Finite Element Analysis of Interaction of Laser Beam with Material in Laser Metal Powder Bed Fusion Process.

A deep understanding of the laser-material interaction mechanism, characterized by laser absorption, is very important in simulating the laser metal powder bed fusion (PBF) process. This is because the laser absorption of material affects the temperature distribution, which influences the thermal stress development and the final quality of parts. In this paper, a three-dimensional finite element analysis model of heat transfer taking into account the effect of material state and phase changes on laser absorption is presented to gain insight into the absorption mechanism, and the evolution of instantaneous absorptance in the laser metal PBF process. The results showed that the instantaneous absorptance was significantly affected by the time of laser radiation, as well as process parameters, such as hatch space, scanning velocity, and laser power, which were consistent with the experiment-based findings. The applicability of this model to temperature simulation was demonstrated by a comparative study, wherein the peak temperature in fusion process was simulated in two scenarios, with and without considering the effect of material state and phase changes on laser absorption, and the simulated results in the two scenarios were then compared with experimental data respectively.

Multiview 3-D Echocardiography Fusion with Breath-Hold Position Tracking Using an Optical Tracking System.

Recent advances in echocardiography allow real-time 3-D dynamic image acquisition of the heart. However, one of the major limitations of 3-D echocardiography is the limited field of view, which results in an acquisition insufficient to cover the whole geometry of the heart. This study proposes the novel approach of fusing multiple 3-D echocardiography images using an optical tracking system that incorporates breath-hold position tracking to infer that the heart remains at the same position during different acquisitions. In six healthy male volunteers, 18 pairs of apical/parasternal 3-D ultrasound data sets were acquired during a single breath-hold as well as in subsequent breath-holds. The proposed method yielded a field of view improvement of 35.4 ± 12.5%. To improve the quality of the fused image, a wavelet-based fusion algorithm was developed that computes pixelwise likelihood values for overlapping voxels from multiple image views. The proposed wavelet-based fusion approach yielded significant improvement in contrast (66.46 ± 21.68%), contrast-to-noise ratio (49.92 ± 28.71%), signal-to-noise ratio (57.59 ± 47.85%) and feature count (13.06 ± 7.44%) in comparison to individual views.

Patient movement compensation for 3D echocardiography fusion.

Limited field of view (FOV) is a major problem for 3D real-time echocardiography (3DRTE), which results in an incomplete representation of cardiac anatomy. Various image registration techniques have been proposed to improve the field of view in 3DRTE by fusing multiple image volumes. However, these techniques require significant overlap between the individual volumes and rely on high image resolution and high signal-to-noise ratio. Changes in the heart position due to patient movement during image acquisition can also reduce the quality of image fusion. In this paper, we propose a multi-camera based optical tracking system which 1) eliminates the need for image overlap and 2) compensates for patient movement during acquisition. We compensate for patient movement by continuously tracking the patient position using skin markers and incorporating this information into the fusion process. We fuse volumes acquired during R-R wave peaks based on Electrocardiogram (ECG) data to account for retrospective image acquisition. The fusion technique was validated using a heart phantom (Shelley Medical Imaging Technologies) and on one healthy volunteer. The fused ultrasound volumes could be generated in within 2 seconds and were found to have complete myocardial boundaries alignment upon visual assessment. No stitching artefacts or movement related artefacts were observed in the fused image.

Myocardial deformation analysis in contrast echocardiography: first results using two-dimensional cardiac performance analysis.

BACKGROUND: Contrast echocardiography (CE) provides closer agreement with magnetic resonance imaging (MRI) for left ventricular (LV) volumes and ejection fraction (EF) than noncontrast echocardiography. However, the feasibility and role of myocardial deformation analysis on contrast echocardiographic images have not been well established. The aim of this study was to assess the feasibility of deformation analysis on CE using a new software tool that provides simultaneous measurements for LV volumes and EF. METHODS: Data from 52 patients who were recruited for the Alberta Heart Failure Etiology and Analysis Research Team Study (34 men; mean age, 64 ± 9 years) and underwent CE and MRI were considered. Contrast bolus injections were administered for optimal endocardial definition. Offline LV volume analysis was performed by standard manual tracing. A single frame was traced manually for two-dimensional (2D) cardiac performance analysis (CPA), which automatically calculated LV volumes, EF, and global longitudinal strain (GLS). Volumes obtained with 2D CPA were compared with those measured with standard CE and MRI. GLS from noncontrast echocardiographic recordings was also calculated with 2D CPA and compared with CE-derived and MRI-derived GLS. RESULTS: Tracing of contrast echocardiographic images with 2D CPA was possible in 49 out of 52 patients, and measurements correlated well with standard CE and MRI (EF: r = 0.93, P < .001, and r = 0.85, P < .001, respectively). Mean GLS from noncontrast echocardiographic and contrast echocardiographic recordings was -13.4 ± 5.8 and -15.3 ± 4.64, respectively (P = .056), and the latter correlated well with MRI-derived GLS (r = 0.78 vs 0.81, respectively). CONCLUSIONS: Simultaneous volumetric and deformation analysis on contrast echocardiographic recordings is feasible and reproducible. While volumes and EF obtained with the new software compare well with those obtained from standard CE and MRI, GLS from CE shows a good correlation with strain measured with MRI.