Transcript Non-Invasive Blood Pressure Device for Use in fMRI

Non-Invasive Blood Pressure Device for Use
in fMRI Imaging Applications
November 18, 2004
Students
Advisors
Jose Alvarado
Ben Huh
Sanjeet Rangarajan
Dr. André Diedrich
Dr. John Gore
Dr. Richard Shiavi
Background

Functional Magnetic-Resonance Imaging (fMRI) has
recently allowed novel insights into the function of individual
brain sites.

Patients with baroreflex failure have extremely labile blood
pressure due to loss of buffering function of blood pressure
control.
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Higher centers of the brain stem and cortical structures
may have potentiating effects on changes in autonomic
outflow.
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Measuring blood pressure continuously during fMRI
procedures could provide numerous benefits to the study of
autonomic disorders.
The Problem

Current commercial devices
such as the FINAPRES,
FINOMETER, and
PORTAPRES are able to
continuously measure blood
pressure but not in the
presence of magnetic fields.

The electrical sensor system
for the finger cuff as well as
the pneumatic pump interfere
with the highly sensitive fMRI
magnet.
Market Analysis


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

Use for only in research and hospital settings.
Large market potential because of applications in other MRI
and fMRI studies.
An optical continuous non-invasive blood pressure measuring
device could be used in conjunction with electromagnetical
trackers which are used in image guided surgery.
Profit will come from selling the design of the fMRI compatible
finger cuff to pre-existing companies that manufacture the
cuffs.
Perhaps too specific of an item to be able to market the device
independently and for this reason it could be a better to sell
the design to a current company.
Our Solution

Retrofit finger cuff blood pressure
devices to use optical transmission
techniques instead of electrical
transmission techniques.

Replace electrical cables and sensors
with optical components:
 Fit cuff with an optical cable
terminator.
 Develop an fiber-optic interface
compatible with existing
commercially available electrical
systems.
 Design fMRI compatible shielding.

Extend length between cuff and
electrical components without losing
pneumatic function.
Estimated Design Cost
Item
Quantity
Cost per Item Total Cost (Dollars)
Fiber Optic Cable
15 Feet $1 per Foot
15
LED's
4 $5-10
40
Air Piping
15 Feet $0.50 per foot
7.5
Photodetector
1
$25
25
Rubber Insulation
2 sq Feet $3 per sq. foot
6
Inflation Bag for Cuff
1
$5
5
Total Cost
98.5
Completed Tasks

We have tested what we expected to
be the first limiting factor, how far the
pneumatic pump can be extended
from the patient and still ensure
proper cuff inflation.

Prediction: The small radius of the
air tubes used with the FINAPRES
creates a large resistance to flow
with increasing tube length. Limited
pump pressure leads to insufficient
air supply to the cuff.

Experimental Result: Using tubing of
the same diameter as the
manufacturer, the maximum
extension length was found to be
around 10 ft.
Current Work

Currently we are testing
tubing of varying radii and
stiffness to determine the
maximum length of extension
while maintaining accurate
blood pressure readings.

We are consulting with Dr.
Gore about the possibility of
shielding the electrical
components in the case that
an ideal extension length is
unattainable using the
manufacturer’s pneumatic
pump.
Future Work

Contact Dr. Gore at the Vanderbilt University Institute for
Imaging Science to become acclimated with the facility and
learn about typical fMRI processes. The Imaging Institute’s
fMRI scanner will eventually be used to test our design.
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Dr. Duco Jansen will be contacted to ask for his expertise
on selecting appropriate fiber-optic components.

Use experimental parameters to predict the necessary
wavelength LED to ensure a proper signal and the
photodetector needed to properly capture the transmitted
light.
Questions
Questions?