoring progression of subglottic mucosal injury. This study is the first to evaluate mucosal injury during simulated intubation using serial OCT imaging and texture analysis. OCT and texture analysis have the potential for early detection of subglottic mucosal injury, which could lead to better management of the neonatal airway and limit the progression to stenosis.

LEVEL OF EVIDENCE

NA Laryngoscope, 127:64-69, 2017.

Functional imaging for regenerative medicine

In vivo imaging is a platform technology with the power to put function in its natural structural context. With the drive to translate stem cell therapies into pre-clinical and clinical trials, early selection of the right imaging techniques is paramount to success. There are many instances in regenerative medicine where the biological, biochemical, and biomechanical mechanisms behind the proposed function of stem cell therapies can be elucidated by appropriate imaging. Imaging techniques can be divided according to whether labels are used and as to whether the imaging can be done in vivo. In vivo human imaging places additional restrictions on the imaging tools that can be used. Microscopies and nanoscopies, especially those requiring fluorescent markers, have made an extraordinary impact on discovery at the molecular and cellular level, but due to their very limited ability to focus in the scattering tissues encountered for in vivo applications they are largely confined to superficial imaging applications in research laboratories. Nanoscopy, which has tremendous benefits in resolution, is limited to the near-field (e.g. near-field scanning optical microscope (NSNOM)) or to very high light intensity (e.g. stimulated emission depletion (STED)) or to slow stochastic events (photo-activated localization microscopy (PALM) and stochastic optical reconstruction microscopy (STORM)). In all cases, nanoscopy is limited to very superficial applications. Imaging depth may be increased using multiphoton or coherence gating tricks. Scattering dominates the limitation on imaging depth in most tissues and this can be mitigated by the application of optical clearing techniques that can impose mild (e.g. topical application of glycerol) or severe (e.g. CLARITY) changes to the tissue to be imaged. Progression of therapies through to clinical trials requires some thought as to the imaging and sensing modalities that should be used. Smoother progression is facilitated by the use of comparable imaging modalities throughout the discovery and trial phases, giving label-free techniques an advantage wherever they can be used, although this is seldom considered in the early stages. In this paper, we will explore the techniques that have found success in aiding discovery in stem cell therapies and try to predict the likely technologies best suited to translation and future directions.