Student Conference Medical Engineering Science 2014

Proceedings


Anthology, 2014
291 Pages
T. M. Buzug et al. (Author)

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Proceedings
Student Conference on
Medical Engineering Science 2014
Lübeck, March 12­14, 2014

Conference Chair
Thorsten M. Buzug (Chair), Institute of Medical Engineering, Universität zu Lübeck
Stephan Klein (Co-Chair), Center for Biomedical Technology, University of Applied Sciences Lübeck
Local Coordination
Kanina Botterweck, Medisert, BioMedTec Science Campus
Martina Galler, Medisert, BioMedTec Science Campus
Christian Kaethner, Institute of Medical Engineering, Universität zu Lübeck
Christina Debbeler, Institute of Medical Engineering, Universität zu Lübeck
Gisela Thaler, Institute of Medical Engineering, Universität zu Lübeck
6FLHQWL¿F 3URJUDP &RPPLWWHH
Reginald Birngruber, Institute of Biomedical Optics, Universität zu Lübeck
Henrik Botterweck, Center for Biomedical Technology, University of Applied Sciences Lübeck
Ralf Brinkmann, Institute of Biomedical Optics, Universität zu Lübeck
Thorsten M. Buzug, Institute of Medical Engineering, Universität zu Lübeck
Hartmut Gehring, Clinic of Anesthesiology, University Medical Center Schleswig-Holstein, Campus Lübeck
Heinz Handels, Institute of Medical Informatics, Universität zu Lübeck
Horst Hellbrück, Center of Excellence CoSA, University of Applied Sciences Lübeck
Christian Hübner, Institute of Physics, Universität zu Lübeck
Gereon Hüttmann, Institute of Biomedical Optics, Universität zu Lübeck
Stephan Klein, Center for Biomedical Technology, University of Applied Sciences Lübeck
Martin Koch, Institute of Medical Engineering, Universität zu Lübeck
Martin Leucker, Institute for Software Engineering and Programming Languages, Universität zu Lübeck
Norbert Linz, Institute of Biomedical Optics, Universität zu Lübeck
Amir Mandany Mamlouk, Institute for Neuro- and Bioinformatics, Universität zu Lübeck
Thomas Martinetz, Institute for Neuro- and Bioinformatics, Universität zu Lübeck
Alfred Mertins, Institute for Signal Processing, Universität zu Lübeck
Stefan Müller, Center for Biomedical Technology, University of Applied Sciences Lübeck
Bodo Nestler, Center for Biomedical Technology, University of Applied Sciences Lübeck
Hauke Paulsen, Institute of Physics, Universität zu Lübeck
Ramtin Rahmanzadeh, Institute of Biomedical Optics, Universität zu Lübeck
Martin Ryschka, Laboratory for Medical Electronics, University of Applied Sciences Lübeck
Arndt-Peter Schulz, Laboratory for Biomechanics and Biomechatronics, Universität zu Lübeck
Achim Schweikard, Institute for Robotics and Cognitive Systems, Universität zu Lübeck
Proceedings
VI

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Preface and Acknowledgements
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jointly offer the international master degree course Biomedical
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science oriented programs of the University (Computer Sci-
ences, Medical Computer Sciences, Mathematics in Medicine
and Life Sciences, Molecular Life Science, Medicine) which
contribute to the success of the Medical Engineering Science
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I want to thank all the people who worked with enthusiasm and
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on behalf of all colleagues of the BioMedTec Science Campus,
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Vice President of the Universität zu Lübeck
Chair of the 3
rd
Student Conference
on Medical Engineering Science 2014
Student Conference on Medical Engineering Science
2014
VII


Biochemical Optics I
Improving the stability of an interferometry-based photoacoustic detection
A. Auner, J. Horstmann, C. Buj, R. Brinkmann
Implementation of a reconstruction algorithm for Photoacoustic Tomography 7
M. Münter, C. Buj, J. Horstmann, R. Brinkmann
/LJKW WUDQVPLVVLRQ PHDVXUHPHQWV DQG EHDP VL]H TXDQWL¿FDWLRQ LQ SRUFLQH H\HV 11
J. Rehra, A. Baade, K. Schlott, R. Brinkmann
Parameter optimization for power controlled retinal photocoagulation 15
W. Schwarzer, A. Baade, R. Brinkmann
Biochemical Optics II
6ROGHU PRGL¿FDWLRQ IRU ¿[DWLRQ RI ZRXQG GUHVVLQJV E\ ODVHU UDGLDWLRQ
N. Tödter, M. Wehner, R. Brinkmann
Imaging of heat and chemical burn affected skin ex vivo with coherent anti-stokes Raman (CARS) microscopy 27
J. Pruessner, A. J. Nichols, C. L. Evans, R. Birngruber
Variable, computer-controlled attenuator for use in a time-gated optical scanning system
K. Fuchs, H. Wabnitz
Development and validation of a measuring setup to determine the transmittance
of the illumination system of endoscopes
C. Hain, C. Holthaus
Biochemical Physics
Effect of substrate stiffness on photodynamic therapy sensitivity of various glioma cell lines in vitro
. 6FKHIÀHU - )LVKHU / ' /LOJH 5 %LUQJUXEHU
Photosensitizer delivery by liposomes 47
L. M. Nießen, A. Rodewald, B. Flucke, R. Rahmanzadeh
Investigation of human skin permeability to zinc oxide nanoparticles formulated as sunscreen 51
S. Bugler, Z. Song, R. Brinkmann, A. V. Zvyagin
Measurement of concentrations of photoreactive liquids with high scattering using a differential polarimeter 55
R. Schmidt, S. Müller
Evaluation of the usability of the metadynamics tool PLUMED2 59
R. Kuehn, H. Paulsen
Contents
Student Conference on Medical Engineering Science
2014
IX

Biomedical Engineering I
Characterisation of Pyroelectric Detectors for the Measurement of Medical and Safety-Relevant Gases 67
B. Redmer, R. Buchtal
Design and implantation of a test bed to separate different drugs in multi-infusion system using gas bubbles 71
S. Abdul-Karim, Y. S. Mutlu, J. Schroeter, B. Nestler
Flow Optimisation through Porous Ceramic Throttle 75
M. Ebner, Y. S. Mutlu, B. Nestler, E. Glatt
RPSUHVVLYH EHKDYLRU DQG LVRWURS\ RI VKRUW¿EHU¿OOHG HSR[\ F\OLQGHUV DV DOWHUQDWLYH WHVW PDWHULDO IRU FRUWLFDO ERQH 79
M. Schlitzke, R. Wendlandt, A. Sitzer, H. Handels
Construction of a Guide Wire Handle for the support of the operation of trochanteric hip fractures
S. E. Heinitz, C. Hoffmann, I. Stoltenberg, A. P. Schulz
Evaluation of needle deformation during brachytherapy 87
P. Koch, A. Schlaefer
Biomedical Engineering II
Practice of reprocessing medical single-use devices in Schleswig-Holstein 95
K. Köhler
Software testing as an important component in the development of medical devices 99
' =ZHUV ' 0HVHUHLW + +HHPH\HU
Design Change of a Flow Sensor for Medical Applications ­ Engineering Tests for System Integration
A. K. Laarmann, T. Wenk
Construction and Optimization of a Bidirectional Transducer to Treat Hearing Loss 107
M. Angerer, M. Koch, A. Hellmuth, S. Pieper, M. Bornitz
Design, Development and Comparison of two Different Measurement Devices for Time-Resolved Determination
of Phase Shifts of Bioimpedances 111
R. Kusche, S. Kaufmann, M. Ryschka
A System for Multi-Modal Assessment of Cardiovascular Parameters ­ Design and Measurements 115
A. Malhotra, G. Ardelt, S. Kaufmann, M. Ryschka
Signal Processing
'UDIW RI D PXOWLFKDQQHO HOHFWURP\RJUDSK\ DPSOL¿HU FLUFXLW ZLWK PRQRSRODU OHDG IRU KDQG SURVWKHVHV FRQWURO
N. Pfeiffer, H. Glindemann
Overcoming electrodes shift variances in multi-channel surface EMG recordings for prosthetic controlling 127
T. Friedrich, A. Mertins
Coil Geometry Optimization and Implementation of a Field Generator for Magnetic Particle Spectroscopy
T. Karisch, T. F. Sattel, T. M. Buzug
Signal Chain Optimization in Magnetic Particle Imaging
A. Behrends, M. Gräser, J. Stelzner, T. M. Buzug
Sparse Representation of Motion-Vector Fields using the Wavelet Transform
S. Bäcker, A. Mertins
Proceedings
X

Imaging and Image Computing I
Dictionary learning for sparse image representation with K-SVD algorithm 147
O. Kazankova, A. Mertins
VimbEye Exhibition Demo ­ an AVT machine vision camera application for eye-blink visualisation 151
3 .OHLQ + +DQGHOV 7 0DVFKPDQQ 1 'HK 2 5HXWHU
Localization of Heart Reference Point of a Lying Patient with Microsoft Kinect Sensor 155
Q. Ma, C. Bollmeyer, Y. Zhu, H. Hellbrück
' LPDJLQJ RI D IHPXU ZLWK D .LQHFW VHQVRU DQG WKH ' VFDQQLQJ VRIWZDUH .LQHFW )XVLRQ IRU WKH GHWHUPLQDWLRQ
of coordinates of points in the CT scan of the femur with the software Amira 159
S. Ketelhut, R. Wendtland, H. Handels
Evaluation of optical features for skin thickness compensated NIR triangulation
' +RIPDQQ 7 :LVVHO % :DJQHU 3 6WEHU ) (UQVW $ 6FKZHLNDUG
Imaging and Image Computing II
Analysis of Streamline Intensity Variances for Pulmonary Emboli Visualization in CTA Images 171
N. Leßmann, T. Klinder, R. Wiemker
Evaluation of Methods for Automatic Fish Segmentation 175
A. Hänler, E. Gutzeit, A. Mertins
An Algorithm for Automated Model Generation of in Vitro Cell Images 179
F. Kaiser, A. Madany Mamlouk
Subtraction Imaging on Double Inversion Recovery Images for Cortical Lesion Detection
in Patients with Multiple Sclerosis
:LQWHU 5 =LYDGLQRY 0 * 'Z\HU
Magnetic Resonance Imaging I
Development and Validation of a Tool for Pulse Wave Velocity Measurements in MRI Phase Contrast Data 191
A. Timmermeyer, M. A. Koch, A. Frydrychowicz
Automatic Image Quality Assessment of Head MRI Study Data 195
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KDVLQJ WKH =HEUD 7KH 4XHVW IRU WKH 2ULJLQ RI D 6WULSH $UWLIDFW LQ 'LIIXVLRQ:HLJKWHG 05,
199
M. Meyer, A. Biber, M. A. Koch
Motion Correction for MRI Exploiting Sparsity
H. Lüthje, A. Mertins
Visualizing Microscopic Hemorrhages with Susceptibility-Weighted Imaging (SWI) for Forensic Applications 207
A. Biber, M. Meyer, M. Koch
Student Conference on Medical Engineering Science
2014
XI

Magnetic Resonance Imaging II
Connection between structural and functional Connectivity: A Magnetic Resonance Study 215
- LHOXFK 7 % '\UE\ 1 %UJJHPDQQ + +DQGHOV + 5 6LHEQHU
Generation of an Accurate Tetrahedral Model of a Brain with Chronic Stroke Lesions
for TMS and tDCS Field Calculations 219
S. Minjoli, A. Thielscher
Spectral editing at 7 T: In vivo GABA separation in mouse brain
A. Niebergall, J. Baudewig, A. Moussavi, S. Boretius
Radiosurgery beyond cancer: Real-time tracking and treatment planning for non-invasive treatment
of cardiac arrhythmia 227
S. Ipsen, O. Blanck, G. Liney, F. Bode, A. Schweikard, P. Keall
LUMEN
Drug release from bone implants: a phenomenological modeling approach
- .ULHJHU 7 .OHSVFK 7 :HQ]HO 'DPLDQL 6W .OHLQ
Modeling diffusion of gentamicin eluted from a coated intramedullary nail
T. Klepsch, J. Krieger, H. Botterweck
Investigation of particle dynamics near the endothelial glycocalyx by multi focus FCS
/ .UHXW]EXUJ 9 'ROH]DO +EQHU
Holographic detection for non-contact Photoacoustic Tomography 247
C. Buj, J. Horstmann, M. Münter, R. Brinkmann
A physical model of perfused pulsating tissue compartments ­ Design concept 251
B. Weber, B. Nestler, V. Hennicke
Measuring the oxygen content of the cerebral efferent vessels 255
K. Rackebrandt, H. Gehring
Insight in Scanner Construction for a Dynamical Field Free Line for Magnetic Particle Imaging 259
M. Weber, K. Bente, T. M. Buzug
$Q DSSURDFK IRU SDWLHQW VSHFL¿F PRGHOLQJ RI WKH DRUWLF YDOYH OHDÀHWV
J. Hagenah, M. Scharfschwerdt, C. Metzner, A. Schlaefer, HH. Sievers, A. Schweikard
Experimental Evaluation Optimization of a UWB Localization System for Medical Applications 267
C. Bollmeyer, H. Hellbrück, H. Gehring
A System for In-Ear Pulse Wave Measurements 271
S. Kaufmann, A. Malhotra, G. Ardelt, N. Hunsche, K. Breßlein, R. Kusche, M. Ryschka
Proceedings
XII



1
Biomedical Optics I
Student Conference on Medical Engineering Science
2014
1






Implementation of a reconstruction algorithm for
Photoacoustic Tomography
M. M¨unter, C. Buj, J. Horstmann and R. Brinkmann
Abstract--Photoacoustic Imaging has become increasing pop-
ular in recent years. It is a non-ionizing imaging-technique with
high potential in medicine, especially suited to image the vascular
system. This paper is based on a full-field surface detection system
by interferometry. Therefore an absorber detection by mathe-
matical time reversal reconstruction is needed. In this paper,
the results of a two-dimensional delay-and-sum reconstruction
algorithm for different sizes of point absorbers are presented,
which have been done by Matlab. It has been shown that the two
dimensional reconstruction is reliable for spherical absorbers.
I. I
NTRODUCTION
Photoacoustic Imaging is a tomographic technique, which
combines the advantages of light and ultrasound. It is based
on the photoacoustic effect, shown schematically in Fig.
1. The absorption of electromagnetic radiation is followed
by temperature increase in the absorber, which results in a
rising pressure in the absorber. This causes in thermoelastic
expansion and pressure wave emission.
Fig. 1.
Schematic representation of the photoacoustic effect
State-of-the-art limitations are a long acquisition time and the
need for acoustic contact, such as the use of a piezoelectric
sensor system to detect the pressure waves [1]. Fig. 2 introduce
a novel non-contact full-field approach by the Medical Laser
Center Luebeck [2] for Photoacoustic Tomography. The detec-
tion system consists of a Mach-Zehnder interferometer and a
M. M¨unter, Medizinische Ingenieurwissenschaft, Universit¨at zu L ¨ubeck; the
work has been carried out at the Institute of Biomedical Optics, Universit¨at
zu L ¨ubeck, Luebeck, Germany (e-mail: muenter@miw.uni-luebeck.de).
C. Buj is with the Institute of Biomedical Optics, Universit¨at zu L ¨ubeck,
Luebeck, Germany (e-mail: buj@bmo.uni-luebeck.de).
J. Horstmann is with the Medical Laser Center Luebeck GmbH, Luebeck,
Germany (e-mail: horstmann@bmo.uni-luebeck.de).
R. Brinkmann is with the Institute of Biomedical Optics,Universit¨at zu
L ¨ubeck, Luebeck, Germany and the Medical Laser Center Luebeck GmbH,
Luebeck, Germany (e-mail: brinkmann@mll.uni-luebeck.de).
Fig. 2. Holographic Photoacoustic Imaging. Excitation pulses are applied to
the volume. The pressure induced surface displacements owing to thermoe-
lastic expansion of absorbers are recorded by an optical-holographic detection
unit.
high-speed CCD-camera (Basler Pilot piA1600-35g), which
captures the object and reference beam from the detection
laser with a frame rate of 20 Hz. The detection laser (CryLas
FTSS 355-50, pulse duration 1 ns) is a frequency doubled
Nd:YAG laser with a wavelength of 532 nm. For excitation a
flashlamp pumped Nd:YAG (Quantel YG571C, pulse energy
25 mJ, spot size 5 mm, repetition rate 10 Hz) laser is used with
a pulse duration of 6 ns and a wavelength of 1064 nm. The
detection of surface deformations is based on the principle of
Electronic Speckle Pattern Interferometry (ESPI), a method
for measuring very small changes in distances in nm range
[3], [4]. In order to calculate the position of the absorber, a
appropriate reconstruction method must be implemented.
II. M
ATERIAL AND
M
ETHODS
The mathematical software programming language Mat-
lab (Mathworks) is used, to develop an algorithm for two-
dimensional reconstruction and to visualize the first concepts.
Student Conference on Medical Engineering Science
2014
7

An adjusted delay-and-sum algorithm on the basis of the work
of Carp Venugopalan [5] and Hoelen du Mul [6] is
implemented to reconstruct the position of the acoustic sources
after data acquisition. The sequences of the algorithm are
schematically visualized in Fig. 3. Due to hardware limitations,
Fig. 3.
Flow chart of the Photoacoustic Imaging program, based on the
delay-and-sum principle.
an equidistant data acquisition was not possible. For this rea-
son, the missing data was interpolated with a shape-preserving
cubic interpolation algorithm for better results . To minimize
the influence of noise of the measured data, a 4x4 Gaussian
filter was applied. Furthermore, to remove background noise,
a simple threshold filter was used to extract artefacts. The
threshold filter extracted the values, who are less than 90 %
of the maximum intersection value.
A. Principle of triangulation
The approach is based on the principle of triangulation.
When the time of surface displacement and the velocity of
the spherical wave are known, the location of the absorber
can be calculated.
c =
m
t
m = c · t,
(1)
where
m is the distance from the absorber to the detection
layer,
t the time from absorption to detection and c the velocity
of the sound wave. The propagation velocity of the acoustic
wave in the silicone phantom is measured to be approximately
830
m
s
to
1050
m
s
. The varying of the velocity is caused by
the hardening of the silicone. For example, there are three
sensors detecting a spherical wave from an unknown source
at different times
t
1
, t
2
, t
3
. The radius (calculated distances
m
1
, m
2
, m
3
) of the circles make up the possible sources of
the spherical wave. If there are at least three sensors in two
dimensions, a definite source can be predicted at the point
of intersection. In addition, depending on the distance to the
center of the spherical wave, the calculated places of origins
were attenuated with a weighting factor
w, which is calculated
through a Gaussian function.
B. Phantom
The two-dimensional reconstruction is used for a phantom,
consisting of three components. A black-stained silicone ball
(absorption coefficient
= 29.6cm
-1
for
= 1064nm), who
serves as an absorber, is stored in a transparent silicone cuboid.
The area, which is sampled is coated with a white thin silicone
layer, in order to enable a better detection.
The absorber is usually located in
5mm ± 1mm depth be-
low the detection surface. The size of the entire cuboid is
10x45x10mm (height, width, depth), shown in Fig. 4.
Fig. 4.
Silicone phantom with a black-stained silicone ball in the center
The high-speed-camera records an image with a resolution
of
1200x1600 pixels, whereby a pixel correlates to 7.4m.
Therefore, an area of
8.88 mm x 11.74 mm is captured with
an imaging scale of 1:1. Fig. 5 shows 6 representative images
at different time steps of the surface deformation, which was
induced by the spherical pressure wave. The gray values can
Fig. 5.
Phase difference images at different time steps, relative to the point
of excitation a) 4,618
s b) 4,760 s c) 5,246 s d) 5,801 s e) 6,334 s
f) 7,568
s
Proceedings
8

be converted into nanometre scale from
-/2 to +/2. For
the two-dimensional reconstruction a line from the data over
time was extracted, as shown in Fig. 6.
Fig. 6.
Extracted sensor line with captured surface deformation
Depending on the position of a pixel and the corresponding
measured time, when the spherical wave is measured, a circle
is stored in an array. The occurred intersections provide the
position and form of the reconstructed absorber.
III. R
ESULTS AND
D
ISCUSSION
Two-dimensional images of two absorbers with different
diameter were reconstructed, to show the abilities of the delay-
and-sum-algorithm. The images were taken at 114 different
time steps for a 2 mm point absorber and for a 1 mm absorber
at 168 time steps. Furthermore, the images were interpolated
to 0.01
s steps from 0 s to 1000 s. A line segment above
the absorber were taken for reconstruction. Fig. 7 shows the
reconstructed image without a threshold filter and points out
the impact of ring artefacts due the art of reconstruction.
To reduce these artefacts, the results were threshold filtered,
shown in Fig. 8.
Fig. 7.
Reconstructed image from 2 mm absorber without threshold filter
In the reconstruction the first 2 mm absorber is located in 4.2
mm depth with a reconstructed diameter of 1.7 mm. As Fig.
8 visualizes, the largest probability of presence of depth is
5
mm.
Fig. 8.
Reconstructed 2 mm absorber with
c = 830
m
s
The 1 mm absorbers is located in 4 mm depth and has a
reconstructed diameter off 1.2 mm.
Fig. 9.
Reconstructed 1 mm absorber with
c = 1054
m
s
The results are concluded in Table I. The algorithm has also
been tested for the reconstruction of two absorbers, shown in
Fig. 10. When the displacement of the first sound wave of
the first absorbers propagates, the second wave arrives and
interferes with the first one.
TABLE I
M
EASURED AND RECONSTRUCTED DIAMETER AND DEPTH
Absorber
rec. Diameter
meas. depth
rec. depth
1 mm
1.2 mm
4 mm
4 mm
2 mm
1.7 mm
4.2 mm
4.3 mm
Student Conference on Medical Engineering Science
2014
9

Fig. 10.
Reconstructed image of two point absorbers
IV. C
ONCLUSION
In this paper, a two-dimensional reconstruction for the non-
contact photoacoustic imaging setup of the Medical Laser
Center Luebeck was developed. The 1 mm absorber, in com-
parison to the 2 mm absorber, has a more spherical shape and
also provides more accurate values for diameter and depth.
In addition, the maximum of all intersections for the 1 mm
absorber was at a depth of 4.5 mm, which corresponds to the
depth of the phantom. A first estimate about the depth can
be determined relatively precisely, but is caused by varieties
by the different values of propagation speed. Additionally, the
shape and diameter can only be assumed, which is unavoidable
due to the art of reconstruction.
A. Outlook
On the one hand, a nearly exact depth and diameter of the
absorber could be found, so that the type of reconstruction
was sufficient for the initial phase of the project. On the
other hand, more proved reconstruction methods [7] could
be investigated. Especially the statistical analysis about depth,
shape and diameter in comparison to established tools, like
optical coherence tomography should be treated and could help
to evaluate the quality of the reconstruction by triangulation
in detail. In the further course, the behaviour in the medium
to the absorber should be more investigated to improve the re-
construction results. In particular, different types of absorbers,
shapes, structures should be measured.
R
EFERENCES
[1] M. Xu and L. V. Wang, "Photoacoustic imaging in biomedicine" Review
of Scientific Instruments, vol. 77, no. 4, pp. 041101 - 041101-22, Apr.
2006 .
[2] J. Horstmann and R. Brinkmann, "Non-contact Photoacoustic Tomogra-
phy using holographic full field detection", Proc. of OSA-SPIE, vol. 8800,
pp. 880007-1, 2013.
[3] R. B¨uttner, "Untersuchung und Aufbau eines Laser-Speckle-Abstand- und
Geschwindigkeitssensors", dissertation, Ernst-Moritz-Universit¨at Greif-
swald, Institut f¨ur Physik , 2008 .
[4] H. Helmers and J. Burke, "Performance of spatial vs. temporal phase
shifting in ESPI", Proc. SPIE, vol. 3744, pp. 188-199, 1999.
[5] S. A. Carp and V. Venugopalan, "Optoacoustic imaging based on the inter-
ferometric measurement of surface displacement" Journal of Biomedical
Optics, vol. 12, no.6, pp. 064001, Nov./Dec. 2007 .
[6] C. A. Hoelen and F. F. M. de Mul, "Image reconstruction for photoa-
coustic scanning of tissue structures", Applied Optics, vol. 39, no. 31,
pp. 5872-5883, 2000 .
[7] M. Xu and L. V. Wang, "Universal back-projection algorithm for photoa-
coustic computed tomography", Phys. Rev. E, vol. 71, no. 1, pp. 016706-1
- 016706-7, 2005 .
Proceedings
10

Light transmission measurements and beam size
quantification in porcine eyes
J. Rehra, A. Baade, K. Schlott, and R. Brinkmann
Abstract--Laser photocoagulation is a leading treatment in a
range of retinal diseases. Besides the therapeutic effects, every
treatment produces an irreversible impairment of the neural
retina which should be as low as possible. The beam diameter
at the fundus as well as the light transmission through the eye
influence the appearance of the lesion as well as the accuracy
of the non-invasive temperature measurement. In this work, a
special holder for porcine eyes that minimizes the deformation
of the eye was designed and constructed. Using this holder,
measurements to determine the transmission and the beam
diameter at the fundus were performed for a wavelength of
532 nm. The transmission through porcine eyes was found to
be
86 %, measured behind a 4 mm-hole in the central fundus,
the beam diameter was found to be in good agreement with the
setting selected at the slit lamp.
I. I
NTRODUCTION
The treatment of retinal diseases by photocoagulation is
being performed since the 50s of the last century. The first
applications were done with focused sunlight by Meyer-
Schwickerath [1], although the development of the Laser in
the 1960s enabled the real breakthrough of the technique [2].
Until today, the laser-photocoagulation is a leading standard
in the treatment of a range of retinal diseases such as macular
edema and the diabetic retinopathy [3], [4].
The therapeutic effect of photocoagulation is based on
thermal damaging of the retina by absorption of light. The
retinal pigment epithelium (RPE) is rich in the pigment
melanin which has a high absorption coefficient in the range
of visible light. Absorbed light is transduced into heat by
internal conversion which leads to a temperature rise in the
surrounding tissue. Proteins in the adjacent tissue are denatured
if a temperature threshold is reached, producing a small area of
necrosis. Nowadays, green light emitting lasers are commonly
used for coagulation due to a reasonable compromise between
a low diffusion in the sclera and a high absorption in the RPE
[4].
Beside the positive effects, every application of intense light
produces a non-reversible impairment in the eye which should
be as low as possible without losing its clinical effect. It is
desired to produce a lesion just above the limit of damaging,
independent of the conditions of the treated fundus and other
J. Rehra, Medizinische Ingenieurwissenschaft, Universit¨at zu L¨ubeck,
the work has been carried out at Medical Laser Center L¨ubeck, (e-mail:
rehra@miw.uni-luebeck.de).
A. Baade is with Medical Laser Center L¨ubeck (telephone: +49 (0)451
500 6521, e-mail: baade@mll.uni-luebeck.de).
K. Schlott is with Medical Laser Center L¨ubeck (telephone: +49 (0)451
500 6417, e-mail: schlott@mll.uni-luebeck.de).
R. Brinkmann is with Medical Laser Center L¨ubeck and with Institute for
Biomedical Optics, Universit¨at zu L¨ubeck (telephone: +49 (0)451 500 6507,
e-mail: brinkmann@bmo.uni-luebeck.de).
influencing factors. However, a wide range of variations, e.g.
pigmentation of the fundus, is found even in the same eye.
This poses difficulties in the dosage of the laser power for the
ophthalmologist.
The decisive factor for the effect of the coagulation is the
temperature reached in the ocular fundus. Optoacoustics, beside
other approaches as reflectometry, magnetic resonance imaging
and optical coherence tomography, looks the most promising
concerning a practically relevant real-time measurement of the
temperature in the fundus of a patient during treatment [5].
Using the optoacoustic effect, the light energy of a short laser
pulse can be transformed into acoustic energy. The absorption
of light in a tissue causes a temperature rise, depending on the
properties of the tissue and the parameters of the laser. This
temperature rise leads to an expansion of the affected tissue. If
the deposed energy per pulse is high enough within a short time
(thermal confinement time), each laser pulse produces a bipolar
pressure wave propagating through the tissue as an ultrasonic
wave. Measuring these ultrasonic wave, the temperature in the
laser focus can be determined after a calibration with a known
temperature [6].
The project "Automatic Photocoagulation of the Retina"
(AutoPhoN) at the Medical Laser Center L¨ubeck GmbH
(MLL) uses this optoacoustic method to realize an online
dosimetrie during treatment of the ocular fundus. For that
application, a second probe laser is coupled into the beam path
of the treatment laser. It repeatedly measures the temperature
with nanosecond pulses. Surveilling the temperature profile
during treatment, the treatment laser can be stopped when
reaching a predefined temperature, corresponding to the desired
coagulation [5].
The exact calculation of the temperature depends on a set
of parameters as described in [6], [7]. The beam diameter and
profile have a great bearing on the calculation and have to
be known correctly, as well as the exact power applied to the
fundus which is influenced by absorption in the setup and the
ocular media. In this work, the beam diameter at the back
of the eye was investigated. The experiments are performed
on enucleated porcine eyes, fixed in a newly designed eye
holder. As a deformation of the eye can lead to distortion of
the laser beam and therefore to inaccuracies in the temperature
calculation, the eye is nearly completely enclosed by the holder
to prevent deformation.
II. M
ATERIAL AND
M
ETHODS
A. Eye holder and basic setup
The eye holder is designed using SolidWorks and manufac-
tured in the mechanical workshop of the Universit¨at zu L¨ubeck.
Student Conference on Medical Engineering Science
2014
11



Fig. 5.
Beam captured with WinCam at a preselected beam size of
1000 m
with lines of measurement. The diameter is calculated as average over the
eight measurements.
changed during the imaging process. It is tested by changing the
beam size from 1000 m to 500 m comparing the determined
scales. The average diameters are listed in Table I.
TABLE I
A
VERAGE DIAMETERS OF BEAMS
(
N
= 4)
WITH STANDARD DEVIATION
MEASURED FOR PRESELECTED BEAM SIZES
Preselected beam size
Measured beam size
m
m
50
55.3
± 5.5
100
114.5
± 12.2
200
203.0
± 11.8
300
297.7
± 12.2
500
436.8
± 73.6
1000
977.3
± 34.0
The measured beam sizes at four specimen correspond to the
beam sizes preselected at the slit lamp within the accuracy of
the measurement. The combination of the slit lamp, the contact
lens used and enucleated porcine eyes with a diameter of
approximately 24.5 mm therefore does not leads to significant
distortions of the laser beam and the beam size on the fundus
can be presumed as preselected at the slit lamp.
IV. C
ONCLUSIONS
The used setup with the new designed eye holder offers
good conditions for the testing of enucleated eyes within a
small variance of the diameter around 24.5 mm. For other sizes,
for example for rabbit eyes, a new eye holder with different
proportions would have to be manufactured. An evaluation of
coagulation treatment with the new eye holder and the full
AutoPhoN-setup compared to the setup as used before is still
pending.
The transmission through the enucleated porcine eye at
a wavelength of 532 nm was determined by (86
± 2) % in
accordance to literature for human eyes [9], [10].
It is shown that the beam size preselected at the slit lamp
is correctly applied to the fundus. Consequently, there is no
need to adjust the temperature measurement to accommodate a
deviation of the beam diameter from the selected one. An exact
determination of the beam profile could be done by further
experiments whereas the images of the beams suggest that
the assumption of a top hat profile is better than a gaussian
approach to simulate the temperature.
R
EFERENCES
[1] G. Meyer-Schwickerath, "Lichtkoagulation," Albrecht von Graefes Archiv
f¨ur Ophthalmologie Vereinigt mit Archiv f¨ur Augenheilkunde, vol. 156,
pp. 2­34, Jan. 1954.
[2] D. V. Palanker, M. S. Blumenkranz, and M. F. Marmor, "Fifty years of
ophthalmic laser therapy.," Archives of ophthalmology, vol. 129, pp. 1613­
1619, Dec. 2011.
[3] M. Nentwich and M. Ulbig, "Diabetische Retinopathie," Der Diabetologe,
vol. 6, pp. 491­502, Aug. 2010.
[4] "Laserkoagulation," in Retina: Diagnostik und Therapie der Erkrankun-
gen des hinteren Augenabschnitts (U. Kellner and J. Wachtlin, eds.),
pp. 77­82, Stuttgart: Thieme, 2008.
[5] K. Schlott, S. Koinzer, L. Ptaszynski, M. Bever, A. Baade, J. Roider,
R. Birngruber, and R. Brinkmann, "Automatic temperature controlled reti-
nal photocoagulation.," Journal of biomedical optics, vol. 17, p. 061223,
June 2012.
[6] R. Brinkmann, S. Koinzer, K. Schlott, L. Ptaszynski, M. Bever, A. Baade,
S. Luft, Y. Miura, J. Roider, and R. Birngruber, "Real-time temperature
determination during retinal photocoagulation on patients.," Journal of
biomedical optics, vol. 17, p. 061219, June 2012.
[7] R. Birngruber, F. Hillenkamp, and V. P. Gabel, "Theoretical investigations
of laser thermal retinal injury.," Health physics, vol. 48, pp. 781­796,
June 1985.
[8] M. D. Abr`amoff, P. J. Magalh~aes, and S. J. Ram, "Image processing with
ImageJ," Biophotonics International, vol. 11, no. 7, pp. 36­42, 2004.
[9] E. A. Boettner and J. R. Wolter, "Transmission of the ocular media.,"
Investigative Ophthalmology Visual Science, vol. 1, no. 6, pp. 776­783,
1962.
[10] E. A. Boettner, "Spectral transmission of the eye," Contract AF41(609)-
2966. USAF School of Aerospace Medicine. Aerospace Medical Division
(AFSC). Brooks Air Force Base, 1967.
Proceedings
14

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Excerpt out of 291 pages

Details

Title
Student Conference Medical Engineering Science 2014
Subtitle
Proceedings
College
University Lübeck
Course
Studierendentagung
Author
Year
2014
Pages
291
Catalog Number
V268650
ISBN (eBook)
9783656596509
ISBN (Book)
9783656596486
File size
101500 KB
Language
English
Series
Student Conference on Medical Engineering Science
Notes
Autor: T. M. Buzug et al. Datei ist ein Dummy, korrekte Version folgt individuelles Cover folgt Bitte der Reihe Student Conference on Medical Engineering Science V200266 zuordnen Format A4, Cover und einzelne Seiten in Farbe
Tags
Biomedical Engineering, X-Ray and Computed Tomography, Magnetic Particle Imaging, Magnetic Resonance Imaging, Biomedical Optics, Medical Image Computing, Biochemical Physics, Signal Processing, Imaging and Image Computing, LUMEN, Medisert
Quote paper
T. M. Buzug et al. (Author), 2014, Student Conference Medical Engineering Science 2014, Munich, GRIN Verlag, https://www.grin.com/document/268650

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