Reproducibility study of intravoxel incoherent motion and apparent diffusion coefficient parameters in normal pancreas

BACKGROUND The consistency of pancreatic apparent diffusion coefficient(ADC)values and intravoxel incoherent motion(IVIM)parameter values across different magnetic resonance imaging(MRI)devices significantly impacts the patient’s diagnosis and treatment.AIM To explore consistency in image quality,ADC values,and IVIM parameter values among different MRI devices in pancreatic examinations.METHODS This retrospective study was approved by the local ethics committee,and informed consent was obtained from all participants.In total,22 healthy volunteers(10 males and 12 females)aged 24-61 years(mean,28.9±2.3 years)underwent pancreatic diffusion-weighted imaging using 3.0T MRI equipment from three vendors.Two independent observers subjectively scored image quality and measured the pancreas’s overall ADC values and signal-to-noise ratios(SNRs).Subsequently,regions of interest(ROIs)were delineated for the IVIM parameters(true diffusion coefficient,pseudo-diffusion coefficient,and perfusion fraction)using post-processing software.These ROIs were on the head,body,and tail of the pancrease.The subjective image ratings were assessed using the kappa consistency test.Intraclass correlation coefficients(ICCs)and mixed linear models were used to evaluate each device’s quantitative parameter values.Finally,a pairwise analysis of IVIM parameter values across each device was performed using Bland-Altman plots.RESULTS The Kappa value for the subjective ratings of the different observers was 0.776(P<0.05).The ICC values for interobserver and intra-observer agreements for the quantitative parameters were 0.803[95% confidence interval(CI):0.684-0.880]and 0.883(95%CI:0.760-0.945),respectively(P<0.05).The ICCs for the SNR between different devices was comparable(P>0.05),and the ICCs for the ADC values from different devices were 0.870,0.707,and 0.808,respectively(P<0.05).Notably,only a few statistically significant inter-device agreements were observed for different IVIM parameters,and among those,the ICC values were generally low.The mixed linear model results indicated differences(P<0.05)in the f-value for the pancreas head,D-value for the pancreas body,and D-value for the pancreas tail obtained using different MRI machines.The Bland-Altman plots showed significant variability at some data points.CONCLUSION ADC values are consistent among different devices,but the IVIM parameters’repeatability is moderate.Therefore,the variability in the IVIM parameter values may be associated with using different MRI machines.Thus,caution should be exercised when using IVIM parameter values to assess the pancreas.

Why the Incoherent Paradigm Is for the Future Wireless Networks?

This material is aimed to attract attention to the “incoherent approach for power NOMA-RIS-MIMO transmission in wireless channels”. Such kind of approach might be successfully applied in future dense networks formed by High-Speed Vehicles (HSV networks, etc.). Those scenarios take place in doubly selective communication channels typical for such kind of radio networks. The proposal for the presented hereafter incoherent view (“paradigm”) is based on several basic principles: 1) Shift from the “coherent “ideology”, i.e. rejection of the application of any type of Channel State Information (CSI, CSIT);2) Application of the so-called “invariant” to the communication channel’s features (distortions) modulation technique together with its incoherent demodulation;3) Orthogonal channel decomposition by means of “universal” eigen basis (in the form of Prolate Spheroidal Wave Functions, PSWF) as “artificial trajectories” of wave propagation;4) Chaotic filtering (chaos parameter settings as UE signatures) together with sequential multiuser parallel detection algorithms for users’ identification (classification). It is shown that the proposed approach might provide an effective use of the radio resource and it is relatively simple for implementation.

Value of Texture Analysis of Intravoxel Incoherent Motion Parameters in Differential Diagnosis of Pancreatic Neuroendocrine Tumor and Pancreatic Adenocarcinoma

Objective To evaluate the value of texture features derived from intravoxel incoherent motion(IVIM) parameters for differentiating pancreatic neuroendocrine tumor(pNET) from pancreatic adenocarcinoma(PAC).Methods Eighteen patients with pNET and 32 patients with PAC were retrospectively enrolled in this study. All patients underwent diffusion-weighted imaging with 10 b values used(from 0 to 800 s/mm2). Based on IVIM model, perfusion-related parameters including perfusion fraction(f), fast component of diffusion(Dfast) and true diffusion parameter slow component of diffusion(Dslow) were calculated on a voxel-by-voxel basis and reorganized into gray-encoded parametric maps. The mean value of each IVIM parameter and texture features [Angular Second Moment(ASM), Inverse Difference Moment(IDM), Correlation, Contrast and Entropy] values of IVIM parameters were measured. Independent sample t-test or Mann-Whitney U test were performed for the betweengroup comparison of quantitative data. Regression model was established by using binary logistic regression analysis, and receiver operating characteristic(ROC) curve was plotted to evaluate the diagnostic efficiency.Results The mean f value of the pNET group were significantly higher than that of the PAC group(27.0% vs. 19.0%, P = 0.001), while the mean values of Dfast and Dslow showed no significant differences between the two groups. All texture features(ASM, IDM, Correlation, Contrast and Entropy) of each IVIM parameter showed significant differences between the pNET and PAC groups(P = 0.000-0.043). Binary logistic regression analysis showed that texture ASM of Dfast and texture Correlation of Dslow were considered as the specific imaging variables for the differential diagnosis of pNET and PAC. ROC analysis revealed that multiple texture features presented better diagnostic performance than IVIM parameters(AUC 0.849-0.899 vs. 0.526-0.776), and texture ASM of Dfast combined with Correlation of Dslow in the model of logistic regression had largest area under ROC curve for distinguishing pNET from PAC(AUC 0.934, cutoff 0.378, sensitivity 0.889, specificity 0.854). Conclusion Texture analysis of IVIM parameters could be an effective and noninvasive tool to differentiate pNET from PAC.

16-Moment Approximation for Ion Velocity Distribution and its Application in Calculations of Incoherent Scatter Spectra

A sixteen moment approximation based on a bi-Maxwellian that contains the stress tensor and the heat flow vector is applied to describe the ion velocity distribution which influences the incoherent scatter spectra. A discussion is made about the effects on the incoherent scatter spectra caused by different values of the normalized perpendicular drift velocity D, aspect angle Φ between the magnetic field and the line-of-sight direction, and the ratio α of the ion-neutral collision to ion cyclotron frequency. Numerical results show that the shifting and asymmetry of incoherent scatter spectra appear parallel to E × B and E as the normalized perpendicular drift velocity D increases due to the ion drift velocity, the stress tensor and the heat flow vector respectively. However, the spectrum is always typically double-humped Maxwellian parallel to B. The ion velocity distribution is more distorted from the Maxwellian as the aspect angle Φ increases from 0° to 90°, and consequently the incoherent scatter spectra is no longer typically double-humped Maxwellian. Asαincreases, the ion velocity distribution becomes Maxwellian and the incoherent scatter spectra become typically double-humped Maxwellian even with a large value of the normalized perpendicular drift velocity D. It is reasonable to use the sixteen-moment approximation to describe the non-Maxwellian plasma characterized by the large temperature anisotropy.

Comparison between Microwave Coherent and Incoherent Scattering Models in Corn Field

[Objective] The aim was to compare and analyze microwave coherent and incoherent scattering models in a corn field. [Method] In the research, based on a coherent scattering model （Stile）, we proposed a coherent scattering model exclusive for corn, in which, physical optics （PO） and infinite-length dielectric cylinder were used to calculate single-scattering matrices of corn leaves and stalks. In addition, coherent components produced from interaction among the scattering mechanisms were also considered and this coherent model was compared with the Michigan Mi- crowave Canopy Scattering （MIMICS） model. The measured data in a corn filed in Gongzhuling in Jilin Province were used as the input parameters of the coherent and incoherent models. We simulated backscattering coefficients of VV and HH po- larization at L and C bands and made a comparison between the simulation results. [Result] The simulation results at L-band were poor, which indicated that we could not find regularity at early growth stage of vegetation. In addition, comparisons be- tween coherent and incoherent scattering models proved that the coherence triggered by the scattering mechanism was small. [Conclusion] In the research, we analyzed differences between coherent and incoherent scattering models with change of incident angle, and further analysis on the differences with change of vegetation and soil needed to be made in future.

Photonic generation of arbitrary waveforms based on incoherent wavelength-to-time mapping

We demonstrate experimentally a radio frequency arbitrary waveform generator using the incoherent wavelength-to-time mapping technique. The system is implemented by amplitude modulation of a broadband optical resource whose spectrum is reshaped by a programmable optical pulse shaper and transmitted over a single mode fiber link. The shape of the generated waveform is controlled by the optical pulse shaper, and the fiber link introduces a certain group velocity delay to implement wavelength-to-time mapping. Assisted by the flexible optical pulse shaper, we obtain different shapes of optical waveforms, such as rectangle, triangle, and sawtooth waveforms. Furthermore, we also demonstrate ultra-wideband generation, such as Gaussian monocycle, doublet, and triplet waveforms, using the incoherent technique.

Near-ultraviolet Incoherent Broadband Cavity Enhanced Absorption Spectroscopy for OCIO and CH20 in Cl-initiated Photooxidation Experiment

Chlorine dioxide （OC10） is an important indicator for Cl-activation. The monitoring of OC10 appears to be crucial for understanding the chemistry of Cl-initialed oxidation and its impact on air quality in polluted coastal regions and industrialized areas. We report the development of a Xe arc lamp based near-ultraviolet （335-375 nm） incoherent broad- band cavity enhanced absorption spectroscopy （IBBCEAS） spectrometer for quantitative assessment of OC10 in an atmospheric simulation chamber. The important intermediate compound CH20, and other key atmospheric trace species （NO2） were also simultaneously measured. The instrumental performance shows a strong potential of this kind of IBBCEAS instrument for field and laboratory studies of atmospheric halogen chemistry.

Intravoxel incoherent motion diffusion-weighted magnetic resonance imaging for predicting histological grade of hepatocellular carcinoma:Comparison with conventional diffusion-weighted imaging

AIM To compare intravoxel incoherent motion(IVIM)-derived parameters with conventional diffusion-weighted imaging(DWI) parameters in predicting the histological grade of hepatocellular carcinoma(h CC) and to evaluate the correlation between the parameters and the histological grades.METHODS A retrospective study was performed. Sixty-two patients with surgically confirmed h CCs underwent diffusion-weighted magnetic resonance imaging with twelve b values(10-1200 s/mm^2). The apparent diffusion coefficient(ADC), pure diffusion coefficient(D), pseudo-diffusion coefficient(D*), and perfusion fraction(f) were calculated by two radiologists. The IVIM and conventional DWI parameters were compared among the different grades by using analysis of variance(ANOVA) and the Kruskal-Wallis test. Receiver operating characteristic(ROC) analysis was performed to evaluate the diagnostic efficiency of distinguishing between low-grade(grade 1, G1) and high-grade(grades 2 and 3, G2 and G3) hC C. The correlation between the parameters and the histological grades was assessed by using the Spearman correlation test. Bland-Altman analysis was used to evaluate the reproducibility of the two radiologists' measurements.RESULTS The differences in the ADC and D values among the groups with G1, G2, and G3 histological grades of HCCs were statistically significant(P < 0.001). The D* and f values had no significant differences among the different histological grades of h CC(P > 0.05). The ROC analyses demonstrated that the D and ADC values had better diagnostic performance in differentiating the low-grade h CC from the high-grade h CC, with areas under the curve(AUCs) of 0.909 and 0.843, respectively, measured by radiologist 1 and of 0.911 and 0.852, respectively, measured by radiologist 2. The following significant correlations were obtained between the ADC, D, and D~* values and the histological grades: r =-0.619(P < 0.001), r =-0.628(P < 0.001), and r =-0.299(P = 0.018), respectively, as measured by radiologist 1; r =-0.622(P < 0.001), r =-0.633(P < 0.001), and r =-0.303(P = 0.017), respectively, as measured by radiologist 2. The intra-class correlation coefficient(ICC) values between the two observers were 0.996 for ADC, 0.997 for D, 0.996 for D*, and 0.992 for f values, which indicated excellent interobserver agreement in the measurements between the two observers.CONCLUSION The IVIM-derived D and ADC values show better diagnostic performance in differentiating high-grade hC C from low-grade hC C, and there is a moderate to good correlation between the ADC and D values and the histological grades.

Liver intravoxel incoherent motion diffusion-weighted imaging for the assessment of hepatic steatosis and fibrosis in children

AIM To evaluate the correlation between intravoxel incoherent motion(IVIM) diffusion-weighted imaging(DWI) parameters and the degree of hepatic steatosis and fibrosis in children.METHODS This retrospective study was approved by the institutional review board. The children(≤ 18 years) who underwent liver IVIM DWI with 8 b-values under the suspicion of hepatic steatosis or fibrosis from February 2013 to November 2016 were included. Subjects were divided into normal, fatty liver(FAT), and fibrotic liver(FIB) groups. The slow diffusion coefficient(D), fast diffusion coefficient(D*), perfusion fraction(f), and apparent diffusion coefficient(ADC) were measured. MR proton density fat fraction(PDFF), MR elastography(MRE), and IVIM values were compared.RESULTS A total of 123 children(median age of 12 years old, range: 6-18 years) were included, with 8 in the normal group, 93 in the FAT group, and 22 in the FIB group. The D* values were lower in the FIB group compared with those of the normal(P = 0.015) and FAT(P = 0.003) groups. The f values were lower in the FIB group compared with the FAT group(P = 0.001). In multivariate analyses, PDFF value was positively correlated with f value(β = 3.194, P < 0.001), and MRE value was negatively correlated with D* value(β =-7.031, P = 0.032). The D and ADC values were not influenced by PDFF or MRE value.CONCLUSION In liver IVIM DWI with multiple b-values in children, there was a positive correlation between hepatic fat and blood volume, and a negative correlation between hepatic stiffness and endovascular blood flow velocity, while diffusion-related parameters were not affected.

Intravoxel incoherent motion diffusion-weighted imaging for monitoring chemotherapeutic efficacy in gastric cancer

AIM: To assess intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) for monitoring early efficacy of chemotherapy in a human gastric cancer mouse model.METHODS: IVIM-DWI was performed with 12 b-values (0-800 s/mm2) in 25 human gastric cancer-bearing nude mice at baseline (day 0), and then they were randomly divided into control and 1-, 3-, 5- and 7-d treatment groups (n = 5 per group). The control group underwent longitudinal MRI scans at days 1, 3, 5 and 7, and the treatment groups underwent subsequent MRI scans after a specified 5-fluorouracil/calcium folinate treatment. Together with tumor volumes (TV), the apparent diffusion coefficient (ADC) and IVIM parameters [true water molecular diffusion coefficient (D), perfusion fraction (f) and pseudo-related diffusion coefficient (D*)] were measured. The differences in those parameters from baseline to each measurement (ΔTV%, ΔADC%, ΔD%, Δf% and ΔD*%) were calculated. After image acquisition, tumor necrosis, microvessel density (MVD) and cellular apoptosis were evaluated by hematoxylin-eosin (HE), CD31 and terminal-deoxynucleotidyl transferase mediated nick end labeling (TUNEL) staining respectively, to confirm the imaging findings. Mann-Whitney test and Spearman’s correlation coefficient analysis were performed.RESULTS: The observed relative volume increase (ΔTV%) in the treatment group were significantly smaller than those in the control group at day 5 (ΔTVtreatment% = 19.63% ± 3.01% and ΔTVcontrol% = 83.60% ± 14.87%, P = 0.008) and day 7 (ΔTVtreatment% = 29.07% ± 10.01% and ΔTVcontrol% = 177.06% ± 63.00%, P = 0.008). The difference in ΔTV% between the treatment and the control groups was not significant at days 1 and 3 after a short duration of treatment. Increases in ADC in the treatment group (ΔADC%treatment, median, 30.10% ± 18.32%, 36.11% ± 21.82%, 45.22% ± 24.36%) were significantly higher compared with the control group (ΔADC%control, median, 4.98% ± 3.39%, 6.26% ± 3.08%, 9.24% ± 6.33%) at days 3, 5 and 7 (P = 0.008, P = 0.016, P = 0.008, respectively). Increases in D in the treatment group (ΔD%treatment, median 17.12% ± 8.20%, 24.16% ± 16.87%, 38.54% ± 19.36%) were higher than those in the control group (ΔD%control, median -0.13% ± 4.23%, 5.89% ± 4.56%, 5.54% ± 4.44%) at days 1, 3, and 5 (P = 0.032, P = 0.008, P = 0.016, respectively). Relative changes in f were significantly lower in the treatment group compared with the control group at days 1, 3, 5 and 7 follow-up (median, -34.13% ± 16.61% vs 1.68% ± 3.40%, P = 0.016; -50.64% ± 6.82% vs 3.01% ± 6.50%, P = 0.008; -49.93% ± 6.05% vs 0.97% ± 4.38%, P = 0.008, and -46.22% ± 7.75% vs 8.14% ± 6.75%, P = 0.008, respectively). D* in the treatment group decreased significantly compared to those in the control group at all time points (median, -32.10% ± 12.22% vs 1.85% ± 5.54%, P = 0.008; -44.14% ± 14.83% vs 2.29% ± 10.38%, P = 0.008; -59.06% ± 19.10% vs 3.86% ± 5.10%, P = 0.008 and -47.20% ± 20.48% vs 7.13% ± 9.88%, P = 0.016, respectively). Furthermore, histopathologic findings showed positive correlations with ADC and D and tumor necrosis (rs = 0.720, P < 0.001; rs = 0.522, P = 0.007, respectively). The cellular apoptosis of the tumor also showed positive correlations with ADC and D (rs = 0.626, P = 0.001; rs = 0.542, P = 0.005, respectively). Perfusion-related parameters (f and D*) were positively correlated to MVD (rs = 0.618, P = 0.001; rs = 0.538, P = 0.006, respectively), and negatively correlated to cellular apoptosis of the tumor (rs = -0.550, P = 0.004; rs = -0.692, P < 0.001, respectively).CONCLUSION: IVIM-DWI is potentially useful for predicting the early efficacy of chemotherapy in a human gastric cancer mouse model.

Chemotherapy response evaluation in a mouse model of gastric cancer using intravoxel incoherent motion diffusionweighted MRI and histopathology

AIM To determine the role of intravoxel incoherent motion(IVIM) diffusion-weighted(DW) magnetic resonance imaging(MRI) using a bi-exponential model in chemotherapy response evaluation in a gastric cancer mouse model.METHODS Mice bearing MKN-45 human gastric adenocarcinoma xenografts were divided into four treated groups(TG1, 2, 3 and 4, n = 5 in each group) which received Fluorouracil and Calcium Folinate and a control group(CG, n = 7). DW-MRI scans with 14 b-values(0-1500 s/mm2) were performed before and after treatment on days 3, 7, 14 and 21. Fast diffusion component(presumably pseudo-perfusion) parameters including the fast diffusion coefficient(D*) and fraction volume(f p), slow diffusion coefficient(D) and the conventional apparent diffusion coefficients(ADC) were calculated by fitting the IVIM model to the measured DW signals. The median changes from the baseline to each posttreatment time point for each measurement(ΔADC, ΔD* and Δf p) were calculated. The differences in the median changes between the two groups were compared using the mixed linear regression model by the restricted maximum likelihood method shown as z values. Histopathological analyses including Ki-67, CD31, TUNEL and H&E were conducted in conjunction with the MRI scans. The median percentage changes were compared with the histopathological analyses between the pre-and post-treatment for each measurement.RESULTS Compared with the control group, D* in the treated group decreased significantly(ΔD*treated% =-30%,-34% and-20%, with z =-5.40,-4.18 and-1.95. P = 0.0001, 0.0001 and 0.0244) and f p increased significantly(Δfptreated% = 93%, 113% and 181%, with z = 4.63, 5.52, and 2.12, P = 0.001, 0.0001 and 0.0336) on day 3, 7 and 14, respectively. Increases in ADC in the treated group were higher than those in the control group on days 3 and 14(z = 2.44 and 2.40, P = 0.0147 and P = 0.0164). CONCLUSION Fast diffusion measurements derived from the biexponential IVIM model may be more sensitive imaging biomarkers than ADC to assess chemotherapy response in gastric adenocarcinoma.

Value of intravoxel incoherent motion in detecting and staging liver fibrosis: A meta-analysis

BACKGROUND Liver fibrosis(LF) is a common pathological feature of all chronic liver diseases.With the accumulation of extracellular matrix in the fibrotic liver, true molecular water diffusion and perfusion-related diffusion are restricted. Intravoxel incoherent motion(IVIM) can capture the information on tissue diffusivity and microcapillary perfusion separately and reflect the fibrotic severity with diffusion coefficients.AIM To investigate the diagnostic performance of IVIM in detecting and staging LF with histology as a reference standard.METHODS A comprehensive literature search was conducted to identify studies on the diagnostic accuracy of IVIM for assessment of histologically proven LF. The stages of LF were classified as F0(no fibrosis), F1(portal fibrosis without septa),F2(periportal fibrosis with few septa), F3(septal fibrosis), and F4(cirrhosis)according to histopathological findings. Data were extracted to calculate the pooled sensitivity, specificity, positive and negative likelihood ratios, and diagnostic odds ratio, as well as the area under the summary receiver operating characteristic curve(AUC) in each group.RESULTS A total of 12 studies with 923 subjects were included in this meta-analysis with 5 studies(n = 465) for LF ≥ F1, 9 studies(n = 757) for LF ≥ F2, 4 studies(n = 413) for LF ≥ F3, and 6 studies(n = 562) for LF = F4. The pooled sensitivity and specificity were estimated to be 0.78(95% confidence interval: 0.73-0.82) and 0.81(0.74-0.86)for LF ≥ F1 detection with IVIM;0.82(0.79-0.86) and 0.80(0.75-0.84) for staging F2 fibrosis;0.85(0.79-0.90) and 0.83(0.77-0.87) for staging F3 fibrosis, and 0.90(0.84-0.94) and 0.75(0.70-0.79) for detecting F4 cirrhosis, respectively. The AUCs for LF≥ F1, F2, F3, F4 detection were 0.862(0.811-0.914), 0.883(0.856-0.909), 0.886(0.865-0.907), and 0.899(0.866-0.932), respectively. Moderate to substantial heterogeneity was observed with inconsistency index(I2) ranging from 0% to 77.9%. No publication bias was detected.CONCLUSION IVIM is a noninvasive tool with good diagnostic performance in detecting and staging LF. Optimized and standardized IVIM protocols are needed to further improve its diagnostic accuracy in clinical practice.

Application of intravoxel incoherent motion diffusion-weighted imaging in hepatocellular carcinoma

The morbidity and mortality of hepatocellular carcinoma(HCC)rank 6th and 4th,respectively,among malignant tumors worldwide.Traditional diffusion-weighted imaging(DWI)uses the apparent diffusion coefficient(ADC)obtained by applying the monoexponential model to reflect water molecule diffusion in active tissue;however,the value of ADC is affected by microcirculation perfusion.Using a biexponential model,intravoxel incoherent motion(IVIM)-DWI quantitatively measures information related to pure water molecule diffusion and microcirculation perfusion,thus compensating for the shortcomings of DWI.The number of studies examining the application of IVIM-DWI in patients with HCC has gradually increased over the last few years,and many results show that IVIMDWI has vital value for HCC differentiation,pathological grading,and predicting and evaluating the treatment response.The present study principally reviews the principle of IVIM-DWI and its research progress in HCC differentiation,pathological grading,predicting and evaluating the treatment response,predicting postoperative recurrence and predicting gene expression prediction.

Could intravoxel incoherent motion diffusion-weighted magnetic resonance imaging be feasible and beneficial to the evaluation of gastrointestinal tumors histopathology and the therapeutic response?

Gastrointestinal tumors(GTs)are among the most com-mon tumors of the digestive system and are among the leading causes of cancer death worldwide.Functional magnetic resonance imaging(MRI)is crucial for assessment of histopathological changes and therapeutic responses of GTs before and after chemotherapy and radiotherapy.A new functional MRI technique,intravoxel incoherent motion(IVIM),could reveal more detailed useful information regarding many diseases.Currently,IVIM is widely used for various tumors because the derived parameters(diffusion coefficient,D;pseudo-perfusion diffusion coefficient,D*;and perfusion fraction,f)are thought to be important surrogate imaging biomarkers for gaining insights into tissue physiology.They can simultaneously reflect the microenvironment,microcirculation in the capillary network(perfusion)and diffusion in tumor tissues without contrast agent intra-venous administration.The sensitivity and specificity of these parameters used in the evaluation of GTs vary,the results of IVIM in GTs are discrepant and the variability of IVIM measurements in response to chemotherapy and/or radiotherapy in these studies remains a source of controversy.Therefore,there are questions as to whether IVIM diffusion-weighted MRI is feasible and helpful in the evaluation of GTs,and whether it is worthy of expanded use.

Preliminary experimental results by the prototype of Sanya Incoherent Scatter Radar

In the past decades,the Incoherent Scatter Radar(ISR)has been demonstrated to be one of the most powerful instruments for ionosphere monitoring.The Institute of Geology and Geophysics at the Chinese Academy of Sciences was founded to build a state-ofthe-art phased-array ISR at Sanya(18.3°N,109.6°E),a low-latitude station on Hainan Island,named the Sanya ISR(SYISR).As a first step,a prototype radar system consisting of eight subarrays(SYISR-8)was built to reduce the technical risk of producing the entire large array.In this work,we have summarized the preliminary experimental results based on the SYISR-8.The amplitude and phase among 256 channels were first calibrated through an embedded internal monitoring network.The mean oscillation of the amplitude and phase after calibration were about 1 dB and 5°,respectively,which met the basic requirements.The beam directivity was confirmed by crossing screen of the International Space Station.The SYISR-8 was further used to detect the tropospheric wind profile and meteors.The derived winds were evaluated by comparison with independent radiosonde and balloon-based GPS measurements.The SYISR-8 was able to observe several typical meteor echoes,such as the meteor head echo,range-spread trail echo,and specular trail echo.These results confirmed the validity and reliability of the SYISR-8 system,thereby reducing the technical risk of producing the entire large array of the SYISR to some extent.

Incoherent digital holographic spectral imaging with high accuracy of image pixel registration

Fresnel incoherent correlation holography(FINCH) is a unique three-dimensional(3D) imaging technique which has the advantages of scanning-free,high resolution,and easy matching with existing mature optical systems.In this article,an incoherent digital holographic spectral imaging method with high accuracy of spectral reconstruction based on liquid crystal tunable filter(LCTF) and FINCH is proposed.Using the programmable characteristics of spatial light modulator(SLM),a series of phase masks,none of whose focal lengths changes with wavelength,is designed and made.For each wavelength of LCTF output,SLM calls three phase masks with different phase constants at the corresponding wavelength,and CCD records three holograms.The spectral images obtained by this method have a constant magnification,which can achieve pixel-level image registration,restrain image registration errors,and improve spectral reconstruction accuracy.The results show that this method can not only obtain the 3D spatial information and spectral information of the object simultaneously,but also have high accuracy of spectral reconstruction and excellent color reproducibility.

Tunable and broadband microwave frequency combs based on a semiconductor laser with incoherent optical feedback

Based on a semiconductor laser （SL） with incoherent optical feedback, a novel all-optical scheme for generating tunable and broadband microwave frequency combs （MFCs） is proposed and investigated numerically. The results show that, under suitable operation parameters, the SL with incoherent optical feedback can be driven to operate at a regular pulsing state, and the generated MFCs have bandwidths broader than 40 GHz within a 10 dB amplitude variation. For a fixed bias current, the line spacing （or repetition frequency） of the MFCs can be easily tuned by varying the feedback delay time and the feedback strength, and the tuning range of the line spacing increases with the increase in the bias current. The linewidth of the MFCs is sensitive to the variation of the feedback delay time and the feedback strength, and a linewidth of tens of KHz can be achieved through finely adjusting the feedback delay time and the feedback strength. In addition, mappings of amplitude variation, repetition frequency, and linewidth of MFCs in the parameter space of the feedback delay time and the feedback strength are presented.

Stimulated Raman scattering excited by incoherent light in plasma

Stimulated Raman scattering(SRS)excited by incoherent light is studied via particle-in-cell simulations.It is shown that a large bandwidth of incoherent light can reduce the growth of SRS and electron heating considerably in the linear stage.However,different components of the incoherent light can be coupled by the Langmuir waves,so that stimulated Raman backward scattering can develop.When the bandwidth of incoherent light is larger than the Langmuir wave frequency,forward SRS can be seeded between different components of the incoherent light.The incoherent light can only increase the time duration for nonlinear saturation but cannot diminish the saturation level obviously.

Intravoxel Incoherent Motion Diffusion Weighted Imaging for the Therapeutic Response of Transarterial Chemoembolization for Hepatocellular Carcinoma

Background: Intravoxel incoherent motion diffusion weighted imaging (IVIM-DWI) can not only observe the diffusion of tissue water molecules but also reflect the blood perfusion information of tissue microcirculation. IVIM-DWI has been applied in many clinical areas. However, few studies have addressed the use of IVIM-DWI for the evaluation of transarterial chemoembolization (TACE) response in hepatocellular carcinoma (HCC) patients. Objectives: The purpose of the present study was to explore the role of IVIM-DWI for the therapeutic response of TACE for HCC. Materials and Methods: Twenty patients underwent IVIM-DWI scan on a 3.0T magnetic resonance imaging instrument 1 - 3 days before and 30 to 40 days after TACE. The values of IVIM-DWI parameters, including standard apparent diffusion coefficient (ADC), pure diffusion coefficient (Dslow), pseudo-diffusion coefficient (Dfast) and perfusion fraction (f) were measured. The values of IVIM-DWI parameters before and after TACE were compared using paired t tests. The values between responsive and non-responsive groups were compared using independent-samples t test. P 0.05 indicated statistical significance. Results: After TACE, the ADC and Dslow values in the tumors increased significantly, and the values of Dfast decreased significantly, while the values of f value did not change obviously. The ADC values in responsive group were remarkably higher than those in non-responsive group, the Dfast values in responsive group were significantly lower than those in non-responsive group, but the values of Dslow and f between the two groups were not different significantly. Conclusions: IVIM-DWI parameters can be used as potential markers for the therapeutic response of TACE for HCC.

Stimulated electromagnetic emissions spectrum observed during an X-mode heating experiment at the European Incoherent Scatter Scientific Association

An extraordinary(X-mode)electromagnetic wave,injected into the ionosphere by the ground-based heating facility at Tromsφ,Norway,was utilized to modify the ionosphere on November 6,2017.The high-power high-frequency transmitter facility located at Tromsφ belongs to the European Incoherent Scatter Scientific Association.In the experiment,stimulated electromagnetic emission(SEE)spectra were observed.A narrow continuum occurred under cold-start conditions and showed an overshoot effect lasting several seconds.Cascading peaks occurred on both sides of the heating frequency only in the preconditioned ionosphere and also showed an overshoot effect.These SEE features are probably related to the ponderomotive process in the X-mode heating experiment and are helpful for understanding the physical mechanism that generated them during the X-mode heating experiment.The features observed in the X-mode heating experiments are novel and require further investigation.