Biomedical Engineering Reference
In-Depth Information
• Nylon
1
2
-13 hex nut
• Mono
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lament, 20-lb test, Shakespeare OMNIFLEXR
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fishing line
• Five gallons of supermarket distilled water
• Sodium chloride, NaCl USP grade (Kosher salt works equally well)
5 cm. Holes were drilled in the
center of each plate to allow for attachment with screws. Holes were drilled in the center
of each side of the 28-qt plastic box. Stainless steel screws were coated with silicone adhe-
sive and then used to attach the titanium pieces to the inside of the box, providing electri-
cal connection to the outside of the box. The louver grid was cut to give two pieces, one
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The titanium sheet stock was cut to four pieces 5 cm
fitting the top ridges and one on the bottom. Six nylon nuts were attached to the bottom
grid with medical adhesive. The nylon threaded rod was cut to 4-in. lengths, six each. A
slot was cut in the top of each rod.
The saline solution should be prepared to the proportions recommended by ANSI/
AAMI PC69:2000, Table 2: 0.027
M
1.8 g/L or 0.18% NaCl concentration at 21°C. To
do so, the salt is
first dried in an oven set at 200°C for 30 minutes. Then 30.6 g of dry salt
can be added to 17 L of distilled water to make enough solution with a concentration of
1.8 g/L. Submersion in a conducting
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fluid facilitates monitoring of the implantable med-
ical device's operation while minimizing the electromagnetic
fl
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field distortion and detection
e
ects of directly attached probes. Monitoring of the implantable medical device's
responses to the applied electromagnetic environment is accomplished by sampling the
test device's output pacing pulses via the square electrodes submerged in the saline solu-
tion. The potentially interfering signals are applied and their magnitude is gradually
changed while the response of the medical device is monitored.
Pacemakers and de
ff
brillators are usually tested in each of their normal operating
modes, and test equipment is set up to determine if, and when, the test device is inhibited
or operating in its noise mode. To do so, these tests are conducted both with and without
external simulated intracardiac electrogram signals injected via the saline solution into the
sensing inputs of the test device.
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Shocking Water
Whereas simulating a single biopotential signal channel is not too complex, generating
accurate signals to validate array processing methods is very problematic. Take, for exam-
ple, the case of validating the performance of
inverse solutions
. In inverse electrocardiog-
raphy, researchers attach a large array (e.g., 128 or 256 electrodes) of electrodes to the
chest instead of the usual 12-lead ECG. The idea is to process the array ECG signals, tak-
ing into consideration the speci
c geometry of the chest and body organs to create three-
dimensional images of the potentials in the heart muscle itself. The potential of such a
technique is tremendous. It would give physicians a noninvasive method to identify
patients at risk of sudden death, for speci
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c diagnosis of rhythm disorders, and for local-
ization of disturbances in the heart in order to guide intervention.
Several computational approaches that attempt to solve the electrocardiographic inverse
problem have been developed to estimate heart surface potential distributions in terms of
torso potentials, but to date their suitability for in vivo and clinical situations has not been
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firmly established. The same can be said about the solution of other inverse problems in
biomedical engineering, such as inverse electroencephalography and electrical impedance
computed tomography. Before any inverse electrical imaging procedure can be used as a
noninvasive diagnostic tool with con
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dence, it must
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first be validated so that recorded
experimental observations can be faithfully reproduced.
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