Abstract:
The invention relates to a system for testing heart valve leaflets. The system includes a leaflet support assembly with a support post for receiving and supporting a leaflet to be tested, the post being disposed in a target region of the support assembly. The system also has a transmitter assembly that includes a light source and is configured and arranged to direct light from the light source onto the target region. The system further includes a receiver assembly that has an image sensor configured and arranged to sense an image of the target region and generate image information indicative of the sensed image, such as leaflet droop.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 61/489,834, filed May 25, 2011, which is herein incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates generally to apparatuses and methods of screening and selecting leaflets for use in prosthetic heart valves. More particularly, it relates to apparatuses and methods for droop testing leaflets that measures flexural stiffness of the tissue in order to screen leaflets for use in prosthetic heart valves, for example prosthetic aortic transcatheter valves (TCV). 
         [0003]    Prosthetic heart valve fabrication, including aortic transcatheter valve (TCV) fabrication, requires leaflets and skirts to be cut in predetermined geometry from animal-derivative tissue (e.g., porcine pericardium) and then sewn together, often as a tri-leaflet valve. Durability and leaflet wear are critical factors in maintaining acceptable performance over the lifetime of the device. A large factor in the durability of a prosthetic tissue heart valve is the processing and selection of the material. For example, there are three main criteria used to select areas of a pericardial sheet used for the leaflets: thickness, stiffness, and surface features. There are existing technologies to perform thickness mapping. There are also existing technologies to measure material extensibility in terms of deflection (along a Z-axis) in response to an applied load. There is a need for technology to evaluate material stiffness in a non-destructive method. There have been studies which indicate good correlation existing between leaflet droop and material extension in response to applied load. 
         [0004]    Material extensibility has shown some indications towards affecting leaflet dynamics and stretching over long duration in wear testing. When a leaflet is suspended from a pin or a forceps, it has a tendency to droop in response to gravity. A leaflet having less stiffness is less resistant to drooping/bending forces, and a leaflet having greater stiffness and higher flexural rigidity is more resistant to drooping/bending. Studies have been conducted to correlate the amount of droop to mechanical properties of the material and which correlates well to a percentage strain at physiological loading. The material property (mechanical properties such as UTS, percentage strain, Young&#39;s Modulus) of pericardial tissue, for example, is highly variable and non-uniform within the sac. Valves constructed with stiff leaflets combined with droopy leaflets can cause asynchronous valve closure causing regurgitant fractions to increase. With quantitative measurements, leaflets can be matched or classified based on their droop values. 
         [0005]    In light of the above, there is a need for a sensitive, reliable, and repeatable measurement apparatus and method to evaluate leaflet droop in a quantitative manner in order to screen leaflets. 
       SUMMARY OF INVENTION 
       [0006]    The present invention features a system for testing heart valve leaflets. The system includes (i) a leaflet support assembly that has a support post for receiving and supporting a leaflet to be tested, the post being disposed in a target region of the support assembly; (ii) a transmitter assembly that includes a light source and is configured and arranged to direct light from the light source onto the target region; and (iii) a receiver assembly including a first image sensor configured and arranged to sense an image of the target region and generate image information indicative of the sensed image, such as leaflet droop. 
         [0007]    In one embodiment of the system, the support post is arranged to support a leaflet to be tested in a manner permitting the corresponding opposing tab ends to freely hang downwardly relative to the post due to gravity. Additionally, the support assembly may include a base configured for placement on a flat surface, and a wall projecting from a floor of the base. In a typical implementation of the invention, the post projects from the wall at a location spaced from the floor to define a vertical spacing between the post and the floor sufficient to permit a leaflet to freely hang from the post. The support assembly may further include a distance indicator located along the wall within the target region and immediately below the post. 
         [0008]    The transmitter assembly of the system may include a lens arrangement configured to direct light from the sensor onto the target region as a collimated beam of light. The light source may include, for example, a high-intensity GaN green LED. 
         [0009]    In certain embodiments, the transmitter assembly is arranged to direct light at a first side of the target region, and the first image sensor is arranged to sense an image of the target region relative to a second side of the target region opposite the first side. Typically, the first image sensor is a high-speed linear CCD configured to sense a shadow image of the target region. The receiver assembly may further include a second image sensor, such as a CMOS image sensor, configured and arranged to sense an image of the target region and generate output information differing from the image information generated by the first image sensor. 
         [0010]    The invention also features a method of testing a leaflet having opposing tab ends for use with an implantable heart valve. The method involves the following steps: loading the leaflet onto a support post of a leaflet support assembly, the leaflet being centrally supported by the post and the opposing tab ends freely hanging downwardly from the post due to gravity; directing light onto the loaded leaflet; collecting an image of the illuminated, loaded leaflet; and determining a parameter related to leaflet droop based upon the collected image. Typically, the collected image is a shadow image, and the parameter related to leaflet droop is the distance between opposing tab ends in the shadow image. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIGS. 1A and 1B  are front and side views of one embodiment of an apparatus in accordance with aspects of the present disclosure; 
           [0012]      FIGS. 2A and 2B  are perspective views of another embodiment of the apparatus in accordance with aspects of the present disclosure; 
           [0013]      FIGS. 3A through 3D  are views of another embodiment of the apparatus in accordance with aspects of the present disclosure; 
           [0014]      FIGS. 4A and 4B  are perspective and side views of another embodiment of the apparatus in accordance with aspects of the present disclosure; 
           [0015]      FIG. 5  is a front view of another embodiment of the apparatus in accordance with aspects of the present disclosure; 
           [0016]      FIG. 6  is a diagram of the droop testing apparatus in accordance with the apparatus of  FIG. 5 ; 
           [0017]      FIG. 7  is a diagram of one aspect of a method of droop testing in accordance with the apparatus of  FIG. 5 ; 
           [0018]      FIG. 8  is a top view of one embodiment of loading template for use with the at least the apparatus of  FIG. 5 ; and 
           [0019]      FIG. 9  is a top view of a material sample on the apparatus of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Several embodiments of droop test apparatuses are described herein that are useful for matching or classifying tissue leaflets (e.g., pericardial tissue from different animal origin or polymer) based on droop values in accordance with principles of the present disclosure. One embodiment of a droop test apparatus  100  is illustrated in  FIGS. 1A and 1B . The droop testing apparatus  100  includes a gage  112  and a specimen pin  114 . The gage  112  can assume various forms appropriate for detecting or measuring height, such as a Mitutoyo Height gage. More particularly, the specimen pin  114  establishes a baseline  116  from which a measurement of an extent of leaflet droop in a “Y” axis direction (labeled in the figures) is gauged. A height probe  118  of the gage  112  is vertically (in the “Y” axis direction) repositionable with respect to the specimen pin  114 . During use, a leaflet  120  is positioned over the specimen pin  114 , with the specimen pin  114  located at an approximate centerline of leaflet  120  (between opposing tabs  122  of the leaflet  120 ), and the leaflet  120  is acted upon by gravitational forces. A user causes the probe  118  to move in the Y direction until the leaflet tabs  122  are contacted, generating a distance measurement in the Y direction that is indicative of droop. 
         [0021]    Accuracy of droop testing using the droop test apparatus  100  may be subjective or dependent upon an operator/user correctly centering the leaflet  120  on the pin  114 , as well as causing or prompting the height gage probe  118  to stop precisely as the height gage probe  118  makes contact with the leaflets tabs  122 . The droop tester apparatus  100  may be used to differentiate between visually droopy (greater “Y” distances), stiff (lower “Y” distances), and intermediate (intermediate “Y” distances) of leaflet droop. The user of this method and apparatus  100  has an option to measure the overall “Y” distance if the leaflet  120  is exhibiting similar droop on either side of the specimen pin  114  or take measurements on both sides of the leaflet  120  (e.g. “Y 1 ” and “Y 2 ”) in a case of asymmetric droop. It may be difficult for a user of the droop testing apparatus  100  to identify a region within the leaflet tabs  122  that would consistently be used for the measurements. This embodiment of the droop test apparatus  100  may be limited in use because the acceptable range for the “Y” distance between droopy and stiff tissue can be minimal and thus the apparatus  100  may not have sufficient sensitivity for a user wishing to classify tissue to match stiffness. Additionally, the accuracy of the measurements may be dependent on the user. 
         [0022]    Another embodiment of a droop testing apparatus  200  in accordance with principles of the present disclosure is shown in  FIGS. 2A and 2B . In this embodiment, at least two lateral pins  202 , a bottom plate  204 , and a center pin  206  are connected to a backboard  212  that projects from a base  214  of the droop testing apparatus  200 . The center pin  206  is fixedly connected to the backboard  212 . The lateral pins  202  and the bottom plate  204  are adjustable to desired positions against which a leaflet (not shown) being tested is designated to either be acceptable or unacceptable. In one embodiment, the lateral pins  202  and the bottom plate  204  are adjustable within slotted connections  208  of the backboard  212 . During use of the droop testing apparatus  200 , both “X” and “Y” axes of a leaflet are measured against the two lateral pins  202  and the bottom plate  204  when the leaflet is suspended from the center pin  206 . With the droop testing apparatus  200 , a leaflet with acceptable droop would not contact the laterally placed pins  202  and the bottom plate  204  when the leaflet is suspended from the center pin  206 . This embodiment provides a qualitative test by indicating whether the leaflet droop is acceptable or not, but does not provide a quantitative test, and may not directly guide a user in classifying the tested leaflets based on droop values. 
         [0023]      FIGS. 3A-3D  illustrate a third embodiment of a droop testing apparatus  300  in accordance with principles of the present disclosure. As illustrated in  FIG. 3B , a specimen pin  302  extends perpendicularly from a template  304 . With the specimen pin  302  as a center point, the template  304  is divided into and marked as pre-designated ranges within which leaflet tabs  308  (see  FIG. 3D ) may extend into when positioned over the specimen pin  302 . An example of pre-designated ranges, or zones, is illustrated in  FIG. 3A  which includes Zone  1 , Zone  2 , and Fail. 
         [0024]    With particular reference to  FIGS. 3C and 3D , using the droop testing apparatus  300 , a leaflet  306  is suspended on the specimen pin  302  and a photograph is taken by a camera (not shown) positioned in line with the specimen pin  302 . Imaging software can be used to measure an “X” axis distance between the leaflet tabs  308 , as illustrated in  FIG. 3C . Imaging software can also be used to measure the angle between a tangent to a falling edge. A specific region of the leaflet tabs  308  can be selected and tracked to determine which zone the leaflet tabs  308  fall within. In particular, the droop testing apparatus  300  provides a front view analysis of leaflets wherein the leaflets can be classified into categorical groups. For example, the groups may include “Group  1 ” (where the leaflet tabs lay in Zone  1 ), “Group  2 ” (where the leaflet tabs lay in Zone  2 ), and “Fail”. 
         [0025]    With the droop testing apparatus  300 , imaging measurements require analysis and is retrospective in nature. Thus, this embodiment may be more beneficial in applications other than manufacturing set-up. The accuracy of this method may be dependent on the operator during specimen placement and imaging analysis, camera placement and validity of imaging software. Further, variations in the leaflet tab orientation may prohibit clear projections on captured images, which could make it difficult to identify a specific region that could be used for measurement. Finally, similar to the droop testing apparatus  200  illustrated in  FIGS. 2A and 2B , the droop testing apparatus  300  provides a qualitative test by indicating whether the leaflet droop is acceptable or not, but does not provide a quantitative test, as it guides in classifying the leaflets based on leaflet droop categories and not specific droop values. 
         [0026]    In another embodiment, as illustrated in  FIGS. 4A and 4B , droop tester apparatus  400  includes a dual caliper head  402  integrated with a caliper system  404  to form a contact based droop tester. The caliper heads  402  are further connected to stainless steel plates  406  that are moveable along a slider  410  to make contact with the tabs of a leaflet  412  being tested.  FIG. 4B  is a top view of the droop tester apparatus  400 , and illustrates the leaflet  412  positioned over a specimen pin  408  and between the plates  406 . In one embodiment, the leaflet droop tester  400  is manually operable instead of automated. The stopping action of the dual caliper head  402  in the droop tester apparatus  400  when it makes contact with the leaflet  412  is operator dependent, thus the accuracy of the measurements may be variable. 
         [0027]    Yet another droop tester apparatus  500  and method of use in accordance with principles of the present disclosure are illustrated in  FIGS. 5-7 . With reference to  FIGS. 5 and 6 , the droop tester apparatus  500  includes a transmitter  502 , a receiver  504 , a loading pin  506 , and a controller  508 . The droop tester apparatus  500  is a non-contact based measurement system. With particular reference to  FIG. 6 , a light source  510 , such as a high-intensity GaN green LED, transmits light through a special diffusion unit  512  and a collimator lens  514  of the transmitter  502 . The receiver  504  includes a telecentric optical system  516 , a beam splitter  518 , a high-speed linear CCD (HL-CCD)  520 , and a CMOS image sensor  522 . The beam splitter  518  splits an image of a target  540 , such as a leaflet, directing one image to the HL-CCD  520  for measurement and another image to the CMOS image sensor  522 . In one embodiment, the high-intensity GaN green LED  510  is used along with the HL-CCD  520  in order that dimensions of the target  540  will be displayed and outputed. The image received by the image sensor CMOS  522  is transmitted to a first analog-to-digital (A/D) converter  524  and then to a frame memory  526  of the controller  508 . From the frame memory  526 , the image data is then transferred to a CPU  528  and a monitor  530  and/or video output for viewing. The image data received by the HL-CCD  520  of the receiver  504  is transmitted to a second A/D converter  532  of the controller  508 . The image data is then processed by a digital edge (DE) processor  534  and the CPU  528 . 
         [0028]    In one embodiment, the droop tester apparatus  500  includes a laser micrometer based measurement system to measure the extent of leaflet droop. With reference to  FIG. 7 , the light source  510  of the transmitter  502  is emitted onto the target  540 . An “X” distance of the shadow image, created by the light source  510  on the target  540 , can be detected by the receiver  504 . Dimensions of the droop of the target  540  are measured by calculating distance of shadow created by the target  540  on the HL-CCD  520 . The extent of the shadow image is detected by finding two edges  536  where light intensity drops using such techniques as digital edge-detection, for example. 
         [0029]      FIG. 8  is a top view of two embodiments of loading templates  10  for use with at least the droop testing apparatus  500  of  FIGS. 5-7 . The loading templates  10  may also be used with the other droop testing apparatuses described above. The loading templates  10  may take a variety of forms corresponding with the desired leaflet tissue sample shape being loaded and tested. An outer contour  12  of the loading templates  10  is geometrically similar to a desired leaflet&#39;s boundaries. An indentation  14  is formed to correspond to and accommodate the loading pin  506  of the droop testing apparatus  500 , for example. In one embodiment, the loading pin  506 , and the associated indentation  14 , may be 2 mm in diameter, for example. 
         [0030]      FIG. 9  is a top view of a tissue sample on the apparatus of  FIG. 5 . In one embodiment a leaflet  20  is blotted and placed on the loading template  10  of  FIG. 8 , described above. The leaflet  20  may be placed on the loading template  10  to guide in consistent loading of the leaflet  20  along an axis of symmetry at the centerline of the loading pin  506 . The leaflet  20  is then loaded onto the loading pin  506  and a measurement reading may be displayed, as discussed above with respect to  FIGS. 5 through 7 . As illustrated in  FIG. 9 , the droop testing apparatus  500  of  FIG. 5  may be used to measure the total shadow distance “X” or individual distances on either sides of pin (i.e. “X 1 ” and “X 2 ”). In one embodiment, in order to calculate X 1  or X 2 , the operator has to manually calculate the distance between ends of CCD detector  520  to a mid-point of the loading pin  506  as the droop tester apparatus  500  read out give measurements of the end of the target shadow to the detector edge. 
         [0031]    Although the present disclosure has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the present disclosure.