 |
Description  |
|
|
Applicant hereby claims priority under 35 U.S.C. 119(e) for the present
application based on a provisional application filed Sep. 6, 1995,
entitled APPARATUS AND METHOD FOR AUTOMATIC PLACEMENT OF TRANSDUCER, Ser.
No. 60/003,293, to the same inventor herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to medical apparatuses and more
particularly, to an apparatus and method for automatically locating a
particular blood vessel within a patient by scanning a plurality of
transducers over an area of the skin.
2. Description of the Prior Art
Measurement of blood flow is particularly important in emergency
situations, such as on a battlefield or at an accident site. Several
techniques are available for measuring blood flow in such situations. One
such technique employs measurement of the signal provided by a transducer
that is placed on the surface of the skin over a blood vessel. This
technique is discussed in U.S. Pat. No. 5,540,230 to Vilkomerson, entitled
DIFFRACTING DOPPLER-TRANSDUCER, issued on Jul. 30, 1996 and in U.S. Pat.
No. 5,488,953 to Vilkomerson, entitled DIFFRACTING DOPPLER-TRANSDUCER,
issued on Feb. 6, 1996. See also the article entitled "Diffractive
Transducers for Angle-Independent Velocity Measurements", by David
Vilkomerson, Proc. 1994 IEEE International Ultrasonics Symposium, pp.
1677-1682.
Such techniques of measuring blood flow initially require the user to
locate a blood vessel for measurement, such as the carotid artery, the
brachial arteries, or the radial arteries. However, if weak signals are
provided at the selected location of the blood vessel, the measurements
obtained may not be dependable. Accordingly, it is highly desirable to
determine the location of the blood vessel providing the strongest signal.
FIG. 1 shows a conventional method of locating a blood vessel manually by
scanning a transducer (not shown) across several positions 11-18 on the
surface of the skin 19 until the position of the blood vessel 15
associated with the strongest signal is determined. However, since this
method may be difficult and time consuming for emergency situations or
dangerous in battlefield situations, manual scanning may be impractical.
Accordingly, it is the object of the present invention to substantially
overcome or eliminate such disadvantages by providing an improved
apparatus and method for quickly and automatically locating a blood vessel
by scanning a plurality of transducers over an area of the skin to
determine the location of the blood vessel associated with the strongest
signal and for measuring the rate of blood flow through the located blood
vessel.
SUMMARY OF THE INVENTION
An apparatus and method is disclosed for locating a desired blood vessel
within a predetermined volume of tissue. The apparatus and method includes
a plurality of transducers which are operable to be positioned over the
tissue. Each of the transducers when driven produces an output signal
indicative of blood flow in a vessel located under each transducer. A
control means for selectively driving the transducers in order to produce
a plurality of output signals and for comparing the plurality of output
signals in order to determine the output signal having the largest
amplitude which corresponds to the transducer positioned over the desired
blood vessel.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, features, and advantages of the invention
will be apparent from the following more particular description of the
preferred embodiments of the invention, as illustrated in the accompanying
drawings, wherein:
FIG. 1 is a schematic view of a prior art method for locating a blood
vessel;
FIG. 2 is a schematic view of the apparatus of the present invention;
FIG. 3 is a plan view of the array of transducers shown in FIG. 2 secured
to a flexible material;
FIG. 4 is a schematic view of the "sequential scanning" procedure of the
present invention;
FIG. 5 is a schematic view of the "sequential halving" procedure of the
present invention; and
FIG. 6 is a schematic view of the "hybrid" procedure of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 2, the present invention comprises an array 150 of
transducers which are coupled to a switching network 60 and are driven by
a control system 70.
Specifically, the array 150 includes eight (8) transducers 152-166 which
are of the type that measure various characteristics of a blood vessel via
placement of the transducers on the surface of the skin over the blood
vessel. An example of such transducers can be found in both U.S. Pat. No.
5,488,953 and U.S. Pat. No. 5,540,230. It should be understood, however,
that non-diffractive Doppler transducers, as well as other transducers
used with blood vessels, e.g. PO.sub.2 type, equally fall within the scope
of this invention. Further, since the transducers 152-166 are placed
directly on the surface of the skin, each transducer 152-166 typically
should have at least one flat surface for communicating with the skin
surface.
Referring to the exemplary embodiment illustrated in FIG. 3, the eight (8)
transducers 152-166 are shown secured to a flexible material 50, such as a
bandage, length of gauze tape, or a BAND-AID.RTM.. It should be understood
that the transducers 152-166 can be affixed to any material or substrate,
providing that the material can be held in place on the surface of the
skin.
The transducers 152-166 are arranged in a linear configuration and are
uniformly spaced apart on the material 50 over a predetermined distance in
order to scan over a predetermined scanning area. It should be understood
that the distance between each of the transducers 152-166 can be varied.
Further, the overall size of the scanning area (the distance between 152
and 166) can be increased or decreased by varying the number of
transducers employed or by varying the spacing between the existing
transducers 152-166. Finally, it should be understood that the transducers
152-166 can be arranged in other configurations, such as a matrix
configuration.
The size and spacing of the transducers 152-166 in the array depends upon
the blood vessel which flow is to be measured. As is known to one skilled
in the art, the best signal-noise ratio is obtained when the transducer is
approximately the same size as the vessel to be measured. The width of the
array should be such that one of the transducers is substantially over the
vessel, if landmarks for the vessel position are easily found. As for some
vessels, the width of the array need not be large, as the approximate
position of the vessel is well defined.
If landmarks for the vessel are not found or equivalently there is a large
degree of variation in the position of the desired vessel with regard to
anatomical marks, the array should be large enough to ensure that the
approximate placement is substantially over the vessel. Knowledge of the
size of the transducer and the total width of the array determines the
number of transducers and their placement.
Referring to FIGS. 2 and 3, each of the transducers 152-166 of the array
150 is coupled to the switching network 60, via an input feed 34-41 and an
output feed 42-49, respectfully. The switching network 60 selectively
couples a predetermined transducer 152-166 to a drive line 170 and a
signal line 172 in response to a select signal developed across a control
line 174. It should be understood that the switching network 60 of the
present invention can comprise any switching means known in the art, such
as mechanical switching devices or electrical switching devices. It should
be understood that in some configurations, the output feeds 42-49 and
input feeds 34-41 can utilize the same feeds when Pulse-Echo Type time
switching is incorporated or other similar techniques.
The switching network 60 of the present invention is coupled to the control
system 70, via the drive line 170, the signal line 172, and the control
line 174. Generally, the control system 70 is designed to "sequentially
scan" each of the transducers 152-166 of the array 150 via a conventional
sorting routine, and to compare the signals provided by the transducers
152-166. The control system 70 then drives the transducer providing the
strongest signal, which measures the rate of blood flow through the
selected blood vessel. It should be understood that any means for driving
the transducers 152-166 and for comparing the signals provided by the
transducers 152-166 falls within the scope of the invention. Further, any
sorting routine known in the art can be employed.
Referring to FIG. 4, the "sequential scanning" procedure 80 is illustrated.
An array of N number of transducers is provided (shown in box 82). Next,
the control system 70 selects and drives the first transducer of the array
(shown in boxes 84 and 86, respectively). The signal amplitude or
"strength" provided by the transducer is then recorded in memory (shown in
box 88).
The next set of steps is performed for each remaining transducer of the
array (shown in boxes 90 and 104). First, the control system 70 selects
and drives the next transducer of the array (shown in boxes 92 and 94,
respectively). In between selecting the next transducer (box 92) and
driving the transducer (box 94), the control system 70 checks to see if
the complete array has been scanned (box 93). If it has, the control
system 70 then advances to the step of box 106. If the complete array has
not been scanned, the control system 70 then drives the next transducer
(box 94).
The control system 70 then compares the strength of the signal provided by
the selected transducer with the strength of the signal recorded in memory
(shown in boxes 98 and 99). If the selected transducer provides a stronger
signal then that recorded in memory, then the memory is updated with the
stronger signal and the transducer is noted (shown in box 100). If the
strength of the signal provided by the current transducer is less then
that recorded in memory, then the signal recorded in memory is carried
forward to be compared to the signal generated by the next transducer
(shown in box 102). Accordingly, the strongest signal will be carried
forward to the end of the procedure.
After the final transducer of the array is scanned, the control system 70
selects the transducer of the array which provided the strongest signal
(shown in box 106). Finally, the selected transducer is driven by the
control system 70 to measure the desired rate of blood flow (shown in box
108).
Such "sequential scanning" methods have proven useful in embodiments
employing Doppler transducers where the Doppler pulse provides a strong
signal-noise ratio signal. For example, the pulse time to reach a vessel
and return, for vessels that are 1 cm deep, is about 13 microseconds (2 cm
round-trip at 1.5 mm/microsecond). Thus, the total measurement and switch
time per transducer is approximately 30 microseconds. For an exemplary
embodiment comprising an array of 64 transducers, the complete array is
measurable in 2 milliseconds, which is a short enough period of time for
the blood flow to be considered constant. Therefore, the optimal
transducer for measurement can be determined.
However, if the switching network 60 is not fast enough, or if the measured
signal strength is so weak that it requires at least 50 pulses for a
determination of the optimal transducer, then the "sequential scanning"
procedure 80 may not be reliable. For example, in an exemplary embodiment
comprising an array of 64 Doppler transducers, 0.1 seconds is required to
scan all of the 64 transducers. Since the blood flow rate may change in
this time period, "sequential scanning" would not be a reliable method.
(It should be noted that the peak blood flow, occurring at systole, lasts
less than a tenth of a second, and repeats at the pulse rate of about once
per second). Further, although each transducer could be connected for an
entire pulse period (1 second), 64 seconds of observation time would then
be required to determine the optimal transducer.
In addition to the "sequential scanning" procedure 80 described herein, the
control system 70 can be designed to perform a "sequential halving"
procedure (perform a series of iterations until the transducer providing
the strongest signal is determined).
Referring to FIG. 5, the "sequential halving" procedure 110 is illustrated.
First, an array of N number of transducers is provided (shown in box 112).
The array is then divided into two halves (shown in box 113). If a whole
number remains (N is evenly dividable by 2), then the array is divided
into a first half of N/2 transducers, from 1 to N/2, and a second half of
N/2 transducers, from ((N/2)+1) to N (shown in boxes 114 and 115,
respectively). However, if N is not evenly divisible by two, then the
array is divided into a first half of ((N-1)/2) transducers, from 1 to
((N-1)/2), and a half section of ((N+1)/2) transducers, from ((N+1)/2) to
N (shown in box 116).
At the end of this "halving" routine, the transducers in each of the halves
are simultaneously scanned for an entire pulse period (shown in box 118).
The control system 70 then compares the signals provided from each of the
halves (shown in box 120). The half providing the strongest signal is then
selected by the control system 70 (shown in box 122).
The "halving" procedure and scanning procedure is then repeated (shown in
box 124) until the selected half comprises only one transducer, which is
the transducer reporting the strongest signal. The selected transducer is
then scanned (shown in box 126).
For arrays having a relatively large number of transducers, this
"sequential halving" procedure 110 is substantially quicker than the
"sequential scanning" procedure described above. For example, an array
having 64 transducers will undergo 6 such halvings (2.sup.6 =64) to
determine the optimal transducer. For the embodiment employing Doppler
transducers, this amounts to a total of 12 seconds (at one second for each
half, or two seconds per halving, times six), which is substantially less
then the 64 seconds required by the "sequential scanning" method for
connecting each of the 64 transducers for an entire pulse period of 1
second.
However, if the signal-noise ratio obtained using 64 Doppler transducers at
a time is too low (because the 32 transducers are equivalent to a
transducer much wider than the vessel, which as noted above reduces the
signal-noise ratio), the control system 70 can be modified to perform a
"hybrid" procedure, combining aspects of both the "sequential scanning"
procedure 80 and the "sequential halving" procedure 110.
Referring to FIG. 6, the "hybrid" procedure 130 is illustrated. First, an
array of N number of transducers is provided (shown in box 132). Next, the
control system 70 divides the array into M sections, each section having
N/M transducers (shown in box 134). For an embodiment having 64
transducers and for M being equal to four, the array is divided into four
sections of sixteen transducers. Each of the sections are then scanned via
the "sequential scanning" procedure 80 described herein to determine which
section of the array provides the strongest signal (shown in box 136). The
section providing the strongest signal is then selected by the control
system 70 (shown in box 138) and undergoes the "sequential halving"
procedure 110 described herein (shown in box 139). This procedure is
repeated until the selected section comprises 1 transducer (shown in box
140). Finally, the remaining transducer is utilized to measure the desired
blood flow rate (shown in box 142).
Although this "hybrid" procedure requires the same 12 seconds (4+2+2+2+2)
as in the embodiment employing Doppler transducers via the sequential
having method, it shows a 2:1 improvement in the signal-noise ratio as
compared to the above "sequential scanning" procedure, because the noise,
which is proportional to the number of transducers (i.e., The effective
width of the transducer), is only half as great (16 versus 32).
While a single channel is assumed above, it is understood that one cab use
more than one channel; if we divide or arrange the array into K segments
for K channels, we can therefore perform K measurements simultaneously to
determine which signal segment is strongest. While this approach involves
additional circuitry and additional costs, it can be used to decrease the
time needed to find the best segment. For example, if we have two
channels, it takes only 1/2 the number of measurement periods, or if we
have K channels for K transducers it takes less than one second.
Accordingly, the present invention provides an apparatus and method for
quickly and without human intervention locating a blood vessel and for
measuring the flow of blood through the located blood vessel. For example,
the present invention can locate a blood vessel to be measured in
substantially less time than many of the devices and methods of the prior
art.
Additionally, the present invention provides an apparatus and method that
measures the rate of blood flow through a blood vessel that comprises a
plurality of transducers.
Further, the present invention provides an apparatus and method that
measures the rate of blood flow through a blood vessel that comprises a
plurality of Doppler transducers.
In addition, the present invention provides an apparatus and method that
automatically determines the location of a blood vessel associated with a
strong signal and measures the rate of blood flow through the blood vessel
at the determined location.
Still further, the present invention provides an apparatus and method for
automatically locating a blood vessel by sequentially scanning a plurality
of transducers and comparing the signal strength provided by each of the
transducers.
Finally, the present invention provides an apparatus and method for
automatically determining the location of a blood vessel by performing a
series of iterations on an array of transducers to determine the
transducer that provides the strongest signal.
While the invention has been particularly shown and described with
reference to preferred embodiments thereof, it will be understood by those
skilled in the art that changes in form and details may be made therein
without departing from the spirit and scope of the present invention.
* * * * *
|
|
 |
|
 |
Description |
|
