Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1997-08-26
2003-03-25
Jaworski, Francis J. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06537222
ABSTRACT:
CROSS REFERENCES TO RELATED APPLICATIONS
1. Field of the Invention
The present invention relates to an improved apparatus and method for detecting contrast agents in ultrasonic imaging and, in particular, apparatus and methods for use of quadrature demodulation in detecting contrast agents.
2. Background of the Invention
Ultrasonic transducers and imaging systems are used in many medical applications and, in particular, for the non-invasive acquisition of images of organs and conditions within a patient, typical examples being the ultrasound imaging of fetuses and the heart. Such systems commonly use a linear or phased array transducer having multiple transmitting and receiving elements to transmit and receive narrowly focused and “steerable” beams, or “lines”, of ultrasonic energy into and from the body. The received beams, or lines, are reflected from the body's internal structures and contain amplitude or phase information, or both, that is used to generate images of the body's internal structures.
A primary problem in ultrasonic imaging has been that many of the body's internal structures have similar characteristics as regards the reflection of ultrasonic energy, so that it is difficult to obtain as clear and detailed images as is desired of many of the structures, such as the muscles of the heart.
This problem led to the development of alternative methods for imaging certain of the body's structures, such as the blood vessels of the heart. One of the most common imaging techniques, for example, referred to as an angiogram, requires the injection of a radio-opaque dye into the vessels to image the blood vessels of the heart with x-rays. Such techniques, however, are invasive or are otherwise unsatisfactory. For example, the use of x-ray imaging carries the risk of potential injury from radiation and involves complex, expensive and hazardous equipment. Also, radio-opaque dyes are potentially toxic to at least some patients and are not broken down in the body but are flushed from the body by natural waste processes, often requiring hours to disappear from the body.
A more recent development has been ultrasonic imaging using contrast agents injected into the blood stream. Ultrasonic contrast agents are now commercially available and are essentially small bubbles of gas, such as air, formed by agitating a liquid or bubbling gas through a liquid, such as a saline solution or a solution containing a bubble forming compound, such as albumin. When insonicated, the bubbles resonate at their resonant frequency and at the second harmonic of their resonant frequency, thereby returning an enhanced signal at or around these frequencies and thereby providing an enhanced image of the liquid or tissue containing the contrast agent. It is also well known that the bubbles “disappear” when insonicated at a high enough power level and the current theory is that the insonication ruptures the bubble's shell, thereby allowing the gas to dissipate into the surrounding liquid or tissue.
The use of ultrasonic contrast agents is thereby advantageous in allowing enhanced imaging using ultrasonics rather than x-rays, thereby eliminating the radiation hazard and allowing the use of equipment that is significantly less expensive and hazardous to use. Also, the agents are non-toxic and dissolve relatively quickly into waste products, such as air and albumin, that are normally found in the body and that are themselves non-toxic. Further, the insonication of the agent in itself destroys the agent, so that the agent can effectively be “erased” during or after the imaging process.
There are, however, a number of persistent problems in ultrasonic imaging using contrast agents, many of which concern the detection of contrast agents in the tissues of interest and the measurement of contrast agent concentrations in the tissues of interest.
For example, many ultrasonic imaging systems using contrast agents generate the desired image from two or more successive returned signals wherein the first returned signal is the sum of a component due to the bubbles being destroyed by the insonication and other components from other sources, such as the tissue, clutter and bubbles that were not destroyed by the insonication. The second returned signal includes components from the other sources, such as the tissue, clutter and bubbles that were not destroyed, but does not have a component from the bubbles being destroyed by the insonication that generated the first returned signal. As a consequence, an image primarily representing the contrast agent, that is, the bubbles being destroyed by the insonication, and thus an enhanced image of the tissues containing the contrast agent, can be generated by subtracting the components of the second returned signal from the components of the first returned signal.
This method may also be used to determine the concentration of contrast agent in the tissues of interest by determining the change in the returned signals between the first and second or later returned, and is thereby useful in other applications. For example, the change in concentration of contrast agent in the tissues of interest may be used to determine the rate of perfusion, that is, blood flow, in the tissues of interest. In a further extension of this method, the difference in rate of perfusion between, for example, a ischemia infarction and the heart muscle tissues may be used to detect the boundaries between the ischemia infarction and surrounding muscle tissue and thereby to generate enhanced images of the heart.
In another example, the ability to control the concentration of contrast agent in a region of interest, for example, by selectably destroying contrast agent through controlled insonication, is a significant advantage because too high a concentration of contrast agent results in saturation and non-linear, flat images due to interference between the bubbles. Also, and as a related problem, a too high a concentration of contrast agent in regions between the transducer and the region of interest will result in a shadowing effect wherein the near region image return will shadow, that is, hide or at least degrade the image in the region of interest.
All of these techniques, however, require the detection of contrast agents in the tissues of interest, or the measurement of contrast agent concentrations in the tissues of interest.
Broadly, the two primary methods for determining the components in returned signals or the difference in components between successive returned signals are, first, simply measuring the amplitude of the returned signals, and, second, measuring the complex vector components, that is, the phasor components, of the returned signals, for example, by quadrature demodulation of the returned signals into their amplitude and phase components. Of these two methods, quadrature demodulation would be generally preferred, for example, as providing more complete and detailed information regarding the returned signals and thus potentially providing superior images.
In quadrature demodulation, however, the returned signal at any particular spatial location in the tissues of interest is generally a complex number, or phasor. That is, the first returned signal is the vector sum of a phasor component due to the bubbles being destroyed by the insonication and other phasor components from other sources, such as the tissue, clutter and bubbles that were not destroyed by the insonication. The second returned signal, in turn, includes phasor components from the other sources, such as the tissue, clutter and bubbles that were not destroyed, but does not have a phasor component from the bubbles being destroyed by the insonication that generated the first returned signal.
The phasor components of the second returned signal, however, will generally differ to a greater or lessor degree from the corresponding phasor components of the first returned signal because of blood, tissue or transducer motion. This difference will generally primarily appear as a phase rotation, and will generally be a re
Clark David W.
Rafter Patrick G.
Jaworski Francis J.
Koninklijke Philips Electronics , N.V.
Vodopia John
LandOfFree
Methods for the detection of contrast agents in ultrasonic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Methods for the detection of contrast agents in ultrasonic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Methods for the detection of contrast agents in ultrasonic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3027390