Method of noninvasive optical measurement of properties of free-flowing blood

Abstract

The invention relates to a method of the noninvasive optical in-vivo measurement of properties of flowing blood in a blood vessel within a body, for example for determining the concentration of blood constituents, wherein the body is irradiated with ultrasound radiation at an ultrasound frequency (f.sub.US) in order to label a blood vessel, the body with the blood vessel is illuminated with light with at least one light wavelength and the back-scattered light is detected with a detector, the light component backscattered by the body outside of the blood vessel is modulated by a frequency (f.sub.MG) that corresponds to the frequency (f.sub.US) of the ultrasound radiation, and the light component backscattered inside the blood vessel is modulated due to the Doppler effect in flowing blood with a frequency (f.sub.MB) that is shifted by the Doppler shift (f.sub.D) with respect to the frequency (f.sub.US) of the ultrasound radiation, and an evaluation device extracts the signal component modulated by the shifted frequency (f.sub.MB) from the detector signal measured at the detector.

Claims

1. A method of noninvasive optical in-vivo measurement of properties of flowing blood in a blood vessel inside a body for determining concentration of blood components, the method comprising the steps of: directing ultrasound radiation at a predetermined modulation frequency at the flowing blood in the blood vessel inside the body, illuminating the flowing blood in the blood vessel and surrounding tissue with light having at least one wavelength of light such that a first portion of the light is back-scattered out of the body from the flowing blood modulated at a different modulation frequency shifted by the Doppler effect from the predetermined modulation frequency by the flowing blood while a second portion of the light is back-scattered from the surrounding tissue at the predetermined modulation frequency with no Doppler shift, detecting with a detector both the first and the second portions of the light back scattered out of the body, extracting from the detected back-scattered light of both of the first and the second portions only the first portion of the back-scattered light that is modulated at Doppler-shifted modulation frequencies other than the predetermined modulation frequency, generating with the detector from the first portion of extracted back-scattered light a signal corresponding to only the back-scattered light of the first portion with the Doppler shift, and extracting and evaluating the signal with an evaluation device to analyze the flowing blood to determine the concentration of the blood components, whereby only the light back-scattered from the flowing blood is analyzed.

2. The method according to claim 1, further comprising the step of: pulsing the ultrasound radiation with a predetermined pulse length and repetition time, and measuring intensity of the back-scattered light at the detector in a time window shifted by a delay, the time window corresponding to the predetermined pulse length of the ultrasound radiation.

3. The method according to claim 2, further comprising the step of: locating the blood vessel prior to measuring the intensity by analysis of an ultrasound echo back-scattered from the body.

4. The method according to claim 1, further comprising the step of: carrying out a reference measurement without light irradiation, and taking into account the reference measurement in the evaluation.

5. The method according to claim 1, further comprising the step of: generating the light by at least one laser light source.

6. The method according to claim 1, wherein the light illuminating the flowing blood and the surrounding tissue is of multiple different wavelengths and is emitted by a plurality of laser light sources, the illuminating and the detecting being performed sequentially or simultaneously.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention is illustrated below in greater detail with reference to one drawing that illustrates one single embodiment.

(2) The sole FIGURE of the drawing schematically shows a device for carrying out the described method.

SPECIFIC DESCRIPTION OF THE INVENTION

(3) The drawing shows a body 1 with a blood vessel 2 and the tissue surrounding the blood vessel 3. A laser device 4, an ultrasound generator 5, a detector 6, and a controller/evaluator 7 are included for the noninvasive optical measurement of properties of the blood. The body 1 with the blood vessel 2 is irradiated by the laser device 4 with light having at least one wavelength. The backscattered light is detected by the detector 6. This detector 6 only measures intensities, that is the backscattered photon stream is detected, without spatial resolution or frequency resolution at the detector. The wavelength of the irradiated laser light depends on the application, and thus on which properties and/or constituents of the blood will be analyzed.

(4) According to the invention, the body 1 is subjected to ultrasound radiation to label the blood vessel 2 with an ultrasound frequency f.sub.US. Due to the interaction of the ultrasound radiation and the blood and/or tissue, the backscattered light intensity is modulated by the frequency of the ultrasound radiation. In this case, the fact that the light component backscattered outside of the blood vessel 2 in the adjacent tissue 3 is modulated by a frequency f.sub.MG that corresponds exactly to the ultrasound frequency f.sub.US, is important. In contrast, the light component that is backscattered within the blood vessel 2 due to the Doppler effect in flowing blood is modulated by a frequency f.sub.MB that is shifted with respect to the ultrasound frequency f.sub.US by the Doppler shift f.sub.D.

(5) As such, the FIGURE indicates that the light components modulated by the frequency f.sub.MB and light components modulated by the frequency f.sub.MG reach the detector 6. The light components modulated by the frequency f.sub.MG are the result of scattering in the tissue 3, while the light components modulated by the frequency f.sub.MB are actually attributable to scattering within the bloodstream 2. In addition, however, light components that are not modulated at all also reach the detector 6, since they originate in areas that do not interact with an ultrasound pulse.

(6) According to the invention, only the photon stream component is extracted that is modulated by the frequency f.sub.MB, and is thus actually scattered back from the area of the moving blood. Consequently, the Doppler shift in the optical signal is analyzed. The entire backscattered photon stream consists of a time-invariant component and two modulated components, one being the modulated tissue component f.sub.MG and the other being the components modulated in the blood by the frequency f.sub.MB.

(7) In addition, background noise is detected at the detector that is independent of the incident light.

(8) The measurement using the described method can be carried out, for example, as follows:

(9) First, a blood vessel is sought. For this purpose, the pulsed ultrasound is directed into the body 1 above the blood vessel 2 at an appropriate angle Φ. The depth is scanned axially with selected travel times. The blood vessel 2 can be located by analyzing the ultrasound echo. The maximum ultrasound echo corresponds to the travel time at which the ultrasound pulse is in the blood vessel. The travel time of the maximum ultrasound echo corresponds to half of the time required by the ultrasound to travel the path through the tissue from the ultrasound transducer to the ultrasound receiver. The ultrasound echo evaluated in this manner then generates a signal, such as an audio signal, a light signal or the like. A trigger signal is then adjusted to a delay, and this delay corresponds to the travel time of the maximum ultrasound echo after the pulse generation. This trigger signal then starts the following optical measurements.

(10) For optical measurement, laser light is irradiated into the body 1. The detector data is detected in the set time window for the maximum ultrasound echo signal. This approach ensures that the time period of the measurement, and thus also the captured data, are restricted to the time regions in which modulation by an ultrasound pulse is actually to be expected in the region of the blood stream. One measurement process of capturing the backscattered light of the laser radiation consists of a sequence of repeated optical captures by the detector in the time window. In this way, the optical signals of the low frequency Doppler shift (audible frequencies in the Hz, KHz region) can be extracted from the optical signals of the frequency of the ultrasound (MHZ region). The laser radiation is irradiated continuously during the repetition within one measuring process, that is, the laser remains on during the repetition. Once the measurement is completed, the laser is switched off and/or the irradiation of the laser light ceases.

(11) In order to be able to extract background noise, the measuring process is also repeated without laser irradiation. If multiple wavelengths are used for a particular measurement, and, by way of example, multiple lasers are used, a repetition of the individual steps can optionally be carried out.

(12) As part of the evaluation, the fact is taken into account that the signal arriving at the detector, that is the photon stream, contains in addition to the laser-independent background noise a unmodulated component and therefore a time-constant component (DC value). In addition, the signal contains two modulated components, and consequently two “AC components”. The modulated component is the result of backscatter from the tissue. This component is modulated by the frequency f.sub.MG that exactly corresponds to the frequency of the ultrasound radiation f.sub.US. This component from the static part of the tissue is therefore periodically modulated by the ultrasound frequency f.sub.US in the megahertz region. In addition, a second modulated component arrives at the detector and is modulated due to the Doppler shift in the flowing blood with a shifted frequency f.sub.MB. This frequency f.sub.MB consequently differs from the ultrasound frequency f.sub.US by the Doppler shift f.sub.D (f.sub.MB=f.sub.US±f.sub.D). Due to pulsation of the blood, a mixture of multiple low frequencies in the hertz and kilohertz region is registered. In this way, it is possible to extract the signal component that is the result of the scattering in the bloodstream, and to determine, in the known manner, the particular properties of the blood, for example the concentration of certain blood components and/or the temperature.

(13) The device according to the invention therefore comprises, as is known, an ultrasound generator 5, at least one light source 4, for example a laser light source, and a detector 6, and particularly a controller/evaluator 7, and the controller/evaluator 7 is adapted in the inventive manner. The ultrasound generator 5 generates the ultrasound radiation, which need not necessarily be focused. It emits a pulsed signal. In addition to an ultrasound source, the ultrasound generator 6 also has one or more receivers that receive the signals that are observed in the set time window. The ultrasound transmitter and ultrasound receiver can be incorporated into the same transducer. A laser light source that generates continuous, monochromatic, coherent light of the desired wavelength is preferably used as the light source 4. It is therefore preferably a CW laser.

(14) The detector 6 has one or more detectors that are connected to each other in series or parallel and that detect the light emerging from the body in a very simple manner. In this case, there is no spatially resolved measurement in the detector, and also no frequency-resolved measurement. There is only the measurement of light intensities.

(15) The controller/evaluator 7 first controls the ultrasound generator 5. It adjusts the time window and generates the trigger signal for the start and stop of the optical captures. It can also switch the laser 4 on or off, and/or start and stop the laser irradiation. It also executes the measurement and evaluation algorithm, and provides appropriate signal conditioning (amplification, filtering, etc.). Therefore, the controller/evaluator 7 separates the unmodulated and the modulated components from the detector signal. In this case, generally known classical methods for isolating low frequencies from high-frequency mixed signals, for example, Fourier analysis, can be employed.