larger size can result in limitedflexibility of the endoscope tube, which may require
patient sedation during use of the endoscope. Consequently, during the evolution to
modern endoscopes, a replacement for thefiber bundle was sought using single
opticalfibers, such as SMF, MMF, DCF, or hollow-core PCF, to reduce the size
and to increase theflexibility of endoscopes, thereby enabling safer, faster, and less
expensive clinical procedures. In some endoscope designs a singlefiber is used for
both delivery of the incident light and image transport. Other endoscope designs use
a centralfiber for illuminations and either another individualfiber or a circular array
offibers for image retrieval.
A major limitation when using MMFs is the temporal variation of the modal
distributions in thefiber, which can lead to imageflickering [ 21 ]. Actually this
situation occurs in all imaging systems that employ MMFs both for the delivery and
the collection of light. SMFs offer better resolution and a decrease in speckle noise
compared with MMFs. Compared to conventional SMF and MMF, the DCF types
described in Sect.4.3can support single-mode light transmission through the core
for illumination of a target area and multimode image transfer (consisting of par-
tially incoherent light reflected from the sample) through the inner cladding back to
an imaging instrument. A DCF thus achieves high-resolution imaging, reduced
speckle effects, and a large depth offield resulting from the larger collection
diameter of the cladding.
In conjunction with evaluating the potentials of using singlefibers are innovative
optical designs, miniature image scanning mechanisms, and specific molecular
probes [ 21 ]. The aims of the combinedfiber plus the technology advances are to
provide images with various colors, more depth, and multiple dimensions in order
to acquire greater biological details from tissue.
10.2.2 Minimally Invasive Surgery.
The traditional use of endoscopes has been to insert them through the natural
openings in a body. Another branch of endoscopy is known as endoscopic surgery
orminimally invasive surgery. This procedure also is referred to aslaparoscopic
surgery. In this surgical discipline, a small incision (nominally 0.5–1.5 cm) is made
in the body through which a small plastic tube containing miniaturized surgical
tools then is inserted in order to treat a medical condition [ 21 – 25 ]. In addition, as
shown in Fig.10.10for orthopedic surgery, a separate opticalfiber endoscopic
probe containing a light source and a miniature video camera normally is inserted
through another small incision in the body to monitor and evaluate the treatment
procedure. This probe, which is known as anarthroscope, can magnify images
from inside a joint up to 30 times. The images obtained by the arthroscope typically
are transmitted to a TV monitor. This setup gives the orthopedic surgeon a clear and
enlarged view of the inside of a joint in order to operate using small surgical tools
inserted through separate minor incisions. Table10.2lists some of many other
kinds of minimally invasive surgery.
10.2 Endoscopy 305