Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2002-05-23
2004-08-31
Jaworski, Francis J. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S437000, C600S462000, C310S320000, C310S321000, C310S322000
Reexamination Certificate
active
06783497
ABSTRACT:
GENERAL
For the convenience of the reader, applicant has added a number of topic headings to make the internal organization of this specification apparent and to facilitate location of certain discussions. These topic headings are merely convenient aids and not limitations on the text found within that particular topic.
In order to promote clarity in the description, common terminology for components is used. The use of a specific term for a component suitable for carrying out some purpose within the disclosed invention should be construed as including all technical equivalents which operate to achieve the same purpose, whether or not the internal operation of the named component and the alternative component use the same principles. The use of such specificity to provide clarity should not be misconstrued as limiting the scope of the disclosure to the named component unless the limitation is made explicit in the description or the claims that follow.
FIELD OF INVENTION
This invention relates to 2D and 3D ultrasound phased array imaging systems for transmitting and receiving ultrasound energy. In particular, this invention relates to an improved sparse array structure that provides an effective aperture and radiation pattern comparable to that of a dense array having a far greater number of array elements. The preferred embodiment of the present invention uses separate arrays of transmit and receive elements and does not employ dual-use “shared transmit/receive elements”. The use of two sets of elements allows for a very simple receive buffer to be placed in the head of the transducer and allows the transducer to utilize different transducer optimization between transmit and receive elements. One such case would be the use of two distinct frequencies for harmonic processing and other advantages.
BACKGROUND OF THE INVENTION
This invention adds to the body of work of image processing. Much of the interest and the earlier work has been in the field of medical image processing.
FIG. 1
introduces the components of a medical imaging device
100
. The medical imaging device comprises a main body
104
connected to a display
108
and various input devices such as a keyboard
112
. A cable
116
containing a set of wires
120
connects an array
124
of transducer elements
128
in the instrument head
132
to the main body
104
.
In medical imaging, the array of transmit elements
128
sends coordinated pulses of energy into the body. The energy bounces back in various directions as the transmitted energy hits the various surfaces of items within the body. The goal is to measure the energy that reflects back and use the measurements to deduce information about the tissue within the body. Most people know that the thunder from a single clap of lightning is heard by people in a village at different times depending on the relative position of the various observers to the lighting. The same principle applies in imaging in that there is information in not just the amount of energy received by the receive elements but in the delay between the transmission of the energy and the receipt of the echo.
In order to get useful information, there are many transmission elements and many receive elements. Timing delays are used so that elements at different distances from a particular piece of the target can be used collectively to form an image of that piece of the target.
This invention builds on prior concepts and addresses the never-ending quest to get more for less. In this case, “more” means higher resolution images with less artifacts. In this context, “less” means using fewer resources such as fewer devices to transmit or receive the measurement signals, and fewer resources to coordinate, control the devices, and process the information acquired from the receive devices.
The goal is to get the information content that is close to as good as would be obtained from a large fully-populated array of shared transmit/receive elements set out in n rows and n columns while using much less than n×n elements. Such an array with fewer than n×n elements is called a sparse array.
One improvement in the search for getting more for less is described in U.S. Pat. No. 5,537,367 to Lockwood et al. for Sparse Array Structures. The Background of the Lockwood patent sets forth the problem.
Arrays of transducers are used to transmit and/or receive electromagnetic or acoustic energy over a specified region of space (the target).
A portion of the energy that is transmitted bounces back each time the energy wave reaches a new surface in the scanned material.
The arrays of elements are controlled with phase shifts (timing delays) and possibly by weighting so that signals sent to or received from the target constructively interfere while signals outside of the target destructively interfere.
The radiation pattern is a plot of the amplitude of the signal transmitted or received by the array as a function of the position in space.
The radiation pattern of an array indicates how well the array achieves the desired constructive and destructive interference. The radiation pattern is usually plotted in polar coordinates at a given distance in front of the array.
The transmit/receive radiation pattern is a combination of the transmit radiation pattern and the receive radiation pattern. The transmit/receive radiation pattern gives a measure of the sensitivity and resolution with which the array will be able to detect objects.
An example of a typical transmit-receive radiation pattern is shown in FIG.
2
. The radiation pattern consists of a prominent main lobe
150
and a number of secondary lobes
154
. The main lobe corresponds to the desired region in space over which energy will be transmitted and from which energy will be received.
The width of the main lobe
150
is inversely proportional to the width of the array and determines the resolution of the array. In other words, a larger array has a narrower main lobe
150
and has better resolution. Lobe width is often described as the distance between the lobe's “shoulders”.
The secondary lobes
154
are caused by imperfect destructive interference outside of the target area and result in the transmission and reception of unwanted energy. The energy received from side lobes does not represent information about the target region and makes it more difficult to detect subtle differences in the target.
Thus, it is a goal when designing an array to minimize the width of the main lobe (to increase resolution) while minimizing the secondary lobes.
One way to get a higher quality image is to add transducer elements to make a larger fully-populated array. Adding array elements has benefits. Experience has shown that the array should be at least as wide as 20 times the wavelength of sound at the transducers' center frequency in order to focus sharply to give high imaging resolution.
However, there are practical limits on how many array elements can be added. The costs associated with adding array elements include:
1) the cost of the additional transmit or receive element,
2) the cost of the circuits to control or process the information from the element,
3) the problem of cross coupling that occurs when too many wires connected to the various transmit and receive elements are running through the cable connecting the head to the main body of the measurement instrument,
4) the undesired weight added to the measurement instrument head; and
5) if transducers are shared for both transmitting and receiving, it will require transmit/receive switching with its added costs and size.
PRIOR ART SOLUTIONS AND THE CONSEQUENCES
A) Increase the Spacing Between Elements
One solution to the desire to have a wide array but control the number of elements would be to use a fully populated array but simply space the elements with greater gaps between them. However, whenever the spacing of elements in a phase array transducer exceeds approximately one half of the wavelength of sound used by the element, the periodic spacing of the elements causes additional unwanted side lobes kno
Grenon Stephen Michael
Hileman Ronald E.
Daniels Daniels & Verdonik, P.A.
Flynn Kevin E.
Jaworski Francis J.
Jung William
Volumetrics Medical Imaging, Inc.
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