Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2000-06-05
2002-09-17
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06450961
ABSTRACT:
BACKGROUND OF THE INVENTION
1. (Field of the Invention)
The present invention relates to a diagnostic ultrasound apparatus, and in particular, a diagnostic ultrasound apparatus capable of performing imaging known as flash echo imaging (FEI) involving the injection of an ultrasound contrast agent into an object.
2. (Description of Prior Art)
An ultrasound diagnostic apparatus has now become an indispensable modality in clinical sites, because, in addition to display images in real time, they have advantages of relatively low in cost, no exposure of X-rays, and allowing blood flow imaging based on an ultrasound Doppler technique.
Particularly, this blood flow imaging, which is a function that is effective in finding lesions in the cardiac system or others, is known as a technique of color flow mapping CFM or color Doppler tomography and is provided as a standard option in most apparatuses.
As widely known, this display requires that the same raster location (direction) of an object be ultrasound-scanned a plurality of N times to acquire time-sequential echo signals and those echo signals undergo the detection of velocities of blood cells at a desired depth position based on the Doppler technique. That is, obtaining a Doppler signal requires the same raster location to be scanned repeatedly at certain intervals. Based on phase shift amounts (Doppler shift amounts) of per unit time obtained from a reflected signal from the blood cells, blood flow velocities can be obtained.
An echo signal resulting from each time of ultrasound scanning contains a reflection wave from objects in motion such as blood cells and a reflection wave from fixed objects almost stationary, such as a blood vessel wall or organic parenchyma. Additionally it is characteristic that the latter is a dominant in terms of reflection intensity, and further, Doppler shifts are caused in the former but not almost caused in the latter (clutter signal). Thus, a Doppler signal is extracted from the echo signal by a quadrature phase detector, and a clutter component is eliminated by an MTI filter from the Doppler signal on the basis of differences in the Doppler shifts, thereby a blood flow Doppler signal being detected efficiently. This blood flow Doppler signal is then subjected to frequency analysis with its N-piece Doppler data at each depth position, thereby a mean of its spectrum (Doppler frequency), dispersion amount, and/or intensity (power) reflected from blood cells being calculated. These pieces of blood flow information are two-dimensionally displayed on a monitor, normally, with a B-mode image placed as a background.
Recently, a technique has eagerly been tried that an ultrasound contrast agent is injected into an object's blood vessel to enhance scattering intensity of ultrasound for improving a diagnostic performance. Particularly, the performances of the contrast agent have noticeably been improved for the fast few years, such that contrast effects have been improved and the agent has been allowed to be injected from the vein, resulting in reduced invasiveness. It is expected that this kind of contrast agent become popular more. In association with this, there has been a need that a diagnostic ultrasound apparatus should have capability of performing diagnosis with making use of all the characters of the contrast agent that has been improving year by year. The background of this need will now be detailed.
An ultrasound contrast agent now under development consists mainly of a few microns of microbubbles. It has been known that these microbubbles easily collapse at almost as similar sound pressures as used for ordinary ultrasound diagnosis, and generates a higher-intensity harmonic corresponding to a harmonic of an ultrasound pulse when the collapse occurs, so that showing a higher contrast effect. An imaging technique called flash echo imaging (FEI) obtaining B-mode images utilizing this character is reported by, for example, a paper “Japanese Journal of Medical Ultrasonics, Vol.23, Supplement 1; June, 1996; 67-195,67-196” (the first report). This paper reports that, after a full charge of microbubbles by temporarily stopping ultrasound radiation, re-radiating an ultrasound pulse will cause large amounts of luminance enhancement in a tomographic image (tomographic image based on a harmonic component) simultaneously with the radiation, then the echo diminish immediately after that enhancement. This phenomenon is referred to as a flash echo phenomenon.
As to a prior art reference between color flow mapping and an ultrasound contrast agent, a paper “Japanese Journal of Medical Ultrasonics, Vol.22, Supplement 2; November, 1995; 66-33” is reported (the second report). This paper reports that, when an operator operates a freezing button to temporarily stop to transmit an ultrasound wave into the lever of a rabbit into which an ultrasound contrast agent was injected, then starts again the scanning with operating the freezing button, which provides the on/off states of transmission, a mosaic color image can be obtained in a velocity mode of color flow mapping. In this report, an image on this phenomenon is called cavitation image. Also reported is that this color image cannot be obtained at sound pressures less than a certain amount.
It is considered that this cavitation image can be obtained due to the same phenomenon as the flash echo image. Namely, considered is that this paper shows the fact that the flash echo phenomenon occurs with the fundamental wave of an ultrasound pulse and be observable using the color flow mapping. This also suggests that tissue blood (perfusion), which could not be imaged by the conventional color flow mapping, can be imaged.
Furthermore, the fact that the flash echo phenomenon is observable with even harmonic CFM images is reported by a paper “Japanese Journal of Medical Ultrasonics, Vol.23, Supplement 2; November, 1996; 68-156” (the third report). Described in this paper is that, when the flash echo phenomenon occurs, a mosaic color image is obtained in the velocity mode of color flow mapping with a harmonic. Also reported by this paper is that a Doppler spectrum of a harmonic on the flash echo phenomenon is broad as shown in FIG.
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This means that the perfusion can be imaged as well and its color image is shown in a mosaic. In other words, since Doppler shifts seldom occur in a clutter component that is an echo reflected by organic parenchyma, this component can be eliminated by an MTI filter, but a harmonic on the flash echo phenomenon passes the MTI filter and is imaged in the end, even if the contrast agent is in motion (for example, in a blood vessel) or at rest (for example, perfusion), because of a broad band of its Doppler spectrum. Additionally, an average of a Doppler spectrum at each of spatial points differ from each other at random, resulting in a mosaic image.
By the way, taking the similarity between the above second and third reports into account, it is assumed that the Doppler spectrum of a fundamental wave on the flash echo phenomenon is also broad in band.
Further, another report on the contrast agent is made by papers “Japanese Journal of Medical Ultrasonics, Vol.23, Supplement 2; November, 1996; 68-157” and “Journal of Medical Ultrasonics, Vol.24, No.3; March, 1997; 69P3-5” (the fourth report). These reports explain spectrums on the flash echo phenomenon occurring in three types of contrast agent. From these spectrums reported, it has been found that the fundamental wave is higher than the harmonics in sensitivity given when the flash echo phenomenon occurs.
Further, there has been known that the intensity of an echo signal on the flash echo phenomenon reduces gradually with time until the microbubbles collapse entirely.
A summary from a clinical point of view can be given as follow: (1) Using the flash echo phenomena enables an ultrasound contrast agent to be detected highly sensitively, (2) the CFM method is usable for observing perfusion, and (3) the CFM method is visualized in color so as to be easy to understand, while the velocity mode is visual
Mine Yoshitaka
Shiki Eiichi
Imam Ali M.
Lateef Marvin M.
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