Dedicated hardware processor and corresponding system-on-chip design for real-time laser speckle imaging

A prototype system of portable laser speckle imager based on embedded graphics processing unit platform

Laser speckle contrast imaging (LSCI) is a high-resolution full-field optical technique for measuring blood flow, which has been widely used in clinical and biomedical research. However, most of the current LSCI instruments are bulky, limiting their application settings. In this work, we proposed a prototype system of portable laser speckle imager. Different from the desktop laser speckle systems that utilize personal computer (PC), our system was designed with embedded GPU system (Jetson TX2, NVIDIA, USA) and a LCD touch screen (16.5 × 12.4 cm in size, 380 g in weight). In-vivo experiments showed that the portable GPU-based system had comparable performance with our laboratory LSCI system. Such a portable LSCI imager could be potentially used in a situation that requires for easy operation and installation, such as intraoperative monitoring or bedside diagnosis.

Cerebral hemodynamic change and metabolic alteration in severe hemorrhagic shock

Understanding the biological mechanism and identifying biomarkers of hemorrhagic shock is important for diagnosis and treatment. We aim to use optical imaging to study how the cerebral blood circulation and metabolism change during the progression of severe hemorrhagic shock, especially the decompensatory stage. We used a multi-parameter (blood pressure (BP), cerebral blood flow (CBF), functional vascular density (FVD), blood oxygenation and mitochondrial NADH signal) cerebral cortex optical imaging system to observe brain hemodynamic change and metabolic alteration of rats in vivo for 4 h. Cerebral circulation and mitochondrial metabolism could be well preserved in the compensatory stage but impaired during the decompensatory stage. The changes of brain hemodynamics and metabolism may provide sensitive indicators for various shock stages including the transition from compensatory stage to decompensatory stage. Our novel imaging observations of hemodynamic and metabolic signals in vivo indicated that the rat brains under hemorrhagic shock suffered irreversible damage which could not be compensated by the autoregulation mechanism, probably due to injured mitochondria.

Monitoring hemodynamic and metabolic alterations during severe hemorrhagic shock in rat brains

RATIONALE AND OBJECTIVES

Our long-term goals are to identify imaging biomarkers for hemorrhagic shock and to understand how the preservation of cerebral microcirculation works. We also seek to understand how the damage occurs to the cerebral hemodynamics and the mitochondrial metabolism during severe hemorrhagic shock.

MATERIALS AND METHODS

We used a multimodal cerebral cortex optical imaging system to obtain 4-hour observations of cerebral hemodynamic and metabolic alterations in exposed rat cortexes during severe hemorrhagic shock. We monitored the mean arterial pressure, heart rate, cerebral blood flow (CBF), functional vascular density (FVD), vascular perfusion and diameter, blood oxygenation, and mitochondrial reduced nicotinamide adenine dinucleotide (NADH) signals.

RESULTS

During the rapid bleeding and compensatory stage, cerebral parenchymal circulation was protected by inhibiting the perfusion of dural vessels. During the compensatory stage, although the brain parenchymal CBF and FVD decreased rapidly, the NADH signal did not show a significant increase. During the decompensatory stage, FVD and CBF maintained the same low level and the NADH signal remained unchanged. However, the NADH signal showed a significant increase after the rapid blood infusion. FVD and CBF rebounded to the baseline after the resuscitation and then declined again.

CONCLUSIONS

We present for the first time simultaneous imaging of cerebral hemodynamics and NADH signals in vivo during the process of hemorrhagic shock. This novel multimodal method demonstrated clearly that severe hemorrhagic shock imparts irreversible tissue damage that is not compensated by the autoregulatory mechanism. Hemodynamic and metabolic signatures including CBF, FVD, and NADH may be further developed to provide sensitive biomarkers for stage transitions in hemorrhagic shock.

Correcting speckle contrast at small speckle size to enhance signal to noise ratio for laser speckle contrast imaging

In laser speckle contrast imaging, it was usually suggested that speckle size should exceed two camera pixels to eliminate the spatial averaging effect. In this work, we show the benefit of enhancing signal to noise ratio by correcting the speckle contrast at small speckle size. Through simulations and experiments, we demonstrated that local speckle contrast, even at speckle size much smaller than one pixel size, can be corrected through dividing the original speckle contrast by the static speckle contrast. Moreover, we show a 50% higher signal to noise ratio of the speckle contrast image at speckle size below 0.5 pixel size than that at speckle size of two pixels. These results indicate the possibility of selecting a relatively large aperture to simultaneously ensure sufficient light intensity and high accuracy and signal to noise ratio, making the laser speckle contrast imaging more flexible.