Mems vascular sensor

Abstract

A micromachined sensor for measuring vascular parameters, such as fluid shear stress, includes a substrate having a front-side surface, and a backside surface opposite the front-side surface. The sensor includes a diaphragm overlying a cavity etched within the substrate, and a heat sensing element disposed on the front-side surface of the substrate and on top of the cavity and the diaphragm. The heat sensing element is electrically couplable to electrode leads formed on the backside surface of the substrate. The sensor includes an electronic system connected to the backside surface and configured to measure a change in heat convection from the sensing element to surrounding fluid when the sensing element is heated by applying an electric current thereto, and further configured to derive from the change in heat convection vascular parameters such as the shear stress of fluid flowing past the sensing element.

1 . A method of measuring shear stress on a blood vessel wall, the method comprising:
 introducing a backside wire bonded MEMS sensor into a desired location in a flow field of blood flowing though a blood vessel, wherein the MEMS sensor includes a heat sensing element disposed on a front-side surface of a substrate, the heat sensing element interfacing the flowing blood and coupled to electrode leads formed on a backside surface of the substrate opposite the front-side surface;   applying an electrical current to the sensing element from a driving circuit coupled to the backside surface;   measuring a change in heat convection from the sensing element to surrounding blood fluid, by measuring a voltage that needs to be applied across the heat sensing element in order to maintain the sensing element at a substantially constant temperature; and   deriving the shear stress at the desired location from the measured change in heat convection.   
     
     
         2 . An apparatus for measuring shear stress from arterial circulation, the apparatus comprising:
 a flexible catheter;   a MEMS sensor attached to the distal end of the flexible catheter;   wherein the MEMS sensor includes a heat sensing element disposed on a front-side surface of a substrate and interfacing a flow of blood through a vessel, the heat sensing element thermally insulated from the substrate through a cavity etched in the substrate, the heat sensing element electrically coupled a backside surface of the substrate by bond wires;   a driving circuit electrically coupled to the backside surface of the substrate and configured to drive the MEMS sensor, the driving circuit configured to apply an electric current through the sensing element to resistively heat the sensing element, the driving circuit further configured to apply a voltage across the sensing element necessary to maintain the sensing element at a substantially constant temperature; and   a processing system configured to determine from the voltage applied by the driving circuit a change in heat convection from the sensing element to blood surrounding the sensing element, and deriving from the change in heat convection a shear stress of blood flowing through the vessel past the sensing element.