Patent ID: 7762958
Filing Date: 2010-07-27
Classification: A61B

Abstract:
1. An apparatus comprising: a needle having dimensions suitable for insertion into a body, a distal portion suitable for insertion into tissue, a distal opening, and a lumen extending from a proximal end to the distal opening and in communication with the distal opening to allow a substance to be delivered through the lumen and out of the opening; a thermally conductive heating element coupled to the distal portion of the needle, the heating element comprising material whose electrical resistance changes in response to a change in temperature; and an interface to a balanced circuit having the heating element and a variable resistor as resistive circuit elements, wherein the balanced circuit measures a first differential resistance between the heating element and the variable resistor in response to a first condition and a second differential resistance in response to a second condition in circuitry to indicate a change of conditions related to a distance of penetration of the thermally conductive heating element into a tissue from a fluid boundary with the tissue, wherein the first condition comprises the distal portion of the needle penetrating a vessel wall first location and disposed in fluid, and the second condition comprises the distal portion of the needle extending through the fluid and disposed within tissue of a vessel wall second location.