KEYWORDS: Thermography, Reflection, Signal to noise ratio, Material characterization, Finite element methods, Defect detection, Infrared radiation, Temperature distribution
Recent years have seen substantial growth of pulsed thermography as a popular non-destructive testing tool to characterise surface and near-surface defects for both metals and composites. The current research focus is on material characterisation to determine material thermal properties such as thermal diffusivity. However, most of these studies have focused on using the reflection mode of pulsed thermography where data is captured from the front wall of the specimen at which the heat flux is applied. The transmission mode, where the heat flux is applied on the front wall and data is acquired at the back wall, has not been investigated as comprehensively as the reflection mode. Research has indicated that the transmission mode is able to detect defects deeper into the specimen when compared to the reflection mode however, it has mainly been used as an indicator to detect defects and not to quantify the depth of subsurface defects within the specimen. This study develops a finite element model using the commercially available software COMSOL to investigate material characterisation using both the reflection and transmission modes of pulsed thermography. A finite element model of a thin steel plate was first created followed by the application of a heat flux to the front surface for the model. The solvers from the software were used to record the temperature variation on both the front and back surfaces. Results show that the thermal contrast curves on the backwall were less sensitive to changes in depth compared to changes in defect size. Furthermore, this study provides motivation for conducting a more in-depth study of the through transmission thermography to better understand its capabilities.
KEYWORDS: Ultrasonography, Fetus, Biometrics, 3D metrology, Reconstruction algorithms, Teleradiology, 3D image processing, 3D displays, 3D acquisition, Image quality
We have built upon an existing freehand 3D ultrasound imaging technique to enable display-less scanning at a local site by novice users and remote reading by integrating an electromagnetic tracker with a 2D probe. Seventy-two volumes are generated using a reconstruction algorithm from data collected by three users in a single longitudinal sweep across a 23- week fetus phantom in four different configurations for six scan durations ranging from 5-s to 30-s. The acquisition is semi-blinded: the user knows the fetal orientation but scans without image display and guidance of a conventional scan. Three non-expert readers and one expert Radiologist extract the clinically relevant planes and measure four key biometric features from the 3D images. In this paper, we propose (1) a risk metric R to rate the quality of the scan as a function of probe motion and contact and (2) a measurability index M for the availability of the 2D planes within the volume and visibility of the biometric features. Our analysis shows that R is the lowest and M the highest for 15-s acquisitions corresponding to an average transducer sweep speed of 2.4-cm/s. The finding is consistent with a reported speed range of 3-4 cm/s recommended for a low cost teleradiology solution for 2D ultrasound. The errors in average biometric measurements compared to the 50th percentile values in the fetal biometry tables for corresponding gestational week are within -3.8 to 5.7%. R, M, accuracy and precision of measurements are useful indicators of performance of the 3D ultrasound system.
An image resolution enhancement approach based on discrete wavelet transform (DWT) and new edge-directed interpolation (NEDI) for degraded satellite images by geometric distortion to correct the errors in image geometry and recover the edge details of directional high-frequency subbands is proposed. The observed image is decomposed into four frequency subbands through DWT, and then the three high-frequency subbands and the observed image are processed with NEDI. To better preserve the edges and remove potential noise in the estimated high-frequency subbands, an adaptive threshold is applied to process the estimated wavelet coefficients. Finally, the enhanced image is reconstructed by applying inverse DWT. Four criteria are introduced, aiming to better assess the overall performance of the proposed approach for different types of satellite images. A public satellite images data set is selected for the validation purpose. The visual and quantitative results show the superiority of the proposed approach over the conventional and state-of-the-art image resolution enhancement techniques.
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