X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
2001-12-20
2004-06-08
Bruce, David V (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S004000, C378S901000
Reexamination Certificate
active
06748045
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a method and apparatus for obtaining physical measures of microscopic features using tomography.
BACKGROUND OF THE INVENTION
In pine and hardwood tree species, which are frequently used for pulp, paper and forest products, plant cells form cells, the cells having a cell wall surrounded by an empty vacuole. Plant cells typically vary in diameter from approximately 10 to 50 &mgr;m. During an annual growth cycle, large-diameter, thin-walled cells are produced at the beginning of the growing season, while smaller-diameter, thicker-walled cells are produced near the end of the growing season, thus producing annual rings. In addition to variation within growth for a given year, wood cell anatomy varies from year to year. The wood formed during the earlier years of growth and near the crown of a tree is considered to be juvenile wood and typically has a lower density and shorter, thinner-walled fibers compared to mature wood. Because final paper and/or lumber quality is determined primarily by cell wall attributes, the ability to measure and separate materials having differing physical measures represents a method for improving wood quality by providing paper and/or lumber having optimized physical properties based on the intended application.
Cell length, diameter, and wall thickness are important parameters in assessing wood quality. Cell structure is a major reason for the visual differences that can be observed in various wood products. Surface texture of cardboard, newsprint, and fine writing paper is related partially to differences in physical cell dimensions. Likewise, in pieces of furniture made from different species of wood such as oak and pine, differences in appearance, durability, and weight can be attributed to microscopic features of wood cells. In general, for pulp and paper processing, the optimal characteristics are longer cells with thicker walls for Kraft paper as used for grocery bags and cardboard boxes and shorter lengths and thinner walls for fine writing paper. Even though product quality is determined by cell quality, little progress has been made in improving such traits because of the time and expense associated with current assessment methods. It has been estimated that optimizing average cell characteristics for a single species, loblolly pine (
Pinus taeda
), could affect 17 million acres of crop production and an annual $8 billion in raw feedstock supply to the pulp and paper industry.
During approximately the last 90 years, softwoods and hardwoods have been used for pulp and paper. These fiber types now account for 94% of the raw material for paper production. The rapid determination of wood-cell morphology could improve the effectiveness of forest genetic-selection studies.
Cell length and cell wall thickness measurements are currently determined using standard visual microscopic techniques. However, sample preparation during traditional cell wall thickness studies requires several meticulous laboratory steps, generally including softening and maceration of the wood and microscope slide preparation. Such preparations generally inadvertently affect the obtained physical measures. In addition to being cumbersome, cell length data obtained by the traditional microscopic methods contains errors because it includes measurements of truncated cells damaged from the preparation process. Furthermore, large sample-preparation and data-analysis time requirements limit the usefulness of the traditional microscopic cell size determination procedure in genetic selection studies in which hundreds of samples need to be processed as quickly as possible.
The use of direct and film X-ray densitometry for wood-density measurements has been reported (Parker, M. L. and Kennedy, R. W., “The status of radiation densitometry for measurement of wood specific gravity.” Proc. Int. Union For. Res. Organ, p. 17, Cape Town, Africa, 1973). In this work, an X-ray film is used to gather attenuation data derivable through analysis of the resulting degree of film darkness from X-rays passing through a sample. Using this method, the wood sample must have a substantially uniform thickness. Otherwise, the attenuation data will contain a false signal component associated with variations in thickness of the sample.
The Oak Ridge National Laboratories (ORNL) has recently improved upon the standard densitometry method by eliminating X-ray film through the use of a commercially manufactured X-ray computed tomography (CT) system. The technique provides a method and system for obtaining density profiles in up to 2-dimensions of wood samples with an improved resolution being approximately 158 microns (Tuskan et al. 1999, entitled “Two High-Throughput Techniques for Determining Wood Properties as Part of a Molecular Genetics Analysis of Hybrid Poplar and Loblolly Pine,” Applied Biochemistry and Biotechnology, vol. 77-79, pages 55-65). The advantages of the CT method for wood analysis include the elimination of the requirement for sample preparation because of the ability to correct for thickness variation, the opportunity for digital data analysis and interpretation, and the reduction in the time of data acquisition to less than ten percent of that required by the non CT X-ray method. Data acquisition is speeded because of electronic data assembly, minimal or no sample preparation and no need for secondary darkness measures.
Thus, X-ray CT-based densitometry represents an improvement over traditional microscopic or X-ray film densitometry methods for density determinations of wood and wood composite samples. However, the spatial resolution the X-ray CT system described by Tuskan et al. is insufficient to permit measurement of structures having feature sizes on the order of several microns, such as cell length and cell wall thickness in wood and wood products.
SUMMARY OF THE INVENTION
A method for obtaining wood-cell attributes from cellulose containing samples includes radiating a cellulose containing sample with a beam of radiation. The radiation can be selected from X-rays, gamma rays, neutrons, positrons or electrons, the radiation having an energy capable of passing through the sample. Radiation attenuation information is collected from radiation which passes through the sample. The source is then rotated relative to the sample. The collecting step is repeated after the rotating step, and a projected image, which includes resolvable features of the sample, is formed from the radiation attenuation information. The above image can be a tomographical image and can be a 3-dimensional image. The resolvable features in the image can be from less than approximately 100 &mgr;m to less than approximately 1 &mgr;m.
This method can further include the step of determining at least one cell dimension of the sample from the image. The cell dimensions can be cell wall thickness, cell diameter (length), or cell vacuole diameter.
The sample can be either wood or a reconstituted wood product. If the sample is a reconstituted wood product, it can be selected from strand board, fiber board, or fiber-resin wood composite products.
The invention includes a method for tomographically imaging features. A sample is radiated with a beam of radiation. The radiation can be selected from X-rays, gamma rays, neutrons, positrons or electrons, the radiation having an energy capable of passing through the sample. Radiation attenuation information is collected from radiation which passes through the sample. The source is rotated relative to the sample. The collecting step is repeated after the rotating step. A projected image, which can be a tomographical image and can be a 3-dimensional image, includes resolvable features of the sample and is formed from the radiated attenuation information. The sample can be rotated while the source remains substantially fixed.
The source can be positioned closer to the target than the target is to the detector, the detector used to form the image. The spot size of the beam of radiation can primarily determine the resolution provid
Paulus Michael J.
Tuskan Gerald A.
West Darrell C.
Wimmer Rupert
Akerman & Senterfitt
Bruce David V
UT-Battelle LLC
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