Artifact Image Research Articles

Single-Step Data-Domain Least-Squares Reverse-Time Migration Using Gabor Deconvolution for Subsalt Imaging

Least-squares reverse-time migration (LSRTM) distinctly improves seismic imaging quality, but at an expensive computation overhead involving tens of iterations. We herein take a computationally cheaper single-step LSRTM solution, which intrinsically performs deblurring through a data-domain Wiener deconvolution. However, the Wiener filter mainly solves the signal estimation problems for stationary signals. Subsalt imaging often suffers from strong salt-related reflections and artifacts. The former and the latter give rise to strong amplitude variance and changed source wavelets in the demigrated data, increasing its nonstationarity and hindering the data-deblurring operation in the single-step LSRTM. To alleviate the nonstationarity during the data-domain deblurring, we consider a Gabor deconvolution method. Testing on the Sigsbee data sets shows that the Gabor deconvolution method is effective, producing subsalt images of more balanced events and fewer artifacts than the raw RTM image. The Gabor deconvolution-related result also outperforms the standard single-step LSRTM result with more robust behavior and better subsalt imaging quality.

X-ray cone-beam computed tomography geometric artefact reduction based on a data-driven strategy.

Cone-beam computed tomography (CBCT) enables three-dimensional imaging of the internal structure of objects in a non-invasive way with high accuracy. Practical misalignment of the CBCT system causes geometric artefacts in reconstructed images, which seriously degrades image quality in ways such as detail loss and decreased spatial resolution. This leads to inaccurate distinction of defects in detection, especially in precise industrial fields like aerospace and instrument manufacturing. This paper presents a method to reduce the geometric artefacts based on a data-driven strategy, which is an end-to-end modified fully convolutional neural network (M-FCNN). The designed M-FCCN contains five convolution layers and five deconvolution layers for feature extraction and output image rebuilding, respectively. In addition, the pooling layer is not used in the designed M-FCNN, considering the preservation of details in the reconstructed image. In this M-FCCN, artefact images with different features have been trained separately. After training, the M-FCNN can be applied to directly reduce geometric artefacts in the reconstructed image. The designed M-FCNN has been demonstrated with different types of synthetic data and has achieved accurate results. It is also validated with practical data, including carbon composite and medical oral phantoms with comparable quality to phantom-based methods, proving that it is an effective way to reduce geometric artefacts in the image domain by means of a data-driven strategy.

Robust Beam Hardening Artifacts Reduction for Computed Tomography Using Spectrum Modeling

The aim of this paper is to develop a fast and accurate beam hardening correction method by modeling physical interactions between X-ray photons and materials for computed tomography (CT) imaging. The nonlinear attenuation process of the X-ray projection is modeled by reprojecting a template image with the estimated polychromatic spectrum. By adding the scaled difference of the monochromatic reprojection data and the polychromatic reprojection to the raw projection data, the raw projection data is mapped into the corresponding monochromatic projection data, which is to reconstruct the beam hardening artifacts corrected images. The algorithm can also be implemented in image-domain which takes the uncorrected image volume as input when there is an adequate model of the spectrum. In this case, the scaled difference is reconstructed to yield a set of artifacts images that can be added directly to the uncorrected images. Numerical simulations, experimental phantom data, and animal data which are acquired on a modern diagnostic CT scanner (Discovery CT750 HD, GE Healthcare, WI, USA), and a modern C-Arm CT scanner (Artis Zee, Siemens Healthcare, Forchheim, Germany), respectively, are used to evaluate the proposed method. The results show the proposed method significantly reduced both cupping and streak artifacts, and successfully recovered the Housfield units accuracy. Extensive studies suggest the proposed model-based method successfully corrects the beam hardening artifacts. This paper is practically useful and is promising to be applied to commercial products.

Wedge Cameras for Minimally Invasive Archaeology

Acquiring images of archaeological artifacts is an essential step for the study and preservation of cultural heritage. In constrained environments, traditional acquisition techniques may fail or be too invasive. We present an optical device including a camera and a wedge waveguide that is optimized for imaging within confined spaces in archeology. The major idea is to redirect light by total internal reflection to circumvent the lack of room, and to compute the final image from the raw data. We tested various applications on site during an archaeological mission in Medamoud (Egypt). Our device was able to successfully record images of the underground from slim trenches of about 15cm wide, including underwater trenches, and between rocks composing a wall temple. Experts agreed that the acquired images were good enough to get useful information that cannot be obtained as easily with traditional techniques.

Metal artifact reduction by monoenergetic extrapolation of dual-energy CT in patients with metallic implants.

The objective of this study is to assess artifact reduction and image quality using dual-energy computed tomography (DECT) and metal artifact reduction techniques in patients with metallic implants. Forty patients with metallic implants, who had targeted CT performed by DECT during March to September 2018, were prospectively recruited. Post-processing with monoenergetic extrapolation at 70 and 150 keV was performed. Forty matched controls with metallic implants with single-energy CT (SECT) performed were selected. Attenuation value, noise, and signal-to-noise ratio (SNR) at the site of maximal artifact were measured at muscle and fat areas. Image quality of three sets of images (70 keV, 150 keV, and SECT) was assessed by two independent reviewers using a 5-point Likert-type scale. Statistical analysis of measured values, Likert-type scales, and radiation doses (volume CT dose index (CTDIvol)) of DECT and SECT were performed with Mann-Whitney U test. As compared to SECT, high keV reconstruction of DECT show (1) significantly higher values within muscle and fat surrounding the implant (DECT vs. SECT-muscle: -96 Hounsfield units (HU) vs. -405 HU, fat: -115 HU vs. -301 HU; p < 0.001), (2) significantly lower mean image noise (75 HU vs. 129 HU; p = 0.02), and (3) higher SNR (-0.8 vs. -4.3; p < 0.001). In addition, image quality of high keV reconstruction was rated superior to the other two groups on Likert-type scales ( p < 0.001). The mean radiation doses (CTDIvol) were comparable between DECT and SECT (14.2 mGy vs. 19.3 mGy; p = 0.08). For patients with metallic implants, monoenergetic extrapolation of DECT at high keV can reduce metal artifacts, increase SNR, and improve qualitative image quality at comparable radiation dose.

Reduction of Metal Artifacts and Improvement in Dose Efficiency Using Photon-Counting Detector Computed Tomography and Tin Filtration.

The aim of this study was to investigate the impact on metal artifacts and dose efficiency of using a tin filter in combination with high-energy threshold (TH) images of a photon-counting detector (PCD) computed tomography (CT) system. A 3D-printed spine with pedicle screws was scanned on a PCD-CT system with and without tin filtration. Image noise and severity of artifacts were measured for low-energy threshold (TL) and TH images. In a prospective, institutional review board-approved, Health Insurance Portability and Accountability Act-compliant study, 20 patients having a clinical energy-integrating detector (EID) CT were scanned on a PCD-CT system using tin filtration. Images were reviewed by 3 radiologists to evaluate visualization of anatomic structures, diagnostic confidence, and image preference. Artifact severity and image noise were measured. Wilcoxon signed rank was used to test differences between PCD-CT TH and EID-CT images. Phantom TH images with tin filtration reduced metal artifacts and had comparable noise (32 HU) to TL images (29 HU) acquired without tin filtration. Visualization scores for the cortex, trabeculae, and implant-trabecular interface from PCD-CT TH images (4.4 ± 0.9, 4.4 ± 1.0, and 4.4 ± 1.0) were significantly higher (P < 0.0001) than EID-CT images (3.3 ± 1.3, 3.3 ± 1.2, and 3.3 ± 1.6). A strong preference was shown for PCD-CT TH images due to improved diagnostic confidence and decreased artifact severity. Noise in PCD-CT TH images (93 ± 41 HU) was significantly lower than that in EID-CT images (133 ± 92 HU, P < 0.05). Threshold high images acquired with tin filtration on PCD-CT demonstrated a substantial decrease in metal artifacts and an increase in dose efficiency compared with EID-CT.

Comparison of End-Expiration Versus End-Inspiration Breath-Holds With Respect to Respiratory Motion Artifacts on T1-Weighted Abdominal MRI.

OBJECTIVE. The purpose of this study was to compare respiratory motion artifact and diagnostic image quality between end-inspiration and end-expiration breath-holding techniques on unenhanced and contrast-enhanced axial T1-weighted MRI of the liver. MATERIALS AND METHODS. This retrospective observational study included 50 consecutive subjects undergoing axial T1-weighted liver MRI, with unenhanced images acquired with both end-inspiration and end-expiration breath-holding techniques, and with contrast-enhanced images acquired for 47 of the subjects with either the end-inspiration or the end-expiration breath-holding technique. Three radiologists performed blinded independent evaluations of each unenhanced sequence, contrast-enhanced sequence, and subtraction (contrast-enhanced minus unenhanced) image, using a scale ranging from 1 point (denoting nondiagnostic imaging) to 5 points (denoting no artifacts). Blinded side-by-side assessment of each pair of unenhanced sequences was also performed. Two-tailed Wilcoxon signed rank and Wilcoxon rank sum tests were used to assess statistical significance. RESULTS. A significant improvement in motion scores was noted for sequences acquired in end-expiration, compared with those acquired in end-inspiration, for unenhanced sequences (mean, 3.35 vs 2.80; p < 0.00001), contrast-enhanced sequences (mean, 4.02 vs 3.46; p = 0.0003), and subtraction images (mean, 3.67 vs 2.41; p < 0.00001). Severe degradation of image quality or nondiagnostic image quality was noted for 15% of unenhanced images (23/150), 0% of contrast-enhanced images, and 8% (5/63) of subtraction images acquired on end-expiration, whereas it was noted for 36% (54/150) of unenhanced images, 13% (10/78) of contrast-enhanced images, and 59% (46/78) of subtraction images acquired on end-inspiration. When side-by-side assessment of paired unenhanced sequences was performed, images acquired in end-expiration were significantly favored in 59% of paired sequences (88/150) (p < 0.00001), and no difference between images acquired with both breath-hold techniques was noted for 21% (32/150) of paired sequences. CONCLUSION. The end-expiration breath-holding technique leads to significant decreases in respiratory motion artifacts, compared with the end-inspiration technique, on unenhanced and contrast-enhanced T1-weighted liver MRI.

Quantitative Cone-Beam CT of Bone Mineral Density Using Model-Based Reconstruction.

We develop and validate a model-based framework for artifact correction and image reconstruction to enable application of Cone-Beam CT (CBCT) in quantitative assessment of bone mineral density (BMD). Compared to conventional quantitative CT, this approach does not require a BMD calibration phantom in the field-of-view during an object scan. The quantitative CBCT (qCBCT) imaging framework combined fast Monte Carlo (MC) scatter estimation, accurate models of detector response, and polyenergetic Poisson likelihood (PolyPL, Elbakri et al 2003). The underlying object model assumed that the tissues were ideal mixtures of water and calcium carbonate (CaCO3). Accuracy and reproducibility of qCBCT was evaluated in benchtop test-retest studies emulating a compact extremity CBCT system (axis-detector distance=56 cm, 90 kVp x-ray beam, ~16 mGy central dose). Various arrangements of Ca inserts (50-500 mg/mL) were placed in water cylinders of ~11 cm to ~15 cm diameter and scanned at multiple positions inside the field-of-view for a total of 20 configurations. In addition, a cadaveric ankle was imaged in five configurations (with and without Ca inserts and water bath). Coefficient of variation (CV) of BMD values across different experimental configurations was used to assess reproducibility under varying imaging conditions. The performance of the model-based qCBCT framework (MC + PolyPL) was compared to FDK with water beam hardening correction and MC scatter correction. The PolyPL framework achieved accuracy of 20 mg/mL or better across all insert densities and experimental configurations. By comparison, the accuracy of the FDK-based BMD estimates deteriorated with higher mineralization, resulting in ~120 mg/mL error for a 500 mg/mL Ca insert. Additionally, the model-based approach mitigated residual streaks that were present in FDK reconstructions. The CV of both methods was ~15% at 50 mg/mL Ca and less than ~8% for higher density inserts, where the PolyPL framework achieved 20-25% lower CV than the FDK-based approach. Accurate and reproducible BMD measurements can be achieved in extremity CBCT, supporting clinical applications in quantitative monitoring of fracture risk, osteoporosis treatment, and early osteoarthritis.

Adaptive Region-Segmentation Multi-Focus Image Fusion Based on Differential Evolution

An adaptive region-segmentation based multi-focus image fusion method is presented using a Laplacian pyramid transform which decomposes the pre-registered source images into approximate and detail coefficients. In order to avoid the disadvantage of fixed-size blocks, the adaptive differential evolution scheme is designed to compute the optimal-size block. Firstly, with approximate coefficients, the optimal-size blocks are iteratively calculated by an adaptive differential evolution algorithm. The initial decision diagram is then completed by comparing the regional sum-modified Laplacian energy of two corresponding blocks after the regional sum-modified Laplacian energy is calculated. Secondly, the initial decision diagram is optimized by the guided image filter to obtain the final decision diagram in order to avoid the block effect of boundary. With the decision diagram, the approximate coefficients are fused using the weighted mean rules, while the detail coefficients are fused using the regional gradient energy method. Finally, an inverse Laplacian pyramid transform is used to reconstruct the fused approximate coefficients and fused detail coefficients, and to acquire the fused image where all objects are clear. The experimental result proves that the proposed method produces fusion images of fewer artifacts or additional noise, with higher computational efficiency. The proposed method is also superior to the other state-of-the-art methods in both subjective visual effect and objective quantitative evaluation indicators.

A new method of three-dimensional morphometry for analyzing the functional potentialities of bifaces. Contribution to the study of artefacts from AU P3 from the “Caune de l’Arago” (France)

The analysis of the functional potential of bifaces, which are artefacts extending beyond our technical memory, is based on direct (micro-wear) or indirect approaches (experimentation, relationship between form/function, comparative ethnography). Indirect approaches are fundamental when artefacts are not well enough preserved for micro-wear analysis, which is frequent for the middle Pleistocene. This article proposes a new method based on the three-dimensional acquisition of artefact images, enabling us to measure cutting edge angles and depth of cut. This process allows us to distinguish, in particular, between cutting edges created for longitudinal or transverse cutting. The application of this analysis to bifaces from UA P3 of the “Caune de l’Arago” brings to light tools with a high functional potential for longitudinal cutting, some of which were used for incising, others for deep cutting. These results corroborate those obtained by most micro-wear analyses and present new ways of interpreting the functional potential of bifaces.

Image Artifacts in Optical Coherence Tomography Angiography Among Patients With Multiple Sclerosis

ABSTRACTPurpose: To evaluate artifacts in optical coherence tomography angiography (OCT-A) images of multiple sclerosis (MS) patients and healthy controls.Materials and methods: This was a prospective cross-sectional study conducted at the Department of Neurology and the Wilmer Eye Institute at Johns Hopkins Hospital. Subjects included patients with an established diagnosis of MS and healthy volunteers. OCT-A was performed using Spectralis® OCT-A prototype, OCT2 (Heidelberg, Germany). The type and frequency of artifacts, the clinical factors associated with them, and their impact on vessel density measurements were assessed.Results: Overall, 385 images from 102 participants were analyzed. The majority of images (97.1%) had some degree of artifact. The most frequent was motion artifact (96.3%), followed by blinking (51.9%), and loss of focus (25.1%). MS patients were more likely to have any artifact vs. controls (OR [95% CI], 3.83 [1.12–12.92]), and were more likely to have motion artifacts with longer disease duration (OR [95% CI], 1.11 [1.03–1.20]) or history of optic neuritis (OR [95% CI], 4.24 [1.19–15.16]). The relative area occupied by the artifact was found to underestimate vessel density measurements in both MS patients and controls.Conclusions: Artifacts are common with OCT-A imaging using this particular Spectralis® OCT-A prototype and can impact quantitative vascular density metrics. Future studies should review images for artifacts before drawing definitive conclusions

Magnetic resonance cholangiopancreatography using optimized integrated combination with parallel imaging and compressed sensing technique.

To assess the combined parallel imaging (PI) and optimized integrated compressed sensing technique (prototype Compressed SENSE) for magnetic resonance cholangiopancreatography (MRCP) compared with conventional MRCP. This prospective study was approved by our Institutional Review Board, and all patients provided written informed consent. A total of 56 consecutive patients (27 men and 29 women; mean age 67.2years) underwent breath-hold three-dimensional (3D) MRCP with PI alone (BH-MRCP; acquisition time, 23s), respiratory-triggered 3D MRCP with PI alone (RT-MRCP; 201s) and respiratory-triggered 3D MRCP with Compressed SENSE (RT-MRCPcs; 45s). Relative duct-to-periductal contrast ratios (RCs) of the pancreaticobiliary ducts were calculated for quantitative image analyses. Two radiologists graded the visibility of the pancreaticobiliary ducts, pancreatic cystic lesion, motion artifact, and overall image quality using a five-point rating scale for qualitative image analyses. Theses qualitative and quantitative measurements were then compared among the three sequences. RCs of the common bile duct, right hepatic duct (RHD), left hepatic duct (LHD), and main pancreatic duct at the pancreatic head, body, and tail segments, were significantly higher RT-MRCP, followed by RT-MRCPcs and BH-MRCP (P < 0.001). The visibility of the peripheral RHD and LHD was slightly better in RT-MRCP than in RT-MRCPcs and BH-MRCP (P < 0.001). The visibility of other pancreaticobiliary ducts, pancreatic cystic lesion, motion artifact, and overall image quality were almost comparable among three sequences. The acquisition time was markedly reduced in RT-MRCPcs compared with conventional RT-MRCP while there were significant differences in both quantitative and qualitative analyses, the differences were small enough that the reduced acquisition time makes up for it.

Improved Visualization of Juxtaprosthetic Tissue Using Metal Artifact Reduction Magnetic Resonance Imaging: Experimental and Clinical Optimization of Compressed Sensing SEMAC.

The purpose of this study was to identify an optimal imaging protocol for metal artifact reduced magnetic resonance imaging by application of different imaging and postprocessing parameters in compressed sensing slice-encoding for metal artifact correction (CS-SEMAC) and to test it in patients with total hip arthroplasty (THA). In an experimental setup, a phantom consisting of a standard THA embedded in gadolinium-containing agarose was scanned at 1.5 T. Pulse sequences included coronal short tau inversion recovery (STIR), T1-weighted (w), and T2-w CS-SEMAC sequences. All pulse sequences were acquired with 11, 19, and 27 slice-encoding steps (SESs), respectively. For each raw dataset, postprocessing was performed with variations of the parameters: (1) number of iterations (5, 10, 20, 30, 50) and (2) normalization factor (0.0005, 0.001, 0.002, 0.003, 0.005). Following, in clinical magnetic resonance scans of patients with THA, identical STIR, T1-w, and T2-w pulse sequences with 11 and 19 SESs were acquired and were postprocessed similarly with variations in parameters. Semiquantitative outcome measures were assessed on a 5-point scale (1 = best, 5 = worst). The overall best image quality was determined. Signal-to-noise ratio and contrast-to-noise ratio were calculated. Statistical analyses included descriptive statistics, t-tests, multivariate regression models, and partial Spearman correlations. Scan times varied between 2:24 (T2-w, 11 SESs) and 8:49 minutes (STIR, 27 SESs). Reconstruction times varied between 3:14 minutes (T1-w, 11 SESs, 5 iterations) and 85:00 minutes (T2-w, 27 SESs, 50 iterations). Signal-to-noise ratio and contrast-to-noise ratio increased with increasing SESs, iterations, and normalization factor. In phantom scans, artifact reduction was optimal with an intermediate normalization factor (0.001) and improved with higher SESs and iterations. However, iterations greater than 20 did not improve artifact reduction or image quality further. On the contrary, ripple artifacts increased with higher SESs and iterations. In clinical scans, up to 20 iterations reduced blurring of the image; no further reduction was observed with iterations greater than 20. A normalization factor of 0.001 or 0.002 was best for reduction of blurring, whereas the soft tissue contrast was better and the distortion of soft tissue was less severe with lower normalization factors. Overall best soft tissue image quality was found for STIR and T1-w images with 19 SESs, 10 iterations, and a normalization factor of 0.001, and for T2-w images with 11 SESs, 10 iterations, and a normalization factor of 0.0005. Optimized advanced acceleration and reconstruction algorithms of CS-SEMAC have been identified to reduce metal artifacts in patients with THA enabling imaging with clinically feasible acquisition and reconstruction times.

Reasons for inadequate or incomplete imaging techniques

Even if imaging has developed considerably during the last decades there still exist several factors which limit its capacities. These factors can either limit the usage of a technique or degrade images making them difficult to interpret. Magnetic resonance imaging (MRI) has, as an absolute contraindication, the presence of metallic devices marked as "MRI unsafe" and metallic foreign bodies close to the eye or vital structures. Claustrophobia and artefacts reduce the application and performance of MRI in a significant proportion of patients. The major disadvantages of computed tomography(CT) are the exposure to ionizing radiation inducing malignancies especially in pediatric patients and the risk of contrast induced allergies and nephropathy. Ultrasound is a safe, easily available and low-cost imaging technique without significant side effects for the patient. Obesity or bloating can severely limit ultrasound capacities.This paper written by radiologists and clinicians, highlights the main reasons leading to inadequate imaging and points out solutions to avoid inaccurate diagnosis due to incomplete imaging or presence of artifacts.

A New Modality for the Diagnosis of Bleomycin-induced Toxicity: Ultrasonography

ObjectiveTo evaluate the role of ultrasonography (USG) in the diagnosis of bleomycin-induced pulmonary toxicity (BT). Material and methodsThe study included patients with suspected BT during treatment with bleomycin due to various oncologic diseases between June 2015 and May 2017. The patients initially underwent clinical and high-resolution computed tomography (HRCT) examinations and pulmonary function tests (PFT)-diffusing capacity of the lung for carbon monoxide (DLCO), followed by registration of USG findings—number of comet tail artifact (CTA) images by a different pulmonologist. We compared the findings from USG, HRCT, and PFT–DLCO tests between BT and non-BT groups. With the diagnosis based on clinical-radiologic and PFT–DLCO assessments taken as the gold standard, we determined the sensitivity and specificity of the USG outcomes for diagnosis of BT. ResultsThe study included a total of 30 patients. Nine patients were diagnosed as having BT according to their clinical and radiologic findings and PFT–DLCO measurements. The mean number of CTA images was 68.7±22 in patients with BT vs 28.2±9.3 in those without BT (P<.001). The difference in CTA images between the patients with and without ground glass density was statistically significant (28.3±9.5 and 64.6±24.5, respectively, P<.001). In patients with BT, there was a negative correlation between the number of CTAs and DLCO% and FVC% values (P=.004; P=.016). USG had a sensitivity of 100%, and a specificity of 95% diagnosing BT in selected patients. ConclusionIn bleomycin-induced toxicity, USG findings are correlated with HRCT and PFT–DLCO findings, with a remarkably increased number of CTAs in BT. Thoracic USG examination is a diagnostic tool with a high sensitivity and specificity for diagnosing BT.

Metal artifact reduction on cervical CT images by deep residual learning

BackgroundCervical cancer is the fifth most common cancer among women, which is the third leading cause of cancer death in women worldwide. Brachytherapy is the most effective treatment for cervical cancer. For brachytherapy, computed tomography (CT) imaging is necessary since it conveys tissue density information which can be used for dose planning. However, the metal artifacts caused by brachytherapy applicators remain a challenge for the automatic processing of image data for image-guided procedures or accurate dose calculations. Therefore, developing an effective metal artifact reduction (MAR) algorithm in cervical CT images is of high demand.MethodsA novel residual learning method based on convolutional neural network (RL-ARCNN) is proposed to reduce metal artifacts in cervical CT images. For MAR, a dataset is generated by simulating various metal artifacts in the first step, which will be applied to train the CNN. This dataset includes artifact-insert, artifact-free, and artifact-residual images. Numerous image patches are extracted from the dataset for training on deep residual learning artifact reduction based on CNN (RL-ARCNN). Afterwards, the trained model can be used for MAR on cervical CT images.ResultsThe proposed method provides a good MAR result with a PSNR of 38.09 on the test set of simulated artifact images. The PSNR of residual learning (38.09) is higher than that of ordinary learning (37.79) which shows that CNN-based residual images achieve favorable artifact reduction. Moreover, for a 512 × 512 image, the average removal artifact time is less than 1 s.ConclusionsThe RL-ARCNN indicates that residual learning of CNN remarkably reduces metal artifacts and improves critical structure visualization and confidence of radiation oncologists in target delineation. Metal artifacts are eliminated efficiently free of sinogram data and complicated post-processing procedure.

ТРИ ФАЛЬШИВІ СЕРЕДНЬОВІЧНІ ЗАХІДНОЄВРОПЕЙСЬКІ ДЕНАРІЇ, ЗНАЙДЕНІ В РІВНЕНСЬКІЙ ОБЛАСТІ

SummaryEach year the interest to the study of the private counterfeits of coins for a loss of the money circulation increases. The introduction to the scientific circulation of the finds of the coins of X-XIII centuries is, in our opinion, also relevant in the context of the existence in the Ukrainian science of the thought that this time in the history of the money circulation was characterized by the almost complete refusal of the population to use the coin, laid the paradigm of the “Coinless period”. During the last five years, the Internet-resource Violiti has been presented at the Ukrainian numismatic forum for the identification of three coins with identical images. These coins have the same appearance, diameter and weight, all of them are false Western European pennies of the XIth -XII centuries, possibly embossed with the same dies (unfortunately, the poor consistency of coins does not give grounds for such a statement). The condition of these coins is generally unsatisfactional, some of the inscriptions and images are lost. All of the fake Western European pennies were excavated in Rivne region in Ukraine. It is tempting to assume that they could be made here. But until the dies or stamps (matrixes) for minting are found, it will remain a hypothesis. Most likely, they were brought in a certain quantity to these countries by visiting it by merchants from the West (or their own) and distributing them to deceive the local population. Also interesting is the fact of various ways of making a silver layer of these identical images of artifacts. We have analyzed the iconography, palaeography and technology of making of these old coin counterfeits. It is proved that these pennies have the same inscriptions and images and may have been manufactured with the same dies. However, they are made in different ways, two of them - by applying amalgams, and one - either by peeling or chipped from silver of a low sample. Excavating threee coins in one area may indicate their possible local fabrication, but proof of this should be stamped here. Most likely they were brought to this territory by merchants to deceive the local population. The common feature of the published counterfeit pennies is the presence of an image on the field of these imitations of a mysterious figure surrounded by dots in the center of the English-style imitation coins and on the sides of the cross in the simulation of Saxon-style pennies. Although these imitations, as experts say, are a distorted look of the face, and on our coins, perhaps, is a schematic image of the person walking to the left. The presence in the finds of the Ukrainian land of private forgeries of medieval Western-European coins and imitation proves once again by the fact that the European small silver coins were spreadly known among the population and it is quite anticipated that there were exist and the finds of it’s fakes are nowadays known. We believe that the presence on the territory of Ukraine of the findings of the private forgeries of the Western European medieval coins further indicates the popularity and widespread distribution of original prototypes of these coins on the territory of our country, which also minimizes the characterization of this historic period as a “Coinless period”.

Terahertz imaging for multiple reflectors using time-domain correlating synthesis method

We had proposed a correlating synthesis method for terahertz imaging using a pulse reflection mode terahertz time-domain spectrometry system. The efficiency of the method for improving the resolution and eliminating fake images was verified by numerical simulations and experiments with two metal cylinders. However, an artifact image between the two reflectors is markedly shown. Moreover, the multi-reflection and the influence of echo distortion caused by the directivity of the terahertz beam have not been discussed. For application of imaging complicated target, this paper addresses following issues: 1) multi-reflection between reflectors, as well as the effect of the direction of polarization of terahertz wave; 2) distortion of echo signals from targets distributed in a broader area, as well as the effect of concave lenses. Finally, the efficiencies of these proposals are verified by an imaging experiment with five metal cylinders.

The quantitative assessment of archaeological artifact groups: Beyond geometric morphometrics

Archaeologists often wish to distinguish between groups of cultural artifacts using information collected from descriptions or measurements of their morphological forms. Morphometric methods have played an increasingly large role in such quantitative assessments. However, standard approaches to morphometric analyses are often poorly suited to many artifact types as much variation of interest to archeologists cannot be quantified adequately by sparse sets of landmarks or semilandmarks. Use of measurement conventions also requires that investigators know which aspects of the artifacts under consideration are important to include at the outset of an investigation. In this review results obtained from landmark-semilandmark-based, and image pixel-based assessments of a common set of Paleoindian fluted projectile points are compared. Results confirm that, by itself, PCA is unsuited for the assessment of between-group differences irrespective of data type, but can be useful as a transformation to reduce the dimensionality of a morphological dataset while retaining its effective information content. Landmark-semilandmark data analysed using geometric morphometric methods delivered the lowest-quality results whereas image pixel data analysed by the Naïve Bayes machine-learning classifier delivered the highest. Direct analyses of artifact images using geometric morphometric methods delivered very good results. These findings suggest that the direct analyses of digital images and 3D scans, using either geometric morphometric data-analysis methods or machine-learning procedures, can provide archaeologists with tools that improve and extend the scope of their assessments of a wide range of artifact types.

Korean Crafts History by Hwang Su-young and Chin Hong-sup : Current Historiography and Future Prospects

Hwang Su-young and Chin Hong-sup conducted historical researches on Korean crafts mainly in 1960s and 1970s. Covering various types of crafts and preserving primary sources that had been disappearing, their researches represent the emergence of the field of Korean crafts history. This article examines their researches in Korean crafts history from historiographical perspectives along with changing research environment and tasks for future prospects in the field. Hwang Su-young, who was a professor in the Dongguk University, wrote excellent articles on Buddhist crafts such as Buddhist bells, bronze gong, incense burners, and Buddhist reliquaries. He carried out in-depth researches about ancient Korean pagodas and Buddhist reliquaries, focusing on the relic enshrinements of the wooden pagoda in Hwangryongsa temple site and of the five-story stone pagoda in Wanggungli temple site. In 1978, he founded the Research Association of Korean Buddhist Bells together with Professor Yeom Young-ha in the College of Engineering in the Seoul National University, initiating interdisciplinary studies about Buddhist bells. While serving as the director of the Gyeongju National Museum in 1950s, Chin Hong-sup made great endeavor to excavate ancient archaeological sites in Gyeongju and to preserve metal works such as golden crowns from ancient tombs of Silla. At the same time, he organized special exhibitions of Korean arts in foreign countries including, but not limited to, the US. his overseas experiences gave him much broader perspectives on methodologies in art history and museology. As a professor in the Ewha Womans University, he excavated ancient tombs, pagodas, and kilns with many students and researchers in the university museum. In addition, he wrote several preliminary research books on Korean metalcrafts and ceramics for education. The shared methodology of the two scholars in their studies of Korean crafts history, that is, close and detailed examination of objects, is still valid in current research in the field. However, the research environment in Korean crafts history has dramatically changed since the late twentieth century with the newly excavated artifacts using more advanced archaeological methods; the development of conservation science; and the increasing prevalence of digital materials. For example, various textual records including the Annals of the Joseon Dynasty have been computerized; images of artifacts collected in museums became accessible on the internet; replicas made with the technologies of three-dimensional scanning and printing began to appear. These changes in research environment in Korean art history greatly have affected current scholars in the field of Korean crafts. Under these circumstances, future studies in Korean crafts history have to be processed by combining the traditional method of careful observations on the original artifacts with a new method of scientific investigation.