CA1117835A - Intravascular loop probe having two mutually perpendicular loop sensors - Google Patents

Abstract

INTRAVASCULAR LOOP PROBE HAVING TWO MUTUALLY PERPENDICULAR
LOOP SENSORS

ABSTRACT OF THE INVENTION

An intravascular loop probe includes two lenticular, compres-sible, resilient, and expansible wire loops disposed in planes substantially mutually perpendicular to each other for operation in a conduit transversed by a magnetic field externally applied.
The loops are insulatively joined at the point of maximum curvature. The open ends of the loops continue as wires that pass through a ground ring and are cemented to form a stem for inserting the probe into the conduit via a catheter. Central portions of loop wires are bared to serve as electrodes. The loop terminal wires which form the stem of the probe are connected to external circuitry so that each of the two orthagonal loops is serviced by a separate circuit.

Description

This invention involves improveMents over those degcribed in ¦ my prior U. S. Patent 3,757,773,issued September 11, 1973, for "External Field Electromagnetic Flow Sensor-Artery".
In mylprior patent I describe a Yy~,tem for the measurement of ~` S ¦ blood flow and vac,cular diameter variations, by employing a single intrava~,cular loop probe in an extracorporeal magnetic field.
Such measurements may be performed over a wide range of arbitrary . . . probe orientations relative to the magnetic field~- The adjustment .~ for optimal probe orientation is desirable for maximum signal, but s,uch adjustments may~be quite troublesome. The reason for this di _ :: ficulty iB the failure of the fine wire probe loop to follow continuously the torsion applied to the probe stem which dwells in an intravascular catheter. As a rule the loop orientation will no change for a given angular torsional deformation of the wire stem resulting from a tWist applied to the probe stem where, it emerges from the catheter.~ When the angle of twist reaches a cert-ain critical value, the loop will "j~mp" discontinuously to a new stable orientation from which it can bs dislodged o~ly by an ~f~ additiona1 angular jump produced by additional torsion.
~ Aacording to the invention the new probe employs two mutually per ~ lc;~lar lc-op sensors in a single flow-diameter probe. When one of the loop~ is unfavorably oriented in the magnetic field, the orientation of the other loop is more favorable. The most S
. un~avo~able ~ase is a 45 angle between the magnetic field and the pla~es of the loops, where the signal drops to 70.7% of the optima ~value. B~ taking the square root of the sum of the squares of the two loop transducer signals, one obtains an output for flow and . ~ ~. , . diameter measurements which is independent of the probe orientatio 1.
't~ ~ ? Thi6 operation may be accomplished electronically~
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;-' l , l : It is therefore a principal object of the present ini~ention to .
¦ provide a multiple-loop in a ~atheter for use in measuring rate of flow of conductive fluid in a blood vessel or other conduit, and for measuring the diameter of the blood vessel or conduit, the probe having ~uch a con~truction that it can yield a measurement ~ignal independent of loop orientation in the conduit for any angle~of rotation about the conduit axis with respect to an ¦ externally applied magnetic field~
Another object of the present invention is to provide an ~10~ electromagnetic probe introduceable via an intravascular catheter which has two wire loops disposed in mutually perpendicular planes for d~eveloping an orientation independent signal to sense changes in the conduit diameter.
A further object of the present invention is to provide a probe a8 described with circuitry for maximizing the fluid flow or ;~ conduit diameter signals regardless of the orientation of the -- , loops of the pxobe with respect to an external magnetic field.
These and other objects and many of the attendant advantages of this in~ention will be readily appreciated as the same becomes , ~20 better understood by reference to the following detailed descrip-tion when considered in connection with the accompanying drawings .
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f ~ Fig~ 1 is a schematic representation of an intrava~cular loop ' ' ` :. robe cohstructed in accordance with the concepts of the present 25~ invention, and illustrated as being inserted into a blood vessel:
Fi~ 2 is a graphic diagram showing orientation of an external ~:; agnetic field with respect to probe loops: and , , 1, , ''` ~ , . _ .. ,. , .. .
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' ,Fig. 3 is a block diagram of the probe loops ard associa~ed circuitry for obtaining a maximwn flow or diameter signal independent of loop orientation.
Referring now to the drawings wherein like reference charac-ters des~ignate like or corresponding parts throughout, there is illustrated in Fig. 1 an orthogonal loop probe generally designate as~ reference numeral 10 embodying the present invention. This probe forms part of a catheter electromagnetic flow meter. The 10 i8 shown inside a blood vessel 12 whose wallsl are contacted by electrodes E'l,E"l of wire loop Ll and by electrodes E'~2,E"2 of another wire loop L2. Each,of the wire loops Ll and L2 includes two bifilar insulated wires I4a, 14b and 16a, 16b respectively. Before continuing the description of the probe 10, the,principle of a single-loop sensor exemplified by loop Ll will be descFibed. The insulation of the wire 14b is remov d at a central section along the length of the loop Ll for a few milli-meters~ to~con~titute one electrode E'l. The insulation of the wire 14a, L~ r~noyed at the same distance along the length of the loop~ Ll to coa~tl~tUte E"l. These bared wire regions act as flow-so~lng electrodes e,mployed in performing the flow meter functions ~of the 1~ ~ensor. At one end of the loop Ll the bifilar wires are secured in a semi-rigid plastic enclosed stem 17 below a bare metal ground collar~18 that is conne¢ted to a ground wire 20 which i~ part of the wire bundle of the stem 17. The loop Ll has a generally lenticular or oval shape and is adapted to be compressed -into a~ elongated configuration so as to pass through a tubing of o 2.3.millimeters in internal diameter for percutaneous -introduction intQ the blood vessel 12.

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- ~1783~ 1 ¦ The magnetic field B is pessimistically oriented witn re~pect to the loop Ll for picking up a flow signal since the field is parallel to the line joining the electrodes. The optimal orientation of the magnetic field vector for the loop Ll would be ~5~ perpendicular to the page. This ~ield orientation would also be ~ ~ ~ optimal for induction of an E.M.F~ in the loop L1 (in each of the ) ~ ~ wires 14a, 14b of the bifilar pair) which acts as a transformer secondary with respect to the AoC~ magnet M which play~ the role of tran~Former primary. This induced E.M.F. provides signal ' ! ' ~.'10 ~ ',. ' information about changes in vascular diameter which is the angio-meter function of the loop sensor.
Loop Ll represents the loop sensor in the most unfavorable orientation wherein a zero signal is conveyed to external flow and diameter sensing amplifiers (not shown~. Now according to the invantion, there is provided a second loop sensor L2 made of insulated bifilax wires 16a, 16b with central bared wire regions ~; - con~tituting electrodes E'2,E"2 of the loop L2. The elongated, compressible loop L2, has an end at the probe terminal 19~ There 3 the ends of the loop~ Ll and L2 can be joined together by insula-tive mean~. The other open end of the loop L2 passes through fhe 3 ground collar 18 and~ i8 secured in the stem 17. Terminal leads 14'a, ~4'b, 16'a, 16'b, are connected to th~ loop wires 14a, 14b, 16a, 16b, respectively and extend heyond the stem outside of the vessel or condu$t 12 for connection to amplifiers and other ~2$ ~-~ external cixcuitry.` The structure of the loops Ll and L2 are identical in the double loop sensor configuration. The plane of '"' ' 1'' ~"''': _~ _ . ~ j '.
"'"~"/' '. ~ ' ' ,,' ~, jA , - , . ~, , .~A ; ~ ~ 4 ¦the loop sensor L2 is perpendicular to that of loop Ll. The ; ~ ¦unfavorable orientation of the loop Ll as mentioned above in Fig. ¦

2 19 effectively compensated by the optimal orientation of the ; ;~; ,`';~` ¦loop L2 which is pe~rpendicular to the field ~. An optimal fluid I
¦ flow signal i~ thus picked up by electrodes E'2,E"2 of loop L2.

¦ By connecting terminal leads 16'a, 16'b of the loop L2 to an -¦ output signal amplifier A2 ( Yig . 4) an optimal amplified flow ¦ signal i 9 obtained~
In general the dou~le loop sen~or probe 10 will form an - ¦ arbitrary angle ~ with a vector Bo of the magnetic field B; see Fig. 2. It will then be possi~le to use the output of that loop which yields the larger flow and diameter signals. The signals dérived from the loops Ll and L2 become equal to each other for ~ , r~ ~ 45O as shown in Fig. 2, which depicts the orientation of the 15~ magnetic vector Bo relative to the mutually perpendicular planes of the loops Ll and L2. Thus, the most unfavorable orientation of ; the sensor probe is for ~ = 45. In this case both of the loops yield a ~ignal which is 70.7/O of the optimal value. For any othe~
~rientatio~, one of the two loops will provide a flow and diamete~
,20~ ~ ~ignal clo~er to 100% of maximum value, rrhe use of probe 10 save~i ~a great deal of time and effort in measuring flow in visceral blood vessels (e.g. superior mesenteric artery and vein) by ~; ~ eliminating need for rotating the subject and for changing the ~ location of the extracorporeal magnet M whose field B is represent _ 25, ed by vector Bo in Fig. 2.

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: I ~n ideally c~nvenient system would be one in which the flow ¦ and diameter ~ignal~ remain constant regardless of the value of angle ~. This can be accomplished on the basis of the ¦ following considerations. The amplitudes of the loop siynal V
~5 and flow ~signal VF are proportional to the component of the magnatic field amplitude Bo which is perpendicular to the plane of - the ~iven loop Ll or L2. Using the symbol V for which either VF
or VL depending on whether the flow signal or the diameter measur-iny loop signal i8 being considered, we can write for the signals ; ~ (VO)l and (Vo)2 derived from loop Ll or loop L2, : ~ . (Vo)l C B

~ ~ ~ (V )2 ~ C Bo .(2~

;` : The proportionality constant C is, of course, different for the flow signal and loop signal. . .-lS Adding the ~quares of equations (1) and (2) we obtain for the summa~ion signal:
~ ~ ~ (YO)2-~VO)l 4(Vo)2 -C Bo (sin ~ cos?~)=c Bo - constant A

;~t ~ , or Vo=CBo ~ con~tant. (3) By summation of the squares of the signals derived from the . two loops (or from the two pairs of electrodes) we obtain a re~ultant~signal V O which is independent from the relative orien-tation between the loop and the direction of the magnetic field, provided the latter is in the plane which is normal to the blood Ye~sel axis. The latter condition is easy to establish exper-. Imentally sincs the loop and flow signals vanish when the magnetic ;-f ! ~ ¦
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~I~L17835 veCtor ~ B parall 1 to the blood vesse1 axis and are maxim~1 when i ~- , 1i~ perpendicular to it. One thus has merely to maximize signal Vo when placing the magnet.
~Fig. 3 shows a circuit for electronically processing the flow S and loop signals derive from the loops Ll and L2 of the probe lO, where a pair of squarer circuits C'l and C"l square the incoming loop,or flow signals ~0 which have been amplified by amplifiers Al ;, A2. ~n adder circuit C2 adds the output from the circuits C'l and C"l. A c,~rcuit C3 yields the square root of the signal derived from the adder C2, thus yielding a flow or diameter sensor signal V O which is independent of the orientation angle of the loops Ll, L2 w1th respect to the magnetic f~eld of the extracorporeal magnetO Th~ squarer circuit, adder circuit and circuit C3 for ~1 obtaining the square root are all conventional components and need 15~ - not be f,urther defined herein.
~ ,',t,,-,;'. ~- Alt~ough the loop sen~ors of the probe lO have been il-- 7 ~' 1, ,,,,, ., ~lu~r~ted with one end joined at the point of maximum curvature , in~80mc applications it may be desirable to have the loop open-i.e '~ne en,d o~aach loop terminates at its respective electrode and th, .
: ~' 20 ~ o~her end of,each loop terminates as hereinbefore described . at the terminalB.
" ' ' , It should be understood that the ~oregoing relates to only a pref~rred embodiment of the invention, and that it is intended to cover all chan~e~ and modifications of the example of the invention herein chosen for the purposes of the disclosure, which do not constitute departures from the spirit and scope of the ¦ invention.

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Claims (11)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An intravascular loop probe comprising:
a first flat deformable wire loop disposed in a first plane;
a second flat deformable wire loop disposed in a second plane substantially perpendicular to and centrally intersecting said first plane, said first and second loops defining said probe, each of said loops being collapsible to an elongated narrow configuration for insertion into a narrow conduit and expansible in a larger conduit; and electrode means formed at diametrically opposite sides of each of said loops for picking up electromagnetically induced signals corresponding to rate of fluid flow in said larger conduit and loop terminals yielding an induced signal corresponding to the width of said larger conduit, whereby an externally applied magnetic field will cause induction of voltages in said flowing fluid and said loops in said larger conduit, said voltages corresponding to the rate of fluid flow in said larger conduit to the diameter of said larger conduit.

2. An intravascular loop probe as defined in Claim 1, wherein each of said first and second wire loops have one end closed and said loops when expanded in said larger conduit form a generally lenticular loop configuration.

3. An intravascular loop probe as defined in Claim 2, further comprising means forming a stem originating at the open ends of said loops to facilitate insertion of said probe through a catheter into said larger conduit and positioning of said probe in said larger conduit.

4. An intravascular loop probe as defined in Claim 2, further comprising a ground ring enclosing said open ends of said loops for grounding said probe.

5. An intravascular loop probe as defined in Claim 3, further comprising insulative means joining said closed ends of said loops to cooperate with said stem in maintaining said loops perpendicular to each other when expanded, and to facilitate in-sertion of said probe into said larger conduit.

6. An intravascular loop probe as defined in Claim 1 further comprising a circuit means connected to said loop terminals for receiving said signals and adapted to maximize the same regardless of the orientation of said loops in said magnetic field.

7. An intravascular loop probe as defined in Claim 6, wherein said circuit means comprises:
an amplifier means for amplifying said signals;
a squarer circuit means arranged to square the amplified signals;
an adder circuit means arranged to add the squared signals: and square root circuit means arranged to derive output voltage signals corresponding to the square root of the added squared signals, whereby said output voltage signals will be independent of rotational orientation of said loops within the conduit in said magnetic field.

8. An intravascular loop probe as defined in Claim 2 further comprising a circuit means connected to said loop terminals for receiving said signals and adapted to maximize the same regardless of the orientation of said loops in said magnetic field.

9. An intravascular loop probe as defined in Claim 8, further comprising means enclosing open ends of said loops to form a semi-rigid stem thereat to facilitate insertion and positioning of said probe in said larger conduit.

10. An intravascular loop probe as defined in Claim 9, further comprising a ground ring enclosing said open ends of said loops, and a ground lead connected to said ring for grounding said probe.

11. An intravascular loop probe as defined in Claim 9, further.
comprising terminal leads connected to said open ends of said loops for connection to said circuit means external of said circuit.