Improving the Accuracy of Direction of Arrival Estimation with Multiple Signal Inputs Using Deep Learning.

In this paper, an innovative cyclic noise reduction method and an improved CAPON algorithm (also the called minimum variance distortionless response (MVDR) algorithm) are proposed to improve the accuracy and reliability of DOA (direction of arrival) estimation. By processing the eigenvalues obtained from the covariance matrix of the received signal, the signal-to-noise ratio (SNR) can be increased by up to 5 dB by the cyclic noise reduction method, which will improve the DOA estimation accuracy. The improved CAPON algorithm has a convolution neural network (CNN) structure, whose input is the processed covariance matrix of the received signal, and the CAPON spectral value is used as the training label to obtain the estimated spatial spectrum. It retains the advantages of the CAPON algorithm, which can achieve blind source estimation, and simulations show that the proposed algorithm exhibits a better performance than the traditional algorithm in conditions of various SNRs and snapshot numbers. The simulation results show that, based on a certain SNR, the root mean square error (RMSE) of the improved CAPON algorithm can be reduced from 0.86° to 0.8° compared to traditional algorithms, and the angle estimation error can be decreased by up to about 0.3°. With the help of the cyclic noise reduction method, the angle estimation error decreases from 0.04° to 0.02°.

Three-Dimensional Location of the Facial Artery in Relation to the Nasolabial Fold in Asian People: A Cadaveric CTA Study.

BACKGROUND: Injection cosmetics have become popular in recent years. The nasolabial fold is one of the most important and dangerous regions in the midface, and its three-dimensional relationship with the facial artery remains unclear. METHODS: Fifty-two cadavers infused with lead oxide contrast medium via the external carotid arteries were scanned by computed tomography (CT). The three-dimensional model was reconstructed using Mimics and Origin software, and the relevant data were calculated using validated algorithms. RESULTS: There were three facial artery types according to its course in relation to the nasolabial fold. In the most common type, accounting for 83.7% of specimens, the facial artery evolves into an angular artery, with a horizontal distance between facial artery and nasolabial fold of - 1.90 ± 2.40, - 3.90 ± 2.95, - 5.18 ± 3.42, - 5.59 ± 3.53, - 5.59 ± 3.83, - 6.07 ± 4.10, - 6.92 ± 3.70, - 6.79 ± 3.37, - 4.52 ± 3.20, and - 2.76 ± 3.60 (mm) from the nasal ala to the oral commissure and a vertical distance of - 4.03 ± 2.56, - 3.27 ± 2.27, - 2.81 ± 2.57, - 2.1 ± 2.64, - 1.5 ± 3.32, - 0.71 ± 3.99, 0.92 ± 4.43, 0.4 ± 5.31, - 4.14 ± 5.14, - 7.05 ± 4.74 (mm). CONCLUSIONS: The facial artery is vulnerable to damage when injecting filler in the nasolabial fold. For the upper 1/3 of the nasolabial fold, the supraperiosteal layer is recommended for injection, while for the lower 2/3 of the nasolabial fold, the dermal layer along the nasolabial fold is recommended. LEVEL OF EVIDENCE IV: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Morphological Aesthetics Assessment of the Predicted 3D Simulation Results and the Actual Results of Breast Augmentation.

BACKGROUND: Although three-dimensional (3D) simulations are becoming more common in preoperative breast augmentation planning, this does not necessarily imply that the simulated results are highly accurate. OBJECTIVES: We aimed to evaluate the accuracy of the 3D simulation technique by comparing the differences in breast morphology between the 3D prediction model and the actual results. METHODS: The simulation and actual postoperative results of 103 patients who underwent breast augmentation were analyzed retrospectively. Therefore, a 3D model was created, and the parameters of line spacing, nipple position, breast projection, surface area, and volume were evaluated. Furthermore, consider the difference in chest circumferences and breast volume. RESULTS: In comparison with the simulation results, the actual results had a mean increase in the nipple to the inframammary fold (N-IMF) of 0.3 cm (P < 0.05) and a mean increase in basal breast width (BW) of 0.3 cm (P < 0.001), a difference that was not statistically significant in patients with larger breast volumes. There was a significant difference in the mean upper and lower breast volume distribution between simulated and actual breasts (upper pole 52.9% vs. 49.2%, P < 0.05, and lower pole 47.1% vs. 50.8%, P < 0.001). However, it was not statistically significant in patients with larger chest circumferences. CONCLUSIONS: Our study shows that 3D simulation has uncertainties related to the patient's chest circumference and breast volume. Therefore, these two critical factors must be considered when using simulation assessment in preoperative planning. LEVEL OF EVIDENCE III: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Clinical Relevance of the Variability of the Infraorbital Arterial Anatomy Evaluated by Three-Dimensional Computed Tomography.

BACKGROUND: Knowledge of the anatomy of the infraorbital artery (IOA) is crucial for the rejuvenation of the anterior medial aspect of the midface; however, studies adequately describing the anatomy of the IOA branches are lacking, and their connection with the ophthalmic artery branches remains unclear. OBJECTIVES: This study aims to elucidate the anatomical characteristics of the IOA in its deployment within the lower eyelid using three-dimensional (3D) technology, thereby offering an anatomical foundation for clinical surgical procedures. METHODS: An analysis was conducted on computed tomography scans of 132 cadaveric head sides post-contrast injection, utilizing the Mimics software for reconstruction. The study focused on examining the anastomosis of the IOA, its principal branches, and the branches emanating from the ophthalmic artery. RESULTS: The prevalence of type I IOA was observed at 38.6% (51/132), while Type II IOA was found in 61.4% (81/132) of cases. A 7.6% incidence (10/132) of IOA directly anastomosing with the angular artery was noted. The presence of palpebral branches (PIOA) was identified in 57.6% (76/132) of instances. In the lower eyelid, four distinct distribution patterns of IOA were discerned: The likelihood of Type I PIOA was 5.3%, whereas for Types IIA, IIB, and IIC PIOA, the probabilities were 8.3%, 32.6%, and 11.4%, respectively. The occurrence of the orbital branch of IOA was recorded at 41.7% (55/132). CONCLUSIONS: 3D technology can map IOA variants and identify the deployment patterns of IOA branches in the lower eyelid vascular vesicles at high resolution as a guide in clinical practice. LEVEL OF EVIDENCE IV: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

The Safety of Injections in the Infraorbital Region.

BACKGROUND:  Infraorbital filler injection is a commonly used minimally invasive cosmetic procedure on the face, which can cause vascular complications. OBJECTIVE:  In this study, we aimed to explore the anatomical structure of the infraorbital vasculature and to establish an accurate protocol for infraorbital filler injection. METHODS:  The vascular structure of the infraorbital region was evaluated in 84 hemifacial specimens using computed tomography. Four segments (P1-P4) and five sections (C1-C5) were considered. We recorded the number of identified arteries in each slice and at each location and the number of deep arteries. Furthermore, we also measured the infraorbital artery (IOA) distribution. RESULTS:  At P1-P4, the lowest number of arteries was detected in segment P4, with a 317/1727 (18.4%) and 65/338 (2.3%) probability of total and deep arterial identification, respectively. The probabilities of encountering an identified artery at the five designated locations (C1-C5) were 277/1727 (16%), 318/1727 (18.4%), 410/1727 (23.7%), 397/1727 (23%), and 325/1727 (18.8%), respectively. The probability of an IOA being identified at C2 was 68/84 (81%). CONCLUSION:  We described an effective filler injection technique in the infraorbital region to minimize the associated risks. LEVEL OF EVIDENCE IV: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Factors affecting the compliance of hepatocellular carcinoma screening among high-risk populations: A systematic review and meta-analysis.

BACKGROUND: Hepatocellular carcinoma (HCC) is the sixth most common cancer worldwide and the third leading cause of cancer mortality. HCC has high morbidity, high mortality, and low survival rates. Screening is one of the most significant methods of lowering incidence and death while also increasing survival. OBJECTIVES: The aim of this study was to identify the facilitators and barriers to participation in HCC screening among high-risk populations. METHODS: A comprehensive and systematic search was undertaken in PubMed, Web of Science, MEDLINE, EMBACE, EBSCOhost and the Cochrane Library. A combination of synonyms of the keywords including HCC, screening, factors and adherence were used for searching. Studies addressing the facilitators and barriers to HCC screening compliance in at-risk individuals were included. Data were synthesized using Review Manager version 5.4. A random/fixed effects model meta-analysis was performed to estimate the pooled data and expressed with odds ratio (OR) and 95% confidence interval (CI). RESULTS: A total of seven articles met the inclusion criteria. Qualitative (n = 1) and quantitative (n = 6) studies using various types of surgery were conducted. The most commonly mentioned barriers were insufficient knowledge and awareness of HCC screening, unawareness of the necessity for early detection of HCC and lack of physician recommendation. A meta-analysis of seven studies showed that individuals with a family history of HCC increased screening uptake by nearly three times (OR: 2.69, 95% CI: 1.93, 3.75). Other most frequently reported facilitators include age, education level, and perceived risk et al. CONCLUSIONS: Many barriers to HCC screening were found. Meanwhile, this review points out that improving the awareness of high-risk populations toward HCC screening is expected to enhance compliance, thereby promoting early diagnosis of liver cancer, reducing mortality, and alleviating the burden of HCC.

[Ginsenoside F1 inhibits cholesterol overload in oxidative-damaged cells through SREBP2/HMGCR pathway].

OBJECTIVE: To investigate the inhibitory mechanisms of ginsenoside F1 on hydrogen peroxide induced cholesterol metabolism disorder and oxidative stress in HepG2 cells. METHODS: 1, 1-diphenyl-2-picrylhydrazyl(DPPH) and oxygen radical absorbance capacity(ORAC) tests were used to detect the scavenging effect of ginsenoside F1 on nitrogen and oxygen free radicals. HepG2 cells were treated with 400 µmol/L hydrogen peroxide and pretreated with 10, 20 and 40 µmol/L ginsenoside F1. Mitochondrial membrane potential(MMP) and total cholesterol levels were detected by JC-1 method and cholesterol kit, respectively. The protein expression levels of sterol-regulatory element binding proteins(SREBP2)and 3-hydroxy-3-methylglutaryl coenzyme A reductase(HMGCR) in cholesterol synthesis pathway were detected by Western blot. RESULTS: The DPPH clearance rate of ginsenoside F1 was much lower than that of 6-hydroxy-2, 5, 7, 8-tetramethylchroman-2-carboxylic acid(Trolox), but the ORAC capability of ginsenoside F1 was stronger, which was comparable to Trolox. The MMP and protein expression of SREBP2 were significantly decreased in injured group(P<0.05). The cholesterol and protein expression of HMGCR were significantly increased(P<0.05). Whereas, compared with the injured group, the MMP and protein expression of SREBP2 were significantly increased after 10, 20 and 40 µmol/L ginsenoside F1 pretreatment of injured cells(P<0.05). The cholesterol level and protein expression of HMGCR were significantly lower than injured group with concentration-dependent decreases(P<0.05). CONCLUSION: Ginsenoside F1 can protect against hydrogen peroxide induced oxidative stress in HepG2 cells by inhibiting oxygen free radicals and protecting mitochondria. And its mechanism may be related to the intervention of SREBP2/HMGCR pathway in regulating cellular cholesterol anabolism.

Characterization of the angular memory effect of dynamic turbid media.

The optical angular memory effect (AME) is a basic feature of turbid media and defines the correlation of speckles when the incident light is tilted. AME based imaging through solid scattering media such as ground glass and biomedical tissue has been recently developed. However, in the case of liquid media such as turbid water or blood, the speckle pattern exhibits dynamic time-varying characteristics, which introduces several challenges. The AME of the thick volume dynamic media is particularly different from the layer scatterers. In practice, there are more parameters, e.g., scattering particle size, shape, density, or even the illuminating beam aperture that can influence the AME range. Experimental demonstration of AME phenomenon in liquid dynamic media and confirm the distinctions will contribution to complete the AME theory. In this paper, a dual-polarization speckle detection setup was developed to characterize the AME of dynamic turbid media, where two orthogonal polarized beams were employed for simultaneous detection by a single CCD. The AME of turbid water, milk and blood were measured. The influence of thickness, concentration, particle size and shape, and beam diameter were analyzed. The AME increasement of upon the decrease of beam diameter was tested and verified. The results demonstrate the feasibility of this method for investigating the AME phenomenon and provide guidance for AME based imaging through scattering media.

A Two-Center, Prospective, Randomized Controlled Trial to Evaluate the Efficacy and Safety of and Satisfaction with Different Methods of ART FILLER® UNIVERSAL Injection for Correcting Moderate to Severe Nasolabial Folds in Chinese Individuals.

BACKGROUND: Hyaluronic acid is the most popular dermal filler in the treatment of nasolabial folds. Injection methods vary among physicians. METHODS: A randomized, two-center, double-blind, intraindividual trial was designed to compare a new method of injecting ART FILLER® UNIVERSAL using the retaining ligament with the traditional method (linear threading and bolus injection) in moderate to severe nasolabial folds. Forty patients with moderate to severe nasolabial folds were randomized into groups A and B. Group A received injections via the traditional method on the left side and the ligament method on the right side, while group B received the reverse. Clinical efficacy and patient safety were independently assessed by a blinded evaluator, the injector, using the Wrinkle Severity Rating Scale (WSRS), the Global Aesthetic Improvement Scale (GAIS), and the Medicis Midface Volume Scale (MMVS) at 4 weeks (before and after the touch-up injection), 8 weeks, 12 weeks, and 24 weeks after the baseline injection. RESULTS: From the perspective of the blinded evaluator, the improvements in WSRS scores from baseline did not differ significantly between the ligament method (0.73 ± 0.61) and the traditional method (0.89 ± 0.61) at week 24 (p > 0.05). The mean GAIS score at week 24 was 1.41 ± 0.49 for the traditional method and 1.32 ± 0.47 for the ligament method (p > 0.05). CONCLUSIONS: The efficacy and safety of the ligament method for the management of nasolabial folds are comparable to those of the traditional method in terms of WSRS and GAIS score improvement in the long run. The ligament method is superior to the traditional method in that it improves midface deficits with fewer adverse events. LEVEL OF EVIDENCE II: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 . CLINICAL TRIAL REGISTRATION: This study was registered with the Chinese Clinical Trial Registry under the registration number ChiCTR2100041702.

Association between serum copper level and reproductive health of Women in the United States: a cross-sectional study.

Copper is an indispensable trace element in metabolism. This study aimed to investigate the relationship between copper and reproductive health, and possibly provide new insights for diagnosis and treatment. This study was based on data extracted from the NHANES database (2013-2014 and 2015-2016). The t-test, ANOVA, Chi-square test, multiple linear regression, and restricted cubic spline analysis were used. Serum copper levels were significantly higher in women with gestational diabetes than in those without gestational diabetes (P = 0.0150). Women with higher copper levels and smoking habits tended to deliver overweight babies (P = 0.028). Women with diabetes had higher serum copper and were prone to deliver overweight babies (P = 0.024). Serum copper levels showed a positive relationship with sex hormone-binding globulin (SHBG) levels (P < 0.0001). In this study, serum copper levels were found to be associated with reproductive health in women. Further studies are required to draw causal inferences.

Clinical efficacy analysis of oocyte cryopreservation: A propensity score matched study.

OBJECTIVE: To investigate the effectiveness of oocyte thawing cycles in the clinical application of assisted reproductive technology (ART). STUDY DESIGN: The clinical data of 78 cases who underwent oocyte thawing cycles in our center were retrospectively analyzed. All patients in this study received oocyte cryopreservation for the husband reason. According to patient age at egg freezing, patients were divided into three observation groups (Group A, <30 years old; Group B, 30-34 years old; Group C, ≥35 years old), and the control groups were selected by propensity score matching with fresh cycles. The clinical outcomes of each group were compared, and the clinical efficacy of oocyte thawing cycles was analyzed. RESULTS: Clinical pregnancy outcomes of oocyte thawing cycles were not significantly different from that of fresh oocytes, but vitrification affected the number of two pronuclei zygotes developing to cleavage stage and the number of high-quality embryos, and the normal fertilization rate after thawing. The cycle cumulative live birth rate in Group C was significantly lower than those in Groups A and B. The live birth rates per egg of Groups A, B, C were 5.03%, 5.61%, and 3.57%, respectively, and the numbers of eggs per live birth were 13.72, 14.43, and 21.0, respectively. CONCLUSIONS: The overall clinical outcomes of oocyte vitrification were similar to that of fresh oocytes, but the cleavage rate and embryo quality of frozen oocytes were slightly reduced. Freezing of oocytes in women over 35 years of age affects the clinical efficacy of ART.

[Attapulgite can improve yield and total ferulic acid content of Angelica sinensis by adjusting source-sink relationship].

Attapulgite(ATP), as a fertilizer slow-release agent and soil conditioner, has shown remarkable effect in improving the utilization rate of fertilizer and the yield and quality of agricultural products and Chinese medicinal materials. This study aims to explore the effect of ATP on the growth and root quality of Angelica sinensis. To be specific, Mingui 1 was used, and through the pot(soil culture) experiment in the Dao-di producing area, the effects of conventional chemical fertilizer added with ATP on the morphology, photosynthesis, soil respiration, and content of ferulic acid and volatile oil in roots of Mingui 1 were detected. The underlying mechanism was discussed from the perspective of source-sink relationship. The results showed that ATP, via the fertilizer slow-release effect, could meet the needs of A. sinensis for nutrients at the root expansion stage, improve the net photosynthetic rate of leaves and aboveground biomass of plants, and promote the transfer and accumulation of nutrients from the aboveground part(source) to the underground root(sink) in advance during the dry matter accumulation period of roots, so as to improve the root weight per plant. ATP can increase the content of total ferulic acid(the sum of free ferulic acid and coniferyl ferulate), the main effective component of Angelicae Sinensis Radix, by promoting the synthesis of ferulic acid in the roots and the transformation to coniferyl ferulate. However, it had little effect on the content of volatile oil. ATP had certain influence on soil respiration, which needs to be further explored from root activity, rhizosphere microorganisms, and soil microorganisms. This study can lay a basis for soil remediation and improvement and ecological cultivation of A. sinensis.

Direct axial plane imaging of particle manipulation with nondiffracting Bessel beams.

Optical manipulation with nondiffracting beams has been attracting great interest and finding widespread applications in many fields such as chemistry, physics, and biomedicine. Generally, optical manipulation is conducted in an optical microscopy system, which, in general, only allows for imaging motions of particles in the transverse plane, rendering the observation of dynamics processes occurring in the axial plane impractical. We propose and demonstrate an optical manipulation system that incorporates an axial plane imaging module. With this system, the trapping behavior in the transverse plane and the transportation process in the axial plane of a particle immersed in a Bessel beam were acquired simultaneously in real time.

[Current status of organophosphorus pesticide residues in root and rhizome medicinal materials and research progress of rapid detection methods].

The medicinal plants with roots and rhizomes as the medicinal parts account for about 1/3 of Chinese medicinal herbs. Root and rhizome medicinal materials are widely used in clinical practice, whereas their wild resource reserves are insufficient to meet the market demand. With the expansion of planting areas, the formation of large-scale production areas, and the increase in planting years, diseases and insect pests of these medicinal plants, which are diverse and have broad transmission routes, strong concealment, and heavy damage, have become more and more serious. The prevention and control of these diseases and insect pests is characterized by multiple ways of pesticide application, large consumption of pesticides, susceptibility to soil barrier, difficulty in the control, and unstable control efficiency. Organophosphorus pesticides(OPPs) are widely used in the cultivation of Chinese medicinal plants because of their diverse varieties, broad-spectrum, good efficacy, and low residues, and have a positive effect on the yield and quality of Chinese medicinal materials. However, the abuse of OPPs not only increases the planting cost, but also affects the quality and safety of Chinese medicinal plants, the safety of clinical use of Chinese medicine, and the ecological safety of production areas. This paper reviewed the research and development progress of OPPs, the registration status of OPPs used in root and rhizome medicinal materials, residue limit standards, residue status, and rapid detection technology progress of OPPs. This review aims to provide research ideas and references for standardizing the use of OPPs in root and rhizome medicinal materials, reducing OPP residues, and establishing a fast, efficient, accurate, and reliable method for the detection of OPP residues in Chinese herbal medicine.

Polarization-dependent micro-structure fabrication with direct femtosecond laser writing on plastic polarizer films.

Iodine-doped polyvinyl alcohol (IDPVA) film has been widely used as a plastic polarizer due to its great linear dichroism. We found that the anisotropic character of the plastic polarizer can be permanently damaged upon exposure of high intensity femtosecond laser pulses. This process is a two-photon-induced chemical reaction and denominated as two-photon-induced isotropy (TPII). The TPII effect can form a high polarization contrast on the base of the original IDPVA films. With this property, polarization-sensitive diffractive optical elements are fabricated in IDPVA films. The low cost of the IDPVA film and the high polarization contrast of TPII make it a promising new candidate for femtosecond laser fabrication of polarization-selective optical elements.

Full-polarization wavefront shaping for imaging through scattering media.

The scattering effect occurring when light passes through inhomogeneous-refractive-index media such as atmosphere or biological tissues will scramble the light wavefront into speckles and impede optical imaging. Wavefront shaping is an emerging technique for imaging through scattering media that works by addressing correction of the disturbed wavefront. In addition to the phase and amplitude, the polarization of the output scattered light will also become spatially randomized in some cases. The recovered image quality and fidelity benefit from correcting as much distortion of the scattered light as possible. Liquid-crystal spatial light modulators (LC-SLMs) are widely used in the wavefront shaping technique, since they can provide a great number of controlled modes and thereby high-precision wavefront correction. However, due to the working principle of LC-SLMs, the wavefront correction is restricted to only one certain linear polarization state, resulting in retrieved image information in only the right polarization, while the information in the orthogonal polarization is lost. In this paper, we describe a full-polarization wavefront correction system for shaping the scattered light wavefront in two orthogonal polarizations with a single LC-SLM. The light speckles in both polarizations are corrected for retrieval of the full polarization information and faithful images of objects. As demonstrated in the experiments, the focusing intensity can be increased by full-polarization wavefront correction, images of objects in arbitrary polarization states can be retrieved, and the polarization state of the object's light can also be recognized.

[Soil ecological effect of attapulgite and its application prospect in ecological planting of Chinese materia medica].

The long-term and extensive use of chemical fertilizers and pesticides in the cultivation of Chinese materia medica has resulted in serious soil ecological and environmental problems such as secondary salinization, soil consolidation, soil acidification, continuous cropping obstacles, micro-ecological imbalance, and serious soil pests and diseases in the production areas of Chinese materia medica. Therefore, promoting the ecological planting of Chinese materia medica is the only way for the production of Chinese materia medica. Attapulgite(ATP) is a kind of water-rich magnesium-rich aluminosilicate clay mineral with layered and chain structure. It has abundant reserves in China, possesses nano-material properties, strong adsorption and ion exchange properties, and has huge high value utilization space. ATP and its functional products have the potential of water and fertilizer conservation, regulating soil structure and micro-ecology, and are widely used in ecological planting of Chinese materia medica. This paper reviews the resource distribution, structural characteristics, the research and application progress in soil ecological effects of ATP, and prospects the application prospects of it in the ecological planting of Chinese materia medica.

Real-time optical manipulation of particles through turbid media.

Complex diffusive scattering media pose significant challenges for light focusing as well as optical imaging to be implemented in practice. Recently, it has been demonstrated that the wavefront shaping technique can be applied to realize focusing and imaging through scattering medium. Here we report dynamic optical manipulation of particles through turbid media by employing the interleaved segment wavefront correction method, which is an improved genetic algorithm providing faster convergence speed and higher peak to background ratio. Manipulating micro-beads behind a scattering medium along both one and two dimensional predesigned trajectories in real time has been successfully demonstrated.

Robust contrast-transfer-function phase retrieval via flexible deep learning networks: publisher's note.

This publisher's note contains corrections to Opt. Lett.44, 5141 (2019)OPLEDP0146-959210.1364/OL.44.005141.

Robust contrast-transfer-function phase retrieval via flexible deep learning networks.

By exploiting the total variation (TV) regularization scheme and the contrast transfer function (CTF), a phase map can be retrieved from single-distance coherent diffraction images via the sparsity of the investigated object. However, the CTF-TV phase retrieval algorithm often struggles in the presence of strong noise, since it is based on the traditional compressive sensing optimization problem. Here, convolutional neural networks, a powerful tool from machine learning, are used to regularize the CTF-based phase retrieval problems and improve the recovery performance. This proposed method, the CTF-Deep phase retrieval algorithm, was tested both via simulations and experiments. The results show that it is robust to noise and fast enough for high-resolution applications, such as in optical, x-ray, or terahertz imaging.