Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2001-10-20
2004-08-10
Jaworski, Francis J. (Department: 3662)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S459000
Reexamination Certificate
active
06773399
ABSTRACT:
BACKGROUND
1. Field of the Invention
The invention is in the field of medical devices and more particularly in the field of ultrasound imaging.
2. Prior Art
Ultrasound imaging is a common method of analysis used for examining a wide range of materials. The method is especially common in medicine because of its relatively non-invasive nature, low cost, and fast response times. Typically, ultrasound imaging is accomplished by generating and directing ultrasonic sound waves into a material under investigation in a transmit phase and observing reflections generated at the boundaries of dissimilar materials in a receive phase. For example, reflections are generated at boundaries between a patient's tissues. The reflections are converted to electrical signals by receiving devices (transducers) and processed, using beam-forming techniques known in the art, to determine the locations of echo sources. The resulting data is displayed using a display device such as a monitor.
Typically, the ultrasonic signal transmitted into the material under investigation is generated by applying continuous or pulsed electronic signals to a transducer. The transmitted ultrasound is commonly in the range of 1 MHz to 15 MHz. The ultrasound propagates through the material under investigation and reflects off of structures such as boundaries between adjacent tissue layers. As it travels, the ultrasonic energy may be scattered, resonated, attenuated, reflected, or transmitted. A portion of the reflected signals are returned to the transducers and detected as echoes. The detecting transducers convert the echo signals to electronic signals and furnish them to a beamformer. The beamformer calculates locations of echo sources along a line (beam) and typically includes simple filters. After beam-forming, an image scan converter uses the calculated positional information, resulting form several beams, to generate two dimensional data that can be presented as an image. In prior art systems the image formation rate (the frame rate) is limited by at least the pulse round trip time. The pulse round trip time is the time between the transmission of ultrasonic sound into the media of interest and the detection of the last reflected signals.
As an ultrasound pulse propagates through a material under investigation, additional harmonic frequency components are generated. These additional harmonic frequency components continue to propagate and, in turn, reflect off of or interact with other structures in the material under investigation. Both fundamental and harmonic signals are detected. The analysis of harmonic signals is generally associated with the visualization of boundaries or image contrast agents designed to re-radiate ultrasound at specific harmonic frequencies.
FIG. 1
shows a prior art ultrasound system, generally designated
100
. The ultrasound system
100
includes an element array
105
of transducer elements
110
A-
110
H, a backing material
120
, and a matching layer
130
. Backing material
120
is designed to support element array
105
and dampen any ultrasound energy that propagates toward backing material
120
. Matching layer
130
transfers ultrasound energy from transducer elements
110
A-
110
H into a material of interest (not shown). Transducer elements
110
A-
110
H are each individually electronically coupled by conductors
115
and
117
, through a transmit/receive switch
140
to a beam transmitter
150
. In the current art, transducer elements
110
A-
110
H are typically piezoelectric crystals. Transmit/receive switch
140
typically includes a multiplexer
145
, allowing the number of conductors
117
to be smaller than the number of conductors
115
. In the transmit phase, beam transmitter
150
generates electronic pulses that are coupled through transmit/receive switch
140
, and applied to transducer elements
110
A-
110
H and converted to ultrasound pulses
160
. Taken together, ultrasound pulses
160
form an ultrasound beam
170
that probes a material of interest. Ultrasound beam
170
is focused to improve the spatial resolution of the ultrasound analysis.
FIGS. 2A and 2B
show a prior art focusing method in which element array
105
is a phased array used to focus ultrasound beam
170
by varying the timing of electronic pulses
210
applied to transducer elements
110
A-
110
H. Electronic pulses
210
, with different delay times, are generated at beam transmitter
150
. When electronic pulses
210
are converted to ultrasound pulses
160
by transducer elements
110
A-
110
H, they form ultrasound beam
170
directed at a focal point
230
.
FIGS. 2A and 2B
show two series of electronic pulses
210
each with a different set of delay times resulting in different focal points
230
. In a similar manner phased excitation of array
105
is used to direct (steer) ultrasound beam
170
in specific directions.
Ultrasound system
100
sends a series of ultrasound beam
170
through different paths to form an image with a cross-sectional area greater than the width of each individual ultrasound beam
170
. Multiple beams are directed from ultrasound system
100
in a scanning or steering process. An ultrasound scan includes transmission of more than one distinct ultrasound beam
170
in order to image an area larger than each individual ultrasound beam
170
. Between each transmit phase a receive phase occurs during which echoes are detected. Since each ultrasound beam
170
, included in the ultrasound scan, requires at least one transmit/receive cycle, the scanning processes can require many times the pulse round trip time. Optionally, an ultrasound beam
170
is transmitted in several transmit/receive cycles before another ultrasound beam
170
is generated. If ultrasound transducers
110
A-
110
H move relative to the material under investigation during the scanning process undesirable artifacts can be generated.
FIG. 3A through 3E
show a prior art scanning process in a transducer array
310
of eight transducer elements, designated
110
A through
110
H. Electrical pulses are applied to subsets
320
A-
320
E of the eight transducer elements
100
A-
110
H. For example,
FIG. 3A
shows ultrasound beam
170
A formed by subset
320
A including transducer elements
110
A-
110
D. The next step in the scanning process includes ultrasound beam
170
B formed by subset
320
B including transducer elements
110
B-
110
E as shown in FIG.
3
B. Subset
320
B includes most (seventy-five percent) of the transducer elements
110
A-
110
H found in subset
320
A. Subset
320
A and subset
320
B differ by two transducer elements
110
A-
110
H, the difference includes the inclusion of one and the removal of another. In the example shown, the center of ultrasound beam
170
B passes through focal point
230
and is displaced from the center of ultrasound beam
170
A by a distance equal to one transducer element
110
. As illustrated by
FIGS. 3C through 3E
, the process continues, each subset
320
C through
320
E, used to produce each ultrasound beam
170
C through
170
E, is displaced by one transducer element
110
relative to the subset
320
B through
320
D used to generate the previous ultrasound beam
170
B through
170
D. Echoes detected in the receive phase that occurs between each ultrasound beam
170
transmission are used to generate beam echo data. Analyses of the beam echo data are combined and scan converted to form an image and the scan process is repeated to produce multiple images. The subsets
320
A-
320
E of transducer elements
110
A-
110
H used to produce ultrasound beams
170
A-
170
E are selected using an array of switches and multiplexer
145
. These switches are typically located in transmit/receive switch
140
.
FIG. 4A through 4E
show prior art examples of the states of switches
410
A-
410
H used to generate five consecutive ultrasound beams
170
A-
170
E. The state of each switch
410
determines which of transducer elements
110
A-
110
H are coupled to beam transmitter
150
and therefore excited. For example, in
FIG. 4A
the first four switches
410
A-
410
D are c
McLaughlin Glen
Tarakci Umit
Xi Xufeng
Carr & Ferrell LLP
Jaworski Francis J.
Patel Maulin
Zonare Medical Systems, Inc.
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