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Optical Fiber Techniques for Medical Applications 329

or diode laser could penetrate deep into the gland, causing 1. Laser Angioplasty Using Laser Catheters
coagulation and shrinkage. These minimally invasive pro-
A common technique for cardiovascular diagnosis is an
cedures are still under investigation, in an attempt to better
X-ray study of the arteries called angiography. A thin
control the thermal effects.
catheter is inserted through an incision in the groin (or
the arm) and is pushed through the arterial system until it
C. Gynecology reaches the coronary arteries. Then an X-ray-opaque liq-
uid is injected through the catheter, and the shadow of this
A hysteroscope is inserted into the uterus and carbon
liquid is examined by X-ray imaging. A blockage in the
dioxide gas or a transparent fluid is injected through
blood flow can thus be examined. If the coronary artery is
the endoscope to expand the cavity. This allows the
only partially blocked, the situation can sometimes be im-
physician to clearly see the internal structure. The sur-
proved by using a method called balloon angioplasty. The
geon can then use mechanical tools or a laser beam sent
more exact name for this method is percutaneous translu-
through a power fiber to treat polyps, scar tissue, or other
minal coronary angioplasty (PTCA). This method makes
abnormalities.
use of a special catheter that includes a tiny balloon at its
Laparoscopes are often used to view the uterus, fallop-
end. The tip of the catheter is inserted through the partially
ian tubes, and ovaries. Abnormalities, such as tube block-
constricted artery, the balloon is inflated under high pres-
age or adhesions, can be corrected, again using mechan-
sure (10 atm), and the blockage is reduced. Unfortunately,
ical tools or fiberoptic laser surgery. Alternatively, thin
PTCA can be successfully used on only a limited num-
fiberoptic endoscopes can be inserted into the fallopian
ber of patients. In many cases, if the arteries are blocked,
tubes, through the cervix and the uterus. These can be used
one has to resort to a surgical procedure called coronary
to view directly tube blockages that may lead to infertil-
artery bypass grafting (CABG). A vein is removed from
ity. Fiberoptic laser surgery could be used in the future to
the vicinity of the blocked artery or from some other part
remove the blockages.
of the body (e.g., the leg) and is implanted in parallel to
the blocked artery. This operation requires an open-heart
D. Fetal Diagnosis and Therapy procedure, which is traumatic, risky, and expensive.
Small diameter fiberoptic fetoscopes can be inserted into With the development of optical fibers that could deliver
the bodies of pregnant women for direct visualization of high laser energy, during cardiac catheterization, when
the fetus. They are useful in cases of complications, where substantial blockage of the coronary arteries is observed,
ultrasound imaging cannot provide sufficient information. an optical fiber could be inserted through the catheter. A
Power fibers inserted through these endoscopes can be laser beam sent through the fiber could then be used to va-
usedforlasersurgeryonthefetus.Forexample,in10–15% porize the plaque and open a clear channel through which
of identical twins one fetus is passing blood to the other blood flow can then resume. This procedure is called laser
fetus over abnormal blood vessels in the placenta. This angioplasty or vascular recanalization, and a schematic
condition is called twin-to-twin Transfusion syndrome cardiovascular laser catheter and its operation is shown in
(TTTS) and in this case, the mortality rate of the fetuses is Fig. 12.
very high. Nd:YAG laser radiation sent through a power Laser angioplasty of the coronary arteries has been suc-
fiber is used to destroy the connecting blood vessels, under cessfully accomplished with laser catheters based on the
direct endoscopic imaging. The success of these prelimi- excimer laser and on pure silica power fibers. Excimer
nary experiments will pave the road for other applications lasers, emitting in the UV (λ< 200 nm), were selected, be-
of surgical fetoscopy. cause they ablate tissue without causing thermal damage.
The tip of the catheter is guided using X-ray fluoroscopy,
and the excimer laser is used to vaporize plaque with little
E. Cardiovascular and Heart Surgery
thermal damage. Thousands of patients have been treated
In the cardiovascular system a major role is played by the by this method. Laser catheters based on other lasers and
coronary arteries, which supply blood to the heart muscle, fibers have also been tried. One of the problems not yet
and a myocardial infarction may result if a coronary artery fully solved is that of monitoring and control of the laser
becomes occluded. A common problem with the arteries is beam during the procedure. Some of the laser catheters
a build up of atherosclerotic plaque on the interior walls. use fiberoptic sensor techniques to distinguish between
The plaque, which contains fatty material and calcium, plaque and normal arterial wall and to prevent perforation
starts blocking the coronary arteries, and the blood flow of the arteries. Progress in the use of laser catheters for
through them is reduced. This results in angina pectoris, laser angioplasty of the coronary arteries has been slower
a condition that afflicts millions of people. than hoped, due to the complexity of the procedure.