Multilayered phantom tissue test structure and fabrication process
Inventors
Hwang, Jeeseong • Stafford, Christopher • Chang, Robert
Assignees
United Stats Of America Commerce, Secretary of • National Institute of Standards and Technology NIST
Publication Number
US-9486179-B2
Publication Date
2016-11-08
Expiration Date
2033-01-03
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Abstract
A multilayered optical tissue phantom fabrication approach and inherently produced test target structure which address the issues of of optical conformity known in the art by controlling the formation of micrometer scale monolayers embedded with light-scattering microspheres.
Core Innovation
The invention is a multilayer phantom test target inherently produced by a disclosed fabrication method. This structure consists of monolayers of micrometer-scale light-scattering microspheres embedded in transparent polymer layers. The microspheres are arranged in an ordered monolayer array on a modified glass substrate via polyelectrolyte multilayers and convective particle flux, then transferred into a polymer host such as polydimethylsiloxane (PDMS). The method enables precise control over microsphere dimensions, spacing, and axial positioning, thereby replicating different spatial frequencies in the axial dimension for calibration.
The core problem addressed by the invention is the lack of uniformity and standardization in fabricating tissue phantoms for accurate optical device calibration, particularly for axial resolution measurement in depth-resolving optical systems like optical coherence tomography (OCT). Existing lateral resolution standards are not applicable to axial resolution, and no widely accepted axial resolution standard phantom test target exists. This issue hampers the ability to ensure optical conformity—uniform light scattering properties that minimize interference from surface irregularities—and thus precise, repeatable calibration of OCT and similar devices.
The layered phantom test target structure replicates the optical scattering behavior of biological tissues and overcomes irregularities common in previous phantoms by embedding uniform microsphere layers within transparent polymers. This structure provides a means for quantitative axial positioning of scattering layers independent of the systems under test, facilitating consistent validation, standardization, and calibration of OCT devices. The method inherently produces test targets with stable, optically uniform multilayer architectures that correspond to predetermined OCT illumination source coherence lengths.
Claims Coverage
The patent contains two independent claims covering both the optically uniform phantom test target structure and the fabrication method for producing it. The claims outline inventive features relating to the multi-layer microsphere-polymer structure, spatial frequency replication, and the controlled fabrication steps involving microsphere arrangement and transfer.
Multilayer optical phantom test target structure with axially varied polymer layers
An optically uniform test target composed of multiple micrometer-scale monolayers each consisting of ordered arrays of light-scattering microspheres embedded in host polymers. The structure includes transparent polymer layers between microsphere monolayers, with at least one polymer layer having a thickness differing from others. The thicknesses replicate different spatial frequencies in the axial dimension and are independently measurable by interferometry.
Microsphere arrangement preserving optical uniformity and axial positioning
Light-scattering microspheres within each monolayer are arranged in ordered arrays, such as hexagonal packing formed by convective particle flux on chemically modified glass substrates. The microspheres do not substantially protrude above the polymer surface to maintain consistent reflective characteristics and optical conformity.
Calibration tool for axial resolution and contrast characterization
The phantom test target structure serves as a calibration device for axial resolution and contrast in depth-resolving optical measurements such as OCT, enabling standardized spatial calibration independent from the system under test.
Fabrication method employing polyelectrolyte multilayers and microsphere deposition
A method involving electrically charging a glass substrate via plasma treatment and layer-by-layer polyelectrolyte deposition to optimize microsphere binding. Microspheres are axially positioned to form dense, ordered monolayers through convective particle flux and subsequently delaminated and transferred into a polymer host. The multilayer test structure is formed by stacking microsphere layers separated by polymer layers. Surface profilometry measures step height changes in the final structure.
The inventive features collectively define a multilayer tissue phantom comprising precisely arranged light-scattering microspheres embedded in polymer layers with varying thicknesses that replicate axial spatial frequencies, and a corresponding fabrication process optimizing microsphere monolayer formation and transfer. This enables standardized calibration of imaging systems, particularly for axial resolution in OCT.
Stated Advantages
Provides highly precise spatial calibration accommodating all types of measurements achievable by OCT technology.
Achieves optical uniformity by minimizing surface irregularities and producing homogeneous scattering layers that appear uniformly bright in imaging.
Enables independent bulk measurement of phantom dimensions for repeatable determination of sub-surface particle distributions and polymer spacings.
Produces portable, stable phantom units without discernible layer interfaces to enhance reliability in imaging calibration.
Allows tuning of phantom properties including microsphere size, polymer layer thickness, and spatial frequency replication for customizable calibration targets.
Documented Applications
Calibration of axial resolution and contrast characterization in optical coherence tomography (OCT) devices.
Standardized calibration and validation of medical imaging systems, especially for quantifying retinal thickness measurements for ophthalmologic diagnostics.
Inter-laboratory comparison, measurement standardization, and physical model validation for scattering-based depth-resolving imaging modalities.
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