Image Quality Value Research Articles

EBSD-based image quality analysis of in-situ tempered martensitic steel generated by L-PBF

Microstructures resulting from additive manufacturing technologies, such as laser powder bed fusion (L-PBF), can exhibit both intended and unintended gradation. Intended in form of functionally graded materials (FGM) providing improved material performance. Un-intended in form of part specific local changes due to variations in thermal boundary conditions resulting from the geometry at hand (e.g. slender lattices or downskin areas). To characterize, avoid and optimize such gradations, vast spacial measurements are necessary. This work investigates if electron backscatter diffraction (EBSD) can provide such information, to characterize the microstructural gradation of low alloy steel. Central to this work is the analysis of the image quality (IQ), since the tempering of martensitic steel microstructures results in a reduction of dislocation density, changes in carbide precipitation as well as crystal structure and thus varying IQ. Based on the multi-peak IQ approach and information about the thermal history, the microstructure is considered as purely martensitic. The analysis of single laser track experiments reveals that the impact of cooling rates as well as in-situ tempering effects can be measured, which present the two major effects regarding microstructural formation in L-PBF. Experiments on in-situ and conventionally heat-treated samples show correlating trends regarding tempering states, hardness and IQ distribution. Vast measurements over a sample size of 10 × 10 mm2 demonstrate the possibility to analyze FGM. Furthermore, micro-gradations are observed within each laser track within the material. Consistent trends and correlations indicate that microstructural changes dominate changes in IQ values, while the impact of EBSD parameter and sample preparation appears to be minor. The results promote the suitability of IQ analysis for the spatial characterization of low alloy steel generated by L-PBF.

Effect of Loading and Unloading Strain Rates on Creep-Fatigue Damage of Polycrystalline Ni-Based Superalloy at Elevated Temperatures

Ni-based superalloys have been subjected to random creep-fatigue load in high-temperature environment to compensate the fluctuation of the output of renewable energies. However, under the creep-fatigue condition, intergranular cracking was found to be accelerated, and the fracture life of the alloy was significantly decreased. Therefore, it is essential to elucidate the mechanism of this acceleration of crack propagation rate of the creep-fatigue damage. In this study, intermittent creep-fatigue tests were applied to Alloy 617, one of the Ni-based superalloys, and the degradation process of its crystallinity was monitored by IQ (Image Quality) values obtained by EBSD (Electron Back-Scatter Diffraction) method. In particular, the effect of strain rate during loading and unloading processes were evaluated in detail. The results showed that under creep-fatigue loading, the faster the strain rate during unloading, the earlier the IQ value decreased and the shorter the time for the initiation of intergranular cracking. It was also found that intergranular cracking appeared when the IQ value reached a critical value regardless of the strain rate.

Electron Backscatter Diffraction (EBSD) analysis of laser-cladded AISI 420 martensitic stainless steel

Laser cladding is a laser-based additive manufacturing (AM) process that is currently being used to coat part of a substrate or to produce a three-dimensional object in layer by layer following a computer-controlled instruction. In this study, laser-cladded AISI 420 martensitic stainless steel was characterized using the Electron Backscatter Diffraction (EBSD) technique to analyze the substructure of martensite in the selected zones such as the bead zone (BZ), the dilution zone (DZ), and the interface with the heat affected zone (HAZ) of the bead. The EBSD prior austenite grain (PAG) maps and inverse pole figure (IPF) revealed planer and columnar grains at the interface and within the adjacent dilution zone, while equiaxed and a combination of both columnar and equiaxed grains were observed in the center of the bead and dilution zone. The Grain Orientation Spread (GOS) and grain average Image Quality (IQ) techniques were used to quantify the grain misorientation and residual strain/stress in those selected zones. The EBSD analysis with the GOS and IQ values confirmed deformation and strain in the crystal lattice structure of those respective zones. The GOS approach revealed that most of the grains at the BZ and HAZ were highly strained and 26–59% fraction of the grains was at a high angle of GOS (3°–5°) indicating the availability of highly deformed grains in both regions. The IQ value was compared and correlated with the experimental values of residual stresses (RS) measured by XRD methods to understand residual strain distribution in those zones. It was revealed that the IQ value is inversely proportional to the RS value found in an earlier study. This EBSD parameter is expected to be used as an alternative method of analyzing RS distribution in the laser-cladded coating.

Back-of-the-envelope image quality estimation using the national image interpretability rating scale.

For an optical imaging system, the critical output is the image itself, and therefore, the quality of that image is of utmost importance. To estimate or predict the image quality (IQ), a simulation/model is typically created to yield an output image, given an imaging system and an object/scene. The IQ is typically graded based on the imaging system along with the scene. Developing an imaging simulation and creating input scenes to produce IQ results can be time-consuming, leading to a desire for a simple method to estimate the predicted IQ. This work develops a national image interpretability rating scale (NIIRS) IQ value based on simplifying assumptions for remote-sensing purposes. While the results are on the optimistic side, this back-of-the-envelope IQ estimation allows the process of developing a new imaging system to move forward more in parallel rather than in series, i.e., developing an imaging full simulation/model in parallel with designing/procuring hardware.

Image quality and diagnostic value of ultra low-voltage, ultra low-contrast coronary CT angiography.

To explore the image quality (IQ) and diagnostic value of 70kVp turbo high-pitch coronary CT angiography (THP-CCTA) using automated tube voltage selection (ATVS) and 30mL of low-concentration contrast agent. Patients who underwent 70kVp THP-CCTA using ATVS with 30mL of contrast agent (group A) were prospectively enrolled, and those who underwent conventional CCTA (100/120kVp, prospective sequential mode with 65-75mL of contrast agent) (group B) were retrospectively selected for study. IQ was assessed subjectively on a 5-point scale, and diagnostic value was assessed based on invasive coronary angiography as the gold standard. Heart rate (HR), HR fluctuation (HRF), body mass index (BMI), effective radiation dose (ED), and iodine uptake (IU) were recorded. A total of 796 patients (398/398 in groups A/B) were included. Between-group differences in age, gender, BMI, HR, HRF, and IQ values were not significant. The ED/IU values were 0.3 ± 0.1mSv/9.0 ± 0.0g and 5.8 ± 1.8mSv/22.9 ± 1.0g in groups A and B, respectively (p < 0.01). The sensitivity, specificity, positive and negative predictive values, and accuracy of THP-CCTA for the diagnosis of ≥ 50% stenosis were 94.8%, 97.5%, 92.0%, 98.4%, and 96.9% respectively. The mean HR and coronary calcium score were independent predictors of diagnostic image quality, and the best cutoff values were 71.5bpm and 444.1 respectively. This third-generation dual-source CT imaging modality, a 70-kVp THP-CCTA system using ATVS with 30mL of low-concentration contrast agent, produces high-quality images with high diagnostic accuracy for significant stenosis, with ultra low ED and IU. This technique was most promising in individuals with an HR < 71.5bpm and coronary calcium score < 444.1. • Turbo high-pitch CCTA using 70kVp via automated tube voltage selection and 30mL of low-concentration contrast agent is feasible. • This protocol provides high diagnostic accuracy for significant coronary stenosis and reduces radiation doses and iodine uptake significantly. • This protocol was most promising in individuals with an HR < 71.5bpm and coronary calcium score < 444.1.

Single-phase coronary artery CT angiography extracted from stress dynamic myocardial CT perfusion on third-generation dual-source CT: Validation by coronary angiography

BackgroundCT advances allow coronary arterial tree to be entirely covered during one CTP scan. Our aim was to investigate the potential value of single-phase coronary CT angiography (SP-CCTA) extracted from stress dynamic myocardial CT perfusion (CTP) for coronary artery stenosis assessment. MethodsConsecutive symptomatic patients were prospectively recruited and scanned with an ATP-stress dynamic myocardial CTP and routine CCTA protocol using third-generation DSCT. Noise reduction was applied to optimize image quality (IQ), the CTP phase with the best enhancement of the coronary arteries was selected as the SP-CCTA. IQ was assessed qualitatively. Using coronary angiography (CAG) as the reference standard, the diagnostic performance for stenosis detection was compared for SP-CCTA and routine CCTA. Results56 patients underwent the CTP and CCTA examination, among which 39 patients underwent CAG. The qualitative IQ scores of SP-CCTA were similar to that of routine CCTA (p > 0.05). On a per-segment basis, the sensitivity, specificity, positive predictive value, negative predictive value, diagnostic accuracy and area under the receiver-operating-characteristic curve results of SP-CCTA and routine CCTA for diagnosis of stenosis ≥50% exhibited no significant difference (SP-CCTA: 78.1%, 94.9%, 77.4%, 95.1%, 91.6% and 0.935 vs. routine CCTA: 74.7%, 95.3%, 78.0%, 95.3%, 91.6% and 0.937; all p > 0.05). The mean effective radiation dose of CTP and routine CCTA plus CTP were 3.92 ± 1.72 mSv and 5.98 ± 2.01 mSv (p < 0.05), respectively. ConclusionsThe IQ and diagnostic value of SP-CCTA was equivalent to routine CCTA on third-generation DSCT. SP-CCTA images from CTP may potentially replace a separate routine CCTA, allowing the possibility of “one-stop” cardiac examination for high-risk CAD patients who need myocardial ischemia assessment.

Effect of the Crystallinity on the Electromigration Resistance of Electroplated Copper Thin-Film Interconnections

Dominant factors of electromigration (EM) resistance of electroplated copper thin-film interconnections were investigated from the viewpoint of temperature and crystallinity of the interconnection. The EM test under the constant current density of 7 mA/cm2 was performed to observe the degradation such as accumulation of copper atoms and voids. Formation of voids and the accumulation occurred along grain boundaries during the EM test, and finally the interconnection was fractured at the not cathode side but at the center part of the interconnection. From the monitoring of temperature of the interconnection by using thermography during the EM test, this abnormal fracture was caused by large Joule heating of itself under high current density. In order to investigate the effect of grain boundaries on the degradation by EM, the crystallinity of grain boundaries in the interconnection was evaluated by using image quality (IQ) value obtained from electron backscatter diffraction (EBSD) analysis. The crystallinity of grain boundaries before the EM test had wide distribution, and the grain boundaries damaged under the EM loading mainly were random grain boundaries with low crystallinity. Thus, high density of Joule heating and high-speed diffusion of copper atoms along low crystallinity grain boundaries accelerated the EM degradation of the interconnection. The change of Joule heating density and activation energy for the EM damage were evaluated by using the interconnection annealed at 400 °C for 3 h. The annealing of the interconnection increased not only average grain size but also crystallinity of grains and grain boundaries drastically. The average IQ value of the interconnection was increased from 4100 to 6200 by the annealing. The improvement of the crystallinity decreased the maximum temperature of the interconnection during the EM test and increased the activation energy from 0.72 eV to 1.07 eV. The estimated lifetime of interconnections is increased about 100 times by these changes. Since the atomic diffusion is accelerated by not only the current density but also temperature and low crystallinity grain boundaries, the lifetime of the interconnections under EM loading is a strong function of their crystallinity. Therefore, it is necessary to evaluate and control the crystallinity of interconnections quantitatively using IQ value to assure their long-term reliability.

Evaluation of automatic image quality assessment in chest CT – A human cadaver study

PurposeThe evaluation of clinical image quality (IQ) is important to optimize CT protocols and to keep patient doses as low as reasonably achievable. Considering the significant amount of effort needed for human observer studies, automatic IQ tools are a promising alternative. The purpose of this study was to evaluate automatic IQ assessment in chest CT using Thiel embalmed cadavers. MethodsChest CT’s of Thiel embalmed cadavers were acquired at different exposures. Clinical IQ was determined by performing a visual grading analysis. Physical-technical IQ (noise, contrast-to-noise and contrast-detail) was assessed in a Catphan phantom. Soft and sharp reconstructions were made with filtered back projection and two strengths of iterative reconstruction. In addition to the classical IQ metrics, an automatic algorithm was used to calculate image quality scores (IQs). To be able to compare datasets reconstructed with different kernels, the IQs values were normalized. ResultsGood correlations were found between IQs and the measured physical-technical image quality: noise (ρ=−1.00), contrast-to-noise (ρ=1.00) and contrast-detail (ρ=0.96). The correlation coefficients between IQs and the observed clinical image quality of soft and sharp reconstructions were 0.88 and 0.93, respectively. ConclusionsThe automatic scoring algorithm is a promising tool for the evaluation of thoracic CT scans in daily clinical practice. It allows monitoring of the image quality of a chest protocol over time, without human intervention. Different reconstruction kernels can be compared after normalization of the IQs.

銅二結晶試料の材料強度評価

In this study, the tensile strength of a bicrystal sample cut from a polycrystalline copper thin film was investigated by applying a micro tensile test system. As the previous researches have showed that the crystallinity of a grain boundary was evaluated quantitatively by using IQ (Image Quality) value obtained from EBSD (Electron Back-Scatter Diffraction) analysis, and plastic deformations started to occur in one grain in the sample when the IQ value was higher than 3500. In this study, the plastic deformation of one grain was observed in detail after the sample was pulled off by using SEM (Scanning electron microscope). Slip bands were observed clearly on the fracture surface.

Effect of Crystallographic Quality of Grain Boundaries on Both Mechanical and Electrical Properties of Electroplated Copper Thin Film Interconnections

Effects of crystallographic quality of grain boundaries on mechanical and electrical properties were investigated experimentally. A novel method using two parameters of image quality (IQ) and confidence index (CI) values based on electron back-scattering diffraction (EBSD) analysis was proposed in order to evaluate crystallographic quality of grain boundaries. IQ value was defined as an index to evaluate crystallinity in region irradiated with electron beam. CI value determined existence of grain boundaries in the region. It was found that brittle intergranular fatigue fracture occurred in the film without annealing and the film annealed at 200 °C because network of grain boundaries with low crystallinity remained in these films. On the other hand, the film annealed at 400 °C caused only ductile transgranular fatigue fracture because grain boundaries with low crystallinity almost disappeared. From results of measurement of electrical properties, electrical resistivity of copper interconnection annealed at 400 °C with high crystallinity (2.09 × 10−8 Ωm) was low and electron migration (EM) resistance was high compared with an copper interconnection without annealing with low crystallinity (3.33 × 10−8 Ωm). It was clarified that the interconnection with high crystallinity had superior electrical properties. Thus, it was clarified that the crystallographic quality of grain boundaries has a strong correlation of mechanical and electrical reliability.

Estimation of Phosphorus-Implanted 4H-SiC Layer Recrystallization by Electron-Back-Scattering Diffraction Pattern Analysis

Image quality (IQ) values of an electron-back-scattering diffraction (EBSD) pattern were used to investigate layer recrystallization for the phosphorus-implanted 4H SiC. We prepared a slope-structured amorphous Si on a Si substrate sample to simulate the recrystallization model of the ion-implanted layer after activation annealing. Phosphorus-implanted and recrystallize-annealed Si and SiC samples were also investigated and the Kikuchi-pattern obscuration was observed for a thicker a-Si layer on the slope-structured sample. The IQ values also decreased. Our results show that ion-implantation damage recovery can be estimated by the EBSD pattern analysis. IQ value variation is in good agreement with the sheet resistance changing with the annealing temperature. The IQ values obtained from the EBSD measurements can be used for crystalline recovery estimation on impurity-implanted SiC layer in a nanoscale resolution.

OS1205 結晶粒界品質の定量的評価手法の提案

A novel evaluation method of the crystallinity of grain boundaries was proposed by analyzing the quality of Kikuchi lines obtained from the conventional EBSD (Electron Backscatter Diffraction) analysis. This method can evaluate the porous and brittle grain boundaries by using the IQ (Image Quality) values and the CI (Confidence Index) values. Both the IQ and CI values are the parameters which are obtained from the observed Kikuchi pattern obtained from the area where electron beams penetrate during EBSD analysis. The position of the grain boundaries is determined by this CI value, and the crystallinity of the film around grain boundaries is evaluated by the IQ value quantitatively. By using this method, the grain boundary degradation of the electroplated copper thin-film interconnection due to SM (Stress-induced Migration) was evaluated quantitatively and the effectiveness of the concept of grain boundaries based on the ordering quality of atomic arrangement which is different from the conventional one based on the crystal orientation has been shown.

Free-Breathing Contrast-Enhanced Multiphase MRI of the Liver Using a Combination of Compressed Sensing, Parallel Imaging, and Golden-Angle Radial Sampling

The objectives of this study were to develop a new method for free-breathing contrast-enhanced multiphase liver magnetic resonance imaging (MRI) using a combination of compressed sensing, parallel imaging, and radial k-space sampling and to demonstrate the feasibility of this method by performing image quality comparison with breath-hold cartesian T1-weighted (conventional) postcontrast acquisitions in healthy participants. This Health Insurance Portability and Accountability Act-compliant prospective study received approval from the institutional review board. Eight participants underwent 3 separate contrast-enhanced fat-saturated T1-weighted gradient-echo MRI examinations with matching imaging parameters: conventional breath-hold examination with cartesian k-space sampling volumetric interpolate breath hold examination (BH-VIBE) and free-breathing acquisitions with interleaved angle-bisection and continuous golden-angle radial sampling schemes. Interleaved angle-bisection and golden-angle data from each 100 consecutive spokes were reconstructed using a combination of compressed sensing and parallel imaging (interleaved-angle radial sparse parallel [IARASP] and golden-angle radial sparse parallel [GRASP]) to generate multiple postcontrast phases.Arterial- and venous-phase BH-VIBE, IARASP, and GRASP reconstructions were evaluated by 2 radiologists in a blinded fashion. The readers independently assessed quality of enhancement (QE), overall image quality (IQ), and other parameters of image quality on a 5-point scale, with the highest score indicating the most desirable examination. Mixed model analysis of variance was used to compare each measure of image quality. Images of BH-VIBE and GRASP had significantly higher QE and IQ values compared with IARASP for both phases (P < 0.05). The differences in QE between BH-VIBE and GRASP for the arterial and venous phases were not significant (P > 0.05). Although GRASP had lower IQ score compared with BH-VIBE for the arterial (3.9 vs 4.8; P < 0.0001) and venous (4.2 vs 4.8; P = 0.005) phases, GRASP received IQ scores of 3 or more in all participants, which was consistent with acceptable or better diagnostic image quality. Contrast-enhanced multiphase liver MRI of diagnostic quality can be performed during free breathing using a combination of compressed sensing, parallel imaging, and golden-angle radial sampling.

Impact of iterative reconstruction on CNR and SNR in dynamic myocardial perfusion imaging in an animal model

To evaluate a new iterative reconstruction (IR) algorithm for radiation dose, image quality (IQ), signal-to-noise-ratio (SNR), and contrast-to-noise-ratio (CNR) in multidetector computed tomography (MDCT) dynamic myocardial perfusion imaging (MPI). ECG-gated 256-slice MDCT dynamic MPI was performed in six pigs after subtotal balloon occlusion of one artery. Two 100 kVp protocols were compared: high dose (HD): 150 mAs; low dose (LD): 100 mAs. HD images were reconstructed with filtered back projection (FBP), LD images with FBP and different strengths of IR (L1, L4, and L7). IQ (5-point scale), SNR, and CNR (ischemic vs. normal myocardium) values derived from the HD (FBP) images and the different LD images were compared. Mean SNR values for myocardium were 16.3, 11.3, 13.1, 17.1, and 28.9 for the HD, LD (FBP), LD (L1), LD (L4), and LD (L7) reconstructions, respectively. Mean CNR values were 8.9, 6.3, 7.8, 9.3, and 12.8. IQ was scored as 4.6, 3.3, 4.4, 4.7, and 3.4, respectively. A significant loss of IQ was observed for the LD (L7) images compared to the HD (FBP) images (P < 0.05). Appropriate levels of iterative reconstruction can improve SNR and CNR, facilitating radiation dose savings in CT-MPI without influencing diagnostic quality. Iterative reconstruction (IR) can reduce radiation dose in myocardial perfusion CT. Our study also demonstrated improvements in image quality (noise, SNR, and CNR). Dynamic CT-MPI could help determine the hemodynamic significance of coronary artery disease. With dynamic CT MPI, myocardial blood flow can be determined quantitatively.