Method and apparatus for measuring the blood flow in the superficial blood vessels of tissue

Claim 1

A method for determining the blood flow in the superficial blood vessels of tissue, comprising the steps of irradiating a section of the surface of said tissue with monochromatic light; capturing light scattered by moving blood cells and adjacent stationary structures within a part of the irradiated tissue section; passing said captured, scattered light to a photodetector arrangement for producing an electric output signal containing fluctuating signal components, hereinafter referred to as the Doppler signal, which derive from interference between light components received by the photo-detector arrangement and having mutually different frequencies due to having been scattered by moving blood cells and thereby subject to shift in their frequency, said Doppler signal containing information concerning the number of blood cells present and the velocity at which they move; deriving from said Doppler signal produced by said photo-detector arrangement a first signal which represents the mean time value of the expression ##EQU4## where ω is the frequency of the Doppler signal, P(ω) is the power density of the Doppler signal as a function of its frequency, and ω 1 and ω 2 represent limit frequencies of a frequency band within which at least a major part of the Doppler signal is located; deriving from said Doppler signal a second signal which is solely dependent on the number of blood cells present, but not their velocity of movement; amplifying said first signal with an amplifying factor which is dependent on said second signal; and using said amplified signal as a measurement of the magnitude of the blood flow.

Claim 2

A method for determining the blood flow in the superficial blood vessels of tissue, comprising the steps of irradiating a section of the surface of said tissue with monochromatic light; capturing light scattered by moving blood cells and adjacent stationary structures within a part of the irradiated tissue section; passing said captured, scattered light to a photodetector arrangement for producing an electric output signal containing fluctuating signal components, hereinafter referred to as the Doppler signal, which derive from interference between light components received by the photo-detector arrangement and having mutually different frequencies due to having been scattered by moving blood cells and thereby subject to shift in their frequency, said Doppler signal containing information concerning the number of blood cells present and the velocity at which they move; deriving from said Doppler signal produced by said photo-detector arrangement a first signal which represents the mean time value of the expression ##EQU4## where ω is the frequency of the Doppler signal, P(ω) is the power density of the Doppler signal as a function of its frequency, and ω 1 and ω 2 represent limit frequencies of a frequency band within which at least a major part of the Doppler signal is located; deriving from said Doppler signal a second signal which is solely dependent on the number of blood cells present, but not their velocity of movement; amplifying said first signal with an amplifying factor which is dependent on said second signal; and using said amplified signal as a measurement of the magnitude of the blood flow.

Claim 9

An apparatus for determining the blood flow in the superficial blood vessels of tissue, comprising a monochromatic light source; means for irradiating a section of the tissue surface with light from said light source; means for collecting light scattered by moving blood cells and adjacent stationary structures within a part of said irradiated section; a photo-detector arrangement for receiving said collected, scattered light and producing a corresponding electric output signal; and a signal processor including high-pass filter circuits to which the output signal of said photo-detector arrangement is applied for removing d.c. signal components therefrom, first circuit means receiving the output signal of said high-pass filter circuits for producing a first signal representing the mean time value of the expression ##EQU6## where ω is the frequency of said output signal, P(ω) is the power of said output signal as a function of its frequency, and ω 1 and ω 2 are limit frequencies of a frequency band within which at least a major part of said output signal lies, second circuit means receiving the output signal of said high-pass filter circuits for producing a second signal proportional to the mean time value of the expression ##EQU7## where ω 3 and ω 4 are limit frequencies of a frequency band within which at least a major part of said output signal lies, and a controllable amplifying circuit having a signal input to which said first signal is applied, a control input to which said second signal is applied, and an amplifying factor controlled by and dependent on said second signal, the output signal of said amplifying circuit constituting a measurement of the blood flow.

Claim 10

An apparatus for determining the blood flow in the superficial blood vessels of tissue, comprising a monochromatic light source; means for irradiating a section of the tissue surface with light from said light source; means for collecting light scattered by moving blood cells and adjacent stationary structures within a part of said irradiated section; a photo-detector arrangement for receiving said collected, scattered light and producing a corresponding electric output signal; and a signal processor including high-pass filter circuits to which the output signal of said photo-detector arrangement is applied for removing d.c. signal components therefrom, first circuit means receiving the output signal of said high-pass filter circuits for producing a first signal representing the mean time value of the expression ##EQU6## where ω is the frequency of said output signal, P(ω) is the power of said output signal as a function of its frequency, and ω 1 and ω 2 are limit frequencies of a frequency band within which at least a major part of said output signal lies, second circuit means receiving the output signal of said high-pass filter circuits for producing a second signal proportional to the mean time value of the expression ##EQU7## where ω 3 and ω 4 are limit frequencies of a frequency band within which at least a major part of said output signal lies, and a controllable amplifying circuit having a signal input to which said first signal is applied, a control input to which said second signal is applied, and an amplifying factor controlled by and dependent on said second signal, the output signal of said amplifying circuit constituting a measurement of the blood flow.