IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 54, NO. 9, SEPTEMBER 2007
1679
Testing the Immunity of Active Implantable Medical
Devices to CW Magnetic Fields up to 1 MHz by an
Immersion Method
Valentin Buzduga3 , Member, IEEE, Donald M. Witters, Senior Member, IEEE, Jon P. Casamento, Member, IEEE,
and Wolfgang Kainz, Member, IEEE
Abstract—This paper presents a magnetic-field system and
the method developed for testing the immunity of the active
implantable medical devices to continuous-wave magnetic fields in
the frequency range up to 1 MHz. The system is able to produce
magnetic fields of 150 A/m for frequencies up to 100 kHz and
strengths decreasing as 1/f between 100 kHz and 1 MHz, with
uniformity of the field within 2.5% in the volume for tests.
To simulate human tissue, the medical device, together with its
leads, is placed on a plastic grid in a saline tank that is introduced
in the magnetic field of the induction coil. This paper offers an
alternative for the injection voltage methods provided in the actual
standards for assessing the protection of the implantable medical
devices from the effects of the magnetic fields up to 1 MHz. This
paper presents the equipment and signals used, the test procedure,
and results from the preliminary tests performed at the Food
and Drug Administration–Center for Devices and Radiological
Health on implantable pacemakers and neurostimulators. The
new system and test method are useful for the EMC research on
the implantable medical devices.
Index Terms—Electromagnetic compatibility (EMC), electromagnetic interference (EMI), implantable biomedical devices,
magnetic fields, pacemakers.
I. INTRODUCTION
BRIEF survey on the applicable standards shows that
the active implantable medical devices (AIMDs) have
to comply with certain requirements for protection from the
effects of the continuous-wave (CW) magnetic fields. For
example, the following requirements are listed from the AIMD
standards PC69 [1], EN45502-2-1 [2], and ISO14708-1 [3]:
1) protection from persisting malfunction due to CW sources
(PC69, clause 4.3.1).
A
Manuscript received August 28, 2006; revised January 5, 2007. This paper
was supported in part by an appointment to the Research Fellowship Program for
the Center for Devices and Radiological Health administered by the Oak Ridge
Associated Universities through a contract with the U.S. Food and Drug Administration. The opinions and conclusions stated in this paper are those of the
author(s) and do not represent the official position of the Department of Health
and Human Services. The mention of commercial products, their sources, or
their use in connection with material reported herein is not to be construed as
either an actual or implied endorsement of such products by the Department of
Health and Human Services. Asterisk indicates corresponding author.
V. Buzduga is with Scantek, Inc., Columbia, MD 21046 USA. He is also
with Capitol College, Laurel, MD 20708 USA (e-mail: buzdugav@yahoo.com).
D. M. Witters, J. P. Casamento, and W. Kainz are with the Food and Drug
Administration, Center for Devices and Radiological Health, Rockville, MD
20852 USA (e-mail: donald.witters@fda.hhs.gov; jon.casamento@fda.hhs.gov;
wolfgang.kainz@fda.hhs.gov).
Digital Object Identifier 10.1109/TBME.2007.893502
2) temporary response to CW sources (PC69 clause 4.4.1).
3) protection from sensing modulated electromagnetic fields
as cardiac signals (PC69, clauses 4.5.1.1 and 4.5.2.1).
4) protection from ac magnetic field exposure in the range 1
to 140 kHz (PC69, clause 4.8.1).
5) protection from electromagnetic nonionizing radiation
(ISO14708-1, clause 27).
Compliance with requirements 1) and 4) is confirmed if after application of the test signal, the AIMD functions prior to the test
without further adjustment. For protection 2), the AIMD should
operate during the test in its set mode or in the interference mode
as described by the manufacturer. The compliance with requirement 3) is confirmed if the AIMD functions in its set mode at
all times irrespective of the application of the test signal, while
the test method for protection 5) is under development.
An important issue for standard methodology is the electromagnetic stress applied to AIMD during these tests. The test
signal is not always the magnetic field, though the goal of the
tests is assessing the behavior of the medical device in the case
of exposure to magnetic fields. For protections 1), 2), and 3),
the test signal is the voltage which is applied to the AIMD leads
in order to simulate the effect of time-varying magnetic fields
on device circuitry. Annex M in PC 69 gives the correlation between the voltage levels used in the standard tests and the radiated field strengths. For protections 4) and 5), the standards
recommend tests with magnetic fields. The test level for protection 4) is 150 A/m (rms) up to 100 kHz and strengths decreasing
from 100 kHz to 140 kHz. The recommended test equipas
ment is formed from a generator and a radiating coil with a dicm and exceeding the largest linear dimension
ameter of
of the AIMD by 50%. The calculations show nonuniformity in
this case up to 30% for the testing field in the volume corresponding to the AIMD can. For protection 5), ISO14708-1 does
not give the test equipment but recommends as a first guide, test
levels of 150 A/m (rms) up to 100 kHz and test levels decreasing
between 100 kHz and 30 MHz.
as
In connection with the standards listed before, this paper
presents a system that is capable of producing magnetic fields
of 150 A/m up to 100 kHz and strengths decreasing as
between 100 kHz and 1 MHz, with uniformity of
% in adequate volume for testing AIMD together with their leads. This
paper describes the system prototyped at FDA–CDRH and the
methods used for testing the immunity of the implantable pacemakers and neurostimulators to CW magnetic fields. The new
test method offers the possibility to characterize the protection
0018-9294/$25.00 © 2007 IEEE
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IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 54, NO. 9, SEPTEMBER 2007
Fig. 1. Block diagram of the magnetic-field test system.
of these medical devices from the effects of the magnetic fields
by means of immunity diagrams in the frequency domain. This
paper presents interference signals caused by CW magnetic
fields, AIMD immunity characteristics obtained with the new
test method, and points out the usefulness of the new test system
and method for AIMD research and standard development.
Fig. 2. Induction coil C28.
II. MAGNETIC-FIELD TEST SYSTEM
Fig. 1 shows the block diagram of the magnetic-field test
system prototyped at FDA–CDRH. The system was designed to
produce the magnetic-field test levels recommended in clause
27 of ISO14708-1 for the frequency range up to 1 MHz, namely
between
150 A/m up to 100 kHz and levels decreasing as
100 kHz and 1 MHz [4]. The system is formed of:
• the CW signal generator model HP 33120A;
• the power-amplifier model 1000A (DC to 1 MHz) manufactured by Industrial Test Equipment Co. Inc. (ITE);
• the induction coil model C28 prototyped at FDA-CDRH
(nonstandard Helmholtz coil).
For producing the magnetic fields for tests, the CW signal
generator drives the power amplifier whose load is the induction
coil. The magnetic field for tests can be adjusted for frequency
and strength in the specified limits by means of the frequency
and amplitude controls of the signal generator. The specifications of the signal generator and power amplifier used in this
system can be found on the manufacturers’ websites and in user
manuals. Next, we present the characteristics of the induction
coil prototyped for this application, brief feasibility calculations
for the test system, and the methods used for measuring the magnetic field in the induction coil during tests.
• inductance:
1.26 H.
.
• resistance:
.
• impedance at 100 kHz:
• coil constant:
.
In the cylindrical volume for tests located at the center of the
induction coil C28, the uniformity of the magnetic field is within
%. Fig. 3 presents the uniformity of the axial component of
the magnetic field H in the midplane (0 cm) and in the two planes
cm). The
which limit the cylindrical volume for tests (at
reference for these diagrams is the magnetic field at the center of
the coil C28. The magnetic-field vector magnitude differs from
the axial component by less than 0.1% in the cylindrical volume
for tests. In a sphere of 9-cm diameter, concentrically placed in
coil C28, the magnetic-field uniformity is within
% with respect to the center value.
A. Induction Coil Model C28
B. Feasibility Calculations
PC69 shows that, at implantation, the AIMD leads form effective loop areas between 191 cm and 232 cm (average values).
Therefore, the induction coil was conceived to produce the magnetic field of 150 A/m at 100 kHz in a cylinder of diameter
17 cm (circular area 227 cm ) and height 3 cm when the coil
is supplied by the ITE amplifier model 1000 A. The coil was
also designed to produce a uniform magnetic field in a sphere
of 9-cm diameter for testing the implantable insulin infusion
pumps whose largest linear dimension is about 8 cm. These
desiderata were achieved with the nonstandard Helmholtz coil
model C 28 shown in Fig. 2, which has the following specifications:
• two single-turn circular loops, series connection;
• material: copper pipe, diameter 1.6 cm;
• diameter of the loops: 28 cm;
• distance between loops: 12 cm.
The frame of the coil system is made of plexiglass. The deviation of the two loops from cylindrical geometry is less than
1 mm. The induction coil model C28 has the following functional parameters.
The equations used in this paper for calculating the magnetic
fields produced by circular loops can be found in the IEEE Standard P1309 [5]. Extended equations for inductance calculations
are given in [6]. The calculations presented next reveal the optimum match of the induction coil C28 with the ratings of the
kHz. The ITE amplifier model
power amplifier for
1000 A is compatible with the inductive loads and has output
ratings 25 V/40 A (rms values) up to 1 MHz. For limiting the
dc offset current of the amplifier on the low-impedance loads,
the manufacturer recommends mounting a series resistor in the
circuit of the load so that it drops 1 to 2 V (rms) at the full current. For a maximum current of 30 A in this test arrangement,
W, type MP9000 (noninwe chose a film resistor of
ductive), mounted on a heat sink. In these conditions, the load of
the amplifier is formed of the induction coil C28 in series with
resistor. The impedance
the connecting leads and the
of this load is given by the equation
Fig. 3. Coil C28: the deviation of the magnetic-field strength with respect to
the center value.
(1)
BUZDUGA et al.: TESTING THE IMMUNITY OF ACTIVE IMPLANTABLE MEDICAL DEVICES
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To keep the load impedance at low values, the connecting leads
are made of close pairwires or just coaxial cables with the lowest
possible length. For the induction coil C28, the load impedance
. On this load, the ampli(1) at 100 kHz is
fier delivers the maximum current given by the equation
(2)
Fig. 4. Available field in the test system with coil C28.
The magnetic field at the center of the coil system is given by
the following equation:
(3)
In (3), is the number of turns, is the current through the
series loops, is the radius of the loops, and is the distance
from the center of the coil system to the center of each loop.
cm and
cm,
For
A/m (rms),
(3) produces the magnetic-field strength
which shows a testing reserve of 6% above 150 A/m at 100 kHz.
Below 100 kHz, the amplifier can deliver higher currents within
the rating of 40 A, provided by the lower value of the load
impedance expressed in (1). Consequently, the system presents
higher reserve for the magnetic-field strength at low frequenkHz, the load impedance given in (1) is mostly
cies. For
reactive and the maximum current through the induction coil
C28 may be calculated with (4)
(4)
The inductances
and
do not change significantly up
to 1 MHz, so that the current given in (4) and implicitly the magbetween
netic field for tests in coil C28 can be decreased as
100 kHz and 1 MHz, provided that the maximum output voltage
of the amplifier is 25 V (rms) in this frequency range. Equation
(3) can be rewritten in the form which defines the constant of
the coil
(5)
For
cm and
the induction coil model C28
cm, (5) gives the constant of
(6)
In practice, the current through coil is measured and used to
calculate the magnetic-field strength at the center of the coil C28
with the following equation:
(7)
The measurements confirmed the above feasibility calculations.
Fig. 4 presents the magnetic-field strength measured at the
center of the induction coil C28 in the frequency range 1 kHz to
1 MHz. With respect to the test levels recommended in clause
27 of ISO14708-1, the system prototyped at FDA–CDRH
provides testing reserve greater than 10% up to 90 kHz and
reserve within few percents for frequencies between 100 kHz
and 1 MHz.
C. Measuring the Magnetic Field in the Induction Coil
The immunity tests require measuring the magnetic-field
strength in the induction coil. The coil should be calibrated
and geometrically stable. Standard P1309 gives a guide for
calibrating Helmholtz coils and those methods can be extended
for the nonstandard Helmholtz coils.
The following methods give accurate data on the magneticfield strength in the induction coil.
• Measuring the current through coil and computing the
magnetic-field strength with (7) or other field calculators.
• Measuring the field with magnetic-field probes. At
FDA–CDRH, we used triaxial magnetic-field sensors
manufactured by Electric Research and Management Co.
Inc. (ERM).
A method for monitoring the magnetic field during tests is to
measure the current through the induction coil and computing
the field strength in the volume for tests. Another method is to
correlate the field in the volume for tests with the field value at
another location and measuring the field strength at that location with magnetic sensors. For example, 139 A/m measured
at the center of the top loop confirms 150 A/m at the center
of the induction coil C28. Alternatively, a small circular loop
may be used as a probe for CW magnetic fields. From
and
, the following
equation is deduced, which gives the strength of the magnetic
field as a function of frequency and the maximum voltage
induced in a loop of diameter :
All quantities in SI base units
(8)
At FDA–CDRH, we used all of these methods for measuring
the magnetic-field strength during tests. The close data from
multiple measurements with different probes confirm the performance of the new system. For quick estimation of the test
level, the magnetic-field strength measured with ERM sensors
at the center of the induction coil can be correlated with the
output voltage level of the CW signal generator. This correlation permits evaluating the field strength in the volume for tests
by reading the output voltage of the signal generator. Though the
amplifier used in this application is not a voltage-controlled cur-
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IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 54, NO. 9, SEPTEMBER 2007
rent source and any change in the load impedance could produce
deviations in a voltage–magnetic-field relationship. Therefore,
the magnetic-field data for the AIMD immunity characteristics
were collected with magnetic-field sensors.
III. TESTING AIMD IN CW MAGNETIC FIELDS UP TO 1 MHZ
The system that was just presented offers the possibility to
investigate the immunity of AIMD to magnetic fields by immersing the device together with its leads into the testing field.
A tissue simulator containing the AIMD is placed in the induction coil so that the medical device and its leads are positioned in
the volume for tests. The AIMD is exposed to magnetic fields of
different strengths and frequencies, while an oscilloscope monitors the signals delivered by the device under test in a tissue simulator. We next describe the tissue simulator and AIMD preparation for tests, the electromagnetic-interference (EMI) criteria
used in the preliminary tests on pacemakers and neurostimulators, and the procedure developed at FDA–CDRH for testing the
immunity of these implantable medical devices to CW magnetic
fields.
Fig. 5. AIMD on plastic grid.
A. Tissue Simulator and AIMD Preparation for Tests
The tissue simulator developed for this test system consists
of a cylindrical plastic tank filled with saline solution of 0.18%
concentration. A tissue simulator with other geometry developed at FDA–CDRH is described in PC69. The saline tank has
an outside diameter 25 cm and height of about 23 cm for fitting the dimensions of the induction coil C28. A horizontal line
marked on the saline tank shows the midplane of the cylindrical volume for tests at a normal position of the tank in coil
C28. Thus, the AIMD of about 1-cm thickness can be properly positioned by visual inspection in the volume for tests of
3-cm height. A plastic grid, which fits the inner diameter of
the cylindrical tank, supports the AIMD together with its leads
as shown in Fig. 5. Four plastic legs that have threaded nuts
permit adjustment of the vertical position of the plastic grid in
the saline tank. The leads of AIMD are positioned on a circular
contour of 17-cm diameter, which delimits an area of about
227 cm . For repeatable results, this area should be kept constant during tests. Therefore, we grooved a circular channel for
leads and a shape for the can of the device on the plastic grid.
The AIMD and its leads are fixed on the grid with thread and
plastic ties. The plastic grid also fixes the sensing cable (pairwire or coaxial) which picks up the signal delivered by AIMD
from saline. The ends of the sensing wires have the insulation
removed on about 1 mm and are positioned a few centimeters
from the tip of the AIMD leads. For testing the AIMD with a
simulated heart signal, a similar cable may be used to inject the
electrocardiographic signal in saline.
The induction coil and the saline tank should be placed on a
wooden or plastic table to avoid distortion of the testing magnetic field. The AIMD is configured for the required operation
mode, the grid is introduced in the saline tank, and the threaded
legs are turned for adjusting the position of AIMD in the volume
for tests. Fig. 6 shows the tissue simulator introduced in the induction coil C28.
The effective area bounded by the leads of the AIMD may be
increased in this test arrangement by extending the length of the
Fig. 6. Tissue simulator in coil C28.
leads and turning more than one loop on the circular contour of
227 cm . This technique may be used for testing neurostimulators whose leads form effective loop areas that are larger than
227 cm at implantation. In such cases, the exposure area
on the circular contour is calculated as the sum of an integer
of loops of 227 cm and the area
of a circular
number
segment defined by the tip of the lead and the can of AIMD
(9)
The area of the circular segment
results from (10), wherein
is the radius of the circular contour in centimeters and is the
length of the arc in centimeters (the length of the lead wrapped
up in excess over the integer number of turns)
(10)
B. EMI Criteria for Medical Devices
The tests performed at FDA–CDRH revealed the degradation
of the signals delivered by AIMD in saline at different frequencies and strengths of the magnetic field. For assessing the immunity level of the AIMD, it is necessary to adopt reference signals
for normal operation of devices and to define EMI criteria for
correlating the AIMD signal degradation with the parameters
of the magnetic field. The reference signal for normal operation of an AIMD is the signal delivered by the device in a tissue
simulator at zero testing level. The EMI is the degradation of
the AIMD signal over certain limits due to the testing field, for
example:
For pacemakers:
• Criterion 1: deviations greater than 20% for the AV (atrioventricular) interval.
BUZDUGA et al.: TESTING THE IMMUNITY OF ACTIVE IMPLANTABLE MEDICAL DEVICES
• Criterion 2: deviations greater than 10% for the pulse
interval.
• Criterion 3: decrease of the atrial (A) or ventricular (V)
pulse amplitude below 50%.
For neurostimulators:
• decrease of the pulse amplitude below 50%.
The EMI criteria just shown were drawn from typical signal
degradations exhibited by AIMD samples during the preliminary tests. These criteria were chosen as a convenient means to
describe the immunity tests for AIMD by using the new system
and do not suggest performance levels to be adopted for pacemakers or neurostimulators although the EMI criterion 2 for
pacemakers is derived from the performance criteria given in
PC69 for the tests between 450 and 3000 MHz.
C. Test Procedure
The preliminary tests on AIMD in the new magnetic-field
system were performed at FDA–CDRH in laboratory conditions
by using the procedure described next.
The test equipment should be connected as shown in Fig. 1,
the induction coil being seated on a wooden table. The medical device is prepared for tests, the tissue simulator is introduced in the induction coil, and the height of the plastic grid
is adjusted for positioning the AIMD in the volume for tests
as described before. A multichannel memory oscilloscope displays the AIMD reference signal on a memory channel while
the signal picked up from saline is continuously displayed on a
measuring channel. For signal analysis, it is useful to display a
sequence of six to ten pulses delivered by AIMD in saline. The
same oscilloscope may be used for measuring the field strength
with magnetic-field sensors during tests. For accurate results,
the relative position of the coil, saline tank, and plastic grid arrangement should be kept unchanged during tests after setting
the reference signal. The power amplifier feeds the induction
coil and the testing magnetic field is adjusted for frequency and
strength from the controls of the signal generator. The noise of
test frequency, which is superposed to the AIMD signal in the
tissue simulator, can be attenuated by using filtering techniques
on the measuring channel. For the tests described in this paper,
we used continuous sinusoidal signals at fixed frequencies between 1 kHz and 1 MHz, at least four distinct frequencies per
decade.
For finding the immunity level of an AIMD to CW magnetic
fields at a given frequency, the strength of the testing field at that
frequency is increased from zero and the signal picked up from
saline is continuously compared with the reference signal on the
oscilloscope. As long as the AIMD signals picked up from saline
do not deviate over the limits assumed in the EMI criteria, we
count the immunity of the device to the applied test level. The
highest magnetic-field strength at which the interference does
not yet occur gives the immunity level of the AIMD to CW magnetic fields at that frequency. Generally, we increased the field
strength with coarse steps of up to 20 A/m and refined the magnetic-field steps when investigating the interference phenomena.
If the AIMD did not exhibit interference, we tested the immunity
up to the maximum available field strength in the test system.
For each testing frequency, we noted the immunity level found
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in measurements (A/m, rms values) and recorded for database
the reference signal and the signal picked up from saline when
the AIMD was exposed to the magnetic field at the immunity
level.
At certain frequencies and test levels, the AIMD pulses
picked up from saline may deviate over the limits chosen
in the EMI criteria. In such cases, the relation between the
AIMD signal degradation and the magnetic-field strength is
investigated through multiple measurements by increasing and
decreasing the field strength with refined steps. The susceptibility is the lack of immunity, and the susceptibility level of
the AIMD at a given frequency may be defined as the lowest
test level at which the interference occurs. In the tests which
revealed interference, we noted details on EMI at test levels
within 5% to 20% above the immunity level of AIMD. Between the immunity level and the test level, which produced
persistent EMI, an interval of uncertain operation (intermittent
interference) was generally found for AIMD. For each testing
frequency, we noted the susceptibility level found in measurements and recorded for database the reference signal and the
signal picked up from saline when the AIMD was exposed to
the magnetic field at the susceptibility level. When EMI at a
given frequency was found, we examined the behavior of the
AIMD up to the test level recommended in ISO14708-1. Two
devices returned to normal operation at field strengths above
the susceptibility level, as shown in the diagram in Fig. 9. PC69
and other standards recommend measurements with continuous
sinusoidal signals either swept over the frequency range, or
applied at four distinct frequencies per decade. As known from
the measurements practice, the swept signals are suitable for
conformity tests, when the device which does not comply with
requirements is rejected. Obviously, if one finds EMI with
swept signals and wants to investigate the phenomena, they
have to stop the frequency sweeping and continue the tests
at fixed frequencies to obtain details about that interference.
Therefore, we only used signals at fixed frequencies in the
immunity tests described in this paper.
IV. EXPERIMENTAL RESULTS
The experiments performed at FDA–CDRH have two goals:
verifying the capability of the new system to produce the test
levels recommended in clause 27 of ISO14708-1 for frequencies up to 1 MHz and developing the procedure for testing the
immunity of implantable pacemakers and neurostimulators to
CW magnetic fields in this system. We tested four pacemakers
and two neurostimulators at two distinct frequencies: 58 kHz
(corresponding to an electronic article surveillance system) and
100 kHz (the highest frequency where the system is required
to produce 150 A/m). Each AIMD was affected at a different
test level. For one pacemaker and two neurostimulators, we extended the tests for finding the immunity characteristics in the
frequency range from 1 kHz to 1 MHz. The pacemakers were
tested without simulated heart signals. From the numerous data
recorded in the FDA–CDRH database from the preliminary tests
on AIMD, we next present signal diagrams which show EMI
at different test frequencies and immunity diagrams in the frequency range of 1 kHz to 1 MHz for implantable pacemakers
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IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 54, NO. 9, SEPTEMBER 2007
Fig. 7. Change of the AV interval in magnetic fields at 5 kHz.
Fig. 10. EMI diagram for the pulse interval.
Fig. 8. EMI diagram for the AV interval.
Fig. 11. EMI diagram for a neurostimulator
H = 31 A/m; f = 15 kHz.
Fig. 9. Change of the pulse interval in magnetic fields at 58 kHz.
and neurostimulators. When interference was found, the phenomena occurred either abruptly or progressively with respect
to the test level.
Fig. 7 presents the abrupt change of the atrioventricular (AV)
interval of a pacemaker tested in magnetic fields at 5 kHz while
Fig. 8 shows the signal diagram for this interference. The acceptable domain for this parameter was assumed to be 150 ms
% (from 120 ms to 180 ms).
Fig. 9 presents the progressive degradation of the pulse interval of a pacemaker in CW magnetic fields at 58 kHz, while
a diagram for this interference is given in Fig. 10. The accept%. For magable pulse interval was assumed within 0.85 s
netic fields between 50 A/m and 120 A/m, this pacemaker delivered pulses at intervals from 0.5 s to 1.7 s. Fig. 9 illustrates
a window effect, and the pacemaker returned to normal pacing
for test levels that were greater than 120 A/m. In other words,
the interference occurred for magnetic-field strengths between
50 and 120 A/m.
Similar diagrams illustrate the degradation of the pulse
amplitude. For example, Fig. 11 shows the signal from an old
model neurostimulator which was exposed to magnetic fields
at 15 kHz.
The data from tests at different frequencies allow drawing
immunity characteristics for AIMD in the frequency domain.
Fig. 12. Immunity diagrams for a pacemaker tested in CW magnetic fields.
Fig. 12 shows immunity diagrams for a pacemaker and Fig. 13
shows immunity diagrams for two neurostimulators in the frequency range from 1 kHz to 1 MHz. In both figures, curve 1
corresponds to the maximum available field in the test system.
In Fig. 12 (for pacemakers), curve 2 shows the immunity
levels corresponding to EMI criterion 1 (AV interval degradation), while curve 3 shows the immunity levels corresponding
to EMI criterion 2 (the pulse interval alteration). The immunity
diagram corresponding to EMI criterion 1 is shown only up to
100 kHz, but the interference occurred at all test frequencies between 100 kHz and 1 MHz at test levels below 2 A/m. During
the tests for finding the immunity levels guided by EMI criterion 2 for this pacemaker, we ignored the parameter deviations
counted for EMI criterion 1.
The pacemaker characterized in Fig. 12 had the settings:
DDD mode, unipolar pace/unipolar sense, atrial amplitude
BUZDUGA et al.: TESTING THE IMMUNITY OF ACTIVE IMPLANTABLE MEDICAL DEVICES
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• Prototyping extended-length leads for obtaining effective
loop areas larger than 300 cm in the induction coil C28.
• Extending the testing frequency up to 30 MHz as recommended in clause 27 of ISO14708-1.
• Increasing the volume for tests by using larger coils and
higher ratings amplifiers.
ACKNOWLEDGMENT
Results of the previous research performed at FDA-CDRH
in the domain of the AIMD testing with magnetic fields can be
found in [7] and [8].
REFERENCES
Fig. 13. Immunity diagrams for neurostimulator samples tested in CW magnetic fields.
5 V, ventricular amplitude 5 V, atrial sensitivity 0.5 mV, and
ventricular sensitivity 1 mV.
In Fig. 13, curve 2 shows the immunity levels of an old neurostimulator model, while curve 3 reveals the improved performance of a new neurostimulator model. The tests with neurostimulators were performed with leads of about 75-cm length.
According to (9) and (10), these leads provide an effective loop
area of about 300 cm on the contour of 17-cm diameter. Higher
exposure areas could reveal lower immunity levels for these
devices.
The immunity characteristics presented in Figs. 12 and
13 indicate targets for further electromagnetic-compatibility
(EMC) design of the AIMD in the frequency range from 1 kHz
to 1 MHz.
V. CONCLUSION
The system presented in this paper offers the possibility
to test the immunity of AIMD to CW magnetic fields up to
1 MHz by the immersion method. The test procedure developed
in conjunction with this system provides an alternative to the
voltage-injection methods recommended in the actual standards
for implantable pacemakers. The new system is able to produce
amplitude-modulated magnetic fields and can be used for
validating the standard test methods with modulated voltages.
The system can also be used for checking the performance
of the history function of medical devices. The experiments
show that the CW magnetic fields may cause various pacing
events which should be accurately recorded by the devices with
history function included. The new test system is feasible, the
test procedure is suitable for pacemakers and neurostimulators
of different makes, and the preliminary tests provided repeatable results. This paper offers a useful tool for the engineers
involved in the research, EMC design, and quality assurance of
the active implantable medical devices.
The test system presented in this paper can be further developed in the following directions.
[1] American Nationals Standards Institute/Association for the Advancement of Medical Instrumentation, ANSI/AAMI PC69, Jan.
2006, Active implantable medical devices—EMC test protocols for
implantable cardiac pacemakers and implantable cardioverter defibrillators, 2nd ed., Committee Draft.
[2] European Committee for Standardization/European Committee for
Electrotechnical Standardization - CEN/CENELEC, EN45502-21:2003, Dec. 2003, Active Implantable Medical Devices, Part 2–1:
Particular requirement for active implantable medical devices intended
to treat bradyarrhythmia (cardiac pacemakers).
[3] Implants for surgery—Active implantable medical devices—Part 1:
General requirements for safety, marking and for information to be
provided by the manufacturer, ISO 14708-1:2000(E), 2000, International Organization for Standardization (ISO), Geneva, Switzerland.
[4] V. Buzduga, Magnetic field test system 1 kHz to 1 MHz (CW), H =
150 A/m at f = 100 kHz Rockville, MD, Tech. Rep. #DP-900-05,
Nov. 2005, FDA-CDRH.
[5] Draft IEEE Standard for Calibration of Electromagnetic Field Sensors
and Probes, Excluding Antennas, from 9 kHz to 40 GHz., IEEE P1309,
May 4, 2004.
[6] F. W. Grover, Inductance Calculations. New York: Dover , 2004.
[7] M. Misakian, J. Casamento, and O. Laug, “Development of emulator
for walk-through metal detectors,” IEEE Trans. Electromagn. Compat.,
vol. 44, no. 3, pp. 486–489, Aug. 2002.
[8] W. Kainz, J. Casamento, P. Ruggera, D. Chan, and D. Witters, “Implantable cardiac pacemaker EMC testing in a novel security system
simulator,” IEEE Trans. Biomed. Eng., vol. 52, no. 3, pp. 520–530, Mar.
2005.
Valentin Buzduga (M’06) received the M.S. degree
in electronics from the Technical University “Gh.
Asachi” Iasi, Romania, in 1977, and the Ph.D.
degree in electronics and telecommunications from
the Politehnica University, Bucharest, Romania, in
2000.
Currently, he is with Scantek, Inc., Columbia,
MD, and an Adjunct Professor with Capitol College,
Laurel, MD. He was a Design and Compliance
Engineer with Tehnoton, Isai, and taught courses
on electronics engineering and electromagnetic
compatibility (EMC) at Technical University “Gh. Asachi” and performed
research in EMC and acoustics. He developed new models for the electromagentic-interference (EMI) analysis in terms of circuits’ theory and published
a number of papers on these topics, including the three-port characterization
of the transmission line. In acoustics, he developed test methods based on the
constant divergence of the sound pressure level which were published in the
Noise Control Engineering Journal. From 2004 to 2006, he participated in a
research fellowship program coordinated by ORISE at FDA–CDRH, where he
performed emission tests with metal detectors, immunity tests with medical
devices, and developed a magnetic-field test system and test methods for
implantable medical devices. His research interest includes the EMC design,
modeling of the electromagnetic interactions for biomedical applications, and
development of acoustical test methods immune to environmental noise.
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IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 54, NO. 9, SEPTEMBER 2007
Donald M. Witters (M’80–SM’93) received the
B.S. degree from the University of Maryland,
College Park, and the M.S. degree in biomedical engineering from Georgetown University, Washington,
D.C.
He has more than 30 years of experience working
at the U.S. Food and Drug Administration’s Center
for Devices and Radiological Health (CDRH), and
chairs the CDRH Electromagnetic Compatibility
(EMC) and Wireless Working Group. This group is
charged with assessing EMC and radio-frequency
wireless technology issues for medical devices and systems and developing
strategy and tools for public health and medical device safety and effectiveness.
He has performed laboratory research on medical device EMC, RF wireless
technology, and precision microwave calibrations, and helped develop and write
several national and international consensus standards. He was instrumental
in the development of the wireless medical telemetry service (WMTS) that
remains the first radio spectrum created to protect wireless medical telemetry
from electromagnetic interference.
Jon P. Casamento (M’79) received the B.S.E.E. degree from the University of Maryland, College Park,
in 1979.
Currently, he is the Deputy Director of the Division of Solid and Fluid Mechanics at the FDA’s
Center for Devices and Radiological Health, Office
of Science and Engineering Laboratories, Rockville,
MD. He was with the Food and Drug Administration
since 1980 and has been testing medical devices for
electromagnetic compatibility with radio-frequency
emitters since 1991. He has made measurements
of electromagnetic emissions from antitheft systems and electromagnetic
surveillance systems. He is interested in broadband magnetic-field sources for
testing medical device immunity to these emissions.
Wolfgang Kainz (M’02) received the M.S. degree in
electrical engineering from the Technical University
of Austria, Vienna, Austria, in 1997 and the Ph.D.
degree in technical science from the Technical University Vienna, Austria, in 2000.
After working for the Austrian Research Centers
Seibersdorf (ARCS) on electromagnetic compatibility of electronic implants and exposure setups
for bio-experiments, he joined The Foundation
for Research on Information Technologies in Society—IT’IS (Zurich, Switzerland) as Associate
Director. He was a Manager for IT’IS together and worked on the development
of in-vivo and in-vitro exposure setups for bio-experiments. In 2002, he joined
the U.S. Food and Drug Administration in the Center for Devices and Radiological Health. He is Chairman of the IEEE Standard Coordination Committee 34,
Subcommittee 2 which develops compliance techniques for wireless devices.
His research interest is focused on the safety and effectiveness of medical
devices and safety in electromagnetic fields. This includes computational
electrodynamics (FDTD simulations) for safety and effectiveness evaluations;
magnetic resonance imaging (MRI) safety; performance and safety of wireless
technology used in medical devices; electromagnetic compatibility of medical
devices, especially electronic implants; and dosimetric exposure assessments.