Patent ID: 6413227
Filing Date: 2002-07-02
Classification: A61B

Abstract:
An apparatus for measuring phase shift in the head of a patient, the patient's head having layers comprised of skin, subcutaneous tissue, bone and intracranial tissue, wherein the interface between the bone and the intracranial tissue is a first interface and the interface between the intracranial tissue and the bone on the opposite side of the patient's head is a second interface, the apparatus comprising:a logic and timing circuit; a variable phase shift circuit; a tone burst formation gate; a fixed frequency oscillator coupled to and sending a constant frequency output to the logic and timing circuit, the variable phase shift circuit as a reference signal, and the tone burst formation gate; a transducer coupled to the tone burst formation gate and being acoustically coupled to the skin of the patient's head, so that an electrical tone burst is sent to the transducer which generates a first echo and a second echo in the patient's head, the first echo reflecting from the first interface in the side of the patient's head coupled to the transducer and the second echo reflecting from the second interface at the other side of the patient's head, the first and second echos being received by the transducer which generates a first electrical echo signal and a second electrical echo signal, wherein the first and second electrical echo signals vary in accordance with the corresponding first and second echos; means for receiving and comparing phases of the first and second electrical signals and the reference signal, and outputting error signal voltages when the phases of the first and second electrical signals and the reference signal are not in quadrature; a first sample and hold circuit and a second sample and hold circuit, wherein the first and second sample and hold circuits receive a corresponding one of the error signal voltages and pass the error signal voltages to integrator circuits which provide control signals for the variable phase shift circuit; means for measuring control signals from the integrator circuits which bring about quadrature via the variable phase shift circuit with the reference signal; and means for combining the control signals of the integrator circuits that control the variable phase shift circuit to bring about the quadrature with each electrical echo signal to remove extracranial effects from the measurements.