Spatial and temporal visualization of gases and vapours in air using computed tomography. Numerical studies.

Numerical studies were performed to evaluate a new method for human exposure assessment and source monitoring, based upon optical remote sensing (ORS) and computed tomography (CT). With an ORS-CT system, two-dimensional maps of chemical concentrations in air, with good spatial and temporal resolution, can be created over a confined space such as a workplace room. The ORS-CT system was evaluated using 15 simulated test maps that model the generation and dispersion of contaminant plumes over time. A program simulated field measurements from these maps assuming different remote sensing scan times. Using these measurements, reconstructed maps were generated and compared with original maps. Qualitative and quantitative methods were used to evaluate the effect on reconstruction quality of sample time, number of iterations used by the maximum likelihood expectation maximization reconstruction algorithm and sample density. For this study, scanning an entire room in 10 min was adequate for exposure evaluation, source monitoring and leak detection.

[1]  S. Levine,et al.  The Limits of Detection for the Monitoring of Semiconductor Manufacturing Gas and Vapor Emissions by Fourier Transform Infrared (FTIR) Spectroscopy , 1989 .

[2]  Eric C. Frey,et al.  Comparison between ML-EM and WLS-CG algorithms for SPECT image reconstruction , 1991 .

[3]  David Leith,et al.  Remote Sensing and Computed Tomography in Industrial Hygiene , 1990 .

[4]  S P Levine,et al.  Imaging indoor tracer-gas concentrations with computed tomography: experimental results with a remote sensing FTIR system. , 1994, American Industrial Hygiene Association journal.

[5]  L. Todd,et al.  Evaluation of optical source-detector configurations for tomographic reconstruction of chemical concentrations in indoor air. , 1994, American Industrial Hygiene Association journal.

[6]  Lori A. Todd,et al.  Mapping chemical concentrations indoors using open-path FTIR spectroscopy and computed tomography: chamber studies , 1995, Other Conferences.

[7]  F Rasouli,et al.  Application of dispersion modeling to indoor gas release scenarios. , 1995, Journal of the Air & Waste Management Association.

[8]  L. Shepp,et al.  Maximum Likelihood Reconstruction for Emission Tomography , 1983, IEEE Transactions on Medical Imaging.

[9]  Steven R. Hanna,et al.  Handbook on atmospheric diffusion , 1982 .

[10]  L. Todd,et al.  Evaluation of algorithms for tomographic reconstruction of chemical concentrations in indoor air. , 1994, American Industrial Hygiene Association journal.