Method and apparatus for measuring the blood flow in the superficial blood vessels of tissue
First Claim
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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.
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Abstract
In a method and an apparatus for measuring the superficial blood flow in tissue, a section of the tissue is irradiated with monochromatic light from a laser source. Light scattered by moving blood cells and adjacent stationary structure within a part of the irradiated section is collected and passed to a photo-detector arrangement, which produces an output signal containing fluctuating signal components, a Doppler signal, deriving from interference between light components having differing frequencies due to having been scattered by moving blood cells and thereby subject to frequency shifts. The Doppler signal contains information concerning the number of blood cells present and the velocity at which they move. By means of a signal processor, there is derived from the Doppler signal a signal which is linearly related to the blood flow expressed as the product of the number of blood cells and their average velocity of movement, and a signal which is linearly related to the number of blood cells present.
122 Citations
13 Claims
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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;
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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4. A method as claimed in claim 1, wherein said first signal is obtained by squaring the Doppler signal, passing the squared signal through a filter having the transfer function H(ω
- )=ω and
then averaging the signal.
- )=ω and
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5. A method as claimed in claim 1, wherein said second signal is obtained by squaring the Doppler signal and averaging the squared signal.
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6. A method as claimed in claim 1, comprising the additional step of subtracting from both said first signal and said second signal a signal which is dependent on the total output signal of the photo-detector arrangement, in order to compensate for noise generated in the photodetector arrangement.
- 7. A method as claimed in claim 2, comprising the additional step of deriving from said second signal a third signal which is-proportional to the expression
- space="preserve" listing-type="equation">1n (1-h(c))
where h(c) is said signal dependent solely upon the number of blood cells present, and using said third signal as a measurement of blood-cell concentration.
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8. 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, anda 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. - View Dependent Claims (9, 10, 11, 12, 13)
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10. An apparatus as claimed in claim 8, wherein said first circuit means include a filter circuit having the transfer function H(ω
- )=ω
, a squaring circuit, and an averaging circuit.
- )=ω
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11. An apparatus as claimed in claim 8, wherein said second circuit means include a squaring circuit and an averaging circuit.
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12. An apparatus as claimed in claim 8, wherein said first and said second circuit means include means for subtracting from said first and said second signals a signal component dependent on the total output signal of the photo-detector arrangement, in order to compensate for noise generated in the photo-detector arrangement.
- 13. An apparatus as claimed in claim 8, wherein said signal processor includes third circuit means receiving said second signal for producing an output signal proportional to the expression
- space="preserve" listing-type="equation">1n (1-h(c))
where h(c) is said second signal, said output signal from said third circuit means constituting a measurement of the blood-cell concentration.
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Specification
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Current AssigneePerimed Kb
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Original AssigneePerimed Kb
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InventorsNilsson, Gert
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Primary Examiner(s)Howell, Kyle L.
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Assistant Examiner(s)Hanley, John C.
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Application NumberUS06/689,489Time in Patent Office505 DaysField of Search128/633, 128/634, 128/665, 128/666, 128/691US Class Current600/479CPC Class CodesA61B 5/0261 using optical means, e.g. i...
