Medical Ultrasound Imaging
Wednesday, 11 December 2024
 Info Sheets  Out- side     | 'Myocardial Perfusion' p2 Searchterm 'Myocardial Perfusion' found in 15 articles 15 definitions [ • ] Result Pages : •
Echocardiography is the ultrasound examination of the heart. Depending on the used ultrasound system, echocardiograms can be two-dimensional slices or 3D real-time images of the heart. Based on the ultrasound principles the direction and speed of blood flow can be utilized e.g., to diagnose a leaking or stenosed valve or to identify intracardiac shunts. Different types of echocardiography:
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contrast echocardiogram (CE);
The transthoracic echocardiogram (images are taken through the chest wall) is a non-invasive, highly accurate and quick assessment of the overall health of the heart. A more invasive method is to insert a specialized scope containing an echocardiography transducer (TEE probe) into the esophagus, and record images from there. The advantages are clearer images, since the transducer is closer to the heart. Contrast echocardiogram (CE) is already a valuable tool to delineate endocardial borders, direct invasive procedures, detect intracardiac shunts, assess myocardial perfusion and viability, and quantify coronary flow reserve and blood volumes (see also hemoglobin). The mechanism of microbubble CE is based on the physical principles of rarefaction and compression, leading to volume pulsations of microbubbles, and it is this change that results in CE signal. Stress echocardiograms are echocardiography exams used for detection of coronary artery disease. See also Diastole, Bicycle Stress Echocardiography, Resistive Index, and M-Mode Echocardiography.  Further Reading: Basics:
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Harmonic B-mode imaging takes advantage of the non-linear oscillation
of microbubbles. During harmonic imaging, the sound signal is transmitted at a frequency of around 1.5 to 2.0 MHz and received at twice this frequency. The microbubbles also reflect waves with wavelengths different from the transmitted one, the detectors can be set to receive only the latter ones and create only images of the contrast agent. Using bandpass filters the transmitted frequency is separated from the received signal to get improved visualization of vessels containing ultrasound contrast agents (USCAs). The signal to noise ratio during the presence of microbubbles in tissue is four- to fivefold higher at the harmonic compared with the basic frequency. Using harmonic B-mode imaging, harmonic frequencies produced by the ultrasound propagation through tissue have to be taken into account. The tissue reflection produces only a small amount harmonic energy compared to USCAs, but has to be removed by background subtraction for quantitative evaluation of myocardial perfusion. See also Non-linear Propagation. •
The earliest introduction of vascular ultrasound contrast agents (USCA) was by Gramiak and Shah in 1968, when they injected agitated saline into the ascending aorta and cardiac chambers during echocardiographic to opacify the left heart chamber. Strong echoes were produced within the heart, due to the acoustic mismatch between free air microbubbles in the saline and the surrounding blood. The disadvantage of this microbubbles produced by agitation, was that the air quickly leak from the thin bubble shell into the blood, where it dissolved. In addition, the small bubbles that were capable of traversing the capillary bed did not survive long enough for imaging because the air quickly dissipated into the blood. Aside from agitated saline, also hydrogen peroxide, indocyanine green dye, and iodinated contrast has been tested. The commercial development of contrast agents began in the 1980s with greatest effort to the stabilization of small microbubbles. The development generations by now:
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first generation USCA = non-transpulmonary vascular;;
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second generation USCA = transpulmonary vascular, with short half-life (less than 5 min);
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third generation USCA = transpulmonary vascular, with longer half-life (greater than 5 min).
To pass through the lung capillaries and enter into the systemic circulation, microspheres should be less than 10 μm in diameter. Air bubbles in that size range persist in solution for only a short time; too short for systemic vascular use. The first developed agent was Echovist (1982), which enabled the enhancement of the right heart. The second generation of echogenic agents, sonicated 5% human albumin-containing air bubbles (Albunex), were capable of transpulmonary passage but often failed to produce adequate imaging of the left heart. Both Albunex and Levovist utilize air as the gas component of the microbubble. In the 1990s newer developed agents with fluorocarbon gases and albumin, surfactant, lipid, or polymer shells have an increased persistence of the microspheres. This smaller, more stable microbubble agents, and improvements in ultrasound technology, have resulted in a wider range of application including myocardial perfusion. See also First Generation USCA, Second Generation USCA, and Third Generation USCA. Further Reading: Basics:
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Lantheus Medical Imaging, Inc. engages in discovering, developing, and marketing medical imaging agents. Lantheus Medical Imaging has headquarters in North Billerica, Massachusetts, and offices in Puerto Rico, Canada, and Australia. During its history, the company launched the products Cardiolite (Technetium Tc99m Sestamibi Preparation Kit), which has become the gold standard for use in myocardial perfusion imaging, and Definity (perflutren lipid microsphere) for use in suboptimal echocardiograms.From 2001 to 2008 Lantheus was part of the Bristol-Myers Squibb Medical Imaging, Inc. group. Ultrasound Contrast Agents:
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MRX 115 is a liposome based microbubble formulation and has been demonstrated as effective for cardiac blood pool imaging, Doppler enhancement and potentially myocardial perfusion imaging. MRX 115 is based upon the demand for a stable, robust blood pool ultrasound contrast agents, also called DMP 115 or Aerosomes™ (ImaRx LLC) and now Definity®. Result Pages : | Share This Page     Look Ups |
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