Endomicroscopy - Biomedical Optical Imaging Technologies: Design and Applications - page 262

Tabl e 8. 4 Comparison of selected commercially available coherent fiber bundles [ 32 , 33 ]

Number of

Active Coating

picture diameter Clad diameter diameter

elements [m] [m] [m]

F & T Fibers and Technology GmbH
FTIFHR200S 3,000 180 200 250

FTIFHR350S 6,000 315 350 420

FTIFHR500S 10,000 450 500 600

FTIFHR800S 30,000 720 800 950

Fujikura
FIGH-016-160S

1,600 140 ˙ 15 160 ˙ 20 210 ˙ 30

FIGH-03-215S 3,000 190 ˙ 20 215 ˙ 25 285 ˙ 30

FIGH-06-300S 6,000 270 ˙ 20 300 ˙ 25 400 ˙ 30

FIGH-10-350S 10,000 325 ˙ 20 350 ˙ 25 450 ˙ 30

FIGH-30-650S 30,000 600 ˙ 30 600 ˙ 30 750 ˙ 50

FIGH-30-850N 30,000 790 ˙ 50 850 ˙ 50 950 ˙ 50

FIGH-50-1100N 50,000 1,025 ˙ 80 1,100 ˙ 80 1,200 ˙ 100

FIGH-70-1300N 70,000 1,200 ˙ 100 1,300 ˙ 100 1,450 ˙ 100

FIGH-100-1500N 100,000 1,400 ˙ 120 1,500 ˙ 120 1,700 ˙ 150

achieves a magnification factor of 2.85 in order to match the fiber bundle NA of
0.35 [ 34 ]. In this case, while the system has good light collection efficiency due to
the high object-side NA, its overall resolution is limited by the discrete sampling
effect due to the fiber bundle. At its design wavelength, this objective alone can
reach a theoretical 0:4 m resolution; however, when used at the distal tip of a fiber
bundle (FTIFHR800S (see Table 8.4 )) with approximate fiber-to-fiber spacing of
3:9 m, the smallest resolvable features were 2:75 m.

8.2.2.3 Coherent Fiber Bundles

Coherent fiber-optic bundles preserve the spatial orientation of fibers throughout
the length of the bundle and can therefore transmit a full-field image, or a scanned
beam, from one end to the other, eliminating the need for a miniature scanner at
the distal tip. However, packing of individual fibers within a bundle requires that a
finite cladding volume is maintained between the light guiding cores. This results in
a pixilated image with dark space between cores, limiting the achievable spatial
resolution, even for the most densely packed bundle. However, the appearance
of this artifact can be reduced by image processing techniques. Examples of
commercially available fiber-optic bundles used for endomicroscopic applications
are presented in Table 8.4 .Fig. 8.2 presents typical optical fiber bundle attenuation in
function of wavelength. The optimal operating range is visible wavelengths through
near infrared where attenuation is the lowest.
As fiber bundles can produce autofluorescent signal, a special attention should
be given for applications with short excitation wavelengths.