Method and apparatus for optical sensing of tissue variation at increased accuracy
First Claim
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1. An apparatus for optical sensing of a variation of a matter provided in a tissue region, the apparatus comprising:
- at least one optical radiation source for transmitting a first optical signal of a first wavelength and a second optical signal of a second wavelength towards a tissue region, wherein a change of the matter'"'"'s wavelength-dependent absorption coefficient between the first wavelength and the second wavelength differs by more than 50 cm-1 from a corresponding change of the wavelength-dependent absorption coefficient of other matter which influences the first and second optical signals during transmission, while the difference between the first and second wavelengths is not greater than 30 nm;
at least one optical radiation detector for detecting a first portion of the first optical signal reflected at or transmitted through the tissue region and a second portion of the second optical signal reflected at or transmitted though the tissue region; and
at least one filter for filtering a predetermined component of the first portion of the first optical signal and a predetermined component of the second optical signal so that an unwanted component caused by the other matter is suppressed before amplification and subsequent signal processing.
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Abstract
The present embodiment relates to a method and apparatus for measuring a tissue variation signal (e.g. a photoplethysmographic (PPG) signal) without large direct current (DC) or low frequency (LF) offset which normally limit the sensor accuracy through motion artefacts and/or dynamic range requirements. The proposed solution is based on a separation of the PPG signal from the disturbance. This can be achieved by creation of a modulated PPG signal, or by creation of a differential PPG signal and an optimized sensor configuration which is adapted to remove DC or LF components.
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18 Claims
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1. An apparatus for optical sensing of a variation of a matter provided in a tissue region, the apparatus comprising:
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at least one optical radiation source for transmitting a first optical signal of a first wavelength and a second optical signal of a second wavelength towards a tissue region, wherein a change of the matter'"'"'s wavelength-dependent absorption coefficient between the first wavelength and the second wavelength differs by more than 50 cm-1 from a corresponding change of the wavelength-dependent absorption coefficient of other matter which influences the first and second optical signals during transmission, while the difference between the first and second wavelengths is not greater than 30 nm; at least one optical radiation detector for detecting a first portion of the first optical signal reflected at or transmitted through the tissue region and a second portion of the second optical signal reflected at or transmitted though the tissue region; and at least one filter for filtering a predetermined component of the first portion of the first optical signal and a predetermined component of the second optical signal so that an unwanted component caused by the other matter is suppressed before amplification and subsequent signal processing. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A method of optical sensing of a variation of a matter provided in a tissue region, the method comprising:
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transmitting by at least one optical radiation source a first optical signal of a first wavelength and a second optical signal of a second wavelength towards a tissue region, wherein a change of the matter'"'"'s wavelength-dependent absorption coefficient between the first wavelength and the second wavelength differs by more than 50 cm-1 from a corresponding change of the wavelength-dependent absorption coefficient of other matter which influences the first and second optical signals during transmission, while the difference between the first and second wavelengths is not greater than 30 nm; detecting by at least one optical radiation detector a first portion of the first optical signal reflected at or transmitted though the tissue region and a second portion of the second optical signal reflected at or transmitted though the tissue region; and filtering by at least one filter a predetermined component of the first portion of the first optical signal and a predetermined component of the second optical signal so that unwanted components caused by the other matter are suppressed before amplification and subsequent signal processing. - View Dependent Claims (18)
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Specification