Method and device for positioning a Doppler ultrasound transducer for blood flow measurement and a system for blood flow measurement

Abstract

The method of positioning a Doppler ultrasound transducer for performing blood flow measurement according to the invention comprises the steps of: detecting a pressure oscillation signal from an inflated cuff placed on patient's artery; detecting an ultrasound pulse signal from the Doppler ultrasound transducer placed along the artery; deriving a first signal from the pressure oscillation signal and the ultrasound pulse signal, the first signal indicating the degree of synchronization between the pressure oscillation signal and the ultrasound pulse signal; and outputting an indication signal to indicate the Doppler ultrasound transducer is in a desired position when the first signal satisfies a predefined condition. Since the synchronization property of the cuff pressure oscillation signal and the ultrasound signal caused by the blood flow is utilized to determine whether the transducer is well positioned or not, ultrasound signal, which is a pulse signal but not reflecting the blood flow of the artery, could be determined as not in synchronization with the oscillation signal and therefore the accuracy of the positioning could be improved.

Claims

1. A method of positioning a Doppler ultrasound transducer for blood flow measurement, comprising: with a pressure sensor, detecting a pressure oscillation from an inflated cuff placed on an artery of a patient and outputting a pressure oscillation signal; with a Doppler ultrasound transducer placed along the artery, detecting an ultrasound pulse and outputting an ultrasound pulse signal; with at least one electronic processor, deriving, from the pressure oscillation signal and the ultrasound pulse signal, a first signal indicating the degree of synchronization between the pressure oscillation signal and the ultrasound pulse signal, the first signal being derived from the time intervals measured between two consecutive peaks of the pressure oscillation signal Δt.sub.osi(i=1 . . . n) and the time intervals measured between two corresponding consecutive pulses of the ultrasound pulse signal Δt.sub.usi(i=1 . . . n); and on a display, indicating that the Doppler ultrasound transducer is in a desired position in response to the first signal satisfying a predefined condition including(Δt.sub.usi−Δt.sub.osi)/Δt.sub.osi≦x %, wherein n is at least two and x is a preselected percent.

2. The method of claim 1, wherein the at least one electronic processor is programmed to: derive the first signal by computing (Δt.sub.usi−Δt.sub.osi)/Δt.sub.osi, and the first signal satisfies the predefined condition in response to (Δt.sub.usi−Δt.sub.osi)/Δt.sub.osi≦8%.

3. The method of claim 2, wherein n is five.

4. The method of claim 1, wherein detecting a pressure oscillation signal from the inflated cuff placed on an artery of a patient comprises, with the at least one electronic processor: obtaining the pressure signal from the pressure sensor connected with the inflated cuff; determine whether the pressure oscillation signal is detected by the Doppler ultrasound transducer; and increasing the pressure in the inflated cuff in response to the pressure oscillation signal not being detected.

5. The method of claim 4, inflating the cuff to about 80 mmHg.

6. The method of claim 4, wherein detecting the ultrasound pulse signal from the Doppler ultrasound transducer placed along the artery comprises: determining, with the Doppler ultrasound transducer, the pulse and outputting the ultrasound pulse signal in response to the pressure oscillation signal being detected.

7. The method of claim 6, further comprising: with the at least one electronic processor, outputting a prompting signal to the display prompting the operator to relocate the Doppler ultrasound transducer in response to the ultrasound signal from the Doppler ultrasound transducer is not a pulse.

8. The method of claim 1, wherein outputting the indication signal comprises: turning on an indication lamp of the Doppler ultrasound transducer or changing the color of the Doppler ultrasound transducer on the display of the Doppler ultrasound device.

9. A device for positioning a Doppler ultrasound transducer for blood flow measurement, comprising: at least one electronic processor programmed to: receive a pressure oscillation signal from an inflated cuff placed on an artery of a patient; receive an ultrasound pulse signal from a Doppler ultrasound transducer placed along the artery; derive a first signal from the pressure oscillation signal and the ultrasound pulse signal, the first signal indicating the degree of synchronization between the pressure oscillation signal and the ultrasound pulse signal, the first signal being derived by from the time intervals measured between two consecutive peaks of the pressure oscillation signal Δt.sub.osi(i=1 . . . n) and the time intervals measured between two corresponding consecutive pulses of the ultrasound pulse signal Δt.sub.usi(i=1 . . . n); and an interface configured to output an indication signal to indicate that the Doppler ultrasound transducer is in a desired position when the first signal satisfies a predefined condition including (Δt.sub.usi−Δt.sub.osi)/Δt.sub.osi≦x %, wherein n is at least two and x is a preselected percent.

10. The device according to claim 9, wherein the at least one electronic processor is programmed to: derive the first signal by computing (Δt.sub.usi−Δt.sub.osi)/Δt.sub.osi, and the first signal satisfies the predefined condition in response to (Δt.sub.usi−Δt.sub.osi)/Δt.sub.osi≦8%.

11. The device according to claim 9, further including a pressure sensor connected with the inflated cuff to sense the pressure oscillations and output a pressure oscillation signal; wherein the at least one electronic processor is further reprogramed to: determine whether the pressure oscillation signal is detected; and increase the pressure in the inflated cuff in response to the pressure oscillation signal not being detected.

12. The device according to claim 11, wherein the at least one electronic processor is programmed to: determine whether the ultrasound signal from the Doppler ultrasound transducer placed along the artery is a pulse signal in response to the pressure oscillation signal being detected.

13. A system for blood flow measurement, comprising a cuff placed on an artery of a patient; a Doppler ultrasound transducer placed along the artery; and the device for positioning a Doppler ultrasound transducer for blood flow measurement according to claim 9.

14. The device according to claim 9, wherein the interface is configured to: output a relocation signal to the display for relocating the Doppler ultrasound transducer when the ultrasound signal from the Doppler ultrasound transducer placed along the artery is not a pulse signal.

15. The device according to claim 14, wherein the interface is configured to at least one of: turn on an indication lamp of the Doppler ultrasound transducer; and change the color of the Doppler ultrasound transducer on a display of the interface.

16. A device for positioning a Doppler ultrasound transducer for blood flow measurement, the device comprising: a cuff placed on an artery of a patient; a pressure sensor connected with the cuff, the pressure sensor being configured to sense pressure oscillations and output a pressure oscillation signal; a Doppler ultrasound transducer placed along an artery, the transducer being configured to sense an ultrasound pulse and output an ultrasound pulse signal; one or more electronic processors programmed to: receive the pressure oscillation signal from the cuff when the cuff is placed on the artery of a patient and inflated; detect an ultrasound pulse signal from the Doppler ultrasound transducer placed along the artery; derive a first signal from the pressure oscillation signal and the ultrasound pulse signal from the time intervals measured between two consecutive peaks of the pressure oscillation signal Δt.sub.osi(i=1 . . . n) and the time intervals measured between two corresponding consecutive pulses of the ultrasound pulse signal Δt.sub.usi(i=1 . . . n); and an interface configured to: output an indication signal to indicate that the Doppler ultrasound transducer is in a desired position when the first signal satisfies a predefined condition, the predefined condition including (Δt.sub.usi−Δt.sub.osi)/Δt.sub.osi≦x %, wherein n is at least two and x is a preselected percent; and output a prompting signal to a display of the interface to relocate the Doppler ultrasound transducer when the ultrasound signal from the Doppler ultrasound transducer placed along the artery is not a pulse signal; wherein the indication signal and the prompting signal each include one of turning on an indication lamp of the Doppler ultrasound transducer, generating a sound, or changing the color of the Doppler ultrasound transducer on the display.

17. The device according to claim 16, wherein the at least one electronic processor is further programmed to: determine whether the pressure oscillation signal is detected; and increase the pressure in the inflated cuff until the pressure oscillation signal is detected.

18. The device according to claim 16 wherein the at least one electronic processor is further programmed to: in response to the pressure oscillation signal being detected, determine whether the ultrasound signal from the Doppler ultrasound transducer placed along the artery is a pulse, wherein x is approximately 8%.

Description

DESCRIPTION OF THE DRAWINGS

(1) The present invention will be described and explained hereinafter in more detail in combination with embodiments and with reference to the drawings, in which

(2) FIG. 1 shows the principle of Doppler ultrasound for blood flow;

(3) FIG. 2 is a block diagram of the device for positioning a Doppler ultrasound transducer for blood flow measurement according to an embodiment of the present invention;

(4) FIG. 3 shows the synchronization characteristic between the oscillation signal and the ultrasound signal; and

(5) FIG. 4 shows a flowchart of the method of positioning a Doppler ultrasound transducer for blood flow measurement according to an embodiment of the present invention.

(6) The same reference signs in the figures indicate similar or corresponding features and/or functionalities.

DETAILED DESCRIPTION

(7) An embodiment of the present invention will be described hereinafter in more detail with reference to the drawings.

(8) FIG. 2 is a block diagram of the device 20 for positioning a Doppler ultrasound transducer for blood flow measurement according to an embodiment of the present invention.

(9) Referring to FIG. 2, the device 20 comprises a first detector 21 for detecting a pressure oscillation signal from an inflated cuff placed on an artery of a patient.

(10) In an embodiment, the first detector 21 processes a pressure signal obtained by a pressure sensor connected with the inflated cuff to determine whether the pressure oscillation signal is detected, and the operator will increase the pressure in the inflated cuff if the pressure oscillation signal is not detected.

(11) In operation, the cuff is first inflated to a proper pressure, which does not have to be a high pressure to occlude the artery. The pressure is acceptable as long as the pressure oscillation signal can be detected. Actually, if the pressure is appropriate and the cuff is well positioned above the artery, an oscillation signal will be generated in the cuff due to the pulse wave of the blood flow of the artery.

(12) In practice, the pressure in the airbag of the cuff is increased to about 80 mmHg.

(13) The device 20 further comprises a second detector 22 for detecting an ultrasound pulse signal from the Doppler ultrasound transducer placed along the artery.

(14) In this embodiment, the second detector 22 determines directly whether the ultrasound signal from the Doppler ultrasound transducer placed along the artery is a pulse signal without the determination result of the first detector 21.

(15) However, as is easily understood by those skilled in the art, in another embodiment, the second detector 22 may determine whether the ultrasound signal from the Doppler ultrasound transducer placed along the artery is a pulse signal only when a pressure oscillation signal is detected by the first detector 21.

(16) In practice, if the transducer is not well positioned, the ultrasound signal from the Doppler ultrasound transducer may be very weak or may not be a pulse signal. In that case, an ultrasound pulse signal cannot be detected by the second detector 22 and it means that the transducer is not well positioned.

(17) If the ultrasound signal from the Doppler ultrasound transducer placed along the artery is not a pulse signal, a prompting signal prompting the operator to relocate the Doppler ultrasound transducer may be outputted.

(18) The device 20 further comprises a processor 23 for deriving a first signal from the pressure oscillation signal and the ultrasound pulse signal, the first signal indicating the degree of synchronization between the pressure oscillation signal and the ultrasound pulse signal.

(19) As mentioned above, if an ultrasound pulse signal detected from the Doppler ultrasound is the signal reflecting the blood flow of the artery, then, taking into account that the pressure oscillation signal and the ultrasound pulse signal relate to the same pulse wave signal of the blood flow of the artery, these two signals should synchronize with each other.

(20) In practice, if the transducer is not well positioned, even if the ultrasound signal is a pulse signal, it does not synchronize with the pressure oscillation signal and therefore the pulse signal detected from the Doppler ultrasound is not the signal reflecting the blood flow of the artery but something else. In that case, the first signal derived from the processor 23 will indicate that these two signals do not synchronize with each other, which means that the transducer is not well positioned.

(21) As for how to derive the first signal indicating the degree of synchronization between the pressure oscillation signal and the ultrasound pulse signal, it will be clear to those skilled in the art that many techniques in signal processing may be used. Details will be further elaborated in the following with reference to FIG. 3.

(22) Device 20 further comprises an interface 24 for outputting an indication signal to indicate that the Doppler ultrasound transducer is in a desired position when the first signal satisfies a predefined condition.

(23) In practice, the indication signal may take many forms.

(24) For example, the indication signal may be outputted by the interface 24 turning on an indication lamp of the Doppler ultrasound transducer or changing the color of the Doppler ultrasound transducer on the display screen of the Doppler ultrasound device.

(25) In a further embodiment of the invention, if the first signal does not satisfy the predefined condition, the interface 24 will also output a prompting signal prompting the operator to relocate the Doppler ultrasound transducer.

(26) In a further embodiment of the invention, as mentioned above, if the ultrasound signal from the Doppler ultrasound transducer placed along the artery is not a pulse signal, the interface 24 may output a prompting signal prompting the operator to relocate the Doppler ultrasound transducer.

(27) FIG. 3 shows the synchronization characteristic between the oscillation signal and the ultrasound signal.

(28) As shown in FIG. 3, the top graph represents the cuff pressure S.sub.1 and it can be seen that there is slight time difference between the detected oscillation signal S.sub.2 and the Doppler ultrasound signal S.sub.3. The time difference is caused by the distance between the cuff and the transducer and also the blood flow speed. Sometimes, when the transducer is positioned far from the cuff, there will be a delay between these two signals. However, when the cuff position and the transducer position are fixed, the time difference is quite stable.

(29) In view of this, in an embodiment in accordance with the present invention, the processor 23 derives the first signal in accordance with the time difference between the time intervals of the two signals, since it should be fairly small if the two signals synchronize.

(30) In an embodiment in accordance with the present invention, the first signal is derived from the time intervals measured between two consecutive peaks of the pressure oscillation signal Δt.sub.osi (i=1 . . . n) and the time intervals measured between two corresponding consecutive pulses of the ultrasound pulse signal Δt.sub.usi (i=1. . . n).

(31) In a further embodiment, the first signal is derived by computing (Δt.sub.usi−Δt.sub.osi)/Δt.sub.osi, and it is determined that the pulse signal synchronizes with the oscillation signal if the time intervals measured between two consecutive peaks of the oscillation signal Δt.sub.osi (i=1 . . . n) and the time intervals measured between two corresponding consecutive pulses of the ultrasound signal Δt.sub.usi (i=1 . . . n) satisfy the following: (Δt.sub.usi−Δt.sub.osi)/Δt.sub.osi≦8%, wherein n is at least two.

(32) In other words, if the first signal satisfies the above predefined condition, it is determined that the two signals synchronize, and the interface 24 outputs an indication signal to indicate that the Doppler ultrasound transducer is in a desired position.

(33) In a preferred embodiment, n could be five or even more in order to avoid error of determination and hence improve the positioning accuracy.

(34) As discussed above, according to the present invention, the operator does not have to listen to the audio output of the ultrasound signal any more and therefore the positioning procedure can be done automatically, thereby reducing the involvement of the operator as much as possible.

(35) Further, since the synchronization property of the cuff pressure oscillation signal and the ultrasound signal caused by the blood flow is utilized to determine whether the transducer is well positioned or not, the ultrasound signal, which is a pulse signal but which does not reflect the blood flow of the artery, could be determined to be not in synchronization with the pressure oscillation signal and therefore the accuracy of the positioning could be improved.

(36) FIG. 4 shows a flowchart of the method 40 of positioning a Doppler ultrasound transducer for blood flow measurement according to an embodiment of the present invention.

(37) As shown in FIG. 4, the method 40 according to the present invention comprises a detecting step 41 of detecting a pressure oscillation signal from an inflated cuff placed on an artery of a patient. The function of step 41 can be executed by the first detector 21.

(38) The method further comprises a detecting step 42 of detecting an ultrasound pulse signal from the Doppler ultrasound transducer placed along the artery. The function of step 42 can be executed by the second detector 22.

(39) The method further comprises a deriving step 43 of deriving a first signal from the pressure oscillation signal and the ultrasound pulse signal, the first signal indicating the degree of synchronization between the pressure oscillation signal and the ultrasound pulse signal. The function of step 43 can be executed by the processor 23.

(40) The method further comprises an outputting step 44 of outputting an indication signal to indicate that the Doppler ultrasound transducer is in a desired position when the first signal satisfies a predefined condition. The function of step 44 can be executed by the interface 24.

(41) In an embodiment, the detecting step 41 of detecting a pressure oscillation signal from the inflated cuff placed on an artery of a patient comprises processing a pressure signal obtained by a pressure sensor connected with the inflated cuff to determine whether the pressure oscillation signal is detected, and increasing the pressure in the inflated cuff if the pressure oscillation signal is not detected.

(42) In a preferred embodiment, the pressure in the inflated cuff is increased to about 80 mmHg.

(43) In an embodiment, the detecting step 42 of detecting an ultrasound pulse signal from the Doppler ultrasound transducer placed along the artery comprises determining whether the ultrasound signal from the Doppler ultrasound transducer placed along the artery is a pulse signal if the pressure oscillation signal is detected. If the ultrasound signal from the Doppler ultrasound transducer placed along the artery is not a pulse signal, a prompting signal prompting the operator to relocate the Doppler ultrasound transducer will be outputted.

(44) In an embodiment, in the deriving step 43, as described above in conjunction with FIG. 3, the first signal is derived from the time intervals measured between two consecutive peaks of the pressure oscillation signal Δt.sub.osi (i=1 . . . n) and the time intervals measured between two corresponding consecutive pulses of the ultrasound pulse signal Δt.sub.usi (i=1 . . . n).

(45) In a further embodiment, the first signal is derived by computing (Δt.sub.usi−Δt.sub.osi)/Δt.sub.osi and it is determined that the pulse signal synchronizes with the oscillation signal if the time intervals measured between two consecutive peaks of the oscillation signal Δt.sub.osi (i=1 . . . n) and the time intervals measured between two corresponding consecutive pulses of the ultrasound signal Δt.sub.usi (i=1 . . . n) satisfy the following: (Δt.sub.usi−Δt.sub.osi)/Δt.sub.osi≦8%, wherein n is at least two.

(46) In other words, if the first signal satisfies the above predefined condition, it is determined that the two signals synchronize with each other and an indication signal will be outputted to indicate that the Doppler ultrasound transducer is in a desired position.

(47) In a preferred embodiment, n could be five or even more in order to avoid error of determination and hence improve the accuracy of the positioning.

(48) In an embodiment, the outputting step 44 of outputting the indication signal comprises turning on an indication lamp of the Doppler ultrasound transducer or changing the color of the Doppler ultrasound transducer on the display screen of the Doppler ultrasound device.

(49) In a further embodiment of the invention, the method further comprises outputting a prompting signal prompting the operator to relocate the Doppler ultrasound transducer if the first signal does not satisfy the predefined condition.

(50) As is easily understood by those skilled in the art, the above described method and device for positioning a Doppler ultrasound transducer can be used in a system for blood flow measurement, which comprises a cuff placed on an artery of a patient, a Doppler ultrasound transducer placed along the artery, and the device (20) for positioning a Doppler ultrasound transducer for blood flow measurement according to the present invention.

(51) It should be noted that the above-mentioned embodiments illustrate rather than limit the invention and that those skilled in the art will be able to design alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word “comprising” does not exclude the presence of elements or steps not listed in a claim or in the description. The word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. In the system claims enumerating several units, several of these units can be embodied by one and the same item of software and/or hardware. The use of the words first, second and third, et cetera, does not indicate any ordering. These words are to be interpreted as names.