Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2000-09-08
2003-04-08
Jaworski, Francis J. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06544177
ABSTRACT:
TECHNICAL FIELD
The invention relates to ultrasonic diagnostic imaging systems and methods and, in particular, to ultrasonic diagnostic imaging systems that produce spatially compounded images and harmonic ultrasonic imaging systems.
BACKGROUND OF THE INVENTION
Spatial compounding is an imaging technique in which a number of ultrasonic images of a given target that have been obtained from multiple vantage points or angles (look directions) are combined into a single compounded image by combining the data received from each point in the compound image target which has been received from each angle. Examples of spatial compounding are described in U.S. Pat. Nos. 4,649,927; 4,319,489; and 4,159,462. Real time spatially compound imaging is performed by rapidly acquiring a series of partially overlapping component image frames from substantially independent spatial directions, and utilizing an array transducer to implement electronic beam steering and/or electronic translation of the component frames. The component frames are combined into a compounded image by summation, averaging, peak detection, or other combinational means. The acquisition sequence and formation of compounded images are repeated continuously at a rate limited by the acquisition frame rate, that is, the time required to acquire the full complement of scanlines over the selected width and depth of imaging.
The compounded image typically shows lower speckle and better specular reflector delineation than conventional ultrasonic images from a single viewpoint. Speckle is reduced (i.e., speckle signal to noise ratio is improved) by the square root of N in a compound image with N component frames, provided that the component frames used to create the compounded image are substantially independent and are averaged. Several criteria can be used to determine the degree of independence of the component frames (see, e.g., O'Donnell et al. in IEEE Trans. UFFC v.35, no.4, pp 470-76 (1988). In practice, for spatially compound imaging with a steered linear array, this implies a minimum steering angle between component frames that is typically on the order of several degrees.
The second way that spatially compound scanning improves image quality is by improving the acquisition of specular interfaces. For example, a curved bone-soft tissue interface produces a strong echo when the ultrasonic beam is exactly perpendicular to the interface, and a very weak echo when the beam is only a few degrees off perpendicular. These interfaces are often curved, and with conventional scanning only a small portion of the interface is visible. Spatially compound scanning acquires views of the interface from many different angles, making the curved interface visible and continuous over a larger field of view. Greater angular diversity generally improves the continuity of specular targets. However, the angular diversity available is limited by the acceptance angle of the transducer array elements. The acceptance angle depends on the transducer array element pitch, frequency, and construction methods.
Another ultrasonic imaging modality is harmonic ultrasonic imaging. It has been known for some time that tissue and fluids have inherent nonlinear properties. Tissue and fluids will, even in the absence of a contrast agent, develop and return their own non-linear echo response signals, including signals at harmonics of the fundamental. Muir and Carstensen explored these properties of water beginning in 1980, and Starritt et al. looked at these properties in human calf muscle and excised bovine liver.
While these non-linear echo components of tissue and fluids are generally not as great in amplitude as the harmonic components returned by harmonic contrast agents, they do exhibit a number of characteristics that have been recognized as being advantageous in conventional ultrasonic imaging. In particular, it has been recognized that negligible harmonic signals are generated very close to the transducer, which allows for clutter reduction when imaging through narrow orifices such as the ribs since fundamental signal reverberations are not being used for imaging. Additionally, it has been recognized that the levels of a harmonic beam side lobe are lower than the corresponding levels of the side lobes of the fundamental beam, which has implications for off-axis clutter reduction. Finally, it has been recognized that the main lobe of the harmonic is narrower than that of its fundamental, which allows for improved lateral resolution.
Although each of these modalities—spatially compounded imaging and harmonic imaging—has advantages in certain situations, each has certain performance limitations. In particular, the performance of ultrasonic imaging systems using spatial compounding is limited because grating lobes generated by a transducer array may cause false returns to be generated. With reference to
FIG. 1
which shows a narrowband example, an ultrasonic array
10
transmits and receives an ultrasonic signal having a main lobe
14
and a plurality of pairs of grating lobes, only one of which
18
is shown in FIG.
1
. The grating lobes
18
are shown with an amplitude that is significantly less than the amplitude of the main lobe
14
because of the limited angular response of the transducer elements. The main lobe
14
has a higher amplitude because the main lobe
14
is transmitted by the array
10
with a higher sensitivity, and the main lobe
14
is received by the array
10
with a higher sensitivity. As is well known in the art, the grating lobe equation is: Sin &phgr;
M
−Sin &phgr;
G
=&lgr;/P, where &phgr;
M
is the angle of the main lobe and &phgr;
G
is the angle of the grating lobe, both relative to the Y-axis. For a look angle of 0 degrees (&phgr;
M
equals 0 degrees), the angle &thgr; between the main lobe
14
and the grating lobes
18
is given by the formula: &thgr;=Sin
−1
&lgr;/P, where P is the pitch of the array
10
, i.e., the center-to-center distance between elements of the array
10
, and &lgr;
0
is the wavelength of the ultrasonic signal. When the wavelength &lgr; of the transmitted ultrasonic signal is equal to the pitch P of the array
10
, the angle &thgr; between the main lobe
14
and the grating lobes
18
is 90 degrees. As a result, an ultrasonic signal is not transmitted into tissues T positioned adjacent the array
10
through the grating lobes
18
so that the only image generated is an image resulting from insonification by the main lobe
14
. Therefore, the grating lobes
18
do not present any problem when the main lobe
18
is directed straight into the tissues T and the angle &thgr; between the main lobe
14
and the grating lobes
18
is 90 degrees or more, as shown in FIG.
1
. If, however, the angle &thgr; between the main lobe
14
and the grating lobes
18
is 45 degrees, as shown in
FIG. 2
, ultrasonic signals are transmitted through the grating lobes
18
into the tissues, and echoes are returned from the tissues T through the grating lobes
18
. As a result, the image generated is an image resulting from the main lobe
14
as well as clutter and possibly a “false image” resulting from the grating lobes
18
.
In spatial compounding, the tissue must be imaged from a variety of beam steering angles or look directions, as shown in
FIG. 3. A
spatially compounded image of an object O in the tissues T is the result of returns from the array
10
at a first angle &phgr;
1
, returns from the array
10
at a second angle &phgr;
2
, returns from the array
10
at a third angle &phgr;
3
, etc. For the array
10
to image at each of these angles &phgr;
3
, it is necessary for the array
10
to steer the main lobe
14
to such angle &phgr;
1
, for example, as shown in FIG.
4
. When the main lobe
14
is steered to an angle &phgr;
1
, the grating lobes
18
are positioned at an angle so that one of the grating lobes
18
a
extends into the tissues T at an angle at which the array has greater sensitivity. Under these circumstances, ultrasonic returns are received from both the main lobe
1
ATL Ultrasound Inc.
Dorsey&Whitney LLP
Jaworski Francis J.
Patel Maulin
LandOfFree
Ultrasonic diagnostic imaging system and method with... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ultrasonic diagnostic imaging system and method with..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ultrasonic diagnostic imaging system and method with... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3048443