Method and apparatus for evaluating the performance characteristics of endoscopes

In a method and apparatus for evaluating the performance characteristics of fiber-optic endoscopes, a beam of light defining a predetermined intensity pattern is transmitted through the endoscope from a tip end through an eyepiece end of the endoscope. The intensity pattern of the beam defines either a uniform intensity, or an intensity which varies sinusoidally in a predetermined direction across the beam. The following tests are performed in order to evaluate both the optical fibers and the lens system of the endoscope, and the intensity pattern is selected in accordance with the requirements of the respective test: (i) a light loss test, (ii) a reflective symmetry test, (iii) a lighted fibers test, (iv) a geometric distortion test, and (v) a MTF test. A video system generates signals indicative of the optical intensity of the beam after transmission through the endoscope at each of a plurality of predetermined locations within the beam. The video signals are in turn evaluated in accordance with the selected tests in order to provide graphical and numerical indicia of the optical performance characteristics of the endoscope.

FIELD OF THE INVENTION 
The present invention relates to systems for testing endoscopes, and more 
specifically to systems for evaluating the optical performance 
characteristics of fiber optic endoscopes. 
BACKGROUND OF THE INVENTION 
A typical endoscope comprises a cylindrical stainless steel case enclosing 
a bundle of optical fibers extending between a distal end (tip end) and 
proximal end of the endoscope for transmitting light through the 
endoscope. A fiber optic cable delivers light from a light source into the 
case through an aperture situated near the proximal end of the endoscope. 
The optical fibers transmit the light through to the distal end, where the 
light exits the endoscope and illuminates the area near the distal end. 
The endoscope in turn transmits an image of that area through a rod and 
lens system to an eyepiece lens at the proximal end. A video camera 
coupled to the eyepiece converts the image into electronic signals and 
transmits the signals to a video monitor, where the image is displayed. 
Endoscopes are used most often in "minimally invasive surgery", in which an 
endoscope is inserted into a patient, allowing a surgeon to illuminate and 
view the interior of the patient with minimal penetration. The use of 
endoscopic surgery is growing, in large part because it is generally safer 
and less expensive than conventional surgery, and patients tend to require 
less time in a hospital after endoscopic surgery. Conservative industry 
experts estimate that about 4 million minimally invasive procedures were 
performed in 1996. As endoscopic surgery becomes more common, there is an 
increasing need to accurately evaluate the performance characteristics of 
endoscopes. 
To obtain a true measure of the performance of an endoscope, both the lens 
and the optical fibers should be evaluated. For example, some optical 
fibers may be damaged and only partially transmit light. In addition, the 
lens may distort images or blur the sharpness of image colors. These and 
other shortcomings in the optical performance of endoscopes may be the 
result of imperfections in the manufacturing process and/or may develop as 
the endoscope is used over time. 
An apparatus for evaluating the performance characteristics of endoscopes 
would be able to validate claims made by endoscope vendors about the 
capabilities of their products. Accordingly, such an apparatus would be 
advantageous for the purchasers and users of endoscopes. In addition, such 
an apparatus would be of great use in evaluating disposable endoscopes, 
which currently have an average life of about 20 to 30 uses. An apparatus 
for evaluating the performance characteristic of endoscopes would be able 
to determine when a disposable endoscope is so degraded that it should be 
discarded. 
Furthermore, an endoscope may be adequate for one surgical procedure but 
inadequate for another which requires more precision, such as when a 
patient is bleeding. Currently, an endoscope which is suspected of having 
any deficiency must be removed from service and sent for repair, which can 
be both costly and time consuming. An apparatus for evaluating the 
performance characteristics of endoscopes would preferably be able to 
identify endoscopes which are appropriate for one type of procedure 
although inadequate for another. 
Such an apparatus would also be most advantageous in a program of 
preventative endoscope maintenance. Endoscopes cost thousands of dollars, 
and typically require repairs at least about twice per year which can cost 
several thousand dollars per repair. There is a need for a tool for 
evaluating the performance characteristics of endoscopes, thereby 
verifying if repairs have been effective. 
An apparatus for evaluating endoscope performance ideally would also be 
able to store the results of past tests and evaluations, thereby allowing 
the system to evaluate changes in endoscope performance after repair 
operations and over the lifetime of the endoscope. In addition, such 
information on changes in endoscope performance would be useful in 
predicting changes in the performance of other endoscopes before their 
performance degrades. This would help predict future endoscope needs. 
The present inventors are not aware of any commercially available tools for 
use in a clinical environment which quantitatively assess the performance 
characteristics of endoscopes. 
A further complication is that endoscopes vary in length, diameter and tip 
angle, which is the angle between the direction of view and the 
longitudinal axis of the endoscope. A system for evaluating endoscope 
performance would ideally also be able to accommodate endoscopes which 
have varying optical and/or physical characteristics. 
Accordingly, it is an object of the present invention is to provide a 
method and apparatus for evaluating the optical performance 
characteristics of fiber optic endoscopes. 
SUMMARY OF THE INVENTION 
The present invention is directed to an apparatus and method for performing 
tests on the fiber optic path and the lens system of an endoscope, and in 
turn evaluating the optical performance of the endoscope in dependence on 
the results of the tests. 
According to the present invention, a beam of light defining a 
predetermined intensity pattern is transmitted through the endoscope from 
a first end of the endoscope through a second end, and signals are 
generated indicative of the optical intensity of the transmitted beam at 
each of a plurality of predetermined locations within the beam. A second 
set of signals indicative of one or more performance characteristics of 
the endoscope are generated in response to the intensity signals and to 
signals indicative of the test type. 
Preferably, a plurality of targets are employed to each generate a 
predetermined intensity pattern defining either a uniform intensity, or an 
intensity which varies periodically, such as a sinusoidal-varying medium, 
in a predetermined direction across the transmitted beam. In the preferred 
embodiment of the invention, the targets are selected to perform each of 
the following tests: (i) a light loss test, (ii) a reflective symmetry 
test, (iii) a lighted fibers test, (iv) a geometric distortion test, and 
(v) a modulation transfer function (MTF) test. A video system generates 
signals indicative of the optical intensity of the beam after transmission 
through the endoscope at each of a plurality of predetermined locations 
within the beam. The video signals are in turn evaluated in accordance 
with the selected tests in order to provide graphical and numerical 
indicia of the optical performance characteristics of the endoscope. 
One advantage of the apparatus and method of the present invention is that 
both the lens and optical fibers of an endoscope are tested and evaluated 
in order to accurately and quantitatively assess the performance 
characteristics of the endoscope. 
Other advantages of the present invention will become apparent in view of 
the following detailed description and accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The preferred embodiment of the present invention is embodied in a low-cost 
endoscope evaluation system which accommodates endoscopes of different tip 
angles, lengths and diameters, performs tests on the endoscopes, and in 
turn evaluates the optical performance of the endoscopes in dependence on 
the results of the tests. The preferred embodiment of the invention 
furthermore performs a selection of tests which evaluate the optical 
performance of both the optical fibers and lens of an endoscope, and 
thereby may provide a relatively accurate assessment of the effectiveness 
of a repair operation performed on an endoscope, as well as determine and 
record changes in the optical performance characteristics of an endoscope 
over its lifetime. 
In FIG. 1, an apparatus embodying the present invention for performing 
tests on endoscopes and for evaluating the optical performance of the 
endoscopes in dependence on the results of the tests is indicated 
generally by the reference numeral 10. The apparatus 10 comprises a test 
station 12 including an adjustable mounting arm 14 for receiving and 
retaining an endoscope to be tested, and a carrier 16 for positioning a 
selected target under the distal end (tip) of the endoscope for performing 
a respective test. 
A variable, high-intensity light source 18, such as a xenon arc lamp or a 
halogen bulb, delivers light along a fiber optic cable 20 which is 
detachably connected to the endoscope through an aperture situated near 
its proximal end. In the currently preferred embodiment, the light source 
18 is a variable xenon short-arc lamp, such as the 150 watt lamp sold 
under model no. 610 by Karl Storz Endoscopy-America Inc. of Culver City, 
Calif. As is described further below, during certain tests the fiber optic 
cable 20 is detached from the endoscope and re-positioned to directly 
illuminate a target on the carrier 16. The test station 12 and the 
position of the fiber optic cable 20 during each of the tests performed on 
a typical endoscope are described in detail below. 
A video system 22 generates signals indicative of the image which is 
projected through the eyepiece at the proximal end of the endoscope. In 
the preferred embodiment, the video system 22 comprises a charge-coupled 
device (CCD) video camera 24 coupled to the eyepiece and a video signal 
processor 26 coupled to the camera. As is known in the art, the CCD video 
camera records an image by storing charges in a plurality of semiconductor 
potential wells, thereby defining a two-dimensional array of charges which 
each correspond to the intensity at a point in the transmitted image. The 
video signal processor 26 transfers the charges out of the wells and 
thereby generates time-varying video signals indicative of the recorded 
image. The CCD video camera 24 is coupled to the endoscope eyepiece with 
an adjustable vice 28 having a lens system with both zoom and focus 
control rings. Thus, the projected image may be properly zoomed and 
focused through the vice lens system 28 before it is recorded by the 
camera 24. 
The video system 22 transmits the signals indicative of the image through a 
BNC connector to a standard video monitor 30 which displays the image, and 
to a desktop computer 32 which processes the signals in accordance with 
the present invention, as is described further below. In the 
currently-preferred embodiment, the computer 32 is an Intel Pentium.TM. 
microprocessor-based desktop computer which includes known computer 
software and peripheral devices as is necessary for its operation, such as 
an operating system, a keyboard, a hard disk, random access memory (RAM), 
a computer monitor and a mouse. The computer 32 further includes a frame 
grabber card (not shown), which is an analog-to-digital converter for 
receiving the image signals from the video system 22 and generating in 
dependence thereon digital signals indicative of the image. The frame 
grabber card thus translates the image signals from the format of the 
video system 22 to a digital format which the computer's microprocessor 
can accept and manipulate. The digital signals generated by the frame 
grabber card are preferably in the format of a 512 by 512 array of pixel 
intensities, and thus the number of pixels generated by the card is 
approximately determined as follows: 512.times.512=262,144 pixels. 
The frame grabber card is preferably a "plug-in card" which is detachably 
connected to the system bus of the computer 32 in a known manner. The 
frame grabber card may be implemented with an "RT Mono".TM. video capture 
board, sold by Digital Vision, Inc. of Dedham, Ma., and driver software 
sold by ViewPoint Solutions of Rochester, N.Y. for providing an interface 
between the video capture board and the standard Pentium.TM.-based 
computer. Alternatively, the frame grabber card may be implemented with an 
IMAC PCI-1408 video capture board, sold by National Instruments of Austin, 
Tex. IMAQ Vision software and NI-IMAQ driver software, also sold by 
National Instruments, may provide the interface between the IMAC PCI-1408 
video capture board and the standard Pentium-based desktop computer. 
The computer 32 is coupled in a known manner to a standard printer 34 for 
printing images processed by the computer. In the preferred embodiment, 
the printer 34 is a laser printer having a resolution of at least about 
600 dots per inch (dpi). 
Turning to FIG. 2, the test station 12 comprises a frame 36 including an 
upstanding arm support 38, and a carrier support 40 defining a horizontal 
support surface. As indicated by the arrows in FIG. 2, the mounting arm 14 
is pivotally coupled to the arm support 38 and the angular position of the 
arm is adjustable relative to the carrier support 40 in order to 
accommodate endoscopes of all possible tip angles. In the preferred 
embodiment, the mounting arm 14 accepts endoscopes having outer diameters 
within the range of approximately 1.9 through 10.0 millimeters, lengths 
within range of approximately 4 inches through 13 inches, and tip angles 
within the range of approximately 0 degrees through 120 degrees. 
As shown in FIG. 2, the carrier 16 is mounted on the carrier support 40 
adjacent to the mounting arm 14 and is moveable relative to the mounting 
arm along rails 31 in order to adjust the position of the carrier relative 
to an endoscope on the mounting arm. As is described further below, the 
carrier 16 includes a plurality of targets, each for performing a 
respective test to evaluate the optical performance of the endoscopes. The 
carrier support 40 defines an aperture 42 extending through the support 
surface immediately below the base of the mounting arm. In the preferred 
embodiment of the test station, the aperture 42 is approximately circular 
and defines a diameter of approximately 1.9 inches. 
As shown schematically in FIG. 1, directly beneath the aperture 42 and 
fixed to the underside of the carrier support 40 is a fiber optic cable 
holder 44 of a type known to those of ordinary skill in the pertinent art. 
The cable holder 44 receives and retains the fiber optic cable 20 in order 
to transmit a beam of light from the light source 18 through the aperture 
42 to the distal end or tip of an endoscope being tested. A collimating 
lens 46 is fixed to the underside of the carrier support 40 and covers the 
aperture 42 in order to collimate the light beam projected through the 
aperture. 
As illustrated in FIG. 3a, in the preferred embodiment there are four 
targets mounted on the carrier 16, each of which is used in at least one 
of five tests for evaluating the performance of the endoscope and 
described in detail below. The term "target" is used herein to broadly 
describe any of the various devices used for receiving and/or reflecting a 
transmitted beam as part of each of the tests for evaluating the 
performance characteristics of the endoscopes, as described further below. 
The first target 47 is a photometer sensor which is coupled to a photometer 
50 for measuring the intensity of light received by the sensor. A fixture 
52 including a base 54 and three upstanding legs 56 is removably mounted 
above the photometer sensor 47 for detachably connecting the fiber optic 
cable 20 to the base in order to illuminate the sensor. As described in 
the above-mentioned co-pending patent application, the upstanding legs 56 
define a predetermined length so that the distance between the base 54 and 
the sensor 50, and thus the distance between the end of the fiber optic 
cable 20 and the sensor, is approximately equal to the distance between 
the photometer sensor and the distal end of an endoscope supported on the 
mounting arm. In the currently-preferred embodiment, this predetermined 
distance is approximately two inches. 
The second target 58, which is used in two tests in the preferred 
embodiment, defines a nonspecular reflective surface 60, such as a Kodak 
R27, 90% reflectance card or a white sheet of paper. As is known in the 
art, a nonspecular reflective surface like the surface 60 is one which 
does not form a mirror-like reflected image, but rather diffuses the 
reflected light. A transparent film 62 having a printed reference pattern 
63 is overlaid on the reflective surface 60 during at least one test. The 
reference pattern 63 printed on the transparent film 62 defines a number 
of reference points having a predetermined separation distance. As shown 
is FIG. 3a, the reference pattern is preferably a black, rectangular grid 
defining two sets of parallel lines spaced approximately 0.2 inches apart, 
wherein each of the first set of lines is perpendicular to each of the 
second set of lines. The reference pattern thus defines a set of squares 
having approximately 0.2 inch sides. 
The third target 64 defines a substantially mirror-like surface 65, and is 
preferably a circular reflector plate formed of a material having a 
reflectance preferably within the range of approximately 5% and 
approximately 40% reflectance, such as Lucite.TM., which is laid over a 
black background to provide the mirror-like quality. The surface 65 thus 
creates a specular (mirror-like) reflection. The reflectance of the 
surface 65 is selected to minimize the reflection of incident light, and 
thereby maintain the intensity of the light reflected back through any 
damaged fibers below a predetermined intensity level. As is described 
below, damaged fibers may be identified by their inability to transmit 
light having an intensity below a predetermined level. The substantially 
mirror-like surface 65 rests on three adjustable legs 61, allowing precise 
control over the separation between the endoscope tip and the reflective 
surface. 
The fourth target is a semi-transparent medium 48, such as a film, and 
defines a transmittance which varies periodically along a predetermined 
direction within the medium. A beam of light which is filtered through the 
semi-transparent medium 48 will therefore have an intensity which varies 
periodically along the predetermined direction within the beam. In the 
preferred embodiment, the semi-transparent medium 48 has a transmittance 
which varies sinusoidally along the semi-transparent medium in a first 
direction, and which is substantially constant along the medium in a 
second direction transverse to the first direction. Also in the preferred 
embodiment, the sinusoidally-varying transmittance of the medium defines a 
spatial frequency of one cycle per millimeter (cycles per unit length), 
and is preferably of the type sold by Sine Patterns, Inc. of Penfield, 
N.Y. 
As shown in FIG. 3b, an approximately circular aperture 49 is formed 
through the carrier 16, a diffusing opal glass plate 55 is superimposed 
over the aperture, a white plastic translucent sheet 57 is superimposed 
over the glass plate, and the semi-transparent medium 48 is seated over 
the plastic sheet. As is described further below, when performing the MTF 
test the carrier 16 is positioned to align the circular aperture 49 with 
the aperture 42 of the carrier support 40, and the free end of the fiber 
optic cable 20 is mounted beneath the aperture 42 to transmit a beam 
through the apertures, and in turn through the glass plate 55, white 
plastic sheet 57 and semi-transparent medium 48. The glass plate 55 and 
plastic sheet 57 together diffuse the beam from the fiber optic cable, 
creating a beam of substantially uniform intensity, and the 
semi-transparent medium 48 in turn filters the substantially uniform 
intensity beam to generate a beam which varies approximately sinusoidally 
along the first direction. 
A black paper mask 59 defining a plurality of apertures is preferably 
inserted between the semi-transparent medium 48 and the white plastic 
sheet 57 in order to block light transmission through portions of the 
medium, and thereby enhance selected points in an image corresponding to 
the non-masked (illuminated) portions of the medium. As is described 
further below, each aperture of the black paper mask 59 defines a 
respective portion of the transmitted beam image within which the MTF is 
measured. 
Test Performance 
As indicated above, the following five tests are preferably performed with 
the apparatus of the invention in order to evaluate both the optical 
fibers and lens system of an endoscope: (i) light loss test, (ii) 
reflective symmetry test, (iii) lighted fibers test, (iv) geometric 
distortion test, and (v) MTF test. The details of each test, along with 
the preferred methods for analyzing the results of these tests to thereby 
evaluate the performance characteristics of the endoscopes, are 
hereinafter described. 
FIG. 4 illustrates a flow chart 66 for performing the first test (light 
loss test) which is directed to measuring the reduction in the intensity 
of light after transmission through an endoscope. In general, the test 
comprises measuring two quantities: the intensity of light which exits the 
fiber optic cable ("light in") and the intensity of light which exits the 
fiber optic cable and is transmitted through the endoscope ("light out"). 
In performing the light loss test, the light source 18 (FIG. 1) is 
activated (step 68), set to a selected intensity level, and preferably 
left active for a predetermined period of time in order to allow the light 
source to reach the selected intensity level. In the preferred embodiment, 
the predetermined intensity level is determined such that the intensity of 
light transmitted through the endoscope is within the preferred operating 
range of the photometer sensor target 47, and the predetermined period of 
time is at least approximately ten minutes. The free end of the fiber 
optic cable 20 (FIG. 1) is then coupled to the fixture 52 (FIG. 3a) and 
thereby spaced a predetermined distance above the photometer sensor target 
47 (which is approximately equal to the distance between the tip end of 
the selected endoscope supported on the mounting arm and the target) to 
thereby illuminate the sensor (step 70). The photometer intensity reading 
is then recorded and designated "light in" (step 72). 
After the "light in" intensity is recorded, the cable 20 is removed from 
the carrier fixture 52 (FIG. 3a) and attached to the proximal end of the 
endoscope supported on the mounting arm 14 (step 74), as indicated in FIG. 
1. The angular position of the mounting arm 14 is adjusted relative to the 
photometer sensor target 47 to correspond to the actual tip angle of the 
endoscope tested. The position of the carrier 16 is also adjusted so that 
the photometer sensor target 47 is positioned directly underneath, or 
aligned with the endoscope tip and spaced the predetermined distance 
(approximately two inches) from the endoscope tip (step 76). In the final 
step of the light loss test, the photometer intensity reading is recorded 
(step 78), and this intensity reading is designated the "light out". Both 
the "light in" and "light out" readings are recorded and used, as 
described below, in measuring the reduction in the intensity of light 
after transmission through the endoscope. 
FIG. 5 illustrates a flow chart 80 for performing the second test 
(reflective symmetry test) which is directed to measuring the reflective 
symmetry of light which exits the eyepiece of the endoscope. When an ideal 
endoscope transmits an image of uniform intensity from its tip end to its 
proximal end, the transmitted image is approximately circularly 
symmetrical about the center of the transmitted image. Thus, the intensity 
in the center of the transmitted image is greatest, and the intensity 
decreases at locations in the transmitted image spaced radially from the 
center. All points which are equally distant from the center of the 
transmitted image have approximately equal intensities, and the intensity 
at the periphery of the transmitted image is lowest. In actual (nonideal) 
endoscopes, deviation from the circular symmetry of the transmitted image 
indicates damaged optical fibers. 
In performing the reflective symmetry test, the light source 18 (FIG. 1) is 
activated (step 82) and set to a selected intensity level. In the 
preferred embodiment, the predetermined intensity level is determined such 
that the intensity of light transmitted through the endoscope is within 
the preferred operating range of the video system 22 (FIG. 1). The fiber 
optic cable 20 (FIG. 1) is attached to the endoscope supported on the 
mounting arm (step 84), and the carrier is positioned so that the second 
target, the reflective surface 65, is positioned directly underneath, or 
aligned with the endoscope tip (step 86). The video system 22 is then 
focused on the reflective surface 65 (step 88). A preferred method for 
focusing the video system is to overlay a reference pattern film, such as 
the transparent film 62 (FIG. 3a), on the reflective surface 65, set the 
adjustable vice 28 connecting the video system 22 (FIG. 1) to the 
endoscope to its maximum zoom setting, and then adjust the focus ring of 
the vice to bring the reference pattern into focus. Once the video system 
22 is focused, the reference pattern film 62 is removed from the 
reflective surface 65. 
As discussed above, the center of the transmitted image should have the 
highest intensity. However, if the endoscope is not oriented properly 
(i.e. if the tip angle is not substantially equal to the angle of the 
mounting arm), the point of highest intensity in the transmitted image 
will not coincide with the center of the transmitted image. Accordingly, 
if necessary, the angular position of the mounting arm must be adjusted 
until the approximate center of the transmitted image has the highest 
intensity (step 90). Unfortunately, endoscope tip angles are generally not 
held to a tight tolerance, and thus the proper angle of the mounting arm 
generally cannot be set based only on the purported (nominal) tip angle of 
the endoscope. 
A preferred method for orienting the endoscope is to adjust the angle of 
the mounting arm 14 while the video system 22 displays the transmitted 
image on the video monitor 30 (FIG. 1) or on a computer monitor of the 
computer system 32 (FIG. 1). In this manner, a human operator can adjust 
the mounting arm 14 by viewing the transmitted image on the monitor and 
simultaneously moving the arm until the center of the transmitted image 
coincides with the point of highest intensity. 
Once the endoscope is properly oriented, the frame grabber card stores the 
transmitted image and generates digital signals indicative of the image 
(step 92). It is preferable that the frame grabber card have an adjustable 
range of intensities which it can accept and translate to digital format. 
It is most preferable that in each test the frame grabber card generates 
signals indicative of white pixels for the highest intensities in the 
stored image, and signals indicative of black pixels for the lowest 
intensities in the stored image. In this manner, the frame grabber card 
produces pixels having intensities which span approximately the entire 
output range of the card, which in turn improves resolution and 
facilitates evaluation of the test results. The computer system 32 
processes the digital signals (pixels) when evaluating the endoscope, as 
described further below. 
FIG. 6 illustrates a flow chart 100 for performing the third test (lighted 
fibers test) which is directed to measuring the ability of the endoscope 
optical fibers to transmit low-intensity light. The light source 18 (FIG. 
1) is activated (step 102) and set to a selected intensity level. In the 
preferred embodiment, the predetermined intensity level is determined such 
that the intensity of light transmitted through the endoscope is within 
the preferred operating range of the video system 22 (FIG. 1). The fiber 
optic cable 20 (FIG. 1) is attached to the proximal end of the endoscope 
supported on the mounting arm (step 104), and the carrier is positioned so 
that the third target defining the substantially mirror-like surface 65 is 
positioned directly underneath, or aligned with the endoscope tip at a 
relatively close distance selected to produce a focused, specular 
reflection of the lighted optical fibers at the endoscope eyepiece (step 
106). This distance is typically less than approximately 0.25 inches. The 
frame grabber card stores the transmitted image and generates digital 
signals indicative of the image (step 108) which the computer 32 processes 
when evaluating the image data. 
FIG. 7 illustrates a flow chart 110 for performing the fourth test 
(geometric distortion test) which is directed to measuring the degree to 
which the endoscope geometrically distorts an image. Distortion at a point 
in the transmitted image is defined as the ratio of the magnification at 
that point to the magnification at the center of the transmitted image. A 
preferred method for measuring distortion is to transmit through the 
endoscope an image of a plurality of equally-sized squares, and to then 
measure and compare the diagonal lengths of the corresponding squares in 
the transmitted image. 
The light source 18 (FIG. 1) is activated (step 112) and set to a selected 
intensity level. In the preferred embodiment, the predetermined intensity 
level is determined such that the intensity of light transmitted through 
the endoscope is within the preferred operating range of the video system 
22 (FIG. 1). The fiber optic cable 20 (FIG. 1) is attached to the proximal 
end of the endoscope supported on the mounting arm (step 114), and the 
carrier is positioned so that the second target 58 defining the reflective 
surface 60 is positioned directly underneath, or aligned with the 
endoscope tip (step 116). In addition, the transparent film 62 with the 
reference pattern 63 is overlaid on the reflective surface 60 and the 
video system 22 is then focused on the pattern (step 118). A preferred 
method of focusing the video system 22 is to set the adjustable vice to 
maximum zoom, and to then adjust the focus ring of the vice to bring the 
reference pattern into focus. Once the video system 22 is focused, the 
frame grabber card stores the transmitted image and generates digital 
signals indicative of the image (step 120). The computer 32 processes the 
digital signals when evaluating the endoscope, as is described further 
below. 
FIG. 8 illustrates a flow chart 130 for performing the fifth test (MTF 
test) which is directed to measuring the modulation transfer function 
(MTF) of the endoscope at a predetermined spatial frequency, which is 
equivalent to measuring the modulation transfer ratio (MTR) of the 
endoscope while it transmits an image having an intensity which varies 
along a direction at the predetermined spatial frequency. 
An image's modulation is correlated with the contrast (sharpness) of the 
image. The modulation at a location in an image is defined by the maximum 
intensity and the minimum intensity at that location as follows: 
EQU modulation=(maximum intensity-minimum intensity).div.(maximum 
intensity+minimum intensity) 
As used herein, the terms "maximum intensity" and "minimum intensity" refer 
to the local maxima and minima, respectively, of a cycle in the 
periodically-varying intensity. 
An endoscope reduces the modulation of a transmitted image, so that the 
transmitted image is not as sharp as the image received at the endoscope 
tip. The MTR is a measure of the change in an image's modulation after 
transmission through the endoscope. The MTR is defined as follows: 
EQU MTR=modulation of image after transmission.div.modulation of image before 
transmission 
FIGS. 9A and 9B illustrate the maximum and minimum intensities in an image 
before and after transmission through an endoscope, respectively. The 
graph 140 in FIG. 9A represents the sinusoidally-varying intensity of an 
image which is received at the endoscope tip (i.e. before transmission 
through the endoscope). Points 146 and 150 have a maximal intensity 142, 
while a point 148 has a minimal intensity 144. The intensity variation 143 
in the image before transmission is the difference between the maximal 
intensity 142 and the minimal intensity 144. 
The graph 160 in FIG. 9B represents the sinusoidally-varying intensity of 
an image after transmission through the endoscope. Points 166 and 170 have 
a maximal intensity 162, while a point 168 has a minimal intensity 164. 
The points 166, 168 and 170 of the transmitted image (FIG. 9B) correspond 
respectively to the points 146, 148 and 150 of the received image (FIG. 
9A). The intensity variation 163 in the image after transmission is the 
difference between the maximal intensity 162 and the minimal intensity 
164. 
The intensity variation 163 in the image after transmission is less than 
the intensity variation 143 in the image before transmission. In other 
words, transmission through the endoscope reduces the sharpness of the 
image. The MTF test is directed to measuring this reduction in sharpness 
at different locations in the transmitted image. 
Referring again to FIG. 8, in performing the MTF test, the light source 18 
(FIG. 1) is activated (step 132) and set to a selected intensity level. In 
the preferred embodiment, the predetermined intensity level is determined 
such that the intensity of light transmitted through the endoscope is 
within the preferred operating range of the video system 22 (FIG. 1). The 
free end of the fiber optic cable 20 (FIG. 1) is attached to the fiber 
optic cable holder 44 (FIG. 1) mounted below the aperture 42 of the 
carrier support 40 (step 134), in order to transmit a light beam through 
the aperture. The carrier 16 is then positioned so that the fourth target, 
the semi-transparent medium 48, is positioned directly underneath the 
endoscope tip and above the carrier support aperture 42 (step 136), 
thereby filtering the beam projected from the fiber optic cable and 
transmitting the filtered beam through the endoscope. The frame grabber 
card stores the transmitted image and generates digital signals indicative 
of the image (step 138). 
In summary, each of the tests described above are preferably performed on 
each endoscope in order to provide test results comprising a set of 
signals indicative of intensities at predetermined locations in a beam of 
light transmitted through the endoscope. As hereinafter described, the 
system of the invention preferably further generates a second set of 
signals responsive to the test result signals and which is indicative of 
the performance characteristics of the endoscope. The manner in which the 
second set of signals is generated depends on the particular test used to 
generate the corresponding test result signals. 
Test Result Evaluation 
For each of the above-described tests, the computer system 32 (FIG. 1) 
receives the signals indicative of the beam intensities, and generates the 
second set of signals in accordance with the intensity signals and further 
in accordance with signals indicative of the test type. FIG. 10 shows an 
exemplary display 180 of a graphical user interface (GUI) generated and 
displayed on the monitor of the computer system 32. As is known in the 
art, a GUI provides both a means for user input and a means for the 
computer system to display information. The GUI provides signals 
indicative of the type of test, typically in accordance with user commands 
such as the actuation of graphical buttons and switches. In the preferred 
embodiment, the GUI is implemented using LabVIEW.RTM. software sold by 
National Instruments of Austin, Tex. Accordingly, the various types of 
displays and input methods of the GUI described herein are those which are 
most easily implemented with LabVIEW.RTM. software. However, those skilled 
in the art will recognize that other types displays and input methods may 
be implemented, including other forms of graphical, textual and audio 
input and output. 
The display 180 includes graphical "buttons" which the user actuates via 
mouse or keyboard actions in a manner known in the art. Upon actuation of 
a button 182, the GUI provides a second display (not shown) into which the 
user may enter information related to the endoscope being tested. Such 
information includes the endoscope identification code, manufacturer, 
diameter, length and tip angle, as well as any reported and observed 
problems with the endoscope. Further types of information may be included 
without departing from the scope of the present invention. 
A graphical indicator 186 displays a message which indicates whether the 
endoscope supported on the mounting arm is untested, has passed a test, or 
has failed a test. Actuation of a button 187 signals that a new endoscope 
is to be evaluated, and that previously stored test results are therefore 
inapplicable to this endoscope. Accordingly, upon actuation of the button 
187, the graphical indicator 186 displays a message indicating that the 
endoscope is untested. 
Actuation of a button 184 provides a third display 200 shown in FIG. 11. 
The display 200 facilitates analysis of the results of the light loss 
test. As described above, performing the light loss test yields signals 
indicative of a Light-In and a Light-Out measurement from the photometer 
sensor 47. The ratio of these two intensities yields the light loss of the 
tested endoscope in units of Optical decibels (dB Optical) in accordance 
with the following relationship: 
EQU Light Loss=10 log (Light-Out/Light-In) 
The user provides the Light-In reading in a text entry region 202 and the 
Light-Out reading in another text entry region 204. Upon entry of valid 
numerical values in both text entry regions 202 and 204, the computer 
system 32 generates signals indicative of the entered readings, and in 
turn generates signals indicative of the Light Loss in accordance with the 
above relationship. Finally, the computer system 32 displays a textual 
indication of the Light Loss in a display region 206. 
The displayed Light Loss allows the user to compare the endoscope under 
test with average or expected Light Loss values, which generally depend on 
the diameter of the endoscope. Typical values for Light Loss are about 
(-6.+-.3) dB Optical for a 10 millimeter diameter endoscope, and about 
(-16.+-.3) dB Optical for endoscopes with diameters between 2 and 4 
millimeters. 
Referring again to FIG. 10, actuation of the buttons 188, 189, 192 and 194 
initiates analyses of the results of the reflective symmetry test, MTF 
test, lighted fibers test and geometric distortion test, respectively. The 
analyses of the results of these four tests are directed generally to 
generating signals which are indicative of the degree to which the tested 
endoscope attenuates the intensity of the transmitted beam at 
predetermined locations within the beam. 
Actuation of the button 188 initiates analysis of the results of the 
reflective symmetry test, and causes the GUI to provide a display of the 
type indicated by the reference numeral 210 of FIG. 12. The display 210 
includes a region 212 showing a graphical display of an intensity pattern 
of the transmitted beam. In the preferred embodiment, the region 212 
defines a two-dimensional array of pixels, and each pixel has a color 
(e.g., a shade of gray) indicating the intensity of the transmitted beam 
at a location in the beam corresponding to the location of the pixel. Also 
in the preferred embodiment, a substantially white pixel indicates a 
location in the beam with the highest intensity relative to all pixels, 
while a substantially black pixel indicates a location in the beam with 
the lowest intensity relative to all pixels. 
As shown in FIG. 12, the region 212 defines a plurality of concentric 
regions, each defining a respective intensity range and corresponding to a 
respective region within the transmitted beam. In the preferred 
embodiment, the intensity of a respective concentric region is indicated 
by the shade of that region. The lighter the shade, the higher is the 
intensity of the region; and the darker the shade, the lower is the 
intensity of the region. 
Referring to the exemplary graphical image shown in the region 212 of FIG. 
12, the region 212 defines an approximately oval central region 230, three 
approximately concentric annular regions 232, 234 and 236 progressively 
spaced outwardly from the central region in the radial direction, and a 
peripheral region 238 surrounding the outermost annular region 236. The 
central region 230 contains pixels which are white, and thus defines the 
region within the beam of highest intensity. Typically, the pixels spaced 
radially outwardly from the central region 230 define progressively darker 
shades, and the pixels at the peripheral region 238 of the display are 
substantially black because they correspond to the periphery of the 
transmitted beam defining the lowest intensity. Although the exemplary 
graphical image shown in the region 212 defines five regions 230, 232, 
234, 236 and 238, and thus the region 212 indicates five intensity ranges, 
those skilled in the art will recognize that a number of intensity ranges 
different than the five shown may be used without departing from the scope 
of the invention. 
The region 212 further includes a vertical indicator bar 226 and a 
horizontal indicator bar 228 which may be moved horizontally and 
vertically, respectively, within the region 212 by appropriate user 
command (e.g. a mouse action or keyboard key press). Each bar 226 and 228 
defines a plurality of collinear pixels in the display and, thus, 
corresponds to a plurality of approximately collinear locations within the 
transmitted beam. 
The display 210 further includes a vertical cross-section display region 
216 showing a graphical display indicative of the intensity of the 
transmitted beam in the approximately collinear locations defined by the 
vertical bar 226 of the region 212. The intensity curve shown in the 
region 216 is formed by a plurality of pixels each having a vertical 
position corresponding to the vertical position of a pixel in the region 
212 along the vertical bar 226, and a horizontal position corresponding to 
the intensity of that pixel. 
Similarly, the display 210 further includes a horizontal cross-section 
display region 214 showing a graphical display indicative of the intensity 
of the transmitted beam in the approximately collinear locations defined 
by the horizontal bar 228 of the region 212. The intensity curve shown is 
formed by a plurality of pixels each having a horizontal position 
corresponding to the horizontal position of a pixel in the region 212 
along the horizontal bar 228, and a vertical position corresponding to the 
intensity of that pixel. 
Upon actuation of a button 222 on the display 210, a display 250 of the 
type shown in FIG. 13 is generated which includes a display region 252 
comprising a three-dimensional image indicative of the intensity of the 
transmitted beam and corresponding to the image of the region 212 (FIG. 
12). A region 254 includes controls for adjusting the point-of-view of the 
three-dimensional image, and a region 256 includes controls for adjusting 
the scale of the three-dimensional image along three 
mutually-perpendicular directions (e.g., the x, y and z coordinate 
directions). 
The three regions 212, 214 and 216 (FIG. 12) and the three-dimensional 
image (FIG. 13) each provide an indication of the degree to which the 
transmitted image is circularly symmetrical, and thus the degree to which 
the intensity of the transmitted beam is symmetrical (or non-symmetrical) 
about its center. A user may be able to evaluate an endoscope based on 
this type of graphical feedback alone, and determine whether or not the 
endoscope is acceptable. However, as discussed below, the computer system 
32 of the invention further provides an explicit indication of whether the 
tested endoscope passes a threshold standard for the reflective symmetry 
test. 
Referring again to FIG. 12, upon actuation of a button 224 on the display 
210, a display 268 of the type shown in FIG. 14 is generated. The display 
268 indicates, for each of a plurality of intensity ranges, the number of 
pixels which correspond to that intensity. The display 268 includes a 
region 262 showing a histogram comprising a plurality of vertical bars. A 
region 260 comprising a plurality of text entry areas allows the user to 
define each intensity range by entering values defining the upper bounds 
of the intensity ranges. A region 258 provides a plurality of numerical 
values corresponding to the number of pixels included in each intensity 
range. And a region 265 provides a plurality of numerical values 
corresponding to the percentage of pixels included in each intensity 
range. Accordingly, the regions 258, 262 and 265 display substantially the 
same information in three different formats. 
A selector 264 is set by the user to select one of the intensity ranges. A 
textual display 266 indicates the percentage of pixels having an intensity 
within or above the range indicated by the selector 264. For example, if 
the selector 264 is set to the second highest intensity range, the textual 
display 266 will indicate the percentage of pixels having an intensity 
included in either the second highest or highest intensity range. 
A textual display 267 indicates whether the endoscope has passed the 
reflective symmetry test. A textual display 220 in FIG. 12 also indicates 
whether the endoscope has passed the reflective symmetry test. In 
accordance with the invention, an endoscope passes the reflective symmetry 
test if more than a predetermined percentage of pixels have an intensity 
greater than a predetermined or threshold intensity level. In the 
preferred embodiment, the predetermined percentage of pixels is 
approximately 30%, and the predetermined intensity is approximately 50% of 
the maximum possible pixel intensity, although these values may be changed 
using the display 268 as described above (FIG. 14). As discussed above, 
the intensity of a pixel corresponds to an intensity of a location in the 
transmitted beam, which itself is defined by the degree to which the 
endoscope attenuates the intensity at that location. Thus, it is 
equivalent to say that an endoscope passes the reflective symmetry test if 
more than a predetermined number of locations in the transmitted beam have 
been attenuated by less than a predetermined attenuation. 
Referring again to FIG. 10, actuation of the button 192 initiates the 
analysis of the results of the lighted fibers test, and a display 270 of 
the type shown in FIG. 15a is generated. The display 270 is substantially 
similar to the display 210 of FIG. 12 for analyzing the results of the 
reflective symmetry test. The display 270 includes a region 272 showing a 
graphical display indicative of the intensity of the transmitted beam. The 
region 272 further includes a vertical indicator bar 286 and a horizontal 
indicator bar 288. As discussed above with reference to the display 210 of 
FIG. 12, the bars 286 and 288 each define a plurality of collinear pixels 
in the display and, therefore, a plurality of substantially collinear 
locations in the transmitted beam. The display 270 further includes a 
horizontal cross-section display region 274 corresponding to the 
horizontal bar 288 of the region 272 and showing the beam intensity at 
each point within the region 274 along the horizontal bar, and a vertical 
cross-section display region 276 corresponding to the vertical bar 286 of 
the region 272 and showing the beam intensity at each point within the 
region 276 along the vertical bar. 
Upon actuation of a button 280 on the display 270, a display 290 of the 
type shown in FIG. 15b is generated which includes a display region 292 
comprising a three-dimensional image indicative of the intensity pattern 
of the transmitted beam and corresponding to the image of the region 272 
(FIG. 15a). A region 294 includes controls for adjusting the point-of-view 
of the three-dimensional image, and a region 296 includes controls for 
adjusting the scale of the three-dimensional image along three 
mutually-perpendicular directions (e.g., the x, y and z coordinate 
directions). 
The three-dimensional image 292 and the three display regions 272, 274 and 
276 each provide an indication of the degree to which optical fibers in 
the endoscope are damaged and do not transmit light. A user may be able to 
evaluate the endoscope based on this type of graphical feedback alone, and 
determine whether or not the endoscope is acceptable. However, as 
discussed below, the computer system 32 of the present invention further 
provides an explicit indication of whether an endoscope being tested has 
passed the lighted fibers test. 
Upon actuation of a button 282 in the display 270, the GUI provides a 
display 297 of the type shown in FIG. 16. The display 297 includes regions 
306 and 308 which indicate, for each of a plurality of intensity ranges, 
the number of pixels which correspond to the respective intensity range. 
In the preferred embodiment, only two ranges are considered: intensities 
above a predetermined intensity ("on") and intensities equal to or below a 
predetermined intensity ("off"). The display 297 includes a selector 304 
with which the user sets the predetermined intensity. 
The display 297 also includes a selector 302 with which the user selects a 
value corresponding to a minimum threshold number of pixels. Another 
selector 300 allows the user to select a range around the selected minimum 
threshold number of pixels. If the actual number of pixels which are "on" 
is within this selected range, the endoscope is considered to have passed 
the lighted fibers test, and the computer system generates signals 
accordingly. A textual display 298 indicates whether the results of the 
lighted fibers test indicate that the endoscope has passed. The display 
270 (FIG. 15A) also includes a textual display 278 which indicates whether 
the results of the lighted fibers test indicate that the endoscope has 
passed. 
As discussed above, the intensity of a pixel corresponds to an intensity of 
a location in the transmitted beam. The number of working fibers in the 
endoscope, which is correlated with the number of white pixels in the 
display region 272 (FIG. 15A), depends on such factors as the endoscope's 
dimensions, the tip angle and the number of damaged optical fibers. As is 
also discussed above, the beam intensity at each location is defined by 
the amount which the endoscope attenuates the intensity at that location. 
Thus, it is equivalent to say that an endoscope has passed the lighted 
fibers test if more than a predetermined number of locations in the 
transmitted beam have been attenuated by less than a predetermined 
attenuation. 
In the preferred embodiment described above, the predetermined intensity, 
the minimum threshold number of pixels, and the range around the selected 
minimum threshold number of pixels have been described as values which the 
user may select. However, those skilled in the art will recognize that 
that such values may be fixed and not alterable by the user. Such an 
embodiment may be preferable if necessary to prevent the user from 
altering values which define preferred threshold values, or the preferred 
range for such values. 
Referring again to FIG. 10, actuation of the button 194 initiates analysis 
of the results of the geometric distortion test, and causes the GUI to 
provide the display 310 of the type shown in FIG. 17. The display 310 is 
substantially similar to the display 210 of FIG. 12 for analyzing the 
results of the reflective symmetry test, and includes a region 312 showing 
a graphical display indicative of an intensity pattern of the transmitted 
beam. 
The region 312 further includes a vertical indicator bar 320 and a 
horizontal indicator bar 318 which may be moved horizontally and 
vertically, respectively, within the region 312 by appropriate user 
command. As discussed above with reference to the display 210 of FIG. 12, 
each of the bars 318 and 320 define a plurality of approximately collinear 
pixels in the display and, therefore, a plurality of substantially 
collinear locations in the transmitted beam. The display 310 further 
includes a horizontal cross-section display region 314 corresponding to 
the horizontal bar 318 of the region 312 and showing the beam intensity at 
each point within the region 314 along the horizontal bar, and a vertical 
cross-section display region 316 corresponding to the vertical bar 320 of 
the region 312 and showing the beam intensity at each point within the 
region 316 along the vertical bar. 
Upon actuation of a button 322 on the display 310, a display is generated 
(not shown) which includes a display region comprising a three-dimensional 
image indicative of the intensity pattern of the transmitted beam and 
corresponding to the image of the region 312 (FIG. 17). Like the displays 
of FIGS. 13 and 15b, the display includes a region defining controls for 
adjusting the point-of-view of the three-dimensional image, and another 
region defining controls for adjusting the scale of the three-dimensional 
image along three mutually-perpendicular directions (e.g., the x, y and z 
coordinate directions). 
The three-dimensional image and the three regions 312, 314 and 316 each 
provide an indication of the degree to which the endoscope geometrically 
distorts the image at different locations in the transmitted beam. A user 
may be able to evaluate the endoscope based on this type of graphical 
feedback alone, and determine whether or not the endoscope is acceptable. 
However, as discussed below, the computer system 32 of the present 
invention further provides an explicit indication of whether an endoscope 
being tested has passed the geometric distortion test. 
Upon actuation of a button 324 in the display 310, the GUI provides a 
display 330 of the type shown in FIG. 18. The display 330 includes 
indicators 332, 334, 336, 338 and 340 which each indicate the degree of 
geometric distortion at a respective location within the transmitted beam. 
The degree of geometric distortion at each location is determined from the 
image of the reference pattern forming a part of the transmitted image. As 
discussed above, the reference pattern 63 (FIG. 3a) defines a set of 
equally-sized squares, and geometric distortion will cause the reference 
pattern in the transmitted image to define squares of different sizes or 
to otherwise distort the shape of one or more squares. Accordingly, the 
geometric distortion at a location is determined based on the length of 
the diagonal of the square at that location. In particular, the distortion 
value at a location is calculated in accordance with the following 
relationship: 
EQU Distortion=(S.sub.1 /S.sub.2)-1 
wherein S.sub.1 =the diagonal length of the square at the respective 
location; and 
S.sub.2 =the diagonal length of the central square. 
Each of the indicators 332, 334, 336, 338 and 340 further indicates whether 
the results of the distortion calculation at the respective location 
indicates either a pass or fail condition. In the preferred embodiment, 
each distortion value is compared to a predetermined distortion threshold. 
Distortion values which are below the predetermined distortion threshold 
are considered "fail" values. If at least one of the plurality of 
distortion values is a fail value, the endoscope will typically fail the 
geometric distortion test. Textual displays 342 (FIG. 18) and 325 (FIG. 
17) indicate whether the endoscope has passed the geometric distortion 
test. 
Referring again to FIG. 10, actuation of the button 189 initiates analysis 
of the results of the MTF test, and causes the GUI to provide a display 
350 of the type shown in FIG. 19. The display 350 is substantially similar 
to the display 210 of FIG. 12 for analyzing the results of the reflective 
symmetry test. The display 350 includes a region 352 showing a graphical 
display indicative of the intensity pattern of the transmitted beam, and 
regions 354 and 356 for displaying cross-sectional views of the display 
352 defined by the bars 358 and 360. With reference to the display region 
352, the apertures of the black paper mask 59 (FIG. 3b) each define a 
respective region 359 of the transmitted beam image within which the MTF 
is measured. In the preferred embodiment, and as shown in FIG. 19, the MTF 
is measured at the approximate center of the transmitted image, and at 
select locations on the periphery of the transmitted image, including 
above center, below center, to the right of center, and to the left of 
center. 
A button 362 on the display 350 allows generation of a three-dimensional 
image corresponding to the image of the display 352 and indicative of the 
intensity pattern of the transmitted beam. The three-dimensional image and 
the three regions 352, 354 and 356 each provide an indication of the MTF 
at different locations in the transmitted image. A user may be able to 
evaluate the endoscope based on this type of graphical feedback alone, and 
determine whether or not the endoscope is acceptable. However, as 
discussed below, the computer system 32 of the present invention further 
provides an explicit indication of whether a tested endoscope has passed 
the MTF test. 
Upon actuation of a button 364 in the display 350, the GUI provides a 
display 370 of the type shown in FIG. 20. The display 370 includes 
indicators 372, 374, 376, 378 and 380 which each indicate the MTF at a 
respective one of the selected locations within the transmitted beam. As 
discussed above, the modulation at a respective location within the 
transmitted beam is defined as follows: 
EQU modulation=(maximum intensity-minimum intensity).div.(maximum 
intensity+minimum intensity); 
and the MTR at the respective location in the transmitted image is further 
defined as follows: 
EQU MTR=modulation of image after transmission.div.modulation of image before 
transmission. 
As discussed above, the sinusoidally-varying medium 48 causes the intensity 
of the transmitted beam to vary sinusoidally along a predetermined 
direction in the beam, and the video signals generated by the video system 
22 correspondingly vary sinusoidally with respect to time and thus are 
indicative of the intensity pattern of the transmitted image. The maximum 
and minimum intensities used in calculating the modulation are each 
measured with respect to an intensity of the video signal corresponding to 
a "black" (dark or unilluminated) intensity. Those skilled in the art will 
note that the signal intensity corresponding to "black" is different from 
the "back porch" level of the video signal, which is typically lower. 
FIG. 21 depicts a graph 390 illustrating the definition of modulation at a 
location within a light beam. The graph 390 includes a curve 392 
representing an intensity which varies sinusoidally along a predetermined 
direction. At a location defined by a range 394 along the predetermined 
direction, the intensity varies from a maximum intensity 396 at a distance 
400 along the predetermined direction to a minimum intensity 398 at a 
distance 402 along the predetermined direction. Thus, the modulation at a 
location defined by the range 394 may be determined from the maximum 
intensity 396 and minimum intensity 398 in the manner defined above. In 
another embodiment, the maximum intensity used in the modulation 
determination is the average of the maximum intensities of two consecutive 
cycles, such as the intensities at distances 400 and 404. Using an average 
of two maximum intensities accounts for maximum intensities which vary 
significantly among consecutive cycles, such as is common at the periphery 
of the transmitted image where the intensity sharply declines. 
It is known in the art that the MTF value of a system is equal to the 
product of the MTF values of the components of the system. The 
above-described MTF values are generated in dependence on the signals 
generated by the frame grabber card, and represent the MTF value of the 
combination of the endoscope and the video system 22. However, since the 
video system is typically optically superior to the endoscope, a fixed 
correction factor can be calculated for the video system and used in 
determining the MTF of the endoscope alone. According to "Video 
Engineering" by Andrew Inglis, McGraw Hill, 1993, which is hereby 
expressly incorporated by reference as part of the present disclosure, a 
correction factor of approximately 0.96 is appropriate for video systems 
such as those used in the present invention. Furthermore, the precision 
micro-densitometer modulation calibration of the semi-transparent medium 
48 also affects the MTF of the entire endoscope evaluation apparatus. The 
semi-transparent medium 48 provided by Sine Patterns, Inc. has a 
modulation calibration of 0.81366. Accordingly, the MTF value for the 
endoscope alone is determined by dividing the above-calculated MTF (which 
is equivalent to the MTR) by the following product: (0.96)*(0.81366). 
Referring again to FIG. 20, each of the indicators 372, 374, 376, 378 and 
380 further indicates whether an MTF value indicates either a "pass" or 
"fail" condition. In the preferred embodiment, each MTF value is compared 
to a predetermined MTF threshold. MTF values which are below the 
predetermined MTF threshold are considered "fail" values. If at least one 
of the plurality of MTF values is a fail value, the endoscope has failed 
the MTF test. Textual displays 382 (FIG. 20) and 366 (FIG. 19) indicate 
whether the endoscope has passed the MTF test. In the preferred 
embodiment, for 10 millimeter diameter endoscopes with 0 degree tip 
angles, the MTF threshold at the center of the transmitted beam is 
approximately 0.70, and at other locations in the transmitted beam is 
approximately 0.20. 
As is known in the art, a spatial frequency is defined by the number of 
cycles (transitions from a maximum intensity to a minimum intensity and 
back again) per unit of length. The semi-transparent medium 48 (FIG. 3a) 
is preferably implemented as the above-mentioned sinusoidally-varying 
medium having a spatial frequency of one cycle per millimeter. Thus, 
filtering a beam of light through this medium during the MTF test 
generates a beam having an intensity which varies approximately 
sinusoidally along a first direction in the generated beam at a spatial 
frequency of about one cycle per millimeter, and which is approximately 
constant along a second direction in the generated beam. The generated 
beam is transmitted through the endoscope and recorded by the video system 
22 (FIG. 1) as set forth above. 
The video system 22 records the transmitted image in a conventional manner: 
the CCD camera sequentially scans in a horizontal scan direction from one 
end of the transmitted image to the other, defining a scan row, and the 
video system generates time-varying video signals indicative of a row of 
pixels for the scanned row. In other words, the video signals generated by 
the video system 22 correspondingly vary sinusoidally with respect to time 
and thus are indicative of the intensity pattern of the transmitted image 
along the scan row. After scanning a row, the CCD camera proceeds to scan 
the next row until all rows have been scanned and all pixels have been 
generated. 
With the sinusoidally-varying medium described above, each row across the 
transmitted beam has an approximately-sinusoidal intensity variation. The 
frequency of the transmitted beam, in units of cycles per degree of the 
apparent field of view of the endoscope, is defined not only by the 
spatial frequency of the medium but also by the distance between the 
medium and the endoscope tip. As is described below, this distance is 
selected so that the frequency of the transmitted beam is approximately 
six cycles per degree of apparent field of view. In accordance with a 
further aspect of the invention, it has been determined that MTF 
measurements at a single spatial frequency of approximately six cycles per 
degree of apparent field of view are an accurate indication of optical 
instrument performance. 
FIG. 22 is a schematic illustration provided for purposes of determining 
the frequency of the transmitted beam. The tip 418 of an exemplary 
endoscope 410 is spaced a predetermined distance "d" from a 
semi-transparent medium 416. The exemplary endoscope 410 has an actual 
field of view of seventy degrees, which is thirty five degrees to each 
side 414. The actual field of view is defined as the angular extent of an 
object visible through the endoscope subtended at the tip of the 
endoscope. Thus, the length "x" of the medium visible in each thirty five 
degree field of view is determined as follows: 
EQU x=(tan 35.degree.)(d)=(0.7)(d) millimeters (1) 
Accordingly, the length of the medium which lies in the entire seventy 
degree field of view is twice the length "x" as defined in equation (1): 
EQU 2x=2(d)(tan 35.degree.)=(1.4)(d) millimeters (2) 
In the preferred embodiment, since the medium 416 defines a spatial 
frequency of approximately one cycle per millimeter, the number of cycles 
across the medium in this direction is determined approximately as 
follows: 
##EQU1## 
As discussed above, in the preferred embodiment the desired frequency of 
the transmitted beam is six cycles per degree of apparent field of view. 
The exemplary endoscope 410 has an apparent field of view 412 of twelve 
degrees. The apparent field of view is the angle between the right and 
left sides of the image as subtended by the eye. The desired number of 
cycles across the medium in the apparent field of view is determined 
approximately as follows: 
EQU (6 cycles/degree)(12 degrees)=72 cycles in the apparent field of view(4) 
Accordingly, the value of "d" is determined from the equality of 
relationships (3) and (4) for the desired number of cycles in the field of 
view: 
##EQU2## 
Thus, the tip 418 of the endoscope 410 is spaced approximately two inches 
from the medium 416. Since the distance d is known, the length of the 
medium which lies in the field of view is determined as follows: 
##EQU3## 
Conventional video systems scan at a rate of approximately one frame every 
1/30th of a second. Since each frame comprises a two-dimensional array 
which is 512 pixels.times.512 pixels, the video system 22 scans 512 rows 
every 1/30th of a second. Thus, the video system scans one row every 
1/15360th of a second (one row every 65 microseconds). Since, from 
relationship (4) above, there are seventy two cycles in the field of view, 
the video system 22 scans 72 cycles in 65 microseconds if the horizontal 
scan direction is substantially parallel to the direction along the medium 
which varies at one cycle per millimeter. 
The scan rate of 72 cycles in 65 microseconds defines a video frequency of 
the time-varying video signals which the video system generates: 
EQU 72 cycle/65 microseconds=1.11 megahertz (MHz) 
Of course, the video frequency is easily determined for video systems which 
scan at a rate different than one frame every 1/30th of a second, and for 
video systems which scan at a number of cycles in the apparent field of 
view different than 72 cycles. 
The time-varying video signals, like most signals, are at least partially 
corrupted by noise. In conventional video systems, the predominant form of 
noise is a color subcarrier signal having a frequency of approximately 
3.57 MHz. The above-stated video frequency of 1.11 MHz is so close to the 
noise frequency of 3.57 MHz that a conventional low-pass filter, such as a 
Butterworth filter implemented in the frame grabber card, will not be able 
to substantially attenuate the noise signals without also attenuating the 
video signals. Thus, the filter will not be able to improve the 
signal-to-noise ratio. 
Two quantities which determine the video frequency, the spatial frequency 
of the sinusoidally-varying medium 48 and the scan time of the video 
system 22, cannot easily be adjusted. The spatial frequency of the 
sinusoidally-varying medium is selected for efficiently testing the 
endoscope, and the scan time of the video system cannot be changed without 
significant hardware redesign. Accordingly, the video frequency is 
preferably not adjusted by adjusting either of these two values. However, 
if the horizontal scan direction is transverse to the direction along the 
medium in which the intensity varies at one cycle per millimeter, then the 
video system scans less than 72 cycles in 65 microseconds. The number of 
cycles scanned in a row decreases as the scan direction becomes less 
parallel and more perpendicular to the direction of variance in the 
medium. As will be seen below, the frequency of the video signal will 
likewise decrease, further separating the video frequency from the noise 
frequency and thereby facilitating noise filtering. 
FIGS. 23a and 23b illustrate the manner in which the total number of cycles 
scanned depends on both the horizontal scan direction and the direction 
along the medium which varies at one cycle per millimeter. FIG. 23a shows 
in schematic form an exemplary medium 420 in which the transmittance 
varies sinusoidally along a direction 430. Maxima (or cycles) in the 
transmittance are indicated by reference numerals 421, 422, 424, 426, 428 
and 429. Thus, the medium 420 illustrated in FIG. 23a includes six cycles 
along the direction 430. A horizontal scan direction 432 is substantially 
parallel to the direction 430 of the medium 420. Accordingly, a scan 
across the scan direction 432 crosses six cycles from one end of the 
medium 420 to the other across a distance 434. 
FIG. 23b shows in schematic form another exemplary semi-transparent medium 
440 which is substantially identical to the medium 420 of FIG. 23a but 
rotated with respect to the horizontal scan direction. The medium 440 
defines a transmittance which varies sinusoidally along a direction 450. 
Maxima (or minima) in the transmittance are indicated by reference 
numerals 441, 442, 444, 446, 448 and 449. Thus, the medium 440 includes 
six cycles along the direction 450. As shown, a horizontal scan direction 
452 is transverse to the direction 450 of the medium 440. Accordingly, a 
scan across the scan direction 452 crosses less than six cycles from one 
end of the medium 440 to the other across a distance 454 equal to the 
distance 434 in FIG. 23a. 
Thus, decreasing the number of cycles scanned in a row by selecting a scan 
direction transverse to the direction of variance in the medium will 
likewise decrease the video frequency without changing the spatial 
frequency of the image. In fact, the angle between the scan direction and 
the direction of variance in the medium defines the decrease in the video 
frequency. The number of cycles scanned in a row is determined by the 
relationship: 
EQU Cycles scanned=(Max Cycles)(cos .theta.) 
wherein: 
.theta. is the angle between the scan direction and the direction of 
variance in the medium; and 
Max Cycles is the number of cycles scanned when .theta.=0. 
Similarly, the frequency of the video signal is determined by the 
relationship: 
EQU Frequency=(Max Frequency)(cos .theta.) 
wherein: 
Max Frequency is the frequency when .theta.=0. 
Thus, to divide the video frequency of 1.11 MHz by a factor of three, the 
angle .theta. is selected in accordance with the following relationship: 
EQU Frequency=(Max Frequency)(cos .theta.) 
EQU 1.11/3=(1.11)(cos .theta.) 
EQU 1/3=cos .theta. 
EQU .theta.=71 degrees 
Thus, orienting the semi-transparent medium relative to the horizontal scan 
direction of the video system to form a 71 degree angle between the scan 
direction and the direction of variance in the medium reduces the video 
frequency approximately as follows: 1.11 MHz/3=0.37 MHz. This reduced 
video frequency is more easily distinguished from the noise frequency of 
3.57 MHz by a low pass filter. For example, a fourth-order Butterworth 
filter having a "cut-off" frequency of 0.66 MHz substantially attenuates 
the 3.57 MHz noise signal while attenuating the 0.37 MHz video signal by 
less than 0.1 dB. 
Of course, other values for the angle .theta. will reduce the video 
frequency by different amounts. For example, an angle of 40 degrees yields 
a decrease by a factor of 1.4, while an angle of 89 degrees yields a 
decrease by a factor of 57. Greater decrease factors may be produced by 
selecting angles which are even closer to 90 degrees, but selecting an 
angle of 90 degrees results in a frequency of zero. 
As is known in the art, the fourth-order Butterworth filter has overshoot 
and ringing characteristics for step input signals. However, according to 
the "Handbook of Filter Synthesis" by Anatol Zverev, John Wiley and Sons, 
Inc., 1967, which is hereby expressly incorporated by reference as part of 
the present disclosure, the overshoot and ringing is reduced to about 1% 
after a delay of 10 normalized periods of the filter cut-off frequency. 
This delay is, in this filter, only approximately 2.4 microseconds, which 
is less than 4.4% of the horizontal scan time and thus not a significant 
source of error. 
FIG. 24 depicts an exemplary graph 460 illustrating in simplified form the 
attenuation characteristics of a low-pass filter. The graph 460 defines a 
first set of frequencies 462 which are virtually unattenuated, and a 
second set of frequencies 464 which are substantially completely 
attenuated. A frequency 470 is the video frequency, such as 1.11 MHz, when 
the horizontal scan direction is parallel to the direction of variance in 
the medium. A frequency 466 is the video frequency, such as 0.37 MHz, 
after selecting a horizontal scan direction transverse to the direction of 
variance in the medium. A frequency 468 defines a threshold below which 
the filter does not substantially attenuate signals. Another threshold 
frequency 472 defines the frequencies above which the filter substantially 
completely attenuates signals. Finally, a frequency 474 is the noise 
frequency, such as 3.57 MHz. The filter substantially attenuates the noise 
frequency 474 since it is greater than the frequency 472. In addition, the 
filter passes substantially unattenuated the frequency 466 since it is 
less than the frequency 468. 
In response to a user command input through the GUI, the computer system 32 
transmits any of the above-described displays to the printer 34. The 
printed display is useful in the analysis of test results, and thus in 
evaluating the performance characteristics of tested endoscopes, in that 
it may be transmitted (i.e., sent by mail, electronic mail or facsimile) 
to distant users unable to view, or otherwise access the monitor or 
computer system of FIG. 1. 
In the preferred embodiment, the computer system 32 (FIG. 1) further 
comprises a database for storing, for each endoscope tested, a unique 
identifier for the endoscope, the endoscope manufacturer, diameter, length 
and tip angle, any reported and observed problems with the endoscope, the 
time and date of testing, the reason for testing, the test results, and 
the evaluation of the results. Such a database allows the system of the 
present invention to evaluate changes in endoscope performance after 
repair operations and over the lifetime of the endoscope. The database can 
be implemented with a variety of commercial software products, such as 
Microsoft Access.TM. or Claris FileMaker Pro.TM.. 
Although the invention has been shown and described with respect to a 
preferred embodiment thereof, it would be understood by those skilled in 
the art that other various changes, omissions and additions thereto may be 
made without departing from the spirit and scope of the invention as 
defined in the appended claims. For example, there are other fiber-optic 
scopes, known as bore scopes, which are similar to endoscopes for use in 
medical applications, but have much larger length-to-diameter ratios. Bore 
scopes are used to examine the internal subassemblies in large engines, 
compressors and turbine machinery. Such bore scope may be tested and 
evaluated using the system of the present invention with minimal 
modification of the preferred embodiment presented herein. Accordingly, 
this detailed description of a preferred embodiment is to be taken in an 
illustrative, as opposed to a limiting sense.