Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2001-12-28
2004-03-30
Imam, Ali M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06712765
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to techniques and apparatus for imaging sections of a body by transmitting ultrasonic energy into the body and determining the characteristics of the ultrasonic energy reflected therefrom and, more particularly, to an improved ultrasonic scanning technique and system for such apparatus.
BACKGROUND OF THE INVENTION
Ultrasonic imaging techniques have become common in clinical diagnosis. Ultrasonic imaging is recognized as having a number of attributes. Ultrasound differs from other forms of radiation in its interaction with living systems in that it has the nature of a mechanical wave. Accordingly, information is available from its use which is of a different nature than that obtained by other methods and it is found to be complementary to other diagnostic methods, such as those employing X-rays. Also, the risk of tissue damage using ultrasound appears to be much less than the apparent risk associated with ionizing radiations such as X-rays.
Many diagnostic techniques using ultrasound are based on the pulse-echo method wherein pulses of ultrasonic energy are periodically generated by a suitable piezoelectric transducer. Each short pulse of ultrasonic energy is focused to a narrow beam which is transmitted into the patient's body wherein it eventually encounters interfaces between various different structures of the body. When there is a characteristic impedance mismatch at an interface, a portion of the ultrasonic energy is reflected at the boundary back toward the transducer. After generation of the pulse, the transducer operates in a “listening” mode wherein it converts received reflected energy or “echoes” from the body back into electrical signals. The time of arrival of these echoes depends on the ranges of the interfaces encountered and the propagation velocity of the ultrasound. Also, the amplitude of the echo is indicative of the reflection properties of the interface and, accordingly, of the nature of the characteristic structures forming the interface.
There are various ways in which the information in the received echoes can be usefully presented. One common form of display is the so-called “B-scan” wherein the echo information is of a form similar to conventional television display; i.e., the received echo signals are utilized to modulate the brightness of the display at each point scanned. This type of display is found especially useful when the ultrasonic energy is scanned transverse the body so that individual “ranging” information yields individual scan lines on the display, and successive transverse positions are utilized to obtain successive scan lines on the display. The two-dimensional B-scan technique yields a cross-sectional picture in the plane of the scan, and the resultant display can be viewed directly and/or recorded. It is known that ultrasound is almost totally reflected at interfaces with gas. This has led to the use of coupling through a fluid such as water or the use of a direct-contact type of transducer. In my U.S. Pat. No. 4,084,582, there is disclosed a type of apparatus having a console which typically includes a timing signal generator, energizing and receiving circuitry, and a display/recorder for displaying and/or recording image-representative electronic signals. A portable scanning head or module, suitable for being hand held, has a fluid-tight enclosure having a scanning window formed of a flexible material. A transducer in the portable scanning module converts energy from the energizing circuitry to ultrasonic energy and also converts received ultrasound echoes back into electrical signals which are coupled to the receiver circuitry. A focusing lens is coupled to the transducer, and a fluid, such as water, fills the portable scanning module in the region between the focusing lens and the scanning window. A reflective scanning mirror is disposed in the fluid, and a driving motor, energized in synchronism with the timing signals, drives the scanning mirror in periodic fashion. The ultrasound beam is reflected off the scanning mirror and into the body being examined via a scanning window formed of a rigid material.
For a two dimensional B-scan taken with the described type of scanning head, the dimensions scanned are: (1) depth into the body, which varies during each display scanline by virtue of the ultrasound beam travelling deeper into the body as time passes; and (2) a slower transverse scan caused by the scanning mirror. The display is typically in a rectangular format, e.g. the familiar television type of display with linear sweeps in both directions. However, the transverse scan of the ultrasound beam itself, as implemented by the scanning mirror, results in a sector scan. For distances deeper in the body, the fanning out of the sectors results in geometrical distortion when displayed on a linear rectangular display. For example, the azimuth dimension in the extreme far field may be, say 2½ times larger than the azimuth dimension in the extreme near field. Thus, the density of information on the left-hand side of a conventional left-to-right display is much higher than the density of information on the right-hand side of the display. In other words, what appear to be equal distances in the body on the left and right hand sides of the display are actually substantially different distances. A solution to this problem was offered in my U.S. Pat. No. 4,325,381, wherein the scanning window was in the form of an acoustic lens for converging the scan of the ultrasound beam incident thereon from within the enclosure. The acoustic lens thereby serves to reduce geometric distortion of the scan of the ultrasound beam. In an embodiment illustrated in the referenced '381 Patent, the window/lens is formed of a rigid plastic material in a substantially plano-concave shape, with the concave surface facing the outside of the enclosure. In this embodiment, the window/lens is provided with a focal length of between one and two times the distance between the reflective scanning means and the window/lens. A focal length of about one and-a-half times the distance between the reflective scanning means and the window/lens is indicated as being particularly suitable for a functioning embodiment.
It is among of the present invention to provide improvement over prior art approaches.
It is also among the objects of the present invention to provide a technique and apparatus that will facilitate the availability of high-quality inexpensive and portable ultrasonic imaging equipment for medical applications.
SUMMARY OF THE INVENTION
By taking advantage of the computing power of a personal computer, it should be possible to make very inexpensive ultrasound scanners for medical applications. By doing this, ultrasound scanners can be used in the physician's office as well as by medical technicians operating telemedicine facilities for remote diagnosis. In order to keep the cost low, the resolution high, and the size and complexity low, it would be desirable to use a system employing mechanically scanned ultrasound because these can be made with relatively large apertures. In the previously referenced '381 Patent there is described a mechanical scanner that had a window lens or “lens membrane” at the skin surface. In the geometry described in that Patent, it was not possible to have the center of the scan to be at the focal point of the lens membrane. A form of the present invention overcomes this deficiency.
It has been found that it is generally preferable to vary the focus of the scanner rather than use dynamic focus. Variable focus maximizes the intensity and resolution at all ranges. The focus cannot be varied dynamically in transmit. In my U.S. Pat. No. 4,257,271, selectable focus was achieved using a tapped delay line and a transducer with multiple electrodes. In accordance with a further form of the invention, a variable focus technique is implemented mechanically rather than electronically. This provides a continuous variation in focus without requiring multiple electrodes on the trans
Florida Atlantic University
Imam Ali M.
Novack Martin
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