Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Patent
1997-12-01
1999-08-24
Kamm, William E.
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
600476, 356432, 250330, A61B 500
Patent
active
059418273
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a system for localizing an object in a turbid medium. The invention also relates to a method for localizing an object in a turbid medium.
Such a system is advantageously used for imaging human or animal tissue. In particular, in the field of mammography detection of an object in a turbid medium is employed to detect a tumour in a woman's breast.
2. Description of the Related Art
Such a system is known from the article Highly sensitive object location in tissue models with linear in-phase and anti-phase multi-element optical arrays in one and two dimensions, by B. Chance et al. in the Proceedings of the National Academy of Science USA Vol. 90 (1993) 3423-3427.
The known system comprises spatially separated light sources emitting substantially the same wavelength. The light sources are amplitude modulated with essentially the same frequency and with a phase difference of about 180.degree.. When the known system would illuminate a homogeneous medium the amplitude modulations cancel along the perpendicular bisector of the separation of the two sources. Any inhomogeneity like an object in the turbid medium causes a deviation from the cancellation of the Amplitude modulation along the perpendicular bisector and as a consequence a signal is detected by a photodetector set-up on the perpendicular bisector. However, the known system does not provide information pertaining to the composition of the object. Hence, the known system is e.g. unable to distinguish a malignant cancerous tumour from a benign tumour.
SUMMARY OF THE INVENTION
An object of the invention is to provide a system for detecting an object in a turbid medium which is substantially sensitive for the composition of the object.
This object is achieved by a system for detecting an object in a turbid medium according to the invention comprising a radiation source for irradiating the turbid medium with radiation components having a first and a second wavelength, respectively, the radiation components of the first and second wavelength being amplitude modulated at substantially equal modulation frequencies, the amplitude modulation of the radiation components of the first and second wavelength having a predetermined phase difference, and a photodetector arranged to detect radiation from the turbid medium.
The radiation source irradiates the turbid medium and radiation having passed through at least a part of the turbid medium is detected by the photodetector. When the turbid medium would be homogeneous the amplitude modulations would superpose at the photodetector in a predetermined way. That superposition is represented by a predetermined photodetector signal. In particular, the superposition of the amplitude modulations would be predetermined by the absorption of the radiation components of the first and second wavelength by the turbid medium and the distance between the position of incidence of the radiation components and the photodetector. The object causes a deviation from the predetermined superposition and the ensuing deviation of the actual photodetector signal from the predetermined photodetector signal contains information on the object. In particular the deviation of the superposition is caused by a difference of the dependence of the absorption on the wavelengths for the turbid medium and for the object. For example, a cancerous tumour in a woman's breast has a different absorption behaviour as a function of the wavelengths as compared to the healthy breast tissue.
The deviation of the actual photodetector signal from the predetermined photodetector signal represents both the position and at least some aspects of the composition of the object. The deviation comprises spectroscopic information pertaining to the object, which represents at least some aspects of its composition. The deviation of the superposition of the amplitude modulations is caused substantially throughout the region in the turbid medium that is traversed by the radiation components. Hence, the
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Kamm William E.
Renfrew, Jr. Dwight H.
Shaw Shawna J.
U.S. Philips Corporation
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