This section introduces aspects that may help facilitate a better understanding of the disclosure. Accordingly, these statements are to be read in this light and are not to be understood as admissions about what is or is not prior art. For the purposes of this disclosure, “optically heterogeneous” means a heterogeneous structure where the heterogeneity leads to differences in optical or related properties.
A variety of optical imaging techniques can be used, for example, in biomedical applications. For example, microscopy methods (MM) and optical coherence tomography (OCT) allow imaging at shallow depths in tissue. In deep tissue, the deleterious effects of scatter require different techniques, such as diffuse optical imaging (DOI) (also known as optical diffusion imaging), where a model of scattered light propagation can assist with image formation. DOI techniques may encompass such imaging methods as hyperspectral reflectance imaging (HRI), speckle imaging, spatial frequency domain imaging (SFDI), diffuse optical tomography (DOT), optical diffusion tomography (ODT), near infrared optical tomography (NIROT), fluorescence diffuse optical tomography (FDOT), and fluorescence optical diffusion tomography (FODT). DOI techniques use light of certain wavelengths to penetrate a body and the tissue portion thereof and form 3D images of the tissue as a result of light scattering and absorption that occurs when inhomogeneities are encountered. Optical imaging techniques can be utilized to obtain information regarding medical conditions and biological activities within living bodies, including conditions and activities of such internal organs as the heart, brain, kidneys, lungs, liver, skeleton, vascular structures, etc.
Imaging techniques and equipment typically require testing and calibration to promote the reliability of their results. For this purpose, optical imaging techniques often involve the fabrication of a “phantom” structure intended to simulate an object of interest, such as an entire body or portion thereof to be evaluated with the imaging technique. Phantoms are particularly useful for calibrating imaging techniques that will be used to evaluate tissue of a living body, as they avoid the need to have actual tissue for calibration, for example, a tissue donor, live subject, cadaver, etc. Consequently, a phantom is preferably fabricated to emulate internal and external physical characteristics of a body and its tissue. In order to do so, a phantom should have controlled optical properties, including but not limited to regions in which the phantom has different scattering, absorption, or fluorescent properties.
Phantoms can be formed of polymeric materials that contain additives intended to adjust its optical properties. External geometry and physical characteristics of the body to be simulated by a phantom are emulated by the mold in which the phantom is formed, whereas internal physical characteristics of, for example, tissue within the body are emulated by attempting to control the optical properties within the phantom with additives that alter the scattering and/or absorption and/or related optical coefficients of the phantom material. These injection molding techniques typically used in the fabrication of phantoms may adequately simulate the external shape of a body, but difficulties arise if the body has a complex external shape. Furthermore, injection molding techniques are not well suited for controllably tuning the internal physical characteristics of a phantom by selectively placing additives in regions that alter the scattering and/or absorption and/or related optical coefficients of the phantom to accurately simulate inhomogeneities such as internal organs.
Thus there is unmet need for phantoms that accurately simulate inhomogeneities of interest within a background medium. The methods detailed within this disclosure are meant to satisfy this unmet need.