Nigel M. Parsad

Major element chemical and isotopic compositions of refractory inclusions in C3 chondrites: The separate roles of condensation and evaporation

Literature data for major element oxide compositions of most coarse-grained Types A and B inclusions in CV3 chondrites may be in error due to non-representative sampling of spinel relative to other phases because of small sample sizes. When reported compositions are corrected to the solar CaO/Al2O3 ratio by addition or subtraction of spinel, distinct trends result on oxide–oxide plots. These trends lie close to trajectories of bulk compositions of equilibrium condensates calculated for solar or dust-enriched gases under various conditions, except on a plot of MgO vs. SiO2 contents, where there is considerable scatter of the data points to the MgO-poor side of the condensation trajectory. The irreversible process of evaporative mass loss from a liquid droplet into an unsaturated H2 gas is modeled as a series of small equilibrium steps. This model is used to show that evolutionary paths of CMAS liquid compositions are identical for evaporation at all PH2 from 1 × 10−15 to 1 bar, with the ratio of the fraction of the SiO2 evaporated to that for MgO increasing both with increasing temperature from 1700 to 2000 K and with increasing SiO2 content of the starting composition. Such calculations show that compositions of most Type B inclusions can be explained by non-equilibrium evaporation of 10 to 30% of the MgO and 0 to 15% of the SiO2 into an H2 gas at 1700 K from liquid droplets whose compositions originated on any one of many possible equilibrium condensation trajectories. Some Type As may have suffered similar evaporative losses of MgO and SiO2 but at higher temperature. This degree of evaporation is consistent with the amount of Mg and Si isotopic mass fractionation observed in Types A and B inclusions. Evaporation probably happened after most Mg and Si were removed from the nebular gas into lower-temperature condensates.

Automatic perceptual color map generation for realistic volume visualization

Advances in computed tomography imaging technology and inexpensive high performance computer graphics hardware are making high-resolution, full color (24-bit) volume visualizations commonplace. However, many of the color maps used in volume rendering provide questionable value in knowledge representation and are non-perceptual thus biasing data analysis or even obscuring information. These drawbacks, coupled with our need for realistic anatomical volume rendering for teaching and surgical planning, has motivated us to explore the auto-generation of color maps that combine natural colorization with the perceptual discriminating capacity of grayscale. As evidenced by the examples shown that have been created by the algorithm described, the merging of perceptually accurate and realistically colorized virtual anatomy appears to insightfully interpret and impartially enhance volume rendered patient data.

An optimized web-based approach for collaborative stereoscopic medical visualization

Objective Medical visualization tools have traditionally been constrained to tethered imaging workstations or proprietary client viewers, typically part of hospital radiology systems. To improve accessibility to real-time, remote, interactive, stereoscopic visualization and to enable collaboration among multiple viewing locations, we developed an open source approach requiring only a standard web browser with no added client-side software. Materials and Methods Our collaborative, web-based, stereoscopic, visualization system, CoWebViz, has been used successfully for the past 2 years at the University of Chicago to teach immersive virtual anatomy classes. It is a server application that streams server-side visualization applications to client front-ends, comprised solely of a standard web browser with no added software. Results We describe optimization considerations, usability, and performance results, which make CoWebViz practical for broad clinical use. We clarify technical advances including: enhanced threaded architecture, optimized visualization distribution algorithms, a wide range of supported stereoscopic presentation technologies, and the salient theoretical and empirical network parameters that affect our web-based visualization approach. Discussion The implementations demonstrate usability and performance benefits of a simple web-based approach for complex clinical visualization scenarios. Using this approach overcomes technical challenges that require third-party web browser plug-ins, resulting in the most lightweight client. Conclusions Compared to special software and hardware deployments, unmodified web browsers enhance remote user accessibility to interactive medical visualization. Whereas local hardware and software deployments may provide better interactivity than remote applications, our implementation demonstrates that a simplified, stable, client approach using standard web browsers is sufficient for high quality three-dimensional, stereoscopic, collaborative and interactive visualization.

Three-Dimensional Stereoscopic Volume Rendering of Malignant Pleural Mesothelioma

Our objective was to investigate the application of three-dimensional (3D) stereoscopic volume rendering with perceptual colorization on preoperative imaging for malignant pleural mesothelioma. At present, we have prospectively enrolled 6 patients being considered for resection of malignant pleural mesothelioma that have undergone a multidetector-row computed tomography (CT) scan of the chest. The CT data sets were volume rendered without preprocessing. The resultant 3D rendering was displayed stereoscopically and used to provide information regarding tumor extent, morphology, and anatomic involvement. To demonstrate this technique, this information was compared with the corresponding two-dimensional CT grayscale axial images from two of these patients. Three-dimensional stereoscopic reconstructions of the CT data sets provided detailed information regarding the local extent of tumor that could be used for preoperative surgical planning. Three-dimensional stereoscopic volume rendering for malignant pleural mesothelioma is a novel approach. Combined with our innovative perceptual colorization algorithm, stereoscopic volumetric analysis potentially allows for the accurate determination of the extent of pleural mesothelioma with results difficult to duplicate using grayscale, multiplanar CT images.