Speckle reduction in quantitative phase imaging by generating spatially incoherent laser field at electroactive optical diffusers.

We studied quantitative phase imaging (QPI) using coherent laser illumination coupled with static and moving optical diffusers. The spatial coherence of a continuous-wave laser was controlled by tuning the particle size and the diffusion angle of optical diffusers for speckle-reduced 3D phase imaging of transparent objects. We used a common-path QPI configuration to investigate the coherent phase mapping of polystyrene micro-beads and breast cancer cells (MCF-7) under different degrees of coherent speckles. The proposed speckle reduction method could provide an avenue for enhancing lateral resolution and suppressing coherent artifacts of the phase images from QPI.

Label-free quantitative measurement of cardiovascular dynamics in a zebrafish embryo using frequency-comb-referenced-quantitative phase imaging.

SIGNIFICANCE: Real-time monitoring of the heart rate and blood flow is crucial for studying cardiovascular dysfunction, which leads to cardiovascular diseases. AIM: This study aims at in-depth understanding of high-speed cardiovascular dynamics in a zebrafish embryo model for various biomedical applications via frequency-comb-referenced quantitative phase imaging (FCR-QPI). APPROACH: Quantitative phase imaging (QPI) has emerged as a powerful technique in the field of biomedicine but has not been actively applied to the monitoring of circulatory/cardiovascular parameters, due to dynamic speckles and low frame rates. We demonstrate FCR-QPI to measure heart rate and blood flow in a zebrafish embryo. FCR-QPI utilizes a high-speed photodetector instead of a conventional camera, so it enables real-time monitoring of individual red blood cell (RBC) flow. RESULTS: The average velocity of zebrafish's RBCs was measured from 192.5 to 608.8 µm / s at 24 to 28 hour-post-fertilization (hpf). In addition, the number of RBCs in a pulsatile blood flow was revealed to 16 cells/pulse at 48 hpf. The heart rates corresponded to 94 and 142 beats-per-minute at 24 and 48 hpf. CONCLUSIONS: This approach will newly enable in-depth understanding of the cardiovascular dynamics in the zebrafish model and possible usage for drug discovery applications in biomedicine.

Optical coherence tomography-guided laser marking with tethered capsule endomicroscopy in unsedated patients.

Tethered capsule endomicroscopy (TCE) is an emerging screening technology that comprehensively obtains microstructural OCT images of the gastrointestinal (GI) tract in unsedated patients. To advance clinical adoption of this imaging technique, it will be important to validate TCE images with co-localized histology, the current diagnostic gold standard. One method for co-localizing OCT images with histology is image-targeted laser marking, which has previously been implemented using a driveshaft-based, balloon OCT catheter, deployed during endoscopy. In this paper, we present a TCE device that scans and targets the imaging beam using a low-cost stepper motor that is integrated inside the capsule. In combination with a 4-laser-diode, high power 1430/1450 nm marking laser system (800 mW on the sample and 1s pulse duration), this technology generated clearly visible marks, with a spatial targeting accuracy of better than 0.5 mm. A laser safety study was done on swine esophagus ex vivo, showing that these exposure parameters did not alter the submucosa, with a large, 4-5x safety margin. The technology was demonstrated in living human subjects and shown to be effective for co-localizing OCT TCE images to biopsies obtained during subsequent endoscopy.

Non-endoscopic biopsy techniques: a review.

INTRODUCTION: Diseases of the stomach and small intestine account for approximately 20% of all gastrointestinal (GI)-related mortality. Biopsy of the stomach and small intestine remains a key diagnostic tool for most of the major diseases that affect the GI tract. While endoscopic means for obtaining biopsy is generally the standard of care, it has several limitations that make it less ideal for pediatric patients and in low resource areas of the world. Therefore, non-endoscopic means for obtaining biopsy samples is of interest in these settings. Areas covered: We review non-endoscopic biopsy techniques reported thus far, and critically examine their merits and demerits regarding their suitability for obtaining biopsy samples in non-sedated subjects. Expert commentary: Esophagogastroduodenoscopy (EGD) is the current standard for acquiring biopsy from the GI tract, however, its limitations include subject sedation, expensive endoscopy infrastructure, expert personnel, and a small but significant risk of complications. A less costly, minimally-invasive and non-endoscopic means for obtaining biopsy samples is therefore of interest for addressing these issues. Such a technology would be of significant impact in low- and middle-income countries where conducting endoscopy is challenging.

High-brightness laser imaging with tunable speckle reduction enabled by electroactive micro-optic diffusers.

High coherence of lasers is desirable in high-speed, high-resolution, and wide-field imaging. However, it also causes unavoidable background speckle noise thus degrades the image quality in traditional microscopy and more significantly in interferometric quantitative phase imaging (QPI). QPI utilizes optical interference for high-precision measurement of the optical properties where the speckle can severely distort the information. To overcome this, we demonstrated a light source system having a wide tunability in the spatial coherence over 43% by controlling the illumination angle, scatterer's size, and the rotational speed of an electroactive-polymer rotational micro-optic diffuser. Spatially random phase modulation was implemented for the lower speckle imaging with over a 50% speckle reduction without a significant degradation in the temporal coherence. Our coherence control technique will provide a unique solution for a low-speckle, full-field, and coherent imaging in optically scattering media in the fields of healthcare sciences, material sciences and high-precision engineering.