Optical: systems and elements – Lens – With graded refractive index
Reexamination Certificate
2001-10-20
2003-09-09
Ben, Loha (Department: 2873)
Optical: systems and elements
Lens
With graded refractive index
C600S459000
Reexamination Certificate
active
06618206
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is in the field of imaging devices and more particularly in the field acoustic lenses for ultrasonic imaging.
2. Description of Prior Art
Ultrasonic imaging is a frequently used method of analysis for examining a wide range of materials. Ultrasonic imaging 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 ultrasonic sound waves into a medium of interest using a set of ultrasound generating transducers and then observing reflections generated at the boundaries of dissimilar materials, such as tissues within a patient, also using a set of ultrasound receiving transducers. The receiving and generating transducers may be arranged in arrays and are typically different sets of transducers, but may differ only in the circuitry to which they are connected. The reflections are converted to electrical signals by the receiving transducers and then processed, using techniques known in the art, to determine the locations of echo sources. The resulting data is displayed using a display device, such as a monitor.
Typically, the ultrasonic signal transmitted into the medium of interest is generated by applying continuous or pulsed electronic signals to an ultrasound generating transducer. The transmitted ultrasound is most commonly in the range of 40 kHz to 15 MHz. The ultrasound propagates through the medium of interest and reflects off interfaces, such as boundaries, between adjacent tissue layers. Scattering of the ultrasonic signal is the deflection of the ultrasonic signal in random directions. Attenuation of the ultrasonic signal is the loss of ultrasonic signal as the signal travels. Reflection of the ultrasonic signal is the bouncing off of the ultrasonic signal from an object and changing its direction of travel. Transmission of the ultrasonic signal is the passing of the ultrasonic signal through a medium. As it travels, the ultrasonic energy is scattered, attenuated, reflected, and/or transmitted. The portion of the reflected signals that return to the transducers are detected as echoes. The detecting transducers convert the echo signals to electronic signals and, after amplification and digitization, furnishes these signals to a beam former. The beam former in turn calculates locations of echo sources, and typically includes simple filters and signal averagers. After beam forming, the calculated positional information is used to generate two-dimensional data that can be presented as an image.
As an ultrasonic signal propagates through a medium of interest, additional harmonic frequency components are generated. These components are analyzed and associated with the visualization of boundaries, or image contrast agents designed to reradiate ultrasound at specific harmonic frequencies. Unwanted reflections within the ultrasound device can cause noise and the appearance of artifacts (i.e., artifacts are image features that result from the imaging system and not from the medium of interest) in the image. Artifacts may obscure the underlying image of the medium of interest.
One-dimensional acoustic arrays have a depth of focus that is usually determined by a nonadjustable passive acoustic focusing means affixed to each transducer. This type of focusing necessitates using multiple transducers for different applications with different depths of focus.
The width of the beam determines the smallest feature size or distance between observable features that can be observed. The imaging system determines position by treating the beam as if it had essentially a point width. Consequently, efforts have been made to achieve a narrow beam of focus, because when the beam is wide, features that are slightly displaced from the point of interest also appear to be at the point of interest. The longer the region having a narrow beam of focus, the greater the range of depth into the medium of interest that can be imaged.
The beam intensity as a function of position may oscillate rather than fall off monotonically as a function of distance from the center of the beam. These oscillations in beam intensity are often called “side lobes.” In the prior art, the term “apodisation” refers to the process of affecting the distribution of beam intensity to reduce side lobes. However, in the remainder of this specification the term “apodisation” is used to refer to tailoring the distribution of beam intensity for a desired beam characteristic such as having a Guassian or sinc function (without the side lobes) distribution of beam intensity.
Steering refers to changing the direction of a beam. Aperture refers to the size of the transducer or group of transducers being used to transmit or receive an acoustic beam.
The prior art process of producing, receiving, and analyzing an ultrasonic beam is called beam forming. The production of ultrasonic beams optionally includes apodisation, steering, focusing, and aperture control. Using a prior art data analysis technique each ultrasonic beam is used to generate a one dimensional set of echolocation data. In a typical implementation, a plurality of ultrasonic beams are used to scan a multi-dimensional volume.
FIG. 1A
shows a prior art acoustic focusing system
100
A, having a lens
102
A with a simple (i.e., a non-compound) surface, focusing a beam
104
A, into a focused region
106
, having a depth of focus
108
.
FIG. 1A
is a two dimensional depiction of the acoustic art focusing system
100
A. The third dimension is not discussed in conjunction with
FIG. 1A
, but will be discussed in conjunction with
FIGS. 1B and 1C
. In contrast to the usage of the terms “simple” and “compound” in optics, in the context of this specification simple and compound are used to describe the complexity of the curvature of the lens surface. Similarly, in this specification a lens having a compound surface curvature may be referred to as having a compound surface. If for each side of the lens the curvature can be described as one mathematically smooth and continuous curve of the same concavity or convexity, the lens is simple even if each side of the lens is characterized by a different curve. Otherwise, the lens and its associated curvature are complex or compound.
Lens
102
A is an acoustic lens, and beam
104
A is an ultrasound beam. The distance from lens
102
A to the center of focused region
106
is the depth of focus
108
. The focused region
106
represents a range of focus in which the beam is in focus. As long as the velocity in the medium surrounding lens
102
A is greater than in lens
102
A, a convex curvature will tend to focus beam
104
A to a point. When the velocity in the medium surrounding lens
102
A is lower than in lens
102
A a concave curvature will focus beam
104
A to a point or line.
The depth of focus
108
in ultrasonic imaging may be a significant parameter in obtaining high resolution. The direction of the depth of focus is normally taken to be perpendicular to the direction along which phased elements are aligned (in the downstream direction).
The prior art utilizes an acoustic lens, such as lens
102
A, of a fixed focus and relies upon a typical depth of focus of the acoustic beam, such as beam
104
A, during penetration of the signal into a medium of interest. The range of the focus or the length of the focused region
106
is often inadequate for imaging many of the different organs or regions of the human body, for example, that may constitute the medium of interest. One reason the range of focus may be inadequate is because the size of the medium of interest such as an organ may be larger than the focused region. Consequently, for some mediums of interest it may be necessary to switch lenses and/or transducer lenses to image the entire medium of interest when using a lens such as lens
102
A. Efforts have been made to extend the length of the focused region
106
by using lenses with compound surfaces.
FIG. 1B
shows a prior art acoustic focusing sy
Tarakci Umit
Xi Xufeng
Ben Loha
Carr & Ferrell LLP
Choi William
Zonare Medical Systems, Inc.
LandOfFree
System and method for acoustic imaging at two focal lengths... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System and method for acoustic imaging at two focal lengths..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System and method for acoustic imaging at two focal lengths... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3064379