Patent Issued for System and Method for Three-Dimensional Ultrasound Imaging

By a News Reporter-Staff News Editor at Journal of Engineering -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Towfiq, Farhad (Dana Point, CA); Busse, Lawrence J. (Fort Mitchell, KY); Douglas, Stephen J. (Cary, NC), filed on August 6, 2008, was cleared and issued on December 4, 2012.

The assignee for this patent, patent number 8323201, is Orison Corporation (Johnson City, TN).

Reporters obtained the following quote from the background information supplied by the inventors: "Timely diagnosis of potential ailments is perhaps the most effective tool available to modern physicians in their battle against serious illnesses. If discovered early enough, many of the deadliest illnesses and diseases pose little threat to a patient with proper treatment. To discover an illness, physicians typically perform a careful examination of a particular part of the human body, either by an invasive, or a non-invasive procedure. An example of an invasive procedure is the biopsy, in which a surgeon removes a sample of human tissue with a needle or a scalpel. Invasive procedures like the biopsy have inherent drawbacks, such as pain for the patient, and the need to heal the area from which the tissue sample was removed. Thankfully, technological and medical advances over the past fifty years have created a number of non-invasive diagnostic procedures.

"Non-invasive diagnostic techniques such as Magnetic Resonance Imaging ('MRI'), Computer Tomography ('CAT' or 'CT'), X-rays, Positron Emission Tomography ('PET') and Ultrasonography are widely used by physicians today. However, while non-invasive techniques are painless and do not require healing time, they may still pose certain dangers to the patient. For example, an unhealthy dose of X-ray radiation may lead to cancer. The strong magnetic fields produced by an MRI machine may also cause adverse health effects in the patient. In contrast with these devices, ultrasonography does not rely on electromagnetic waves or ionizing radiation. Ultrasound machines instead depend on mechanical vibrations to perform measurements.

"Briefly, ultrasound machines include a transducer array, a beamformer, a processor, and a display. A transducer is a device that converts one type of energy to another type of energy. Ultrasound machines mostly use electroacoustic transducers, which convert electrical energy (voltage potential across the transducer) into mechanical energy (vibrations), and vice versa. The beamformer sets the phase delay and amplitude of each transducer element to enable dynamic focusing and beam steering. Where appropriate, a lens is mounted on the transducer array to focus the transmitted pulses and received echoes. In operation, the transducer array sends out a number of pulses directed toward the anatomical area of a patient to be imaged, and after a certain propagation delay receives echoes that were reflected back by the patient's anatomy. The received signal can then be presented on a display for immediate examination or recorded for a later review.

"Over time, the industry has developed a commonly understood terminology for describing various components of an ultrasound machine. The various combinations of transducer arrays and multiplexers were in particular need of a common term, due to the different goals and performance attributable to each combination. While terminology used by the industry is generally agreed upon, certain variations exist, mostly regarding the multiplexing structures that connect transducer arrays to the beamformer.

"The terms are generally understood by persons in the art as follows: 1D arrays have a fixed elevation aperture and are focused at a static range. 1.5D arrays have a variable elevation aperture, and either static or dynamic focusing (Industry terminology for this category differs. For example, General Electric (GE) splits these arrays into two categories: 1.25D and 1.5D. In GE terms, a 1.25D array provides for variable elevation aperture, but its focusing remains static. However, a 1.5D array, in GE terms, has a dynamically variable aperture, shading, and focusing, all which are symmetric about the elevational centerline of the array. A GE article titled 'Elevation Performance of 1.25D and 1.5D Transducer Arrays' by Wildes et al., the entire contents of which are incorporated herein by reference, provides an overview of various linear transducer arrays.). 2D arrays permit focusing and steering in both azimuthal and elevational directions, with comparable results.

"Regarding actual ultrasound machines, ordinary hand-held and stationary scanners such as the ones depicted in FIGS. 1A and 1B have been used since the 1970s. As technology progressed, so did the quality of images provided by ultrasound machines. Phased arrays, such as the 1D array pictured in FIG. 2A, have drastically improved lateral and axial resolutions of ultrasound machines. Axial resolution is the minimum separation required between reflecting objects stationed in the path of the ultrasonic pulse. If two reflecting objects are too close together, the received echoes are also too close together, appearing as if they were reflected by a single object. Lateral resolution is the minimum separation required between reflecting objects in the direction perpendicular to the path of the ultrasonic pulse. While 1D phased or linear arrays improve lateral and axial resolutions, their elevation performance is controlled by using a simple lens, which leads to a more uniform slice thickness but only permits elevation focusing at a single focal distance, with a depth of focus that depends on the elevation aperture. The elevation aperture must be proportional to the focal distance, and at the same time narrow enough to provide a sufficient depth of focus. However, a narrower elevation aperture provides less effective focusing, and hence results in a lower lateral resolution.

"More recent developments, such as the 1.5D array depicted in FIG. 2B, have improved elevation slice-thickness performance both in the near- and far-fields, while still using only a single beamformer for both azimuthal and elevation focusing. However, these kinds of arrays suffer from limited penetration depth, the possibility of beam-splitting caused by the shape of the lens, and also by their cumbersome and slow multiplexing structures.

"Lenses with a cross-section shown in FIG. 2b, are prone to a phenomenon known as beam-splitting, because their cross-sectional depth does not take into account a wave's propagation time. For example, the lens's center row is the first to receive and quickly pass the echo through to the multiplexer. However, by the time the lens's outer rows receive and pass through their own parts of the echo, the time-frame has shifted, and it is unclear which echoes are being passed through. Thus, the beam is actually 'split' into components which might not be received simultaneously by the beamformer.

"Another downside of the 1.5D array depicted in FIG. 2b is its slow multiplexing structure, or more accurately its two multiplexing structures. Such an array, described in U.S. Pat. No. 5,882,309 to Chiao et al., the entire contents of which are incorporated herein by reference, actually has two multiplexers. One multiplexer controls elevation aperture growth, while the other controls azimuthal aperture growth. This results in very slow scanning, as the two multiplexers cannot be switched independently of one another.

"Convex 1D arrays, such as the one depicted in FIG. 3, suffer from a very limited penetration depth and lower resolutions because their geometry requires smaller elements to sustain the same f -number at greater depths.

"Turning to three-dimensional (3D) imaging, performance in elevation focusing, depth of penetration and high resolution become very important, particularly in the medical field. When using ordinary ultrasound scanners, like the one depicted in FIG. 1A, physicians and ultrasound specialists receive one or more two-dimensional images in the azimuthal plane. As mentioned earlier, modern transducer arrays capable of dynamic focusing provide a large azimuthal aperture, leading to high quality two-dimensional images. In the medical field, the same resolution quality would also be expected of 3D images. Thus, elevation focusing performance of the 2D image slices making up the 3D image becomes very important. In addition, an automated 3D ultrasound imaging machine should also provide high resolution quality at greater depths, since there is no operator to make needed adjustments, as there would be with a manual ultrasound scanner. Accordingly, there is a need to provide an ultrasound system for three-dimensional imaging, without the drawbacks associated with the prior art. To this end, it is desirable to provide a system capable of an increased penetration depth, shorter imaging time, more efficient multiplexing structure, and greater flexibility in azimuthal and elevational focusing."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "Under one aspect, an ultrasound system for producing a representation of an object includes: a concave transducer array configured to transmit ultrasonic pulses into the object and to receive ultrasonic pulses from the object, the ultrasonic pulses from the object containing structural information about the object, each transducer in the array generating an output signal representative of a portion of the structural information about the object; a multi-focal lens structure for focusing the transmitted ultrasonic pulses; a multiplexing structure in operable communication with the concave transducer array and including logic for coupling the output signals from at least one pair of transducers in the concave transducer array; and a beamformer in operable communication with the multiplexing structure and including logic for constructing a representation of structural information about the object based on the coupled output signals from the multiplexing structure.

"In some embodiments, the concave transducer array comprises multiple rows of transducers. In some embodiments, the logic of the multiplexing structure includes instructions for varying at least one of a depth to which the ultrasonic pulses penetrate the object and an f-number of the array by uncoupling a subset of the transducers from the beamformer. Some embodiments further include a dome configured to accept the object, wherein the concave transducer array is mounted over a slit in the dome. Some embodiments further include a motor for rotating the concave transducer array about an axis of the dome, wherein the logic of the beamformer is configured to create image slices of the object located inside the dome as the motor rotates the array. Some embodiments further include logic for assembling a three-dimensional representation of the object located inside the dome by combining the stored image slices. In some embodiments, at least one of the multiplexing structure and the beamformer is mounted on the dome. Some embodiments further include a probe housing, wherein the dome is constructed and arranged within the housing such that the object can be imaged without compression. In some embodiments, the object is a breast.

"Under another aspect, a method of producing a representation of an object includes: transmitting ultrasonic pulses into the object with a concave transducer array; focusing the ultrasonic pulses with a multi-focal lens structure coupled to the array; receiving ultrasonic pulses from the object, the received ultrasonic pulses containing structural information about the object; generating a plurality of output signals, each output signal representative of a portion of the structural information about the object; multiplexing a subset of the output signals; and obtaining a representation of structural information about the object based on the multiplexed subset of output signals.

"Some embodiments further include receiving ultrasonic pulses from a variety of angles about the object, obtaining image slices of the object based on the received ultrasonic pulses, and creating a three-dimensional rendering of the object based on the image slices.

"Under another aspect, a concave ultrasonic transducer array includes a plurality of curvilinear transducer rows, each transducer row comprising at least one ultrasonic transducer element; and a concave multi-focus lens coupled to the ultrasonic transducer elements.

"In some embodiments, the concave multi-focus lens comprises a plurality of lens rows, one lens row coupled to each curvilinear transducer row. In some embodiments, some of the lens rows have at least one of a different dimension and a different focal length than other of the lens rows. In some embodiments, at least some of the transducer rows have a different dimension than other of the transducer rows. In some embodiments, each row comprises between 100 and 1000 transducer elements. In some embodiments, each row comprises between 300 and 600 transducer elements.

"Under another aspect, a concave multi-focus acoustic lens includes a plurality of concave rows, wherein rows symmetric in elevation along an azimuthal centerline of the lens have the same focal points as each other, and wherein at least a subset of the rows are offset from other rows in a range direction.

"In some embodiments, at least a subset of the rows have a different lateral dimension than other of the rows. In some embodiments, the lens is made of a material having a speed of sound of less than 1.5 mm/.mu.s. In some embodiments, the material comprises one of silicone and urethane.

"Under another aspect, a method of multiplexing signals from transducer elements in a concave transducer array includes: turning on rows of transducer elements in the concave transducer array based on a desired elevational beam performance; turning on columns of transducer elements in the concave transducer array based on a desired azimuthal beam performance; and connecting the turned on rows and columns to a beamformer."

For more information, see this patent: Towfiq, Farhad; Busse, Lawrence J.; Douglas, Stephen J.. System and Method for Three-Dimensional Ultrasound Imaging. U.S. Patent Number 8323201, filed August 6, 2008, and issued December 4, 2012. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=94&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=4667&f=G&l=50&co1=AND&d=PTXT&s1=20121204.PD.&OS=ISD/20121204&RS=ISD/20121204

Keywords for this news article include: Orison Corporation.

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