SIGNAL PROCESSING UNIT FOR INTRAVASCULAR BLOOD FLOW DETERMINATION

Abstract

The invention relates to a signal processing unit (208) for determining a value of a blood flow quantity characterizing blood flow inside a blood vessel, wherein the signal processing unit comprises a vibration sensor signal input, which is configured to receive vibration sensor signals from an intravascular vibration sensor at two different measuring times, the vibration sensor signal comprising a vibration sensor signal component caused by blood flow oscillations of intravascular blood flow, and a blood flow determination unit which, for each measuring time, is configured to determine the vibration sensor signal components using the vibration sensor signal, to determine a respective oscillation frequency of the blood flow oscillations using the vibration sensor signal component and to determine and provide a frequency ratio of the determined oscillation frequencies as the value of the blood flow quantity.

Claims

1. A signal processing unit for determining a value of a flow reserve characterizing blood flow inside a blood vessel, the signal processing unit comprising: a vibration sensor signal input, which is configured to receive vibration sensor signals from a vibration sensor at two different measuring times corresponding to a rest and a hyperemia condition while an intravascular device comprising the vibration sensor is not moved within the blood vessel, the vibration sensor signals comprising vibration sensor signal components caused by blood flow oscillations of intravascular blood flow at respective measuring times; and a blood flow determination unit which is configured, using the vibration sensor signals, to determine the vibration sensor signal components at the two different measuring times; using the vibration sensor signal components, to determine a respective oscillation frequency of the blood flow oscillations at the two different measuring times; and, using the determined oscillation frequencies of the blood flow oscillations, to determine and provide a frequency ratio of the determined oscillation frequencies at the two different measuring times as the value of the flow reserve.

2. The signal processing unit of claim 1, wherein the blood flow determination unit comprises a signal transformation unit, which is configured to determine a frequency-domain representation of the vibration sensor signal received during a predetermined measuring time span and to determine the oscillation frequency of the blood flow oscillations using the frequency-domain representation.

3. The signal processing unit of claim 2, wherein the blood flow determination unit comprises a filter unit configured to filter out frequency components of the vibration sensor signal that are associated with a heartbeat frequency.

4. The signal processing unit of claim 1, wherein the flow reserve is a coronary flow reserve.

5. The signal processing unit of claim 1, further comprising a user interface configured to allow a user providing a user input for triggering a measurement for providing to the signal processing unit a first vibration sensor signal, wherein the blood flow determination unit, in response to receiving the user input, is configured to receive a sequence of vibration sensor signals at different measuring times, and to determine and provide the frequency ratio of the determined oscillation frequencies for the given different measuring times with respect to the oscillation frequency determined from the first vibration sensor signal.

6. The signal processing unit of claim further configured to extract the vibration sensor signals from a wireless carrier signal.

7. An intravascular blood flow sensor system, which comprises: an intravascular device such as a guidewire or catheter for intravascular insertion; and a vibration sensor arranged and configured to provide vibration sensor signals indicative of the oscillation frequency of blood flow oscillations; and a signal processing unit according to claim 1.

8. The intravascular blood flow sensor system of claim 7, wherein the intravascular device has a bluff part that is shaped for generation of vortices propagating along a main direction of intravascular blood flow.

9. The intravascular blood flow sensor system of claim 7, further comprising a signal communication unit configured to receive the vibration sensor signals and to transmit the vibration sensor signals via a wireless carrier signal to the signal processing unit; and wherein the signal processing unit is a signal processing unit further configured to extract the vibration sensor signals from a wireless carrier signal.

10. The intravascular blood flow sensor system of claim 7, wherein the vibration sensor is arranged in a tip section of the intravascular device and wherein the tip section is elastically deformable in a direction perpendicular to a main direction of intravascular blood flow by the blood flow oscillations.

11. The intravascular blood flow sensor system of claim 7, wherein the vibration sensor comprises a flagellum that extends from the intravascular device in the main direction of intravascular blood flow and is elastically deformable in the direction perpendicular to the main direction of intravascular blood flow by the blood flow oscillations.

12. The intravascular blood flow sensor system of claim 11, wherein the flagellum is an optical fiber segment configured to receive and guide light to and from a reflective fiber-segment tip; further comprising a light source configured to provide light for coupling into the fiber segment; and a light sensor arranged to receive light reflected from the fiber-segment tip and modulated in intensity by oscillating deformation of the fiber segment, the light sensor being configured to provide the vibration sensor signal in the form of a light-sensor signal indicative of a time-varying reflected light intensity.

13. The intravascular blood flow sensor system of claim 7, wherein the vibration sensor comprises: one or more pressure sensors arranged on a surface of the intravascular device, the pressure sensor being arranged and configured to measure a time-varying pressure exerted in the direction perpendicular to the main direction of intravascular blood flow by the blood flow oscillations and to generate and provide the vibration sensor signal in the form of a time-varying electrical signal depending on the measured pressure.

14. The intravascular blood flow sensor system of claim 11, wherein the bluff part comprises a barrier section that protrudes from the intravascular device in the direction perpendicular to the main direction of intravascular blood flow for generation of vortices propagating along the main direction of intravascular blood flow.

15. A computer program comprising executable code for performing, when executed by a programmable processor of a computer, a method for operating a signal processing unit for determining a value of a flow reserve characterizing blood flow inside a blood vessel, the method comprising: receiving vibration sensor signals from vibration sensor at two different measuring times corresponding to a rest and a hyperemia condition while an intravascular device comprising the vibration sensor is not moved within the blood vessel, the vibration sensor signals comprising a vibration sensor signal component caused by blood flow oscillations of intravascular blood flow; determining, using the vibration sensor signals, the vibration sensor signal component at the two different measuring times; determining, using the vibration sensor signal component, a respective oscillation frequency of the blood flow oscillations at the two different measuring times; and determining and providing, using the oscillation frequencies of the blood flow oscillations, a frequency ratio of the determined oscillation frequencies at the two different measuring times as the value of the flow reserve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0074] In the following drawings:

[0075] FIG. 1a shows a schematic representation of a flow of a medium around stream-line shaped object;

[0076] FIG. 1b shows a schematic representation of the same flow of the medium around a bluff or barrier generating vortices in the flow;

[0077] FIG. 2 illustrates an embodiment of an intravascular blood flow sensor system comprising a signal processing unit and an intravascular blood flow sensor;

[0078] FIG. 3 shows another embodiment of an intravascular blood flow sensor system;

[0079] FIG. 4 shows another embodiment of an intravascular blood flow sensor system;

[0080] FIG. 5 shows another embodiment of an intravascular blood flow sensor system;

[0081] FIG. 6 is a flow diagram of a method for controlling operation of an intravascular blood flow sensor; and

[0082] FIG. 7 is a flow diagram of a method for operating a signal processing unit for determining a value of a blood flow quantity characterizing blood flow inside a blood vessel.

DETAILED DESCRIPTION OF EMBODIMENTS

[0083] FIG. 1a and FIG. 1b show schematic illustrations of blood flow around a stream-line shaped object 100.a and around a bluff body 100.b in a blood vessel 101 at a fixed time. An incoming blood flow 102 in a main direction of blood flow that is indicated by the arrows 103 is the same in both figures and generally illustrated by straight flow lines upstream of the bluff body. In FIG. 1a, a stream-lined shape of the object 100.a does not generate vortices in the blood flow behind the object 104.a. In the case of FIG. 1b, the bluff body 100.b generates vortex shedding in the blood flow behind it.

[0084] Generally, vortex shedding is known per se as an oscillating flow that occurs under suitable circumstances when a fluid flows past a bluff body. The parameters relevant for vortex shedding to occur comprise a viscosity of the fluid, a flow velocity, as well as a size and shape of the object. The former can be characterized, for example, by a Reynolds number. The vortex shedding induced by the presence of the bluff body 100.b in the blood flow 102 generates a so-called Krmn vortex street 104.b downstream of the bluff body 100.b. Existing vortices propagate to positions further away from the bluff body along the main direction of blood flow indicated by the arrows 102, while new vortices are generated close to the body 100.b. Vortices are generated at alternating sides of the body and are associated with oscillations in the blood flow in a direction perpendicular to the main flow direction. At a given time, the vortices generated are distributed as exemplarily shown in FIG. 1b.

[0085] It is noted that the use of vortex-generated blood flow oscillations forms an advantageous embodiment. However, blood flow oscillations generated by other causes can be used to the same effect in other embodiments. The generation of such blood flow oscillations may be due to the inserted guidewire or catheter, or it may be due to intrinsic causes such as the geometry of the blood vessel. The present description of embodiments with reference to the drawings focuses in some parts on the example of vortex-generated blood flow oscillations without intention to thereby restrict the scope of the invention to such cases.

[0086] FIG. 2 is a schematic illustration of an embodiment of an intravascular blood flow sensor system 200 for measuring blood flow inside a blood vessel 201. The intravascular blood flow sensor 200 comprises an intravascular blood flow sensor 203 and a signal processing unit 208 for determining a value of a blood flow quantity characterizing blood flow inside a blood vessel 201. The signal processing unit 208 comprises a vibration sensor signal input 211 that receives vibration sensor signals from an intravascular vibration sensor at two different measuring times. The vibration sensor signals comprise a vibration sensor signal component caused by, for instance, vortex-generated blood flow oscillations of intravascular blood flow at a respective one of the measuring times. In general, the vibration sensor signal component caused by the vortex-generated blood flow oscillations is a component in a direction perpendicular to the main direction of blood flow. The signal processing unit 208 further comprises a blood flow determination unit 213 with is configured to determine the vibration sensor signal component at the two different measuring times using the vibration sensor signal, to determine the oscillation frequencies of the vortex-generated blood flow oscillations at the two different measuring times using the vibration sensor signal components, and to determine and provide a frequency ratio of the determined oscillation frequencies at the two different measuring times as the value of the blood flow quantity, using the determined oscillation frequencies. In this exemplary signal processing unit 208 these three distinct tasks are performed by three respective units 213.1, 213.2 and 213.3. In other signal processing units, the three described tasks are performed by a processor.

[0087] Some signal processing units include a blood flow determination unit that additionally comprises a signal transformation unit (212), which is configured to determine a frequency-domain representation of the vibration sensor signal received during a predetermined measuring time span and to determine the oscillation frequency of the (e.g. vortex-generated) blood flow oscillations using the frequency-domain representation. To this end, the signal transformation unit 212 receives the vibration sensor signals from the vibration sensor signal input over a predetermined measuring time span associated with a given measuring time. The signal transformation unit 212 determines the oscillation frequency for the given measuring time using a frequency-domain representation of the vibration sensor signal during the respective measuring time span. Suitably, the signal transformation unit 212 is a Fast Fourier Transform unit that determines the Fourier Transform of the vibration sensor signal. From the transformed vibration sensor signal, an oscillation frequency can be determined in a simple manner as a frequency of a Fourier component having a maximum amplitude in an expected oscillation frequency range above 100 Hz, typically in the range of a few hundred Hz.

[0088] To make detection of the oscillation frequency easier, some signal processing units of the present embodiment further comprises a filter unit 214 that is configured to filter out frequency components from the vibration sensor signal that are associated with heart beat frequency. The heart beat frequency range is typically below 100 Hz.

[0089] The signal processing unit determines a frequency ratio of the determined oscillation frequencies at two measuring times. This way, blood flow quantities can be determined. Such blood flow quantities provide important information regarding the current physiological state of a blood vessel, and assist in the identification and quantitative characterization of a stenosis. For calculation and output of the CFR value, the measurements are made in a state of hyperemia and in a state of normal blood flow (e.g., at rest). The coronary flow reserve (CFR) is then determined and provided by the signal-processing unit with particular ease and reliability as the frequency ratio of respective vibration sensor signals at the measuring time corresponding to the state of hyperemia and at the measuring time corresponding to the state of normal blood flow.

[0090] In some signal processing units, a user interface 210 is provided for user input of control signals, such as for triggering the oscillation measurements by controlling the operation of the vibration sensor signal input, and for output of the value of the blood flow quantity determined. The user interface is in some embodiments used to provide geometrical data indicative of a characteristic size of the blood vessel at a current intravascular position of the intravascular blood flow sensor, which is required to provide a value of a flow velocity according to:

[00003]$v=\frac{f.Math.d}{S},$

wherein [0091] v is the flow velocity; [0092] f is the determined oscillation frequency of the vortex-generated blood flow oscillation; [0093] d is the characteristic size of the blood vessel; and [0094] S is a constant representing the Strouhal number applicable to blood flow in the given blood vessel.

[0095] In other signal processing units, the geometrical data is locally stored in a storage unit 215 which is accessed by the blood flow determination unit 213 for determining the value of the flow velocity v.

[0096] In other embodiments, the signal processing unit receives the geometrical data from an external imaging device or an external image processing device that is configured to image the blood vessel at a current intravascular position of the intravascular blood flow sensor and to determine and provide the geometrical data at that position.

[0097] As another mode of operation, which is available to a user as an alternative to the CFR determination, the signal processing unit 208 determines and provides relative changes in blood flow over time from a sequence of measurements, as compared to a first measurement of the sequence that can be triggered by user input.

[0098] The intravascular blood flow sensor system 200 comprises an intravascular blood flow sensor 203. In this particular intravascular blood flow sensor system, the intravascular blood flow sensor includes an intravascular guidewire 202 that has a guidewire body 204 with an atraumatic tip section 204.1 comprising a bluff part 205 that is suitably shaped for generation of vortices propagating along a main direction L of intravascular blood flow. It is noted that the bluff part 205 of the intravascular blood flow sensor need not necessarily be different in shape from other parts of the guide wire body 204 for enabling the formation of vortices. However, to facilitate reliable generation of vortices even at low blood flow velocities, it is advantageous to add features that shape the body of a typical guide wire or catheter in a less stream-lined way, such as for example providing a guidewire or a catheter comprising a bluff part.

[0099] The guidewire body 204 may have a rotational symmetry along its longitudinal direction, which in FIG. 2 corresponds to the direction L. However, in other embodiments (not shown), the generation of vortices is alternatively or additionally made possible or enhanced by providing a shape of the microcatheter or guidewire that exhibits a break of a rotational symmetry in at least part of the tip.

[0100] The tip section 204.1 includes a vibration sensor 206. The vibration sensor 206 comprises a flagellum 206.1 extending from a front surface of the tip section 204.1 in the main direction L of the intravascular blood flow. The flagellum 206.1 is elastically deformable in a direction P perpendicular to L which in the present example are the two mutually opposite directions P. An oscillating bending motion of the flagellum 206.1 in the direction P is driven by the vortex-generated oscillating motion of blood, as explained with reference to FIG. 1b. At a given time, the propagating vortices thus show a respective distribution that alternates vortices at different downstream positions of the tip section 204.1 in the longitudinal direction L (as exemplarily shown in FIG. 1b). Vortex-generated oscillations may occur in any direction that is perpendicular to the longitudinal direction L.

[0101] In a real 3D vessel, more complex vortex configurations are possible that cannot be faithfully represented in a 2D illustration such as FIGS. 1a and 1b. The vibration sensor is thus configured to provide a vibration sensor signal indicative of the blood flow oscillations, but not necessarily of the propagation direction of the vortices.

[0102] The flagellum 206.1 is shown in FIG. 2 in two different phases of an oscillating bending motion corresponding to two different bending positions of the flagellum 206.1. A first phase of the oscillating motion is represented by a solid line, and a second phase is represented by a dotted line.

[0103] The flagellum 206.1 comprised by the vibration sensor 206 can be made of an electro-active polymer material and configured to generate and provide the vibration sensor signal in the form of a time-varying electrical signal having an amplitude depending on a deformation amount in the direction perpendicular to the main direction of intravascular blood flow.

[0104] In a variant of the intravascular blood flow sensor of FIG. 2, the flagellum comprised by the vibration sensor 206 is an optical fiber segment configured to receive and guide light to and from a reflective fiber-segment tip. These particular intravascular flow sensors also comprise a light source that is configured to provide light for coupling into the fiber segment and a light sensor arranged to receive light reflected from the fiber-segment tip and modulated in intensity by oscillating deformation of the fiber segment. The light sensor is configured to provide the vibration sensor signal in the form of an electronic light-sensor signal indicative of a time-varying reflected light intensity.

[0105] A further variant of the intravascular blood flow sensor of FIG. 2, which is not shown, comprises, instead of the guidewire 202, a microcatheter provided with the flagellum-type vibration sensor 206 in its tip section. The above description is otherwise equally applicable to that variant.

[0106] FIG. 3 illustrates another exemplary embodiment of an intravascular blood flow sensor system 300 for measuring blood flow inside a blood vessel 301. The blood flow sensor system 300 comprises a micro-catheter 302 for intravascular insertion. A catheter body 304 of the micro-catheter may have a rotational symmetry along its longitudinal direction, which in FIG. 3 corresponds to the direction L. A tip section 304.1 of the catheter body 304 forms a bluff body part and is suitably shaped for generation of vortices propagating along a main direction L of intravascular blood flow. The tip section 304.1 is elastically deformable by vortex-generated blood flow oscillations in the directions P perpendicular to the main direction L of intravascular blood flow. A vibration sensor 306 is arranged in the tip section 304.1. The vibration sensor 306 is a motion sensor, suitably an acceleration sensor. As such, it provides an electrical sensor signal indicative of an oscillatory bending motion of the tip section 304.1 driven by the vortex-generated oscillations of blood flow in the vessel 301 at the location of the tip section 304.1. This sensor signal thus forms a suitable vibration sensor signal that is indicative of the oscillation frequency of the vortex-generated blood flow oscillations that propagate in the direction L.

[0107] The vibration sensor signals are provided by the vibration sensor 306 and received by a signal processing unit 308, which is arranged outside the body of the patient. Details of signal communication and signal processing have been described in the context of the embodiment of FIG. 2 and are applicable here as well. A user may interact with the intravascular flow sensor 300 via a user interface 310, as also described above in more detail with reference to FIG. 2.

[0108] A variant of the intravascular blood flow sensor system of FIG. 3, which is not shown, comprises, instead of the microcatheter 302, a guidewire provided with the vibration sensor 306 in its tip section. The above description is otherwise equally applicable to that variant.

[0109] A variant of the intravascular blood flow sensor system of FIG. 3 comprises an additional bluff part 312 in the microcatheter body 304 of the microcatheter 302. The bluff part 312 is arranged at a short distance from the tip section 304.1 in direction of the proximal end of the microcatheter 302. The presence of the bluff part 312 further enhances vortex shedding that induces a vibration of the tip section 304.1, where the vibration sensor 306 is arranged.

[0110] FIG. 4 illustrates another embodiment of an intravascular blood flow sensor system 400 for measuring blood flow inside a blood vessel 401.

[0111] The intravascular blood flow sensor system 400 comprises a microcatheter 402 with a catheter body 404 for intravascular insertion. A tip section 404.1 of the catheter body comprises a barrier section 405 that protrudes from the catheter body in a direction P perpendicular to the main direction of intravascular blood flow, in order to enhance the generation of vortices propagating along the main direction L of intravascular blood flow. Such a barrier 405 may also be present in the tip section in variants of the embodiments of FIGS. 1 to 3. The shape of the barrier section 405 is only schematically indicated in FIG. 4. Any shape that is suitable to favor generation of vortices over laminar blood flow along the tip section 404.1 of the catheter body 404 can be used.

[0112] A vibration sensor is provided in the form of a pressure sensor 406 located on a surface of the tip section 404.1 of the catheter body 404. The pressure sensor 406 is arranged and configured to measure pressure exerted in the direction P perpendicular to the main direction L of the turbulent intravascular blood flow, and thus particularly detects the vortex-generated blood flow oscillations as corresponding pressure oscillations. The pressure sensor 406 generates a vibration sensor signal in the form of a time-varying electrical signal depending on the pressure currently sensed. The pressure sensor 406 provides the vibration sensor signal to a signal processing unit 408, using one of the signal communication techniques explained in the context of the embodiment of FIG. 2. A user may interact with the intravascular blood flow sensor 400 via a user interface 410, as also explained hereinabove.

[0113] Intravascular blood flood devices comprising one or more pressure sensors such as the pressure sensor 406 can additionally determine a value of a fractional flow reserve (FFR). Fractional flow reserve is the ratio of blood pressure after i.e., distal to a stenosis and the blood pressure before the stenosis. This determination is based on evaluating a low frequency band of the measured time-varying electrical signal. As mentioned, Vortex-induced frequencies within the vibration signal typically are at frequencies in the range of a few 100 Hz and are overlaid with low-frequency signal components associated with the heartbeat. The latter components have a frequency clearly below 100 Hz, typically around 1 Hz. FFR can thus be determined from the low frequency pressure signal that depicts the pressure changes over the heart cycle while CFR can be determined from the high frequency vortex-induced component.

[0114] A variant of the intravascular blood flow sensor system of FIG. 4, which is not shown, comprises two pressure sensors on opposite sides of the of guide wire body 404. Then they can derive a flow sensing frequency signal by determining the differences between two pressure signals determined by the respective pressure sensors. The intravascular blood flow sensor is then configured to compute a blood pressure signal (for FFR) by averaging over the two signals determined by each of the two pressure sensors.

[0115] A variant of the intravascular blood flow sensor system of FIG. 4, which is not shown, comprises, instead of the microcatheter 402, a guidewire provided with the pressure sensor 406 in its tip section. The above description is otherwise equally applicable to that variant.

[0116] FIG. 5 shows a further embodiment of an intravascular blood flow sensor system 500 in an inserted state inside a blood vessel 501. The blood flow sensor system 500 comprises a guidewire 502 with a guidewire body 504. The blood flow sensor system 500 also comprises a vibration sensor 506 implemented as any of the different kinds of vibration sensors discussed with reference to the embodiments of FIGS. 2-4.

[0117] The blood flow sensor system 500 further comprises a signal communication unit 508 that is configured to receive the vibration sensor signals from the vibration sensor 506 and to perform wireless transmission of the vibration sensor signals to the signal processing unit 510 using a carrier signal. The signal processing unit 510 has a corresponding signal communication unit, of which only an antenna 511 is shown, that is configured to receive the carrier signal and to extract the vibration sensor signals from the carrier signal. The signal processing unit 510 then determines respective oscillation frequencies of vortex-generated blood flow oscillations at at least two different measuring times and determines and provides as an output a frequency ratio of the determined oscillation frequencies at the two measuring times. A user may interact with the blood flow sensor 500 via a user interface 512, as explained above. The user input may also be provided using wireless communication.

[0118] As shown in FIG. 5, the signal communication unit 508 is to be located outside the living being under examination. However, in a variant (not shown), the signal communication unit 508 is integrated into the guidewire body 504 and thus inserted in the blood vessel during operation. In these cases, the transmission of the vibration sensor signals is suitably performed using radio communication protocols such as for example any of the IEEE 801.11 standards for wireless communication, a Bluetooth-based wireless communication protocol, or any other radio-based wireless communication protocol.

[0119] FIG. 6 shows a flow diagram of a method 600 for controlling operation of an intravascular blood flow sensor. The method comprises a step 602 in which an intravascular blood flow sensor for measuring blood flow inside a blood vessel is provided. The intravascular blood flow sensor comprises a guidewire or catheter for intravascular insertion having a bluff part that is shaped for generation of vortices propagating along a main direction of intravascular blood flow and a vibration sensor arranged and configured to provide a vibration sensor signal indicative of an oscillation frequency of vortex-generated blood flow oscillations in a direction perpendicular to the main direction of intravascular blood flow.

[0120] In a step 604, a vibration sensor signal is measured at two different measuring times using the vibration sensor. In a step 606, respective oscillation frequencies of the vortex-generated blood flow oscillations at the two different measuring times are determined. In a final step 608, a frequency ratio of the determined oscillation frequencies at the two measuring times is determined.

[0121] FIG. 7 shows a flow diagram describing a method 700 for operating a signal processing unit for determining a value of a blood flow quantity characterizing blood flow inside a blood vessel. The method comprises a step 702 in which a signal processing unit receives vibration sensor signals from an intravascular vibration sensor at two different measuring times, the vibration sensor signals comprising a vibration sensor signal component caused by vortex-generated blood flow oscillations of intravascular blood flow at a respective one of the measuring times. In a step 704, the signal processing unit determines the vibration sensor signal component at the two different measuring times using the vibration sensor signal. In a step 706, the signal processing unit determines a respective oscillation frequency of the vortex-generated blood flow oscillations at the two different measuring times using the vibration sensor signal components, and finally, in a step 708, the signal processing unit determines, using the oscillation frequency of the vortex-generated blood flow oscillations, and provides, the value of the blood flow quantity. In summary, a signal processing unit for determining, in an alternative way, a value of a blood flow quantity characterizing blood flow inside a blood vessel comprises a vibration sensor signal input, which is configured to receive vibration sensor signals from an intravascular vibration sensor at two different measuring times, the vibration sensor signal comprising a vibration sensor signal component caused by blood flow oscillations of intravascular blood flow, and a blood flow determination unit which for each measuring time, is configured to determine the vibration sensor signal components using the vibration sensor signal, to determine a respective oscillation frequency of the blood flow oscillations using the vibration sensor signal component and to determine and provide a frequency ratio of the determined oscillation frequencies as the value of the blood flow quantity.

[0122] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0123] In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality.

[0124] A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium, supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0125] Any reference signs in the claims should not be construed as limiting the scope.