1999 Progress Report: X-ray CT-based Assessment of Variations in Human Airway Geometry: Implications for Evaluation of Particle Deposition and Dose to Different Populations

EPA Grant Number: R827351C002
Subproject: this is subproject number 002 , established and managed by the Center Director under grant R827351
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: EPA NYU PM Center: Health Risks of PM Components
Center Director: N/A
Title: X-ray CT-based Assessment of Variations in Human Airway Geometry: Implications for Evaluation of Particle Deposition and Dose to Different Populations
Investigators: Cohen, Beverly S. , Hoffman, Eric
Institution: New York University School of Medicine , University of Iowa
EPA Project Officer: Chung, Serena
Project Period: June 1, 1999 through May 31, 2005 (Extended to May 31, 2006)
Project Period Covered by this Report: June 1, 1999 through May 31, 2000
RFA: Airborne Particulate Matter (PM) Centers (1999) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Particulate Matter , Air

Objective:

The objectives of this research project are to: (1) develop methods for extraction of airway morphometry data from individual computerized tomography (CT) scans; and (2) utilize the resulting computerized morphometric data files to produce hollow airway casts by stereolithography (STL) for subsequent use in particle deposition studies.

Progress Summary:

As a first step, before creating hollow airway casts from in vivo acquired x-ray CT image data, we have utilized a hollow human airway cast (shown in the left panel of Figure 1). The cast was made from a postmortem human lung. Images of the cast were obtained using an electron beam CT scanner (Imatron Corporation, South San Francisco, CA) with an image matrix size of 512 x 512, contiguous 1.5 mm thick slices, and pixel dimensions of 0.508 mm. Airway generations down to 1.04 mm inner diameter were semiautomatically segmented utilizing an inhouse software package, Volumetric Image Display and Analysis. Shape-based interpolation was used to create isotropic voxels. A volumetric rendering of the resultant segmented luminal space of the airway tree phantom was generated utilizing a marching cubes algorithm. This rendering is shown in the left panel of Figure 2. Marching cubes is an algorithm for rendering isosurfaces in volumetric data. We created triangular patches that divide the cube between regions within the isosurface and regions outside. By connecting the patches from all of the cubes on the isosurface boundary, we get a surface representation. Each triangular patch consists of a single normal vector and three of the vertices.

These three-dimensional images were converted to an STL file format required by the rapid prototyping device, and a physical solid model of the hollow airway was created. The STL format is an ASCII or binary file used in manufacturing. It is a list of the triangular surfaces that describe a computer-generated solid model. This is the standard input for most rapid prototyping machines. The ASCII .stl file must start with the lower case keyword “solid” and end with “endsolid.” Within these keywords are listings of individual triangles that define the faces of the solid model. Each individual triangle description defines a single normal vector directed away from the solid’s surface, followed by the xyz components for all three of the vertices. These values are Cartesian coordinates and are floating-point values. The triangle values should be positive and contained within the building volume. Figure 3 shows a sample ASCII description of a single triangle within an STL file.

Right Panel Original Human Airway Cast

Figure 1.Right Panel–Original Human Airway Cast; Middle Panel–Hollow Airway Cast Generated by Rapid Prototyping Machine; Right Panel–Solid Model of Airway Lumen Space Generated by Rapid Prototyping Machine. Note the darker gray material in the middle and left panels. This is the material laid down to provide support for the model as it is being built.

Right Panel Shaded Surface Display of Airway Lumen

Figure 2.Right Panel–Shaded Surface Display of Airway Lumen as Segmented From the Scan of the Original Airway Cast; Left Panel–Shaded Surface Display of the Airway Lumen as Segmented From the Scan of the Hollow Lumen Cast Made by the Rapid Prototype Machine

A Sample ASCII Description of a Single Triangle Within an STL File

Figure 3. A Sample ASCII Description of a Single Triangle Within an STL File

STL is a “rapid-prototyping” process that produces a physical, three-dimensional object from a three-dimensional file. An STL machine uses a computer-controlled arm connected to a plastic extrusion device to build volumetric structures layer by layer. Two heads are present on the machine, one to lay down the plastic compound for the structure of interest and a second head to lay down needed support material for the structure as it is being built, which later can be separated from the structure.

The fused deposition modeling (FDM) 2000 (Stratasys, Minneapolis, MN), used for this study and shown in Figure 4, provides quick production of high-quality models and prototypes in a variety of materials. Table 1 provides an outline of some of the key features of the system.

FDM 2000

Figure 4. FDM 2000

Table 1. FDM 2000 System Specifications

FDM 2000 System Specifications

Two models were generated: (1) a hollow model in which the endoluminal surface represented the dimensions assessed from the CT scans of the original model, but for the purposes of strength, the airway wall thickness was made thicker than in the original model; and (2) a solid model representing the endoluminal air in the original model. The new rapid prototype-derived hollow airway cast was scanned via electron beam CT identically to the scanning of the original model, and the resultant images of the airway lumen were measured for compassion with the original model.

The hollow and solid models made by STL are shown in the middle and right panels, respectively, of Figure 1. Support material has been left attached to maintain the strength of the model. The left panel of Figure 2 displays the tree structure, which was delivered to the STL facility. This image can be used for comparison with the resultant model to determine the success of the STL rendition. As a second comparison, in the right panel of Figure 2 we show a three-dimensional shaded surface display derived by CT scanning of the STL-based hollow model. A few of the more peripheral airway branches were not rendered in the STL process. We believe that these branches were lost in the process, whereby the STL operator defines the location of the support structure, which needs to be laid down to build these peripheral branches. The loss of these branches can be corrected both through increased operator experience and through an iterative process whereby a second model is built following construction of the first model. As a second test of the accuracy of the model, we measured the cross-sectional area of 20 airway segments of the original and STL-derived models imaged by x-ray CT. Airway segments were selected on the basis of their local long axes having been oriented nearly perpendicular to the CT scan plane. Airway lumenal areas tested ranged from 23.92 mm to 3.2 mm, representing 20 segments of the airway tree. These data are graphed in Figure 5. The mean error of inner diameter was 0.19 ± 0.04 mm (scanning electron microscopy [SEM]), and the mean percent error was 1.87 ± 0.36 percent (SEM). There was no significant difference between original phantom and a new airway model in terms of lumenal areas. Figure 6 shows two endoluminal views of the original human airway model and the hollow model derived from CT scanning and STL. Images were gathered via endoluminal bronchoscopy. Although the luminal views look notably similar, endoluminal support structures had to be built into the STL model. Although this renders the current model useless for airway deposition studies, this problem can be overcome by the fact that with an alternative head available for the FDM 2000 rapid prototyping system, the support material can be constructed of a water-soluble compound. We currently are exploring the possibility of purchasing this alternative head.

Comparison of the Luminal Area Calculated From CT Images

Figure 5. Comparison of the Luminal Area Calculated From CT Images of the Original Human Airway Model and CT Images of the STL-Derived Hollow Airway Model. Twenty sample airway segments, which happened to be sliced nearly perpendicular to their local long axis by the CT image plane, were selected for this comparison.

Video Bronchoscopic-Derived Endoluminal Views

Figure 6. Video Bronchoscopic-Derived Endoluminal Views of the Original (Upper Row) and CT/STL-Derived (Lower Row) Human Airway Tree Models. Visually, the views are similar with the exception of the support structure present in the STL-derived model.

Future Activities:

We will use rapid prototype processing to create a physical (solid) model of the segmented airway lumens. Shape-based interpolation will be used to create isotropic voxels and to smooth the surface of an airway model. A volumetric rendering of the resultant segmented luminal space of the airway tree phantom will be generated utilizing a marching cubes algorithm. Triangular patches divide the cube between regions within the isosurface and regions outside of the airway tree. By connecting the triangular patches from all cubes on the isosurface boundary, we will produce a surface representation of airway tree. These triangular patches will be converted to the STL file format required by the rapid prototyping device.

Journal Articles:

No journal articles submitted with this report: View all 1 publications for this subproject

Supplemental Keywords:

thoracic particles, particulate matter, PM, PM10, fine particles, PM2.5, ultrafine particles, PM0.1, lung dosimetry models, human exposure models, pulmonary responses, cardiovascular responses, immunological responses, criteria air pollutants, concentrated ambient aerosols, air, health, waste, biochemistry, biology, chemical engineering, chemistry, children’s health, civil engineering, environmental engineering, environmental chemistry, physics, analytical chemistry, epidemiology, health risk assessment, immunology, incineration, combustion, combustion contaminants, combustion emissions, air toxics, tropospheric ozone, aerosol, air pollutants, air pollution, airborne pollutants, airway disease, airway inflammation, airway variability, allergen, ambient air, ambient air quality, assessment of exposure, asthma, asthma morbidity, atmospheric monitoring, biological markers, childhood respiratory disease, children, compliance monitoring, dosimetry, exposure, exposure and effects, health effects, heart rate variability, human exposure, human health, human health effects, lead, lung, mercury, morbidity, pulmonary, pulmonary disease, respiratory, particulate deposition, computerized tomagraphy, CT, x-ray, human airway, morphometric data, three-dimensional images, stereolithography, STL, volume, x-ray tomography, x-ray CT, acute lung injury, aerosol composition, airborne particulate matter, airway contractile properties, ambient air monitoring, atmospheric aerosol particles, atmospheric particles, atmospheric particulate matter, chemical characteristics, environmental risks, exposure assessment, human health risk, particulates,, RFA, Health, Scientific Discipline, PHYSICAL ASPECTS, Air, ENVIRONMENTAL MANAGEMENT, particulate matter, Environmental Chemistry, Health Risk Assessment, Risk Assessments, Environmental Monitoring, Physical Processes, Atmospheric Sciences, Risk Assessment, ambient air quality, atmospheric particulate matter, particulates, air toxics, atmospheric particles, chemical characteristics, toxicology, ambient air monitoring, acute lung injury, airborne particulate matter, environmental risks, exposure, epidemelogy, air pollution, aerosol composition, atmospheric aerosol particles, human exposure, PM, X-ray tomagraphy, airway contractile properties, exposure assessment

Relevant Websites:

http://www.med.nyu.edu/environmental/centers/epa/ Exit

Progress and Final Reports:

Original Abstract
  • 2000 Progress Report
  • 2001 Progress Report
  • 2002 Progress Report
  • 2003 Progress Report
  • 2004
  • Final Report

  • Main Center Abstract and Reports:

    R827351    EPA NYU PM Center: Health Risks of PM Components

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R827351C001 Exposure Characterization Error
    R827351C002 X-ray CT-based Assessment of Variations in Human Airway Geometry: Implications for Evaluation of Particle Deposition and Dose to Different Populations
    R827351C003 Asthma Susceptibility to PM2.5
    R827351C004 Health Effects of Ambient Air PM in Controlled Human Exposures
    R827351C005 Physicochemical Parameters of Combustion Generated Atmospheres as Determinants of PM Toxicity
    R827351C006 Effects of Particle-Associated Irritants on the Cardiovascular System
    R827351C007 Role of PM-Associated Transition Metals in Exacerbating Infectious Pneumoniae in Exposed Rats
    R827351C008 Immunomodulation by PM: Role of Metal Composition and Pulmonary Phagocyte Iron Status
    R827351C009 Health Risks of Particulate Matter Components: Center Service Core
    R827351C010 Lung Hypoxia as Potential Mechanisms for PM-Induced Health Effects
    R827351C011 Urban PM2.5 Surface Chemistry and Interactions with Bronchoalveolar Lavage Fluid (BALF)
    R827351C012 Subchronic PM2.5 Exposure Study at the NYU PM Center
    R827351C013 Long Term Health Effects of Concentrated Ambient PM2.5
    R827351C014 PM Components and NYC Respiratory and Cardiovascular Morbidity
    R827351C015 Development of a Real-Time Monitoring System for Acidity and Soluble Components in Airborne Particulate Matter
    R827351C016 Automated Real-Time Ambient Fine PM Monitoring System