Abstract:
A micro-electromechanical system (MEMS) probe package is provided including a first reflective element receiving a light beam directed into to the probe package and a second reflective element receiving light directed from the first reflective element. The second reflective element directs light in an optical path extending from the probe package. At least one of the reflective elements includes a MEMS mirror. An embodiment of the package is made with a monolithic housing having mounting surfaces formed therein for aligning the first reflective element with the second reflective element. The monolithic housing also includes a mounting surface for aligning at least one lens with at least one of the reflective elements.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. Provisional Patent Application No. 60/908,473 filed on Mar. 28, 2007 which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to biomedical imaging systems, and more particularly to a microelectromechanical systems (MEMS) based imaging systems. 
       BACKGROUND OF THE INVENTION 
       [0003]    Optical Coherence Tomography (OCT) is a high resolution optical imaging technique that enables sub-surface, tomographic imaging of a variety of materials. OCT imaging is based on coherence interferometry using a wide band light source, usually infrared light in the wavelength range of 750-1300 nanometers. 
         [0004]    Light in an OCT system is typically split into a sample path and a reference path. The sample path is focused on the material or specimen to be imaged and the reference path provides a variable optical delay. Reflected light from the sample path and the reference path are combined in an interferometer and the interference signal detected thereby separating the non-coherent scattered light returning from the sample and the coherent non-scattered reflected light. The sampled signal is then used to construct an image of the scanned specimen. 
         [0005]    MEMS devices including MEMS mirrors may be used to direct the light path in OCT imaging systems. Such MEMS devices are fragile and must be precisely positioned within a probe. Such MEMS devices may also require protection from clinical environments and electrostatic charges. It has heretofore been difficult to align and protect MEMS devices in a probe package. Further, MEMS devices must be electrically connected to external components. It has heretofore been difficult to provide electrical connections between a MEMS device and external components for control of the MEMS device. 
         [0006]    Certain OCT applications require application specific or custom probes to perform various clinical functions. It has been inefficient to use a plurality of different probes for different applications. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides a minimally invasive, non-destructive, high-resolution, three-dimensional MEMS based OCT probe that can be fabricated without requiring difficult processing steps. 
         [0008]    An illustrative embodiment of the invention provides a micro-electromechanical system (MEMS) probe package including a first reflective element receiving a light beam directed into to the probe package and a second reflective element receiving light directed from the first reflective element. The second reflective element directs light in an optical path extending from the probe package. At least one of the reflective elements includes a MEMS mirror. An embodiment of the package is made with a monolithic housing having mounting surfaces formed therein for aligning the first reflective element with the second reflective element. The monolithic housing also includes a mounting surface for aligning at least one lens with at least one of the reflective elements. 
         [0009]    While illustrative embodiments of the present invention are described as including a camera in a functional tip of a MEMS package, it should be understood that the illustrative embodiments of the invention also may include one or more cameras in the MEMS package itself regardless of whether a functional tip is used. 
         [0010]    While the illustrative embodiments of the invention are described herein generally with respect to an OCT probe, it should be understood that the various embodiments of the invention can be used with a variety of other probe types such as, a hand held probe which may be optimized for examining an oral cavity, ear, nose, or skin for example. 
         [0011]    Another embodiment of the invention provides a MEMS package including a housing having at least one MEMS device mounting surface and at least one optical component mounting surface for aligning at least one MEMS device with at least one optical device. The package also includes a removable functional module mounted externally to said housing 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0012]    The features and advantages of the present invention will be better understood when reading the following detailed description, taken together with the following drawings in which: 
           [0013]      FIG. 1  is a cross sectional view of a MEMS probe package having a laterally directed optical path; 
           [0014]      FIG. 2  is a cross sectional view of a MEMS probe package having a longitudinally directed optical path according to an illustrative embodiment of the invention; and 
           [0015]      FIG. 3  is a three-dimensional view of a MEMS probe package including a plurality of optional functional probe tips according to an illustrative embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION  
       [0016]      FIG. 1  illustrates a typical configuration of a MEMS based probe package  100  in which light propagates down a waveguide  102  such as a single mode, multimode, double clad, or photonic crystal optical fiber, from the proximal end of the probe to the distal end of the probe. At the distal end of the probe, a lens  104  or series of lenses focuses or collimates the light emitted from the waveguide  102  into a beam  106  which is then reflected perpendicular to main axis of the probe package  100  and scanned using a MEMS mirror  108  through an imaging window  110 , or a post-scan lens, for example. The mirror is typically mounted at a 45 degree angle relative to the waveguide, thereby resulting in a 90 degree deflection in the light path for side scanning. The mirror may alternatively be mounted at angles greater or less than 45 degrees. 
         [0017]    An illustrative embodiment of the present invention provides a forward scanning MEMS based probe package as described with reference to  FIG. 2 . Forward scanning is achieved by a MEMS based probe package  200  utilizing the a lens  202  to receive light from a waveguide  204 . A first reflective element  206  and a second reflective element  208  mounted in the package  200  are arranged to fold the optical path twice. The first reflective element  206  is employed to bend the light beam  210  by 90 degrees and the second reflective element  208  bends the light beam  210  by a second 90 degrees. This results in a beam emitting in the forward direction from the distal end  212  of the probe. 
         [0018]    The first reflective element  206  and/or the second reflective element  208  may be a MEMS mirror, a simple mirror, or a prism, for example. To achieve 2D scanning, each mirror may be a single axis MEMS device where each provides one axis of scanning. Alternatively, one of the reflective elements may be a 2 axis device for providing two dimensional scanning while the other may be a simple mirror, for example. In an illustrative embodiment, the mirror may be a curved reflecting surface that provides adaptive focus control. In another embodiment, the reflective element could comprise a deformable mirror for wavefront shaping and aberration correction, as well as focus control. 
         [0019]    Alternative embodiments of the present invention may also be employed to provide MEMS based forward scanning. For example, in an alternative embodiment of the invention, a MEMS based device is provided to scan an optical waveguide that is coupled to an endoscope&#39;s input waveguide. The output of the scanned waveguide is then directed into a lens to achieve forward scanning. In yet another embodiment of the invention, a microlens or series of microlenses is scanned by an actuator to direct a beam of light. 
         [0020]    A secondary reflecting element can also be used to realize a forward scanning probe employing MEMS mirrors according to the present invention. The optical path may be modified by placing a reflective mirror in the optical path between the pre-scan collimating or focusing objectives and the MEMS mirror. The optical path may be folded 90 degrees, or any arbitrary angle, by a first reflective element such as a simple flat mirror to simply fold the optical path. 
         [0021]    The first reflective element may be a curved mirror or optical surface to provide focusing, as well as beam folding. The first reflective element may also be a scanning MEMS device, with one axis, or two axes, of scanning capability. The first reflective element can also be a deformable optical surface (universal optical element) providing wavefront shaping, aberration correction and focus control in addition to beam folding. The first reflective element may also be a prism which may be in the path of the optical beam or may be directly attached to the waveguide/GRIN lens assembly. The first reflective element may also be a two axis MEMS scanner, which folds the optical path and scans the beam. 
         [0022]    The second reflective element folds the optical path a second time to direct the beam out the front of the probe. The second reflective element may be a simple flat mirror to simply fold the optical path. The second reflective element may also be a scanning MEMS device, with one or two axis of scanning capability. If the initial scanning device is a one axis scanner and the second device is a one axis scanner, orientated in an orthogonal direction two axis scanning is achieved. The second reflective element may be a prism which folds the optical path and redirects a scanned beam. The second reflective element may be a two axis MEMS scanner, which folds the optical path and scans the beam in two dimensions. The second reflective element may be a curved surface which serves to fold the optical path and also expand or focus the beam and scan angle. 
         [0023]    Any of the reflective elements may be realized as a curved surface, which acts as a focusing element as well as a reflecting element, and these surfaces may be either spherical or aspherical. The reflective elements, may also be realized by molding of polymers at either microscale (for a MEMS aperture) or macroscale for serving as a large reflective element. Machining and polishing of a hard surface such as glass or ceramic followed by subsequent metallization may be employed to realize the mirror surface of the reflective elements. The reflective elements may be realized by controlled surface wetting and a curable polymer or epoxy. Micromachining may be utilized to create the mirror surface of the reflective elements, and stress control employed to control the curvature of the surface. 
         [0024]    Deformable mirrors for wavefront correction and dynamic focus control may be realized via arrays of individual mirrors with pistoning or tip-tilt and piston capabilities, or a single membrane with individual actuators in discrete locations for surface adjustment (z axis or pistoning control). 
         [0025]    It is often desirable to pass a standardized optical coherence tomography (OCT) probe down a biopsy channel of an endoscope to perform an optical biopsy. Such probes may be utilized to provide OCT imaging in various applications. It is also often beneficial to employ custom endoscopes that are optimized for OCT imaging in specific regions wherein the internal components and channel configuration are optimized for the OCT imaging systems. 
         [0026]    Flexible endoscopes allow the scope to traverse curved and folded internal pathways and employ mechanical transduction to allow the operator to manipulate the distal end of the probe from the proximal end. This manipulation may include 2-axis displacement as well as rotation. Rigid and telescopic endoscopes allow the clinician to directly manipulate the distal end of the probe by motion at the proximal end via direct non-flexible mechanical coupling. Illustrative embodiments of the invention provide endoscopic OCT probes may incorporate any combination of innovative components describe herein. 
         [0027]    In one illustrative embodiment, a scan-head provides beam scanning for OCT imaging in 2 or 3 dimensions. The scan-head may also be used to scan an ablation laser or may be employed for multimodal optical imaging techniques including confocal microscopy, CARS imaging, multi-photon imaging and fluorescence microscopy. The scan-head may be forward or side looking. In the illustrative embodiment, the scan-head and endoscope may be permanently integrated with each other and may have a specified operational lifetime. Alternatively, the scan-head may be removed and replaced after a specified lifetime. Different versions of the scan-head allow trade-offs between imaging speed, resolution and field of view. 
         [0028]    In an embodiment of the invention, fiber optic illumination provides a conduit for light from an external source at the proximal end of the probe to be delivered to the distal end of the probe. Fiber optic visualization couples an optical signal from the distal end of the probe to the proximal end to allow direct visualization by the operator. Embodiments of the invention include biopsy forceps which allow removal of tissue for external analysis, confirmation of observations or excision of diseased tissue. An access channel for obtaining biopsies, drug delivery, dye or marker delivery can be included to provide a flexible use access path to the distal end of the probe. Additionally, channels for vacuum aspiration and fluid delivery may be provided according to the invention to keep the optical elements clean and remove body fluids from the imaging region when necessary. 
         [0029]    Fiber for ablation laser delivery allows delivery of light from an external ablation laser to a scan-head or fixed optical system at the distal end of the probe for ablation of tissue or region marking. Radio frequency (RF) or thermal ablation transducers can be used in illustrative embodiments of the invention to provide a means of immediately destroying small regions of tissue identified by the imaging system. 
         [0030]    Capacitive sensors for motion detection utilizing capacitive electrodes may also be used in embodiments of the invention to detect the proximity of the probe to the tissue and also to provide feedback to the imaging system. This allows automated detection of motion during an imaging scan. 
         [0031]    LED illumination (white light, UV, red, blue green or IR wavelengths) may be used in illustrative embodiments of the invention to provide illumination for visualization of tissue by the operator and also for tissue heating or an excitement wavelength for specific markers (i.e. fluorescence imaging or multimodal imaging). CCD or CMOS imaging systems may also provide tissue surface visualization as well as direct visualization of the region being imaged, biopsied or ablated during an imaging session. Additionally, such imaging systems may be used to detect optical effects caused by the laser, such as diffraction. Various operating wavelengths may be used to allow monitoring of temperature or identification of markers under specific illumination conditions. The imaging system provided by these embodiments of the invention also allows identification of motion during an imaging scan. 
         [0032]    Ultrasound transducers may be incorporated for larger scale (i.e. 100 μm or larger) tomographic 2 D or 3D imaging, or may provide a larger field of view with deeper penetration at a lower resolution of about 100 μm, for example. The probe position may also be precisely tracked by an external 3D ultrasound system, this can be aided by the emission of ultrasonic signal by the probe-head. Also provides enhancement of OCT image via non-linear optical processes. 
         [0033]    The various illustrative embodiments of the invention described herein may be fabricated using MEMS probe packaging technologies that are described in Applicants&#39; co-pending U.S. Patent Application No. 60/908,473 filed on Mar. 28, 2007 which is incorporated herein by reference. 
         [0034]    Illustrative embodiments of the present invention also provide a modular system wherein a variety of modular microsurgical functional tips can be attached to the leading edge of an OCT probe. A modular microsurgical functional tip may be comprised of a generally cylindrical shape which may be split longitudinally to provide two semi-cylindrical parts, which are joined together. The distal end of the functional tip may be conical or flat with pre-molded attachment features for control of the entire microsurgical OCT probe. Along the proximal end of the functional tip, a cylindrical ridged engagement member allows the attachment to the OCT probe. A keyed feature located at the proximal end allows orientated attachment, whereas electrical contact features control and power the functions of various tips. Certain tips may be ejected remotely, separating themselves from the microsurgical OCT probe while in use. Internally, the tip may contain a variety of components, singularly or in any combination. For example, such components may include a camera, a light source, inertial sensors, a thermocouple(s), a balloon(s), marking apparatus, fluid delivery system or drug delivery system (radiation source, chemical source). Functional tips may be attached during the manufacturing process or by the end user. A functional tip may be activated and/or controlled by the electromechanical control systems of the OCT probe. 
         [0035]    The inventive microsurgical functional tip to be attached externally to and used in conjunction with a microsurgical OCT probe provides additional functionality not easily accomplished internally because of space limitations, integration difficulties or functional feasibility. The invention provides instruments such as camera, light source, inertial sensors, thermocouple, balloon, physical actuation, marking apparatus, fluid delivery system and drug delivery system (radiation source, chemical source) to be held internally or externally by the functional tip. The inventive functional tips may also include multiple microsurgical instruments such as camera, light source, knife etc. which are often used simultaneously during treatment or diagnosis by a physician. 
         [0036]      FIG. 3  illustrates an OCT probe package  300  and a plurality of functional tips in accordance with several illustrative embodiments of the present invention. A first functional tip embodiment includes a thread steerable tip  302 , having a generally tapered cylindrical configuration. This embodiment may include a ring portion extending from the distal end whereby a guide line or floss can be attached by knot or loop to allow actuation and manipulation of the entire OCT probe. A cylindrical ridged engagement member  304  allows for the attachment of the functional tip  302  to the OCT probe package  300 . The engagement member  304  may also have a gasket to create a seal between the functional tip and the OCT probe package  300 . A keyed feature may be located on the engagement member to provide orientation of the functional tip. 
         [0037]    In another embodiment, a functional tip  306  includes a side facing camera  308  and a side facing light source  310 . In yet another embodiment, a functional tip  312  includes a forward facing flattened optically clear window  314  through which the camera and light source may be directed. Depending on the desired focal point and angle, the window  314  may be raised or depressed in relation to the exterior of the functional tip  312 . The camera maybe focused on the particular OCT spot or any area around it. Electrical contact features (not shown) allow control and power of the camera and light through the main OCT probe system controls. 
         [0038]    Another embodiment of a functional tip  316  includes a micro nozzle  318 . The nozzle may be directed upwards, distally, and proximally diagonally and may emit a fan shaped flow of fluid or a higher speed jet of fluid. In this embodiment, the fluid may be useful in cleaning deposits or mucus off of the main OCT probe while in use, thereby minimizing the need to extract the probe for cleaning during a particular treatment or diagnosis. Internally, the functional tip may include a small fluid reservoir. Alternatively, a fluid line may be connected to the OCT probe. 
         [0039]    In another embodiment of the invention, a functional tip may include a drug source. Such a functional tip may include a flattened window made up of a biodegradable material or specific permeability membrane where the drug source can diffuse through. The entire functional tip may also be made of a biodegradable material. Depending on the desired size of treatment area and position of treatment area and location of treatment area, the window maybe raised or depressed or otherwise configured in relation to the exterior of the functional tip. 
         [0040]    Once the functional tip is positioned, the functional tip may be held in place for a short amount of time with the probe. For longer treatments, a functional tip may be attached to the area of interest with glue or biodegradable pins (micro staples), with the functional tip ejected or disconnected from the main OCT probe. In an illustrative embodiment, ejection of a functional tip may be accomplished through the stoppage of electrical current to electromagnets holding the functional tip to the probe, or other electromechanical mechanism which may be controlled through the main OCT probe system controls. 
         [0041]    Another embodiment of a functional tip may include a nozzle which emits a fan shaped flow of dye or a higher speed jet of dye. Such dyes may include dyes for florescence imaging, multiphoton imaging, confocal imaging and the like. Many types of dye may be used including traditional tissue markers, fluorescence, and silver nitrate. Such a dye emitting functional tip is useful as a marker for places of interest to revisit with the OCT probe or other method of treatment and diagnosis. A dye emitting functional tip may also inject dyes directly into cells and/or may emit nano-sized dielectric particles, such as quantum dots or other nanoparticles for diagnostic and therapeutic applications. 
         [0042]    Components of the various functional tips according to the present invention may be formed from optically clear polymer and variants and the various parts may be joined where appropriate by being snap-fitted, molded, or glued together, for example. 
         [0043]    It should be noted that the present invention as described herein provides an improved microsurgical instrument which has considerable advantages over previously known instruments. For example, the attachment point of the first embodiment of the functional tip allows the surgeon to readily manipulate the position of the OCT probe using innate and easily understood methods when it is necessary to reposition the probe during the performance of a diagnosis or treatment. Furthermore, the integrated camera, with integrated control and output display with the OCT system abolishes the need for coordination of movement by two or more operators during diagnosis and treatment. The fact that the functional tips may have capabilities that are very different from those of the main section of the OCT probe simplifies the entire microsurgical instrument development process and allows the physician to accomplish more diverse tasks simultaneously. 
         [0044]    While the invention has been described and illustrated in connection with preferred embodiments, many variations and modifications as will be evident to those skilled in this art may be made without departing from the spirit and scope of the invention, and the invention is thus not to be limited to the precise details of methodology or construction set forth above as such variations and modification are intended to be included within the scope of the invention as set forth in the claims.