Image guided intravascular therapy catheter utilizing a thin chip multiplexor

Abstract

A medical device that includes an array of ultrasound elements and an integrated circuit, proximal to the ultrasound elements, having a thickness of less than 40 μm, and having an array of ultrasound element driving-and-receiving contacts, matching the array of ultrasound elements and collectively electrically connected to each of the ultrasound elements. The integrated circuit also having a set of input-output signal contacts, the set being collectively switchable into contact with any one of a set of predefined blocks of driving-and-receiving contacts, and a set of control contacts, wherein inputs received by the control contacts collectively command some aspect of chip operation. The medical device further includes a set a protective covering.

Description

BACKGROUND

U.S. Pat. No. 8,702,609, which is assigned to the assignee of the present application, discloses an image guided-therapy catheter that uses ultrasound to form an image of the interior of a blood vessel directly in front of the catheter, to determine the locations of plaque, and then permits the use of this information in driving a set of RF ablation electrodes to selectively ablate plaque, while avoiding damaging the interior surfaces of the blood vessel. A number of challenging issues are presented in the design of this type of device. Among these is the acoustic characteristics of the medical device and how to avoid harmful interference to the returning signal from signal that has reflected from the portion of the device proximal (that is, further back from the tip) to the ultrasound array.

Another troublesome issue in the design of the system is the multiplexing of the driving/receiving coax lines for the ultrasound elements. With a large array, it would be impossible to have a separate coax line for each element. Multiplexors, however, require an increasing number of control inputs for an increasing number of multiplexed lines. With catheter space at an extreme premium, fitting a high number of control lines into a catheter is also very problematic.

SUMMARY

The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements.

The present invention may take the form of an intravenous ultrasound catheter having a distal tip and having a forward-facing array of ultrasound elements near to the distal tip of the device. Also, an integrated circuit (IC) die, abuts and is proximal to the ultrasound elements, having a thickness of less than 80 μm, and further having a first face, facing the forward-facing array, and having an array of ultrasound element driving and receiving contacts, in mating arrangement to the array of ultrasound elements, so that the array of ultrasound element driving and receiving contacts collectively physically abut and electrically connect to each of the ultrasound elements; a second face, opposed to the first face, and having a set of input-output signal contacts, the set being fewer in number than the array of ultrasound element driving and receiving contacts and each being switchable into contact with any one of a set of the ultrasound element driving and receiving contacts, the second face also having a set of control contacts, wherein inputs received by the control contacts positively collectively command some aspect of operation of the IC die; and a set of amplifiers, interposed between the first face and the second face, including an amplifier for each one of the driving and receiving electrical contacts. A flex circuit assembly is proximal to the integrated circuit and includes coax cables and a contact portion, has a set of contact pads abutting and electrically connects the input-output signal contacts of the IC die to the coax cables. Finally, backing material, abutting and directly proximal to the contact portion, thereby forming an interface and wherein the backing material and the contact portion material have equal acoustic impedance, thereby preventing reflection at the interface.

In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following detailed descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are illustrated in referenced drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.

FIG. 1 is a block diagram of the ultrasound system of a medical device, according to the present invention.

FIG. 2 is a physical representation of the proximal side of the mux and amp chip shown in block form in FIG. 1.

FIG. 3 is a proximal side view of the elements of the ultrasound array, shown in block form in FIG. 1, showing one allocation of ultrasound elements into eighteen blocks 1 through H.

FIG. 4 is a side rear isometric view of the imaging head of the system of FIG. 1.

FIG. 5 is a view of an article of flex circuit used in the system of FIG. 1.

FIG. 6 is an illustration of the flip chip technique which may be used as a step in the production of the imaging head of FIG. 5.

FIG. 7 is a side rear isometric view of the imaging head of FIG. 5, shown including further proximal elements.

FIG. 8 is a diagram of a catheter configured for placement through an opening and into the body of a human patient or subject.

FIG. 9 is a cross-sectional view of a catheter in a Seldinger sheath.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2, in a first preferred embodiment of an ultrasound imaging system 10, having a distal portion housed in a catheter sized to enter cardiac arteries, a processor assembly 12 commands a waveform signal generating network 14, which generates 35 MHz waveforms for 32 coax signal lines 16, which drive and receive from a set of 32 input/output contacts 17, on an integrated circuit die (henceforth “multiplexor chip” or “chip”) 18. In one preferred embodiment, multiplexor chip 18 is less than 12 μm in thickness. In alternative embodiments, chip 18 is less than 20, 40, 60 and 80 μm. Control lines 20A-20D extend from processor 12 to multiplexor 18, attaching to contact pads 21A-21D, respectively, and must command multiplexor 18, for each phase to switch the 32 signal lines 16 to a one out of a set of 18 designated blocks 22 of drive/sense contacts, to drive one out of 18 blocks of thirty-two ultrasound elements in a 24×24 (576) ultrasound element array 30. In a preferred embodiment, array 30 is made of a piezoelectric material, such as a piezoelectric ceramic. It is possible that at some point another technology, such as capacitive micromachined ultrasound transducers (CMUT), may be usable in this application. Thirty-two micro-coax lines are required for the input/output contacts 17 with the grounds tied together and then eventually to a common ground (analog ground 19) on the chip 18. Plus, four more wires are required for digital or logic control and power to the IC chip 18. In addition, in one embodiment, four wires are required to transmit the RF signals to RF ablation electrodes (noted below). These wires physically bypass chip 18.

The basic function of the chip 18 is to allow 32 micro-coax acoustic channels to selectively connect to any group of thirty-two ultrasound array elements and to amplify the return signals from the ultrasound elements, as they are transmitted to the coax signal lines 16. On power-up, the ultrasound system resets the chip 18 and asserts the Tx/Rx line placing the MUX in transmit mode for elements 1-32. The ultrasound system 10 then transmits an electrical analog pulse through each of the micro-coax cables 16 to contacts 17. The electrical pulses are then transferred to elements 1-32 of the piezoelectric array. After the ultrasonic pulses have left elements 1-32, the Tx/Rx line is de-asserted placing the MUX in receive mode. In the receive mode, mechanical energy reflected from the tissue or blood is converted to electrical energy by the piezoelectric elements 1-32 and the power transferred back through the chip 18 where the signal is amplified (using power received on contact pad 23), matched to the cable and sent back through each micro-coax to the ultrasound system for conversion to digital data at the front end of the imaging system. The receive mode lasts for approximately 8 μS. Tx/Rx is then re-asserted and the cycle repeats for elements 33-64 and so forth. A chip ground 25 is electrically connected to a further ground at the proximal end of a linear conductor.

During the transmit cycle, the input electrical impedance of the IC chip 18 on the flex side of the chip 18 is matched to that of the coaxial cable 16 (typically 50 to 100 Ohm characteristic impedance), whereas the output impedance of the IC chip 18 is matched, or optimized, to the electrical impedance of the individual piezoelectric elements of the array 30 (typically 10,000 Ohms). The electrical impedance matching scheme works also in the receive cycle to enable optimal transmission of power.

In summary, the IC chip 18 performs multiple functions in the operation of the imaging system 10: It enables the electrical connection of multiple micro-coaxial cables 16 to the individual elements of the array 30, it matches the electrical impedance of the coaxial cables 16 to that of the piezoelectric elements, it acts as multiplexer so the entire array 30 of elements can be addressed and as an amplifier of the weak receive signals (of the order of a few microvolts) in receive mode.

In one scheme of driving the ultrasound array 30, the following transmit receive sequence is performed, where B₁ is the first block of elements, B₂ is the second block of elements and so on until B₃₂ is the 32^nd block of elements and TB_n indicates transmission through the nth block of elements, and RB_n means receiving on the nth block of elements:TB₁,RB₁,TB₁,RB₂, . . . ,TB₁,RB_n,TB₂,RB₁,TB₂,RB₂, . . . TB₂,RB_n, . . . ,TB_nRB₁, . . . TB_nRB_n  (S1)

In a catheter designed to be introduced into cardiac arteries, space is at a great premium, and any design aspects that reduce the number of lines that must extend through the catheter yield a great benefit. Although a traditional multiplex device would permit any block 32 to be chosen at any time, this would require five control lines (yielding 32 combinations), not counting a transmit/receive choice line. Lowering the number of blocks to 16 would require blocks of 36—requiring four more coax signal lines 16, also difficult to fit into the catheter. To accommodate the above pattern of transmit and receive sequences, in one preferred embodiment control line 20b is a transmit line increment. In one preferred embodiment, chip 18 includes an incrementing register for transmit periods, incremented by a transmit increment line 20b and a separate incrementing register for receive periods, incremented by a receive increment line 20c. A transmit/receive selector line 20a thereby permits each to be incremented through its repeated cycles, as shown in sequence S1, listed above. In another embodiment, transmit/receive selector line 20a is used to increment the transmit and receive block registers, with for example, each rising edge counting as a transmit block increment and each falling edge counting as received block increments. A counter is placed in series with the transmit register so that only every 18th transition to transmit increments the transmit register and with every transition to receive incrementing the receive register, as indicated in sequence S1. This permits the transmit and receive increment lines to be eliminated. In yet another preferred embodiment, a single block increment line steps through the 18×18 (324) transmit/receive pairs sequence S1, which must be stored in a memory 36 of chip 18.

Chip 18 is connected to array 30, by way of different techniques such as a flip chip bonding technique, pressure bonding through a thin layer of low viscosity adhesive (1-2 microns) or indium bonding. These are known techniques in the semiconductor/microchip industry. In the case of flip chip bonding, for example, a solder ball 40 (FIG. 6) is constructed on each chip contact 42, and then these solder balls 40 are pressed into array 30, slightly crushing solder balls 40, to form a good bond, and to create robust electrical connections between each chip contact 42, and each element of array 30. In this process, the thinness of chip 18 is a great advantage, because even though solder balls 40 have some thickness, the capability of chip 18 to bend slightly, due to its thinness, greatly facilitates the formation of a robust bond between solder balls 40 and each element of array 30. Adhesive filler is added among the thin solder balls 40 to increase strength as well as conduct acoustic energy into the dissipative backing. In the case of pressure bonding, electrical conductivity is achieved through the surface roughness of the bonded substrates, the high points of which penetrate enough through the thin layer of adhesive to assure electrical connection. In the case of indium bonding conductive pads on both substrates (silicon chip and flex circuit) are metalized with a one to three thousand angstroms of indium which then flows through the application of heat at a low temperature (about 170 C). In addition, chip 18 is approximately 10 μm thick thus effectively becoming an “anti-matching” layer and an integral part of the acoustic architecture as opposed to a thicker chip. Computer simulations indicate that the thickness of the silicon chip 18 can be further tweaked to achieve improved pulse properties.

The waveforms created by waveform generator 14 are typically two-cycle 35 MHz pulses, having pulse width of 5.7 nsec and pulse repetition frequency for 6 mm maximum penetration of 125 kHz or pulse repetition period of 8 usec. It should be noted that other frequencies in the range of 25 to 50 MHz may be utilized depending on resolution or penetration desired.

Referring, now, to FIGS. 4, 5, 6 and 7, in one preferred embodiment, multiplex chip 18 forms a portion of an imaging and ablation head 41 as described in detail in U.S. Pat. No. 8,702,609. The proximal side of multiplex chip 18 is attached to a central portion 43 (which may also be referred to as the “contact portion”) of a flex circuit 44, having four arms 46, that are bent proximally and that each include a number of the signal coax cables 16, and for which at least one includes one or more control lines, such as lines 20A-D. Ultrasound absorbent backing material 48 is proximal to central portion 42. This material is a polymer or polymer blend chosen for its ability to absorb high frequency ultrasound and in particular, ultrasound in the range of 20-50 MHz. The lossy backing material has the same acoustic impedance as the flex circuit material, including the material of contact portion 43, to avoid reflection at the interface between the two. Proximal to backing material 48 is a radiopaque marker 50. After extending proximally past marker 50, flex circuit arms 46 are connected to a group of coax cables and other conductors, for signals to travel to a base station (not shown).

Referring to FIG. 8, in a preferred embodiment, ultrasound system 10 is physically implemented in a vascular imaging and plaque ablation catheter system 60. System 60 is arranged to provide images internal to body B for medical diagnosis and/or medical treatment. System 60 includes a control station comprising an ultrasound imaging system 62, of which processor assembly 12 and waveform generator and receive amplifier 14 (FIG. 1) form a portion, and an RF therapy system 70, each of which are operatively coupled to catheter 80, as well as appropriate operator input devices (e.g. keyboard and mouse or other pointing device of a standard variety) and operator display device (e.g. CRT, LCD, plasma screen, or OLED monitor).

Catheter 80 is configured for placement through opening O and into body B of a human patient or subject, as schematically represented in FIG. 8. Catheter 80 is preferably configured for insertion into a blood vessel or similar lumen L of the patient by any conventional vascular insertion technique. Catheter 80 includes a guide wire lumen that extends from a proximal port 82 through the distal tip 84 of the catheter 80, which is used to insert catheter 80 over a pre-inserted guidewire (not shown) via a conventional over the wire insertion technique. The guidewire exit port may be spaced proximally from the distal tip, accordingly, to known design. Catheter 80 may be configured with a shortened guidewire lumen so as to employ a monorail type insertion technique, or catheter 80 may be configured without any guidewire lumen and instead configured for insertion through the lumen of a pre-inserted guide catheter.

Referring to FIG. 9, in one catheter embodiment 110, designed to be introduced into a blood vessel by way of a sheath 112, according to the Seldinger method of catheter placement, a larger area lumen 114 is available for placement of coax cables 16, because the space for a guidewire is no longer necessary. RF and digital control wires 116 extend inside the side wall 118. In the Seldinger method a guidewire is used to facilitate the placement of the sheath 112. The guidewire is removed, and the sheath 112 is then used to guide the catheter 110. Because the space for the guidewire is eliminated, the number of coax cables may be increased, relative to an embodiment in which there is a space for a guidewire. There is an indication that with the embodiment of FIG. 8, 64 coaxial cables could be fit into the catheter, indicating that a 576 element array could be driven in nine transmit/receive cycles.

Referring now to FIG. 8, the mux and amp chip 18 (FIGS. 1, 2, 4, 6, and 7) and ultrasound elements array 30 (FIGS. 1, 3, 4, and 6) are located in distal end 84, whereas a set of RF ablation electrodes (not shown) form distal tip 86, which is designed to ablate arterial plaque P. Mini coax cables 16 (FIG. 1) extend through a side cable 88 and then through a lumen in catheter 80, together with control signal wires 20A-20D (which in one embodiment extend through the flexible exterior wall of catheter 80).

If the supporting tip surface is constructed of a suitable synthetic material capable of withstanding the high temperatures generated by the electrodes, the electrode material may be deposited or applied directly onto the tip. Suitable synthetic materials include high temperature plastics (e.g. Torlon, available from Solvay Advanced Polymers LLC, Alpharetta, Ga.) or silicone rubber materials (e.g. RTV325, Eager Plastics, Inc. Chicago, Ill. or RTV 560 GE Plastics). Another suitable material, TPX (4-polymethylpentene) is available from Mitsui Chemicals Inc., Tokyo, Japan. TPX is a solid plastic with acoustic properties similar to human tissue and therefore transports acoustic energy to tissue efficiently with little loss. The acoustic impedance of human tissue is about 1.55 MRayls while that of TPX is 1.78 MRayls (implying 93% transmission). TPX also has a relatively high softening temperature (about 350 F) and melting temperature of about 460 F, which makes it suitable for the ablation application, in which elevated temperatures may occur.

While a number of exemplary aspects and embodiments have been discussed above, those possessed of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.

Claims

1. An intravenous ultrasound catheter having a distal tip and comprising: (a) a forward facing array of ultrasound elements near to said distal tip of said device;(b) an integrated circuit (IC) die, abutting and proximal to said ultrasound elements, having a thickness of less than 80 μm, and having: (i) a first face, facing said forward facing array, and having an array of ultrasound element driving and receiving contacts, in mating arrangement to said array of ultrasound elements, so that said array of ultrasound element driving and receiving contacts collectively physically abut and electrically connect to each of said ultrasound elements;(ii) a second face, opposed to said first face, and having a set of input-output signal contacts, said set being fewer in number than said array of ultrasound element driving and receiving contacts and each being switchable into contact with any one of a set of said ultrasound element driving and receiving contacts, said second face also having a set of control contacts, wherein inputs received by said control contacts positively collectively command some aspect of operation of said IC die; and(iii) a set of amplifiers, interposed between said first face and said second face, including an amplifier for each one of said driving and receiving electrical contacts;(iv) wherein impedance of said ultrasound element driving and receiving contacts is matched to impedance of said ultrasound elements;(c) a flex circuit assembly, proximal to said integrated circuit and including coax cables and a contact portion, having a set of contact pads abutting and electrically connecting said input output signal contacts of said IC die, to said coax cables; and(d) backing material, abutting and directly proximal to said contact portion, thereby forming an interface and wherein said backing material and said contact portion material have equal acoustic impedance, thereby preventing reflection at said interface.

2. The intravenous ultrasound catheter of claim 1, wherein said flex circuit includes a central portion, having contact pads for said input/output and control contacts of said IC die and also includes arms having signal lines for carrying signals from and to said IC die.

3. The intravenous ultrasound catheter of claim 1, wherein said ultrasound array includes more than 256 elements and has dimensions of less than 2 mm by 2 mm.

4. The intravenous ultrasound catheter of claim 1, further including a set of ablation electrodes, positioned forward of said array of ultrasound elements so that said ultrasound elements transmit and receive through said set of ablation electrodes.

5. The intravenous ultrasound catheter of claim 1, wherein said array of ultrasound element driving and receiving contacts is flip chip bonded to said array of ultrasound elements.

6. The intravenous ultrasound catheter of claim 1, wherein said flex circuit further includes a coax cable for each input/output contact.

7. The intravenous ultrasound catheter of claim 1, further including a waveform generator, generating a waveform having a frequency of between 20 MHz and 50 MHz, and wherein said thin chip has a thickness of one-quarter of the waveform wavelength for the speed of sound through said thin chip material.

8. The intravenous ultrasound catheter of claim 1, further including RF ablation electrodes positioned distal to said ultrasound elements.

9. The intravenous ultrasound catheter of claim 1, wherein said IC die has a thickness of less than 20 μm.

10. The intravenous ultrasound catheter of claim 1, wherein said IC die has a thickness of less than 12 μm.

11. The intravenous ultrasound catheter of claim 1, wherein impedance of said input-output signal contacts matches impedance of contacts pads of said flex circuit.