Biomedical Engineering Reference
In-Depth Information
2.1
Measurement of Aneurism Sac Pressure
None of the medical imaging exams presently used provides measures of the
pressure inside the aneurysm sac. This information is important because can be
evidence of low-flow endoleaks or endotension [ 10 ].
Published data describe the use of catheters to measure pressure in the residual
aneurysm sac [ 11 ]. However, although these methods provide precise measurements
[ 4 ], they are invasive and bear multiple risks.
An alternative method for the measurement of the aneurysm sac's pressure is the
implant of remote pressure transducers during EVAR. This solution is advantageous
since measurements can be done when needed (hourly, weekly, etc.) in the patient's
home or office instead of a hospital once or twice a year. Another important feature
is the possibility to measure both the mean pressure and the pulsatile pressure
without increasing risks for the patients. Following, the three telemetric pressure
sensors currently available will be addressed.
3
Impressure AAA Sac Pressure Transducer
In 2003, the Impressure AAA Sac Pressure Transducer or RemonAAA from
Israeli Remon Medical Technologies was the first permanently implantable,
ultrasound-activated remote pressure transducer to measure intrasac pressure after
EVAR [ 12 ].
The transducer, hand sewn to the outside of a stent-graft, contains a piezoelectric
membrane that energizes a capacitor when actuated by ultrasound waves from a
hand-held probe. Once charged, the aneurysm sac pressure is measured followed
by the generation of an acoustic signal that is relayed to the hand-held probe. The
probe then converts the acoustic signal to a pressure waveform that is presented on
a computer screen.
In spite of ultrasound being safe and widely used for medical imaging, the
measurement requires the use of an ultrasonic gel and direct contact between the
skin and the transducer. Another drawback of this sensor is the impossibility of ul-
trasound to travel through air or bone, which may lead to difficulties communicating
with the aneurysm sac.
The ImPressure sensor is the smallest (3 mm
1.5 mm) of the three
sensors described here, is the least radiopaque but still visible. As the sensor is sewn
to the stent-graft, the fixation location must be carefully chosen in such a way that
the sensor will measure the pressure inside the excluded aneurysm sac without being
pushed against the aneurysm wall.
In October 2006, Remon Medical Technologies announced the first European
implant of the sensor.
9mm
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