138 CHINESE OPTICS LETTERS / Vol. 7, No. 2 / February 10, 2009
Influence of scanning velocity on bovine shank bone
ablation with pulsed CO
2
laser
Xianzeng Zhang (
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1
, Shusen Xie (
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1∗
, Qing Ye (
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2,3
, and Zhenlin Zhan (
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)
1
1
Institute of Laser and Optoelectronics Technology, Fujian Provincial Key Laboratory for Photonics Techonology,
Key Laboratory of Opto-Electronic Science and Technology for Medicine of Ministry of Education,
Fujian Normal University, Fuzhou 350007
2
Department of Otolaryngology, Fujian Provincial Hospital, Fuzhou 350001
3
Provincial Clinical College of Fujian Medical University, Fuzhou 350001
∗
E-mail: ssxie@fjnu.edu.cn
Received July 15, 2008
The influence of scanning speed on hard bone tissue ablation is studied with a 10.6-µm laser. The groove
morphology and the thermal damage created in bovine shank bone by pulsed CO
2
laser are examined
as a function of incident fluence by optical microscope following standard histological processing. The
results show that ablation groove width, depth and ablation volume, as well as the zone of thermal injury,
increase gradually with incident fluence. As compared to the result for high scanning speed, the lower
scanning speed always produces larger ablation volume but thicker zone of thermal injury. It is evident
that scanning speed plays an important role in the ablation process. In clinical applications, it is important
to select appropriate scanning speed to obtain both high ablation rates and minimal thermal injury.
OCIS codes: 170.1020, 140.3470, 350.5340.
doi: 10.3788/COL20090702.0138.
Conventional methods to perform the incision or exci-
sion of hard biological tissues (e.g., bone and teeth) in
today’s medical practice are mechanical tools such as
saw and drill. Unfortunately, the traditional mechani-
cal tools always produce unconquerable drawbacks such
as broad cut, thermal side-effect, and metal abrasion,
which noticeably delay the healing processes. Thanks
to the unique advantages such as free cut geometry, no
vibration, haemostatic and aseptic effect, lasers as one
of the most promising tools to compensate/substitute
the traditional instruments for the removal of hard bi-
ological tissues have been paid more and more atten-
tions. A number of ex vivo investigations and animal
trials have been done with different types of biologi-
cal tissue by using various laser systems
[1−6]
. Since the
strong absorption peaks of compact bone overlap with
the Er:YAG (2.94 µm) and CO
2
(9.6 and 10.6 µm) laser
wavelengths, it seems that Er:YAG and CO
2
lasers may
be the most suitable candidates for practical applica-
tions. However, early attempts with continuous-wave
(CW) and long-pulse (pulse duration within millisecond
level) CO
2
lasers always produce strong thermal side-
effects. Since the importance of the pulse duration in
laser medicine has been quickly realized, the so-called
“superpulsed” CO
2
lasers (pulse duration 65 − 600 µs) or
even shorter pulse lasers (0.1 − 1 µs) were used to reduce
the thermal damage. However, shorter pulse duration
will lead to lower ablation efficiency or cutting speed,
which of course is unsuitable for medical applications.
Another recognized method to prevent dehydration of
the tissue and additionally cool it during irradiation is
to combine the short-pulse laser with a fast multi-pass
beam scanning and using an air-water spray
[7−9]
. With
this technique, a relatively long CO
2
laser pulse (about
100 µs) can obtain efficient and clear ablation
[10]
. The
influence of the water content in dental enamel and
dentin and the amount of water externally supplied by
air-water spray on ablation has been reported
[11]
. How-
ever, the systematic study of the influence of scanning
velocity of laser beam on ablation effects has not been
reported. In this letter, we experimentally study this
influence with a pulsed CO
2
laser.
The laser source used in this study is a pulsed CO
2
laser (Sharplan 30 C, Israel) with a wavelength of 10.6 µm
and a pulse length of about 10 ms. The laser beam was
transmitted through an articulated-mirror-arm system
and focused to a spot diameter of about 510 µm on the
bone sample surface directly with a 125-mm lens. The
radiant exposure delivered to the tissue was set to prede-
termined values of 5 − 45 J/cm
2
which was confirmed by
reading the laser pulse energy with a pyroelectric detec-
tor and relating to the beam area. The repetition rate
was 60 Hz.
Bovine shank bone obtained no later than six hours
postmortem from a local slaughterhouse was used in this
experiment. Areas of the bone surface exhibiting a clean,
smooth cortical surface were prepared by scraping the
surface with a razor blade to remove the periosteum. And
then the bone was cut into rectangular blocks (∼ 2 × 4
(cm) with original thickness) with a diamond saw. In
order to value the influence of scanning velocity on bone
ablation, the prepared bone samples were divided into
two groups named A and B randomly. For each group,
the sample was put on a computer-controlled motorized
linear driving stage and moved repeatedly through the
focused beam. For group A, the sample was repeatedly
moved at a rate of 20 mm/s for 6 times, while for group
B, the sample was moved at 3.3 mm/s for once. We
define the pulse overlap factor n as the ratio of pulse
radius to the translation of the laser spot. For groups
1671-7694/2009/020138-04
c
2009 Chinese Optics Letters