Monitoring blood-flow in the mouse cochlea using an endoscopic laser speckle contrast imaging system

Multimodal imaging of laser speckle contrast imaging combined with mosaic filter-based hyperspectral imaging for precise surgical guidance

OBJECTIVE

To enable a real-time surgical guidance system that simultaneously monitors blood vessel perfusion, oxygen saturation, thrombosis, and tissue recovery by combining multiple optical imaging techniques into a single system: visible imaging, mosaic filter-based snapshot hyperspectral imaging (HSI), and laser speckle contrast imaging (LSCI).

METHODS

The multimodal optical imaging system was demonstrated by clamping blood vessels in the small intestines of rats to create areas of restricted blood flow. Subsequent tissue damage and regeneration were monitored during procedures. Using LSCI, vessel perfusion was measured, revealing the biological activity and survival of organ tissues. Blood oxygen saturation was monitored using HSI in the near-infrared region. Principal component analysis was used over the spectral dimension to identify an HSI wavelength combination optimized for hemodynamic biomarker visualization. HSI and LSCI were complimentary, identifying thrombus generation and tissue recovery, which was not possible in either modality alone.

RESULTS AND CONCLUSION

By analyzing multimodal tissue information from visible imaging, LSCI perfusion imaging, and HSI, a recovery prognosis could be determined based on the blood supply to the organ. The unique combination of the complementary imaging techniques into a single surgical microscope holds promise for improving the real-time determination of blood supply and tissue prognosis during surgery.

SIGNIFICANCE

Precise real-time monitoring for vascular anomalies promises to reduce the risk of organ damage in precise surgical operations such as tissue resection and transplantation. In addition, the convergence of label-free imaging technologies removes delays associated with the injection and diffusion of vascular monitoring dyes.

Ninjinyoeito Has a Protective Effect on the Auditory Nerve and Suppresses the Progression of Age-Related Hearing Loss in Mice

Currently, there are limited reports available regarding the treatment and prevention of progressive age-related hearing loss. This is because age-related hearing loss is not a critical disease with direct fatalities and has several well-established countermeasures such as hearing aids and cochlear implants. This study evaluated the efficacy of Ninjinyoeito (NYT) in the treatment of age-related hearing loss. C57BL/6J mice were divided into three groups: baseline group, untreated group, and NYT-treated group, with the latter receiving NYT treatment for 2 months. The mice were fed with NYT extract mixed with 4% mouse normal chow. Hearing loss was confirmed by a reduction in intact cell density of the auditory nerve from the age of 5–7 months. The suppression of hearing loss with aging and decrease in the intact cell density of the auditory nerve were significant in mice fed with NYT for 2 months. NYT has been reported to improve blood flow and enhance mitochondrial activity and may exert its protective effects on spiral neurons through these mechanisms. There was no decrease in the size of the stria vascularis from the age of 5–7 months in C57BL/6J mice. The present model failed to reveal the effect of NYT on atrophy of the stria vascularis of the cochlear duct. In conclusion, NYT appears to have a protective effect on the auditory nerve and suppress the progression of age-related hearing loss by reducing age-related auditory nerve degeneration.

Non-invasive postoperative monitoring of pedicled rat skin flap using laser speckle contrast imaging

PURPOSE

This study used non-invasive laser speckle contrast imaging (LSCI) modality to evaluate the blood flow changes in murine flap model and to investigate the clinical feasibility of the LSCI for postoperative monitoring.

METHODS

Ten of 6-8 weeks old Spraque-Dawley rats with superficial inferior epigastric vessel based pedicled skin flaps were used in this experiment. The color changes of skin flap were evaluated by naked eyes and the LSCI modality 6, 24, and 48 h after surgery.

RESULTS

In vessel ligated region of skin flap, skin color began to change to a bluish color immediately postoperatively. At 24 h postoperatively, skin necrosis was detectable with the naked eye and total necrosis occurred at 48 h postoperatively. Changes in laser speckle signal were consistent with changes observed with the naked eye, and blood flow index also presented significant differences between the ligated and non-ligated region.

CONCLUSION

These correlated laser speckle signal patterns suggest that non-invasive monitoring of perfusion by LSCI is a useful technology that may be used to identify the ischemic skin flap.

Velocity measurements with structured light transmitted through a multimode optical fiber using digital optical phase conjugation

Lensless fiber microendoscopes enable optical diagnostics and therapy with minimal invasiveness. Because of their small diameters, multimode fibers are ideal candidates, but mode scrambling hinders the transmission of structured light fields. We present the generation of a localized fringe system at variable distances from the distal fiber end by exploiting digital optical phase conjugation. The replayed fringe system was used for quantitative metrology. Velocity measurements of a microchannel flow in the immediate proximity of the fiber end without the use of any imaging lenses are shown. Lensless multimode fiber systems are of interest especially for biomedical imaging and stimulation as well as technical inspection and flow measurements.

Clinical applications of laser speckle contrast imaging: a review

When a biological tissue is illuminated with coherent light, an interference pattern will be formed at the detector, the so-called speckle pattern. Laser speckle contrast imaging (LSCI) is a technique based on the dynamic change in this backscattered light as a result of interaction with red blood cells. It can be used to visualize perfusion in various tissues and, even though this technique has been extensively described in the literature, the actual clinical implementation lags behind. We provide an overview of LSCI as a tool to image tissue perfusion. We present a brief introduction to the theory, review clinical studies from various medical fields, and discuss current limitations impeding clinical acceptance.

Dual-display laparoscopic laser speckle contrast imaging for real-time surgical assistance

Laser speckle contrast imaging (LSCI) utilizes the speckle pattern of a laser to determine the blood flow in tissues. The current approaches for its use in a clinical setting require a camera system with a laser source on a separate optical axis making it unsuitable for minimally invasive surgery (MIS). With blood flow visualization, bowel viability, for example, can be determined. Thus, LSCI can be a valuable tool in gastrointestinal surgery. In this work, we develop the first-of-its-kind dual-display laparoscopic vision system integrating LSCI with a commercially available 10mm rigid laparoscope where the laser has the same optical axis as the laparoscope. Designed for MIS, our system permits standard color RGB, label-free vasculature imaging, and fused display modes. A graphics processing unit accelerated algorithm enables the real-time display of three different modes at the surgical site. We demonstrate the capability of our system for imaging relative flow rates in a microfluidic phantom with channels as small as 200 μm at a working distance of 1-5 cm from the laparoscope tip to the phantom surface. Using our system, we reveal early changes in bowel perfusion, which are invisible to standard color vision using a rat bowel occlusion model. Furthermore, we apply our system for the first time for imaging intestinal vasculature during MIS in a swine.

Laser speckle contrast imaging of blood flow in the deep brain using microendoscopy

Poor blood flow circulation can occur in the subcortical regions of the brain in many brain diseases. However, the limitations of light penetration imaging techniques hinder the detection of blood flow in deep brain tissues in vivo. Hence, in this Letter, we present a gradient index lens-based laser speckle contrast imaging system for time-lapse blood flow detection in subcortical regions of the brain. We monitored the hemodynamic changes in the thalamus of mouse models of acute hypoxia and transient middle cerebral artery occlusion as a proof of concept for practical applications.