# US 4,391,148 A · Methods and apparatus for measuring the cross-sectional area of a duct and the volume flow rate of fluid in the duct

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- Number: US 4,391,148 A
- Document ID: US4391148A
- Status: Granted
- Kind: A
- Application number: 06/238,952
- Filed: 1981-02-27
- Granted: 1983-07-05
- Earliest claimed: 1980-02-29
- Assignees: National Research Development Corporation
- Inventors: Antonio J. Sainz; Victor C. Roberts
- Web page: https://patentgrep.com/patent/US4391148A

## CPC

- A61B 8/06: Measuring blood flow
- G01F 1/663: by measuring Doppler frequency shift
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)
- G01F: MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME

## Abstract

The invention is particularly related to the measurement of the area of a blood vessel and the volume flow rate of blood in such vessels. An ultrasonic Doppler velocimeter which derives a number of velocity signals dependent on the number of different velocities in a duct is coupled by way of a limiter to a frequency-to-voltage converter which therefore has an output with one component for each velocity signal. A further frequency-to-voltage converter provides a signal dependent on the number of velocity signals and since this number depends on the duct area, the output from the further converter is a measure of this area. By using another frequency-to-voltage converter and a mean detector, a mean velocity signal is obtained which when multiplied by the area signal generates volume flow rate.

## Claims

### Claim 1

Apparatus for measuring the cross-sectional area of a duct containing a fluid, comprising
means for deriving a plurality of velocity signals, each having a frequency which corresponds to a respective velocity of fluid in a duct, the number of velocity signals depending on the number of different velocities currently present in the duct,
a frequency-to-voltage converter coupled to receive the velocity signals, and
means responsive to the varying output of the said converter to provide a signal representative of duct cross-sectional area.

### Claim 2 (depends on 1)

Apparatus according to claim 1 for additionally measuring volume flow rate, comprising
means for deriving a signal representative of mean fluid velocity in the duct, and
means for forming a signal representative of the product of the signal representative of duct cross-sectional area and the signal representative of mean fluid velocity in the duct.

### Claim 3 (depends on 1)

Apparatus according claim 1 wherein
an amplitude limiter circuit is coupled to the input of said converter.

### Claim 4 (depends on 1)

Apparatus according to claim 1 wherein
the means responsive to the varying output of said converter comprises a further frequency-to-voltage converter.

### Claim 5 (depends on 4)

Apparatus according to claim 4 including
means coupled between the two converters for removing low frequency signals at the input of the further frequency-to-voltage converter.

### Claim 6 (depends on 4)

Apparatus according to claim 4 including
a linearizer circuit coupled to the output of the further frequency-to-voltage converter.

### Claim 7 (depends on 4)

Apparatus according to claim 4 wherein
at least one of the frequency-to-voltage converters comprises a phase-locked loop circuit.

### Claim 8 (depends on 6)

Apparatus according to claim 6 wherein
the further frequency-to-voltage converter comprises a phase-locked loop and the linearizer circuit is based on a square law characteristic.

### Claim 9 (depends on 1)

Apparatus according to claim 1 wherein the means for deriving a plurality of velocity signals comprises
an oscillator coupled to an ultrasound transmission transducer, and
an ultrasound transmission receiver which derives a plurality of signals each having a frequency dependent on a respective fluid velocity in the duct.