Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2001-12-18
2003-06-03
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C128S916000
Reexamination Certificate
active
06572549
ABSTRACT:
TECHNICAL FIELD
This invention relates to ultrasound diagnostic imaging systems and, in particular, to a method and apparatus for rapidly obtaining extended field of view ultrasound images.
BACKGROUND OF THE INVENTION
Diagnostic ultrasound systems are commonly used to generate two-dimensional (“2-D”) and three-dimensional (“3-D”) images of tissues, vessels and organs within a patient's body. To do so, a sonographer positions an ultrasound scanhead having an array of transducer elements adjacent to a target area. The transducer elements emit ultrasound energy that propagates into the patient where it is absorbed, dispersed, refracted, and reflected by internal structures. Reflected ultrasound energy is received back at the scanhead where it is converted back into electronic signals. An image is then created from the electronic signals.
The received electronic signals undergo beamforming to coordinate the samples in time and space to a target area. Exemplary beamforming methods for controlling the imaging process include focus, steering, apodization and aperture. Focus is a time delay profile of active transducer elements. Steering is the control of focus depth points along azimuth and elevation axes of the transducer elements. Apodization is a voltage weighting profile of active transducer elements. Aperture is the control of the number of transducer elements that are active along an axis of the scanhead. The beamformed signals are processed to display an image showing echo and Doppler flow information, which may be in the form of a cross-sectional image.
A conventional cross-sectional image is a brightness image (i.e., referred to as a “B-mode” or “B-scan” image) in which component pixels are brightened in proportion to the intensity of a corresponding echo signal. Existing B-scan ultrasound imaging systems use scanheads having one-dimensional linear arrays to generate B-scan images of the body. The images produced by B-scan ultrasound imaging systems are composed of discrete image frames, the characteristics of which depend on the number of transducer elements that are active, the relative spacing of the elements and the steering and focus of the transducer elements. Each B-scan image frame represents a two-dimensional (“2D” ) image plane that is taken through a cross-section of the body that extends inwardly from the linear transducer array.
A drawback of such B-scan imaging is that most of the imaged tissues or vessels appear only as cross sections since most tissues or vessels of interest do not extend along the image plane. It is therefore often difficult using B-scan imaging to visualize tissues or vessels extending through the body at approximately a constant distance from a skin surface with which the scanhead is in contact.
One approach to making B-scan imaging more useful is to combine a large number of 2-D image frames to create an “extended field of view” (“EFOV”) or “panoramic” image. In these systems, the scanhead is moved along a skinline to produce successive 2-D B-scan image frames that represent respective spatially offset 2-D image planes, as explained above. Each image plane is defined by a centerline of the scanhead array, i.e., the path along which the ultrasound is directed, and a direction that extends along the axis of the transducer array. The scanhead is scanned in a direction extending along the axis of the array to create a series of 2-D B-scan image frames. The image frames lie in a common plane and have regions that spatially overlap each other. The image frames are then combined by registering the overlapping areas of adjacent image frames. The resulting image is a 2-D EFOV B-scan image lying in a plane extending in the scanning direction. Alternatively, the scanhead may be scanned in a direction that is perpendicular to the axis of the array to create a series of B-scan image frames that lie in different planes that are parallel to each other. The image frames are obtained sufficiently close to each other that beam patterns of the frames spatially overlap each other in elevation. The image frames are then combined by registering the adjacent image frames. The resulting image is a 3-D EFOV B-scan image containing all of the B-scan image frames.
In order to make proper registration of the image frames possible, accurate information about the distance between adjacent frames must be known. Early EFOV imaging systems, known as “B-arm scanning systems,” included a single beam ultrasound scanhead mounted at the end of an articulated arm. The joints of the articulated arm contained sensors that produced an electrical signal indicative of the spatial position of the scanhead. As the scanhead was scanned over the body of the patient, an image frame was produced from the ultrasound returns obtained from the scanhead and the relative spatial locations of the scanhead while the returns were being obtained. The image frames from multiple adjacent scans of the scanhead were computed and stored, and then assembled in consecutive, side-by-side locations to create an EFOV image. These early EFOV systems were capable of generating an ultrasound image that could laterally extend for the maximum number of successive image frames that the system could store and display and extend vertically over the range of positions that arm could extend.
EFOV imaging systems relying on hardware position sensors have several shortcomings. First, position sensors based on electromagnetic energy emissions may interfere with the transmitted and received ultrasound energy. Other hardware position sensors tend to be less accurate requiring longer and more frequent calibration processes. Also, it is a challenge to integrate the sensor's detection scheme into the ultrasound image capturing process. The position sensor captures data samples. Such samples need to be synchronized to the ultrasound sampling process and the ultrasound data processing data. Finally, EFOV imaging systems having scanheads mounted at the end of an arm are cumbersome to operate because the arm tends to restrict freedom of movement.
In recent years, systems have been developed for electronically registering B-scan images to produce an EFOV image. As previously explained, the scanhead in these systems is scanned along a skinline to produce successive, spatially offset 2-D image frames, . Each image frame is spatially registered with a previously acquired overlapping image frame, and the image frames are then combined to produce an EFOV image that is laterally extensive in the direction of motion of the scanhead.
One conventional technique for producing a 2-D EFOV B-scan image is shown in FIG.
1
. An ultrasound scanhead
10
having a linear array of transducer elements
12
is placed in contact with a skinline
14
of a patient. The ultrasound scanhead
10
is coupled to an imaging system (not shown in
FIG. 1
) by a cable
16
. In the example shown in
FIG. 1
, the ultrasound scanhead
10
is being used to scan tissues
20
beneath the skinline
14
containing a blood vessel
24
that divides into two branches
26
,
28
at one end. However, it will be understood that the ultrasound scanhead
10
can likewise be used to scan other blood vessels as well as tissues, vessels or organs.
To scan a length of the blood vessels
24
,
26
,
28
, the sonographer slides the ultrasound scanhead
10
in the direction
30
. With reference, also, to
FIG. 2
, as the ultrasound scanhead
10
is moved in the direction
30
, successive 2-D B-scan image frames
34
,
36
,
38
lying in substantially the same plane are acquired. Each of the image frames
34
,
36
,
38
is composed of data from ultrasound echoes returned from all locations in a thin volume represented by the image frame. Each image frame
34
,
36
,
38
is slightly displaced from the previous image frame in the direction
30
. The magnitude of the image frame displacement is a function of the speed the scanhead
10
is moved and the rate at which image frames
34
,
36
,
38
are acquired. As explained in greater detail below, the displacement between su
Detmer Paul
Jong Jing-Ming
Dorsey & Whitney LLP
Imam Ali M.
Koninklijke Philips Electronics NV
Lateef Marvin M.
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