Broad-beam imaging

Details Broad-beam imaging Broad-beam imaging

2002-08-01

2004-02-03

Jaworski, Francis J. (Department: 3662)

Surgery

Diagnostic testing

Detecting nuclear, electromagnetic, or ultrasonic radiation

Reexamination Certificate

active

06685645

ABSTRACT:

BACKGROUND
1. Field of the Invention
The invention is in the field of imaging and more specifically in the field of ultrasonic imaging.
2. Prior Art
Ultrasonic imaging is a 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, ultrasonic imaging is accomplished by generating and directing an ultrasound beam 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, in medical applications observed reflections are generated at boundaries between a patient's tissues. The observed reflections are converted to electrical signals (channel data) by receiving devices (transducers) and processed, using methods known in the art, to determine the locations of echo sources. The resulting data is displayed using a display device such as a monitor.
The prior art processes of producing an ultrasound beam and analyzing resulting echoes is called “beam forming.” The production process optionally includes defining “transmit” beam characteristics through aperture apodization, steering, and/or focusing. The analysis process optionally includes calculating a “receive beam” wherein received echoes are processed to isolate those echoes generated along a narrow region. This calculation includes the identifying one-dimensional line along which echoes are assumed to have been generated, and is therefore referred to herein as “echo line calculation.” Through beam forming a one-dimensional set of echolocation data is generated using each transmit and/or receive beam. Echolocation data is positional data relating to the physical location of one or more echo source and optionally includes intensity, velocity and/or similar physical information. Echolocation data may include post-beam forming raw data, detected data, or image data. Multidimensional echolocation data, such as an ultrasound image, is generated by scanning a field of view within the material under investigation using multiple transmit and/or receive beams.
The ultrasound beam transmitted into the material under investigation during the transmit phase is generated by applying electronic signals to a transducer. The ultrasound beam may be scattered, resonated, attenuated, and/or reflected as it propagates through the material under investigation. A portion of the reflected signals are received at transducers and detected as echoes. The receiving transducers convert the echo signals to electronic signals and optionally furnish them to an echo line calculator (beam former) that performs the echo line calculation inherent to analysis using a receive beam.
After beam forming, an image scan converter uses the calculated echolocation data to generate image data. In prior art systems the image formation rate (the frame rate) is limited by at least the total pulse return times of all ultrasound beams used to generate each image. The pulse return time is the time between the transmission of the ultrasound beam into the material under investigation and the detection of the last resulting reflected echoes. The limited frame rate may result in temporal artifacts caused by relative movement between the ultrasound system and a material under investigation.
FIG. 1
shows a prior art ultrasound system, generally designated
100
. Ultrasound system
100
includes an element array
105
of transducer elements
110
, a backing material
120
, an optional matching layer
130
, a transmit/receive switch
140
and a beam transmitter
150
. 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
into the material under investigation (not shown). Transducer elements
110
, include individual transducer elements
110
A-
110
H individually coupled by conductors
115
and
117
, through transmit/receive switch
140
, to a beam transmitter
150
. Transmit/receive switch
140
may include a multiplexer
145
that allows 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
, applied to some or all of transducer elements
110
A-
110
H, and converted to ultrasound pulses
160
. Taken together, ultrasound pulses
160
form an ultrasound beam
170
that probes the material under investigation.
Ultrasound beam
170
may be focused to limit the region in which echoes are generated. When echo sources are restricted to a narrow region the calculation of echo location data may be simplified by assuming that the echo sources lie along a “transmit line.” With this assumption, the task of the echo beam calculator is reduced to a problem of determining the position of an echo source in one dimension. This position is established using the return time of the echo. The accuracy of this assumption and the spacing of transmit lines are significant factors in determining the resolution of prior art ultrasound systems. Finely focused beams facilitate higher resolution than poorly focused beams. Analogous assumptions and consequences are found in analyses involving calculated receive beams.
FIG. 2
shows a prior art focusing system in which element array
105
is a phased array configured to focus ultrasound beam
170
by varying the timing of electronic pulses
210
applied to transducer elements
110
A-
110
H. In this system, electronic pulses
210
, are generated at beam transmitter
150
and passed through transmit/receive switch
140
. Electronic pulses
210
are delayed using a delay generator (not shown) and coupled to transducer elements
110
A-H. Ultrasound beam
170
is formed when transducer elements
110
A-H convert properly delayed electronic pulses
210
to ultrasound pulses
160
(FIG.
1
). Once formed, ultrasound beam
170
is directed along a transmit beam line
250
including a focal point
230
with a resulting beam waist
240
characterized by a width of ultrasound beam
170
. In a similar manner phased excitation of element array
105
is used to direct (steer) ultrasound beam
170
in specific directions. The cross-sectional intensity of ultrasound beam
170
is typically Gaussian around a focal point and includes a maximum along transmit beam line
250
. The shape of ultrasound beam
170
may depend on aperture apodization.
In a scanning process, ultrasound system
100
sends a series of distinct ultrasound beam
170
along another, different transmit beam line
250
to form an image over more than one spatial dimension. A specific ultrasound beam
170
is optionally transmitted in several transmit/receive cycles before generating another ultrasound beam
170
. Between each transmit phase a receive phase occurs, during which echoes are detected. Since each ultrasound beam
170
, included in an ultrasound scan, requires at least one transmit/receive cycle the scanning processes may take many times the pulse return time. This pulse return time, determined by the speed of sound in the material under investigation, is a primary limitation on the rate at which prior art ultrasound images can be generated. In addition, undesirable temporal anomalies can be generated if transducer elements
110
A-
110
H move relative to the material under investigation during the scanning process.
FIGS. 3A through 3E
show a prior art scanning process in a phased array
310
of eight transducer elements, designated
110
A through
110
H. Subsets
320
A-
320
E of the eight transducer elements
100
A-
110
H are each used to generate one of distinct ultrasound beams
170
A-
170
E. 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 forming ultrasound beam
170
B using subset
320
B including transducer e

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