Abstract:
A device, system, and method for measuring the depth of a material layer such as a blood vessel plaque layer is disclosed. A fiber optic bundle housed in a balloon catheter projects a laser dot toward a conical mirror, which reflects the dot perpendicularly onto the surface of the plaque. The laser dot is reflected back from the plaque layer with a substantially Gaussian intensity profile. The conical mirror directs the reflected image back to the fiber optic bundle, which delivers the image to a sensor. The depth of the plaque layer can be determined by comparing the diameter of the image intensity profile to a pre-obtained normalized data set.

Description:
PRIORITY CLAIM 
       [0001]    The present application is a non-provisional patent application, claiming the benefit of priority of U.S. Provisional Application No. 61/135,930, filed on Jul. 25, 2008, entitled, “IMAGING CATHETER USING LASER PROFILE FOR PLAQUE DEPTH MEASUREMENT.” 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to a catheter imaging system and, more specifically, to a catheter imaging system which uses the Gaussian profile of projected laser dots to determine plaque depth in blood vessels. 
       BACKGROUND OF INVENTION 
       [0003]    Blood vessel diseases such as atherosclerosis are usually caused by progressive accumulation of plaque, including fat and cholesterol, on the inner vessel walls. Balloon imaging catheters are widely used as a minimally invasive tool for diagnostics or treatment of blood vessel diseases. The thickness of deposited plaque characterizes the seriousness of the disease. Therefore, having an accurate depth measurement of the plaque will provide useful information for diagnostics and in turn significantly enhance the effects of medical treatments. While current imaging systems inside a balloon catheter can obtain planar information regarding the surrounding vessel, measuring the depth of fat and cholesterol deposits along the vessel walls remains a challenge. 
         [0004]    Therefore, a continuing need exists for a catheter imaging system which can measure the depth of plaque deposits along blood vessel walls. 
       SUMMARY OF INVENTION 
       [0005]    The present invention relates to a catheter imaging system and, more specifically, to a catheter imaging system which uses the Gaussian profile of projected laser dots to determine plaque depth in blood vessels. In one aspect, the present invention is a device comprising a fiber optic bundle, a mirror, and a sensor. The fiber optic bundle extends along an axis and comprises a projection portion and a receiving portion. The projection portion is configured to project light onto a material layer surface. The receiving portion is configured to receive a reflected image signal of the projected light from the material layer. A mirror is positioned at a terminus of the fiber optic bundle. The mirror is configured to reflect projected light from the projection portion of the fiber optic bundle at an angle substantially perpendicular to the axis of the fiber optic bundle to illuminate the material surface. The mirror is further configured to reflect the reflected image signal of the projected light from the material layer at an angle substantially perpendicular to the axis of the fiber optic bundle, such that the reflected image signal can be received by the receiving portion of the fiber optic bundle. The sensor is configured to receive the reflected image signal from the receiving portion of the fiber optic bundle, whereby the image signal can be analyzed to determine the depth of the material layer. 
         [0006]    In another aspect of the device, the fiber optic bundle is mounted within a balloon catheter. 
         [0007]    In yet another aspect, the device is configured to move axially within the balloon catheter. 
         [0008]    In a further aspect of the device, the conical mirror is held by a holder portion near a center of the fiber optic bundle. 
         [0009]    In yet another aspect of the device, the mirror is substantially conical in shape, and positioned such that an apex of the conical mirror is located proximal to the terminus of the fiber optic bundle. 
         [0010]    Another aspect of the present invention is a method for determining a depth of a material layer. The method comprises a first act of projecting light onto a surface of the material layer. Next, a reflected image signal of the projected light is received from the material layer surface. The reflected image signal is then with a sensor. An image intensity profile of the captured image is measured. Typically the measurement is a diameter of the image intensity profile. From this measurement, the depth of the material layer can be determined by comparison of the measured image intensity profile with a pre-obtained normalized data set. 
         [0011]    In another aspect of the method of the present invention, the acts of projecting, receiving, and capturing are executed using a catheter imaging system consistent with the device of the present invention, as previously described. 
         [0012]    As can be appreciated by one skilled in the art, another aspect of the present invention is a data processing system for measuring the depth of a material layer, comprising one or more processors configured to perform operations of the method of the present invention, as previously described. 
         [0013]    In another aspect, the operations of projecting, receiving, and capturing are executed using a catheter imaging system consistent with the device of the present invention, as previously described. 
         [0014]    In yet another aspect, as can be appreciated by one skilled in the art, the present invention comprises a computer program product, comprising computer instruction means encoded on a computer-readable medium executable by a computer having a processor for causing the processor to perform the operations of the method of the present invention, as previously described. 
         [0015]    In another aspect of the computer program product, the operations of projecting, receiving, and capturing are executed using a catheter imaging system consistent with the device of the present invention, as previously described. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The objects, features and advantages of the present invention will be apparent from the following detailed descriptions of the various aspects of the invention in conjunction with reference to the following drawings, where: 
           [0017]      FIG. 1  is an illustration showing the device of the present invention situated within a blood vessel; 
           [0018]      FIG. 2A  is a graph showing an image intensity profile for a sample of 2.2 mm chicken fat; 
           [0019]      FIG. 2B  is a graph showing an image intensity profile for a sample of 4.4 mm chicken fat; 
           [0020]      FIG. 3  is a graph comparing normalized Gaussian profile of image intensity vs. depth of material layer; 
           [0021]      FIG. 4  is a flow diagram showing the acts in the method of the present invention; 
           [0022]      FIG. 5  is a block diagram showing the components of a data processing system in accordance with the present invention; and 
           [0023]      FIG. 6  is an illustration showing computer program products in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    The present invention relates to a catheter imaging system and, more specifically, to a catheter imaging system which uses the Gaussian profile of projected laser dots to determine plaque depth in blood vessels. The following description is presented to enable one of ordinary skill in the art to make and use the invention and to incorporate it in the context of particular applications. Various modifications, as well as a variety of uses in different applications will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to a wide range of embodiments. Thus, the present invention is not intended to be limited to the embodiments presented, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. 
         [0025]    In the following detailed description, numerous specific details are set forth in order to provide a more thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without necessarily being limited to these specific details. In other instances, well-known structures and devices are shown in block diagram form, rather than in detail, in order to avoid obscuring the present invention. 
         [0026]    The reader&#39;s attention is directed to all papers and documents which are filed concurrently with this specification and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All the features disclosed in this specification, (including any accompanying claims, abstract, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. 
         [0027]    Furthermore, any element in a claim that does not explicitly state “means for” performing a specified function, or “step for” performing a specific function, is not to be interpreted as a “means” or “step” clause as specified in 35 U.S.C. Section 112, Paragraph 6. In particular, the use of “step of” or “act of” in the claims herein is not intended to invoke the provisions of 35 U.S.C. 112, Paragraph 6. 
         [0028]    (1) Description 
         [0029]    The present invention relates to a catheter imaging system and, more specifically, to a catheter imaging system which uses the Gaussian profile of projected laser dots to determine plaque depth in blood vessels. It has been observed that when a narrow band laser beam shines on a plaque surface, both the Gaussian profile and the intensity profile of the laser dot vary depending on the thickness of the fat and cholesterol comprising the plaque. The present invention utilizes this phenomenon to measure the depth of plaque on the inner walls of blood vessels. 
         [0030]      FIG. 1  is an illustration showing an imaging device  100  in accordance with the present invention situated within a blood vessel having fat and cholesterol plaque  102  on the inner vessel walls  104 . Imaging components including a mirror  106 , fiber optic bundle  108  having a terminus  109 , and sensor  110  reside inside a catheter tube  112  having a transparent catheter balloon  114  which expands to meet the plaque  102  surface. In a desired aspect, the imaging components are capable of moving axially  115  within the catheter tube  112 . In a further desired aspect, the mirror  106  is substantially conical in shape, although any mirror shape capable of performing the reflection needs of the system may be used. The conical mirror  106  is held at an apex by a holder  116  at the center of the fiber optic bundle  108 . The holder  116  can be independent or connected with a guide wire of the catheter. A projection portion  119  of the fiber optic bundle  108  are used to project several narrow band laser beam dots  120  around the center, which are then reflected by the conical mirror  106  and transmitted through the transparent balloon  114  to the plaque tissues  102  on the vessel walls  104 . The projected laser dots  120  on the plaques  102  are reflected back as an image signal  121  to the fiber optic bundle  108 , where a receiving portion  122  of the fiber optic bundle  108  receives and transmits the reflected image signal  121  to the sensor  110 . The sensor  110  can be anything known in the art for capturing a light signal, including a camera, charge coupled device (CCD), diode, or photo cell. A non-coherent portion of the reflected image signal  121  is expected to have a substantially Gaussian profile. The shape of the Gaussian profile or a best fit curve of the diffusive image intensity of the reflected laser dot varies with respect to the depth of the plaque. Therefore, the depth of the plaque on the blood vessel can be resolved by measuring the laser dot profile. This method works on the non-coherent portions of the reflected light, or it can be used in conjunction with optical coherence tomography. 
         [0031]    It should be noted that other research, as described in U.S. Patent Publication No. US 2005/0251116 A1, incorporated by reference as though fully disclosed herein, uses a prism coupled with a mechanical rotation device to obtain images of the surrounding tissues from all angles. This system, however, will cause major challenges in packaging due to the relative large size of the mechanical equipment. In contrast, since the small conical mirror of the present invention can reflect the laser beam to all angles of the surrounding tissues as well as direct the images from all angles back to the fiber bundle, the rotating mechanical equipment of the above cited publication is not required. Furthermore, the configuration of the present invention allows the entire plaque surface surrounding the balloon catheter to be measured simultaneously. 
         [0032]      FIG. 2A  shows the Gaussian profile  200  of a cross section  202  of a diffusive laser dot image  204  on a chicken fat surface with a depth of 2.2 mm. The diameter of the Gaussian profile  200  is 100 pixels. Similarly,  FIG. 2B  shows the Gaussian profile  206  of a cross section  208  of a diffusive laser dot image  204  on a thicker chicken fat surface with a depth of 4.4 mm. The diameter of the Gaussian profile is 120 pixels. As can be seen from the graphs in  FIGS. 2A and 2B , the diameter of the diffusive dot image and therefore width of the Gaussian profile increases with the depth of the fat layer. 
         [0033]    A normalized graph of Gaussian profiles at various depths can be constructed using experimental data as shown in  FIG. 3 . The graph in  FIG. 3  plots fat layer depth  300  against normalized Gaussian profile diameter  302 . The graph contains two best fit curves, one for a series of data points taken for chicken fat  304 , and one for a series of data points taken for mayonnaise  306 . A similar best fit curve can be constructed for a layer of human fat and cholesterol as found in the plaques on blood vessel walls. When a patient is tested using the catheter imaging system of the present invention, the Gaussian profile obtained is compared to a best-fit curve in a normalized graph as in  FIG. 3  to determine the depth of the plaque on the patient&#39;s vessel walls. 
         [0034]    The present invention also comprises the general method of obtaining depth information of material coating from an intensity profile of reflected light. The acts in the method are illustrated in  FIG. 4 . The first act is illuminating  400  the surface of a material layer with coherent light. The material layer may be a layer of blood vessel plaque, but the method is generally applicable to any material layer which will produce a reflected image having a substantially Gaussian intensity distribution. The light reflected from the material layer will be non-coherent and have a substantially Gaussian profile. The non-coherent light is then collected  402  and directed to a sensor where the non-coherent light image is captured  404  by the sensor. The length of a diametrical profile of the reflected non-coherent image is then measured  406  and compared with previously obtained normalized graphical data representing the relationship between profile diameter and material layer depth (as in  FIG. 3 ), whereby the depth of the material layer is obtained  408 . 
         [0035]    As can be appreciated by one skilled in the art, the present invention also comprises a data processing system for executing the method of the present invention, as previously mentioned. A block diagram depicting the components of an image processing system of the present invention is provided in  FIG. 5 . The image processing system  500  comprises an input  502  for receiving information from at least one sensor for use in detecting image intensity of the non-coherent light captured by the sensor. Note that the input  502  may include multiple “ports.” Typically, input is received from at least one sensor, non-limiting examples of which include video image sensors. An output  504  is connected with the processor for providing information regarding the intensity profile of the image to other systems in order that a network of computer systems may serve as an image processing system. Output may also be provided to other devices or other programs; e.g., to other software modules, for use therein. The input  502  and the output  504  are both coupled with a processor  506 , which may be a general-purpose computer processor or a specialized processor designed specifically for use with the present invention. The processor  506  is coupled with a memory  508  to permit storage of data and software that are to be manipulated by commands to the processor  506 . 
         [0036]    The present invention also comprises a computer program product. An illustrative diagram of a computer program product embodying the present invention is depicted in  FIG. 6 . The computer program product  600  is depicted as an optical disk such as a CD or DVD. However, as mentioned previously, the computer program product generally represents computer-readable instruction means stored on any compatible computer-readable medium. The term “instruction means” as used with respect to this invention generally indicates a set of operations to be performed on a computer, and may represent pieces of a whole program or individual, separable, software modules. Non-limiting examples of “instruction means” include computer program code (source or object code) and “hard-coded” electronics (i.e. computer operations coded into a computer chip). The “instruction means” may be stored in the memory of a computer or on a computer-readable medium such as a floppy disk, a CD-ROM, and a flash drive.