Phased array transducers and applications thereof

Abstract

A phased array transducer for cardiac ultrasound diagnostic imaging includes: a transducer head; a housing unit; and a wire cable. The transducer head has a shape adapted for coupling with a human chest. A method of obtaining cardiac ultrasound images behind human rib bones includes: providing a phased array transducer that comprises a transducer head having a shape adapted for coupling with a human chest; and applying a beamforming method to generate the ultrasound images.

Description

PHASED ARRAY TRANSDUCERS AND APPLICATIONS THEREOFThis application claims priority to US Provisional Patent Application Nos. 63 / 597,305, filed on November 8, 2023, and 63 / 555,562, filed on February 20, 2024, both of which are incorporated by reference for all purposes as if fully set forth herein.FIELD OF THE INVENTION

[0001] The present invention relates to a phased array transducer for cardiac ultrasound diagnostic imaging and a method of obtaining cardiac ultrasound images behind human rib bones.BACKGROUND OF THE INVENTION

[0002] Medical ultrasound imaging for diagnosis has advantages, such as reasonable cost, real-time imaging, portability, and its harmless effect, over computerized tomography (CT) and magnetic resonance imaging (MRI). However, the resolution of the ultrasound imaging system is usually lower than that of CT and MRI systems, which is especially true for diagnostic imaging of human heart.

[0003] A phased array ultrasound transducer is typically 2-3 cm long, consisting of 64-96 elements, to fit into the intercostal space of human chest ribs [1-2], It is a smaller assembly than a sequential array and can be either linear or curvilinear. A sector field of view is produced by all elements firing to create a single waveform. Small delays in element firing allow for electronic field steering and focusing without moving the ultrasound probe. All elements will be fired multiple times with different degrees of steering to create an image. Echoes are detected by all elements and used in an algorithm to form the image. Line density decreases at the bottom of the image. The sensitivity of the image reduces at extremes of steering. The benefits of a phased array include: a small transducer allowing for imaging in intercostal spaces between ribs and being able to change the focus of the ultrasound beams.

[0004] The phased array ultrasound transducers, however, have some shortcomings. For example, the field of view is very small at shallow and middle depth intervals, and theimage resolution degrades rapidly as a function of depth. There is a need for new phased array transducers that overcome these shortcomings.SUMMARY OF THE INVENTION[0005J In one embodiment, the present application discloses a phased array transducer for cardiac ultrasound diagnostic imaging that includes: a transducer head; a housing unit; and a wire cable. The transducer head has a shape adapted for coupling with a human chest.

[0006] In another embodiment, the transducer head has a concave shape.

[0007] In another embodiment, the transducer head has a length that is larger than a intercostal space of human chest ribs.

[0008] In another embodiment, the length of the transducer head is between 3.1 cm and 8 cm.

[0009] In another embodiment, the transducer head includes at least 96 acoustic elements.

[0010] In another embodiment, the transducer head comprises at least 192 acoustic elements.

[0011] In another embodiment, the acoustic elements have a pitch size that is between 0.25mm and 0.50 mm.

[0012] In another embodiment, the phased array transducer is adapted for applying a beamforming method and generating ultrasound images without noticeable shadows of chest bones.

[0013] In another embodiment, the present application discloses a method of obtaining cardiac ultrasound images behind human rib bones. The method includes providing a phased array transducer that comprises a transducer head having a shape adapted for coupling with a human chest; and applying a beamforming method to generate the ultrasound images.

[0014] In another embodiment, the ultrasound images have a view of visualization of a human heart and surrounding tissues.

[0015] In another embodiment, the ultrasound images are free of human rib bones shadows.

[0016] In another embodiment, the phased array transducer has a larger array aperture.

[0017] In another embodiment, the ultrasound images have an improved image resolution because of the larger array aperture.

[0018] In another embodiment, the ultrasound images have an improved signal to noise ratio because of the larger array aperture.

[0019] In another embodiment, the beamforming method includes: (1) spraying a data sample of an ultrasound beam along an impulse response curve into an output image domain; (2) binning each point on the impulse response curve by a value of an unique attribute; (3) summing an image value at the each point on the impulse response curve into a corresponding partial image volume associated with the unique attribute; (4) repeating steps (l)-(3) for all data samples of all ultrasound beams to obtain a plurality of partial image volumes; (5) sorting the partial image volumes by the unique attribute to generate common image point gathers; and (6) obtaining an image of the tissues by stacking common image point gathers at all output locations.

[0020] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

[0022] In the drawings:

[0023] Figure 1 shows a phased array transducer for cardiac ultrasound diagnostic imaging of the present application.

[0024] Figure 2 is an illustration of the head structure of the phased array transducer. In this design a total of 192 acoustic elements are used (black rectangles, only a few representative ones are shown here). The bottom acoustic lens is flat in the center portion of the transducer and increases in thickness towards both edges. The outer length of the transducer is 75mm. The acoustically active portion is 68.92mm in length. The supporting structure on both edges is 3.04mm in width. The maximum thickness of acoustic lens on both edges is 3mm.

[0025] Figure 3 shows computer renditions of the head portion of the phased array transducer. Top is a side 3D view and Bottom is a front face view.

[0026] Figure 4 shows a phantom model for computer simulation: white dots are point scatters and white lines are reflectors.

[0027] Figure 5 shows the comparison of ultrasound image of a conventional phased array transducer (left) and the new phased array transducer (right): Left is with a 2cm phased array. Right is with a 6.8cm long phased array. The white dash lines show the effective field of view.DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0028] Reference will now be made in detail to embodiments of the present invention, an example of which is illustrated in the accompanying drawings.

[0029] The present invention relates to a new design of phased array transducer for cardiac ultrasound diagnostic imaging. In particular, the invention addresses two urgent needs in cardiac imaging: (1) the field of view is very small at shallow and middle depth intervals, and (2) the image resolution degrades rapidly as a function of depth. The present application discloses the internal structure of the new phased array transducer and its applications in cardiac ultrasound diagnostic imaging. The new transducer can be placed anywhere on thehuman chest without worrying about shadows caused by chest rib bones blocking ultrasound signals. It also provides a wide view of the heart and surrounding tissues. Cardiac ultrasound image quality, in both resolution and signal to noise ratio, will be greatly improved.

[0030] The phased array transducer for cardiac ultrasound diagnostic imaging greatly increases the length of a phased array by adding more acoustic elements, increasing pitch size, or both. To provide better coupling between the long transducer and human chest, the inventor makes the acoustic lens concave in shape: the acoustic lens is thinner at the center portion and increases in thickness towards both edges. When the transducer is pressed onto human chest the acoustic gel is squeezed towards the edges to fill any air gap caused by chest bones resisting the squeeze. Special beamforming methods are used to generate ultrasound images without noticeable shadows of chest bones. Otherwise, one would see shadows in ultrasound images at every bone location, rendering these images unusable.

[0031] As shown in Figure 1, a phased array transducer for cardiac ultrasound diagnostic imaging includes: a transducer head 1, a housing unit 2, and a wire cable 3. The transducer head 1 has a shape adapted for coupling with a human chest.

[0032] Description

[0033] Phased array transducers used in cardiac diagnostic applications are short in length, typically less than 2cm, to illuminate a heart from the intercostal space of human chest ribs. A phased array transducer consists of three parts: a head, a wire cable, and a housing unit. A lot of technologies are inside the transducer head. Typically, 64 to 96 piezoelectric elements are tightly packed along the lateral direction. The center frequency of each element is less than 3 MHz. Frequency bandwidth is approximately 80%. The acoustic lens (or face of the transducer) is flat in the lateral direction and is convex-shaped in the elevation direction providing mechanical focus in the off-plane dimension.

[0034] New Phased Array Transducer Specification

[0035] The phased array transducer of the present application is much longer than existing phased array transducers on the market. The large aperture will enable us to achieve much improved resolution at depth and at the same time provide a much larger field of view.The inventor choses to increase both the number of acoustic elements (e g., 192 elements) and the pitch size (e.g., 0.36mm). One problem with a long array is human rib bones preventing good acoustic coupling of elements with chest skin on both edges of the transducer. To mitigate the problem, the inventor makes the acoustic lens concave-shaped, with the lens being thicker on both edges. Figure 2 is an illustration of the design. Numeral 100 represents an acoustic backing layer which absorbs acoustic energies traveling upward from each acoustic element (numeral 102, a total of 192 elements in this design). Numeral 101 represents a base material that the piezoelectric elements are attached to. The base material has acoustic impedance like the piezoelectric elements. Numeral 103 is the first matching layer whose acoustic impedance value is less than that of the base material. Numeral 104 represents the second impedance matching layer whose acoustic impedance value is less than that of the first matching layer. Numeral 105 represents the flat portion of the acoustic lens whose acoustic impedance is less than the second matching layer. Numeral 106 is the thick part of the acoustic lens whose thickness increases towards both edges.

[0036] It is important to note that the dimensions and the element count in Figure 2 are for illustration purposes. The actual numbers can vary depending on cost consideration, targeted patient population, and desired operating frequency.

[0037] Figure 3 shows two 3D renditions of the head of a long array transducer per the design. The top picture is a 3D side view, showing the acoustic backing material and acoustic lens. The bottom picture is a front view of the head. The look and feel of the new phased array transducer are very different from a conventional phased array transducer, and so is the quality of ultrasound images.

[0038] Beamforming Methods

[0039] To take advantage of the raw ultrasound data collected with the new phased array transducers, at a minimum, a beamforming method that can perform dynamic focusing on both transmit and receive is needed. Further, to reduce noises in the resulting images, one needs to know how to distinguish between acoustic energies that travel through a bone and acoustic energies that travel around the bone. This becomes more significant for large bones or in positions and directions that are over and parallel to the bones. One special beamformingmethod disclosed in a pending application US 18 / 288,376, filed on October 25, 2023 (national stage application of PCT / US2022 / 032059) can satisfy this special requirement. US 18 / 288,376 is hereby incorporated by reference in its entity. Other similar methods can also be devised to achieve similar goals.

[0040] The beamforming method, for example, can include: (1) spraying a data sample of an ultrasound beam along an impulse response curve into an output image domain; (2) binning each point on the impulse response curve by a value of an unique attribute; (3) summing an image value at the each point on the impulse response curve into a corresponding partial image volume associated with the unique attribute; (4) repeating steps (1 )-(3) for all data samples of all ultrasound beams to obtain a plurality of partial image volumes; (5) sorting the partial image volumes by the unique attribute to generate common image point gathers; and (6) obtaining an image of the tissues by stacking common image point gathers at all output locations.

[0041] Computer Simulation

[0042] The inventor uses a modified version of Fresnel Simulator from Ultrasound Toolbox (USTB, https: / / www.ustb.co) for generation of numerical ultrasound beam data. The use of this simulator is subject to the citation rule. The inventor sincerely thanks the authors for making it available in the public domain [3], The simulator is based on Fresnel approximation of diffraction of acoustic waves for rectangular transducers in a linear time invariant (LTI) system. Inputs to the simulator include a phantom model specification, a transducer specification, and a waveform specification. The phantom model used in this simulation contains:• Two rectangular boxes with a depth range between 7 - 9mm,• 4 flat continuous reflectors at 20mm, 40mm, 60mm and 80mm depth,A hyperechoic target with 8mm radius at 70mm depth and a second hyperechoic target with 6 mm radius at 50mm depth,• A row of scatter points at 30mm depth and a column of scatter points at the center of the model.

[0043] Figure 4 is a depiction of the phantom model. The central frequency of the simulated echo data is 3MHz with 80% useful bandwidth and sampling frequency is 24MHz.

[0044] The inventor ran two simulations of ultrasound beam data. One simulates 64 focused beams of a conventional 2 cm phased array transducer with 64 acoustic elements. Another one simulates 192 focused beams of a 6.8 cm phased array transducer with 192 acoustic elements per the invention. The inventor processed the two sets of echo data using the same beamforming software [2], Figure 4 shows a comparison of the ultrasound images of the phantom model. The left one is the image using the conventional phased array transducer. The right one is the image of the same phantom using the new phased array transducer. The left image has a smaller field of view because the array aperture is small. The diffractors are well imaged at shallow depth and are not focused on deep level. The horizontal reflectors are partially imaged. The right image has a much bigger field of view. Diffractors are well focused at both shallow and deep levels. The horizontal reflectors are well imaged as well. For cardiac ultrasound applications the right image is significantly better than the left one.

[0045] It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

[0046] References[1] Richard S. C. Cobbold (2007), Foundations of Biomedical Ultrasound, Oxford University Press.[2] B. S. Hertzberg and W. D. Middleton (2016), Ultrasound : The Requisites, The Third Edition, Elsevier. Chapter 1, pages 3 - 31. Also at expertconsult.com.[3] A. Rodriguez-Molares, Fresnel simulator, http: / / www.ustb.no / examples / fresnel /

Claims

WHAT IS CLAIMED IS:

1. A phased array transducer for cardiac ultrasound diagnostic imaging, comprising: a transducer head; a housing unit; and a wire cable, wherein the transducer head has a shape adapted for coupling with a human chest.

2. The phased array transducer of claim 1, wherein the transducer head has a concave shape.

3. The phased array transducer of claim 1, wherein the transducer head has a length that is larger than an intercostal space of human chest ribs.

4. The phased array transducer of claim 3, wherein the length of the transducer head is between 3.1 cm and 8 cm.

5. The phased array transducer of claim 1, wherein the transducer head comprises at least 96 acoustic elements.

6. The phased array transducer of claim 5, wherein the transducer head comprises at least 192 acoustic elements.

7. The phased array transducer of claim 5, wherein the acoustic elements have a pitch size that is between 0.25 mm and 0.50 mm.

8. The phased array transducer of claim 1, wherein the phased array transducer is adapted for applying a beamforming method and generating ultrasound images without noticeable shadows of chest bones.

9. A method of obtaining cardiac ultrasound images behind human rib bones, comprising: providing a phased array transducer that comprises a transducer head having a shape adapted for coupling with a human chest; and applying a beamforming method to generate ultrasound images.

10. The method of claim 9, wherein the ultrasound images have a view of visualization of a human heart and surrounding tissues.

11. The method of claim 9, wherein the ultrasound images are free of human rib bones shadows.

12. The method of claim 9, wherein the phased array transducer has a larger array aperture.

13. The method of claim 12, wherein the ultrasound images have an improved image resolution because of the larger array aperture.

13. The method of claim 12, wherein the ultrasound images have an improved signal to noise ratio because of the larger array aperture.

14. The method of claim 9, wherein the beamforming method comprises:(1) spraying a data sample of an ultrasound beam along an impulse response curve into an output image domain;(2) binning each point on the impulse response curve by a value of an unique attribute;(3) summing an image value at the each point on the impulse response curve into a corresponding partial image volume associated with the unique attribute;(4) repeating steps (1 )-(3) for all data samples of all ultrasound beams to obtain a plurality of partial image volumes;(5) sorting the partial image volumes by the unique attribute to generate common image point gathers; and(6) obtaining an image of the tissues by stacking common image point gathers at all output locations.

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