Digital subtraction myocardial contrast echocardiography: design and application of a new analysis program for myocardial perfusion imaging

Combination of contrast with stress echocardiography: a practical guide to methods and interpretation

Contrast echocardiography has an established role for enhancement of the right heart Doppler signals, the detection of intra-cardiac shunts, and most recently for left ventricular cavity opacification (LVO). The use of intravenously administered micro-bubbles to traverse the myocardial microcirculation in order to outline myocardial viability and perfusion has been the source of research studies for a number of years. Despite the enthusiasm of investigators, myocardial contrast echocardiography (MCE) has not attained routine clinical use and LV opacification during stress has been less widely adopted than the data would support. The purpose of this review is to facilitate an understanding of the involved imaging technologies that have made this technique more feasible for clinical practice, and to guide its introduction into the practice of the non-expert user.

Heterogeneity of contrast effect during intermittent second harmonic myocardial contrast echocardiography in healthy patients

Intermittent harmonic imaging with contrast is increasingly used to detect perfusion defects in patients with coronary disease. To achieve this, image homogeneity and the ability to visualize segments on the lateral and distal portions of the imaging field are important. The objective of this study was to evaluate whether the use of specific postprocessing algorithms, such as background subtraction with color coding and parametric display, allows for improved image homogeneity compared with conventional intermittent second harmonic imaging. For this purpose, 20 participants who were free of cardiac abnormalities and in whom myocardial perfusion should by definition be homogeneously distributed, underwent contrast echocardiography during the constant intravenous infusion of 1.0 +/- 0.3 mL/min of perfluorocarbon-enhanced sonicated dextrose albumin. End-systolic ECG-triggered images were obtained from the apical 4-chamber view at pulsing intervals of 300-ms 1, 3, 5, and 8 cardiac cycles. For analysis, each set of images was aligned, averaged, background subtracted, and color coded. Pulsing intervals versus videointensity plots were then generated for each pixel in the images and fitted to an exponential function to produce parametric images of beta (an index of microbubble velocity) and A (a measure of myocardial blood volume). The heterogeneity of the contrast effect was evaluated by computing the coefficients of variation in each image. Contrast heterogeneity was >20% with all 4 methods. However, it was greater in gray-scale second harmonic (39 +/- 13%) and color-coded (47 +/- 16%) images than in parametric images of beta and A (24 +/- 14 and 24 +/- 8%, respectively; both P <.05 vs gray-scale second harmonic and color-coded images). With all 4 methods, basal- and apical-lateral segments contributed most to image heterogeneity, albeit significantly less so with parametric imaging. In conclusion, our data indicate that myocardial opacification is frequently heterogeneous in healthy participants, particularly when using gray-scale second harmonic and background-subtracted with color-coding imaging. Parametric imaging allows reduction, albeit incomplete, of the heterogeneity of the contrast effect and therefore improves image quality.

Digital analysis of myocardial contrast echocardiography: a clinical study using an air-filled agent in normal subjects

The purpose of the present study was to determine whether direct digital image analysis would allow improved detection of myocardial contrast. Eighteen normal subjects were recruited and separated into two groups. In group 1, the time-brightness curves of the left ventricular cavity and three myocardial perfusion beds were formed from digitized video tape, with output power and imaging time as secondary variables. In group 2, curves constructed from direct polar digital data were compared, with fundamental and second harmonic image formation as variables. In group 1 subjects, using fundamental imaging, the area under the curve in the left ventricular cavity increased slightly with intermittent imaging. No consistent myocardial opacification was identified. In group 2 subjects, using intermittent imaging, the area under the myocardial curve and peak intensity increased with high output, second harmonic imaging in the left anterior descending and right coronary artery regions. Intermittent, second harmonic imaging and digital processing can demonstrate myocardial contrast even with an air-filled agent.

Computerized analysis of myocardial echocardiographic enhancement during coronary revascularization by high-speed rotational atherectomy

A previous report demonstrated transient myocardial echocardiographic contrast (MEC) enhancement following high-speed rotational atherectomy (HSRA). This phenomenon was found to be correlated to the speed and duration of rotation and related to creation of cavitations. To determine other correlations and the significance of MEC, continuous echocardiographic recording was performed in 10 patients undergoing HSRA. Images were digitized and videointensity-time curves generated. Curve parameters were calculated and correlated with procedural variables, plaque mass, and side effects. Twenty-nine ablation passes in 10 patients were analyzed. Videointensity peaked 9-44 sec from initiation of ablation and decayed to a higher baseline level after each consecutive ablation. Increase in peak contrast intensity (PCI) from baseline and the percentage of the left ventricle undergoing enhancement were highest (33 +/- 31 gray level/pixel and 32% +/- 8%, mean +/- SD, respectively) after the second rotation and were not influenced by the duration of rotation. PCI, side effects, and transient left ventricular wall motion abnormalities were positively correlated with plaque mass, defined by the product of lesion length, diameter, and percent stenosis. HSRA resulted in significant myocardial echocardiographic contrast. PCI is related to ablation sequence and plaque mass. Plaque debris embolization is probably responsible for myocardial echocardiographic contrast and transient wall motion abnormalities. Cathet. Cardiovasc. Intervent. 49:39-44, 2000.

Effect of color coding and subtraction on the accuracy of contrast echocardiography

BACKGROUND

Contrast echocardiography may be used to assess myocardial perfusion. However, gray scale assessment of myocardial contrast echocardiography (MCE) is difficult because of variations in regional backscatter intensity, difficulties in distinguishing varying shades of gray, and artifacts or attenuation. We sought to determine whether the assessment of rest myocardial perfusion by MCE could be improved with subtraction and color coding.

METHODS AND RESULTS

MCE was performed in 31 patients with previous myocardial infarction with a 2nd generation agent (NC100100, Nycomed AS), using harmonic triggered or continuous imaging and gain settings were kept constant throughout the study. Digitized images were post processed by subtraction of baseline from contrast data and colorized to reflect the intensity of myocardial contrast. Gray scale MCE alone, MCE images combined with baseline and subtracted colorized images were scored independently using a 16 segment model. The presence and severity of myocardial contrast abnormalities were compared with perfusion defined by rest MIBI-SPECT. Segments that were not visualized by continuous (17%) or triggered imaging (14%) after color processing were excluded from further analysis. The specificity of gray scale MCE alone (56%) or MCE combined with baseline 2D (47%) was significantly enhanced by subtraction and color coding (76%, p<0.001) of triggered images. The accuracy of the gray scale approaches (respectively 52% and 47%) was increased to 70% (p<0.001). Similarly, for continuous images, the specificity of gray scale MCE with and without baseline comparison was 23% and 42% respectively, compared with 60% after post processing (p<0.001). The accuracy of colorized images (59%) was also significantly greater than gray scale MCE (43% and 29%, p<0.001). The sensitivity of MCE for both acquisitions was not altered by subtraction.

CONCLUSION

Post-processing with subtraction and color coding significantly improves the accuracy and specificity of MCE for detection of perfusion defects.

Contrast echocardiography: influence of ultrasonic machine settings, mixing conditions, and pressurization on pixel intensity and microsphere size of Albunex solutions in vitro

To use Albunex as a blood-flow tracer, the stability and consistency of microspheres under mixing conditions must be known. This study examined the effects of mixing conditions and machine settings on the size and echogenicity of Albunex solutions in vitro. Acoustic power, log compression, time-gain compensation, and transducer frequency were varied as Albunex solutions were imaged after mixing with magnetic stirring and pressurized. Higher acoustic power and lower transducer frequency decreased mean pixel intensity of Albunex solution images over time. Intensity, size, and number of Albunex microspheres were not significantly different between stirring speeds. The echogenicity of the Albunex solutions decreased with pressurization, and the critical pressure necessary to reduce the intensity to half its initial value increased with the logarithm of concentration (r = 0.91; p < 0.001). The microsphere size decreased with pressurization and remained smaller after pressure release (3.66 +/- 2.13 versus 1.47 +/- 0.95 microns; p < 0.01). These data indicate that acoustic power and transducer frequency may affect the physical properties of Albunex microspheres, decreasing mean videointensity. Pressure sensitivity of Albunex caused the decrease of videointensity and microsphere size.