Student Conference Medical Engineering Science 2014

Proceedings

Anthology , 2014 , 291 Pages

Medicine - Biomedical Engineering

The Student Conference on Medical Engineering Science is an annual event at the BioMedTec Science Campus Luebeck. The Student Congress is organized by the University of Lübeck and Medisert and is supported by NORGENTA, the life science cluster agency in north Germany. Master students of programs related to medical engineering science present results of their recent research projects.
Die Studierendentagung Medizintechnik ›findet jährlich auf dem BioMedTec Wissenschaftscampus Lübeck statt. Der Kongress wird von der Universität zu Lübeck und Medisert organisiert und von der norddeutschen Life-Science-Clusteragentur NORGENTA unterstützt. Studierende in Masterprogrammen der Medizintechnik und der Lebenswissenschaften präsentieren die Ergebnisse ihrer jüngsten Forschungsprojekte.

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Exhibitors

Cooperation Partners

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Proceedings

Student Conference on

Medical Engineering Science 2014

Lübeck, March 12­14, 2014

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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

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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

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Student Conference on Medical Engineering Science

2014 shows a steady growth in quality and quantity of scien-

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BioMedTec Science Campus Lübeck in cooperation with Nor-

genta, the North German Life Science Agency, has spared no

effort to provide a wonderful conference, where master stu-

dents of the campus present their recent research results to

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show how physics, engineering and computer sciences can

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ference offers a good opportunity for both students and com-

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Students from the Life Sciences programs at the BioMedTec

Science Campus present their results from projects carried out

at the laboratories and institutes of Lübeck's Universities, in

international research facilities and research-oriented industri-

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established at the University of Applied Sciences Lübeck for

decades and Medical Engineering Science (Medizinische Inge-

nieurwissenschaft ­ MIW) is an important bachelor and master

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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thanks go to the technology transfer platform Medisert of the

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of Kanina Botterweck and her Medisert team has contributed

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on behalf of all colleagues of the BioMedTec Science Campus,

I especially want to thank Christian Kaethner and Christina

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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

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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

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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

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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

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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

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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

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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

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1

Biomedical Optics I

Student Conference on Medical Engineering Science

2014

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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: [e-mail]).

C. Buj is with the Institute of Biomedical Optics, Universit¨at zu L ¨ubeck,

Luebeck, Germany (e-mail: [e-mail]).

J. Horstmann is with the Medical Laser Center Luebeck GmbH, Luebeck,

Germany (e-mail: [e-mail]).

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: [e-mail]).

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

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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

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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

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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

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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:

[e-mail]).

A. Baade is with Medical Laser Center L¨ubeck (telephone: +49 (0)451

500 6521, e-mail: [e-mail]).

K. Schlott is with Medical Laser Center L¨ubeck (telephone: +49 (0)451

500 6417, e-mail: [e-mail]).

R. Brinkmann is with Medical Laser Center L¨ubeck and with Institute for

Biomedical Optics, Universit¨at zu L¨ubeck (telephone: [phone],

e-mail: [e-mail]).

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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• College: University Lübeck
• Course: Studierendentagung
• Author: T. M. Buzug et al. (Author)
• Publication Year: 2014
• Pages: 291
• Catalog Number: V268650
• ISBN (eBook): 9783656596509
• ISBN (Book): 9783656596486
• Language: English
• 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