Transcript Photo-Thermal Coherent Confocal Microscope Mark

Photo-Thermal Coherent Confocal Microscope
Mark Andrews, Sean Sullivan, Matthew Bouchard, Alex Nieva, Purnima Ratilal, and Charles A. DiMarzio
Optical Science Laboratory, Northeastern University, Boston, MA.
"This work was supported in part by CenSSIS, the Center for Subsurface Sensing and Imaging Systems,
under the Engineering Research Centers Program of the National Science Foundation (Award Number EEC-9986821)."
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Optical
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Fundamental
Science
Photothermal
Better skin images
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r, Distance,  m
Objective
Lens
Point Detector
Aperture
Focal plane
Out of focus
scatter
• Above, some out of focus light is scattered back along the same
incident path, ends up going through the pinhole and to the
detector. This contributes to signal clutter.
• Confocal Microscopy provides resolutions down to 1μm but has
limited depth penetration due to out of focus scattering [2].
Beyond 100m depth, signal to clutter ratio becomes too small.
• Photothermal Microscope provides a solution to filter this out
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• The Photothermal Coherent Confocal Microscope will provide us with
images at increased depths for use in skin imaging.
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SIGNIFICANCE AND RELATION TO CenSSIS
Confocal
GOALS
Improve upon performance of reflectance confocal microscope:
•Filter out the out of focus scattered light
•Increase depth of penetration
•Increase information content of image by quantifying the
coefficient of thermal expansion
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PHOTOTHERMAL COHERENT CONFOCAL MICROSCOPE LAYOUT
T, Temperature Rise, K
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t, Time, s
Heat Source, W/m
0
•A heating laser directed along
same path of imaging laser creates
thermal expansion at the focus in
the sample. (shown on left)
•Heating laser is pulsed to create
periodic expansion and contraction
•A computer simulation of this is
shown on the right, where a 1s
pulse is seen as an expansion to
either side of the focus
•Thermal expansion will be
measured with a photothermal
microscope.
t, Time,s
CONCEPT OF PHOTOTHERMAL MICROSCOPE
t, Time, s
ABSTRACT
Confocal microscopy has been shown to be useful in imaging
skin slightly below the junction of the dermis and epidermis.
However, the depth of imaging is a significant limitation. We
present a novel concept designed both to improve the depth of
penetration and to increase the information content of images
obtained with a reflectance confocal microscope. Using an
approach similar to optoacoustics, we plan to explore the use of
laser heating to generate tissue expansion, which will be
measured by the microscope. The microscope will incorporate a
pulsed heating laser along the same optical path as the imaging
laser in order to generate localized heating. This will result in
periodic thermal expansion and contraction at the focus. Optical
Quadrature detection is used to measure the phase of the
scattered light, and Doppler techniques will be employed to
quantify the thermal expansion. For the purposes of imaging,
two lasers of different wavelengths will be needed to resolve
phase ambiguities in the expansion measurement. The motion
resulting from thermal expansion will provide additional
discrimination against multiply scattered light. It will also provide
a measurement of a mechanical parameter, the coefficient of
thermal expansion, which may aid in the characterization of
different types of tissue.
• The above microscope layout incorporates the heating laser (bottom right)
with two imaging lasers (bottom left), using dichroic mirrors. The three
combined beams are focused onto the sample, shown in pink.
• The back-scattered light from the sample returns along the same path until
it is separated from the incoming beam at the polarizing beam splitter
(Custom PBS, center), and directed towards the Q and I detectors (top).
• Using Optical Quadrature Detection, the phase information can be
extracted by mixing the reference beam with the backscattered light at the
polarizing beam splitter, and then detecting each polarization component at
the I and Q detectors. This is done for both imaging wavelengths.
• Using Doppler techniques, the thermal expansion at the sample can then
be measured using the phase changes for both imaging wavelengths.
REFERENCES
• [1] Nieva, Alex, Matthew Bouchard, Charles A. DiMarzio, “Opto-acoustic
Signal Detection with a Coherent Confocal Microscope Setup,” Proc.
SPIE, Vol. 5697. Presented at Photonics West in San Jose, CA, Jan 05.
Publication expected, July 05.
• [2] Nieva, Luis A., and Charles A. DiMarzio, Ultrasound Assisted
Confocal Microscopy, NU Disclosure NU--667XX. April 2004.
• [3] D. O. Hogenboom, and C. A. DiMarzio, “Quadrature Detection of a
Doppler Signal”, Applied Optics, 37(13), page 2569, 1998.
• [4] J. B. Pawley, ed., “Handbook of Biological Confocal Microscopy”, 3rd
ed. (Plenum, New York, 1996).
• [5] A. F. Fercher, W. Drexler, C. K. Hitzenberger, and T. Lasser, “Optical
coherence tomography-principles and applications”, Rep. Prog. Phys. 66
(2003) 239-303.
PI CONTACT INFORMATION
Prof. Charles A. DiMarzio
Northeastern University
Phone: 617-373-2034
[email protected]
ACKNOWLEDGEMENTS
Thanks to Prof. Ronald Roy, Prof.
Todd Murray and Lei Sui for providing
the phantoms and equipment for the
ultrasonic transducers.
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