Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2002-06-18
2003-09-02
Jaworski, Francis J. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06612989
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present disclosure relates to ultrasonic imaging. More particularly, the invention relates to a system and method that improves contrast agent imaging diagnostic evaluations.
2. Discussion of the Related Art
Harmonic Imaging of Tissue
Ultrasonic imaging has quickly replaced conventional X-rays in many clinical applications because of its image quality, safety, and low cost. Ultrasonic images are typically formed through the use of phased or linear array transducers which are capable of transmitting and receiving pressure waves directed into a medium such as the human body. Such transducers normally comprise multi-element piezoelectric materials, which vibrate in response to an applied voltage to produce the desired pressure waves. Piezoelectric transducer elements are typically constructed of lead zirconate titanate (PZT), with a plurality of elements being arranged to form a transducer assembly. A new generation ultrasonic transducer known as a micro-machined ultrasonic transducer (MUT) is also available. MUTs are typically fabricated using semiconductor-manufacturing techniques with a number of elements typically formed on a common substrate to form a transducer assembly. Regardless of the type of transducer element, the transducer elements may be further assembled into a housing possibly containing control electronics, the combination of which forms an ultrasonic probe. The ultrasonic probe may include acoustic matching layers between the surface of the various types of elements and the probe body. Ultrasonic probes may then be used along with an ultrasonic transceiver to transmit and receive ultrasonic pressure waves through the various tissues of the body. The various ultrasonic responses may be further processed by an ultrasonic imaging system to display the various structures and tissues of the body.
To obtain high quality images, the ultrasonic probe must be constructed so as to produce specified frequencies of pressure waves. Generally speaking, low frequency pressure waves provide deep penetration into the medium (e.g., the body), but produce poor resolution images due to the length of the transmitted wavelengths. On the other hand, high frequency pressure waves provide high resolution, but with poor penetration. Accordingly, the selection of a transmitting frequency has involved balancing resolution and penetration concerns. Unfortunately, resolution has suffered at the expense of deeper penetration and vice versa. Traditionally, the frequency selection problem has been addressed by selecting the highest imaging frequency (i.e., best resolution) which offers adequate penetration for a given application. For example, in adult cardiac imaging, frequencies in the 2 MHz to 3 MHz range are typically selected in order to penetrate the chest wall. Lower frequencies have not been used due to the lack of sufficient image resolution. Higher frequencies are often used for radiology and vascular applications where fine resolution is required to image small lesions and arteries affected by stenotic obstructions.
Recently, new methods have been studied in an effort to obtain both high resolution and deep penetration. One such method is known as harmonic imaging. Harmonic imaging is grounded on the phenomenon that objects, such as human tissues, develop and return their own non-fundamental frequencies, i.e., harmonics of the fundamental frequency. This phenomenon and increased image processing capabilities of digital technology, make it is possible to excite an object to be imaged by transmitting at a low (and therefore deeply penetrating) fundamental frequency (f
o
) and receiving reflections at a higher frequency harmonic (e.g., 2f
o
) to form a high resolution image of an object. By way of example, a wave having a frequency less than 2 MHz can be transmitted into the human body and one or more harmonic waves having frequencies greater than 3 MHz can be received to form the image. By imaging in this manner, deep penetration can be achieved without a concomitant loss of image resolution.
However, in order to achieve the benefits of transmitting at a lower frequency for tissue penetration and receiving a harmonic frequency for improved imaging resolution, broadband transducers are required which can transmit sufficient bandwidth about the fundamental frequency and receive sufficient bandwidth about the harmonic(s). The s
4
transducer available with the SONOS™ 5500 an ultrasound imaging system manufactured by and commercially available from Agilent Technologies, U.S.A., has a suitable bandwidth to achieve harmonic imaging with a single transducer thus providing a significant clinical improvement. Furthermore, the combination of the s
4
transducer and the SONOS™ 5500 provide multiple imaging parameter choices using a single transducer, thus providing a penetration choice as well as a resolution choice.
Conventional ultrasound scanners can create two-dimensional B-mode images of tissue in which the brightness of a pixel is based on the intensity of the received ultrasonic echoes. In color flow imaging, the flow of blood or movement of tissue can be imaged. Measurement of blood flow in the heart and vessels using the Doppler effect is well known. The frequency shift of backscattered ultrasound waves may be used to measure the velocity of the backscatterers from tissues or blood. The frequency of sound waves reflecting from the inside of blood vessels, heart cavities, etc. is shifted in proportion to the velocity of the blood cells. The frequency of ultrasonic waves reflected from cells moving towards the transducer is positively shifted. Conversely, the frequency of ultrasonic reflections from cells moving away from the transducer is negatively shifted. The Doppler shift may be displayed using different colors to represent speed and direction of flow. In order to assist diagnosticians and operators the color flow image may be superimposed on the B-mode image.
Persistence Processing
Ultrasound images, like other images are subject to noise which may adversely affect the intensity values associated with the various pixels used to recreate the object or objects being observed. Ultrasound images, like some other images, also suffer from the effects of temporal noise in real-time image sequences. Conventional ultrasound imaging systems normally have an image frame filtering function, which acts on data in either polar or Cartesian coordinate formats.
One method for reducing temporal noise from an image is to use a filter which weights and sums corresponding pixel intensity values from the previous frame with a present input frame to generate a display pixel intensity. This is sometimes called “temporal filtering” or “persistence filtering.” In this method, a previous display frame's pixel may be averaged with an input frame's pixel, using a weighting value &agr;. The weighting value applies an equal degree of temporal filtering to all pixels in the frame. As a result, the method is data independent, i.e., not adaptive to changes in the underlying image data. While temporal noise is reduced, this simple filtering has the untoward effect of blurring or degrading small structures, the border of structures, or the borders of structures moving in the image field.
As will be further described below, continuous persistence filtering may be inappropriate when used in association with real-time imaging and high-power ultrasonic transmit pulses.
Contrast Imaging
Harmonic imaging can also be particularly effective when used in conjunction with contrast agents. In contrast agent imaging, gas or fluid filled micro-sphere contrast agents known as microbubbles are typically injected into a medium, normally the bloodstream. Because of their strong nonlinear response characteristics when insonified at particular frequencies, contrast agent resonation can be easily detected by an ultrasound transducer. By using harmonic imaging after introducing contrast agents, medical personnel can significantly enhance imaging capability for diagnosin
Jaworski Francis J.
Koninklijke Philips Electronics , N.V.
Patel Maulin
Vodopia John
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