MEdicAL ThERAPY
solutions. ‘Frequency-doubled Nd:YAG lasers ‘In general, laser surgery works through an
were used, firstly at 532nm and then most interaction of light with a target chromophore
recently 561nm, which is close to the absorption – a molecule that absorbs light at a specific
peak of oxyhaemoglobin and was a state-of-the- wavelength,’ Frost states. ‘In the case of surgically
art solution until about a year ago.’ removing varicose veins, 900 to 1450nm has
Coherent has developed optically pumped been demonstrated to produce good results.’
semiconductor laser (OPSL) technology, which Fibre lasers are often used in medical
is highly suited to this application as the applications, largely in combination with
wavelength can be adjusted accordingly, in this endoscopes, which allow surgeons to deliver
case to 577nm. Schulze notes that with solid- laser technology to areas inside the body. One
state Nd:YAG lasers the wavelength of light
Newport’s Prosario diode laser is suited to
such endoscopic application is the treatment of
endoscopic applications. Rated up to 60W from a
generated by the gain material is very specific.
400µm diameter 0.22NA fibre in the 800 to
an enlarged prostate, or benign prostatic
‘The crystal can produce 1064nm, which can be 1000nm range, it is supplied with an integrated hyperplasia (BPH). BPH is caused by an
frequency doubled to 532nm, but can’t be made
aiming beam to allow accurate positioning of the
excessive growth of prostate cells, which
fibre tip under the skin.
to generate 1065nm,’ he says. The semiconductor constricts the urethra making it difficult to
diode material, however, used in the place of the body that are easily accessible, such as the eyes, empty the bladder. The prostate, which is found
Nd:YAG crystal, can be grown in such a way as skin, mouth, throat, and oesophagus. However, only in men, is a gland located just below the
to produce any wavelength specified. The power one possible application of PDT involves bladder that surrounds the urethra, the tube
of the laser beam is also scalable when using surgeons sewing fibre optic cables into the body through which urine passes from the bladder
OPSL technology, providing the surgeon with after removing a tumour to deliver light to the out through the penis. BHP is common, affecting
the power required for the application. area. PDT is then used to mop up and destroy approximately one third of men over 50.
Another advantage with the OPSL technology any remaining tumour cells not excised by the Transurethral laser vaporisation is one
is the packaging of the semiconductor: there are surgery. technique for the removal of material
fewer components meaning the device is Laser surgery is also used in vascular surrounding the urethra to widen it. The
compact, and it’s also more heat efficient than applications to treat varicose veins, for example. procedure uses a fibre-coupled diode laser,
alternative Nd:YAG technology. Varicose veins are swollen or enlarged veins and which emits the beam from the side of the fibre,
Matching the laser output specifically to the are a common condition, affecting women more to vaporise water in the cells, thereby destroying
oxyhaemoglobin absorption peak improves than men. The condition is not usually serious them. The tissue is simultaneously flushed with
comfort for the patient, and lowers the amount and in the large majority of cases is purely cold water to reduce the heat produced by the
of collateral damage caused by the laser. Schulze cosmetic. However, in some patients, it can lead laser. A laser in the 100W range is typically used
says: ‘There is always a concern about putting to complications, such as skin complaints, and the surgery takes around 30 to 60 minutes,
excess energy into the eye and any design venous ulcers, and blood clots. although a lower power laser would be sufficient,
attributes that improve efficiency and reduce the The recognised procedure for surgically but would lengthen the procedure.
thermal loading in the eye are hugely beneficial. removing varicose veins is a technique known The target chromophore is an important
‘This is a nice example of a solution to a as ligation and stripping, which involves making aspect of laser surgery and will determine the
problem where the benefits are obvious: the two small incisions at either end of the vein and wavelength of light required. Power and cost are
absorption peak of oxygenated haemoglobin is a thin flexible wire is passed through to remove also key factors that end users take into
577nm and these lasers can be designed to it entirely. ‘Laser surgery is proving to be an consideration. ‘There is always a need for higher-
specifically target that wavelength.’ effective alternative to ligation and stripping,’ power, lower-cost lasers in medical applications,’
A second treatment for wet AMD is comments Rick Frost, market development comments Newport’s Frost. ‘In the case of
photodynamic therapy (PDT), which uses a manager at Newport Corporation, a global surgically removing varicose veins, 20-70W is
photosensitising agent – a drug activated by company providing products and solutions in a typically used, depending on the size of the
light of a specific wavelength – and laser number of photonics-related fields, including veins to be treated.’
illumination to destroy unwanted tissue. The life and health sciences. A small incision is made Frost continues: ‘There is also a need to
drug produces an oxygen triplet (a form of and a fibre optic catheter is inserted into the engineer these higher power laser beams into
oxygen) that kills the cell. One such drug, vein. The laser beam is used to coagulate the smaller fibres, as in endoscopic applications a
verteporfin, targets and binds to the new, blood and the fibre is pulled out collapsing the reduction in the diameter of fibre optics is highly
abnormally growing blood vessels in the eye and vein. The method is less invasive than ligation advantageous.’ Fibre optic cables allow surgeons
a 90-second burst of red light activates it to and stripping and there is also less discomfort to carry out minimally invasive procedures to
destroy the blood vessels. PDT is also used as a for the patient. treat conditions that would otherwise be difficult
cancer treatment and there are a number of Guiding the fibre optic cable beneath the skin to reach or difficult to treat and, in this respect,
photosensitising agents that can be engineered is carried out either by ultrasound or by coupling laser technology is an essential tool for the
to bind to cancer cells. an aiming beam to the cable. ‘An aiming beam medical industry.
The photosensitising agents used respond to allows the surgeon to see where the end of the
light in the visible region of the spectrum (500- cable is under the skin, so that it can be positioned
Further information
700nm), which can’t pass through tissue more accordingly,’ explains Frost. Newport’s Prosario
than approximately 1cm in depth. Therefore, diode laser incorporates an aiming beam and is
Coherent: www.coherent.com
PDT is most commonly used to treat areas of the suited to most endoscopic applications.
Newport Corporation: www.newport.com
www.lasersystemseurope.com issue 2 • LASER SYSTEMS EUROPE 15
LSEspr09 pp14-15 Medical.indd 15 3/3/09 10:43:33
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