Biomedical subjects

S B Feinstein

Publications and source records attributed to S B Feinstein.

44 records · Page 3Linked to original sources

PubMed1984

Two-dimensional contrast echocardiography. I. In vitro development and quantitative analysis of echo contrast agents.

To facilitate the passage of echo contrast agents through the microcirculation and the echocardiographic study of myocardial perfusion, ultrasonic energy (sonication) was employed to produce contrast agents consisting of relatively uniform, stable and small (less than 10 mu diameter) gaseous microbubbles suspended in liquid solutions. The size and persistence of the microbubbles was verified by light microscopy and an in vitro system were employed for comparative assessment of peak echo amplitude and echo persistence characteristics of various contrast agents. The study indicated that although a variety of hand-agitated and sonicated contrast agents provided satisfactory echo intensities, sonication was clearly superior to the hand-agitation method, because sonication produced smaller, more uniform and more stable microbubbles that may be suitable for myocardial contrast echocardiography. It is concluded that of the contrast agents examined, sonicated solutions of sorbitol (70%) and dextrose (70%) appeared to have particular potential because of the small sizes of the microbubbles (6 +/- 2 and 8 +/- 3 mu, respectively) and their prolonged in vitro persistence. The use of sonication to produce standardized, small and stable microbubbles should facilitate physiologic passage of the contrast agent through the capillary beds and allow two-dimensional imaging of the left heart myocardium during right-sided, aortic root, coronary sinus or intracoronary contrast injections.

Contrast Media↗

PubMedDate not supplied

The influence of intravenous Albunex injections on pulmonary arterial pressure, gas exchange, and left ventricular peak intensity.

Contrast ultrasonography may be used to assess regional tissue perfusion. The purpose of this study was to evaluate the safety and efficacy of a new, commercially prepared ultrasound contrast agent (Albunex) in dogs. The injections were administered from peripheral intravenous (IV), right atrial (RA), and pulmonary artery (PA) sites. Acute pulmonary hemodynamic and gas exchange effects of low-dose (0.5, 1.0, 2.0 ml) Phase I injections, and high-dose (2.0, 5.0, 10, 20 ml) Phase II injections of Albunex were evaluated in nine dogs. Immediately before and after each injection, pulmonary artery pressure (PAP) and oxygen tension (PO2) were determined. In addition, left ventricular cavity opacification was assessed visually and by videodensitometric off-line analysis. Visual assessment was performed by four blinded observers who graded on a scale of 0 to 3 (0 = no contrast enhancement of the left ventricular (LV) cavity; 1 = weak or suboptimal contrast enhancement; 2 = optimal or excellent contrast enhancement; and 3 = attenuation of the ultrasound signal following a contrast injection). Peak pixel intensity was also determined with videodensitometric analysis. Results showed that significant changes in PAP or PO2 were not noted after Albunex injections, regardless of injection site or dose range. The average change in PAP after Albunex injection was 1.0 mm Hg +/- 1.2 mm Hg (NS), and the average change in PO2 after Albunex injections was 6.2 mm Hg +/- 6.7 mm Hg (NS). The left ventricular cavity peak pixel intensity was dependent on both injection site (PA = RA > IV) and dose range (2.0 = 1.0 > 0.5).(ABSTRACT TRUNCATED AT 250 WORDS)

Albumins↗

PubMedDate not supplied

Pitfalls in quantitative contrast echocardiography: the steps to quantitation of perfusion.

Current methods used clinically to assess myocardial perfusion are invasive and expensive. As the technology of ultrasound imaging improves, CE may provide a relatively inexpensive, noninvasive means of quantitating myocardial perfusion. Issues regarding stability of microbubble contrast agents must be studied more closely under physiologic conditions. As such, encapsulated microbubbles may provide more stability under physiologic pressures than free gas microbubbles. Introducing high concentrations of contrast, either by hyperconcentrating the contrast agent or by increasing the injection rate, may provide greater stability under physiologic conditions. Further, before quantitative statement of tissue perfusion can be made, the relationship between tracer concentration and system response must be established. Further, a "linear" postprocessing ultrasound setting does not eliminate this requirement as data must still undergo nonlinear transformation during log compression and time-gain compensation. Additionally, issues regarding "electronic thresholding" must be explored more extensively in vivo. Commercial ultrasound scanners, in their present form, may not offer adequate sensitivity for absolute quantitative studies. Further development of modified ultrasound systems may provide sufficient sensitivity for quantitative perfusion imaging. CE offers a potentially powerful tool in the clinical management of patients with ischemic heart disease. Conventional coronary angiography provides information on the size of a lesion, but accompanying tissue perfusion distal to the lesion cannot be determined. Doppler ultrasonography determines velocity of blood flow in large vessels but does not offer the potential to quantitate tissue perfusion. Clearly, CE has a place in the future of diagnostic imaging. The recent work of Ito et al. demonstrated the qualitative potential of CE in the identification of "areas at risk" in patients who had undergone thrombolysis or percutaneous transluminal coronary angioplasty after an acute myocardial infarction. With further improvement in the ultrasound imaging techniques and microbubble stability, CE may offer an inexpensive, noninvasive means of assessing myocardial perfusion.

Albumins↗

PubMedDate not supplied

In vitro calculation of flow by use of contrast ultrasonography.

Contrast echocardiography has been used for qualitative assessment of cardiac function, and its potential for quantitative assessment of blood flow is being explored. With the development of an ultrasound contrast agent capable of passage through the microcirculation, a mathematical model based on classic dye dilution theory, and a digital ultrasound acquisition system, absolute quantitation of myocardial perfusion may be feasible. This study validates the mathematical model in a simple in vitro tube system. Flow was delivered at variable rates through an in vitro tube system while a longitudinal section was imaged with a modified commercial ultrasound scanner. Albunex contrast agent was injected, and videointensity data were captured and analyzed off line. Time-intensity curves were generated, and flow was calculated by use of a mathematical model derived from classic dye dilution mathematics. For 39 different flow rates, ranging for 9.2 to 110 ml/seconds, a correlation coefficient of r = 0.928 (p < 0.001) with a slope of 0.97 was calculated. We conclude that (1) contrast ultrasonography is capable of quantitative determination of flow in an in vitro system, and (2) a mathematical model based on dye dilution theory can be used to calculate flow with accuracy and precision.

Albumins↗

PubMedDate not supplied

Sonicated echocardiographic contrast agents: reproducibility studies.

This article describes the production, analysis, and reproducibility of forming microbubbles for contrast ultrasound imaging. The sonication method used to generate microbubbles was tested by four independent observers, and a subsequent laser particle counter analysis of microbubble size and concentration determined the reproducibility of the method. The results indicated that the mean bubble size was 3.3 +/- 1.2 microns for the entire group, based on three trials of each of the four participants. The characteristics of the bubble size of the microbubbles between observers were assessed with a Poisson distribution with the reproducibility based on the sample mean for each observer's trials. Standardization and calibration of the laser particle counter was accomplished with commercially available latex spheres, sonicated albumin microspheres, and a Coulter counter analysis. Our results indicate that the sonication technique generates small microbubbles with a reproducible uniform size distribution. The method of microbubble production is reproducible and can be widely applied for use in contrast echocardiographic perfusion imaging of tissue in a variety of research and clinical studies.

Air↗

PubMedDate not supplied

Optimizing albunex in the left ventricle: an analysis of the technical parameters of four ultrasound systems in canines and humans.

Albunex, an intravascular ultrasound contrast agent, has been used clinically to enhance echocardiographic images. The purpose of this study if (1) to determine whether varying the settings on commercially available ultrasound machines has an effect on left ventricular opacification after intravenously administered Albunex and if there is an effect on left ventricular opacification and (2) to determine the ideal settings for each ultrasound scanner. Six canine hearts were imaged with 1 ml injections of intravenously administered Albunex while varying the transducer frequency, preprocessing curves, postprocessing curves, and dynamic range on a variety of ultrasound units. Subsequently 50 human subjects underwent imaging with the various machines while the dynamic range and transducer frequencies were altered. All subjects received two or three intravenous injections of 10 ml Albunex. The opacification of the left ventricular cavitary images in both parts of the study were interpreted visually on a scale of 0 to 4 (0 = none, 1 = trace, 2 = moderate, 3 = dense, and 4 = ideal) by four observers. The maximum compression and transducer frequency of 3.5 MHz showed significant improvement of left ventricular opacification in both canines and humans. These studies have shown that (1) varying the ultrasound unit's parameters affects the quality of left ventricular imaging when Albunex is used to enhance the image, and (2) higher compression and a transducer frequency of 3.5 MHz tend to enhance Albunex images of canine and human hearts.

Albumins↗

PubMedDate not supplied

Reduced forward output states affect the left ventricular opacification of intravenously administered Albunex.

Albunex is an Food and Drug Administration-approved ultrasound contrast agent used for the enhancement of left ventricular endocardial borders. To determine the efficacy of intravenously administered Albunex with regard to left ventricular opacification (LVO), a retrospective analysis of 117 patients who received 202 injections of Albunex for enhancement of endocardial borders was done (dose 0.08 to 0.22 ml /kg). Patients were routinely referred to our echocardiography laboratory for stress echocardiography for standard indications. Optimized settings for contrast enhancement (3.5 MHz transducer frequency and maximum dynamic range) were used. Four observers graded LVO on a scale from 0 to 3 (0 = no Albunex seen in the ventricular cavity; 3 = Albunex densely seen in the ventricular cavity). Overall, LVO was reported in 166 (82%) of 202 injections or in 91 (78%) of 117 patients. A significant reduction in LVO was noted in patients with mitral regurgitation, tricuspid regurgitation, atrial fibrillation, systolic dysfunction, or pulmonary hypertension (increased pulmonary artery systemic pressure). LVO was seen in 88% of the patients without these conditions. However, only 12 (44%) of 27 patients with one or more of the above conditions had LVO (p < 0.05). LVO can be achieved in the majority of patients after intravenously administered Albunex when imaged with optimal transducer settings. A subset of patients with systolic dysfunction, mitral regurgitation, tricuspid regurgitation, atrial fibrillation, or increased pulmonary artery systemic pressure has less effective LVO with Albunex. Heart disease associated with decreased forward flow appears to be associated with diminished LVO.

Adult↗

PubMedDate not supplied

Advances in contrast echocardiography: intraoperative perfusion assessment.

Contrast ultrasound techniques provide on-line assessments of regional tissue perfusion. Intraoperative clinical studies of cardiac revascularization and renal transplantation have been performed and are currently under active clinical investigation. The potential to diagnose and manage patients through the use of contrast ultrasound techniques is just beginning to be realized. With continued development of the contrast agents and improved computer-aided software analyses programs, the future of the real-time perfusion imaging looks bright.

Cardiac Surgical Procedures↗