CA2180559A1 - Ultrasonic transducer with selectable beamwidth and method - Google Patents
Ultrasonic transducer with selectable beamwidth and methodInfo
- Publication number
- CA2180559A1 CA2180559A1 CA002180559A CA2180559A CA2180559A1 CA 2180559 A1 CA2180559 A1 CA 2180559A1 CA 002180559 A CA002180559 A CA 002180559A CA 2180559 A CA2180559 A CA 2180559A CA 2180559 A1 CA2180559 A1 CA 2180559A1
- Authority
- CA
- Canada
- Prior art keywords
- transducer
- diameter
- approximately
- high frequency
- distal
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 238000000034 method Methods 0.000 title claims description 12
- 239000000463 material Substances 0.000 claims abstract description 13
- 230000008878 coupling Effects 0.000 claims description 8
- 238000010168 coupling process Methods 0.000 claims description 8
- 238000005859 coupling reaction Methods 0.000 claims description 8
- 239000004020 conductor Substances 0.000 claims description 6
- 230000009977 dual effect Effects 0.000 claims description 6
- 230000000644 propagated effect Effects 0.000 claims description 4
- 239000000853 adhesive Substances 0.000 claims description 2
- 230000001070 adhesive effect Effects 0.000 claims description 2
- 230000032683 aging Effects 0.000 claims description 2
- 238000005259 measurement Methods 0.000 claims description 2
- 230000005284 excitation Effects 0.000 claims 9
- 239000000919 ceramic Substances 0.000 description 5
- 238000002604 ultrasonography Methods 0.000 description 4
- 101100345589 Mus musculus Mical1 gene Proteins 0.000 description 3
- 239000008280 blood Substances 0.000 description 3
- 210000004369 blood Anatomy 0.000 description 3
- 230000017531 blood circulation Effects 0.000 description 3
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 2
- 240000001973 Ficus microcarpa Species 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 238000003754 machining Methods 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 230000005477 standard model Effects 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
- ZVQOOHYFBIDMTQ-UHFFFAOYSA-N [methyl(oxido){1-[6-(trifluoromethyl)pyridin-3-yl]ethyl}-lambda(6)-sulfanylidene]cyanamide Chemical compound N#CN=S(C)(=O)C(C)C1=CC=C(C(F)(F)F)N=C1 ZVQOOHYFBIDMTQ-UHFFFAOYSA-N 0.000 description 1
- 210000001367 artery Anatomy 0.000 description 1
- 230000002490 cerebral effect Effects 0.000 description 1
- 210000004351 coronary vessel Anatomy 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 235000012489 doughnuts Nutrition 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 210000001105 femoral artery Anatomy 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- ZBSCCQXBYNSKPV-UHFFFAOYSA-N oxolead;oxomagnesium;2,4,5-trioxa-1$l^{5},3$l^{5}-diniobabicyclo[1.1.1]pentane 1,3-dioxide Chemical compound [Mg]=O.[Pb]=O.[Pb]=O.[Pb]=O.O1[Nb]2(=O)O[Nb]1(=O)O2 ZBSCCQXBYNSKPV-UHFFFAOYSA-N 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- QYPNKSZPJQQLRK-UHFFFAOYSA-N tebufenozide Chemical compound C1=CC(CC)=CC=C1C(=O)NN(C(C)(C)C)C(=O)C1=CC(C)=CC(C)=C1 QYPNKSZPJQQLRK-UHFFFAOYSA-N 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
- B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
- B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
- B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
- B06B1/06—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction
- B06B1/0644—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using a single piezoelectric element
- B06B1/0655—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using a single piezoelectric element of cylindrical shape
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
- B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
- B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
- B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
- B06B1/06—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction
- B06B1/0644—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using a single piezoelectric element
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
- A61B8/06—Measuring blood flow
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
- A61B8/12—Diagnosis using ultrasonic, sonic or infrasonic waves in body cavities or body tracts, e.g. by using catheters
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/42—Piezoelectric device making
Abstract
Ultrasonic transducer with a selectable beamwidth comprising a body of piezoelectric material in the form of an annulus (21) having an outer diameter D and a thickness T. The body has proximal and distal generally planar parallel surfaces and a centrally disposed hole extending therethrough. The body has a cylindrical wall with a width W extending from the hole to the outer diameter. The transducer is capable of operating at low and high resonance being determined by the diameter D and an aspect ratio of D/T and the high frequency resonance being determined by the thickness T and an aspect ratio of W/T.
Description
o WO 95119049 2 1 8 0 5 5 9 P~
rJr ~ C rr ~Qnur ~ WITH 8ELECTA BLB BEAIIWIDT~
AND NET~:OD
This invention relates to a miniature, high efficiency dual frequency ultrasonic transducer with selectable beamwidth, an assembly t]nereof and method.
In United States Letters Patent 5, 059, 851, there is 5 ~;~rlr~P-l a miniature ultrasound trAnc~ rpr assembly which utilizes a trAn~ rPr in the form of a disk without a hole.
With such a disk, it is known that there are two strong rP~nAnc!P~ one related t:o the lateral (~iameter) r~c~mAnre and one related to the thickness resonance. In such 10 trAn~ rPrs~ however, since the thickness is close to the ~; Pr (typically, the fiiA' ' Pr was approximately twice the thickness), there waG a strong interaction between the ~;Ar ~r and thickness ]^pqnnAncpc. Attempts to optimize efficiency between the two resonances were found to be 15 difficult to achieve because of the undesired coupling between the two rPcnnAnce modes which caused inefficiencies.
Figures 3 and 4 of U.S. Patent 5,059,851 show a dc,L.ylllluL-shaped trAn~ rPr. The specification suggests an appropriate aspect ratio of 0.5-to-1. The distance from the 20 outer circumference to the outer margin of the hole would be approximately one-fourth to one-third of the width extending across the entire doughnut-shaped trAncd~lrPr. At the time of the disclosure in Figures 3 and 4, certain advantageous features of such a constr~lction were not appreciated. There 25 is therefore a need for a new and improved ultrasonic W095119049 ' 21 805 5q r~ J J
tr~n~ r~r, assembly thereof and method which takes full advantage of the characteristics of such a transducer.
In general, it is an obj ect of the present invention to provide an ultrasonic trAn~ rPr~ assembly thereof and 5 method which is capable of dual frequency operation providing selectable beamwidth.
Another object of the invention is to provide -a trAn~ rPr of the above character which although of miniature size is of high efficiency.
Another object of the invention is to provide a trAn~l11rPr and method of the above character in which ef f icient broadband operation can be achieved .
Another object of the invention is to provide a trAn~11rPr assembly and method of the above character which is particularly applicable to intravascular Doppler tr~n~ ,. for coronary or cerebral applications.
Another object of the invention is to provide a trAn~tl11ror assembly and method of the above character which i5 capable of operating in the 5-20 MHz range.
Additional objects and features of the invention will appear from the following description in which the preferred : '--'i l is set forth in detail in conjunction with the 7~r nying drawings.
FIG. l is an enlarged cross-sectional view of a tr~n~ rPr and an assembly thereof incorporating the present invention .
FIG. 2 is an end elevational view looking along the line 2-2 of FIG. l.
FIG . 3 is an enlarged ~;L uss-scctional view of the tr~n~ 11rPr shown in FIG. l.
FIG. 4 is an enlarged isometric view of the trAncrlllrpr shown in FIG. 3.
FIG. 5 is a block diagram and a schematic illustration showing the manner in which selectable beam width can be achieved u~i 1 i 7~n~ the tr~n~ lrPr shown in FIGS. 1 through 4.
The ultrasonic tr~n~d--rPr of the present invention is comprised of a body of piezoelectric material in the form of o WO 95/19049 2 18 0 5 5 9 r~.,v .
an annulus having a centrally rl i ~roSocl hole extending therethrough. It has an outer diameter D and proximal and distal generally planar ~urfaces. An electrode covers each of the proximal and distal planar surfaces. The 5 pi.o~opler~ric material also has a thickness T extending from the proximal to the di~tal surfaces and a wall width W
extending from the oute~- margir of the hole to the outer diameter. The body ic capable of operating at a low r~cnnAnre frequency and a high resonance frequency. The low 10 frequency r~conAnne is principally det~rm;nPd by the diameter D and the aspect ratio of D/T. The high frequency r~C~nAnr~e is principally ~l~tr~rm;n~d by the thickness T and the aspect ratio of W/T.
More in particular, the trAnC~9llr~r assembly 11 15 incorporating the presen1: invention forms a part of a guide wire 12 which i5 of the type described in Patent No. 5, 059, 851. This guide wire 12 as described therein is typically comprised of ~ flexible elongate member in the form of a stainless steel tube having a suitable length as 20 for example 150 cm. ThiC flexible elongate member can have a suitable diameter ranging from 0 . 018" to 0 . 010" . The f lexible elongate member is provided with a passageway extending the length the~-eof. The distal extremity of the flexible elongate meml:er may typically be secured to a coil 25 spring and the coil spring is secured to a cylindrical tip 16 which as described therein may be secured to the distal extremity of the spring by having the coil spring threaded onto the tip 16. The tip 16 is provided with a cup-shaped cylindrical recess 17 which receives the trAnC~ rF~r 21 of 3 0 the present invention .
The trAnc~lllr~r 21 is forme~ of a body 22 of a material of the type described in Patent No. 5,059,851 as for example a piezoelectric material suitable for use as an ultrasonic as for example a piezoelectric ceramic. One piezoelectric 35 ceramic found to be particularly satisfactory is EC-98 lead magnesium niobate available from EDO Corporation, Wester Division, Ceramics Division, 2645 South 300 West, Salt Lake City, T~tah 84115. The EC-98 composition was selected because it provides a higher dielectric constant, low aging characteristics, excellent coupling characteristics and a high strain co~stant which makes it particularly suitable for miniature trAnC~ r~rs of the present invention.
The body 24 which has been formed as hereinafter described has the form of an annulus or ring and can be characterized as being doughnut shaped. The body 24 has substantially planar proximal and distal parallel surfaces 26 and 27 with the distal surface 27 facing distally or outwardly from the distal extremity of the guide wire 12 as shown in FIG. 1. The body 24 is provided with an outer cylindrical surface 28 which extends in a direction generally perp~n~;r~l1Ar to the planar surfaces 26 and 27.
The body 24 is also provided with a centrally disposed hole 29 which extends through the surfaces 26 and 27 at substantially right angles thereto.
The trAnccl~rPr assembly 11 is particularly constructed to be used in small-diameter guide wires as for example those ranging below 0.018" and below. The trAnC~ r~r 21 therefore must have co~ in~ly small dimensions so they can be utilized in the distal extremities of such guide wires .
In order to achieve reliable manufacture of such tr~C l .r~- ~, it has been found desirable to utilize laser machining. Such laser r-^h;n;ng forms cuts and holes with slight tapers, as for example 5 or les5 which are shown in exaggerated form in FIG. 3. In connection with the present invention to provide such trAnC~r~rs 21, a sheet (not shown) of the piezoelectric material having the desired thickness as for example 3.8 mils is used. The transducers 21 are formed by a step-and-repeat process from the sheet of material. The amount of taper is det~rm;n-~cl by the type of laser being utilized and the focal length of the objective lens for the laser beam. By providing a lens having an increased focal length it is possible to reduce the taper.
By ut; l; ~;n~ an X-Y motion table in conjunction with a YAG
laser, it has been found that it is possible to provide a laser having a spot size ranging from 0 . 8 to 1. 0 mil and o wo 9S/19049 2 ~ 8 0 5 5 9 P~l/.J~ 'L ~f having a pulse repetition rate ranging from 50 to 150 Hz to cut both the outside diameter and the inside diameter for the tri~n~ cPr to provide the cylindrical body 22 with the hole 29 extending centra]Lly therethrough. Good results were 5 achieved ut;l;~;ng a YAG laser having an operating frequency of 1064 nanometers.
It should be apprl~ciated that other types of lasers can be used. For exampll~, an excimer laser can be utilized and may be desirable because it has a low thermal distortion 10 but the cut rates are less than that which can be accomplished with a YAG Laser. The excimer laser typically operates at 308 nm.
With the use of the YAG laser, it is possible to produce the trAnC~llcprs 21 at a relatively rapid production 15 rate with minimal damage to the crystailine structure. It has been found that any material evaporated onto the surfaces 26 and 27 o~ the body 22 during the laser machining operation can be readil~r removed with a suitable solvent such as acetone or alcohol utilizing a Q-tip. Thus there 20 remains a very small heat affected zone near the outer perimeter of the hole 29 adjacent the cylindrical surface 28 and the inner perimeter adjacent the hole 29.
In order for the tri~nc~lcpr 21 to fit within the cylindrical recess 17 of the tip 16, the tri~nR~ Pr 21 25 should have an appropriate diameter. Thus, by way of example, for a guide wire having an outside ~i;i Pr of 0.014", the tri~nc~ Pr 21 should have an outside diameter of approximately 0.010". Using la6er r-^h;n;n~ for such a size trAn~ Pr it has been possible to achieve the cylindrical 30 surfaces 28 and the hole 29 in the surfaces 26 and 27 with a taper of approximately 5 . This taper can be improved to approximately 2-3 with an obj ective lens having a longer f oca 1 length .
In connection with the present invention of a guide 35 wire 12 of the type show1l in FIG. 1, it is desirable that the tri~ncdu~pr 21 produce a broad beam- to make it possible to cover as wide a cross-section as possible of the vessel in which it is disposed, and preferably to extend to the side walls of the veæsel so that it is ensured that the velocity of the liquid, as for example blood, flowing through center of the lumen is accurately measured by ensuring that the beam covers at least the center of the vessel lumen.
As mentioned previously, the preferred sizes for intravascular guidewires are in the range of 0. 010" to 0.018" diameter, with some as large as 0.030" or greater.
The optimum Doppler frequencies for intravascular operations (considering attenuation, backscatter efficiency, c~ nninq distance, etc. ) are typically in the range of 5-20 MHz (corrpcpr~ ; n~ to acoustic wavelengths in blood of 0.003 inch to 0.012 inch) . These ranges for tr~ncd~ r size and ultrasound wavelength correspond to acoustic tr~nc~ rs having diameters ranging from approximately 1 to lO
wavelengths, with the most desirable combinations being tr;~nR~ c~- 6 having diameters in the range of 1 to 5 wavelengths .
In connection with the present invention, it has been found to be desirable to utilize the doughnut-shaped or ring-type transducer 21 which has the capability of providing two strong resonant freguencies, one of which can be characterized as high-resonant frequency and the other of which can be characterized as a low-resonant frequency.
The low resonant frequency is strongly related to the largest dimension of the trAnR~l~r~r 21 which is the outside diameter D. The r-~C~n~n~ can be characterized by its frequency and efficiency. These parameters can be predicted using a standard model for disk-shaped trAnRdllr~rs. For example, Kunkel et al. in Finite-~lement Analvsis of Vihrational Modes in Piezoelectric Ceramic Disks, IEEE, Vol.
37, No. 4, July 1990 use finite element analysis to calculate the normalized rf-R~n~n~e frequency and the elt:-L~ --h;~nical coupling coefficient (which is an 1 Li lIL element of trAnC~ r efficiency) as a function of the diameter to thickness aspect ratio D/T of a ceramic disk trAnRdllr~r. The diameter D can then be used to trans~orm the normalized resonance frequency to an actual resonance _7 ~; R~ ?~ 8 1 "19~5 frequency. The centra~ ly disposed hole 29 has only a small effect on the frequency and ele~ LL - ~nical coupling coefficient of the fu~damental low frequency mode, but it does act to suppress many of the undesirable disk modes 5 which would otherwise waste energy and thereby reduce the efficiency of the trAncd-lcPr. Thus the ring-type transducer offers the possibility of an efficient low frequency tr~ncAt~rPr, with a ~ery pure resonant mode and weak harmonics .
The second or higher frequency resonant mode is strongly related to the cross section of the doughnut-shaped or ring-type transducer. The rpcnn~n~p can be characterized by its frequency and efficiency. These parameters can be predicted using a standard model for linear transducers of 15 rectangular cross section, since the ring-type tr~ncdll-Pr can be envisioned as a linear element bent into a ring shape. Mason in Phvsical Acoustics Principles and Methods, Academic Press, Vol. I, Part A, 1964 used analytical techniques to calculate the normalized resonance frequency 20 and ele-:~L -h~nical coupling coefficient (which is an important element of transducer efficiency1, as a function of the width to thickness aspect ratio W/T of the ring cross section . The thickness T can then be used to transf orm the normalized rPcon~nr e frequency into an actual resonance 25 frequency. For width to thickness aspect ratios less than 1, the fl~n-q tal rpcnnAncp mode for a rectangular cross section is often referred to as the length extensional mode.
Theory predicts, and experiments conf irm that the ele- ~L, o~h~n;cal coupling coefficient is maximized for a 3 0 width to thickness aspect ratio of approximately 0 . 6, and this coupling coefficient is significantly higher than that found in a conventional thickness mode rPson~nc e transducer.
Proper choice of the three key tr~nc~lllcpr dimensions, r Pr D, thickness T, and annular width W permits the 35 efficient operation of a miniature transducer at two distinct frequencies. The centrally disposed hole suppresses the unwanted disk resonance modes and permits efficient operation using a low frequency lateral resonant 4Mi:NDE3 S~IE'-T
O Wo 95/19049 2 1 8 0 5 5 9 mode . At the same time the centrally rl 1 eposed hole permits the tri~nRd~l~r~r to take advantage of the efficient length PYpi~nA~r mode of vibration in the thickness resonant mode, with the aspect ratio W/T close to the theoretical optimum 5 of approximately 0 . 6 .
In the past in c:onnection with trilne~ rDrs it was typically desired to provide a transducer which has a single mode of operation with the other frequency modes being unwanted. In the present application, the present 10 tri~nRAll~-~r takes advantage of an unwanted mode by creating a low-frequency lateral mode to provide a tr~nC~l-lr~r which has two strong modes and wherein other spurious modes have been limited to provicle a dual-frequency tri~nC~r~r to optimize the operation of the guide wire 12 as hereinafter 15 described. It should be appreciated that either one of the two resonant frequencies may be chosen to be optimized to provide the best performance for a specific application at the expense of foregoing the flexibility of dual frequency operation. It can be further appreciated that if the high 20 and low resonant frequencies are designed to be close to one another, the two r-~cnn~nr~C will blend together to provide a single broad rPsnn:~nre, thereby providing an efficient broadband tri~ne~lr~r design.
By way of example, a tri~ne~lr~r 21 incorporating the 25 present invention had a diameter D extending across the distal surface 27 of 10 . 2 mils and a diameter D extending along the proximal surface 26 of 9 . 4 mils. It had a th;rkn~c,s T of 3.8 mils. The hole 29 had a diameter at the proximal surface 26 of 3.3 mils and a r~ r at the distal 30 surface 27 of 2.5 mils. With such dimensions, the distance W from the outer margin of the hole 29 to the outer surface 28 was 3.85 mils at the distal surface 27 and 3.0 mils at the proximal surface 26. The transducer 21 was mounted in the cup-shaped cylindrical recess 17 by suitable means such 35 as a medical-grade adhesive of the type disclosed in Patent No. 5,059,851. Also a matching layer 32 was provided at the distal surface 27 of a suitable material such as described in Patent No. 5,059,851 to provide a flush surface and to o Wo 9~/19049 - ~I/IJ~ ~
_g_ ill the recess 17 as shown particularly in FIG. 1. Such a trAnr~ r~r 21 was found to have a low-frequency mode of operation of approximat:ely 6.5 NHz and a high-frequency rDc~n~nre of 15 . O M~}z . For other dual frequencies of 6 . o 5 ME~z and 10 . O ~Iz the tr~n~:flllrDr 21 would have a diameter D
extending across the distal surface, would be approximately 10 . 8 mils and the thick.ness T would be approximately 6 . 7 mils. For dual frequencies of 6. O MHz and 12 . O MHz, the LL~ r;~ rDr 21 would have a diameter D extending across the 10 distal surface, would be approximately 10 . 5 mils and the thickness T would be approximately 5 . 2 mils .
The trAnr-dl~rPr 21 was activated at these frequencies by a conventional power supply, transmitter and receiver represented by the block 36 in FIG. 5. The block 36 was 15 provided with a frequency select switch 37 which has the rArAhi l; ty of selecting various frequencies as for example a specific low frequency or a specific high frequency from a range of frequencies a~ for example 5 Mhz, 6 M~z, 7.5 MHz, 10 NHZ, 12 NHz, 15 MHz and 20 MHz. These selected 20 frequencies were applied to a pair of lines 38 and 44 connected to a pair of illsulated conductors 39 and 42. The cqn~ tor 39 extends through the hole 29 and was bent over and soldered to the distal surface 27 of the trAnqcl-lr~r 21 as shown in FIG . 3 . The conductor 3 9 was provided with an 25 insulating covering 41. The conductor 42 was provided and had its distal extremity bent and soldered to the proximal surface 26 of the trAn~:rl~lc~r 21. It was also provided with an insulating covering 43. The Doppler transmitter from the block 36 supplied pulses of electrical energy to the 30 ultrasonic trAnr-~ r~r 21 which produced ultrasonic pulses that were propagated outwardly from the distal surface 27 in a forwardly extending conically-shaped beam 46 in which the conical beam subtended an angle or had a beam width of approximately 30 to analyze a sample volume 47 at a 35 suitable distance a6 for ~xample approximately 5 mm from the distal surface 27. Whe~ the transducer 21 was excited at the low frequency, a conical-shaped beam 48 was propagated forwardly and subtended an angle or had a beam width of Wo 95/19049 2 1 8 0 5 5 9 P~
approximately 600 to analyze a sample volume 49 as shown in FIG. 5 at a distance of approximately 10 mm from the distal surface 27. In general, the width of the beam from a small ultrasonic trAn~ Pr (expressed in radians is A/D, where A
5 is the wavelength of the ultr2sound and D is the trisnc~ Pr ' Pr~ a lower frequency (with its coLLp~lJol~l;ng longer wavelength) will provide a proportionally broader beam ed to higher frequêncy opêration.
In making Doppler blood flow mea~uL ~8 with the 10 guide wire 12 having a tri~nS~ lrpr assembly 11 of the presênt invention mounted therêon, it is important that the beam propagated by the transducer covers at least the central region of the vessel to properly ascertain spatial peak blood flow, because it is in this region that the blood is 15 f lowing at the f astest rate . Thus in order to be sure that the proper blood flow is being measured, it may be desirable to utilize the lower operating frequency with its corrPqp~n~l;n~ wider beam to ensure that substantially all of the cross-sectional area of a mea,,uL~ L location of a 20 vessel, or at least a substantial portion of the same which i nrl ~ pc the central region of the vessel is covered by the ultrasound beam. However, if the ultrasound beam is much larger than the vessel, a great deal of acoustic energy will be lost as the beam spreads beyond the vessel walls. Thus 25 in order to ensure that the Doppler signal is as strong as possihlP~ it may be desirable to utilize the higher operating frequency with its corrPCpon~l;n~ narrower beam as long as the beam is large ênough to cover a substantial portion of the vessel. For example, with a large vessel as 30 for example a femoral artery having a 10 mm diameter, there is an Pyrpl 1 Pnt O~PUL Lu~lity to pick up the central f low in the artery with the wider beam 4 8, whereas this might be difficult to do with the smaller beam 46. Conversely, in the case of a small vessel as for example a coronary artery 35 having a diameter of 3 mm, the narrower beam 46 will be adequate to cover a substantial portion of the vessel, whereas the wider beam 48 might provide a weak Doppler signal. Thus, with the present invention, it is possible to O WO95119049 2 1 8 0 5 5 9 ~ - `
make accurate mea~uL~ 5 in a wide range of vessel sizes even though the distal extremity of the guide wire may be bent to A' 'qte pas6ing into side branches and tortuous vessels and thus may nol: be centered in the vessel.
From the foregoin~ it can be seen that there has been provided a trAncdurPr assembly for use on a guide wire which is particularly adapted to making f low measurements in a vessel in a body as f or example the human body . The tr ~ncr~ Pr is one which has dual-frequency operation with high and low rPc~nAnre frequencies which are substantially equally efficient. By ut:ilizing such a trqnccll~Pr, a method can be utilized to provide narrow and wide beams to ensure that at least the center of the vessel where maximum f low occurs will be in the sample volume being measured.
rJr ~ C rr ~Qnur ~ WITH 8ELECTA BLB BEAIIWIDT~
AND NET~:OD
This invention relates to a miniature, high efficiency dual frequency ultrasonic transducer with selectable beamwidth, an assembly t]nereof and method.
In United States Letters Patent 5, 059, 851, there is 5 ~;~rlr~P-l a miniature ultrasound trAnc~ rpr assembly which utilizes a trAn~ rPr in the form of a disk without a hole.
With such a disk, it is known that there are two strong rP~nAnc!P~ one related t:o the lateral (~iameter) r~c~mAnre and one related to the thickness resonance. In such 10 trAn~ rPrs~ however, since the thickness is close to the ~; Pr (typically, the fiiA' ' Pr was approximately twice the thickness), there waG a strong interaction between the ~;Ar ~r and thickness ]^pqnnAncpc. Attempts to optimize efficiency between the two resonances were found to be 15 difficult to achieve because of the undesired coupling between the two rPcnnAnce modes which caused inefficiencies.
Figures 3 and 4 of U.S. Patent 5,059,851 show a dc,L.ylllluL-shaped trAn~ rPr. The specification suggests an appropriate aspect ratio of 0.5-to-1. The distance from the 20 outer circumference to the outer margin of the hole would be approximately one-fourth to one-third of the width extending across the entire doughnut-shaped trAncd~lrPr. At the time of the disclosure in Figures 3 and 4, certain advantageous features of such a constr~lction were not appreciated. There 25 is therefore a need for a new and improved ultrasonic W095119049 ' 21 805 5q r~ J J
tr~n~ r~r, assembly thereof and method which takes full advantage of the characteristics of such a transducer.
In general, it is an obj ect of the present invention to provide an ultrasonic trAn~ rPr~ assembly thereof and 5 method which is capable of dual frequency operation providing selectable beamwidth.
Another object of the invention is to provide -a trAn~ rPr of the above character which although of miniature size is of high efficiency.
Another object of the invention is to provide a trAn~l11rPr and method of the above character in which ef f icient broadband operation can be achieved .
Another object of the invention is to provide a trAn~11rPr assembly and method of the above character which is particularly applicable to intravascular Doppler tr~n~ ,. for coronary or cerebral applications.
Another object of the invention is to provide a trAn~tl11ror assembly and method of the above character which i5 capable of operating in the 5-20 MHz range.
Additional objects and features of the invention will appear from the following description in which the preferred : '--'i l is set forth in detail in conjunction with the 7~r nying drawings.
FIG. l is an enlarged cross-sectional view of a tr~n~ rPr and an assembly thereof incorporating the present invention .
FIG. 2 is an end elevational view looking along the line 2-2 of FIG. l.
FIG . 3 is an enlarged ~;L uss-scctional view of the tr~n~ 11rPr shown in FIG. l.
FIG. 4 is an enlarged isometric view of the trAncrlllrpr shown in FIG. 3.
FIG. 5 is a block diagram and a schematic illustration showing the manner in which selectable beam width can be achieved u~i 1 i 7~n~ the tr~n~ lrPr shown in FIGS. 1 through 4.
The ultrasonic tr~n~d--rPr of the present invention is comprised of a body of piezoelectric material in the form of o WO 95/19049 2 18 0 5 5 9 r~.,v .
an annulus having a centrally rl i ~roSocl hole extending therethrough. It has an outer diameter D and proximal and distal generally planar ~urfaces. An electrode covers each of the proximal and distal planar surfaces. The 5 pi.o~opler~ric material also has a thickness T extending from the proximal to the di~tal surfaces and a wall width W
extending from the oute~- margir of the hole to the outer diameter. The body ic capable of operating at a low r~cnnAnre frequency and a high resonance frequency. The low 10 frequency r~conAnne is principally det~rm;nPd by the diameter D and the aspect ratio of D/T. The high frequency r~C~nAnr~e is principally ~l~tr~rm;n~d by the thickness T and the aspect ratio of W/T.
More in particular, the trAnC~9llr~r assembly 11 15 incorporating the presen1: invention forms a part of a guide wire 12 which i5 of the type described in Patent No. 5, 059, 851. This guide wire 12 as described therein is typically comprised of ~ flexible elongate member in the form of a stainless steel tube having a suitable length as 20 for example 150 cm. ThiC flexible elongate member can have a suitable diameter ranging from 0 . 018" to 0 . 010" . The f lexible elongate member is provided with a passageway extending the length the~-eof. The distal extremity of the flexible elongate meml:er may typically be secured to a coil 25 spring and the coil spring is secured to a cylindrical tip 16 which as described therein may be secured to the distal extremity of the spring by having the coil spring threaded onto the tip 16. The tip 16 is provided with a cup-shaped cylindrical recess 17 which receives the trAnC~ rF~r 21 of 3 0 the present invention .
The trAnc~lllr~r 21 is forme~ of a body 22 of a material of the type described in Patent No. 5,059,851 as for example a piezoelectric material suitable for use as an ultrasonic as for example a piezoelectric ceramic. One piezoelectric 35 ceramic found to be particularly satisfactory is EC-98 lead magnesium niobate available from EDO Corporation, Wester Division, Ceramics Division, 2645 South 300 West, Salt Lake City, T~tah 84115. The EC-98 composition was selected because it provides a higher dielectric constant, low aging characteristics, excellent coupling characteristics and a high strain co~stant which makes it particularly suitable for miniature trAnC~ r~rs of the present invention.
The body 24 which has been formed as hereinafter described has the form of an annulus or ring and can be characterized as being doughnut shaped. The body 24 has substantially planar proximal and distal parallel surfaces 26 and 27 with the distal surface 27 facing distally or outwardly from the distal extremity of the guide wire 12 as shown in FIG. 1. The body 24 is provided with an outer cylindrical surface 28 which extends in a direction generally perp~n~;r~l1Ar to the planar surfaces 26 and 27.
The body 24 is also provided with a centrally disposed hole 29 which extends through the surfaces 26 and 27 at substantially right angles thereto.
The trAnccl~rPr assembly 11 is particularly constructed to be used in small-diameter guide wires as for example those ranging below 0.018" and below. The trAnC~ r~r 21 therefore must have co~ in~ly small dimensions so they can be utilized in the distal extremities of such guide wires .
In order to achieve reliable manufacture of such tr~C l .r~- ~, it has been found desirable to utilize laser machining. Such laser r-^h;n;ng forms cuts and holes with slight tapers, as for example 5 or les5 which are shown in exaggerated form in FIG. 3. In connection with the present invention to provide such trAnC~r~rs 21, a sheet (not shown) of the piezoelectric material having the desired thickness as for example 3.8 mils is used. The transducers 21 are formed by a step-and-repeat process from the sheet of material. The amount of taper is det~rm;n-~cl by the type of laser being utilized and the focal length of the objective lens for the laser beam. By providing a lens having an increased focal length it is possible to reduce the taper.
By ut; l; ~;n~ an X-Y motion table in conjunction with a YAG
laser, it has been found that it is possible to provide a laser having a spot size ranging from 0 . 8 to 1. 0 mil and o wo 9S/19049 2 ~ 8 0 5 5 9 P~l/.J~ 'L ~f having a pulse repetition rate ranging from 50 to 150 Hz to cut both the outside diameter and the inside diameter for the tri~n~ cPr to provide the cylindrical body 22 with the hole 29 extending centra]Lly therethrough. Good results were 5 achieved ut;l;~;ng a YAG laser having an operating frequency of 1064 nanometers.
It should be apprl~ciated that other types of lasers can be used. For exampll~, an excimer laser can be utilized and may be desirable because it has a low thermal distortion 10 but the cut rates are less than that which can be accomplished with a YAG Laser. The excimer laser typically operates at 308 nm.
With the use of the YAG laser, it is possible to produce the trAnC~llcprs 21 at a relatively rapid production 15 rate with minimal damage to the crystailine structure. It has been found that any material evaporated onto the surfaces 26 and 27 o~ the body 22 during the laser machining operation can be readil~r removed with a suitable solvent such as acetone or alcohol utilizing a Q-tip. Thus there 20 remains a very small heat affected zone near the outer perimeter of the hole 29 adjacent the cylindrical surface 28 and the inner perimeter adjacent the hole 29.
In order for the tri~nc~lcpr 21 to fit within the cylindrical recess 17 of the tip 16, the tri~nR~ Pr 21 25 should have an appropriate diameter. Thus, by way of example, for a guide wire having an outside ~i;i Pr of 0.014", the tri~nc~ Pr 21 should have an outside diameter of approximately 0.010". Using la6er r-^h;n;n~ for such a size trAn~ Pr it has been possible to achieve the cylindrical 30 surfaces 28 and the hole 29 in the surfaces 26 and 27 with a taper of approximately 5 . This taper can be improved to approximately 2-3 with an obj ective lens having a longer f oca 1 length .
In connection with the present invention of a guide 35 wire 12 of the type show1l in FIG. 1, it is desirable that the tri~ncdu~pr 21 produce a broad beam- to make it possible to cover as wide a cross-section as possible of the vessel in which it is disposed, and preferably to extend to the side walls of the veæsel so that it is ensured that the velocity of the liquid, as for example blood, flowing through center of the lumen is accurately measured by ensuring that the beam covers at least the center of the vessel lumen.
As mentioned previously, the preferred sizes for intravascular guidewires are in the range of 0. 010" to 0.018" diameter, with some as large as 0.030" or greater.
The optimum Doppler frequencies for intravascular operations (considering attenuation, backscatter efficiency, c~ nninq distance, etc. ) are typically in the range of 5-20 MHz (corrpcpr~ ; n~ to acoustic wavelengths in blood of 0.003 inch to 0.012 inch) . These ranges for tr~ncd~ r size and ultrasound wavelength correspond to acoustic tr~nc~ rs having diameters ranging from approximately 1 to lO
wavelengths, with the most desirable combinations being tr;~nR~ c~- 6 having diameters in the range of 1 to 5 wavelengths .
In connection with the present invention, it has been found to be desirable to utilize the doughnut-shaped or ring-type transducer 21 which has the capability of providing two strong resonant freguencies, one of which can be characterized as high-resonant frequency and the other of which can be characterized as a low-resonant frequency.
The low resonant frequency is strongly related to the largest dimension of the trAnR~l~r~r 21 which is the outside diameter D. The r-~C~n~n~ can be characterized by its frequency and efficiency. These parameters can be predicted using a standard model for disk-shaped trAnRdllr~rs. For example, Kunkel et al. in Finite-~lement Analvsis of Vihrational Modes in Piezoelectric Ceramic Disks, IEEE, Vol.
37, No. 4, July 1990 use finite element analysis to calculate the normalized rf-R~n~n~e frequency and the elt:-L~ --h;~nical coupling coefficient (which is an 1 Li lIL element of trAnC~ r efficiency) as a function of the diameter to thickness aspect ratio D/T of a ceramic disk trAnRdllr~r. The diameter D can then be used to trans~orm the normalized resonance frequency to an actual resonance _7 ~; R~ ?~ 8 1 "19~5 frequency. The centra~ ly disposed hole 29 has only a small effect on the frequency and ele~ LL - ~nical coupling coefficient of the fu~damental low frequency mode, but it does act to suppress many of the undesirable disk modes 5 which would otherwise waste energy and thereby reduce the efficiency of the trAncd-lcPr. Thus the ring-type transducer offers the possibility of an efficient low frequency tr~ncAt~rPr, with a ~ery pure resonant mode and weak harmonics .
The second or higher frequency resonant mode is strongly related to the cross section of the doughnut-shaped or ring-type transducer. The rpcnn~n~p can be characterized by its frequency and efficiency. These parameters can be predicted using a standard model for linear transducers of 15 rectangular cross section, since the ring-type tr~ncdll-Pr can be envisioned as a linear element bent into a ring shape. Mason in Phvsical Acoustics Principles and Methods, Academic Press, Vol. I, Part A, 1964 used analytical techniques to calculate the normalized resonance frequency 20 and ele-:~L -h~nical coupling coefficient (which is an important element of transducer efficiency1, as a function of the width to thickness aspect ratio W/T of the ring cross section . The thickness T can then be used to transf orm the normalized rPcon~nr e frequency into an actual resonance 25 frequency. For width to thickness aspect ratios less than 1, the fl~n-q tal rpcnnAncp mode for a rectangular cross section is often referred to as the length extensional mode.
Theory predicts, and experiments conf irm that the ele- ~L, o~h~n;cal coupling coefficient is maximized for a 3 0 width to thickness aspect ratio of approximately 0 . 6, and this coupling coefficient is significantly higher than that found in a conventional thickness mode rPson~nc e transducer.
Proper choice of the three key tr~nc~lllcpr dimensions, r Pr D, thickness T, and annular width W permits the 35 efficient operation of a miniature transducer at two distinct frequencies. The centrally disposed hole suppresses the unwanted disk resonance modes and permits efficient operation using a low frequency lateral resonant 4Mi:NDE3 S~IE'-T
O Wo 95/19049 2 1 8 0 5 5 9 mode . At the same time the centrally rl 1 eposed hole permits the tri~nRd~l~r~r to take advantage of the efficient length PYpi~nA~r mode of vibration in the thickness resonant mode, with the aspect ratio W/T close to the theoretical optimum 5 of approximately 0 . 6 .
In the past in c:onnection with trilne~ rDrs it was typically desired to provide a transducer which has a single mode of operation with the other frequency modes being unwanted. In the present application, the present 10 tri~nRAll~-~r takes advantage of an unwanted mode by creating a low-frequency lateral mode to provide a tr~nC~l-lr~r which has two strong modes and wherein other spurious modes have been limited to provicle a dual-frequency tri~nC~r~r to optimize the operation of the guide wire 12 as hereinafter 15 described. It should be appreciated that either one of the two resonant frequencies may be chosen to be optimized to provide the best performance for a specific application at the expense of foregoing the flexibility of dual frequency operation. It can be further appreciated that if the high 20 and low resonant frequencies are designed to be close to one another, the two r-~cnn~nr~C will blend together to provide a single broad rPsnn:~nre, thereby providing an efficient broadband tri~ne~lr~r design.
By way of example, a tri~ne~lr~r 21 incorporating the 25 present invention had a diameter D extending across the distal surface 27 of 10 . 2 mils and a diameter D extending along the proximal surface 26 of 9 . 4 mils. It had a th;rkn~c,s T of 3.8 mils. The hole 29 had a diameter at the proximal surface 26 of 3.3 mils and a r~ r at the distal 30 surface 27 of 2.5 mils. With such dimensions, the distance W from the outer margin of the hole 29 to the outer surface 28 was 3.85 mils at the distal surface 27 and 3.0 mils at the proximal surface 26. The transducer 21 was mounted in the cup-shaped cylindrical recess 17 by suitable means such 35 as a medical-grade adhesive of the type disclosed in Patent No. 5,059,851. Also a matching layer 32 was provided at the distal surface 27 of a suitable material such as described in Patent No. 5,059,851 to provide a flush surface and to o Wo 9~/19049 - ~I/IJ~ ~
_g_ ill the recess 17 as shown particularly in FIG. 1. Such a trAnr~ r~r 21 was found to have a low-frequency mode of operation of approximat:ely 6.5 NHz and a high-frequency rDc~n~nre of 15 . O M~}z . For other dual frequencies of 6 . o 5 ME~z and 10 . O ~Iz the tr~n~:flllrDr 21 would have a diameter D
extending across the distal surface, would be approximately 10 . 8 mils and the thick.ness T would be approximately 6 . 7 mils. For dual frequencies of 6. O MHz and 12 . O MHz, the LL~ r;~ rDr 21 would have a diameter D extending across the 10 distal surface, would be approximately 10 . 5 mils and the thickness T would be approximately 5 . 2 mils .
The trAnr-dl~rPr 21 was activated at these frequencies by a conventional power supply, transmitter and receiver represented by the block 36 in FIG. 5. The block 36 was 15 provided with a frequency select switch 37 which has the rArAhi l; ty of selecting various frequencies as for example a specific low frequency or a specific high frequency from a range of frequencies a~ for example 5 Mhz, 6 M~z, 7.5 MHz, 10 NHZ, 12 NHz, 15 MHz and 20 MHz. These selected 20 frequencies were applied to a pair of lines 38 and 44 connected to a pair of illsulated conductors 39 and 42. The cqn~ tor 39 extends through the hole 29 and was bent over and soldered to the distal surface 27 of the trAnqcl-lr~r 21 as shown in FIG . 3 . The conductor 3 9 was provided with an 25 insulating covering 41. The conductor 42 was provided and had its distal extremity bent and soldered to the proximal surface 26 of the trAn~:rl~lc~r 21. It was also provided with an insulating covering 43. The Doppler transmitter from the block 36 supplied pulses of electrical energy to the 30 ultrasonic trAnr-~ r~r 21 which produced ultrasonic pulses that were propagated outwardly from the distal surface 27 in a forwardly extending conically-shaped beam 46 in which the conical beam subtended an angle or had a beam width of approximately 30 to analyze a sample volume 47 at a 35 suitable distance a6 for ~xample approximately 5 mm from the distal surface 27. Whe~ the transducer 21 was excited at the low frequency, a conical-shaped beam 48 was propagated forwardly and subtended an angle or had a beam width of Wo 95/19049 2 1 8 0 5 5 9 P~
approximately 600 to analyze a sample volume 49 as shown in FIG. 5 at a distance of approximately 10 mm from the distal surface 27. In general, the width of the beam from a small ultrasonic trAn~ Pr (expressed in radians is A/D, where A
5 is the wavelength of the ultr2sound and D is the trisnc~ Pr ' Pr~ a lower frequency (with its coLLp~lJol~l;ng longer wavelength) will provide a proportionally broader beam ed to higher frequêncy opêration.
In making Doppler blood flow mea~uL ~8 with the 10 guide wire 12 having a tri~nS~ lrpr assembly 11 of the presênt invention mounted therêon, it is important that the beam propagated by the transducer covers at least the central region of the vessel to properly ascertain spatial peak blood flow, because it is in this region that the blood is 15 f lowing at the f astest rate . Thus in order to be sure that the proper blood flow is being measured, it may be desirable to utilize the lower operating frequency with its corrPqp~n~l;n~ wider beam to ensure that substantially all of the cross-sectional area of a mea,,uL~ L location of a 20 vessel, or at least a substantial portion of the same which i nrl ~ pc the central region of the vessel is covered by the ultrasound beam. However, if the ultrasound beam is much larger than the vessel, a great deal of acoustic energy will be lost as the beam spreads beyond the vessel walls. Thus 25 in order to ensure that the Doppler signal is as strong as possihlP~ it may be desirable to utilize the higher operating frequency with its corrPCpon~l;n~ narrower beam as long as the beam is large ênough to cover a substantial portion of the vessel. For example, with a large vessel as 30 for example a femoral artery having a 10 mm diameter, there is an Pyrpl 1 Pnt O~PUL Lu~lity to pick up the central f low in the artery with the wider beam 4 8, whereas this might be difficult to do with the smaller beam 46. Conversely, in the case of a small vessel as for example a coronary artery 35 having a diameter of 3 mm, the narrower beam 46 will be adequate to cover a substantial portion of the vessel, whereas the wider beam 48 might provide a weak Doppler signal. Thus, with the present invention, it is possible to O WO95119049 2 1 8 0 5 5 9 ~ - `
make accurate mea~uL~ 5 in a wide range of vessel sizes even though the distal extremity of the guide wire may be bent to A' 'qte pas6ing into side branches and tortuous vessels and thus may nol: be centered in the vessel.
From the foregoin~ it can be seen that there has been provided a trAncdurPr assembly for use on a guide wire which is particularly adapted to making f low measurements in a vessel in a body as f or example the human body . The tr ~ncr~ Pr is one which has dual-frequency operation with high and low rPc~nAnre frequencies which are substantially equally efficient. By ut:ilizing such a trqnccll~Pr, a method can be utilized to provide narrow and wide beams to ensure that at least the center of the vessel where maximum f low occurs will be in the sample volume being measured.
Claims (16)
1. An ultrasonic transducer for obtaining first and second beamwidths in response to low frequency excitation pulses and high frequency excitation pulses respectively and for use with a power supply supplying low frequency excitation pulses and high frequency excitation pulses, said transducer being for use on the distal extremity of a guide wire having a diameter ranging from 0.010 to 0.018 inch, comprising a body of piezoelectric material in the form of an annulus having an outer diameter D of 0.018 inch and less and a thickness T, the body having proximal and distal generally planar parallel surfaces and having a centrally disposed hole extending through the proximal and distal surfaces, the body having an inner perimeter commencing at the hole and an outer perimeter with a width W extending from the inner perimeter to the outer perimeter, the diameter D, the thickness T and the width W being selected so that the body will resonate at a low frequency resonance in response to said low frequency pulses and will resonate at a high frequency resonance in response to said high frequency pulses to provide usable energy levels in said first and second beamwidths, said low frequency resonance being determined by the diameter D and an aspect ratio of D/T and said high frequency resonance being determined by the thickness T and an aspect ratio W/T of approximately .6, said body being sized so that it can be mounted on the distal extremity of the guide wire so that beams of said first and second beamwidths are propagated forwardly from the body in a direction generally perpendicular of the first and second surfaces.
2. A transducer as in Claim 1 wherein the body is provided with an outer cylindrical surface which is generally perpendicular to the proximal and distal surfaces and wherein said hole extends in a direction generally perpendicular to the proximal and distal generally planar surfaces.
3. A transducer as in Claim 2 wherein said outer cylindrical surface and the surface forming the hole have a taper therein.
4. A transducer as in Claim 3 wherein said distal surface has a diameter of approximately 10.2 mils and said proximal surface has a diameter of approximately 9.4 mils and said thickness is approximately 3.8 mils.
5. A transducer as in Claim 4 wherein said hole has a diameter at the distal surface of 2.5 mils and said hole has a diameter at the proximal surface of approximately 3.3 mils.
6. A transducer as in Claim 1 wherein said low frequency resonance is approximately one-half of the high frequency resonance.
7. A transducer as in Claim 6 wherein said low frequency resonance is at 6.5 MHz and the high frequency resonance is at 15.0 MHz.
8. A transducer as in Claim 7 wherein the transducer produces a beam having a beamwidth of approximately 60° at the low frequency resonance and a beam having a beamwidth of approximately 30° at the high frequency resonance.
9. A transducer as in Claim 1 wherein said piezoelectric material has a high dielectric content, low aging characteristics, excellent coupling characteristics and a high strain constant.
10. A transducer as in Claim 9 wherein said piezoelectric material is EC-98.
11. A transducer assembly comprising a cylindrical tip of 0.018 inch and less in diameter and having an outwardly facing cup-shaped recess provided therein, an ultrasonic transducer formed of a piezoelectric material disposed in the recess, said body being in the form of an annulus having a centrally disposed hole extending therethrough and inner and outer margins and proximal and distal parallel, generally planar surfaces and having an outer diameter and a thickness of T extending from the proximal to the distal surfaces and a wall width of W
extending from the inner margin to the outer margin, adhesive means securing said body in said recess, a first conductor extending through the hole and being bonded to the distal surface, a second conductor bonded to the proximal surface, said transducer being capable of operating at a low frequency resonance and a high frequency resonance, said low frequency resonance being determined by the diameter D and an aspect ratio D/T of approximately 0.6 and said high frequency resonance being determined by the thickness T and an aspect ratio of W/T.
extending from the inner margin to the outer margin, adhesive means securing said body in said recess, a first conductor extending through the hole and being bonded to the distal surface, a second conductor bonded to the proximal surface, said transducer being capable of operating at a low frequency resonance and a high frequency resonance, said low frequency resonance being determined by the diameter D and an aspect ratio D/T of approximately 0.6 and said high frequency resonance being determined by the thickness T and an aspect ratio of W/T.
12. An assembly as in Claim 11 wherein the aspect ratio of W/T is equal to approximately 0.6.
13. An assembly as in Claim 11 together with means for supplying power to the conductors connected to the transducer for supplying low frequency excitation pulses and high frequency excitation pulses to the transducer and selection means for selecting either a low frequency excitation or a high frequency excitation to thereby make possible the selection of the beamwidth of the transducer.
14. An assembly in Claim 13 wherein the beamwidth for the high frequency resonance is in the vicinity of 30° and wherein the bandwidth for the low frequency resonance is in the vicinity of 60°.
15. In a method for measuring flow in a vessel by the use of a dual frequency ultrasonic transducer, positioning the transducer in the vessel, selecting a first frequency for operation of the transducer to provide a first beamwidth and thereafter selecting a second frequency for excitation of the transducer to provide a second beamwidth which subtends a greater angle than the first beamwidth.
16. A method as in Claim 15 wherein first and second beamwidths are utilized to ensure that the sample volume being measured includes the center of the vessel in which the measurement is being made.
Applications Claiming Priority (2)
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| US17808194A | 1994-01-06 | 1994-01-06 | |
| US08/178,081 | 1994-01-06 |
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| CA2180559A1 true CA2180559A1 (en) | 1995-07-13 |
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| CA002180559A Abandoned CA2180559A1 (en) | 1994-01-06 | 1995-01-05 | Ultrasonic transducer with selectable beamwidth and method |
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| EP (1) | EP0738427A4 (en) |
| JP (1) | JPH09508242A (en) |
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| CA (1) | CA2180559A1 (en) |
| WO (1) | WO1995019049A1 (en) |
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| US4807636A (en) * | 1986-09-09 | 1989-02-28 | Vital Science Corporation | Method and apparatus for measuring volume fluid flow |
| US5059851A (en) * | 1990-09-06 | 1991-10-22 | Cardiometrics, Inc. | Miniature ultrasound high efficiency transducer assembly, guidewire using the same and method |
| EP0738427A4 (en) * | 1994-01-06 | 1999-02-03 | Cardiometrics Inc | Ultrasonic transducer with selectable beamwidth and method |
-
1995
- 1995-01-05 EP EP95907977A patent/EP0738427A4/en not_active Withdrawn
- 1995-01-05 AU AU15978/95A patent/AU1597895A/en not_active Abandoned
- 1995-01-05 WO PCT/US1995/000086 patent/WO1995019049A1/en not_active Application Discontinuation
- 1995-01-05 CA CA002180559A patent/CA2180559A1/en not_active Abandoned
- 1995-01-05 JP JP7518577A patent/JPH09508242A/en active Pending
- 1995-05-23 US US08/447,993 patent/US5581144A/en not_active Expired - Lifetime
-
1996
- 1996-12-02 US US08/759,054 patent/US5740596A/en not_active Expired - Lifetime
-
1998
- 1998-02-18 US US09/025,540 patent/US6025670A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0738427A4 (en) | 1999-02-03 |
| EP0738427A1 (en) | 1996-10-23 |
| WO1995019049A1 (en) | 1995-07-13 |
| US6025670A (en) | 2000-02-15 |
| AU1597895A (en) | 1995-08-01 |
| US5581144A (en) | 1996-12-03 |
| JPH09508242A (en) | 1997-08-19 |
| US5740596A (en) | 1998-04-21 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |