WO2014080312A1

WO2014080312A1 - Frameless ultrasound probes with heat dissipation

Info

Publication number: WO2014080312A1
Application number: PCT/IB2013/059991
Authority: WO
Inventors: Dino Francesco CUSCUNA; James Francis PAOLINO
Original assignee: Koninklijke Philips N.V.
Priority date: 2012-11-20
Filing date: 2013-11-08
Publication date: 2014-05-30

Abstract

Amatrix array ultrasound probe having a sensor module with an array transducer and a beamformer ASIC is assembled without a sensor module frame. The sensor module is held in place in the probe by a surrounding heatspreader, which not only retains the sensor module in place but also provides peripheral heat transfer away from the array transducer and ASIC and RFI/EMI shielding of the sensor module.

Description

FRAMELESS ULTRASOUND PROBES WITH HEAT DISSIPATION

This invention relates to medical diagnostic ultrasound systems and, in particular, to transducer probes for ultrasound systems which are built without a sensor module frame and exhibit good thermal dissipation .

Conventional transducer probes for two

dimensional (2D) and three dimensional (3D) imaging are actuated by transmit drive circuitry located in the system mainframe. The probe cable is plugged into the system mainframe and the transducer elements of the array at the probe face are driven for transmission by the drive circuitry in the mainframe system. While the heat generated by piezoelectric actuation of the transducer elements must be

dissipated by the probe, the heat generated by the high voltage drive circuitry in the system mainframe can be relatively easily dissipated by the system. However, solid-state 3D imaging probes have a two dimensional matrix of transducer elements numbering in the thousands, and a cable with thousands of coaxial drive signal conductors is impractical.

Consequently a beamformer ASIC (microbeamformer) is employed in the probe with integrated drive circuitry and receive circuitry for the transducer elements in the probe itself. The beamformer ASIC controls and performs at least part of the transmit and receive beamforming so that only a relatively few signal path conductors are needed in the cable, enabling the use of a practical, thin cable for the 3D imaging probe. Probe beamformer ASICs are now also used in 2D imaging probes with a one dimensional (ID) transducer array .

With the transmit beamforming ASIC and drive circuitry in the probe, the heat generated by this circuitry must now be dissipated from the probe, not the system mainframe. Since the beamforming ASIC is attached directly behind the transducer array, the heat of the transducer stack and ASIC is now at the front of the probe, just behind the lens which contacts the patient. Various approaches have been taken in the past to dissipate heat from the front of an ultrasound probe. One approach shown in US Pat. 5,213,103 (Martin et al . ) is to use a heatsink extending from the transducer at the front of the probe to the cable braid at the back. Heat is conducted away from the transducer by the heatsink and into the cable braid, from which it dissipates through the cable and the probe housing. Martin et al . are only transporting the heat from the

piezoelectric transducer without the drive circuitry, as the drive circuitry for the Martin et al . probe is presumably in the system mainframe; there is no microbeamformer or drive circuitry in the Martin et al . probe. A more aggressive approach to cooling is to use active cooling as described in US Pat.

5,560,362 (Sliwa, Jr. et al . ) or a thermoelectric cooler as described in US Pat. pub. no. US

2008/0188755 (Hart) . Active cooling with a coolant requires the necessary space and apparatus to circulate the coolant as well as the hazard of coolant leaks, and both approaches complicate the component complexity and spacing inside the probe.

Another technique for dissipating heat from a matrix array probe is described in international patent application no. PCT/IB2012/052363, filed May 11, 2012 (Davidsen et al . ) . The Davidsen et al .

technique uses passive heat dissipation to dissipate heat generated by the matrix array transducer and ASIC. The heat generated by these elements is conducted to a heat spreader which distributes the heat through a surface area beneath the probe housing. The distribution of heat by the heat spreader prevents the buildup of hotspots at a particular point or points of the handle portion of the probe housing. The distributed heat is then dissipated through the probe housing and probe cable.

The Davidsen et al . probe is built around a chassis or frame on which printed circuit boards and other components are assembled. The frame is thermally conductive and aids in the dissipation of heat by conducting heat away from the transducer array and ASIC at the front of the probe. The heat is conducted to the heatspreader by the thermal coupling of the frame to the heatspreader and also is conducted into the cable braid at the rear of the probe for additional heat dissipation. While the frame of the Davidsen et al . probe thus provides numerous benefits and functions in the probe design, it also takes up space and contributes its own weight to that of the rest of the probe components. It is always desirable to enable an ultrasound probe to be made small and light so it can be easily held and manipulated by a sonographer and minimizes fatigue during lengthy ultrasound exams. It would thus be desirable to provide all the benefits in the design of an ultrasound probe afforded by Davidsen et al . but without the need for space and weight of a probe frame or chassis.

In accordance with the principles of the present invention, an ultrasound probe is described which is built and assembled without a probe frame or chassis. In an illustrated implementation the sensor module including the transducer array and beamformer ASIC are assembled in a transfer fixture. A cable is coupled to the sensor module which is then clamped together by a surrounding heatspreader . At the distal end of the probe the heatspreader is in thermally conductive contact with the heat produced by the transducer array and beamformer ASIC. At the proximal end of the probe the heatspreader is in thermally conductive contact with the cable braid. The heatspreader thus holds the internal components of the probe together in the absence of a chassis, conducts heat away from the transducer array and beamformer ASIC, and conducts this heat for

dissipation through the cable and through the outer housing or case of the probe.

In the drawings :

FIGURE 1 is an exploded assembly drawing of the major component parts of a matrix array probe of the prior art.

FIGURE 2 illustrates a probe sensor module which is retained during assembly in a transfer fixture.

FIGURE 3 illustrates a matrix array probe constructed in accordance with the principles of the present invention prior to attachment of a

heatspreader .

FIGURE 4 is a cross sectional view of a matrix array probe constructed in accordance with the principles of the present invention.

FIGURE 5 is a partially cross sectional

perspective view of a battery-powered probe of the present invention.

Referring first to FIGURE 1, a prior art matrix array probe is shown in an exploded view. The sensor assembly, also commonly called the transducer stack, including the matrix array transducer and beamformer ASIC mounted on a thermally conductive graphite backing block (not shown in this drawing) are fastened to the top of a probe chassis or frame 16. Printed circuit boards 18a and 18b which carry electrical components and cable connectors are fastened to opposite sides of the frame 16. Wires from a cable 28 are connected to connectors on the printed circuit boards and clamp halves 26a and 26b is clamped around the strain relief and braid of the cable 28 and the clamp is also clamped to two rails 17a and 17b extending from the proximal end of the frame 16. The primary thermal path in this probe assembly is from the transducer array and beamformer ASIC to the thermally conductive backing block which is thermally coupled to the frame 16, then in the proximal direction to the cable and laterally outward from the frame to a heatspreader . The coupling of the proximal end of the frame 16 to the cable braid promotes the transfer of heat from the frame into the cable braid and away from the distal end of the probe. A thermal gasket or thermal putty covers the surfaces of flanges 38 of the frame 16 and the two halves 20a and 20b of the heatspreader are fastened to the flange sides of the frame 16 with screws. The nosepiece 24 and lens 36 are placed on the distal end of the assembly over the transducer stack. The outer surface of the assembled heatspreader (or the inner surfaces of the case or housing halves 22a and 22b) are coated with thermal putty and the housing is put in place around and in contact with the heatspreader and thermal putty with the seams of the housing and nosepiece sealed to prevent fluid ingress. Further details of the probe of FIGURE 1 can be found in the aforementioned Davidsen et al . application.

FIGURE 2 illustrates the assembly of the sensor module 60 of a matrix array ultrasound probe in accordance with the principles of the present invention. In this implementation the sensor module is assembled in a transfer fixture 40 which retains the module during assembly. At the distal end of the module is the transducer array 10 which is mounted to the beamformer ASIC 12. The integrated circuitry of the ASIC controls transmission by the transducer elements of the transducer array 10 and performs both transmit and receive beamforming of signals

transmitted and received by the array. An interposer can be employed if desired to couple the elements of the transducer array to the circuitry of the ASIC. One such interposer is described in international patent pub. WO 2009/083896 (Weekamp et al . ) , for instance. Behind the matrix array transducer and

ASIC is a graphic backing block 14 which attenuates acoustic reverberations emanating from the back of the matrix array and conducts heat developed by the matrix array and ASIC away from the distal end of the probe. Further details of the graphic backing block may be found in international patent publications WO 2012/123906 and WO 2012/123908. One or more printed circuit boards 32, preferably flex circuits, are electrically coupled to the beamformer ASIC to couple signals to and from the ASIC and transducer array.

In the illustrated implementation a connector 34 is mounted on flex circuit 32 to electrically couple the sensor module 60 to conductors of a cable 28.

After the sensor module 60 is assembled it is removed from the transfer fixture for completion of the probe assembly. The electrical conductors 27 of a cable 28 are terminated at connectors 29 which are connected to mating connectors 34 of the sensor module. A nosepiece 24 and lens 36 are mounted to the distal end of the sensor module. The distal ends of a two-piece heatspreader 52, 54 are tucked under the nosepiece and fastened with screws around the sensor module and cable clamp 26 to hold the assembly together and in place at the end of the cable. The heatspreader 52, 54 is made of a lightweight, thermally conductive material such as aluminum or magnesium. The distal end of the heatspreader is clamped to and in thermally conductive contact with the thermally conductive backing block 14, enabling it to readily conduct heat away from the transducer array, ASIC, and backing block. When the

heatspreader is made of a metallic material it further provides RFI and EMI shielding and isolation for the sensor module, obviating the need for additional electrical shielding gaskets or RFI flaps.

The heatspreader 52, 54 provides the primary

thermally conductive path for heat away from the array and ASIC. But unlike the central frame assembly of FIGURE 1, this thermal path is not through the center of the probe but peripherally just beneath the case. The conducted heat is not confined to the center of the probe but is immediately peripheral to the module where it can be conducted through the outer case or housing of the probe and into the external environment. To complete the assembly a two-piece polymeric housing or case 22 is mounted around the heatspreader (see FIGURE 4), preferably in good thermal contact with the

heatspreader so that heat is dissipated through the case to the external environment. The heat conducted by the heatspreader is thus conducted from the outer surface of the heatspreader 52, 54 to the inner surface of the housing 22 from which it dissipates through the housing and into the air. To promote the transfer of heat into the housing 22 from the heatspreader 52, 54, a layer of thermal putty may be spread between the heatspreader and the housing, carrying heat into the housing over its entire inner surface area and further preventing the buildup of hotspots in the housing.

FIGURE 4 is a cross-sectional view of the finished probe. In this illustration it can be seen that the distal end 56 of the heatspreader 52, 54 is clamped around and in good thermal contact with the backing block 14 at the distal end of the probe. The sensor module 60 is retained in place between the two halves 52, 54 of the heatspreader. At the proximal end of the probe the proximal end 58 of the

heatspreader is clamped around the cable clamp 26 to conduct heat into the cable clamp and braid. The case 22 encloses the heatspreader 52, 54, conducting heat radially outward from the probe through the handle of the probe.

With the central volume of the sensor module 60 no longer occupied by a frame as in the prior art designs, this space can be occupied if desired by other components. FIGURE 5 illustrates a wireless probe which does not have a cable and communicates with an ultrasound system by wireless communication. In this partial cross-sectional view with the case removed, it can be seen that the central volume is occupied by a battery 70 which powers the probe. The space and weight of the frame have been replaced by a battery to power the wireless probe, with no increase in the size of the probe and little or no increase in its weight.

Claims

WHAT IS CLAIMED IS:

1. An ultrasonic transducer array probe comprising :

a sensor module having a distally located array of transducer elements coupled to an application specific integrated circuit (ASIC) for a transducer array and electrical connections to the ASIC;

an outer housing forming a probe handle and enclosing probe components proximal to the transducer elements and ASIC;

a proximally located probe cable having

conductors electrically coupled to the electrical connections of the sensor module; and

a thermally conductive heatspreader which encloses the sensor module and retains it in position in the probe in the absence of a sensor module frame.

2. The ultrasonic transducer array probe of Claim 1, wherein the array of transducer elements further comprises a two dimensional matrix array of transducer elements.

3. The ultrasonic transducer array probe of Claim 1, wherein the ASIC further comprises a beamformer ASIC which at least partially beamforms transmit beams transmitted by the transducer array and echo signal received by elements of the

transducer array.

4. The ultrasonic transducer array probe of Claim 1, wherein the sensor module further comprises a thermally conductive backing block located proximal to and in thermally conductive contact with the ASIC, wherein the heatspreader further comprises a distal end clamped in thermal contact with the backing block.

5. The ultrasonic transducer array probe of Claim 1, wherein the heatspreader further comprises a proximal end clamped in thermal contact with the probe cable.

6. The ultrasonic transducer array probe of Claim 5, wherein the probe cable further comprises a metallic braid,

wherein the proximal end of the heatspreader is thermally coupled to the metallic braid of the cable.

7. The ultrasonic transducer array probe of Claim 1, wherein the sensor module further comprises a printed circuit board,

wherein the electrical connections further comprise a connector located on the printed circuit board,

wherein the probe cable conductors further comprise a connector coupled to the sensor module of the printed circuit board.

8. The ultrasonic transducer array probe of Claim 1, wherein the heatspreader further comprises the primary retaining structure for the sensor module .

9. The ultrasonic transducer array probe of Claim 8, wherein the heatspreader further comprises the primary thermal conductive path from the ASIC to the probe cable, the conductive path being peripheral to the sensor module.

10. The ultrasonic transducer array probe of Claim 9, wherein outer housing encloses the

heatspreader, and

wherein the heatspreader further comprises a radial thermal conductive path which conducts heat to the outer housing for dissipation in the external environment .

11. The ultrasonic transducer array probe of Claim 10, wherein the heatspreader further provides RFI and EMI shielding of the sensor module.

12. The ultrasonic transducer array probe of Claim 1, further comprising a transfer fixture used to assemble the sensor module prior to assembly of the sensor module with the heatspreader and outer housing .

13. The ultrasonic transducer array probe of Claim 1, wherein the heatspreader is made of aluminum or magnesium.

14. An ultrasonic transducer array probe comprising :

a proximally located probe cable having

conductors electrically coupled to the electrical connections of the sensor module;

a battery coupled to the sensor module which powers the ASIC; and

15. The ultrasonic transducer array probe of Claim 14, wherein the battery is located in the sensor module.