Combined Transcranial Doppler and Melatonin Levels to Predict Delayed Cerebral Ischemia After Subarachnoid Hemorrhage.

OBJECTIVE: To investigate the early prediction value of transcranial Doppler ultrasound (TCD) combined with serum melatonin level for delayed cerebral ischemia (DCI) caused by subarachnoid hemorrhage (SAH). METHODS: This paper is a prospective study. A total of 120 patients with SAH treated were included. The patients were divided into the DCI group (40 cases) and non-DCI group (80 cases) according to whether DCI occurred 14 days after SAH (DCI usually occurs 4 to 14 d after bleeding). Baseline data, serum melatonin level, and TCD test results within 24 hours after admission were compared between the 2 groups. Multivariate logistic analysis was used to analyze the factors affecting the occurrence of DCI after SAH. The value of serum melatonin level, middle cerebral artery mean blood flow velocity (MBFV) and their combination in predicting DCI in SAH patients was evaluated. RESULTS: Univariate analysis showed that there were statistically significant differences in the proportion of Fisher grade, Hunt-Hess grade, serum melatonin level, middle cerebral artery systolic blood flow velocity (Vs), MBFV and pulse index (PI) between the 2 groups ( P <0.05). Serum melatonin levels, middle cerebral artery Vs, MBFV, and PI in the DCI group were higher than those in non-DCI group. Logistic regression (LR) analysis showed that serum melatonin level (OR=1.796, 95% CI: 1.575-4.123) and middle cerebral artery MBFV (OR=3.279, 95% CI: 2.112-4.720] were the influencing factors for DCI in SAH patients ( P <0.05). CONCLUSION: Middle cerebral artery MBFV and serum melatonin levels were higher in patients with SAH complicated with DCI, and the combination of the 2 could provide a reference for early clinical prediction of DCI in patients with aneurysmal subarachnoid hemorrhage (aSAH).

Securing 2D information carriers over dynamic and turbulent media in a free-space optical channel.

In this Letter, a new, to the best of our knowledge, scheme is proposed to realize high-fidelity secured free-space optical information transmission through dynamic and turbulent media by encoding 2D information carriers. The data are transformed into a series of 2D patterns as information carriers. A novel differential method is developed to suppress noise, and a series of random keys are also generated. A different number of absorptive filters are arbitrarily combined to be placed in the optical channel to generate ciphertext with high randomness. It is experimentally demonstrated that the plaintext can be retrieved only when correct security keys are applied. Experimental results demonstrate that the proposed method is feasible and effective. The proposed method provides an avenue for securing high-fidelity optical information transmission over dynamic and turbulent media in a free-space optical channel.

Optical analog-signal transmission system in a dynamic and complex scattering environment using binary encoding with a modified differential method.

High-fidelity optical transmission through dynamic scattering media is challenging, since transmission errors are induced due to dynamic scattering media. In this paper, a new scheme is proposed to realize high-fidelity free-space optical analog-signal transmission in dynamic and complex scattering environments using binary encoding with a modified differential method. Each pixel of an analog signal to be transmitted is first divided into two values, and each of them is encoded into a random matrix. Then, a modified error diffusion algorithm is utilized to transform the random matrix into a 2D binary array. Each pixel of the analog signal to be transmitted is eventually encoded into only two 2D binary arrays, and transmission errors and dynamic scaling factors induced by dynamic and complex scattering media can be temporally corrected. Dynamic smoke and non-line-of-sight (NLOS) are created as a dynamic and complex scattering environment to verify the proposed method. It is experimentally demonstrated that analog signals retrieved at the receiving end are always of high fidelity using the proposed method, when average path loss (APL) is less than 29.0 dB. Only the half number of measurements is used compared to that in conventional methods. The proposed method could open up a novel research perspective for high-fidelity free-space optical analog-signal transmission through dynamic and complex scattering media.

Optical data transmission through highly dynamic and turbid water using dynamic scaling factors and single-pixel detector.

Free-space optical data transmission through non-static scattering media, e.g., dynamic and turbid water, is challenging. In this paper, we propose a new method to realize high-fidelity and high-robustness free-space optical data transmission through highly dynamic and turbid water using a series of dynamic scaling factors to correct light intensities recorded by a single-pixel bucket detector. A fixed reference pattern is utilized to obtain the series of dynamic scaling factors during optical data transmission in free space. To verify the proposed method, different turbidity levels, different strengths of water-flow-induced turbulence and a laser with different wavelengths are studied in optical experiments. It is demonstrated that the proposed scheme is robust against water-flow-induced turbulence and turbid water, and high-fidelity free-space optical information transmission is realized at wavelengths of 658.0 nm and 520.0 nm. The proposed method could shed light on the development of high-fidelity and high-robustness free-space optical data transmission through highly dynamic and turbid water.

High-fidelity temporally-corrected transmission through dynamic smoke via pixel-to-plane data encoding.

We propose a new approach for high-fidelity free-space optical data transmission through dynamic smoke using a series of 2D arrays of random numbers as information carriers. Data to be transmitted in dynamic smoke environment is first encoded into a series of 2D arrays of random numbers. Then, the generated 2D arrays of random numbers and the fixed reference pattern are alternately embedded into amplitude-only spatial light modulator, and are illuminated to propagate through dynamic smoke in free space. Real-time optical thickness (OT) is calculated to describe temporal change of the properties of optical wave in dynamic smoke environment, and transmission noise and errors caused by dynamic smoke are temporally suppressed or corrected. Optical experiments are conducted to analyze the proposed method using different experimental parameters in various scenarios. Experimental results fully verify feasibility and effectiveness of the proposed method. It is experimentally demonstrated that irregular analog signals can always be retrieved with high fidelity at the receiving end by using the proposed method, when average optical thickness (AOT) is lower than 2.5. The proposed method also shows high robustness against dynamic smoke with different concentrations. The proposed method could open up an avenue for high-fidelity free-space optical data transmission through dynamic smoke.

Physically-secured high-fidelity free-space optical data transmission through scattering media using dynamic scaling factors.

In this paper, we propose a method of physically-secured high-fidelity free-space optical data transmission through scattering media using physically- and dynamically-generated scaling factors. Optical channel characteristics are explored, and scaling factors are physically and dynamically generated to serve as security keys in the developed free-space optical data transmission system. The generated dynamic scaling factors provide a security layer for free-space optical data transmission. To the best of our knowledge, it is the first time to physically and dynamically generate scaling factors in free-space optical data transmission system to realize data encryption. The scaling factors existing in free-space optical data transmission channel are physically and dynamically controlled by using two optical devices, i.e., variable beam attenuator (VBA) and amplitude-only spatial light modulator (SLM). Nonlinear and dynamic variation of scaling factors is realized in different free-space wave propagation environments. It is experimentally demonstrated that high security can be guaranteed in the developed physically-secured high-fidelity free-space optical data transmission system, since one random scaling factor is physically and dynamically generated for the transmission of each signal pixel value. In addition, the proposed physically-secured free-space optical data transmission scheme is robust to noise and scattering, and high-fidelity signals are retrieved at the receiving end. The proposed method could open up a new research perspective for the secured free-space optical data transmission.

Physically-enhanced ghost encoding.

In this Letter, we propose a physically enhanced ghost encoding scheme that is realized by exploring optical channel characteristics, i.e., physically and dynamically generated scaling factors. It is found that scaling factors can be physically and dynamically generated to serve as security keys in a ghost encoding scheme, dramatically enlarging the key space and enhancing the security of optical ghost encoding schemes. To the best of our knowledge, this is the first time that dynamic scaling factors have been controlled in the optical path to realize physically enhanced ghost encoding. In addition to the illumination patterns used in optical ghost encoding schemes, the proposed method applies a variable beam attenuator and an amplitude-only spatial light modulator (SLM) to physically generate dynamic scaling factors as keys. Nonlinear variation of scaling factors is achieved in different free-space wave-propagation environments in the proposed method. A series of optical experiments are conducted to verify the feasibility and effectiveness of the proposed physically enhanced ghost encoding scheme. The proposed method could open up new research perspectives in optical ghost encoding.

Non-line-of-sight optical information transmission through turbid water.

In this paper, a new and robust method is proposed to realize high-fidelity non-line-of-sight (NLOS) optical information transmission through turbid water around a corner. A series of 2D random amplitude-only patterns are generated by using the zero-frequency modulation method, which are used as optical information carriers. The laser beam modulated by random amplitude-only patterns propagates through turbid water, and the wave diffused by turbid water is further reflected around a corner. A single-pixel detector is used to collect light intensity at the receiving end. To demonstrate feasibility and effectiveness of the proposed NLOS free-space optical information transmission system, many optical experiments are conducted. The proposed method is fully verified by using different turbid water conditions, different separation distances around a corner and different detection angles of the single-pixel detector. Optical experimental results demonstrate that the proposed method is able to achieve high fidelity and high robustness for free-space optical information transmission through turbid water. Even when there is an obstacle behind turbid water, high-fidelity free-space optical information transmission is still realized by using the proposed method. In addition, the proposed method possesses a wide detection range at the receiving end, which is of great significance in practical applications. The proposed method is a promising application for NLOS free-space optical information transmission.

Optical hiding based on single-input multiple-output and binary amplitude-only holograms via the modified Gerchberg-Saxton algorithm.

Optics has provided a promising means for the development of information hiding in recent years. However, conventional optical information hiding systems can only hide a limited number of images, and optical implementation complexity is usually high in conventional methods. In this paper, we propose a new scheme to implement optical information hiding based on single-input multiple-output (SIMO) and binary amplitude-only holograms (AOHs) using the modified Gerchberg-Saxton algorithm (MGSA). Different from conventional optical hiding methods with the limited multiplexing capacity, the proposed scheme can retrieve a large number of different secret images from one single host image during optical retrieval. In addition, it is also illustrated that optical implementation complexity is reduced in the proposed method. Simulations and optical experiments are conducted to verify feasibility, security and robustness of the proposed method. It is expected that the proposed method could open up a different research perspective for optical multiple-image hiding.

Optical analog-signal transmission and retrieval through turbid water.

In this paper, we propose a new, to the best of our knowledge, and robust method to optically transmit analog signals in free space through turbid water. In the proposed method, each pixel of original signal is sequentially encoded into random amplitude-only patterns as information carrier. A single-pixel detector is utilized to collect light intensity at the receiving end. To verify feasibility and effectiveness of the proposed method, a number of optical experiments are carried out in different kinds of water conditions, e.g., clean water, water mixed with milk, water with salt, and water with salt and milk. In addition, real seawater samples are also tested. Experimental results demonstrate that the proposed method shows high robustness against different propagation distances through turbid water and resists the effect of various turbulence factors. The proposed method is applicable to transmit information with high fidelity and high robustness against light wave diffusion in free space through complex environment. Furthermore, the proposed method is easy to operate and is cost-effective, which could open up a novel insight into optical signal transmission in free space through turbid water.