Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2001-03-28
2004-04-06
Bennett, Henry (Department: 3743)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S476000, C600S407000, C356S432000, C250S341100
Reexamination Certificate
active
06718195
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of localizing a deviant region in a turbid medium that is represented by a set of volume elements, which method includes a first measuring step in which the turbid medium is irradiated by means of light comprising radiation of mainly a fist wavelength and in which intensities of a part of the light comprising radiation of mainly the first wavelength that is transported along a plurality of light paths through the turbid medium are measured, and an imaging step for reconstructing an image of the turbid medium from the measured intensities.
The invention also relates to a device for carrying out such a method.
In the context of the present application the term light is to be understood to mean electromagnetic radiation of a wavelength in the visible or infrared range between approximately 400 and 1400 nm. A turbid medium is to be understood to mean a substance consisting of a highly light dispersive material. More specifically, in the context of the present application the term turbid medium is to be understood to mean biological tissue. A deviant region is to be understood to mean a region in which the turbid medium deviates in any way or form from the turbid medium in the surrounding region. More specifically, in the context of the present application such an area is to be understood to mean a region comprising tumor tissue. The turbid medium is represented by a set of volume elements. Volume elements of this kind are also known as voxels. The size and shape of the volume elements may be the same for all volume elements. However, it is alternatively possible for the volume elements to have mutually different dimensions and shapes.
A method and a device of this kind are known from “Clinical Optical Tomography and NIR Spectroscopy for Breast Cancer Detection”, S. B. Colak et al, IEEE Journal of Selected Tops in Quantum Electronics, Vol. 5, No. 4, July/August 1999. The known method and device are used for imaging the interior of biological tissues. The method and the device can be used inter alia in medical diagnostics for in vivo breast examinations for visual localization of any tumors present in the breast tissue of a human or animal female body. According to the known method a turbid medium is successively irradiated by light from various irradiation positions. Subsequently, the intensity of the light having been transported along different light paths through the turbid medium that extend from their irradiation position is measured in a number of measuring positions. The intensities measured are used for the reconstruction of an image of the turbid medium. A spatial distribution of the attenuation of the light through the tissue is reproduced in this image. Light is attenuated by tissue in that the tissue disperses and absorbs the light.
A possibly deviant region can be visually localized in the image if the attenuation of the light by the tissue in the deviant region deviates sufficiently from the attenuation of the light by the tissue in the surrounding region. A plurality of individual images can be formed by carrying out the known method repeatedly while using light of different wavelengths.
The known method and device have a drawback in that the images thus obtained are insufficiently clear so as to enable accurate visual localization of deviant regions.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method that yields an image of the turbid medium in which deviant regions can be accurately localized visually.
This object is achieved by a method of the kind set forth in the preamble which is characterized in that the method also includes at least a second measuring step in which the turbid medium is irradiated by means of light comprising radiation of mainly a second wavelength which is not equal to the first wavelength, and in which intensities of a part of the light comprising radiation of mainly the second wavelength that is transported along a plurality of light paths through the turbid medium are measured, the imaging step including the following steps: a first calculation step in which a value is assigned to at least a first parameter in dependence on the intensities measured for a volume element in the measuring steps, said first parameter representing a property of the turbid medium, a second calculation step in which a significance value is assigned to the volume element in dependence on the value of at least the first parameter, a display step for displaying the significance value of the corresponding volume element in the image of the turbid medium for each point in the image that corresponds to one of the volume elements.
The invention is based on the one hand on the insight that the combining of measured intensities derived from a plurality of measurements with light of different wavelengths can yield values for parameters representing properties of the tissue, which properties enable (separately or in combination), normal tissue to be distinguished from deviant tissue. The parameters thus obtained can represent inter alia components constituting the turbid medium. For example, it is possible for a parameter to represent a spatial distribution of a quantity of water through the turbid medium.
The invention is also based on the recognition of the fact that regions that are deemed to be deviant on the basis of the parameter values obtained can be marked in the image. The attention of a user, for example a radiologist, is thus drawn to the region in the image that is considered to be deviant.
The significance value can be represented in the image of the turbid medium, for example by utilizing colors. Distinct colors can thus be assigned to different significance values. Should the significance value vary continuously, alternatively smoothly varying colors can be added to the image. Known color scales, for example the rainbow scale, can be used for this purpose.
A version of the method in accordance with the invention is characterized in that it includes a third measuring step in which the turbid medium is irradiated by means of light comprising radiation of mainly a third wavelength that is not equal to the first wavelength or the second wavelength and in which intensities of a part of the light comprising radiation of mainly the third wavelength that is transported along a plurality of light paths through the turbid medium are measured, and that in the first calculation step a value is assigned to a second parameter in dependence on the intensities measured for a volume element in the measuring steps, said second parameter representing a property of the turbid medium that is not the same as that represented by the first parameter, and that in the second calculation step a significance value is assigned to the volume element in dependence on the value of the first parameter and on the value of the second parameter.
Each measuring step in this version produces a set of measured data. The values for two parameters are determined from the three sets of measured data obtained. When the wavelengths of the light are sufficiently far apart in the three measuring steps, the sets of measured data will not be correlated and, using known mathematical techniques, it will in all cases be possible to determine values for the mutually independent parameters from the sets of measured data.
A version of the method in accordance with the invention is characterized in that the first wavelength has a value of between 830 nm and 900 nm, that the second wavelength has a value of between 750 nm and 830 nm, and that the third wavelength has a value of between 655 nm and 750 nm. Light with the above-mentioned wave lengths can easily be generated by state of the art semi-conductor lasers.
When the wavelengths of the light used in the three measuring steps lie in the above ranges, the spatial distribution of inter alia hemoglobin (Hb) and oxyhemoglobin (HbO
2
) through the tissue can be suitably approximated. This is because the attenuation of the light due to dispersion and absorption by biological t
'T Hooft Gert Wim
Van Der Mark Martinus Bernardus
Wachters Arthur Johannes Hubertus
Bennett Henry
Dahbour Fadi H.
Koninklijke Philips Electronics , N.V.
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