# Patent

## Title
Method and device for incremental wavelength variation to analyze tissue

## Abstract

A method of imaging a target using a miniaturized imaging device is disclosed comprising providing a miniaturized imaging device having a stationary lens system and an imaging array, wherein the distance from a distal end of the stationary lens system to the imaging array is fixed. The miniaturized imaging device is advanced near the desired target and a distance from a distal end of the stationary lens system to the desired target is determined. A desired wavelength of light is calculated based on the determined distance from the distal end of the stationary lens system to the desired target and the desired wavelength of light is propagated onto the target.

## Background
CLAIM OF PRIORITY
This application claims priority to U.S. Provisional Application No. 61/084,755 filed on Jul. 30, 2008 and is incorporated herein by reference in its entirety.
RELATED CASES
The present invention is related to co-pending U.S. patent application Ser. Nos. 10/391,489; 10/391,490; 11/810,702; 10/391,513; 11/292,902; and 12/079,741 and U.S. Pat. No. 7,166,537 all of which are incorporated herein by reference in their entireties.


FIELD OF THE INVENTION
The present invention relates to the field of miniaturized imaging devices. More specifically it relates to a device having a light source capable of propagating a predetermined wavelength of light onto a target, a lens system configured to receive light reflected from the target, and a non-linear optical media disposed behind the lens system.
BACKGROUND
Minimally invasive diagnostic medical procedures are used to assess the interior surfaces of an organ by inserting a tube into the body. The instruments utilized may have a rigid or flexible tube and provide an image for visual inspection and photography, but also enable taking biopsies and retrieval of foreign objects. Analysis of image data collected during the inspection and imaging of the interior of the body cavity is a critical component of proper diagnosis of disease and other related conditions.
In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge. An image, or image point or region, is in focus if light from object points is converged almost as much as possible in the image, and out of focus if light is not well converged. A principal focus or focal point is a special focus. For a lens, or a spherical or parabolic mirror, it is a point onto which collimated light parallel to the axis is focused. The distance in air from the lens or mirror's principal plane to the focus is called the focal length.
When a lens (such as a photographic lens) is set to “infinity”, its rear nodal point is separated from the sensor or film, at the focal plane, by the lens' focal length. Objects far away from the camera then produce sharp images on the sensor or film, which is also at the image plane. Photographers sometimes refer to the image plane as the focal plane; these planes coincide when the object is at infinity, but for closer objects the focal plane is fixed, relative to the lens, and the image plane moves, by the standard optical definitions.
Generally speaking, to render objects in focus, the lens must be adjusted to increase the distance between the rear nodal point and the film, to put the film at the image plane. The focal length f, the distance from the front nodal point to the object to photograph or image S1, and the distance from the rear nodal point to the image plane S2 are then related by:




  
    
      1
      
        S
        1
      
    
    +
    
      1
      
        S
        2
      
    
  
  =
  
    1
    f
  




As S1 is decreased, S2 must be increased. For example, consider a normal lens for a 35 mm camera with a focal length off=50 mm. To focus a distant object (S1≈∞) the rear nodal point of the lens must be located a distance S2=50 mm from the image plane. To focus an object 1 m away (S1=1000 mm), the lens must be moved 2.6 mm further away from the image plane, to S2=52.6 mm.

SUMMARY OF THE INVENTION
It has been recognized that it would be advantageous to develop an improved miniaturized micro-camera catheter device capable of analyzing tissues without the need to physically move a lens system with respect to the tissue and/or with respect to an image sensor.
According to one embodiment of the present invention, as broadly described and claimed herein, the present invention features a method of imaging a desired target using a miniaturized imaging device. The method comprises providing a miniaturized imaging device comprising a lens system and an imaging array, wherein the distance from a distal end of the lens system to the imaging array is fixed. The method further comprises advancing the miniaturized imaging device near the desired target and determining a distance from a distal end of the lens system to the desired target. The method further comprises calculating a desired wavelength of light based on the determined distance from the distal end of the lens system to the desired target and propagating the desired wavelength of light onto the target. The method also comprises receiving the desired wavelength of light reflected off of the target.
In accordance with another embodiment, the present invention further features a method of imaging a target within a cavity using a miniaturized imaging device comprising providing a miniaturized imaging device having a stationary lens system and an imaging array, wherein the distance from a distal end of each of the stationary lens systems to the imaging array is fixed. The method further comprises advancing the miniaturized imaging device within a cavity and propagating a starting wavelength of light onto the target within the cavity. The method further comprises receiving the starting wavelength of light reflected from the target onto the imaging array and incrementally adjusting the starting wavelength of light to a different wavelength of light. The method further comprises propagating the different wavelength of light onto the target within the cavity and receiving the different wavelength of light reflected from the target onto the imaging array. The method further comprises determining an optimal wavelength of light for imaging an object in focus.
In accordance with an additional embodiment, the present invention also resides in a miniaturized imaging device disposed on a distal end of a catheter, comprising at least one imaging array disposed on a distal end of the catheter and a plurality of lens systems disposed on the at least one imaging array, wherein the distance from a distal end of the stationary lens system to the at least one imaging array is fixed, wherein each of the plurality of lens systems has a different longitudinal length. A light source is disposed on a distal end of the catheter and is adapted to propagate a starting monochromatic wavelength of light onto a target and incrementally adjust the starting monochromatic wavelength of light to a different monochromatic wavelength of light. In one aspect of the invention, the plurality of lens systems comprises a plurality of GRIN lenses.
In accordance with an additional embodiment, the present invention also resides in an imaging array disposed on a distal end of the catheter and a plurality of lens systems disposed on the imaging array, wherein the distance from a distal end of the stationary lens system to the imaging array is fixed. The plurality of lens systems are configured substantially parallel to one another and the distance from a front surface of each of the plurality of lens systems to the target is different.



BRIEF DESCRIPTION OF THE DRAWINGS
Additional features and advantages of the invention will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate, by way of example, features of the invention; and, wherein:
FIG. 1 is an exemplary view of a medical imaging system in accordance with an embodiment of the present invention;
FIG. 2 is a side view of a micro-catheter in accordance with one embodiment of the present invention;
FIG. 3 is a perspective view of an imaging structure according to one embodiment of the present invention;
FIG. 4 is a perspective view of an imaging structure according to one embodiment of the present invention;
FIG. 5 is a top view of an imaging structure having a plurality of GRIN lenses in accordance with one embodiment of the present invention;
FIG. 6 is a side view of the imaging structure of FIG. 5; and
FIG. 7 is a side view of an imaging structure having a plurality of GRIN lenses in accordance with one embodiment of the present invention.



DETAILED DESCRIPTION OF EXAMPLE EMBODIMENT(S)
Reference will now be made to, among other things, the exemplary embodiments illustrated in the drawings, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Alterations and further modifications of the inventive features illustrated herein, and additional applications of the principles of the inventions as illustrated herein, which would occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the invention.
It must be noted that, as used in this specification and the appended claims, singular forms of “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.
An “SSID,” “solid state imaging device,” or “SSID chip” in the exemplary embodiments generally comprises an imaging array or pixel array for gathering image data, and can further comprise conductive pads electrically coupled to the imaging array, which facilitates electrical communication therebetween. In one embodiment, the SSID can comprise a silicon chip substrate or other semiconductor chip substrate (e.g., InGaAs) or amorphous silicon thin film transistors (TFT) having features typically manufactured therein. The SSID can also comprise a non-semiconductor chip substrate treated with a semiconductor material. Features can include the imaging array, the conductive pads, metal traces, circuitry, etc. Other integrated circuit components can also be present for desired applications. However, it is not required that all of these components be present, as long as there is a means of gathering visual or photon data, and a means of sending that data to provide a visual image or image reconstruction.
The term “umbilical” can include the collection of utilities that operate the SSID or the micro-camera as a whole. Typically, an umbilical includes a conductive line, such as electrical wire(s) or other conductors, for providing power, ground, clock signal, and output signal with respect to the SSID, though not all of these are strictly required. For example, ground can be provided by another means than through an electrical wire, e.g., to a camera housing such as micromachined tubing, etc. The umbilical can also include other utilities such as a light source, temperature sensors, force sensors, fluid irrigation or aspiration members, pressure sensors, fiber optics, microforceps, material retrieval tools, drug delivery devices, radiation emitting devices, laser diodes, electric cauterizers, and electric stimulators, for example. Other utilities will also be apparent to those skilled in the art and are thus comprehended by this disclosure.
“GRIN lens” or “graduated refractive index lens” refers to a specialized lens that has a refractive index that is varied radially from a center optical axis to the outer diameter of the lens. In one embodiment, such a lens can be configured in a cylindrical shape, with the optical axis extending from a first flat end to a second flat end. Thus, because of the differing refractive index in a radial direction from the optical axis, a lens of this shape can simulate the effects of a more traditionally shaped lens.
With these definitions in mind, reference will now be made to, among other things, the accompanying drawings, which illustrate, by way of example, embodiments of the invention.
As noted above, to capture an image that is in focus, efforts must be made to ensure that for a lens system with a given focal length f, the distance from the front nodal point of a lens system to the object to image S1 (the object plane), and the distance from the rear nodal point to the image plane S2 are related by:




  
    
      1
      
        S
        1
      
    
    +
    
      1
      
        S
        2
      
    
  
  =
  
    1
    f
  




As S1 is decreased, S2 must be increased. For older image capturing systems (e.g., photographic cameras) wherein the lens system was fixed with respect to the image plane (e.g., the film), in order to capture an image in focus, the distance from the object to be photographed and the lens system had to be fixed. With advancements in technology, lens systems could be used within the camera to adjust the distance from the lens system to the image plane, thereby allowing the respective movement needed to capture an image in focus to happen within the camera itself. However, it is important to note that this type of movement becomes increasingly more difficult and much less reliable when operating imaging systems at the microscopic scale. Accordingly, the present invention resides in a method and device for capturing an image in focus with a miniaturized imaging system, without having to physically adjust the distance from the lens system of the imaging device with respect to the image plane and/or the object plane.

For purposes of discussion, for a thick lens (one which has a non-negligible thickness), or an imaging system consisting of several lenses and/or mirrors (e.g., a photographic lens or a telescope), the focal length is often called the effective focal length (EFL), to distinguish it from other commonly-used parameters; front focal length (FFL) or front focal distance (FFD) (the distance from the front focal point of the system to the vertex of the first optical surface) and back focal length (BFL) or back focal distance (BFD) (the distance from the vertex of the last optical surface of the system to the rear focal point). For an optical system in air, the effective focal length gives the distance from the front and rear principal planes to the corresponding focal points. If the surrounding medium is not air, then the distance is multiplied by the refractive index of the medium. In general, the focal length or EFL is the value that describes the ability of the optical system to focus light, and is the value used to calculate the magnification of the system. The other parameters are used in determining where an image will be formed for a given object position. For the case of a lens of thickness d in air, and surfaces with radii of curvature R1 and R2, the effective focal length f is given by:




  
    
      1
      f
    
    =
    
      
        (
        
          n
          -
          1
        
        )
      
      ⁡
      
        [
        
          
            1
            
              R
              1
            
          
          -
          
            1
            
              R
              2
            
          
          +
          
            
              
                (
                
                  n
                  -
                  1
                
                )
              
              ⁢
              d
            
            
              
                nR
                1
              
              ⁢
              
                R
                2
              
            
          
        
        ]
      
    
  
  ,




where n is the refractive index of the lens medium. The quantity 1/f is also known as the optical power of the lens.

The corresponding front focal distance is:





  
    FFD
    =
    
      f
      ⁡
      
        (
        
          1
          +
          
            
              
                (
                
                  n
                  -
                  1
                
                )
              
              ⁢
              d
            
            
              nR
              2
            
          
        
        )
      
    
  
  ,




and the back focal distance:





  BFD
  =
  
    
      f
      ⁡
      
        (
        
          1
          -
          
            
              
                (
                
                  n
                  -
                  1
                
                )
              
              ⁢
              d
            
            
              nR
              2
            
          
        
        )
      
    
    .
  




As will be recognized by one skilled in the art, as noted above, in standard lens systems, focal length can generally be thought of as the distance from a point within the lens system to the focal plane when the lens is imaging an object at infinity. The term working distance is thought of as the distance from an end of the lens system (e.g., a distal end) to the focal plane. While the working distance and the focal length are different, they share the location of the focal plane in common. For a GRIN lens, the geometrical gradient constant “g” and the lens length “z” determine the focal length “f” and the working distance “s” of the lens as represented below where “n” represents the refractive index of the lens at the center of the lens profile:




  
    s
    =
    
      1
      
        
          ng
          ⁢
          tan
        
        ⁡
        
          (
          gz
          )
        
      
    
  
  ,
  
    f
    =
    
      
        1
        
          
            ng
            ⁢
            sin
          
          ⁢
          
            
          
          ⁢
          
            (
            gz
            )
          
        
      
      .
    
  




Micro-Camera Device
Turning to the drawings, in which like reference numerals represent like or corresponding elements in the drawings, in one embodiment of the present invention, FIG. 1 illustrates a medical imaging system 10 comprising a micro-catheter 12 having an imaging device disposed at a distal tip 15 of the micro-catheter 12. A processor 22, such as an appropriately programmed computer, is provided to control the imaging system 10 and create an image of anatomy adjacent the distal tip portion 15, within a patient (not shown), displayable on a monitor 24, and storable in a data storage device 26. An interface 28 is provided which supplies power to the imaging device 14 and feeds a digital image signal to the processor based on a signal received from the imaging device via an electrical umbilical, including conductive wires through the micro-catheter 12. A light source may also be provided at the distal end of the micro-catheter 12. In one aspect, the system further includes a fitting 16 enabling an imaging fluid, such as a clear saline solution, to be dispensed to the distal tip portion of the micro-catheter 12 from a reservoir 18 through an elongated tubular member removably attached to the micro-catheter 12 or through a lumen of the micro-catheter 12 to displace body fluids as needed to provide a clearer image. Fluids may be pumped to the distal end of the micro-catheter for other reasons described herein. A pump 20 is provided, and is manually actuated by a medical practitioner performing a medical imaging procedure, or can be automated and electronically controlled so as to dispense fluid on demand according to control signals from the practitioner, sensors, or according to software commands.
With reference now to FIGS. 2 and 3, according to one embodiment of the present invention, an imaging device 30 is disposed on a distal end of a micro-catheter 12. Micro-machined cuts 13 are disposed non parallel to a longitudinal direction of the micro-catheter 12 to enable a user, such as a medical practitioner, to guide and steer the distal end of the micro-catheter 12 within a cavity of a patient. In one aspect of the present invention, the micro-catheter may incorporate structure and principles of operation from a catheter disclosed in U.S. Pat. No. 6,014,919 to Jacobsen et al., which is incorporated herein by reference.
In one aspect of the invention, imaging device 30 comprises at least two conductive wires 35a, 35b for conducting electronic image data to the data processor 22 and for securing an imaging structure 36 between the at least two conductive wires 35a, 35b. As illustrated in FIG. 3 however, a plurality of conductive wires 35a, 35b, 35c, 35d may be utilized. The at least two conductive wires 35a, 35b are oriented along a longitudinal axis of the imaging structure 36 and are disposed within alignment apertures 40 of a planar support member 45. The planar support member 45 comprises at least two alignment apertures 40 disposed on opposing sides of the planar support member 45. The alignment apertures 40 are configured to receive and align the at least two conductive wires 35a, 35b along the longitudinal axis of the imaging structure 36. The imaging structure 36 is at least partially secured between the at least two conductive wires 35a, 35b and is disposed adjacent a top surface of the planar support member 45. In one aspect of the invention, the imaging structure 36 comprises a GRIN lens 50 optically coupled to a SSID 55 and disposed adjacent the SSID 55. The GRIN lens 50 is stationary with respect to the SSID and the imaging array. The imaging structure further comprises an imaging array 60 disposed on a top surface of the SSID 55. In one embodiment, the GRIN lens 50 is positioned directly on top of the imaging array 60 of the SSID 55.
The at least two conductive wires 35a, 35b are operatively coupled to the imaging structure 36 and are configured to align the imaging structure 36 therebetween. In one aspect, the conductive wires 35a, 35b are bonded to the imaging structure 36 at contact points 56 disposed on the periphery of a top surface of the SSID 55. In yet another embodiment, the conductive wires 35a, 35b are bonded to a side surface of the SSID 55.
In one embodiment, the alignment apertures 40 are oriented perpendicular to the top surface of the planar support member 45. However, the alignment apertures may also be disposed in any orientation which is not non-parallel to the planar support member 45 as required to optimally align the imaging structure 36 as desired. In one embodiment, the imaging structure is mounted and aligned such that the image plane of the imaging structure 36 is non parallel to a longitudinal axis of the micro-catheter 12. In one aspect of the invention, a light source (e.g., a fiber optic member, LED, etc.) 62 is disposed within an aperture of the planar support member 45 to provide light for imaging. In yet another aspect of the present invention, the imaging structure 36 may incorporate structure and principles of operation from an imaging device disclosed in U.S. Pat. No. 7,166,537 to Jacobsen et al., which is incorporated herein by reference.
Referring now to FIGS. 3 and 4, the imaging device 30 further comprises a light blocking member 65. In one aspect, the light blocking member 65 is bonded to a top surface of the SSID 55. In another aspect, the light blocking member 65 is bonded to a side surface of the SSID 55. In yet another aspect, the light blocking member 65 is bonded to a top surface of the planar support member 40. In any event, the light blocking member 65 is oriented adjacent a side surface of the GRIN lens 50 to prevent stray light from the light source entering the side of the GRIN lens. In one aspect, the light blocking member 65 also serves to stabilize and align the GRIN lens 50 on the SSID 55.
In an additional aspect of the invention, a first sleeve member 70 is disposed about the imaging structure 36. An adhesive is disposed within the first sleeve member 70 securing the components of the imaging structure 36 in place as well as securing the first sleeve member 70 to the imaging structure 36. In an additional embodiment, a second sleeve member 75 is disposed about the first sleeve member 70 and secured with an adhesive. In one aspect of the invention, the second sleeve member 75 comprises an opaque material to eliminate secondary light from impacting image quality.
While reference has been made specifically herein to a single GRIN lens 50 used in connection with a SSID 55, it is understood and contemplated herein that a plurality of GRIN lens (not shown) could be used with a plurality of SSIDs (not shown). In one aspect, each of the single GRIN lens/SSID pairs is provided with a filter media designed to pass and reflect different wavelengths of light. Advantageously, each GRIN lens/SSID pair would receive light reflected from the same target but would receive different wavelengths of light reflected from the target. A composite image could be created from the plurality of imaging devices receiving different wavelengths of light reflected from the same target. In another aspect, an optimal image may be selected from each of the GRIN lens/SSID pairs and utilized for display of the target area.
With reference now to FIGS. 5 and 6, in accordance with one embodiment of the present invention, a miniaturized imaging device is disclosed. As with the other miniaturized imaging devices discussed herein, the device is adapted to be disposed on a distal end of a catheter. The device comprises at least one imaging array 60 disposed on a SSID 55, however, a plurality of imaging arrays 60 are shown. A plurality of GRIN lenses 50a, 50b, 50c are disposed on the imaging arrays 60. In this aspect, the distance from a distal end of the GRIN lenses 50a, 50b, 50c to the imaging arrays 60 is fixed and each of the GRIN lenses 50a, 50b, 50c has a different longitudinal length. As such, the working distance (and focal length) of each of the GRIN lenses is also different.
In one aspect of the invention, the back focal length of the plurality of GRIN lens is approximately zero for a predetermined monochromatic wavelength of light. In this manner, the GRIN lenses 50a, 50b, 50c can be disposed directly in contact with the imaging arrays 60 and a rear plane of each of the plurality of GRIN lenses can be substantially coplanar. While not shown on FIGS. 5 and 6, a light source may be disposed on a distal end of the catheter and can be configured to propagate a starting monochromatic wavelength of light onto a target and incrementally adjust the starting monochromatic wavelength of light to a different monochromatic wavelength of light. For example, the light source may be adapted to propagate light at 550 nanometers and thereafter increase or decrease the wavelength of light in 10 nanometer increments, 100 nanometer increments, or other increments as suits a particular application. The amount of the increment and the timing of the increment may be manually adjusted by the user and/or may be set to adjust automatically as suits a particular application.
In accordance with an additional embodiment of the present invention, as illustrated on FIG. 7, a plurality of GRIN lens/SSID pairs 80 are disposed on a planar guide member 45. A longitudinal length of each of the GRIN lenses is different. In this manner, because each GRIN lens has a different length, the respective working distance of each of the GRIN lenses is also different. As shown, the SSIDs 55a, 55b, 55c of each of the GRIN lens/SSID pairs have a different longitudinal length. The longitudinal length of each of the SSID's is configured such that the distal end of each of the GRIN lenses 50a, 50b, 50c are substantially coplanar.
Method of Operation
In optics, chromatic aberration is caused by a lens having a different refractive index for different wavelengths of light (the dispersion of the lens). Longitudinal and lateral chromatic aberration of a lens is seen as “fringes” of color around the image, because each color in the optical spectrum cannot be focused at a single common point on the optical axis. As the focal length of a lens system is dependent on its specific geometry and configuration, different wavelengths of light will be focused on different positions. That is, for a single lens system with a fixed geometry and fixed relative to an image plane, different wavelengths of light reflected from an object to an image plane will not each be in focus.
As noted and as is known in the art, different wavelengths of light reflected from an object and passing through a lens system converge at different points. It is with this principle in mind that particular embodiments of the present invention are directed. For a particular lens system having an object a determined distance away from the distal end of the lens system, an optimal wavelength of light exists for achieving optimal focus of the image on the image plane. For example, for a GRIN lens, such as a Grintech IRFL-035-005 the working distance is 5 mm. For a target object that is 5 mm away from the distal end of said GRIN lens, an optimal wavelength of light for capturing an image that is in focus is thought to be approximately 550 nm when used in embodiments of the imaging system described herein. That is, for the specific GRIN lens noted above, light at a wavelength of approximately 550 nm which is reflected from an object 5 mm away from the distal end of the GRIN lens is thought to converge at substantially the same point of the rear end of the GRIN lens. In like manner, when a target object is 3 mm away from the distal end of the same GRIN lens system, an optimal wavelength of light for capturing an image that is in focus is thought to be approximately 450 nm. In like manner, when a target object is 10 mm away from the distal end of the same GRIN lens system, an optimal wavelength of light for capturing an image that is in focus is thought to be approximately 650 nm.
Accordingly, in one embodiment of the present invention, a method of imaging a target using a miniaturized imaging device is disclosed comprising providing a miniaturized imaging device having a stationary lens system (such as the GRIN lens system described above) and an imaging array, wherein the distance from the stationary lens system to the imaging array is fixed. The method further comprises advancing the miniaturized imaging device near the desired target and determining a distance from a distal end of the stationary lens system to the desired target. The distance from the distal end of the stationary lens system to the desired target may be calculated by an infrared range calculation device or any other suitable process (e.g., an active autofocus technique discussed in more detail below). The method further comprises calculating a desired wavelength of light based on the determined distance from the distal end of the stationary lens system to the desired target. The desired wavelength of light is propagating onto the target and is received through the lens system. In this manner, the optimal wavelength of light for capturing an image that is in focus may be calculated and utilized as the light source to illuminate the desired target. Advantageously, no movement of the lens system with respect to the image sensor (e.g., SSID) and/or the target to be imaged is required in order to properly capture a focused image of the object. Additionally, as the image is captured using an achromatic source of light, problems associated with chromatic aberration as noted above are not encountered.
In accordance with an additional embodiment of the present invention, a method of imaging a target within a cavity using a miniaturized imaging device is disclosed. The method comprises providing a miniaturized imaging device having a stationary lens system and an imaging array, wherein the distance from the stationary lens system to the imaging array is fixed. In other words, the lens system is stationary with respect to the imaging array. The miniaturized imaging device is advanced within the cavity to a desired location and a starting wavelength of light is propagated onto the target within the cavity. The starting wavelength of light reflected from the target is received onto the imaging array after which the starting wavelength of light is incrementally adjusted to a different wavelength of light. The different wavelength of light is propagated onto the target within the cavity and received onto the imaging array as with the starting wavelength of light.
The incremental adjustments of wavelength may be through frequency and or amplitude variation of the wavelength and may be performed on an as needed basis to determine an optimal wavelength of light based on the focal length of a given lens system and the distance of the object from the distal end of the lens system. That is, in one aspect, as the miniaturized imaging device is advanced within a patient the medical practitioner may wish to stop advancing the imaging device and capture images of a fixed object. In this manner, the incremental adjustments of the wavelength need only be conducted until an optimal wavelength of light is detected. However, if the medical practitioner wishes to image portions of the patient while advancing the imaging device within the patient, the incremental adjustments may be ongoing at a relatively rapid pace. Because the movement of the imaging device within the patient will result in a variation in distances from the distal end of the imaging device to any particular target, a collection of both in focus and out of focus images will be captured by the imaging device and sent to the imaging system processor. However, depending on the particular settings and processes employed by the overall imaging system, only those images which are determined to be in focus would be provided on the system display. In this manner, the medical practitioner may advance the imaging device within a patient and view an in focus image of the patient irrespective of the exact distance from the distal end of the imaging device to a particular target.
In accordance with one aspect of the present invention, the optimal wavelength may be determined using an autofocus technique. The autofocus system (not shown) relies on one or more sensors to determine correct focus. Autofocus systems may be categorized into passive and active systems. An active autofocus system (not shown) measures the distance to the subject independently of the optical system, and subsequently adjusts the optical system (e.g., the wavelength of light propagated onto a target) for correct focus. There are various ways to measure distance with an active autofocus system, including ultrasonic sound waves and infrared light. In the first case, sound waves and/or infrared light is emitted from the imaging device, and by measuring the delay in their reflection, distance to the subject is calculated. Once the distance is calculated, an optimal wavelength of light may be determined for a particular lens system geometry.
Passive autofocus systems determine correct focus by performing passive analysis of the image that is entering the optical system. They generally do not direct any energy, such as ultrasonic sound or infrared light waves, toward the subject. However, an autofocus assist beam of usually infrared light may be required when there is not enough light to take passive measurements. Passive autofocusing can be achieved by phase detection or contrast measurement.
Phase detection is achieved by dividing the incoming light into pairs of images and comparing them. In one aspect, the system uses a beam splitter (implemented as a small semi-transparent area of the main reflex mirror, coupled with a small secondary mirror) to direct light to an autofocus sensor disposed on the imaging device. Two optical prisms capture the light rays coming from the opposite sides of the lens and divert it to the autofocus sensor, creating a simple rangefinder with a base identical to the lens' diameter. The two images are then analyzed for similar light intensity patterns (peaks and valleys) and the phase difference is calculated in order to find if the object is in front focus or back focus position. Contrast measurement is achieved by measuring contrast within a sensor field, through the lens system. The intensity difference between adjacent pixels of the sensor naturally increases with correct image focus. The optical system can thereby be adjusted until the maximum contrast is detected. In this method, autofocus does not involve actual distance measurement.
One example of a passive autofocus embodiment includes use of a SSID that provides input to algorithms that compute the contrast of actual image elements. The SSID is typically a single strip of 100 or 200 pixels. Light from the target hits this strip and the microprocessor looks at the values from each pixel. The imaging systems processor evaluates the difference in intensity among adjacent pixels. If the target is out of focus, adjacent pixels have very similar intensities. As incremental modifications are made to the wavelength of light, the processor again evaluates the difference in intensity between adjacent pixels to see if the intensity increased or decreased. The processor then searches for the point where there is maximum intensity difference between adjacent pixels, wherein the maximum intensity difference between adjacent pixels is the point of best focus.
As described in more detail above, the lens system may comprise a plurality of GRIN lenses each having a different effective focal length. While not necessary, each one of the plurality of GRIN lenses may also be positioned on a different imaging array. In this manner, the number of possible “in focus” images resulting from operation of the imaging device as described herein is expanded thereby giving the imaging device a greater depth of operation. That is, because each of the plurality of GRIN lenses has a different effective focal length, and hence a different depth of field, the overall depth at which the imaging device may return an image that is in focus is enhanced.
While the foregoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

## Claims

1. A method of imaging a desired target using a miniaturized imaging device, comprising:
providing a miniaturized imaging device comprising a lens system and an imaging array, wherein a distance from the distal end of the lens system to the imaging array is fixed;
advancing the miniaturized imaging device near the desired target;
determining a distance from the distal end of the lens system to the desired target;
calculating a range of potential optimal wavelengths of light to image the target in focus based on the determined distance from the distal end of the lens system to the desired target, including a starting wavelength of light;
propagating the starting wavelength of light onto the target;
receiving the starting wavelength of light reflected off of the target;
incrementally adjusting the starting wavelength of light through the range of potential optimal wavelengths of light and propagating each of the wavelengths of light within the range of potential optimal wavelengths of light onto the target at different times; and
determining a wavelength of light for optimally imaging a target in focus.

2. The method of claim 1, further comprising the step of creating an image from the desired wavelength of light reflected off of the target.

3. The method of claim 1, wherein the lens system comprises a single GRIN lens.

4. The method of claim 3, wherein the GRIN lens is mounted directly on a top surface of the imaging array.

5. The method of claim 1, wherein the distance from the distal end of the lens system to the desired target is calculated by an infrared range calculation device.

6. The method of claim 1, wherein the lens system comprises a plurality of GRIN lenses.

7. The method of claim 6, wherein each one of the plurality of GRIN lenses has a different longitudinal length.

8. The method of claim 7, wherein each one of the plurality of GRIN lenses is positioned on a different imaging array.

9. A method of imaging a target within a cavity using a miniaturized imaging device, comprising:
providing a miniaturized imaging device comprising a lens system and an imaging array, wherein a distance from a distal end of the lens system to the imaging array is fixed;
advancing the miniaturized imaging device within the cavity;
determining a distance from the lens system to the target and calculating a starting wavelength of light based on said distance calculation;
propagating the starting wavelength of light onto the target within the cavity;
receiving the starting wavelength of light reflected from the target onto the imaging array;
creating an image from the starting wavelength of light reflected from the target;
incrementally adjusting the starting wavelength of light to a plurality of different wavelengths of light and propagating the plurality of different wavelengths of light onto the target within the cavity;
receiving the plurality of different wavelengths of light reflected from the target onto the imaging array;
creating an image from each of the different wavelengths of light reflected from the target onto the imaging array; and
determining an optimal wavelength of light for imaging the target in focus based on the plurality of different wavelengths of light received onto the imaging array.

10. The method of claim 9, wherein the optimal wavelength of light is determined with a passive autofocus technique.

11. The method of claim 10, wherein the passive autofocus technique comprises a phase detection technique.

12. The method of claim 10, wherein the passive autofocus technique comprises a contrast measurement technique.

13. The method of claim 9, wherein the optimal wavelength of light is determined with an active autofocus technique.

14. The method of claim 13, wherein the active autofocus technique comprises use of an infrared signal.

15. A miniaturized imaging device disposed on a distal end of a catheter, comprising:
at least one imaging array disposed on a distal end of the catheter;
a plurality of at least two longitudinally parallel lens systems disposed on the at least one imaging array, wherein the distal ends of each of the lens systems is coplanar to the distal end of the lens system and wherein each of the plurality of lens systems has a different longitudinal length;
a light source disposed on a distal end of the catheter adapted to propagate a starting monochromatic wavelength of light onto a target and incrementally adjust the starting monochromatic wavelength of light over different time intervals to a different monochromatic wavelength of light; and
a processor coupled to the imaging array configured to generate an image from the plurality of different monochromatic wavelengths of light reflected from the target and further configured to determine an optimal monochromatic wavelength of light to optimize image focus based on the light reflected from the target.

16. The miniaturized imaging device of claim 15, wherein the plurality of lens systems comprises a plurality of GRIN lenses.

17. The miniaturized imaging device of claim 16, further comprising a plurality of imaging arrays, wherein each of the plurality of GRIN lenses is disposed in direct contact with a separate imaging array.

18. The miniaturized imaging device of claim 17, wherein the working distance of at least one of the plurality of GRIN lens is approximately zero for a predetermined monochromatic wavelength of light.

19. A miniaturized imaging device disposed on a distal end of a catheter, comprising:
a light source disposed on a distal end of the catheter configured to propagate a starting monochromatic wavelength of light onto a target and incrementally adjust the starting monochromatic wavelength of light over different time intervals to a plurality of different monochromatic wavelengths of light;
a plurality of substantially parallel lens systems disposed on an imaging array configured to receive light reflected from the target, wherein the distance from a distal end of each of the stationary lens systems to the imaging array is fixed;
wherein each of the lens systems has a different longitudinal length and wherein the distance from a front surface of each of the plurality of lens systems to the target is different;
means for determining the distance from a distal end of each of the lens system to the target; and
a processor coupled to the imaging array configured to generate an image from the plurality of different monochromatic wavelengths of light and further configured to determine an optimal monochromatic wavelength of light to optimize image focus based on the light reflected from the target.

20. The miniaturized imaging device of claim 19, wherein each of the plurality of lens systems has a different effective focal length.

21. The method of claim 9, further comprising placing a distal end of the lens system in direct contact with the target, wherein the working distance of at least one of the lens systems is approximately zero for a predetermined monochromatic wavelength of light.