Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-11-23
2002-04-09
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06368276
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to creating images by transmitting signals and sensing the effect of objects in the field of view on the signals.
2. Description of the Prior Art
Using available light and optical methods, popular video cameras and television receivers produce high quality pictures in the format of human vision in real time. Beamforming techniques emulate optical methods by transmitting and receiving signals with transducer arrays and processing such signals. These techniques are especially important where light fails to penetrate effectively. However, it is difficult to match quality of familiar television system images using such beamforming methods.
The beamformed television method, U.S. Pat. No. 5,598,206 (January 1997) Bullis, approaches this goal with a practical hardware configuration. It provides visual format images at a frame rate that enables motion viewing. A three dimensional variation, U.S. Pat. No. 5,966,169 (October 1999) Bullis, emphasizes a practical method to achieve fine grain range resolution to enable viewing from any arbitrary perspective. The three dimensional block acquisition enables tissue tracking, guidance of therapeutic instruments and monitoring of healing.
Beamformed television, as disclosed in U.S. Pat. No. 5,598,206 (January 1997) Bullis, used a pair of orthogonal linear arrays. One array was for transmitting signals and one array was for receiving signals. A system of intersecting beams resolved a scene, as required for visual format imaging. This method requires that beams be narrow in one dimension and wide in the other dimension. These beams were described as fan beams. They are asymmetrical about the beam axis. The linear array configuration efficiently produces such beams. However, efficient formation of a useful field of view leads to transducer However, efficient formation of a useful field of view leads to transducer spacing, on center, also called pitch, that results in grating lobe effects. The general idea was to utilize one dimension of each array to resolve one angular, or cross range dimension, of a scene and the other dimension of that array to suppress grating lobes. The two arrays together resolved both cross range dimensions and limited the field of view in these dimensions. A variation involved limited steering that moved the field of view.
Although the directive effects of transmit array and receive array are described in beam pattern terms, there are important differences in the actual beamforming processes. Receive beamforming simply means adjusting for arrival time and adding signals to focus the collection of received signals. Simultaneous receive beamforming is based on the same set of received signals, except differing sets of arrival time adjustments are applied to sense in different directions and at differing focal zones. With sufficient computing power, all possible receive beam directions and focal zones can be sensed in a single transmit and receive event. Transmit beamforming means arranging signals to cause signals to be transmitted in a time relationship that causes focus in a selected direction and focal zone. Parallel transmit beamforming degenerates unless there is a way to separate signals. However, a need for rapid acquisition requires a similar parallel process.
A coding method was utilized. This enabled simultaneous excitation at different angles and at different focal zones. This was the needed complementary counterpart to simultaneous receive beamforming.
A combination of these complementary processes, operating with arrays that are orthogonal, provides highly efficient resolution in two cross range, or angular, dimensions. The resolving system can be accomplished with arrays that are straight line arrangements of elements that are called linear arrays.
It was found that grating lobe suppression could be accomplished by utilizing the width dimension of the linear arrays. A widening method was disclosed that utilized multiple transducers in a transverse arrangement relative to the line of the array. A specified alternative was to widen the transducers in the transverse direction. These widening provisions tended to improve power handling and gain of the system but the disclosure, U.S. Pat. No. 5,598,206 (January 1997) Bullis, primarily discussed the grating lobe suppression effects. This prior disclosure noted that beam descriptions were inexact, especially in the near field. Thus, the possibilities of widening were not fully explored.
Three dimensional systems, U.S. Pat. No. 5,966,169 (October 1999) Bullis, were made practical by the step chirp method for resolving the range dimension of the field of view. This was found to be possible to operate in combination with the coding method and other features of the preceding invention, U.S. Pat. No. 5,598,206 (January 1997) Bullis.
The three dimensional method made medical imaging a compelling development project because it solved the fundamental problem of wide slice thickness that is inescapably the result of a narrow aperture that is the width dimension of the conventional, single array systems. The orthogonal array method was a leap ahead of industry efforts that are based on “1.5D” methods. But it was a completely electronic scanning system. The industry tendency is to utilize the conventional architecture with mechanical scanning apparatus to acquire a three dimensional block of image data.
Because the architecture of the orthogonal array applications is so different from the conventional form, it became useful to use a differentiating term. Instead of calling this technology ultrasound, the name orthosound was chosen. This emphasizes the orthogonal relationships in the architecture and helps to convey that this is not a small improvement to the familiar form, but is a major change in system architecture with very substantial benefits.
However, there are deep penetration issues with medical imaging using orthogonal array technology. In the terminology of this disclosure, these issues are categorized as (1) signal to noise ratio effects, (2) signal to clutter ratio effects, and (3) waveform and wave-front distortion effects. Signal to noise ratio can be improved by increasing transmitted signal level. Signal to clutter ratio stays the same if transmitted signal level is changed. Both of these can be improved by improving resolution where signal to noise ratio benefits from improved gain and signal to clutter level improves because clutter sources are excluded from a given resolution cell. Clutter is distinguished from artifacts. Clutter is a general background level that shows no recognizable shape. It comes from reflection signals that overpower the system capability to discriminate. Artifacts are similar except they are objects in the image that are recognizable representations of real objects that are incorrectly brought into the field of view. A pixel of a display represents the composite signal strength of the scattering sources that are within an associated voxel. A voxel is a volume resolution cell. Distortion effects degrade the signal processing operations.
The important qualities of a system begin with the capability to resolve a voxel. The degree of noise and clutter that are represented in the voxel also determine system capability. Contrast must be sufficient that objects can be discerned in the presence of interference by the noise and clutter. However, a well resolved set of voxels can represent objects such that these objects can be recognized by a pattern that approximates their shape. This is a powerful system gain effect. Distortion of signal waveform and wave-front shape modifies the capability to resolve a voxel, causing reduction in signal level and reduction in capability to reject interference. Distortion effects also disturb patterns so that shapes are not adequately recognizable.
The term real time describes timeliness of the imaging operation, but it is not clearly or consistently used. It definitely does not mean a delay in processing such as developing a film. Fo
Imam Ali M.
Lateef Marvin M.
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