High-repetition-rate pulsed fiber laser based on virtually imaged phased array

High-repetition-rate(HRR) pulsed fiber lasers have attracted much attention in various fields. To effectively achieve HRR pulses in fiber lasers, dissipative four-wave-mixing mode-locking is a promising method. In this work, we demonstrated an HRR pulsed fiber laser based on a virtually imaged phased array(VIPA), serving as a comb filter. Due to the high spectral resolution and low polarization sensitivity features of VIPA, the 30 GHz pulse with high quality and high stability could be obtained. In the experiments, both the single-waveband and dual-waveband HRR pulses were achieved. Such an HRR pulsed fiber laser could have potential applications in related fields, such as optical communications.

Shear Wave Elastography of Invasive Ductal Carcinoma:Correlations between Shear Wave Velocity and Histological Prognostic Factors

The correlations between shear wave velocity(SWV)calculated from virtual touch tissue imaging quantification(VTIQ)technique and histological prognostic factors of invasive ductal carcinoma was investigated.A total of 76 breast tumors histologically confirmed as invasive ductal carcinomas were included in this study.SWV values were measured by VTIQ for each lesion preoperatively or prior to breast biopsy.The maximum values were recorded for statistical analysis.Medical records were reviewed to determine tumor size,histological grade,lymph node status and immunohistochemical results.Tumor subtypes were categorized as luminal A,luminal B,human epidermal growth factor receptor 2(HER2)positive and triple negative.The correlations between SWV and histological prognostic factors were analyzed.It was found that tumor size showed positive association with SWV(r=0.465,P<0.001).Larger tumors had significantly higher SWV than smaller ones(P=0.001).Histological grade 1 tumors had significantly lower SWV values than those with higher histological grade(P=0.015).The Ki67 expression,tumor subtypes and lymph node status showed no statistically significant correlations with SWV,although triple negative tumors and lymph node-positive tumors showed higher SWV values.It was concluded that tumor size was significantly associated with SWV.Higher histological grade was associated with increased SWV.There was no statistically significant correlations between SWV and other histological prognostic factors.

Gadolinium Enhances Dual-energy Computed Tomography Scan of Pulmonary Artery

Objective To evaluate the feasibility of using gadopentetate dimeglumine(Gd-DTPA)for dual-energy computed tomography pulmonary angiography(CTPA).Methods Sixty-six patients were randomly divided into three groups and underwent CTPA.Group A had a turbo flash scan using an iohexol injection,Group B had a turbo flash scan using Gd-DTPA,and Group C had a dual-energy scan using Gd-DTPA.The original images of Group C were linearly blended with a blending factor of 0.5 or reconstructed at 40,50,60,70,80,90,100,and 110 keV,respectively.The groups were compared in terms of pulmonary artery CT value,image quality,and radiation dose.Results The pulmonary artery CT values were significantly higher in Group C40keV than in Groups B and C,but lower than in Group A.There was no significant difference in the image noise of Groups C40keV,B,and C.Moreover,Group A had the largest beam hardening artifacts of the superior vena cava(SVC),followed by Groups B and C.Group C40keV showed better vascular branching than the other three groups,among which Group B was superior to Group A.The subjective score of the image quality of Groups A,B,and C showed no significant difference,but the score was significantly higher in Group C40keV than in Groups A and B.The radiation dose was significantly lower in Group B than in Groups A and C.Conclusion Gd-CTPA is recommended to patients who are unsuitable for receiving an iodine-based CTPA.Furthermore,a turbo flash scan could surpass a dual-energy scan without consideration for virtual monoenergetic imaging.

Application of Computed Tomography Virtual Noncontrast Spectral Imaging in Evaluation of Hepatic Metastases： A Preliminary Study

Objective：The objective was to qualitatively and quantitatively evaluate hepatic metastases using computed tomography （CT） virtual noncontrast （VNC） spectral imaging in a retrospective analysis.Methods：Forty hepatic metastases patients underwent CT scans including the conventional true noncontrast （TNC） and the tri-phasic contrast-enhanced dual energy spectral scans in the hepatic arterial,portal venous,and equilibrium phases.The tri-phasic spectral CT images were used to obtain three groups of VNC images including in the arterial （VNCa）,venous （VNCv）,and equilibrium （VNCe） phase by the material decomposition process using water and iodine as a base material pair.The image quality and the contrast-to-noise ratio （CNR） of metastasis of the four groups were compared with ANOVA analysis.The metastasis detection rates with the four nonenhanced image groups were calculated and compared using the Chisquare test.Results：There were no significant differences in image quality among TNC,VNCa and VNCv images （P 〉 0.05）.The quality of VNCe images was significantly worse than that of other three groups （P 〈 0.05）.The mean CNR of metastasis in the TNC and VNCs images was 1.86,2.42,1.92,and 1.94,respectively; the mean CNR of metastasis in VNCa images was significantly higher than that in other three groups （P 〈 0.05）,while no statistically significant difference was observed among VNCv,VNCe and TNC images （P 〉 0.05）.The metastasis detection rate of the four nonenhanced groups with no statistically significant difference （P 〉 0.05）.Conclusions：The quality of VNCa and VNCv images is identical to that of TNC images,and the metastasis detection rate in VNC images is similar to that in TNC images.VNC images obtained from arterial phase show metastases more clearly.Thus,VNCa imaging may be a surrogate to TNC imaging in hepatic metastasis diagnosis.

Virtual reality system for diagnosis and therapeutic planning of cerebral aneurysms

Background The virtual reality （VR） system can provide the neurosurgeon to intuitively interact with and manipulate the three dimensional （3-D） image similarly to manipulate a real object.it was seldom reported that the system was used in diagnosis and treatment of cerebral aneurysms.This study aimed to investigate the application of VR system in diagnosis and therapeutic planning of cerebral aneurysms.Methods A total of 24 cases of cerebral aneurysms were enrolled in this study from 2006 to 2008, which diagnosed by 3-D digital subtraction angiography （3D-DSA） or VR-based computed tomography angiographies （CTA）.The VR system and 3D-DSA system were used to observe and measure aneurysms and the adjacent vessels.The data of observation and measurements were compared between VR image and 3D-DSA image.All the patients underwent surgical plan and simulated neurosurgical procedures in the VR system.Results There were 28 aneurysms detected in VR system and 3D-DSA system.The VR system generated clear and vivid 3-D virtual images which clearly displayed the location and size of the aneurysms and their precise anatomical spatial relations to the parent arteries and skull.The location, size and shape of the aneurysms and their anatomical relationship with the adjacent vessels were similar between 3-D virtual image and 3D-DSA, but the spatial relationship between aneurysms and skull only been displayed by VR system.This VR system also could simulate simple surgical procedures and surgical environments.Conclusions The VR system can provide a highly effective way to provide precise imaging details as same as 3D-DSA system and assist the diagnosis of cerebral aneurysms with virtual 3-D data based on CTA.It significantly enhances the chosen therapeutic strategy of cerebral aneurysms.

Similarity Solution for the Synchronous Grouting of Shield Tunnel Under the Vertical Non-Axisymmetric Displacement Boundary Condition

Abstract.Similarity solution is investigated for the synchronous grouting of shield tunnel under the vertical non-axisymmetric displacement boundary condition in the paper.The synchronous grouting process of shield tunnel was simplified as the cylindrical expansion problem,which was based on the mechanism between the slurry and stratum of the synchronous grouting.The stress harmonic function on the horizontal and vertical ground surfaces is improved.Based on the virtual image technique,stress function solutions and Boussinesq’s solution,elastic solution under the vertical non-axisymmetric displacement boundary condition on the vertical surface was proposed for synchronous grouting problems of shield tunnel.In addition,the maximum grouting pressure was also obtained to control the vertical displacement of horizontal ground surface.The validity of the proposed approach was proved by the numerical method.It can be known fromthe parameter analysis that larger vertical displacement of the horizontal ground surface was induced by smaller tunnel depth,smaller tunnel excavation radius,shorter limb distance,larger expansion pressure and smaller elastic modulus of soils.

VR content creation and exploration with deep learning: A survey

Virtual reality(VR)offers an artificial,computer generated simulation of a real life environment.It originated in the 1960 s and has evolved to provide increasing immersion,interactivity,imagination,and intelligence.Because deep learning systems are able to represent and compose information at various levels in a deep hierarchical fashion,they can build very powerful models which leverage large quantities of visual media data.Intelligence of VR methods and applications has been significantly boosted by the recent developments in deep learning techniques.VR content creation and exploration relates to image and video analysis,synthesis and editing,so deep learning methods such as fully convolutional networks and general adversarial networks are widely employed,designed specifically to handle panoramic images and video and virtual 3 D scenes.This article surveys recent research that uses such deep learning methods for VR content creation and exploration.It considers the problems involved,and discusses possible future directions in this active and emerging research area.

VIPA-based two-component detection for a coherent population trapping experiment

We demonstrate a two-component detection of a coherent population trapping(CPT)resonance based on virtually imaged phased array(VIPA).After passing through a VIPA,the two coupling lights with different frequencies in the CPT experiment are separated in space and detected individually.The asymmetric lineshape is observed experimentally in the CPT signal for each component,and the comparison with the conventional detection is presented.The shift of the CPT resonant frequency is studied with both the two-component and one-component detections.Our scheme provides a convenient way to further study the CPT phenomenon for each frequency component.