Phase recovery and holographic image reconstruction using deep learning in neural networks

Phase recovery from intensity-only measurements forms the heart of coherent imaging techniques and holography.In this study,we demonstrate that a neural network can learn to perform phase recovery and holographic image reconstruction after appropriate training.This deep learning-based approach provides an entirely new framework to conduct holographic imaging by rapidly eliminating twin-image and self-interference-related spatial artifacts.This neural network-based method is fast to compute and reconstructs phase and amplitude images of the objects using only one hologram,requiring fewer measurements in addition to being computationally faster.We validated this method by reconstructing the phase and amplitude images of various samples,including blood and Pap smears and tissue sections.These results highlight that challenging problems in imaging science can be overcome through machine learning,providing new avenues to design powerful computational imaging systems.

Phase Transition in Recovery Process of Complex Networks

The dynamic characteristic of complex network failure and recovery is one of the main research topics in complex networks. Real world systems such as traffic jams and Internet recovery could be described by the complex network theory. We propose a model to study the recovery process in complex networks. Two different recovery mechanisms are considered in three kinds of networks： external recovery and internal recovery. By simulating the process of the nodes recovery in networks, it is found that the system exhibits the feature of first-order phase transition only when the external recovery is considered. Internal recovery cannot induce such a kind of transitions. As external recovery and internal recovery coexist on networks, the systems will retain the most efficient part of external recovery and internal recovery. Meanwhile, a hysteresis could be observed when increasing or decreasing the failure probability. Finally, a largest degree node protection strategy is proposed for improving the robustness of networks.

Blind estimation of phase offset in OFDM subcarrier for coherent demodulation

An adaptive algorithm named low complexity phase off- set estimation （LC-POE） is proposed for orthogonal frequency division multiplexing （OFDM） signals. Depending on the requirement, the estimation procedure is divided into several scales to accelerate the adaptive convergence speed and ensure the estimation accuracy. The true phase offset is estimated through shrinking the detection range and raising the resolution scale step by step. Both the convergence performance and complexity are discussed in the paper. Simulation results show the effectiveness of the proposed algorithm. The LC-POE algorithm is promising in the application of OFDM systems.

Metrology of Optical Communication Systems Using Error Vector Magnitude

Error vector magnitude (EVM) as a performance metric for M-ary quadrature amplitude modulation (QAM) formats in optical coherent systems is presented. It is shown that the calibrated BER, which would otherwise be under-estimated without the correction factor, can reliably monitor the performance of optical coherent systems near the target BER of 10-3 for quadrature phase shift keying (QPSK), 16-QAM, and 64-QAM employing carrier phase recovery with differential decoding to compensate for laser phase noise. The impact on the number of symbols used to estimate the BER from EVM analysis is also presented and compared to the BER obtained by error counting.

Limited value of recovery phase-limited ST segment depression of treadmill exercise test

Background Clinical meaning of recovery phase limited ST segment depression of a treadmill exercise test is controversial.The aim of this study was to re-assess the diagnostic and prognostic value of ST segment depression during the recovery phase with the active phase of a treadmill exercise test in suspected coronary artery disease patients.Methods Clinical,exercise and angiographic data were retrospectively collected from 602 patients in the study.Five hundred and seventy-six patients developed ST segment depression during the active phase of the treadmill exercise test （group 1） and 26 patients developed ST segment depression only during the recovery phase （group 2）.Results With similar major clinical features,the prevalence of significant coronary artery stenosis and average Gensini scores were lower in the recovery phase-limited depression patients （group 2 vs.group 1,50.0% vs.66.9%,P=0.031 and group 2 vs.group 1,1.5 vs.8.5,P=0.04）.At a median follow up of 50.9 months for 22 group 2 and 34.8 months for 438 group 1 patients,the prevalence of total cardiac events was higher in group 1 than in group 2 patients （RR 1.60,95% Cl 1.00-2.54,P=0.049）.Conclusion The present study provides preliminary evidence that the diagnostic and prognostic value of recovery phaselimited ST segment depression of treadmill exercise test is limited.

Application of MAGnetic resonance imaging compilation in acute ischemic stroke

BACKGROUND Synthetic magnetic resonance imaging(MRI)MAGnetic resonance imaging compilation(MAGiC)is a new MRI technology.Conventional T1,T2,T2-fluidattenuated inversion recovery(FLAIR)contrast images,quantitative images of T1 and T2 mapping,and MAGiC phase sensitive inversion recovery(PSIR)Vessel cerebrovascular images can be obtained simultaneously through post-processing at the same time after completing a scan.In recent years,studies have reported that MAGiC can be applied to patients with acute ischemic stroke.We hypothesized that the synthetic MRI vascular screening scheme can evaluate the degree of cerebral artery stenosis in patients with acute ischemic stroke.AIM To explore the application value of vascular images obtained by synthetic MRI in diagnosing acute ischemic stroke.METHODS A total of 64 patients with acute ischemic stroke were selected and examined by MRI in the current retrospective cohort study.The scanning sequences included traditional T1,T2,and T2-FLAIR,three-dimensional time-of-flight magnetic resonance angiography(3D TOF MRA),diffusion-weighted imaging(DWI),and synthetic MRI.Conventional contrast images(T1,T2,and T2-FLAIR)and intracranial vessel images(MAGiC PSIR Vessel]were automatically reconstructed using synthetic MRI raw data.The contrast-to-noise ratio(CNR)values of traditional T1,T2,and T2-FLAIR images and MAGiC reconstructed T1,T2,and T2-FLAIR images in DWI diffusion restriction areas were measured and compared.MAGiC PSIR Vessel and TOF MRA images were used to measure and calculate the stenosis degree of bilateral middle cerebral artery stenosis areas.The consistency of MAGiC PSIR Vessel and TOF MRA in displaying the degree of vascular stenosis with computed tomography angiography(CTA)was compared.RESULTS Among the 64 patients with acute ischemic stroke,79 vascular stenosis areas showed that the correlation between MAGiC PSIR Vessel and CTA(r=0.90,P<0.01)was higher than that between TOF MRA and CTA(r=0.84,P<0.01).With a degree of vascular stenosis>50%assessed by CTA as a reference,the area under the receiver operating characteristic(ROC)curve of MAGiC PSIR Vessel[area under the curve(AUC)=0.906,P<0.01]was higher than that of TOF MRA(AUC=0.790,P<0.01).Among the 64 patients with acute ischemic stroke,39 were scanned for traditional T1,T2,and T2-FLAIR images and MAGiC images simultaneously,and CNR values in DWI diffusion restriction areas were measured,which were:Traditional T2=21.2,traditional T1=-6.7,and traditional T2-FLAIR=11.9;and MAGiC T2=7.1,MAGiC T1=-3.9,and MAGiC T2-FLAIR=4.5.CONCLUSION The synthetic MRI vascular screening scheme for patients with acute ischemic stroke can accurately evaluate the degree of bilateral middle cerebral artery stenosis,which is of great significance to early thrombolytic interventional therapy and improving patients’quality of life.

Clinical study on high-resolution CT and pulmonary function in severe acute respiratory syndrome patients during recovery phase

Severe acute respiratory syndrome (SARS) is an acute respiratory infectious disease caused by a novel coronavirus, firstly broke out in November 2002 in Guangdong and prevailed quickly in Beijing, Hong Kong, Taiwan and other regions of China. It was one of the most potential pandemic diseases and had affected more than 20 other countries.^(1,2) There have been a lot of resear-ches^(2-7) in terms of its etiology, epidemiology, pathogenesis, clinical characteristics, diagnostics, treatment and prevention, vaccines and so on.Along with control of the epidemic situation, a great number of SARS patients were in the recovery phase, therefore, we undertook a half-year follow-up investigation on their clinical, laboratory and image situations.

Effectiveness of Xiangsha Liujun pills(香砂六君丸)on decreased digestive function in convalescent patients of coronavirus disease 2019:a randomized,double blind,placebo controlled clinical trial

OBJECTIVE:To evaluate the effectiveness and safety of Xiangsha Liujun pills(香砂六君丸) on the decreased digestive function in patients in the recovery phase of the Coronavirus disease 2019(COVID-19).METHODS:A randomized,double blind,placebo controlled clinical trial was conducted.A total of 200 COVID-19 patients in the recovery phase were included in our study in Ezhou Hospital of Traditional Chinese Medicine.Totally 200 subjects were randomly divided into a treatment group(Xiangsha Liujun pills) and a control group(placebo),with 100 in each group.Subjects took Xiangsha Liujun pills or placebo orally three times a day for two weeks.Three visits were scheduled at week 0(baseline),week 1(the middle of the intervention) and week 2(the end of the intervention) for each eligible patient.The total efficacy rates for improving the Traditional Chinese Medicine(TCM) symptoms(fatigue,poor appetite,abdominal distension and loose stools) and the disappearance rates of symptoms were observed and compared in the treatment and control groups.Adverse events were recorded during the study period.SAS 9.4 was used to analyze the data.RESULTS:A total of 200 patients were included in this study,among which 4 participants withdrew because the drugs did not work.Three patients were excluded for age.Before the treatment,there was no significant difference between the TCM symptoms scores of subjects.After 1 week of treatment,the full analysis set(FAS) showed that the efficacy rates for abdominal distension and loose stools in the treatment group were significantly higher than the control group(P < 0.05).There were no significant differences in the efficacy rates for fatigue and poor appetite between the two groups(P > 0.05).In addition,the disappearance rate of fatigue in the treatment group was significantly higher than the control group(P < 0.05);there were no significant differences between the two groups after treatment in the rates of poor appetite,abdominal distension,and loose stools(P > 0.05).After 2 weeks of treatment,the efficacy rates for fatigue,poor appetite,abdominal distension,and loose stools in the treatment group were significantly higher than the control group(P < 0.05).The disappearance rate of loose stools in the treatment group was significantly higher than the control group(P < 0.05).However,there were no significant differences in the disappearance rates of fatigue,poor appetite,and abdominal distension between the two groups(P > 0.05).No severe adverse events were reported by subjects during the study.CONCLUSIONS:This clinical study confirmed that Xiangsha Liujun pills can effectively improve the symptoms related to the decreased digestive function in COVID-19 convalescent patients.

Correlation Holography with A Single-Pixel Detector:A Review

Correlation holography uses incoherent light to reconstruct holograms.This technique reconstructs objects as distributions of two-point coherence function rather than using optical fields,as in conventional holography.The basic principle of correlation holography is derived from the van Cittert--Zernike theorem and relies on the similarity between the optical field and the coherence functions.Experimental implementation of the correlation holography techniques requires a field or intensity interferometer,and fringe analysis and crosscovariance measurement in these interferometers require a conventional camera with array detectors.With the availability of digitally controlled diffractive elements,it is possible to replace the incoherent light source,such as a rotating ground glass,with a digital source loaded with the random patterns in sequence.Such strategies ease the burden on the detector and allow for correlation holography with a single-pixel detector(SPD)to be used.This review paper discusses a close connection between digital holography and correlation holography.The principles of correlation holography with the SPD are reviewed in detail,and the advantages of using digital sources to mimic incoherent illumination in the correlation holography are examined in the context of three-dimensional and complex field imaging.

The nighttime ionospheric response and occurrence of equatorial plasma irregularities during geomagnetic storms:a case study

Recent studies revealed that the long-lasting daytime ionospheric enhancements of Total Electron Content(TEC)were sometimes observed in the Asian sector during the recovery phase of geomagnetic storms e.g.,Lei(J Geophys Res Space Phys 123:3217-3232,2018),Li(J Geophys Res Space Phys 125:e2020JA028238,2020).However,they focused only on the dayside ionosphere,and no dedicated studies have been performed to investigate the nighttime ionospheric behavior during such kinds of storm recovery phases.In this study,we focused on two geomagnetic storms that happened on 7-8 September 2017 and 25-26 August 2018,which showed the prominent daytime TEC enhancements in the Asian sector during their recovery phases,to explore the nighttime large-scale ionospheric responses as well as the small-scale Equatorial Plasma Irregularities(EPIs).It is found that during the September 2017 storm recovery phase,the nighttime ionosphere in the American sector is largely depressed,which is similar to the daytime ionospheric response in the same longitude sector;while in the Asian sector,only a small TEC increase is observed at nighttime,which is much weaker than the prominent daytime TEC enhancement in this longitude sector.During the recovery phase of the August 2018 storm,a slight TEC increase is observed on the night side at all longitudes,which is also weaker than the prominent daytime TEC enhancement.For the small-scale EPIs,they are enhanced and extended to higher latitudes during the main phase of both storms.However,during the recovery phases of the first storm,the EPIs are largely enhanced and suppressed in the Asian and American sectors,respectively,while no prominent nighttime EPIs are observed during the second storm recovery phase.The clear north-south asymmetry of equatorial ionization anomaly crests during the second storm should be responsible for the suppression of EPIs during this storm.In addition,our results also suggest that the dusk side ionospheric response could be affected by the daytime ionospheric plasma density/TEC variations during the recovery phase of geomagnetic storms,which further modulates the vertical plasma drift and plasma gradient.As a result,the growth rate of post-sunset EPIs will be enhanced or inhibited.