Experimental Study of the
Magnetohydrodynamic (MHD)
Effect with respect to
Intracardiac ECG Signals
W. B. Buchenberg1, G. Hoppe1, R. Lorenz1, W. Mader2, P. Laudy3,
C. Bienek4 and B. Jung1
1Dept.
of Radiology, Medical Physics, University Medical Center, Freiburg, Germany,
2Freiburg Center for Data Analysis and Modeling, Albert-Ludwigs-University, Freiburg, Germany,
3CardioTek B.V., Maastricht-Airport, Netherlands,
4R&D, Schwarzer GmbH, Heilbronn, Germany
20.09.2013
ELECTROPHYSIOLOGIC (EP) STUDIES
• assess cardiac electrical system
• diagnosis and therapy of EP disorders
• catheter guidance:
 X-ray fluoroscopic imaging
disadvantages:
 x-ray exposure (staff + patient)
 poor tissue contrast
 alternative imaging modalities:
Magnetic Resonance Imaging
(MRI)
1
SERVIER Medical Art
1
MAGNETOHYDRODYNAMIC (MHD) EFFECT
surface ECGs
B ≈ 1.5 T
B=0T
distortion of surface ECGs1,2,3 and intracardiac ECGs (iEGMs)4
1 Tenforde
et al. Bioelectromagnetics 1983;4:1-9
3 Gupta et al. IEEE 2008; 55(7):1890-96
2 Tenforde
4 Tse
Biophysics & Molecular Biology 2005;151:521-23
et al. ISMRM2012 talk #206
MAGNETOHYDRODYNAMIC (MHD) EFFECT
1 Gupta
induced voltage1,2:
U M R I,ca lc  v  B 0  d
if v  B 0
0
v
3
mean flow velocity of axial
symmetrical flow profile
B0 external magnetic field
d
et al. IEEE 2008; 55(7):1890-96
2 Kolin
electrode distance
A. Review of Scientific Instruments 1945;16(6): 109-116
3 SERVIER
Medical Art
OBJECTIVES
establish experimental setup for simulating MHD signal with
common clinical EP-devices
 characterization of measured MHD-signal Umeas (bipolar):
 magnetic field strength
 electrode distance
 filter settings of recording modality
 comparison of Umeas with UMRI,calc from MR flow measurements

implementation of methods to remove MHD signals from
intracardiac ECG signal (iEGMs)
EXPERIMENTAL SETUP
simulate electrical conductivity of blood: dist. H2O + NaCl
1.5 Tesla
50
bpm
EXPERIMENTAL SETUP
simulate electrical conductivity of blood: dist. H2O + NaCl
1.5 Tesla
50
bpm
VAD (Ventricular Assist Device):
EXPERIMENTAL SETUP
simulate electrical conductivity of blood: dist. H2O + NaCl
1.5 Tesla
50
bpm
UMHD
(1)
catheter positioning:
EXPERIMENTAL SETUP
simulate electrical conductivity of blood: dist. H2O + NaCl
1.5 Tesla
50
bpm
(1)
EXPERIMENTAL SETUP
simulate electrical conductivity of blood: dist. H2O + NaCl
1.5 Tesla
50
bpm
(1)
MRI FLOW MEASUREMENTS
imaging parameters
TE / TR [ ms ]
4.9 / 7.2
temp. res. [ ms ]
2D slice
7.2
voxel size
0.9 x 0.9 x 6.0
[ mm³ ]
VENC IN / THROUGH- 0.15 / 0.55
PLANE [ m/s ]
v z [m /s]
v  B0
UMHD,PP
RESULTS – MHD SIGNAL vs. TIME
𝑼MHD,PP [mV]
1/10
2/9
3/8
4/7
5/6
8.30 ± 0.27
8.34 ± 0.17
6.62 ± 0.12
4.92 ± 0.05
1.23 ± 0.12
UMHD,PP
RESULTS – MHD SIGNAL vs. TIME
1/10
2/9
3/8
4/7
5/6
𝑼MHD,PP [mV]
8.30 ± 0.27
8.34 ± 0.17
6.62 ± 0.12
4.92 ± 0.05
1.23 ± 0.12
UMRI,calc [mV]
8.67 ± 1.43
8.47 ± 1.40
6.59 ± 1.09
5.00 ± 0.83
1.08 ± 0.18
RESULTS – MHD VOLTAGE vs. DISTANCE
Δv [cm/s]
24.3 ± 1.0
MRI
~ 25.3
RESULTS – MHD VOLTAGE vs. MAGNETIC FIELD
Δv [cm/s]
24.3 ± 1.0
MRI
Δv [cm/s]
~ 25.3
1/10
2/9
3/8
4/7
5/6
22.4 ± 1.1
25.1 ± 1.3
24.1 ± 1.2
24.0 ± 1.2
24.0 ± 1.2
RESULTS – MHD VOLTAGES
(2/9)
RESULTS – MHD VOLTAGES
high pass filtered (fcut off = 0.05 Hz)
(2/9)
RESULTS – HIGH PASS FILTERS
• UMHD,PP (fcut off : 0.2 Hz) ≈ UMHD,PP (fcut off : 0.05 Hz)
(within ± 4%)
UMHD,PP
100
• UMHD,PP (fcut off : 40 Hz)
remaining UMHD,PP ≤ 3%
80
60
40
• UMHD,PP (fcut off : 80 Hz)
remaining UMHD,PP ≤ 2%
20
0
0.05
0.2
40
80
DISCUSSION & OUTLOOK
 experimental setup established successfully
 MHD potential (bipolar measured) was characterized:
• shows linear dependency on B0, d
• follows characteristics of velocity pattern
• same order of magnitude as intracardiac signals1
 MR flow data - post processing:
• MHD signal reconstructed using MR velocity data
• measured and calculated MHD signal agree very well
Outlook
iEGM data correction based on MR flow measurements
1 Cassidy
et al. Circulation 1984;70(1):37-42.
THANK YOU FOR YOUR ATTENTION!
ACKNOWLEDGEMENTS:
Christoph Benk
Mr. Knieriem, St. Jude Medical
Mr. Simon, Mr. Baecke, seleon gmbh
Grant support by
EUROSTARS Program Grant #01QE1004D