Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2002-06-25
2004-05-18
Manuel, George (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06736780
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to ultrasound imaging, and more particularly, to a synthetic aperture focusing method for ultrasound imaging based on planar waves.
BACKGROUND OF THE INVENTION
An ultrasound imaging system for medical use provides real-time two-dimensional (2-D) images by using transducers that transmit ultrasound signals into the human body and applying various signal processes on the reflected signals. As shown in
FIG. 1
, the resolution of the ultrasound image is determined by resolutions in: axial direction
2
, the direction of the transmitted beam orthogonal to the width of the transducer; lateral direction
4
, the direction orthogonal to axial direction
2
and in the plane of the width of the transducer; and elevational direction
6
, the direction orthogonal to axial direction
2
and the width of the transducer. The axial resolution is not a critical factor in determination of the entire resolution of an ultrasound image since the axial resolution is generally three to five times higher than the other resolution components. However, unlike the axial resolution, the lateral and elevational resolutions vary depending on the transmit/receive focusing technique.
It is known that the lateral resolution can be improved by performing real-time receive dynamic focusing on all imaging points. Details of the real-time receive dynamic focusing will now be illustrated with reference FIG.
2
. Referring to
FIG. 2
, transmission signals (not shown) of the ultrasound imaging system are delayed by the delay time corresponding to the focusing depth of each transducer
9
of transducer array
13
by transmit focusing delay
8
. The transmission signals with the time delay are stored in transmission pattern memory
10
and transmit-focused to the target object(not shown) by transducer array
13
through transmitter
11
and transmitting/receiving switch
12
. All transmitted beams are focused to fixed transmit focal point
14
. After that, echo signals are reflected from focal point
14
and converted to electronic signals through each transducer
9
of transducer array
13
. They are stored in reception pattern memory
16
through transmitting/receiving switch
12
and receiver
15
. The echo signals stored in reception pattern memory
16
have different phases which vary in accordance with the different focusing depths of each transducer
9
. Thus, a variable time delay is added through receive focusing delay
17
so that the echo signals are in phase. The in-phase echo signals are combined at beamformer
18
and processed at signal processor
19
, and displayed on display
21
through scan converter
20
.
While only one fixed transmit focal point
14
has been discussed, receive dynamic focusing is also possible with respect to all imaging points constituting one transmit scan line from echo signals obtained by a single transmission. Receive dynamic focusing is performed by compensating for the differences in distance between the transducers and the focal point.
However, the two-way dynamic focusing is performed only at the focal point
14
because the transmit focusing illustrated in
FIG. 2
is performed at the focal point
14
. As a result, the lateral resolution may be degraded as the beams rapidly spread if they pass through the focal point
14
.
Referring to
FIG. 3
, the lateral resolution is degraded, depending on the focusing depth. When the delay time for the receive focusing is compensated, echo signals received by respective transducers, n
1
, n
2
, and n
3
, are the combination of signals reflected from reflectors
22
a
and
22
b
on curved surfaces W
1
, W
2
, and W
3
. Curves W
1
, W
2
, and W
3
lie on circles centered on transducers n
1
, n
2
, and n
3
with radii equal to the distance between each transducer and focusing depth Z
1
, respectively. If two reflectors
22
a
and
22
b
exist on Z
1
and echo signals reflected from the two reflectors are combined, then only the power of echo signals reflected from reflector
22
a
on line L
0
is strengthened. However, if echo signals reflected from two reflectors
24
a
and
24
b
on Z
2
are combined, then the powers of echo signals reflected from reflector
24
a
on line L
1
and reflector
24
b
on line L
0
are simultaneously strengthened. Difference in the lateral resolution based on focusing depth arises because whereas the three curves at Z
1
only overlap with respect to reflector
22
a
on line L
0
, the curves at Z
2
overlap with respect to reflector
24
a
on line L
1
and reflector
24
b
on line L
0
, lowering the lateral resolution.
SUMMARY OF THE INVENTION
It is, therefore, the objective of the present invention to provide a synthetic aperture focusing method which is capable of two-way dynamic focusing through the use of planar waves, thereby improving the lateral resolution.
In accordance with a preferred embodiment of the present invention, there is provided to a synthetic aperture focusing method for an ultrasound imaging system comprising the steps of: producing planar waves by a plurality of transducers; transmitting the planar waves to a target object; receiving signals reflected from the target object through a plurality of receive subapertures, wherein each receive subaperture is comprised of at least one of the plurality of transducers; dynamic-focusing the received signals; and combining the dynamic-focused signals to form at least one beam pattern.
REFERENCES:
patent: 5186177 (1993-02-01), O'Donnell et al.
patent: 5465722 (1995-11-01), Fort et al.
patent: 5951479 (1999-09-01), Holm et al.
patent: 2001-0051946 (2001-06-01), None
METMBS'01—“Proceedings of the International Conference on Mathematics and Engineering Techniques in Medicine and Biological Sciences” by F. Valafar; Las Vegas, Nevada, USA Jun. 25, 28, 2001 CSREA Press.*
Korean Office Action, application number 2003-032629012, date of mailing Aug. 26, 2003.
Chang Jin Ho
Song Tai Kyong
Jain Ruby
Manuel George
Medison Co. Ltd.
Ritchie David B.
Thelen Reid & Priest LLP
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