TY - JOUR
T1 - Demonstration that a new flow sensor can operate in the clinical range for cerebrospinal fluid flow
AU - Raj, Rahul
AU - Lakshmanan, Shanmugamurthy
AU - Apigo, David
AU - Kanwal, Alokik
AU - Liu, Sheng
AU - Russell, Thomas
AU - Madsen, Joseph R.
AU - Thomas, Gordon A.
AU - Farrow, Reginald C.
N1 - Funding Information:
The work was supported by the National Institutes of Health (NINDS) under grant R43NS056628-01A2 and a grant from the New Jersey Commission on Science and Technology . The variable capacitors were fabricated at the Microcircuit Fabrication Center (MFC) at NJIT and at the Cornell Nanofabrication Facility (CNF) at Cornell University.
Publisher Copyright:
© 2014 Elsevier B.V. All rights reserved.
PY - 2015/10/1
Y1 - 2015/10/1
N2 - A flow sensor has been fabricated and tested that is capable of measuring the slow flow characteristic of the cerebrospinal fluid in the range from less than 4 mL/h to above 100 mL/h. This sensor is suitable for long-term implantation because it uses a wireless external spectrometer to measure passive subcutaneous components. The sensors are pressure-sensitive capacitors, in the range of 5 pF with an air gap at atmospheric pressure. Each capacitor is in series with an inductor to provide a resonant frequency that varies with flow rate. At constant flow, the system is steady with drift <0.3 mL/h over a month. At variable flow rate, V, the resonant frequency, f0, which is in the 200-400 MHz range, follows a second order polynomial with respect to V. For this sensor system the uncertainty in measuring f0 is 30 kHz which corresponds to a sensitivity in measuring flow of ΔV= 0.6 mL/hr. Pressures up to 20 cm H2O relative to ambient pressure were also measured. An implantable twin capacitor system is proposed that can measure flow, which is fully compensated for all hydrostatic pressures. For twin capacitors, other sources of systematic variation within clinical range, such as temperature and ambient pressure, are smaller than our sensitivity and we delineate a calibration method that should maintain clinically useful accuracy over long times.
AB - A flow sensor has been fabricated and tested that is capable of measuring the slow flow characteristic of the cerebrospinal fluid in the range from less than 4 mL/h to above 100 mL/h. This sensor is suitable for long-term implantation because it uses a wireless external spectrometer to measure passive subcutaneous components. The sensors are pressure-sensitive capacitors, in the range of 5 pF with an air gap at atmospheric pressure. Each capacitor is in series with an inductor to provide a resonant frequency that varies with flow rate. At constant flow, the system is steady with drift <0.3 mL/h over a month. At variable flow rate, V, the resonant frequency, f0, which is in the 200-400 MHz range, follows a second order polynomial with respect to V. For this sensor system the uncertainty in measuring f0 is 30 kHz which corresponds to a sensitivity in measuring flow of ΔV= 0.6 mL/hr. Pressures up to 20 cm H2O relative to ambient pressure were also measured. An implantable twin capacitor system is proposed that can measure flow, which is fully compensated for all hydrostatic pressures. For twin capacitors, other sources of systematic variation within clinical range, such as temperature and ambient pressure, are smaller than our sensitivity and we delineate a calibration method that should maintain clinically useful accuracy over long times.
KW - Cerebrospinal flow
KW - Flow sensor
KW - Hydrocephalus
KW - Intracranial pressure
KW - Pressure sensor
KW - Shunt
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U2 - 10.1016/j.sna.2015.08.023
DO - 10.1016/j.sna.2015.08.023
M3 - Article
AN - SCOPUS:84941978953
SN - 0924-4247
VL - 234
SP - 223
EP - 231
JO - Sensors and Actuators, A: Physical
JF - Sensors and Actuators, A: Physical
ER -