The Laser Microtome

 

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The Laser Microtome
Prepared by: Alnoor norain
Ahmed abdulkareem
Supervised by: Dr. Mohammed fathalla
A laser microtome is a new sectioning device, which cuts tissue or other
material with the help of photons instead of steel blades. The method is
contact-free and enables to cut tissue in its native state, Special preparation
techniques are not required.
Laser microtome provides micro structuring and imaging of biological
tissue and various materials. Femtosecond laser technology is the key for this
novel generation of microtomes . Ultrafast laser pulses enable precise, noncontact
processing o specimens. A main advantage of the laser microtome is
its ability to cut native tissue as well as hard tissue without decalcification. The
LMT F14 is optionally available with a Navigation Modul. This tool is based on
Optical Coherence Tomography (OCT), a three dimensional imaging
technology. The unique combination of laser microtomy and OCT imaging
allows 3-D navigated cutting, making the LMT F14 suitable for a wide range of
applications in life sciences and materials research.
Technical details
The Navigation Module is equipped with a Spectral Radar OCT imaging
system and an additional OCT-module containing the reference arm and
optics for dispersion compensation. Based on a NIR laser the OCT system
allows for deep penetration of biological tissues. A piezo-driven three–axis
positioning stage enables 3-D imaging and cutting.

ectinin -D cuttin and structurin
Main component of the LMT F14 is a NIR femtosecond laser. Nearinfrared
radiation is well suited for processing biological material, because
most biological tissues have a very low absorption coefficient for this part of
the spectrum. Thus specimens can even be manipulated inside. To perform a
cut the laser beam is tightly focused into the specimen by a high numerical
aperture objective. Because of the very high photon density inside the laser
focus, on-linear optical processes are induced, which finally lead to ablation.

 

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But this effect is only limited to the very small focal volume, thus allowing cuts
with micrometer precision.
It can also be used to prepare thin tissue sections for microscopic
examinations or to obtain cell material for the purpose of cultivation. The laser
microtome is also ideal for micro structuring However, in combination with the
Navigation Module the LMT F14 does not only allow for two-dimensional
sectioning but also for three-dimensional cutting. This provides great flexibility
and enables novel applications.
Principle
The cutting process is performed by a femtosecond laser, emitting
radiation in the near-infrared range. Within this wavelength range, the laser is
able to penetrate the tissue up to a certain depth without causing thermal
damage. By tight focusing the laser radiation, intensities over 1 TW/cm2 (1 TW
= 1012 watts) arise inside the laser focus. These extreme intensities induce
nonlinear effects and optical breakdown occurs. This causes the disruption of
the material, limited to the focal point. The process is known as photo
disruption.
Due to the ultra short pulse duration of only a few femtoseconds (1 fs =
10-15 seconds) there is only very low energy of a few nano joules (1 nJ = 10-9
joules) per laser pulse deposits into the tissue. This limits the interaction range
to diameters below one micrometer (1 μm = 10-6 meters). Out of this range
there is no thermal or mechanical damage.
Mechanism f actin
Multi photon absorption causes ionization of the tissue. This process is
called optical breakdown and leads to the formation of a plasma. The fast
expansion of the plasma causes disruption of the tissue and is responsible for
the cutting process (Fig. 1).Sectioning and 3-D cutting To prepare tissue
sections the laser beam and the specimen are moved simultaneously – the
laser beam fast scanner and the specimen by a three-axis piezo-driven
positioning stage. Depending on the aterial being processed slice thicknesses
of 7 to 100 μm are feasible. The method is not only suited to prepare thin slices
but 3-D sections as well.
Figure1:
Working principle of the laser
microtome. A laser induced plasma
is used to cut the tissue without any
mechanical forces applied. The near
infrared radiation of the laser
penetrates the tissue up to one
millimeter.

 

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See what you cut:
OCT controlled 3D processing Cutting of flat sections by femtosecond
laser technology is only
the first step into a new
direction in laser
microtomy. For the next
step, OCT imaging will be
implemented into
the system. Optical
coherence tomography
(OCT ) is a method for
imaging different layers of
transparent or scattering
tissue by scanning the
area of interest with a low
coherent light source. The
measuring principle is similar to ultrasound imaging. Due to differences in their
optical path lengths, photons reflected from different layers inside the tissue,
can be distinguished by interference measurements with an external
reference plane. Fig. 2 shows an OCT image of a finger tip, where some
respiratory glands can be seen as spiral pattern. Having such a tomographic
imaging system implemented, real 3D cutting near the surface of tissue
sample is possible, targeting specific areas or volumes of interest.
A pwerful cmbinatin
The Navigate Module gives full control of cutting processes. It assists to
predefine cutting geometries, to assess the cutting quality or to measure
distances. Applications include controlled sectioning of biological tissues as
well as cutting along predefined structures or even cell layers. OCT imaging is
also suited to visualize the inner structure of different materials. This makes the
LMT F14 with Navigation Module perfect for materials research. It can be used
to identify regions of interest and to cut material samples.
Intuitive raphical user interface
The LMT F14 software provides an easy to use, intuitive graphical user
interface. The software includes functions for sectioning, three-dimensional
cutting and data storage. It also includes distance-measurement tools and
different imaging features.
Cntrl and safety
Figure 2:
3-D OCT image of
a kiwi fruit section.
3-D OCT image of a
ceramic scaffold for
tissue engineering

 

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An integrated camera allows for positioning of specimens and for online-monitoring of cutting
processes. If necessary, the cutting process can be interrupted at any time. In this case the laser
shutter closes automatically.
References:

51, Holger Lubatschowski Rowiak ,GmbH Garbsener Landstr, 1030419 Hannover , Germany ,
Tel.: +49 (0)511 277 29 54 , Fax: +49 (0)511 277 29 59, E-mail: hl@rowiak.de
Website: www.rowiak.de

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