Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
1998-08-28
2001-05-01
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C428S313500, C428S323000, C428S327000, C428S407000, C128S897000, C356S036000, C356S128000, C356S311000
Reexamination Certificate
active
06224969
ABSTRACT:
The present invention relates to an optical phantom that is suitable for simulating the optical properties of biological material and to a method of producing said phantom.
Materials are known from practice, whose light scattering and light absorption levels are known. When said materials are used for the simulation of the optical properties of biological material, they are also called optical phantoms. To obtain light scattering in optical phantoms discreet particles are mixed with a transparent material, also called matrix, whose refractive index differs from the refractive index of the particles. Light absorption is realized by the addition of a dye.
The optical phantoms described in the literature up to date can generally be divided into the following categories:
a mixture of a polymeric matrix and glass spheres or ceramic particles;
a mixture of a matrix based on water and small fat globules (for example Intralipid®) or polymer spheres such as polystyrene. If desired, the particles may be fixed by adding gelatine.
There are, however, some disadvantages attached to the known optical phantoms of this type.
With the mixture of a polymeric matrix and glass spheres or ceramic particles, the attainable level of light scattering is limited because the refractive index of the glass differs little from that of the matrix, so that it is not possible to quantitatively represent, for example, human tissue. The arbitrary shape of the ceramic particles renders an accurate description of the scattering properties impossible. The addition of polymer spheres, for example polystyrene, to a polymeric matrix is problematic because dry polymer spheres are difficult to work with.
The phantoms comprising a mixture of a matrix on water basis and small fat globules or polymer spheres such as polystyrene, have a limited shelf life due to dehydration and fungal growth.
Moreover, with all the known phantoms it is very difficult or impossible to make layered structures that have a high vertical resolution. To simulate the stratification of skin tissue, a resolution of approximately 20-50 &mgr;m is required.
It is the objective of the present invention to remove these disadvantages. According to the present invention this objective is attained in that the optical tissue phantom is comprised of a matrix of poly(vinyl alcohol) (PVA) and substantially spherical particles whose refractive index differs from that of the PVA.
An important aspect of the phantom according to the present invention is that with this phantom a greater light scattering is possible than with the phantoms of the prior art which comprise a polymeric matrix, with the result that biological tissue can be quantitatively simulated. The shelf life is at least equal to that of the prior art phantoms on polymer basis. A further advantage is that it is simple to add polymer spheres, facilitating the quantitative description of the scattering properties and allowing stratified structures to be made, having a vertical resolution of approximately 20 &mgr;m.
In accordance with a further characteristic of the present invention, the PVA has a level of hydrolysis of 75-100 mole percent, preferably >98 mole percent. A wealth of literature about PVA indicates that PVA becomes less hydrophilic as the level of hydrolysis increases. Thus PVA with a higher level of hydrolysis absorbs less ambient moisture. As water absorption lowers the refractive index of the matrix, this is an important aspect for an optical tissue phantom. PVA with a high level of hydrolysis is preferred. In addition, when a PVA film is being manufactured it can be removed from the glass plate onto which it is cast more easily if the PVA has a higher level of hydrolysis.
In accordance with another characteristic of the present invention the diameters of the particles range from 0.45-1.5 &mgr;m, preferably from 0.9-1.2 &mgr;m.
In accordance with another favourable characteristic of the present invention the particles are hollow particles. When hollow particles are used, it is possible to attain a high level of light scattering.
In accordance with another characteristic of the present invention the hollow particles are filled with gas. By this means a high level of light scattering is attained.
In accordance with a further characteristic of the present invention the particles are polystyrene particles. Basically any small particles that can be suspended in water are eligible for use as particles with a different refractive index than that of PVA. These may include, for example, ceramic particles, glass spheres, polymethylene melamine, PMMA, polycarbonate, etc. Polystyrene is preferred, as polystyrene spheres of specific dimensions, which vary very little, are commercially available. This finally results in a homogenous film. Moreover, polystyrene is preferred to glass because polystyrene has a lower density than glass, which ensures that the film is more homogenous.
In accordance with a further characteristic of the present invention the optical tissue phantom also comprises a colourless solid. If, apart from the light-diffusing particles, another solid is added, the phantom becomes useful for the development and calibration of optical equipment by means of which the concentration of that same substance in, for example, tissue is measured.
In accordance with a further characteristic of the present invention the colourless solid is glucose. The use of glucose helps with the examination and calibration of optical techniques and medical equipment in which such techniques are applied when determining the glucose level of diabetics.
In accordance with another characteristic of the present invention the optical tissue phantom also comprises at least one light-absorbing substance. This allows the simulation of light absorption. Basically any water soluble dyes may be admixed. It is also possible to use a mixture of several light-absorbing substances. The absorption spectrum is a linear combination of the absorption spectra of the separate dyes. The narrower the absorption peaks of the separate dyes, the greater the freedom in choosing an absorption ratio in the mixture applying for specific wavelengths. For skin tissue the absorption ratio between 780 nm, 630 nm and 540 nm is approximately 1:2:3. Thus this can be simulated by making a suitable mixture of three dyes.
In accordance with another characteristic of the present invention the light absorbing substance is Talens Ecoline® paint. The advantage of Talens Ecoline® paint is that it does not comprise any solid pigment; in other words, Talens Ecoline® paint only absorbs without diffusing. This is not the case with Indian ink, which is slightly light-diffusing.
The present invention also relates to a method of producing an optical tissue phantom, characterized in that PVA is dissolved in an aqueous solvent, whereafter substantially spherical particles having a refractive index different to that of PVA are added to the solution, the thus obtained mixture is cast onto a substantially flat surface and the solvent is evaporated.
According to the invention, PVA is conveniently dissolved at a temperature of 20° C.-100° C., preferably at 95° C.-100° C. The temperature above which PVA dissolves in water depends on the level of hydrolysis. The preferred PVA, i.e. one having a high level of hydrolysis, dissolves at a temperature of 95° C. or higher.
According to another characteristic of the present invention, PVA having a level of hydrolysis of 75-100%, preferably >98%, is dissolved.
According to another characteristic of the present invention, the concentration of PVA added to the solvent is 1-15% by weight and preferably 8-12% by weight. This provides a workable solution.
According to another characteristic of the present invention the solvent for PVA is water. Other possible solvents for PVA include, for example, DMSO, acetamide, glycols, DMF, glycerol, piperazine, triethylene diamine, formamide and HMTP. Solution in water is preferred, as this facilitates admixing aqueous suspensions of the light-diffusing particles.
According to another c
De Mul Frits Frans Maria
Greve Jan
Steenbergen Wiendelt
Myers Jeffrey D.
Pangrle Brian J.
Stichting Voor De Technische Wetenschappen
Thibodeau Paul
Zacharia Ramsey
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