Radiant energy – Irradiation of objects or material
Reexamination Certificate
2000-05-11
2003-09-16
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
C250S580000
Reexamination Certificate
active
06621086
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to radiochromic imaging methods for generating a permanent, colored two or three dimensional spatial representation of an irradiation pattern wherein the intensity of the color of the image correlates to the dose level of irradiation, and more particularly to methods of utilizing these imaged color changes in applications such as tissue-equivalent dosimeters for medical radiotherapy to assess precise radiation targeting within a patient and in-other applications such as chromatographic analysis to determine the location and quantity of separated components.
BACKGROUND OF THE INVENTION
Quantification of objects in a given environment has been a longstanding requirement since man has been able to count. Beside the obvious need in commerce to know how many of one item might be traded for another, there are many other areas where quantification plays an important role. For example, in the physical sciences, quantification of exposure to chemicals or radiation, or dosage of medicine all play a role in our well being. Even when no direct contact with these materials is an issue, quantification plays an important role in analytical testing for these materials.
Quantification can be performed directly (i.e., by counting the objects of interest) or indirectly (i.e., by correlating the number of objects to some other measurable parameter).
Indirect quantification has been widely used in correlating the intensity of color to the quantity of a substance. In spectroscopy the relationship is defined by Beers Law. Simply stated, there is typically a correlation between the amount of a given material and the intensity of light absorbed by that material. If the absorbed light is of a given wavelength or range of wavelengths within the visible spectrum then the absorption of this light creates color.
It has also been known that the interaction of electromagnetic radiation and matter can create new chemical materials. In some cases the new material will be colored. It is then possible to correlate the three parameters: amount of radiation, amount of reactant matter, and intensity of coloration of the product. In this manner if two of the three parameters are known then the third can be quantified indirectly. Studies of this kind can be conducted either over time or space to obtain a temporal and/or spatial quantification of either the amount of radiation or the amount of the reactant material if the intensity of the coloration can be determined.
Chromatographic techniques for separating multicomponent mixtures has been an invaluable tool to the scientific community. Such techniques provide the ability to not only separate but also quantify and ultimately identify the various components in the mixture. Depending on the specific chromatographic technique many different types of materials can be separated from one another even though they may be structurally very similar. Such materials include anionic and cationic ions, simple organic molecules and more complex organic polymers. These polymers may be synthetically derived as is the case with polyesters, polyethers, or polyolefins or may be naturally produced as are proteins, polynucleotides, or complex starches and carbohydrates. Separation methods can be based on chemical or physical properties such as electronic charge, chemical reactivity, molecular mass, or molecular volume.
In virtually all cases, the mixture to be separated must be incorporated in a system that has a mobile phase and a stationary phase. The mobile phase carries the individual components across the stationary phase and may consist of gas, a liquid, or mixtures thereof. Most commonly inert gases such as nitrogen, helium, carbon dioxide or the like are used. Common liquids include pure water, salt-containing water, organic solvents and mixtures thereof.
The stationary phase may be composed of materials that are either inertized or activated and may be derived from synthetic or natural materials. The critical factors in selecting a stationary phase are that it must be essentially stable over time and not be soluble in the mobile phase. Another important attribute of the stationary phase is that it provide sufficient adsorption of the individual components to effect separation. This is typically achieved by having the stationary phase comprise very small particles having a large surface area or in some cases to have the stationary phase have hollow portions that the individual components must migrate.
Many materials can be employed for use as a stationary phase including insoluble salts, clays, talc, polyolefins, resins, and the like. The interaction of the individual components with the mobile phase and the stationary phase causes the individual components to migrate through the stationary phase at different rates, thereby causing them to separate. Separation is thus obtained by each component having a unique rate of migration. In a fairly recent innovation the stationary phase and the mobile phase can actually be reduced to one phase. In this case the stationary phase is in the form of a polymeric material dissolved in the mobile phase to essentially form a gel material. In the gel the stationary phase does not migrate, especially if the stationary phase polymeric material is crosslinked. In this system there is an extremely high propensity for interaction of the individual components with the stationary phase since contact is essentially made with individual molecules of the polymeric stationary phase. Bulk effects that would limit interaction of the individual components and the stationary phase are essentially eliminated.
The flow of the mixture to be separated is achieved by having the mobile phase flow either under gravity or pressure or by diffusion from an inlet side to an outlet side. More recently a technique that does not require the mobile phase to physically flow has been achieved. In this method the mixture is dissolved in the mobile phase and the stationary phase is placed in a environment that subjects the system to an electric current and the components in the mixture are separated due to their electrical charge and the interaction with the stationary phase. One such method is electrophoresis, wherein substances disposed within a gel are subjected to an electrical current. These substances migrate in the gel, under the influence of an electrical field.
Unless the components in the mixture are inherently colored, visualization of the separated components requires an additional step. This can be achieved without the need of other materials by such techniques as measuring spectroscopic absorbtivity in the ultraviolet or infrared region of the components themselves. In other techniques color formers are applied to the migrated components to generate color regions. Coloring the substances with a dye reveals their migrated position within the gel. This electrophoretic method is used in present day DNA and protein analyses. A problem common to DNA testing, or electrophoretic methods, is the overlap of certain migrating substances within the gel. Those overlapping substances cannot be easily distinguished from each other. Other problems that typically arise when employing chromatographic techniques is that even when coloring has successfully identified the location of the various components, the color fades with time. This is of particular concern if the object is to quantify the amount of each component using the intensity of the color to correlate to the quantity of the component.
The quantification of radiation exposure has been performed directly using such tools as Geiger counters. Techniques of this type provide basically bulk information and cannot be used for determining the irradiation level at various depths within a subject material. In other words a three dimensional, spatial profile of irradiation dose is not feasible with such direct techniques. This type of information, however, is invaluable in such areas of science as radiation therapy and food sterilization.
It is critical in medical radiotherapy th
Kalivoda Christopher M.
Lee John R.
Rutgers The State University of New Jersey
Salzman & Levy
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