Device for localizing an object in a turbid medium

Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation

Reexamination Certificate

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Details

C600S473000, C600S476000, C356S432000, C385S016000

Reexamination Certificate

active

06327488

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a device for localizing an object in a turbid medium, which device includes a light source and a holder for accommodating the turbid medium, which holder is provided with a plurality of entrance openings for coupling the light to be generated by the light source into the turbid medium and a plurality of exit openings, whereto photodetectors are coupled, which device also includes a selection unit for optically coupling the light source to an entrance opening to be selected from the plurality of entrance openings.
BACKGROUND OF THE INVENTION
A device of this kind is known from the international patent application WO 96/20638. In the context of the cited patent application a light source is to be understood as a source which emits electromagnetic radiation of a wavelength in a range of between 400 and 1400 nm. The known device can be used for the imaging of the interior of biological tissues. In medical diagnostics the device could be used for the imaging of tumors in breast tissue. Light generated by the light source in the known device is applied to the turbid medium via successively selected entrance openings in the holder, the same entrance opening being selected several times. Subsequently, detectors at the exit openings of the holder measure the intensity of the light having been transported through the turbid medium along different optical paths from the selected entrance opening. The measured intensities are used to localize the object in the turbid medium. It is a drawback of the known device that in the localizing of the object in the turbid medium on the basis of the measured intensities an error occurs relative to the actual position of the object in the turbid medium.
SUMMARY OF THE INVENTION
It is inter alia an object of the invention to provide a device in which the error in localizing the object in the turbid medium is mitigated. To achieve this, the device according to the invention is characterized in that it includes means for counteracting variations in a transmission of an optical path between the light source and the selected entrance opening. The invention is based on the idea that errors arise in the localization of the object in the turbid medium because variations occur in the intensity of the light through the selected entrance opening when this entrance opening is selected several times during the execution of successive measurements on the object. The use of means which counteract the variations in the light intensity through the selected entrance opening results in a smaller contribution to the error in the localization of the object in the turbid medium.
A special device according to the invention is characterized in that the selection unit is provided with an entrance light conductor and exit light conductors, a first end of said entrance light conductor being optically coupled to the light source whereas a second end is positioned so as to be displaceable for the optical coupling to a first end of one of the exit light conductors, a second end of said exit light conductor being coupled to the selected entrance opening and a numerical aperture of the first end of each exit light conductor being larger than a numerical aperture of the second end of the entrance light conductor. Because of the larger numerical aperture of the first end of the exit light conductor relative to the second end of the entrance light conductor, the transmission is rendered less dependent on a positioning error of the second end of the entrance light conductor relative to the first end of the exit light conductor. This results in a smaller variation of the transmission of the optical path between the light source and the selected entrance opening in the case of repeated selection of the same light source.
A further device according to the invention is characterized in that the entrance light conductor of the selection unit includes an optical fiber of a first type and that each exit light conductor of the selection unit includes an optical fiber of a second type. The use of optical fibers enables a compact construction of the device.
A further device according to the invention is characterized in that each exit light conductor also includes an optical fiber of a third type which has a property deviating from that of the optical fiber of the second type and is optically coupled, via a fiber-optical connector unit, to the optical fiber of the second type of the same exit light conductor. As a result of the use of an optical fiber of the third type, having optical or mechanical properties which deviate from those of the optical fibers of the second type, the optical fibers of the second type as well as those of the third type can be optimized for a specific application in the device.
A further device according to the invention is characterized in that the optical fiber of the second type contains quartz. As a result of this choice, the transmission of the optical fiber of the second type can be optimized because of the low damping factor of the optical fiber of the second type.
A further device according to the invention is characterized in that the optical fiber of the third type contains a synthetic material. Because of a low elasticity modulus of an optical fiber of the third type, this choice simplifies the coupling of the device to and the assembly with the holder in a small space.
A further device according to the invention is characterized in that the fiber-optical connector unit includes a first section which contains a second end of the optical fiber of the second type and a second section which contains a first end of the optical fiber of the third type, a light-absorbing material being arranged between the first section and the second section and being provided with a light-conducting channel for optically coupling the optical fiber of the second type to the optical fiber of the third type. Because the light-absorbing material in the connector unit is provided with several channels, crosstalk between adjacently situated transmission paths in the optical connector unit is counteracted. The crosstalk occurring may be due, for example to the non-coaxial positioning of the second end of an optical fiber of the second type relative to the first end of the optical fiber of the third type, so that reflection causes a part of the light to be conducted to a first end of a neighboring optical fiber of the third type.
A further device according to the invention is characterized in that the light-absorbing material also has elastic properties. This step offers a greater tolerance in respect of the dimensional accuracy of the areas of the first and the second section adjoining one another in the assembled state of the optical connector unit. Because of the greater tolerance, the manufacture of the first and second sections of the optical connector unit can be simpler and less expensive.


REFERENCES:
patent: 5876339 (1999-03-01), Lemire
patent: 5907406 (1999-05-01), Papaioannou et al.
patent: 5987351 (1999-11-01), Chance
patent: 0178366A2 (1986-04-01), None
patent: WO 9620638 (1996-07-01), None
patent: WO9710568 (1997-03-01), None

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