Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2001-07-31
2003-10-28
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S473000, C600S476000, C356S342000, C351S221000
Reexamination Certificate
active
06640124
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of image processing. More particularly, it relates to methods and devices for separating multiply scattered light from directly scattered light. The invention further relates to methods and devices that utilize the resultant data sets in the characterization of an optical target beyond that routinely performed in directly scattered light.
BACKGROUND OF THE INVENTION
In many imaging applications, the object to be imaged includes a highly remittive layer. When light illuminates such an object, the resulting image consists of a directly scattered light component reflected from this highly remittive layer and a multiply scattered light component that is scattered from points that are within the object but outside the highly remittive layer. Because the layer is highly remittive, the directly scattered light component tends to dominate the image. As a result, it is difficult to capture the multiply scattered light component of the image.
An example of an object having a highly remittive layer is the human retina. In the retina, certain structures are visible only by examination of the directly scattered light component of the image. These structures cannot be seen clearly by examination of the multiply scattered light component. Examples of such structures include small blood vessels and superficial features of the optic nerve head. Conversely, there exist other retinal structures, such as drusen, clumped pigment, choroidal tumors, subretinal new blood vessels, subretinal edema, and the choroidal rim of the optic nerve head, which are visible to a far greater extent in the multiply scattered light component than in the directly scattered light component.
In some applications, such as ophthalmologic ones, it is desirable to locate precisely a structure which can be imaged in the multiply scattered light component with respect to a known feature observable only in the directly scattered light component. For example, it may be useful to know that a particular region of drusen or edema is located near the intersection of two blood vessels. Conversely, it is desirable in some applications to locate precisely a structure that can be imaged in the directly scattered light component with respect to a known feature observable only in the multiply scattered light component. For example, it may be desirable to use the choroidal rim, a feature readily observed in the multiply scattered light component, as a point of reference for imaging blood vessels in the vicinity of the macula.
A known technique for separating a multiply scattered light component from a directly scattered light component is to illuminate the retina with a point light source and to direct the remitted image field through a field stop confocal to the light source. By providing the field stop with a pinhole aperture, one can observe the directly scattered light component of the image. Alternatively, by providing a field stop with an annular opening, one can observe the multiply scattered light component of the image. These techniques are described in Elsner A. E., Burns S. A., Weiter J. J., and Delori F. C.,
Infrared imaging of subretinal structures in the human ocular fundus,
Vision Research 36, 191-205, 1996.
Using the foregoing technique, one can provide a field stop with a pinhole aperture, observe the directly scattered light component of the image, replace the pinhole aperture with an annular aperture, and then observe the multiply scattered light component of the image. By scanning in two dimensions, one can generate a two-dimensional image that includes only the multiply scattered light component and create another image that includes only the directly scattered light component. Similarly, by using known techniques of tomography, one can obtain pairs of cross-sections, each pair including one image based on the multiply scattered light component and another based on the directly scattered light component.
A disadvantage of the foregoing technique is that a significant time interval elapses between the measurement of the directly scattered light component and the subsequent measurement of the multiply scattered light component. This interval arises because of the time required to replace the pinhole aperture with an annular aperture. A lengthy interval leads to artifacts in comparison or other combination of information from the two components. Such artifacts reduce the effectiveness of image or data processing techniques in yielding meaningful information concerning the light scattering properties of the target. A lengthy interval allows potential motion or other alterations concerning the target to preclude accuracy in such observations, comparisons, or computations.
Using the forgoing technique, one can, in principle, precisely locate a structure visible in one component relative to a feature visible in the other component by capturing an image or collecting data restricted primarily to the directly scattered field and overlay it on the image or data of the multiply scattered field. By aligning the image or data from the multiply scattered light component with the image or data from the directly scattered light component, one can endeavor to locate a structure visible only in one component relative to a structure visible only in the other component.
In practice, however, the effectiveness of localization is also severely limited by the time interval that elapses between collecting the data from the directly scattered light component and the multiply scattered light component. This is because a target can undergo motion or change over time. For example, the retina is subject to rapid and unpredictable motion. As a result, in the interval, referred to as a blanking interval, that elapses as the two apertures are alternated, the retina may have moved by some unknown amount or in some unknown direction. Typically the mechanical inertia associated with alternating between two apertures prevents the blanking interval from being made short enough to capture two successive images without significant alteration to the target, e.g. movement of the retina, between images. Since a patient cannot entirely control eye movements, the position of the retina during observation of the multiply scattered light component will, in general, not be the same as the position of the retina during observation of the directly scattered light component. This unpredictable motion or alteration of the target, e.g. the retina, causes unpredictable errors in the reliable alignment of two or more image components or data sets and the further processing of the data therein.
SUMMARY OF THE INVENTION
What is desirable in the art is an apparatus and method for reducing the blanking interval, thereby permitting observation of the directly scattered light component and the multiply scattered light component of a target at least substantially simultaneously. For example, if the blanking interval could be made short enough, the retinal target would move or be altered by a negligible amount between the observation of the directly scattered light component and the observation of the multiply scattered light component.
This invention provides apparatus and methods permitting an operator to switch easily between observation of the directly scattered light component and observation of the multiply scattered light component of the image. Near simultaneous collection of the separated components allows their use in further observation, comparison, or computations for characterizing an object, specimen, or structure. In certain embodiments, the invention provides apparatus and methods for observation, evaluation, diagnosis, and therapeutic manipulation of anatomical regions of interest. In certain embodiments, the invention provides apparatus and methods for observation, evaluation, diagnosis, and therapeutic manipulation of the human retina. In the ophthalmologic field, it is desirable to provide an imaging apparatus to allow an operator to use substantially simultaneously both the directly scattered lig
Burns Stephen A.
Dreher Andreas W.
Elsner Ann E.
Webb Robert H.
Foley & Hoag LLP
Lateef Marvin M.
Pass Barry
The Schepens Eye Research Institute
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