Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2000-01-21
2002-07-02
Smith, Ruth S. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S476000, C356S432000
Reexamination Certificate
active
06415172
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to optical imaging of turbid media, e.g. breast tissue.
BACKGROUND OF THE INVENTION
Optical mammography is likely to become a relevant technology for breast cancer detection. Light scatting is the main problem that limits the potential of efficiently detecting small lesions especially when located in the central region of the breast. Structures close to surface are easily detected by optical techniques while more deep structures are more difficultly detected. A technique to preferentially probe in the central region of the breast is thus of interest.
The present text will refer by way of example only to breast tissue; however, other types of turbid media (i.e. other types of (living) tissue) may also be imaged using the techniques described herein.
Optical imaging of turbid media has been the subject of much research activity and has seen an increase in interest since the early 1990's. This type of imaging is based on the fact that the propagation of light in a turbid medium depends on the absorption and scattering properties of the medium. Absorption results from energy level transitions of the constituent atoms and molecules in the medium. The absorption property of the medium is quantified by its absorption coefficient &mgr;
a
defined as the probability of a photon being absorbed per infinitesimal pathlength. Scattering results from variations in the index of refraction of the different structures present in the medium. In a highly diffusive medium, scattering is quantified by the reduced scattering coefficient &mgr;′
s
, defined as the probability of a photon being isotropically scattered per infinitesimal pathlength. Characteristics such as intensity, coherence and polarization of the incident light change as it is absorbed and scattered by the medium resulting in diffuse transmittance of the light. In particular, scattering causes a collimated laser beam to spread over a sizeable volume element. This complicates the imaging of a turbid medium. Special imaging modalities must be implemented to offset the detrimental light diffusion. For example, time-resolved methods use short light pulses from a fast laser source to illuminate the medium. The emergent light is collected by a fast detector capable of reproducing its time variation, which can provide further information about the turbid medium. A simple data processing approach in this case is time-gating, by which only the earliest part of the output light pulses is used to produce an image. This amounts to using only the light with the straightest trajectory through the scattering medium, thus improving spatial resolution (please see J. C. Hebden and R. A. Kruger, “Transillumination imaging performance: Spatial resolution simulation studies”. Med. Phys. 17, 41-47 (1990)) Reference may also be made to the following documents for additional information with respect to optical scanning techniques: S. B. Colak, D. G. Papaioannou, G. W. Hooft, M. B. Van der Mark, H. Schomberg, J. C. J. Paasschens, J. B. M. Melissen, and N. A. A. J. Van Asten, “Tomographic image reconstruction from optical projections in light-diffusing media”, Appl. Opt. 36, 180-213 (1997); M. S. Patterson, B. Chance, and B. C. Wilson, “Time-resolved reflectance and transmittance for the noninvasive measurement of tissue optical properties”, Appl. Opt. 28, 2331-2336 (1989); D. Contini, F. Martelli, and G. Zaccanti, “Photon migration through a turbid slab described by a model based on diffusion approximation. I. Theory”, Appl. Opt. 36, 4587-4599 (1997); M. Morin, S. Chatigny, A. Mailloux, Y. Painchaud, and P. Beaudry. “Time-domain perturbation analysis of a scattering slab”, in
Optical Tomography and Spectroscopy of Tissue III
, B. Chance, R. R. Alfano, and B. J. Tromberg, eds., Proc. SPIE 3597, 67-78 (1999); Y. Painchaud, A. Mailloux, M. Morin, S. Verreault and P. Beaudry, “Time-domain optical imaging: discrimination between scattering and absorption”, Appl. Opt. 38, 3686-3693 (1999); as well as U.S. Pat. No. 5,808,304).
The strong interest in optical imaging of scattering media stems from the need for biomedical diagnostic techniques that are safe and non-invasive. The optical properties of biological tissues are at the heart of optically based biomedical diagnostic techniques. As for the general case of a turbid medium, the manner in which light propagates through tissue depends on its absorption and scattering properties. Thus, if abnormal tissue can be said to differ from normal in its absorption or scattering of light for some physiological or morphological reason, it then becomes possible to optically differentiate between normal and abnormal conditions. A specific application is optical mammography where tumors could be differentiated from normal breast tissue on the basis of optical properties.
SUMMARY OF THE INVENTION
It would, for example, be advantageous to have a mechanism for the detection of an anomaly(ies) in turbid medium such as for example a tumour in tissue such as breast tissue.
Accordingly, the present invention in one aspect provides in a method for scanning a turbid medium for generating an image thereof for the detection of one or more anomalies contained within the turbid medium, said turbid medium having a first face and an opposite second face, wherein said turbid medium is scanned by displacing an optical signal source and a corresponding optical detector from one respective spatial location to another about the turbid medium, each spatial location being associated with a corresponding input region on said first face and a corresponding output region on the opposite dsecond face, said optical signal source directing an optical signal (e.g. laser beam) to each of said input regions, said optical detector in response to optical signals detected from each of said output regions sending corresponding detector output signal data to an image processing means for generating a set of image data of the turbid medium, the improvement comprising
generating a primary set of image data derived by scanning said turbid medium using for each input region a first input region of predetermined size and using for each output region a first output region of predetermined size, and
generating a secondary set of image data derived by scanning said turbid medium using for each input region said first region of predetermined size and using for each output region a second output region of predetermined size.
The present invention in another aspect provides in a method for scanning a turbid medium for generating an image thereof for the detection of one or more anomalies contained within the turbid medium, said turbid medium having a first face and an opposite second face, wherein said turbid medium is scanned by displacing an optical signal source and a corresponding optical detector from one respective spatial location to another about the turbid medium, each spatial location being associated with a corresponding input region on said first face and a corresponding output region on the opposite second face, said optical signal source directing an optical signal (e.g. laser beam) to each of said input regions, said optical detector in response to optical signals detected from each of said output regions sending corresponding detector output signal data to an image processing means for generating a set of image data of the turbid medium, the improvement comprising
generating a primary set of image data derived by scanning said turbid medium using for each input region a first input region of predetermined size and using for each output region a first output region of predetermined size, and
generating a further set of image data derived by scanning said turbid medium using for each input region a second input region of predetermined size greater than that of said first input region and using for each output region said first output region of predetermined size.
The present invention in another aspect provides in a method for scanning a turbid medium for generating an image thereof for the det
Chatigny Stéphane
Morin Michel
Painchaud Yves
Art Advanced Research Technologies Inc.
Fay Sharpe Fagan Minnich & McKee LLP
Smith Ruth S.
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