Myocardial contrast echo effect: the dilemma of coronary blood flow and volume

Comparison of Uterine Receptivity between Fertile and Unexplained Infertile Women by Assessment of Endometrial and Subendometrial Perfusion Using Contrast-Enhanced Ultrasound: Which Index is Better--Peak Intensity or Area under the Curve?

The goal of this study was to compare uterine receptivity between women with normal fertility and those with unexplained infertility during natural cycles by assessment of endometrial and subendometrial perfusion using contrast-enhanced ultrasound (CEUS). We wanted to determine the better index: peak intensity (PI) or area under the curve (AUC). Thirty women with unexplained infertility were recruited into the study group, and 30 women with normal fertility were recruited into the control group. All women underwent CEUS during the late proliferative phase, ovulation phase, and implantation window of a menstrual cycle. Endometrial PI, endometrial AUC, subendometrial PI and subendometrial AUC were analyzed. In the late proliferative phase, the control group had a significantly higher endometrial PI (p < 0.001) as well as subendometrial PI (p < 0.001) and AUC (p = 0.004) than the study group. In the ovulation phase, the control group had a significantly higher endometrial PI (p < 0.001) and AUC (p = 0.021), as well as subendometrial PI (p < 0.001) and AUC (p = 0.003). During the implantation window, there were no significant differences between the two groups. Only subendometrial PI underwent a significant periodic change during the menstrual cycle in both groups. This finding was further confirmed by evaluation of the microvessel density of endometria. In conclusion, CEUS can be used to assess endometrial and subendometrial perfusion to evaluate uterine receptivity. Subendometrial PI was the most sensitive index compared with endometrial PI, endometrial AUC and subendometrial AUC.

Clinical experience with SonoVue in myocardial perfusion imaging

Ultrasound-enhancing agents have the potential to evaluate myocardial perfusion, adding a new dimension to echocardiography. This article summarizes the clinical studies involving SonoVue, a new intravenous ultrasound contrast agent, in assessing myocardial perfusion. Safe and well tolerated, SonoVue coupled with echocardiography has the capability to identify perfusion abnormalities, as confirmed by scintigraphic imaging. While the optimal modalities for ultrasound perfusion assessment are not yet determined, numerous technical advances have been introduced: continuous infusion or slow intravenous administration of the agent, harmonic intermittent imaging, pulse inversion, background subtraction, color coding, and others. SonoVue is a promising new agent in the booming field of myocardial contrast echocardiography.

Abnormal myocardial blood flow distribution in patients with angina pectoris and normal coronary arteriograms

To evaluate coronary microvascular function and its relation to the genesis of chest pain and ST-segment depression during exercise in patients with syndrome X, pacing-induced changes in transmural myocardial blood flow distribution were quantitatively assessed by 2-dimensional myocardial contrast echocardiography. Of 25 patients with a history of chest pain and normal coronary arteries with the negative ergonovine test, 11 had exercise-induced chest pain and ST-segment depression (syndrome X), and 14 did not (controls). Myocardial blood flow distribution before and after pacing stress was assessed by measuring the ratio of the endocardial to epicardial gray level (ie, endo/epi gray level ratio) in the territory of the left anterior descending coronary artery. Pacing-induced chest pain and ST-segment depression were observed in syndrome X, but not in controls. The endo/epi gray level ratio in syndrome X significantly decreased after pacing (from 0.98+/-0.10 to 0.76+/-0.17, p<0.01), but not in controls (from 0.97+/-0.08 to 0.99+/-0.08, NS). Abnormal myocardial blood flow distribution may play an important role in exercise-induced chest pain and ST-segment depression in these patients.

Contrast echocardiography: review and future directions

Recent developments and advances in contrast echocardiography have been made to improve the diagnosis and evaluation of cardiac structures and function. By coupling new developments in acoustic instrumentation with new contrast agents, information that was previously difficult or impossible to gather by standard 2-dimensional echocardiography can now be obtained. Numerous studies have been published confirming the advantages of using contrast during echocardiographic studies, particularly with stress testing and myocardial perfusion. This review aims to summarize (1) the various contrast agents that are available or being developed; (2) factors that have been found to affect the strength of enhanced signals; (3) the new developments in instrumentation that improve the ability of scanners to differentiate echo contrast from cardiac tissue; and (4) the documented and possible future uses of contrast echocardiography.

[Applications of contrast media in echocardiography]

The development of contrast media in ultrasound has been slow and sporadic, and there are no fully satisfactory agents for clinical imaging to date. Most contrast agents consist of air filled microbubbles which generate scattered echoes and enhance the ultrasound information. In this article we review the different phases of contrast echocardiography their potentials and clinical applications. First, right-sided echocontrast which is mainly used for the assessment of intracardiac shunts. Second, left-sided contrast agents with smaller and more stable microbubbles, that allow the visualization of the left ventricle after intravenous injection. With these agents, one it is now possible to study myocardial perfusion which is one of the most attractive potentials of these types of agents.

[Methods for coronary functional assessment]

Functional evaluation of coronary vasomotion encompasses the assessment of dynamic changes in coronary lumen, vessel wall, blood flow, intracoronary pressure and myocardial perfusion in response to specific pharmacologic stimuli. These parameters are obtained to characterize mechanisms of physiologic regulation and to evaluate pathophysiologic processes and potential therapeutic strategies, especially with regard to the development of coronary atherosclerosis. To this end, a variety of direct (invasive) and indirect (non-invasive) diagnostic tools are employed. Among the invasive methods are registration of intracoronary Doppler flow, coronary pressure measurements, quantitative coronary angiography and intravascular ultrasound. The non-invasive modalities consist of coronary Doppler echocardiography, positron emission tomography, myocardial scintigraphy and magnetic resonance imaging. Because of the different technical and physiological principles involved, these methods are complementary by providing independent access to different aspects. The combined invasive functional testing as employed in the cardiac catheterization laboratory allows for a simultaneous synopsis of high-resolution coronary imaging and direct measurement of physiologic parameters during local application of defined pharmacologically active substances. However, the demands in terms of equipment, time and operator skills are high and limit this combined invasive approach to specialized centers. Besides these research purposes, a number of functional methods has entered the clinical arena. They are employed to evaluate the hemodynamic significance of coronary lesions and to assess functional outcome of therapeutic interventions in the catheterization laboratory. The underlying principles and applications of the different methods are described and an overview of selected results is presented.

Relation of contrast echo intensity and flow velocity to the amplification of contrast opacification produced by intermittent ultrasound transmission

Intermittent ultrasound transmission during contrast echocardiography, so-called transient response imaging (TRI), amplifies contrast intensity. This effect of TRI is attributed to decreased microbubble destruction by reduced exposure time to ultrasound energy. The present study examined the hypothesis that the signal amplification produced by TRI is related to the baseline intensity present in the image and the velocity of flow. We performed second harmonic (2.5/5.0 MHz) imaging during both continuous (frame rate 55 Hz) and electrocardiogram-triggered TRI mode. Contrast images produced by perfluorohexane microbubbles (AF0150) in a steady flow model were obtained every minute throughout the decay phase at transit velocities of 8.1, 6.2, 3.4, 1.9, and 0.7 cm/sec. The decay of videointensity over time could be fitted to a sigmoid curve for both imaging modes with r > 0.99 for individual velocities. The intensity with TRI was greater than that with continuous imaging (CI) at any time and velocity. The mean increase in intensity between modes throughout decay was 8.2 +/- 3.7, 12.8 +/- 4.2, 25.7 +/- 5.8, 49.5 +/- 8.0, and 64.0 +/- 14.4 gray levels for the respective velocity levels studied (p < 0.0001). Although varying with baseline intensity at early and late phases, the TRI amplification plateaued during middecay, and within the intensity range of 16 to 143 gray levels for CI and 67 to 186 gray levels for TRI, it showed no overlap among the different velocity levels. Thus the ability of TRI to enhance contrast opacification is much greater at low flow velocities, which has implications regarding the mechanism of TRI effect and preferential visualization of intramyocardial coronary arteries by this agent. Although this effect was influenced by the baseline intensity, it was relatively constant for each velocity level within an optimal intensity range during middecay, providing the basis for flow velocity measurement by contrast echo.

Flow-function relation in patients with chronic coronary artery disease and reduced regional function. A positron emission tomographic and two-dimensional echocardiographic study with coronary vasodilator stress

OBJECTIVES

We sought to elucidate the flow-function relation in chronic postischemic dysfunction during vasodilator stress.

BACKGROUND

In patients with ischemia and regional dysfunction, stress echocardiography can elicit three responses in the dysfunctioning segments: no change, improvement or worsening. The physiology underlying these responses is unclear.

METHODS

Seventeen patients with ischemia and left ventricular dysfunction underwent evaluation of regional function by two-dimensional echocardiography and myocardial blood flow by positron emission tomography and 13N-ammonia. Flow (ml/min per g) and function (regional wall motion score [RWMS] from 1 = normal to 4 = dyskinetic) were evaluated both at rest and after dipyridamole (0.56 mg/kg body weight over 4 min).

RESULTS

In 45 normal segments, rest to dipyridamole flow increased from 0.83 +/- 0.22 (mean +/- 1 SD) to 1.87 +/- 0.90 (p < 0.01) with a hyperkinetic contraction pattern. Among dysfunctioning segments, responders (n = 11) showed an upsloping flow-function curve during stress (i.e., increased function [RWMS rest 2.5 +/- 0.5 vs. dipyridamole 1.2 +/- 0.4] and increased flow [rest 0.69 +/- 0.30 vs. dipyridamole 1.89 +/- 1.43, p < 0.01]); nonresponders (n = 20) had a flat flow-function curve during dipyridamole (i.e., fixed function [RWMS rest and dipyridamole 2.6 +/- 0.5] and no flow increase [rest 0.64 +/- 0.24 vs. dipyridamole 0.87 +/- 0.51, p = NS): Ischemic segments (n = 9) exhibited a downsloping flow-function curve during dipyridamole (i.e., worsened function [RWMS rest 2 +/- 0.5, dipyridamole 3.1 +/- 0.6] and no significant flow change [rest 0.67 +/- 0.29 vs. dipyridamole 0.79 +/- 0.23, p = NS]).

CONCLUSIONS

Myocardial segments with rest dysfunction and a contractile reserve elicitable by a vasodilator stress more often exhibit residual flow reserve, whereas segments with a fixed or worsening mechanical response during stress show a flat flow response.

[New developments in parameter-oriented roentgen densitometry perfusion analysis within the scope of heart catheter studies]

X-ray densitometric evaluation of digital subtraction coronary arteriograms allows a qualitative and quantitative detection of contrast medium propagation through the epicardial coronary arteries, the capillary system and the coronary venous system. So-called "time-density-curves" (TDCs) can be generated following Lambert-Beer's law similar to indicator dilution curves by using contrast medium as the indicator. Several time and density parameters can be derived from these TDCs, which are related to local myocardial perfusion. Different animal validation studies have shown the applicability of this concept for in-vivo evaluation of coronary blood flow and myocardial perfusion. Nevertheless, absolute measurement of volumetric coronary blood flow or myocardial perfusion failed. Therefore, relative changes in coronary blood flow or myocardial perfusion in response to pharmacologically induced maximum hyperemia were measured and coronary or myocardial perfusion reserve was calculated as the ratio of hyperemic flow or perfusion divided by baseline values. Despite theoretical attractions for an application during routine cardiac catheterization, this densitometric approach did not get a wide acceptance. Primary reason for this limited use in specialized centers was the time consuming process of densitometric evaluation of the subtraction coronary arteriograms, which require digital cine angiography and necessitates enormous computer hard ware. This main limitation has been overcome since more powerful computer hard ware (processor speed, hard disk space, digitization boards) has become rapidly available during the last years at more moderate pricing and digital techniques today are state of the art in cardiac catheterization laboratories. In addition, soft ware program packages allowed an automatization of the digitization and densitometric evaluation process. These programs include ECG triggered cine image digitization with improved temporal resolution, semiautomatic definition of regions-of-interest including definition of reference regions-of-interest for the detection of background density changes and quality-controlled densitometric parameter analysis. This progress made an application during routine cardiac catheterization feasible. In animal validation studies this improved X-ray densitometric approach for evaluation of local myocardial perfusion was validated versus colour-coded microsphere techniques. The time parameter "rise time", defined as the time from the start of local contrast medium induced density change to its maximum revealed a close correlation (r2 = 0.965) to the results of the microsphere technique over a wide range of perfusion. We have applied this technique before and after coronary interventions such as balloon angioplasty and stenting. Results documented an improvement of poststenotic myocardial perfusion reserve immediately after coronary balloon angioplasty and an additional improvement after adjunct coronary stenting. Only after stenting but usually not after coronary balloon angioplasty alone poststenotic myocardial perfusion reserve gained the intraindividual reference level, measured in a perfusion bed supplied by an epicardial coronary artery without stenoses. These results documented the functional benefit of coronary stenting on poststenotic myocardial perfusion in addition to the well known morphologic benefit with the creation of a larger and more circular conduit.

Contrast ultrasonography for 2-D opacification of heart cavities, peripheral vessels, kidney and muscle

Contrast ultrasonography of peripheral vessels and peripheral organs has been only sparsely used to evaluate peripheral tissue blood flow. The purpose of the study was to characterize intraluminal opacification of renal and femoral arteries and veins, of skeletal muscle and renal parenchyma after intraarterial (IA) injection of BY963, a newly developed ultrasound contrast agent being evaluated in Phase II and III trials, and to compare it with opacification of heart cavities after intravenous injection (IV) in dogs. A further purpose was to quantitate possible opacification losses during the first transcapillary passage of BY963 through pulmonary and peripheral microcirculation. BY963 was administered at the dose of 5 mL/animal/vascular territory (0.2 mL/kg). The peak intensity (intensity units = IU) and the area-under-the-curve (AUC, IU x heart cycles) were estimated from regions-of-interest placed in the right ventricle (RV), left ventricle (LV), main renal artery and vein, kidney, femoral artery and vein and adductor muscle. Following single IV injection, the average peak intensity and AUC values were 33 +/- 3 (mean +/- SE) and 674 +/- 109 for the RV, and 27 +/- 2 and 870 +/- 74 for the LV (p < 0.05), respectively. Following single IA injection in the descending aorta, the average peak intensities and AUC values were 35 +/- 2 and 613 +/- 139 in the renal artery and 26 +/- 4 (p < 0.05) and 639 +/- 151 in the renal vein (nonsignificant), respectively. For the femoral vessels, the average peak intensities and AUC values were 30 +/- 3 and 469 +/- 63 in the femoral artery, and 21 +/- 2 (p < 0.05) and 517 +/- 44 in the femoral vein (nonsignificant), respectively. The values for the output-to-input intensity ratios for peak intensity and AUC were 0.82 +/- 0.06 and 1.36 +/- 0.12 for the LV/RV ratio, 0.73 +/- 0.08 and 1.02 +/- 0.05 for the renal vein/renal artery ratio, and 0.71 +/- 0.09 and 1.16 +/- 0.13 for the femoral vein/femoral artery ratio, respectively (nonsignificant). In conclusion, these results demonstrate the high opacification potency of BY963 in the LV, renal and femoral veins, being of the same order of magnitude as that in the RV, renal and femoral arteries, respectively. Finally, the loss of opacification properties of BY963 during the first transcapillary (pulmonary or peripheral-capillary) passage is minimal.

Detection of regional perfusion abnormalities during adenosine stress echocardiography with intravenous perfluorocarbon-exposed sonicated dextrose albumin

Although perfluorocarbon-exposed sonicated dextrose albumin (PESDA) microbubbles produce myocardial contrast after intravenous injection, it is unknown whether their use can accurately identify myocardial blood-flow abnormalities during stress echocardiography. Accordingly, we compared the background-subtracted peak myocardial videointensity (PMVI) after intravenous injections of PESDA before and during adenosine stress (100 to 140 units/kg/min) in 10 open-chest dogs with angiographically significant left circumflex artery disease. The ratios of PMVI in the ischemic region compared with the adjacent normal left anterior descending perfusion bed were measured, as were wall-thickening and coronary-flow ratios. In the dogs with a >50% diameter stenosis, there was a decrease in PMVI ratio during adenosine stress by >0.20 in 9, whereas wall-thickening ratios decreased in only 5. PMVI in the ischemic zone increased by <1.5 units during adenosine infusion in 8 of 10 dogs, whereas it increased by >1.5 units in 8 of 1O adjacent normal zones. We conclude that regional myocardial-perfusion abnormalities can be detected with intravenous PESDA during adenosine stress echocardiography.