Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-09-03
2001-05-01
Casler, Brian L. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06224553
ABSTRACT:
BACKGROUND OF THE INVENTION
Mechanical Variability of the Heart
Various cardiovascular variables demonstrate beat-to-beat variability around a constant or slowly changing mean value: Heart-rate variability (the beat-to-beat variability of cardiac cycle length, Woo et al., “Patterns of beat-to-beat heart rate variability in advanced heart failure”. American Heart Journal. 123(3):704-10, 1992), blood pressure variability (Parati et al, “Neural cardiovascular regulation and 24-hour blood pressure and heart rate variability”, Annals of the New York Academy of Sciences. 783:47-63, 1996), QT-interval variability and dispersion, the temporal and spatial variability of myocardial relaxation (Barr et al., “QT dispersion and sudden unexpected death in chronic heart failure”, The Lancet. vol. 343:327-329, 1994), T-wave alternans (Verrier and Nearing, “Electrophysiologic basis for T-wave alternans as an index of vulnerability to ventricular fibrillation”, Journal of Cardiovascular Electrophysiology, 5:445-461, 1994). Most of these indices are derived from the ECG and thus represent variabilities of electrical activation and relaxation mechanisms, either directly due to inherent factors or indirectly induced by other mechanisms (e.g. the effect of breathing on heart rate and blood pressure variabilities). Since mechanical variability is associated with electrical variability through electrical-mechanical coupling, partial information about mechanical variability can be gained from the electrical variability. However, there is no methodology and apparatus for direct evaluation of mechanical variability of myocardial activity, namely variability in the contraction, relaxation and filling phases of the heart cycle.
The aforementioned variability indices were demonstrated to be clinically useful in the evaluation of heart failure (Woo et ale. “Patterns of beat-to-beat heart rate variability in advanced heart failure”, American Heart Journal. 1223(3):704-10, 1992), risk of sudden-death (American College of Cardiology Cardiovascular Technology Assessment Committee, “Heart rate variability for risk stratification of life-threatening arrhythmias”, Journal of the American College of Cardiology, 22(3):948-50, 1993; Barr et al., “QT dispersion and sudden unexpected death in chronic heart failure”, The Lancet, 343:327-329, 1994), vulnerability to arrhythmia (e.g. Verrier and Nearing, “Electrophysiologic basis for T-wave alternans as an index of vulnerabilily to ventricular fibrillation”, Journal of Cardiovascular Electrophysiology, 5:445-461, 1994). These methodologies do not directly evaluate the mechanical variability of the heart and cannot provide cardiac regional variability. For many patients with regional myocardial injuries (like acute myocardial infarct), these methodologies may not be sensitive enough to contribute to the diagnosis. Accordingly, there is a need for a non-invasive methodology which can directly measure mechanical variability both globally (for the whole heart) and locally, and thus increase the sensitivity and specificity of correct diagnosis of various cardiac diseases.
Ultrasound Contrast Imaging
Ultrasound contrast imaging, the use of contrast agents to enhance ultrasound-derived images, is clinically useful to enable better evaluation of the scanned structures (e.g. enhancement of cardiac chambers) or to enable quantitative assessment of blood perfusion to various organs. Compared with other contrast-enhanced imaging modalities, like CT and MRI, ultrasonic imaging is simpler, faster and less expensive (Thomas J D, Griffin B P, White R D, “Cardiac imaging techniques: which, when, and why”, Cleveland Clinic Journal of Medicine, 63(4):213-20, 1996).
Although currently available contrast agents significantly enhance ultrasound imaging and enable assessment of blood perfusion to various organs (Porter T R, Li S, Kricsfeld D, Armbruster R W, “Detection of myocardial perfusion in multiple echocardiographic windows with one intravenous injection of micro bubbles using transient response second harmonic imaging”, Journal of the American College of Cardiology, 29(4):791-9, 1997), there is a need to further enhance the ultrasound-derived images in order to achieve efficacy comparable to other imaging modalities. This can be achieved by development of better contrast agents, or by enhancing the contrast agent effect through specifically designed ultrasound systems or ultrasound image modalities. The second-harmonic and power harmonic (Porter T, Xie F, Kricsfeld D, Armbruster R W, “Improved myocardial contrast with second harmonic transient ultrasound response imaging in humans using intravenous perfluorocarbon-exposed sonicated dextrose albumin”, Journal of the American College of Cardiology, 27(6):1497-501, 1996) are examples of contrast enhancement through changes in the ultrasound scanning technology. Yet another potential approach is to achieve the enhancement through processing of the ultrasound-derived images. Kaul and colleagues have used image subtraction methodology to enhance the contrast effect for myocardial perfusion studies (Kaul S, “Myocardial Contrast Echo”, Current Problems in Cardiology, 22(11):572-582, 1997). They have averaged several pre-contrast images and several with-contrast images and then subtracted the two averages to achieve an image composed mainly of the change between the pre-contrast and the contrast states. However, due to the random nature of the echoes from the bubbles the averaging process result in attenuation of the contrast effect.
Objects of the Invention
It is therefore an object of the present invention to provide a method and apparatus for the evaluation of myocardial variability through the measurement of the variability of ultrasound-derived images of the heart.
It is another object of the present invention to present the variability of the image of the heart using easily interpreted display for various clinical applications.
It is another object of the present invention to provide a method and apparatus for the enhancement of contrast ultrasound imaging through variability analysis of the contrast-echo images, either in real-time or by off-line analysis.
It is another object of the present invention to enhance blood-pool images (e.g. heart chambers) through variability analysis of the contrast-enhanced images.
Yet another object of the present invention is to enable quantitative assessment of the dynamics of blood perfusion to various organs and tissues based on variability analysis of the contrast-enhanced images.
Still another object of the present invention is to develop a methodology to present the enhanced contrast-echo image to the operator through either real-time or off-line image display.
In general, variability of an imaged object can be assessed by acquisition of multiple images and evaluation of the variation of the acquired images of the object. When the imaged object is the beating heart, or when one is interested in blood perfusion or flow, a difficulty arises due to the dynamic change of the cardiac shape or the pulsatile nature of blood flow. This can be overcome by comparing images acquired during the same phase of heart activity, which can be achieved by gating the images to a specific event which marks a specific phase at each cycle. The use of the R-wave of the ECG for gating the scanned images of cardiologic echo-Doppler system to achieve image enhancement by averaging the gated images was disclosed in a co-pending provisional patent application Ser. No. 60/018,466 of Nevo et al., filed May 28, 1996, now PCT/US97/09455, published Dec. 4, 1997 as WO 97/45058.
The current invention uses the gated images to evaluate the variability of the mechanical activity of the beating heart. The heart cycle is divided into “m” equal sequences, which are timed with respect to a fiducial point on the QRS complex, like the tip of the R-wave. Gating the acquired images of the heart eliminates the temporal variation of the image due to functional movement of heart structures (during contraction, relaxation and filling of the cardiac c
Casler Brian L.
Patel Maulin
Robin Medical Inc.
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