Non-Invasive Blood Pressure Device for Use in fMRI Imaging Applications January 21, 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. Higher centers of the brain stem and cortical structures may have potentiating effects on changes in autonomic outflow. Measuring blood pressure continuously during fMRI procedures could provide numerous benefits to the study of autonomic disorders.

The Problem Current commercial devices 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 leading to distortion of the MRI images. Also, some components of the cuff are made up of ferromagnetic materials are dangerous when placed in close proximity to an fMRI machine.

Market Analysis 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 electromagnetic 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. Keep all electrical components that may cause potential interference in the observation room.

Estimated Design Cost Item Quantity Cost per Item Total US Dollars Fiber Optic Cable 15 feet $1/foot $15.00 LEDs 4 $5-$10 $40.00 Air Piping $0.50/foot $7.50 Photodetector 1 $25 $25.00 Rubber Insulation 2 square feet $3/foot2 $6.00 Inflation Bag for Cuff $5 $5.00 Total Cost: $98.50

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. Increasing the tube diameter has no effect in increasing the maximal extension length as anticipated which may be caused by the limited strength of the pneumatic pump. Using a stiff tube with as few turns as possible had no significant effect in increasing the maximal extension length.

Current Work We have been researching the use of fiber optics to be able to transmit the blood pressure signal with the aid of Dr. Duco Jansen. Since the idea of decreasing air resistance in the tubing by increasing the tube diameter failed, we are looking at other means of attaining the proper pressure in the finger cuff so that accurate blood pressure measurements can be made over extended distances. Changing to a larger pneumatic pump. Electrically shielding the components so that the pneumatic pump can be placed closer to the MRI unit. Finding a method of amplifying the pressure and maintaining the smaller 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. Purchase fiber optic components after verifying the ones that are needed through work in Dr. Jansen’s optics lab. Meet with Dr. Jim Davidson to discuss the possibility of using carbon materials to shield electrical components which will allow them to be placed closer to the actual MRI unit.

Questions Questions?