Ultrasonic transducer devices

• US 3,987,673 A
• Filed: 01/03/1975
• Issued: 10/26/1976
• Est. Priority Date: 01/03/1974
• Status: Expired due to Term

• Current Assignee: National Research Development Corporation
• Original Assignee: National Research Development Corporation
• Inventors: Hansen, Per Loubaerg
• Primary Examiner(s): Ruehl, Charles A.
• Application Number:
  US05/538,325
• Time in Patent Office: 662 Days
• Field of Search: 73/194 A, 128/2.05 F, 128/2.05 Z
• US Class Current: 73/861.25
• CPC Class Codes: A61B 8/06 Measuring blood flow measuring volume flow in general G01F, e.g. G01F1/66, G01F1/72; measuring speed of fluids in general G01P5/00
• CPC Class Codes: G01F 1/663 by measuring Doppler frequency shift
• CPC Class Codes: G01S 15/8952 using discrete, multiple frequencies
• CPC Class Codes: G01S 15/8984 Measuring the velocity vector

Abstract

A flowmeter for measuring blood flow in a vascular channel by Doppler Techniques has an assembly of electro-ultrasonic transducers which direct ultrasonic radiation to a zone spaced from the assembly and receive radiation reflected therefrom. The transducers are spaced apart and capable of providing two radiation beam paths from transmitting to receiving transducers after reflection from the zone. The transducers are directed such that part of one of the beam paths forms an acute angle with the direction of blood flow and part of the other beam path forms an obtuse angle with the direction of blood flow. The reflected signals are shifted in frequency by Doppler effect and their instantaneous difference frequency is monitored and expressed directly in terms of velocity.

Claims

1. A Doppler flowmeter for measuring blood flow in a vascular channel, comprising:

an assembly of electro-ultrasonic transducers arranged to direct ultrasonic radiation to a zone spaced from the assembly and to receive radiation reflected therefrom, the transducers being spaced apart and capable of providing first and second radiation beam paths from a transmitting transducer to a receiving transducer after reflection from said zone such that the resultants of the beam paths lie in substantially opposite directions, and processing means coupled with the transducer assembly for receiving signals indicative of the reflected radiation having means for monitoring the instantaneous frequency difference between reflections derived from radiation following said first and second paths and for providing an indication proportional to said instantaneous frequency difference, the transducer assembly being operable to project radiation to said zone positioned within the channel such that part of the first path forms an acute angle with the direction of blood flow and part of the second path between the transducer assembly and channel forms an obtuse angle with the direction of blood flow, whereby the radiation frequency is Doppler shifted during reflection to provide frequency difference signals spaced in frequency by a factor related directly to flow velocity in the channel.

2. A flowmeter as claimed in claim 1, wherein the processing means comprises a spectrum analyser coupled with the transducer assembly for providing a visual display of the Doppler shifted spectrum and scaled to enable measurement of maximum frequency spacing between radiation components derived from first and second paths.

3. A flowmeter as claimed in claim 1, wherein the processing means comprises a multiplicity of narrow band pass filter channels each coupled with the transducer assembly and of frequency incremented spacing for passing signals of respective predetermined Doppler shifted frequency to respective outputs and a recording device having a continuously moveable recording tape and a multiplicity of writing devices coupled one with each filter output and arranged to write side by side across the tape in ascending order of frequency on receipt of a predetermined signal level from their respective filter to display a combined bar pattern the outline of which is a time/velocity function of the maximum flow velocity at said zone in the vascular channel.

4. A flowmeter as claimed in claim 3, wherein said writing devices are mounted in spaced apart disposition relative to a tape transport path of the recording device and wherein the tape width is subdivided by calibration lines extending longitudinally of the tape and defining the position of each writing implement each line being indicative of a predetermined Doppler frequency shift whereby maximum flow velocity at any recorded instant in time is determinable by the line spacing of the outline of the recorded bar pattern measured transversely of the tape.

5. A flowmeter as claimed in claim 1 wherein the processing means comprises a variable frequency oscillator coupled with the means for monitoring the frequency difference and phase lockable to the difference frequency between radiation derived from first and second paths, whereby the instantaneous oscillator frequency is proportional to flow velocity in said vascular channel.

6. A flowmeter as claimed in claim 1 wherein the processing means comprises a series arrangement of a frequency transposing means followed by a rejection means, said series arrangement being coupled between said transducer assembly and said means for monitoring the instantaneous frequency difference between reflections whereby the received radiation is shifted to a lower frequency band and frequencies outside a predetermined doppler frequency shifted range are attenuated.

7. A flowmeter as claimed in claim 1 wherein the assembly of electro-ultrasonic transducers comprises a device having a face adapted for location on the body of a patient, and two pairs of transducers located on said device each pair being mutually spaced apart and adapted to direct mutually angled beam paths which intersect at a respective location in said zone, whereby each pair directs transcutaneously respective separate beams one following a path having a portion forming an acute angle to the flow direction in a vascular channel and the other beam following a path having a portion forming an obtuse angle with the flow direction.

8. A flowmeter as claimed in claim 7 wherein the mutually outer ones of the transducers of the two pairs are coupled with an exciting source input, whereby they act as transmitters to direct a radiation beam at an acute angle and an obtuse angle to the flow direction in a vascular channel respectively and the inner one of each pair are coupled with the processing means, whereby they receive the radiation from their respective transmitter after Doppler shifted reflection from the channel and relay the received radiation to the processing means.

9. A flowmeter as claimed in claim 7 wherein the mutually inner ones of the transducers of the two pairs are coupled with an exciting source input, whereby they act as transmitters to direct respective radiation beams to the vascular channel and the outer ones of each pair are coupled with the processing means, whereby they receive the radiation from their respective transmitter along paths extending at an acute angle and an obtuse angle to the flow direction in the channel respectively and relay the received radiation to the processing means.

10. A flowmeter as claimed in claim 1 wherein the assembly of electro-ultrasonic transducers comprises a device having three transducers mounted thereon in spaced sequence to define mutually angled beam paths which intersect at a common zone spaced from the device.

11. A flowmeter as claimed in claim 10, wherein two of said three transducers are mounted such that their beam paths will intersect at substantially 90°

and the other of said transducers will provide a beam path forming an acute angle with the beams of each of the other two transducers.

12. A flowmeter as claimed in claim 10, including adjusting means coupled with two of said three transducers and adapted to alter the disposition of the two transducers, whereby adjustment of said adjusting means influences the spacing from the device of said common zone at which zone the three beams intersect.

13. A flowmeter as claimed in claim 12 wherein the adjusting means is coupled with the outer ones of said three transducers and is adapted to move said two outer transducers relative towards or away from each other whereby adjustment of the spacing of said common zone from the device is effected without altering the relative beam angles.

14. A flowmeter as claimed in claim 10 wherein the outer ones of said three transducers are coupled with an exciting source input whereby they act as transmitters to direct a radiation beam at an acute angle and an obtuse angle to the flow direction in a vascular channel respectively and the intermediate one of said three transducers is coupled with the processing means, whereby the intermediate one of said three transducers is arranged to receive Doppler frequency shifted radiation derived from each transmitted radiation beam after reflection from the channel and to relay the received radiation to the processing means.

15. A flowmeter as claimed in claim 14 wherein the first and second exciting source inputs are coupled with respective ones of said two outer transducers which inputs are for different exciting frequencies, whereby ultrasonic radiation transmitted by the two outer transducers is of different frequency and the frequency difference between received Doppler shifted radiations is influenced by flow direction in the vascular channel.

16. A flowmeter as claimed in claim 10, wherein the inner one of said three transducers is coupled with an exciting source input, whereby it acts as a transmitter to direct a radiation beam into the vascular channel and the outer ones of said three transducers are coupled with the processing means, whereby the outer ones of said three transducers are arranged to receive said radiation, along paths extending at an acute angle and an obtuse angle to the flow direction in the channel respectively, after reflection from and Doppler frequency shifting in the channel and to relay the radiation to the processing means.

17. A flowmeter as claimed in claim 10 including frequency transforming means coupled with one of the outer transducers effective to introduced a predetermined component of frequency displacement between the signals received by the outer ones of the three transducers whereby said frequency difference monitored by said means for monitoring the instantaneous frequency difference is influenced by flow direction in the vascular channel.