Abstrict A catheter probe flow meter and method of determining the volume
flow of a fluid through a conduit, at least one of the fluid and
the conduit having energy-scattering interfaces. The method in one
embodiment includes transmitting at least two and receiving at least
one or transmitting at least one and receiving at least two sound
beams through the fluid, resolving the Doppler vectors into an average
velocity vector for each transmitting/receiving combination, and
resolving the resolved velocity vectors into their component parts.
Claims We claim:
1. A method for measuring the effective velocity of a fluid along
a selected axis, the fluid flowing in a conduit, the conduit having
one or more regions and the fluid having energy-scattering interfaces,
the method comprising the steps of:
transmitting two or more pulsed sound beams at a predetermined
angle with respect to each other through the fluid;
detecting at least some of the sound beams reflected by the energy-scattering
interfaces in a region in the fluid with one or more receivers,
each transmitted pulsed sound beam and each detected sound beam
forming a transmitter/receiver group;
repeating the transmitting and receiving steps for each of the
one or more fluid regions;
obtaining a Doppler signal which is representative of the velocity
vector from each transmitter/receiver group for each region; and
in any order combining the one or more Doppler signals for each
transmitter/receiver group of each region into a signal representative
of the velocity vector for each transmitter/receiver group, resolving
the transmitter/receiver group velocity signals into their component
parts along the selected axis, and vectorially combining the signals
of the transmitter/receiver groups, thereby obtaining the effective
velocity vector in said axis.
2. A method for measuring the effective velocity of a fluid flowing
through a conduit as claimed in claim 1 comprising the steps of:
transmitting two pulsed sound beams at a predetermined angle with
respect to each other through the fluid; detecting at least some
of the sound beams reflected by the energy-scattering interfaces
with two receivers, the two transmitted sound beams and the two
received sound beams forming two transmitter/receiver groups,
combining the one or more Doppler signals into two signals representative
of the velocity vectors, one for each transmitter/receiver group;
and
resolving and vectorially combining these two velocity signals
into their component parts to obtain the effective velocity vector.
3. A method for measuring the effective velocity of a fluid along
a selected axis, the fluid flowing in a conduit, the conduit having
one or more regions and the fluid having energy scattering interfaces,
the method comprising the steps of:
transmitting one or more pulsed sound beams with transmitter means
at a predetermind angle thereto through the fluid;
detecting at least some of the sound beams reflected by energy-scattered
interfaces in a region in the fluid with two or more receivers,
each transmitted pulsed sound beam and each detected sound beam
forming a transmitter/receiver group;
repeating the transmitting and receiving steps for each of the
one or more fluid regions;
obtaining a Doppler signal which is representative of the velocity
vector from each transmitter receiving group for each region; and
in any order, combining the one or more Doppler signals for each
transmitter/receiver group of each region into a signal representative
of the velocity vector for each transmitter/receiver group, resolving
the transmitter/receiver group signals into their component parts
along the selected axis, and vectorially combining the signals of
the transmitter/receiver groups, thereby obtaining the effective
velocity vector in said axis.
4. A method for determining the volume flow of a fluid flowing
through a conduit, the conduit having one or more regions along
a selected direction and the fluid containing energy-scattering
interfaces, wherein the method comprising the steps of:
irradiating the conduit with a pulsed sound radiation field;
receiving with a receiver means sound beams reflected by the energy-scattering
interfaces from two, selected directions in said one or more regions
in each direction;
determining the effective cross-sectional area of the conduit where
the effective cross-sectional area is defined as the cross-sectional
area of the conduit taken along any surface which extends completely
through the conduit and is independent of the orientation of the
receiver to the direction of fluid flow with the steps comprising:
measuring the power returned from the irradiated total cross-sectional
area,
range-gating a received signal such that said range-gated signal
is returned from a known region totally within the conduit,
measuring the power of this range-gated signal, and
dividing said measured total returned power by said measured range
gated power, thereby obtaining said effective cross-sectional area;
determining the effective velocity vector of the fluid flowing
through the conduit through said effective cross-sectional area
where the effective velocity vector is defined as a vector vectorially
combined from resolved representative velocity vectors associated
with corresponding said selected directions, and combined from one
or more individual velocity vectors, each individual velocity vector
representing the velocity of the fluid at an individual region in
the effective cross-sectional area, the representative velocity
vector being resolved independently of the orientation of the receiver
to the direction of fluid flow in a known relationship to said surface,
and combined with one or more further individual velocity vectors;
and
calculating the volume flow through the conduit by taking the vector
dot product of the effective velocity vector and the effective cross-sectional
area.
5. A method as claimed in claim 4 for determining the volume flow
of a fluid through a conduit wherein said conduit is irradiated
by an array of transducers operating within a fixed time relationship
as a phased array.
6. A method for using a plurality of transducers as a phased array
of transducers operating within a fixed time relationship to simulate
a complex transducer for determining the effective velocity of a
fluid along a selected axis, the fluid flowing through a conduit
having a plurality of regions and at least the fluid containing
energy-scattering interfaces, whereby the method comprises:
transmitting pulsed sound beams from the phased array through the
fluid;
detecting with said phased array at least some of the sound beams
reflected by the energy-scattering interfaces in a region of the
fluid in at least two directions from said array;
repeating the transmitting and detecting steps for each of the
fluid regions;
determining a Doppler signal for each region;
combining the Doppler signals into at least two signals representative
of a velocity vector, each signal corresponding to a direction;
and
resolving these at least two velocity signals into their component
parts about said axis and vectorially combining said component parts,
thereby obtaining the effective velocity vector.
7. A method for determining the volume flow of a fluid flowing
through a conduit, the conduit having at least one region and the
fluid containing energy-scattering interfaces, wherein the method
comprises:
irradiating the conduit with `m` pulsed sound beams at a predetermined
angle with respect to each other through the fluid;
receiving from each region a sound beam reflected by the energy-scattering
interfaces with `n` receivers, each transmitted sound beam and each
receiver forming a transmitter/receiver group;
where `m` and `n` are integers equal to or greater than 1 and selected
so as to provide at least two transmitter/receiver groups;
determining an effective cross-sectional area of the conduit where
the effective cross-sectional area is defined as the area of the
conduit taken along a surface which transects the conduit and which
is independent of the orientation of said transmitter/receiver group
to the direction of fluid flow;
determining the effective velocity vector of the flowing fluid
through said effective cross-sectional area where the effective
velocity vector is defined as a vector combined vectorially from
a plurality of transmitter/receiver group velocity vectors, each
group velocity vector being a resolved representative velocity vector
of, the representative velocity vector being resolved in a known
relationship to said surface;
calculating the volume flow through the conduit by taking the vector
dot product of the effective velocity vector and the effective cross-sectional
area.
8. A method for determining the volume flow of a fluid flowing
through a conduit, the conduit having at least one region and the
fluid containing energy-scattering interfaces, wherein the method
comprises:
irradiating the conduit with `m` pulsed sound beams at a predetermined
angle with respect to each other through the fluid;
receiving from each region a sound beam reflected by the energy-scattering
interfaces with `n` receivers, each transmitted sound beam and receiver
forming a transmitter/receiver group;
where `m` and `n` are integers equal to or greater than 1 and selected
so as to provide at least two transmitter/receiver groups;
determining an effective cross-sectional area of the conduit where
the effective cross-sectional area is defined as the area of the
conduit taken along a surface which transects the conduit and which
is independent of the orientation of the transmitter/receiver group
to the direction of fluid flow;
determining the effective velocity of the flowing fluid through
said effective cross-sectional area by:
obtaining a Doppler signal from each transmitter/receiver group
for each region; and
in any order combining the Doppler signal for each transmitter/receiver
group of each region into a signal representative of the velocity
vector for each transmitter/receiver group, resolving the plurality
of transmitter/receiver group velocity signals into their component
parts about an axis which intersects said surface at a known angle,
and combining vectorially the signals of the transmitter/receiver
groups, thereby obtaining said effective velocity vector about said
axis;
and calculating the volume flow through the conduit by taking the
vector dot product of the effective velocity vector and the effective
cross-sectional area.
9. The method as claimed in claim 8 wherein said `m` irradiating
sound beams are irradiated by `m` transmitters and wherein said
`m` transmitters and said `n` receivers are mounted in a probe along
said axis.
10. The method as claimed in claim 9 wherein said probe is included
in a catheter and said method further comprises initially inserting
said catheter into a blood vessel of a patient.
11. A method for determining the volume flow of a fluid flowing
through a conduit, the conduit having at least one region and the
fluid containing energy-scattering interfaces, wherein the method
comprises:
irradiating the conduit with `m` pulsed sound beams at a predetermined
angle with respect to each other through the fluid;
receiving from each region a sound beam reflected by the energy-scattering
interfaces with `n` receivers, each transmitted sound beam and receiver
forming a transmitter/receiver group;
where `m` and`n` are integers equal to or greater than 1 and selected
so as to provide at least two transmitter/receiver groups;
determining an effective cross-sectional area of the conduit where
the effective cross-sectional area is defined as the area of the
conduit taken along a surface which transects the conduit and which
is independent of the orientation of the transmitter/receiver group
to the direction of fluid flow;
determining the effective velocity of the flowing fluid through
said effective cross-sectional area by:
obtaining a Doppler signal from each transmitter/receiver group
for each region; and
in any order combining the Doppler signal for each transmitter/receiver
group of each region into a signal representative of the velocity
vector for each transmitter/receiver group, wherein said representative
velocity signal is obtained by multiplying each individual velocity
signal with a weighting function and summing the weighted individual
velocity signals, resolving the plurality of transmitter/receiver
group velocity signals into their component parts about an axis
which intersects said surface at a known angle, and combining vectorially
the signals of the transmitter/receiver groups, thereby obtaining
said effective velocity vector about said axis;
and calculating the volume flow through the conduit by taking the
vector dot product of the effective velocity vector and the effective
cross-sectional area.
12. A method for determining the volume flow of a fluid flowing
through a conduit, the conduit having a plurality of regions and
the fluid containing energy-scattering interfaces, wherein the method
comprises:
irradiating the conduit with `m` pulsed sound beams at a predetermined
angle with respect to each other through the fluid;
receiving from each region a sound beam reflected by the energy-scattering
interfaces with `n` receivers, each transmitted sound beam and receiver
forming a transmitter/receiver group;
where `m` and `n` are integers equal to or greater than 1 and selected
so as to provide at least two transmitter/receiver groups, said
`m` sound beams and `n` receivers forming a first functional set;
irradiating the conduit with `i` pulsed sound beams at a predetermined
angle with respect to each other through the fluid;
receiving from each region a sound beam reflected by the energy-scattering
interfaces with `j` receivers, each transmitted sound beam and receiver
forming a transmitter/receiver group;
where `i` and `j` are integers equal to or greater than 1 and selected
so as to provide at least two transmitter/receiver groups, said
`i` sound beams and `j` receivers forming a second functional set;
determining an effective cross-sectional area of the conduit as
follows:
detecting the sound beams reflected from the walls of the conduit
with said at least two transmitter/receiver groups of said first
functional set;
calculating the distance to the walls from the detected sound beams
using Doppler range gating techniques;
repeating the above detecting and calculating steps for said second
functional set;
constructing a geometrical surface from said calculated distances
to the wall obtained from each functional set; and
calculating the area of said surface, said area being the effective
cross-sectional area;
determining the effective velocity vector of the flowing fluid
through said effective cross-sectional area where the effective
velocity vector is defined as a vector combined vectorially from
a plurality of transmitter/receiver group velocity vectors, each
group velocity vector being a combined and resolved representative
velocity vector of at least one individual velocity vector, each
individual velocity vector representing the velocity of the fluid
at an individual region in the effective cross-sectional area, the
representative velocity vector being resolved in a known relationship
to said surface;
and calculating the volume flow through the conduit by taking the
vector dot product of the effective velocity vector and the effective
cross-sectional area.
13. The method as claimed in claim 12 wherein said transmitters
and receivers of said first and second functional sets are operated
as an array of transducers.
14. A method for determining the volume flow of a fluid flowing
through a conduit, the conduit having at least one region and the
fluid containing energy-scattering interfaces, wherein the method
comprises:
irradiating the conduit with `m` pulsed sound beams at a predetermined
angle with respect to each other through the fluid; at
receiving from each region a sound beam reflected by the energy-scattering
interfaces with `n` receivers, each transmitted sound beam and receiver
forming a transmitter/receiver group;
where `m` and `n` are integers equal to or greater than 1 and selected
so as to provide a6t least two transmitter/receiver groups;
determining an effective cross-sectional area of the conduit which
is independent of the orientation of the transmitter/receiver group
to the direction of fluid flow as follows:
transmitting a sound beam through the fluid such that the total
sound radiation pattern includes a total cross-sectional area of
the conduit;
detecting at least some of the reflected sound beams and calculating
the Doppler signal therewith;
determining the total power of the calculated Doppler signal, the
total power being representative of the uncalibrated area of the
conduit;
detecting at least a part of a sound beam which is reflected only
from a selected volume that is entirely contained within the conduit
and calculating the Doppler signal therewith;
measuring the power return from said selected volume Doppler signal
thereby obtaining a calibration factor; and
dividing the determined total power by the calibration factor to
obtain the effective cross-sectional area of the conduit;
determining the effective velocity vector of the fluid through
said effective cross-sectional area of the conduit where the effective
velocity vector is defined as a vector combined vectorially from
a plurality of transmitter/receiver group velocity vectors, each
group velocity vector being the resolved average velocity vector
of a plurality of individual velocity vectors, each individual velocity
vector representing the velocity of the fluid at an individual region
in the effective cross-sectional area, the average velocity vector
being resolved in a known relationship to a predetermined axis;
calculating the volume flow through the conduit by taking the vector
dot product of the effective velocity vector and the effective cross-sectional
area.
15. A method for determining the volume flow of a fluid flowing
through a conduit, the conduit having at least one region and the
fluid containing energy-scattering interfaces, wherein the method
comprises:
irradiating the conduit with `m` pulsed sound beams at a predetermined
angle with respect to each other through the fluid;
receiving from each region a sound beam reflected by the energy-scattering
interfaces with `n` receivers, each transmitted sound beam and each
receiver forming a transmitter/receiver group;
where `m` and `n` are integers equal to or greater than 1 and selected
so as to provide at least two transmitter/receiver groups;
determining an effective cross-sectional area of the conduit which
is independent of the orientation of the transmitter receiver groups
to the direction of the fluid flow as follows:
transmitting a sound beam through the fluid such that the total
sound radiation pattern includes the total cross-sectional area
of the conduit;
detecting at least some of the reflected sound beams and calculating
the Doppler signal therewith;
determining the total power of the calculated Doppler signal, the
total power being representative of the uncalibrated area of the
conduit;
detecting at least a part of a sound beam which is reflected only
from a selected volume that is entirely contained within the conduit
and calculating the Doppler signal therewith;
measuring the power return from said selected volume Doppler signal
thereby obtaining a calibration factor; and
dividing the determined total power by the calibration factor to
obtain the effective cross-sectional area of the conduit;
determining the effective velocity vector of the fluid through
said effective cross-sectional area of the conduit by:
obtaining a Doppler signal from each transmitter/receiver group
for each region; and
in any order combining the plurality of Doppler signals for each
transmitter/receiver group of each region into a representative
velocity vector for each transmitter/receiver group, resolving the
plurality of transmitter/receiver group representative velocity
signals into their component parts about an axis which intersects
said effective area at a known angle and which is independent of
the orientation of the transmitter/receiver group to the direction
of the fluid flow, and combining vectorially the signals of the
transmitter/receiver groups, thereby obtaining said effective velocity
vector about said axis;
and calculating the volume flow through the conduit by taking the
vector dot product of the effective velocity vector and the effective
cross-sectional area.
16. A method for determining the volume flow of a fluid flowing
through a conduit, the conduit having at least one region and the
fluid containing energy-scattering interfaces, wherein the method
comprises:
irradiating the conduit with a pulsed sound beam generated by a
phased array of transducers comprising a plurality of transducers
operating within a fixed time relationship to simulate a complex
transducer such that the total radiation pattern includes a total
cross-sectional area of the conduit;
receiving from each region with said phased array at least some
of the sound beams reflected by the energy-scattering interfaces
in that region;
calculating a Doppler signal with the received sound beams from
each region;
determining the total power return to the receivers of the Doppler
signal;
scanning with said phased array a known volume that is entirely
contained within the conduit;
determining the power return of the calculated Doppler signal from
the scanned volume, said power being defined as the calibration
factor for the transducers and sound beams of the array and the
fluid;
obtaining the effective cross-sectional area of the conduit by
dividing the total power return by the calibration factor;
determining the effective velocity vector of the fluid through
said effective cross-sectional area of the conduit where the effective
velocity vector is defined as the resolved combined velocity vector
of a plurality of individual velocity vectors, each individual velocity
vector representing the velocity of the fluid at an individual region
in the effective cross-sectional area, the average velocity vector
being resolved in a known relationship to said axis;
calculating the volume flow through the conduit by taking the vector
dot product of the effective velocity vector and the effective cross-sectional
area.
17. A method for measuring the effective velocity of a fluid along
a selected axis, the fluid flowing in a conduit, the conduit having
a plurality of regions and the fluid having energy-scattering interfaces,
the method comprising the steps of:
transmitting two or more pulsed sounds beams at a predetermined
angle with respect to each other through the fluid;
detecting at least some of the sound beams reflected by the energy-scattering
interfaces in a region in the fluid with one or more receivers,
each transmitted pulsed sound beam and each detected sound beam
forming a transmitter/receiver group;
repeating the transmitting and receiving steps for each region;
obtaining a Doppler signal which is representative of the velocity
vector from each transmitter/receiver group for each region; and
in any order combining the one or more Doppler signals for each
transmitter/receiver group of each region into a signal representative
of the velocity vector for each transmitter/receiver group, resolving
the transmitter/receiver group velocity signals into their component
parts along the selected axis, and combining vectorially the signals
of the transmitter/receiver groups, thereby obtaining the effective
velocity vector in said axis.
18. A method for measuring the effective velocity of a fluid along
a selected axis, the fluid flowing in a conduit, the conduit having
a plurality of regions and the fluid having energy-scattering interfaces,
the method comprising the steps of:
transmitting one or more pulsed sound beams at a predetermined
angle or angles through the fluid;
detecting at least some of the sound beams reflected by energy-scattering
interfaces in a region in the fluid with two or more receivers,
each transmitted pulsed sound beam and each detected sound beam
forming a transmitter/receiver group;
repeating the transmitting and receiving steps for each region;
obtaining a Doppler signal which is representative of the velocity
vector from each transmitter/receiver group for each region; and
in any order, combining the one or more Doppler signals for each
transmitter/receiver group of each region into a signal representative
of the velocity vector for each transmitter/receiver group, resolving
the transmitter/receiver group velocity vectors into their component
parts along the selected axis, and combining vectorially the signals
of the transmitter/receiver groups, thereby obtaining the effective
velocity vector in said axis.
19. A method for determining the volume flow of a fluid flowing
through a conduit, the conduit having a plurality of regions and
the fluid containing energy-scattering interfaces, wherein the method
comprises the steps of:
irradiating the conduit with a pulsed sound radiation field from
a transmitter;
receiving with a receiver means sound beams reflected by the energy-scattering
interfaces in said regions;
determining the effective cross-sectional area of the conduit where
the effective cross-sectional area is defined as the cross-sectional
area of the conduit taken along any surface which extends completely
through the conduit and is independent of the orientation of the
receiver to the direction of fluid flow;
determining the effective velocity vector of the fluid flowing
through the conduit through said effective cross-sectional area
where the effective velocity vector is defined as a vector combined
vectorially from a plurality of group velocity vectors, one group
velocity vector being associated with each different direction from
which a sound beam is received and the group velocity vectors each
representing a combined and resolved velocity vector of individual
velocity vectors, each individual velocity vector representing the
velocity of the fluid at an individual region in the effective cross-sectional
area, the group velocity vector being resolved independently of
the orientation of the receiver to the direction of fluid flow and
in a known relationship to said surface; and
calculating the volume flow through the conduit by taking the vector
dot product of the effective velocity vector and the effective cross-sectional
area.
20. A method for determining the volume flow of a fluid flowing
through a conduit, the conduit having a plurality of regions and
the fluid containing energy-scattering interfaces, wherein the method
comprises:
irradiating the conduit with `m` pulsed sound beams at a predetermined
angle with respect to each other through the fluid;
receiving from each region a sound beam reflected by the energy-scattering
interfaces with `n` receivers, each transmitted sound beam and each
receiver forming a transmitter/receiver group;
where `m` and `n` are integers equal to or greater than 1 and selected
so as to provide at least two transmitter/receiver groups;
determining an effective cross-sectional area of the conduit where
the effective cross-sectional area is defined as the area of the
conduit taken along a surface which transects the conduit and which
is independent of the orientation of said transmitter/receiver group
to the direction of fluid flow;
determining the effective velocity vector of the flowing fluid
through said effective cross-sectional area where the effective
velocity vector is defined as a vector combined vectorially from
a plurality of transmitter/receiver group velocity vectors, each
group velocity vector being a combined and resolved representative
velocity vector of a plurality of individual velocity vectors, each
individual velocity vector representing the velocity of the fluid
through an individual region in the effective cross-sectional area,
the representative velocity vector being resolved in a known relationship
to said surface;
calculating the volume flow through the conduit by taking the vector
dot product of the effective velocity vector and the effective cross-sectional
area.
21. A method for determining the volume flow of a fluid flowing
through a conduit, the conduit having a plurality of regions and
the fluid containing energy-scattering interfaces, wherein the method
comprises:
irradiating the conduit with `m` pulsed sound beams at a predetermined
angle with respect to each other through the fluid;
receiving from each region a sound beam reflected by the energy-scattering
interfaces with `n` receivers, each transmitted sound beam and receiver
forming a transmitter/receiver group;
where `m` and `n` are integers equal to or greater than 1 and selected
so as to provide at least two transmitter/receiver groups;
determining an effective cross-sectional area of the conduit where
the effective cross-sectional area is defined as the area of the
conduit taken along a surface which transects the conduit and which
is independent of the orientation of the transmitter/receiver group
to the direction of fluid flow;
determining the effective velocity of the flowing fluid through
said effective cross-sectional area by:
obtaining a Doppler signal from each transmitter/receiver group
for each region; and
in any order combining the plurality of Doppler signals for each
transmitter/receiver group of each region into a signal representative
of the combined velocity vector for each transmitter/receiver group,
resolving the plurality of transmitter/receiver group velocity signals
into their component parts about an axis which intersects said surface
at a known angle, and combining vectorially the signals of the transmitter/receiver
groups, thereby obtaining said effective velocity vector about said
axis;
and calculating the volume flow through the conduit by taking the
vector dot product of the effective velocity vector and the effective
cross-sectional area.
22. The method as claimed in claim 21 wherein said `m` irradiating
sound beams are irradiated by `m` transmitters and wherein said
`m` transmitters and said `n` receivers are mounted in a probe along
said axis.
23. A method as claimed in claim 21 wherein said combined velocity
vector is obtained by multiplying each individual velocity signal
with a weighting function and summing the weighted individual velocity
signals.
24. A method for determining the volume flow of a fluid flowing
through a conduit, the conduit having a plurality of regions and
the fluid containing energy-scattering interfaces, wherein the method
comprises:
irradiating the conduit with `m` pulsed sound beams at a predetermined
angle with respect to each other through the fluid;
receiving from each region a sound beam reflected by the energy-scattering
interfaces with `n` receivers, each transmitted sound beam and each
receiver forming a transmitter/receiver group;
where `m` and `n` are integers equal to or greater than 1 and selected
so as to provide at least two transmitter/receiver groups;
determining an effective cross-sectional area of the conduit which
is independent of the orientation of the transmitter/receiver groups
to the direction of the fluid flow as follows:
transmitting a sound beam through the fluid such that the total
sound radiation pattern includes the total cross-sectional area
of the conduit;
detecting at least some of the reflected sound beams and calculating
the Doppler signal therewith;
determining the total power of the calculated Doppler signal, the
total power being representative of the uncalibrated area of the
conduit;
detecting at least a part of a sound beam which is reflected only
from a selected volume that is entirely contained within the conduit
and calculating the Doppler signal therewith;
measuring the power return from said selected volume Doppler signal
thereby obtaining a calibration factor; and
dividing the determined total power by the calibration factor to
obtain the effective cross-sectional area of the conduit; determining
the effective velocity vector of the fluid through said effective
cross-sectional area of the conduit by:
obtaining a Doppler signal from each transmitter/receiver group
for each region; and
in any order combining the plurality of Doppler signals for each
transmitrer/receiver group into a representative velocity signal
for each transmitter/receiver group, resolving the plurality of
transmitter/receiver group velocity signals into their component
parts about an axis which intersects said effective area at a known
angle and which is independent of the orientation of the transmitter/receiver
group to the direction of the fluid flow, and combining vectorially
the signals of the transmitter/receiver groups, thereby obtaining
said effective velocity vector about said axis; and calculating
the volume flow through the conduit by taking the vector dot product
of the effective velocity vector and the effective cross-sectional
area.
Description FIELD OF THE INVENTION
This invention relates generally to apparatus and methods for measuring
the flow of energy scattering interfaces within a fluid inside a
conduit and more particularly to ultrasonic pulse Doppler apparatus
and methods for measuring blood flow in a patient's circulatory
system.
DESCRIPTION OF THE PRIOR ART
Ultrasonic Doppler flowmeters for measuring the flow of particulate-containing
fluid in a conduit are well known. Examples of such devices adapted
for measurement of blood flow in a patient's circulatory system
are described in U.S. Pat. Nos. 3430625 (McLeod); 3888238 (Meindl
et al); 3901077 (McCarty et al); 3554030 (Peronneau); 3542014
(Peronneau); 3827115 (Bom); and 3766517 (Fahrbach). As disclosed
in these references, the flowmeter usually includes a catheter for
insertion into a blood vessel of the patient.
A disadvantage of these and other prior art devices is that the
accuracy of the velocity and lumen cross-sectional area measurements
obtained is dependent on the orientation of the catheter with respect
to the blood flow axis. All of these previous designs require a
fixed orientation or position to measure the size of the lumen or
the velocity.
A further disadvantage of the prior art is that either separate,
specialized function transducer arrangements are required to measure
both velocity and lumen area or sensitive and difficult to-implement
measurement techniques must be used in order to measure velocity
and lumen area with a single, dual-purpose transducer arrangement.
A further disadvantage of the prior art catheters is their complexity
and the consequent difficulty of their manufacture.
SUMMARY OF THE INVENTION
These and other disadvantages of the prior art are overcome by
the apparatus and methods of the present Invention. The present
method is independent of the orientation and position for the measurement
of volume flow.
One embodiment of the invention comprises a method for measuring
the velocity of a fluid flowing in a conduit wherein at least one
of the fluid and the conduit has energy-scattering interfaces. The
method comprises transmitting either at least two sound beams at
a predetermined angle with respect to each other through the fluid
and detecting at least some of the sound beams reflected by the
energy scattering interfaces with at least one receiver or transmitting
at least one sound beam and detecting the reflected sound beams
with at least two receivers. The corresponding Doppler vector for
at least two pairs of transmitted and detected sound beams is combined
into an average velocity vector and the two or more resolved average
velocity vectors are resolved into their component parts to obtain
the effective velocity vector.
A second embodiment of the invention relates to determining the
effective cross-sectional area of a conduit having a fluid flowing
therethrough wherein at least one of the conduit and the fluid has
energy-scattering interfaces. The method uses a means for transmitting
a sound beam and a means for detecting at least a component thereof
and comprises transmitting at least one sound beam per functional
set, and calculating the distance to the wall with Doppler range
gating techniques. These steps are repeated for a plurality of functional
sets and a geometrical shape is constructed. Then the effective
cross-sectional area of the constructed shape is calculated.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a block diagram of a flowmeter constructed according
to the pesent invention.
FIG. 2a is a side view, partially in section, of a first embodiment
of an intravenous catheter constructed according to the present
invention with a first embodiment of transducers 22.
FIG. 2b is a transverse cross-section view of the catheter in FIG.
2a taken along line A-A.
FIG. 2c is a longitudinal cross-section view of a second embodiment
of transducers 22.
FIG. 3a is a side view, partially in section, of the catheter of
FIG. 2a with a third embodiment of transducers 22.
FIG. 3b is a longitudinal cross-section view of a fourth embodiment
of transducers 22.
FIG. 4a is a perspective view of a fifth embodiment of transducers
22.
FIG. 4b is a longitudinal cross-section view of the embodiment
of transducers 22 illustrated in FIG. 4a.
FIG. 4c is a transverse cross-section view taken along the lines
A--A of the embodiment of transducers 22 illustrated in FIGS. 4a
and 4b.
FIG. 5a is a perspective view of a sixth embodiment of transducers
22.
FIG. 5b is a longitudinal cross-section view of the embodiment
of transducers 22 illustrated in FIG. 5a.
FIG. 5c is a top view of the embodiment of transducers 22 illustrated
in FIGS. 5a and 5b.
FIG. 6 is a side view, partially in section, of a second embodiment
of a catheter constructed according to the present invention having
mounted thereon a seventh embodiment of transducers 22.
FIG. 7 is a longitudinal cross-section view of an eighth embodiment
of transducers 22.
FIG. 8a is a longitudinal cross-section view of a ninth embodiment
of transducers 22.
FIG. 8b is a transverse cross-section view taken along the line
A-13 A of the embodiment of transducers 22 illustrated in FIG. 8a.
FIG. 9a is a longitudinal cross-section view of a tenth embodiment
of transducers 22.
FIG. 9b is an end view of the embodiment of transducers 22 illustrated
in FIG. 9a.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The mathematical starting point for determining flow is the Doppler
shift vector equation. This equation is as follows:
f = the change in frequency
f.sub.o = the base frequency
V = vector velocity of the fluid
C = velocity of sound in that media
T = unit vector representing the direction of the transmitted sound
beam
R = unit vector representing the direction of the received sound
beam
(T-R) = Direction Vector of observed Doppler beam
The volume flow through any conduit is the vector dot product of
the average velocity vector and a cross-sectional area through which
that velocity flows. The present method and apparatus employ techniques
for velocity measurement and cross-sectional area determinations
which are independent of the orientation and position of the transducers.
In order to eliminate the orientation of the transducers from being
a factor in the determination of the flow velocity, in one embodiment
of the invention two sound beams are used. This is because in this
embodiment the field radiation pattern is not sufficiently uniform
to allow the use of only one transducer. These sound beams can either
be transmitted as two or more separate beams and received on one
or more receivers or received as two or more separate beams which
have been transmitted by one or more transmitters, such as by the
transducers described hereinbelow and shown in FIGS. 2 through 9.
Each transducer (or transducers) receives signals from the entire
cross-section of the conduit. A range gate is moved out in time
from the transducers in order to measure a selected region of the
conduit. Conventional apparatus and techniques for transmitting
and receiving pulsed sound waves and obtaining pulsed Doppler signals
on the one hand, and for using the range-gating technique to selectively
provide measurements in a plurality of regions in a conduit, on
the other hand, are disclosed for example in the aforementioned
Peronneau U.S. Pat. No. 3554030 and the following articles, Hottinger
& Meindl, "An Ultrasonic Technique for Unambiguous Measurement
of Blood Volume Flow"; 174 Ultrasonic Symposium Proceedings,
IEEE Cat. No. 74 CHO 896-ISU (Hottinger et al article); and in McLeod,
"Multichannel Doppler Techniques", published as Chapter
7 of the Proceedings of the International Symposium on Ultrasonics,
Janssen, Beerse, Belgium (1973), respectively. Alternately, the
signal received can be processed either sequentially with a single
movable gate or in parallel with multiple gates or in combinations
thereof. Each measurement is the representation of the average velocity
through that sampled region. All of the discrete range-gated velocity
measurements are summed into an average velocity measurement by
the use of a weighting function. This weighting function is calculated
to take into account the radar equation, that is to account for
transducer radiation pattern, attenuation losses, and the scattering
characteristics of the reflective interface. Conventional apparatus
and techniques for calculating the velocity from a received range-gated
pulse Doppler signal are disclosed for example in the aforementioned
Peronneau ('030) and McLeod patents and in an article by Jorgensen,
Campan, Baker, "Physical Characteristics and Mathematical Modelling
of the Pulsed Ultrasonic Flowmeter", July 1973 Medical and
Biological Engineering 404 (Jorgensen article), the Jorgensen article
also disclosing the conventional use of a weighting function to
sum the velocity measurements into an average velocity measurement.
Simultaneously or sequentially, the other transducer (or sets of
transducers) scans the conduit and similarly obtains an average
velocity measurement as seen by that transducer or transducers.
The rate of scan of the transducers must be sufficiently fast that
no appreciable change in velocity takes place during the measurement
period. Use of these two velocity vectors allows the resolution
of the effective velocity component along the axis of the probe
in this case. This is done by taking the sums and differences of
the vectors in manner consistent with vector algebra. The mathematical
vector resolution of the Doppler signals is conventionally done
for example by multiplying the signal by a constant which represents
the sine or cosine of the known angle between the receiving transducers
and the axis of resolution (e.g., the probe axis) as is disclosed
for example in the aforementioned Fahrbach patent and the Hokanson
U.S. Pat. No. 3777740. The aforementioned Fahrbach patent also
discloses apparatus and techniques for taking the sums and differences
of the vectors. It should be noted that this effective velocity
vector need not be parallel to the probe or to the transducers.
This effective velocity vector would be an average velocity vector
for the effective cross-sectional area in question, as determined
hereinbelow.
The next step in the measurement of flow is to measure an effective
diameter or cross-sectional area. One method employs the power returned
from a Doppler signal. This power is directly proportional to the
size of the sampled volume. If the total sampled region over which
this measurement takes place is greater than the cross-sectional
area of the conduit and includes the conduit in question, the total
uncalibrated cross-sectional area would be determined. This measurement
can be done as a single measurement or as a sum of separate measurements.
A conventional apparatus and technique for performing a power measurement
are disclosed for example in the Hottinger et al article. The uncalibrated
area is a function of the probe angle to the conduit wall. This
uncalibrated area would also vary with different ultrasonic transducers.
To obtain the effective cross-sectional area of the conduit, the
uncalibrated area must be calibrated and this can be done by the
following method. The power returned from a known region completely
within the conduit is measured. In the preferred embodiment this
is accomplished by using very close range-gating techniques. This
technique simultaneously allows the calibration of each individual
transducer for gain and gives the power reflected for a known area
(volume) of the fluid. Dividing this new factor into the uncalibrated
power area mentioned above gives the effective cross-sectional area.
The effective velocity vector and the effective surface area need
not necessarily be orthogonal to each other. If they are not orthogonal,
the angle between the two vectors must be known so that the dot
product can be determined.
Since the effective cross-sectional area is known and calibrated
orthogonal to the transducers in the preferred embodiment and the
effective velocity vector is known parallel to the axis of the transducers,
the flow in the conduit is the product of these factors without
any other factors having to be known or calculated.
A second method for determining the cross-sectional area is to
range to the wall by the use of multiple sets of transducers. Conventional
apparatus and techniques for ranging the wall are disclosed in both
the aforementioned Peronneau patents. This can be accomplished with
two or more or more receivers and one or more transmitters or one
or more receivers with two or more transmitters per functional set.
In these cases, the low frequency Doppler signals, as returned from
the wall, can be used to determine the wall position. The preferred
embodiment uses sets of transducers to allow the construction of
a radiation pattern orthogonal to the catheter. A surface plane
of known dimensions can be constructed from these vectors. Conventional
apparatus and techniques for construction of a surface plane orthogonal
to the radiation pattern are disclosed in the aforementioned Meindl
et al patent. Once this effective cross-sectional area is known
then this area can be multiplied by the effective velocity vector
to give the volume flow through the conduit. A sufficient number
of sets of transducers must be used to sample the wall for any significant
irregularities, and for the distance to the wall from the sets of
transducers. Construction of one or more planes can now be made
from the sets of transducers. The angle that the beams were transmitted
and received on are known from the geometry of the probes. Since
the wall has been sufficiently illuminated, the vessel shape, position
of the catheter and the cross-section can all be determined by known
algebraic and geometric techniques such as taught for example in
the aforementioned Peronneau patents.
The method of using two or more transducers allows the production
of a known radiated field. If a known uniform pattern of radiation
could be produced with one transmitter/receiver, it would be sufficient
to determine the volume flow in a manner to be described hereinafter.
A phased array is a multiple set of transducers generating or operating
within a fixed time relationship to simulate a complex transducer,
lens, reflector or field. Conventional apparatus and techniques
for generating and using a phased array are disclosed in the aforesaid
Bom patent. Once the field has been produced, the techniques for
measuring the effective velocity, cross-sectional area and calibrations
are as previously described.
The preferred embodiment is FIG. 2A and 2B. It is to be noted that
the methods described herein do not require that one of the exemplary
transducer arrangements be utilized. The only requirement for the
sound field is that the direction vectors must not be parallel.
The direction vector is defined as the vector quantity (T--R).
Several unique characteristics are embodied in the catheters. These
are that functional pairs of ultrasonic beams having non parallel
Doppler direction vectors can be used for the measurement of velocity.
Within this constraint, as stated above, any arrangement of one
or more transmitters with two or more receivers would work as well
as one or more receivers with two or more transmitters. The transmitter/receiver
can be a single transducer or multiple transducer.
Another unique feature is a lens or prism to produce a selected
field. This lens or prism can be of any material or materials that
would refract or bend an ultrasonic signal either received or transmitted.
A third unique feature is the use of a reflector. A reflector is
any material from which ultrasonic signals would be reflected or
be directed as to give the desired angle or field pattern to the
beams. The shape of the reflector or reflectors can be varied to
give the desired field of radiation or reception. It should be noted
that combinations of these effects could be used.
Obviously, the aforementioned concepts can all be adapted extra-luminally.
Arrays of two or more transmitters and one or more receivers or
two or more receivers and one or more transmitters can be used.
A preferred embodiment uses three or more sets of transmitters and
one or more receivers or three or more receivers with one or more
transmitters. This is done to eliminate the possibility of a misalignment
between the conduit and the transducers and therefore possibly erroneous
results.
All functional combinations of transducers taken two at a time
must radiate in a field pattern which includes the conduit, and
the Doppler direction vectors must not be parallel. The techniques
for velocity measurement and cross-sectional area determination
are all as previously stated.
The single transducer case involves producing a known uniform ultrasonic
field to illuminate the total cross-section of the conduit. Conventional
apparatus and techniques for generating and using a known uniform
ultrasonic field are disclosed for example in the aforesaid Meindl
et al patent and the Hottinger et al article. Since the field pattern
is defined, velocity measurements can be obtained. The pulse length
and sampling period are selected to produce a sampling region normal
to the direction of propagation of the sound beam. Under these conditions,
the velocity component is everywhere normal to the sampling surface.
Integration of the Doppler Frequency over this surface yields a
signal, the first moment of which is proportional to the flow. Conventional
apparatus and techniques for calculating the integral and the moment
are disclosed for example in the Hottinger et al article. Calibration
is provided by the same technique as previously described.
For purposes of illustration, an embodiment of a flowmeter constructed
according to the present invention which is adapted for measuring
blood flow in a patient's circulatory system using an intravenous
catheter in the preferred embodiment will now be described.
Referring to FIG. 1 the flowmeter, which is generally denoted
10 comprises a catheter 20 having disposed therein first and second
transducers, denoted 22A and 22B and referred to collectively as
transducers 22 for transmitting and receiving ultrasonic sound
waves; generator 30 for pulsing transducers 22; receiver 40 for
receiving the signals produced by transducers 22; and data analyzer
50 for determining the blood flow velocity and an effective cross-sectional
area of the vessel lumen in the region of measurement.
Referring to FIGS. 2a and 2b, catheter 20 in a first embodiment
comprises a catheter housing 24 dimensioned for insertion into a
blood vessel of the patient. Transducers 22A and 22B are coaxially
disposed in catheter housing 24 on the longitudinal axis of catheter
20. As shown, catheter housing 24 may be tubular and have a blunt
tip 24A. A central bore 26 is provided which houses the electrical
conductors (not shown) used to connect transducers 22A and 22B with
generator 30 and receiver 40.
Referring to FIG. 6 catheter 20 in a second embodiment comprises
a support member 28 having a central bore 26' and a base 28A on
which transducers 22A and 22B are mounted.
Transducers 22A and 22B are configured and arranged such that first
and second beams of ultrasonic sound waves are radiated outwardly
at a predetermined angle with respect to each other such that the
Doppler vectors representing the sound beams are nonparallel.
Referring to FIGS. 2-9 transducers 22 may comprise a piezoelectric
transducer or transducers 110 having transmitting/receiving faces
112 of various configuration, and means 120 for directing the sound
waves outwardly from catheter 20 in either converging or diverging
directions. In the embodiment of transducers 22 illustrated in FIGS.
2a and 2b, transducers 110 are disposed in spaced substantially
coaxial relationship, with planar transducer faces 112 disposed
in opposed relationship, facing toward each other, and substantially
perpendicular to the axis of catheter 20. As shown in FIG. 2b, transducer
faces 112 may have a circular peripheral configuration, or any other
peripheral configuration desired. Sound directing means 120 comprises
a reflector 122 substantially coaxially disposed between transducers
110. Reflector 122 may have the shape of two back-to-back conical
frustrum portions 122A and 122B joined at their enlarged bases,
defining two oppositely facing reflecting surfaces 124A and 124B,
as shown, The sound beams radiated from transducer faces 112 are
thus reflected outwardly from catheter 20.
Reflector 122 may also be shaped such that the reflecting surfaces
124A and 124B of frustrum portions 122A and 122B are curved as viewed
in longitudinal cross-section, as shown in FIG. 2c, in order to
allow the production of a different ultrasonic field.
Referring to FIG. 3a, in which elements similar to those of the
embodiment of FIGS. 2a and 2b have been given the same reference
numbers, with primes attached, transducers 110' are substantially
coaxially disposed in juxtaposed, electrically insulated, relationship,
such that transducer faces 112 face in opposite directions away
from each other. The conical frustrum portions 122A' and 122B' of
reflector 122' are spaced, each disposed with the smaller base relatively
adjacent the corresponding transducer face, as shown. An embodiment
of reflector 122' having curved reflecting surfaces, as viewed in
longitudinal cross-section, is shown in FIG. 3b.
In the embodiment of transducers 22 illustrated in FIGS. 4a to
4c, a single, hollow, cylindrical transducer 114 is transversely
divided to form two electrically isolated coaxial portions 114A
and 114B, as shown. If a lead-titanate-zirconate (LTZ) piezoelectric
transducer is used, both the inner and outer walls thereof are silver
coated, and portions 114A and 114B are formed by breaking the silver
coating on one or both walls or by assembling two separate substantially
coaxially disposed shapes. It is to be noted that transducer 114
may have any desired configuration and need not be in the form of
a hollow cylinder.
Surrounding the outer cylindrical surface of transducer 114 is
a refracting lens or refractor 116 having the shape of two conical
frustrums with a common enlarged base, such that the peripheral
configuration defines a triangle, or prism, as viewed in longitudinal
cross-section. Refractor 116 is aligned with respect to transducer
114 such that the apex 118 of refractor 116 is in substantially
coplanar alignment with the dividing line 110 between transducer
portions 114A and 114B. The sound waves radiated outwardly from
transducer portions 114A and 114B are thus refracted in diverging
or converging directions depending upon the media and the diffractive
index of the material, for example as indicated by the arrows D.
Refractor 116 may have a laminate construction or utilize a variable
density composition to achieve a greater or lesser degree of diffraction.
The embodiment of transducers 22 illustrated in FIGS. 5a to 5c
includes elements similar to those of the embodiment of FIGS. 4a
to 4c and these elements have been given the same reference numbers,
with primes attached. Refractor 116' has a double conical frustrum
shape similar to that of refractor 116 except that the frustrum
portions are joined at their smaller bases. Refractor 116' is aligned
with respect to transducer 114' such that the line of joiner 118'
of the two frustrum portions of refractor 116' is in coplanar alignment
with the dividing line 119' between crystal portions 114A' and 114B'.
The sound waves radiated outwardly from transducer portions 114A'
and 114B' are thus refracted in converging or diverging directions,
depending upon the media and the refractive index of the material.
With reference to FIGS. 6 and 7 the desired sound beam propagation
patterns and directions may also be effected through use of transducers
22A and 22B comprising a piezoelectric transducer or transducers
70 having suitably configured and/or oriented transmitting/receiving
faces 72 rather than through use of distinct refracting or reflecting
sound directing means. FIGS. 6 and 7 illustrate exemplary embodiments
in which transducer 70 are conical, the outer conical surfaces of
which define transducers faces 72. The transducers 70 shown in FIG.
6 are so disposed with respect to each other that the respective
sound beams radiated therefrom converge, while the transducers 70
shown in FIG. 7 are so disposed that the respective sound beams
diverge.
Embodiments of transducers 22 which are advantageously adapted
for obtaining "real time" velocity profiles are shown
in FIGS. 8 and 9 and comprise first and second pairs of discrete
transducers 80A and 80B having transmitting/receiving faces 82 of
any desired peripheral configuration and mounted on supporting surfaces
84 which are inclined so as to provide the desired orientations
for the respective sound beams radiated from each pair of transducers
80A and 80B.
It is to be noted that the methods to be described hereinbelow
do not require that one of the exemplary transducer arrangements
described hereinabove be utilized.
Although the invention has been described in detail with respect
to exemplary embodiments thereof, it will be understood by those
of odinary skill in the art that variations and modifications may
be effected within the scope and spirit of the invention.
|