Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2002-07-03
2004-02-24
Imam, Ali M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S443000, C128S916000
Reexamination Certificate
active
06695778
ABSTRACT:
BACKGROUND
The present invention relates generally to methods and systems for obtaining ultrasound images, and more particularly, to such methods and systems that provide real-time ultrasound images having clinical quality.
An ultrasound system can typically include a transducer array, a signal processing unit and a display. The transducer elements generate ultrasonic waves, transmit the waves into a region to be imaged, and receive returning echoes, generated in response to the transmitted waves, by one or more scatterers in the region. The signal processing unit utilizes the echoes to construct an image of the scatterers, which can then be presented to a viewer on the display.
In traditional ultrasound systems, narrow beams are employed for image acquisition. In many such systems, the transducer elements transmit identically-shaped pulse signals which are delayed relative to each other to ensure that the pulses arrive at a desired focal point at the same time, thus forming a beam in a particular direction. During the receiving step, the echoes generated in response to the pulses are similarly delayed so that at any particular time, the echo signals sent by the transducers to the processing unit correspond to signals generated at the same point along the beam. The image values corresponding to scatterers located along the beam direction are set to the sum of the intensities of the respective echo signals. This procedure is often referred to as “delay-and-sum”, or “beamforming”. An image of a selected region is constructed by repeating this process along a number of transmitted beam directions. The system component, typically hardware, that performs delaying and adding of the echo signals to isolate the scatter properties in a particular location is called a “beamformer”.
In most traditional ultrasound systems, the transducer elements are arranged along a single straight or curved line, which confines the transmitted waves to an imaging plane. A resulting image corresponds to a cross-section of an imaged object along the imaging plane. More recently, matrix (2-dimensional) transducer arrays have been introduced that allow full volumetric imaging. Alternatively, a linear array can be moved/rocked to transmit pulses in all directions in a given volume.
The data collection time in the systems described above is proportional to the number of beams required to generate the image. The number of beams required to generate a volumetric image is equal to the square of the number of beams required to form a planar image of the same resolution. For example, to extend a two-dimensional 64-beam image into three dimensions (3D) while maintaining the same resolution, 64×64=4,096 beams are needed. Similarly, extending a 128-beam image into 3D requires 128×128=16,384 beams. Hence, a transition from planar to volumetric imaging can result in approximately two orders of magnitude increase in the amount of data and the acquisition time. Since the time of each transmit-receive iteration (i.e., transmitting a single beam and receiving the echoes from the scatterers in the selected region) is determined by the speed of sound in the region to be imaged (e.g., tissue), the number of beams that the system can transmit and receive in any given time is inherently limited (approximately 5000 per second). At real-time frame rates (e.g., 30 frames per second), this corresponds to approximately 150 beams per image, which is insufficient for volumetric imaging.
Thus, there is a need for improved ultrasound imaging methods and associated systems. There is also a need for such ultrasound imaging methods and systems that allow efficiently generating ultrasound images in real-time.
SUMMARY OF THE INVENTION
The invention provides a method of generating an ultrasound image of a plurality of scatterers disposed in a target region by constructing response functions for each of a plurality of transducers for a given ultrasound interrogation pattern and a given distribution of scattering media. The interrogation pattern can be selected to include a set of unfocused ultrasound waves generated by one or more of the transducers. The phrase “unfocused ultrasound wave”, as used herein, refers to one or more ultrasound waves that have not been designed, for example, by selection of their relative phases, to substantially interfere constructively in a selected region. The interrogation pattern is transmitted into the target region, and the transducers are utilized to detect echoes generated by scatterers in the target region in response to the interrogation pattern.
An image of the scatterers is then globally constructed based on comparison of the detected echoes and echoes predicted by the response functions. The term “globally constructing an image”, as used herein, refers to computing the ultrasound image by mathematically processing echoes received from any part of an entire portion of the target region that is illuminated by the unfocused transmitted ultrasound waves, including any interferences among these echoes, without the need for beamforming. Hence, the method of the invention generates an ultrasound image of a selected target region without utilizing beamforming either in transmission of ultrasound waves into a target region or in detection and processing of echoes generated by scatterers in that region in response to the transmitted waves.
In a related aspect, an echo signal f
n
(t) detected by the n-th transducer of a plurality of transducers is defined in accord with the relation:
f
n
(
t
)=∫
&ngr;
F
n
(
t, v
)
dv
wherein &ngr; represents a selected region to be imaged, v represents a particular location in the selected region &ngr;, and F
n
(t, v) represents a function predicting echo signal that is reflected by scatter at point v and detected by the n-th transducer.
In many embodiments of the invention, a linear model is utilized for predicting echoes detected by each transducer. For example, an echo signal f
n
(t) detected by n-th transducer can be defined in accord with the relation:
f
n
(
t
)=∫
&ngr;
B
n
(
t, v
)
s
(
v
)
dv
wherein s(v) represents a scattering parameter of a scatterer positioned at point v in the selected region &ngr;, B
n
(t, v) represents a linear response function associated with the n-th transducer element corresponding to a point v in the selected region &ngr;.
In a related aspect, the echoes detected by the transducers are discretized. This discretization process can be accomplished uniformly, for example, by sampling and digitizing each echo signal at uniform temporal intervals. Alternatively, the echo signals can be discretized non-uniformly, for example, by sampling and digitizing each echo signal at temporal intervals having different durations. For example, an echo signal associated with the n-th transducer f
n
(t) can be discretized into a plurality of echo signals f
n
(k), each of which is defined in accord with the relation:
f
n
(
k
)=∫
&ngr;
B
n
(
k, v
)
s
(
v
)
dv
wherein k is an index representing a discrete echo sample, ranging from 1 to K, and B(k, v) is the response function associated with the n-th transducer discretized using the same time intervals as the detected echo signal.
In some embodiments, the target region can be represented as a plurality of discrete portions. The discrete portions can have the same or variable sizes. Further, the discrete portions can be distributed through the target region in a uniform or non-uniform manner. In such a case, an echo f
n
(t) associated with the n-th transducer can be defined in accord with the relation:
f
n
(
t
)
=
∑
v
=
1
V
B
n
(
t
,
v
)
s
(
v
)
where &ugr; enumerates the discrete portions ranging from 1 to V.
In a related aspect, in a method of generating an ultrasound image as described above, the model response functions are derived based on any of computational modeling, measurements using a calibration phantom, or a combination thereof. For example, the step of deriving model response functions
Golland Polina
Ho Stacy
AITech, Inc.
Engellenner Thomas J.
Imam Ali M.
Mollaaghababa Reza
Nutter & McClennen & Fish LLP
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