Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2001-07-06
2003-05-13
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S437000, C600S443000
Reexamination Certificate
active
06561982
ABSTRACT:
REFERENCE TO RELATED APPLICATION
The present patent application claims foreign priority benefits under 35 U.S.C. §119 to Italian patent application No. SV2000A000029, filed Jul. 6, 2000, now pending.
BACKGROUND OF THE INVENTION
The invention relates to a method for ultrasound imaging in the presence of contrast agents, particularly in the field of cardiology, including the following steps:
detecting physiological, especially electrocardiographic signals (ECG);
transforming said signals or a part thereof into pulses for controlling the activation of an ultrasonic probe pointed to the heart region, to synchronize scanning and echo signal acquisition with the heart cycle;
performing image acquisitions at predetermined phases of the heart cycle for predetermined limited times, with a predetermined ultrasonic beam intensity (I);
processing the received signals and transforming them into control signals which are viewable on a display.
A problem involved in the use of contrast agents consists in the need to limit ultrasonic pulse intensity to avoid destruction or damaging of contrast agent microbubbles.
Such intensity limitation has the side effect of decreasing the signal-to-noise ratio, thereby affecting image quality which is particularly important particularly in cardiology for assessment of ventricular wall motion.
Intensity reduction also generates problems in that reflected signals produced by contrast agent microbubbles have a typical frequency which is of the order of harmonics of the fundamental frequency of the ultrasonic beams transmitted to the body under examination, particularly of the second harmonic. Obviously, the amplitude of the second harmonic signal is lower, as compared with the one having the fundamental frequency whereby, in order to achieve sufficient intensities of second harmonic reflected signals, the power of the ultrasonic beams emitted by the probe shall normally be increased. If the intensity of second harmonic or higher-order harmonic reflected echoes is not sufficient, the fundamental frequency reflected signal, related to more echogenic tissues is similar to or higher than the second harmonic reflected signal related to contrast agents, whereby these echo signals from contrast agents can no longer be detected, the probe being somehow “dazzled” by fundamental frequency signals.
In order to obviate this drawback, several different scan protocols are known which allow to limit microbubble destruction to a certain predetermined amount.
According to U.S. Pat. No. 5,735,281, the control signal provided by an electrocardiogram is used to identify the heart cycle phase during which scanning is to be performed. In this document, at the beginning of each heart cycle phase, an image (referred to as image frame) is acquired by using high or full intensity ultrasonic scan beams, and this first image acquisition is followed, within the predetermined phase of each heart cycle, by a succession of image acquisitions with low intensity ultrasonic beams referred to as locator frames.
These subsequent low intensity scans/image acquisitions are used to form a real-time image only allowing to make sure that the probe is properly positioned. Due to the above reasons, image acquisitions which use low intensity ultrasonic beams do not allow to detect useful second harmonic signals, and for instance the presence of contrast agents in the object region, i.e. the coincidence of the scan with the presence of contrast agents in the object region cannot be detected. Contrast agents take a certain time before spreading in the object region.
According to the above mentioned document, the high or full intensity acquisition beam is repeatedly transmitted in every heart cycle at different times or phases of the cycle, which are defined on the basis of a predetermined variation rule, which may be also a statistically random rule. Images acquired at a high intensity are processed and displayed after acquisition. Such method does indeed at least limit the destruction of the microbubbles of the contrast agent due to the high mechanic index of the transmitted beam. However the method disclosed teaches to wait for the next heart cycle for acquiring the next image frame. Thus the acquisition of the useful images useful for diagnostic investigation is limited approximately to only a frame for each heart cyclus or to very long time periods between successive image frame acquisitions. This leads to a very low frame rate for the diagnostic useful image frame. The image refresh rate is very low.
Another draw back relates to the fact that only some image frames are taken in considering the physiological meaning of the heart cycle. In fact acquiring different image frames distributed during the entire heart cycles leads to mixing up images taken in different conditions of the blood circulation and may lead to incorrect interpretations of the results.
U.S. Pat. No. 5,957,845 provides a scan/acquisition protocol similar to the previous document, only differing in that the heart cycle phase during which high or full intensity scanning, i.e. image frame acquisitions, and the subsequent low intensity locator frame acquisitions are performed, is identical in each cycle, i.e. has an identical time location and an identical length in each heart cycle. Although this method discloses a multiple image frame acquisition in each heart cycle, according to the disclosure of U.S. Pat. No. 5,957,845, the time delay between the acquisition of high intensity image frames is very long, so that also in this case there is a very low image refresh rate of the diagnostically useful high resolution and quality images. Furthermore also the teaching of U.S. Pat. No. 5,957,845 does not consider the physiological effect on the conditions of circulation of the blood of the different phases of the heart cycle.
Document WO/030541 teaches to acquire only a high intensity image frame for each heart cycle. No particular choice of the time of acquisition of the image frame within the heart frame is made and no reason for the particular choice disclosed is given. The physiological meaning of the heart cycle on the condition of the blood circulation is totally ignored.
The above acquisition methods have serious limits, especially as regards the definition of the image obtained by the transmission of low or limited intensity ultrasonic beams. Reflected signals do not provide real-time images having a high definition, or anyway such a definition as to allow the use thereof for diagnostic purposes, but are only limited to the function of verifying the proper orientation of the probe with respect to the heart.
Moreover, in order to obtain high signal-to-noise ratio images, these methods require long scanning times distributed over a considerable number of heart cycles, to obtain a diagnostically valid image. Therefore they do not allow a real-time display of the ultrasound image derived by reflected echoes of high intensity ultrasonic signals.
A further drawback consists in that the images acquired by low intensity ultrasonic beams are not adapted to generate echoes having a sufficient intensity at the frequency of the second harmonic or of higher-order harmonics. This actually prevents a real-time detection of the presence of contrast agents which, as is known, reflect in a non linear manner, i.e. the echoes produced thereby have frequencies equal to the second harmonic of the fundamental frequency of illuminating ultrasonic beams, or to higher-order harmonics. In these conditions, i.e. with low intensity beam acquisitions, the reflected signal having frequencies equal to the second harmonic, i.e. relating to contrast agents, has a lower intensity as compared to the one having the fundamental frequency and relating to echogenic or hyperechogenic tissues. Therefore, it is apparent that low intensity acquisitions do not allow to verify in real-time and with due certainty that acquisition takes place while contrast agents are present in the object region.
Since images obtained by high or full intensity acquisition cannot be displayed in r
Cerofolini Marino
Greppi Barbara
Esaote S.p.A.
Jain Ruby
Lateef Marvin M.
Woodard, Emhardt, Naughton Moriarty & McNett LLP
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