Differential transesophageal echocardiographic diagnosis between linear artifacts and intraluminal flap of aortic dissection or disruption

BACKGROUND

The relatively low specificity of transesophageal echocardiography (TEE) for the diagnosis of aortic dissection (AD) or traumatic disruption of the aorta (TDA) has been attributed to linear artifacts. We sought to determine the incidence of intra-aortic linear artifacts in a cohort of patients with suspected AD or TDA, to establish the differential TEE diagnostic criteria between these artifacts and true aortic flaps, and to evaluate their impact on TEE diagnostic accuracy.

METHODS AND RESULTS

During an 8-year period, patients at high risk of AD (n = 261) or TDA (n = 90) who underwent a TEE study and had confirmed final diagnoses were studied. In an initial retrospective series, linear artifacts were observed within the ascending and descending aorta in 59 of 230 patients (26%) and 17 of 230 patients (7%), respectively. TEE findings associated with linear artifacts in the ascending aorta were as follows: displacement parallel to aortic walls; similar blood flow velocities on both sides; angle with the aortic wall > 85 degrees; and thickness > 2.5 mm. Diagnostic criteria of reverberant images in the descending aorta were as follows: displacement parallel to aortic walls, overimposition of blood flow, and similar blood flow velocities on both sides of the image. In a subsequent prospective series (n = 121), systematic use of these diagnostic criteria resulted in improved TEE specificity for the identification of true intra-aortic flaps.

CONCLUSIONS

Misleading intra-aortic linear artifacts are frequently observed in patients undergoing a TEE study for suspected AD or TDA. Routine use of the herein-proposed diagnostic criteria promises to further improve TEE diagnostic accuracy in the setting of severely ill patients with potential need for prompt surgery.

Accuracy of echocardiographic estimates of left ventricular mass in mice

Genetically modified mice have created the need for accurate noninvasive left ventricular mass (LVM) measurements. Recent technical advances provide two-dimensional images adequate for LVM calculation using the area-length method, which in humans is more accurate than M-mode methods. We compared the standard M-mode and area-length methods in mice over a wide range of LV sizes and weights (62-210 mg). Ninety-one CD-1 mice (38 normal, 44 aortic banded, and 9 inherited dilated cardiomyopathy) were imaged transthoracically (15 MHz linear transducer, 120 Hz). Compared with necropsy weights, area-length measurements showed higher correlation than the M-mode method (r = 0.92 vs. 0.81), increased accuracy (bias +/- SD: 1.4 +/- 27.1% vs. 36.7 +/- 51.6%), and improved reproducibility. There was no significant difference between end-systolic and end-diastolic estimates. The truncated ellipsoid estimation produced results similar in accuracy to the area-length method. Whereas current echocardiographic technology can accurately and reproducibly estimate LVM with the two-dimensional, area-length formula in a variety of mouse models, additional technological improvements, rather than refinement of geometric models, will likely improve the accuracy of this methodology.

Recent advances in echocardiographic evaluation of left ventricular anatomy, perfusion, and function

This article provides a brief overview of several recently developed, emerging technologies and discusses their potential uses on clinical grounds. These new technologies include three-dimensional imaging, objective automated evaluation of ventricular function with acoustic quantification, assessment of regional ventricular performance using color kinesis and tissue Doppler imaging, harmonic imaging, and power Doppler imaging. Our hope is that readers will gain a better understanding of the principles underlying these technological advances, which will help them to integrate these new techniques efficiently into their clinical practices.

Detection of regional temporal abnormalities in left ventricular function during acute myocardial ischemia

Echocardiographic diagnosis of myocardial ischemia is based on visualizing hypokinesis, which occurs late in the ischemic cascade. We hypothesized that temporal changes in endocardial motion may constitute sensitive early markers of ischemia. Two protocols were performed in 19 anesthetized pigs. Protocol 1 included 54 intracoronary balloon occlusions. Transthoracic images were acquired at baseline and every 15 s during 5 min of occlusion and reperfusion. In protocol 2, ischemia was induced in 12 animals by use of graded dobutamine infusion, after creating significant partial occlusions without a resting wall motion abnormality. Systolic and diastolic endocardial motion was color encoded using color kinesis and analyzed using custom software. All ischemic episodes caused detectable and reversible changes. The earliest sign of ischemia was tardokinesis in 31/54 occlusions, whereas hypokinesis appeared first in 23/54 cases. Dobutamine-induced ischemia caused tardokinesis first in 9/12 and hypokinesis in 3/12 animals. Reversible ischemic changes in regional left ventricular performance can be objectively detected using analysis of echocardiographic images and will likely improve the early noninvasive diagnosis of acute ischemia.

The left ventricular stress-velocity relation in transgenic mice expressing a dominant negative CREB transgene in the heart

OBJECTIVE

CREB(A133) transgenic mice that express a dominant negative CREB transcription factor in cardiomyocytes develop a dilated cardiomyopathy that is anatomically, physiologically, and clinically similar to human idiopathic dilated cardiomyopathy. The goals of this study were to quantitate left ventricular (LV) contractility and measure cardiac reserve in CREB(A133) mice by using the relation of end-systolic wall stress to the velocity of fiber shortening.

METHODS

A total of 37 adult CD-1 mice (including both nontransgenic and CREB(A133) transgenic mice) were studied with simultaneously acquired high-fidelity instantaneous aortic pressures and 2-dimensionally targeted M-mode echocardiograms.

RESULTS

CREB(A133) mice displayed significantly lower values of LV fiber shortening velocities over a wide range of afterloads, and they displayed smaller dobutamine-induced shifts from baseline contractility relations. Counterbalancing effects of differences in LV geometry and aortic pressures resulted in comparable levels of LV wall stress during ejection in both groups.

CONCLUSION

These results demonstrate directly that CREB(A133) mice display reduced LV contractility at baseline and decreased cardiac reserve.

Effects of aging on left atrial reservoir, conduit, and booster pump function: a multi-institution acoustic quantification study

OBJECTIVE

To assess the feasibility of measuring left atrial (LA) function with acoustic quantification (AQ) and then assess the effects of age and sex on LA reservoir, conduit, and booster pump function.

PATIENTS AND SETTING

165 subjects without cardiovascular disease, 3-79 years old, were enrolled by six tertiary hospital centres.

INTERVENTIONS

Continuous LA AQ area data were acquired and signal averaged to form composite waveforms which were analysed off-line.

MAIN OUTCOME MEASURES

Parameters of LA performance according to age and sex.

RESULTS

Signal averaged LA waveforms were sufficiently stable and detailed to allow automated analysis in all cases. An age related increase in LA area was noted. LA reservoir function did not vary with age or sex. All parameters of LA passive and active emptying revealed a significant age dependency. Overall, the passive emptying phase accounted for 66% of total LA emptying ranging from 76% in the youngest to 44% in the oldest decade. LA contraction accounted for 34% of atrial emptying in all subjects combined with the older subjects being more dependent on atrial booster pump function. When adjusted for atrial size, there were no sex related differences in LA function.

CONCLUSIONS

LA reservoir, conduit, and booster pump function can be assessed with automated analysis of signal averaged LA area waveforms. As LA performance varies with age, establishment of normal values should enhance the evaluation of pathologic states in which LA function is important.

Validation of a mouse conductance system to determine LV volume: comparison to echocardiography and crystals

The application of left ventricular pressure-volume analysis to transgenic mice to characterize the cardiac phenotype has been problematic due to the small size of the mouse heart and the rapid heartbeat. Conductance technology has been miniaturized for the mouse and can solve this problem. However, there has been no validation of this technique. Accordingly, we performed echocardiography followed by simultaneous ultrasonic crystals, flow probe, and conductance studies in 18 CD-1 mice. Raw conductance volumes were corrected for an inhomogenous electrical field (alpha) and parallel conductance (G(pi)) yielding a stroke volume of 14.1 +/- 3.7 microliter/beat, end-diastolic volume of 20.8 +/- 6.5 microliter, and end-systolic volume of 9.0 +/- 5.8 microliter. The mean conductance volumes were no different from those derived by flow probe and echocardiography but did differ from ultrasonic crystals. G(pi) was determined to be 14.9 +/- 8.7 microliter. However, hypertonic saline altered dimension and pressure in the mouse left ventricle. Although G(pi) can be determined by the hypertonic saline method, saline altered hemodynamics, questioning its validity in the mouse. Although mean measures of absolute volume may be similar among different techniques, individual values did not correlate.

Electronic transmission of digital echocardiographic studies: effects of MPEG compression

The acquisition, storage and retrieval of digital echocardiographic studies greatly facilitates image review and quantitation and permits the transmission of studies electronically. However, the considerable size of digital echocardiographic data files makes transmission over existing networks slow and impractical. Reduction in the size of these data files can be accomplished with digital image compression. We sought to evaluate the effects of MPEG-1 compression on the transfer time of digital echocardiographic studies over currently available network connections. Ninety consecutive routine clinical echocardiographic studies were randomly compressed at one of three compression ratios 60:1, 80:1, or 120:1 and sent to a receiving terminal using simulated transmission rates. Compression of digital echocardiographic studies at these ratios which, have been shown to maintain diagnostic image quality, reduced the size of digital echocardiographic studies to less than 1% of their original sizes which allowed transmission of echocardiographic studies over networks using 3ISDN or T1 lines with minimal waiting time.

Power Doppler imaging as a basis for automated endocardial border detection during left ventricular contrast enhancement

Echocardiographic evaluation of left ventricular (LV) systolic function relies on endocardial visualization, which can be improved when necessary using contrast enhancement. However, there is no method to automatically detect the endocardial boundary from contrast-enhanced images. We hypothesized that this could be achieved using harmonic power Doppler imaging. Twenty-two patients were studied in two protocols: (1) 11 patients with poorly visualized endocardium (> 3 contiguous segments not visualized) and (2) 11 consecutive patients referred for dobutamine stress echocardiography who were studied at rest and at peak dobutamine infusion. Patients were imaged in the apical four-chamber view using harmonic power Doppler mode (HP SONOS 5500) during LV contrast enhancement (Optison or Definity DMP115). Digital images were analyzed using custom software designed to automatically extract the endocardial boundary from power Doppler color overlays. LV cavity area was automatically measured frame-by-frame throughout the cardiac cycle, and fractional area change calculated and compared with those obtained by manually tracing the endocardial boundary in end-systolic and end-diastolic gray scale images. Successful border detection and tracking throughout the cardiac cycle was possible in 9 of 11 patients with poor endocardial definition and in 10 of 11 unselected patients undergoing dobutamine stress testing. Fractional area change obtained from power Doppler images correlated well with manually traced area changes (r = 0.82 and r = 0.97, in protocols 1 and 2, respectively). Harmonic power Doppler imaging with contrast may provide a simple method for semi-automated border detection and thus facilitate the objective evaluation of LV function both at rest and under conditions of stress testing. This methodology may prove to be particularly useful in patients with poorly visualized endocardium.

Effects of exercise training on LV performance and mortality in a murine model of dilated cardiomyopathy

Dilated cardiomyopathy (DC) is a leading cause of cardiovascular morbidity, and nonpharmacological therapies, such as exercise training, have been suggested. The effects of exercise on left ventricular (LV) function and mortality remain controversial. Using a recently described murine model of DC, which involves a dominant-negative form of the cAMP response element binding protein (CREB) transcription factor (CREB(A133)) under the control of the cardiac myocyte-specific alpha-myosin heavy chain promoter, we sought to assess the effects of moderate-intensity exercise training on LV performance and mortality. Thirty-two transgenic mice were subjected to exercise training and compared with sedentary controls. There was progressive enlargement in LV dimensions in both the sedentary and exercise-trained mice. LV performance was progressively impaired, and exercise training did not prevent this decline. The sedentary CREB(A133) mice displayed a significantly increased rate of death, and exercise training did not prevent or delay this excess mortality. The CREB(A133) murine model of inherited DC demonstrated progressive ventricular dilatation and dysfunction with increased mortality, which was not altered with 12 wk of moderate-intensity exercise training.

Spectral analysis of left ventricular area variability as a tool to improve the understanding of cardiac autonomic control

Spectral analysis of the fluctuations in heart rate (HR) or blood pressure (BP) has been extensively used as a tool for the noninvasive assessment of autonomic control of the heart. The recently developed echocardiographic acoustic quantification allows noninvasive continuous measurement of the left ventricular cross-sectional area (LVA) signal. In this study, we investigated whether the LVA signal, and more specifically its fluctuations, can be reliably subjected to spectral analysis, and whether the results of such analysis may improve the understanding of the cardiovascular control mechanisms. Our results show that the general pattern of power spectra of LVA fluctuations, as well as their reproducibility, is similar to the power spectra of HR and BP fluctuations. Analysis of LVA signals obtained in normal subjects at rest as well as under vagal blockade and under held respiration, and in patients with known autonomic dysfunction, showed significant differences between groups and states. The effects of age, related to the reduction in parasympathetic activity, were not evident in the spectral content of the LVA and BP signals. The high frequency LVA fluctuations are mainly of mechanical origin, since they were eliminated by breath-holding. We observed an increase in the high frequency LVA fluctuations under vagal blockade, indicating that under normal (control) conditions, these high frequency fluctuations are attenuated by parasympathetic activity. The enhancement in high frequency fluctuations in LVA observed in diabetic patients can thus be attributed to reduced parasympathetic activity. The analysis of LVA variability may be used as a tool for basic research and, possibly, as a quantitative clinical measure for specific disease states.

Effect of age, heart rate and tricuspid regurgitation on the Doppler echocardiographic evaluation of right ventricular diastolic function

Pulsed-wave Doppler analysis of tricuspid inflow and hepatic venous flow allows the determination of multiple parameters of right-ventricular (RV) diastolic function. This study sought to evaluate the influence of heart rate, age and tricuspid regurgitation on Doppler parameters of RV diastolic performance. We studied 80 subjects (20 normal and 60 with RV pathology) with Doppler recordings of the tricuspid inflow and hepatic vein. All tricuspid Doppler parameters were dependent on heart rate, age or regurgitation severity as were the hepatic vein S wave, S/D ratio and systolic filling fraction. The atrial reversal velocity in the hepatic vein Doppler tracing was not affected by age, heart rate or regurgitation. In addition, the inspiratory increase in this parameter was significantly elevated in RV pathologic states. This study demonstrates that most Doppler echocardiographic parameters of RV diastolic performance are dependent on age, tricuspid regurgitation or heart rate.

The role of echocardiographic harmonic imaging and contrast enhancement for improvement of endocardial border delineation

Despite advances in imaging technology, many myocardial segments remain poorly visualized with echocardiography; however, both contrast enhancement and harmonic imaging have shown promise for improving endocardial definition. Fifty subjects with technically limited echocardiograms were studied with fundamental and harmonic imaging as well as during echocardiographic contrast injection. Overall endocardial visualization scores improved with both techniques compared with fundamental imaging. Harmonic imaging improved endocardial visualization in 43% of all segments and in 57% of segments nonvisualized with fundamental imaging. The benefit of harmonic imaging was seen in all segments. Contrast echocardiography had similar overall improvements in visualization (42% of all segments, 67% of segments nonvisualized with fundamental imaging) but was not helpful in all regions. Harmonic imaging outperformed contrast in 9 of 22 segments, whereas contrast was superior in 4 of 22. In a subgroup of patients with very poor images, contrast enhancement was superior, with a greater increase in overall score and a higher salvage rate than harmonic (68% vs 40%).

Effects of MPEG compression on the quality and diagnostic accuracy of digital echocardiography studies

The advantages of digital echocardiography studies include ease of retrieval, review, comparison, duplication, and quantitation as well as the potential for moving studies over networks. However, the large amounts of data associated with digital echocardiography studies have posed new problems. Reduction of the amount of data can be accomplished with image compression, in particular MPEG-1 (Moving Pictures Expert Group), which is designed for dynamic image sequences. However the effects of different levels of compression on the quality and diagnostic content of echocardiographic images need to be established. Digital sequences of single cardiac cycles were acquired in 40 consecutive patients, MPEG-1-compressed at different effective ratios (60:1, 80:1, 120:1, 200:1, 300:1, 370:1, 500:1), reviewed, and scored for endocardial visualization. The overall visualization scores and percentages of nonvisualized segments in the compressed images were not different from the uncompressed images up to a compression ratio of 200:1. Differential effects of compression were noted on a segmental basis and also varied with baseline image quality. The ability to correctly identify regional wall motion abnormalities did not decrease until compression ratios of 1:200 or higher were used. Digital echocardiography loops, MPEG-1-compressed at an effective ratio of 200:1, demonstrate no degradation in endocardial visualization quality or diagnostic content. Compression at this ratio has the potential to reduce the storage size of digital echocardiography studies to less than 1% of their current size.

Three-dimensional echocardiography in adult patients: comparison between transthoracic and transesophageal reconstructions

BACKGROUND

Three-dimensional (3D) echocardiography is a relatively new technique typically implemented with transesophageal imaging with multiplane transducers.

OBJECTIVES

The goals of this study were (1) to test the feasibility of 3D reconstruction with a new transthoracic multiplane transducer in adult subjects with excellent quality of 2-dimensional images and (2) to compare these reconstructions with those obtained in the same patients with the transesophageal approach.

METHODS

Transthoracic multiplane image acquisition was performed in 37 patients who were selected on the basis of the quality of their 2-dimensional images. In addition, transesophageal acquisition was also performed in 19 of 37 patients. Three-dimensional reconstruction of mitral and aortic valves was performed. Three-dimensional images were reviewed, and the visualization of various anatomic features was graded.

RESULTS

The reconstruction of 25 mitral valves and 16 aortic valves, normal and pathologic, was feasible and resulted in visualization of anatomic detail. Score indexes of all valvular characteristics studied were not significantly different when transthoracic and transesophageal reconstructions were compared.

CONCLUSIONS

Transthoracic 3D echocardiography with a multiplane transducer in adult patients with good acoustic windows is feasible. This technique will allow easy noninvasive serial assessment of valvular pathophysiologic characteristics.

Left atrial appendage stenosis

Narrowing at the mouth of the left atrial appendage has been reported after partial surgical ligation of the appendage. This report describes a patient, without prior cardiac surgery, who had an anatomic narrowing at the opening of the left atrial appendage demonstrated by 2-dimensional, Doppler, and color Doppler echocardiography.

Identification of cardiac masses and abnormal blood flow patterns with harmonic power Doppler contrast echocardiography

Power Doppler is an ultrasound technique that color-encodes the change in amplitude of the ultrasound signal, which reflects changes in the position of scatterers between ultrasound pulses. Power Doppler can be used with echocardiographic contrast agents in a harmonic imaging mode to opacify a cardiac chamber. The opacification of a cardiac chamber can aid in visualizing the silhouette of intracardiac masses and displaying blood flow patterns. Four cases are presented that demonstrate the use of harmonic power Doppler to aid in the identification of a left ventricular apical thrombus, a left atrial thrombus, and a left ventricular pseudoaneurysm.

Objective evaluation of regional left ventricular wall motion during dobutamine stress echocardiographic studies using segmental analysis of color kinesis images

OBJECTIVES

To test the feasibility of objective and automated evaluation of echocardiographic stress tests, we studied the ability of segmental analysis of color kinesis (CK) images to detect dobutamine-induced wall motion abnormalities and compared this technique with inexperienced reviewers of conventional gray-scale images.

BACKGROUND

Conventional interpretation of stress echocardiographic studies is subjective and experience dependent.

METHODS

CK images were obtained in 89 of 104 consecutive patients undergoing clinical dobutamine stress studies and were analyzed using custom software to calculate regional fractional area change in 22 segments in four standard views. Each patient's data obtained at rest was used as a control for automated detection of dobutamine-induced wall motion abnormalities. Independently, studies were reviewed without CK overlays by two inexperienced readers who classified each segment's response to dobutamine. A consensus reading of two experienced reviewers was used as the gold standard for comparisons. In a subgroup of 16 patients, these consensus readings and CK detection of wall motion abnormalities were compared with coronary angiography.

RESULTS

The consensus reading detected ischemic response to dobutamine in 43 of 1958 segments in 23 of 89 patients. Automated detection of stress-induced wall motion abnormalities correlated more closely with the standard technique than the inexperienced reviewers (sensitivity 0.76 vs. 0.55, specificity 0.98 vs. 0.94 and accuracy 0.97 vs. 0.92). When compared with coronary angiography in a subgroup of patients, analysis of CK images differentiated between normal and abnormal wall motion more accurately than expert readers of gray-scale images (accuracy of 0.93 vs. 0.82).

CONCLUSIONS

Analysis of CK images allows fast, objective and automated evaluation of regional wall motion, sensitive enough for clinical dobutamine stress data and more accurate than inexperienced readers. This method may result in a valuable adjunct to conventional visual interpretation of dobutamine stress echocardiography.

A modified definition for peripartum cardiomyopathy and prognosis based on echocardiography

The diagnosis of peripartum cardiomyopathy is one of exclusion, made after careful search for an underlying cause. Research in this area is compromised by the reliance of some on clinical criteria alone without strict echocardiographic criteria. This article argues for uniform criteria that define peripartum cardiomyopathy, similar to the criteria for idiopathic dilated cardiomyopathy set forth by a National Heart, Lung, and Blood Institute-sponsored workshop and proposes that the new definition include heart failure within the last month of pregnancy or 5 months postpartum; absence of preexisting heart disease; no determinable etiology, the traditional definition; and strict echocardiographic criteria of left ventricular dysfunction: ejection fraction less than 45%, or M-mode fractional shortening less than 30%, or both, and end-diastolic dimension more than 2.7 cm/m2. Mortality from peripartum cardiomyopathy remains high, 25-50%, and a recent review related long-term prognosis to echocardiographic measures of left ventricular chamber dimension and function at diagnosis and recovery. We describe a modified pharmacologic echocardiographic stress test that might be useful in determining left ventricular contractile reserve in women believed to be recovered by routine echocardiographic studies. The test reproduces hemodynamic stress akin to pregnancy, and the data might be useful when counseling women on future childbearing. Women who respond with reduced cardiac reserve might be advised to avoid pregnancy.

Quantitative assessment of regional right ventricular function with color kinesis

We used color kinesis, a recent echocardiographic technique that provides regional information on the magnitude and timing of endocardial wall motion, to quantitatively assess regional right ventricular (RV) systolic and diastolic properties in 76 subjects who were divided into five groups, as follows: normal (n = 20), heart failure (n = 15), pressure/volume overload (n = 14), pressure overload (n = 12), and RV hypertrophy (n = 15). Quantitative segmental analysis of color kinesis images was used to obtain regional fractional area change (RFAC), which was displayed in the form of stacked histograms to determine patterns of endocardial wall motion. Time curves of integrated RFAC were used to objectively identify asynchrony of diastolic endocardial motion. When compared with normal subjects, patients with pressure overload or heart failure exhibited significantly decreased endocardial motion along the RV free wall. In the presence of mixed pressure/volume overload, the markedly increased ventricular septal motion compensated for decreased RV free wall motion. Diastolic endocardial wall motion was delayed in 17 of 72 segments (24%) in patients with RV pressure overload, and in 31 of 90 segments (34%) in patients with RV hypertrophy. Asynchrony of diastolic endocardial wall motion was greater in the latter group than in normal subjects (16% versus 10%: p < 0.01). Segmental analysis of color kinesis images allows quantitative assessment of regional RV systolic and diastolic properties.

Quantitative evaluation of left ventricular function in a TransgenicMouse model of dilated cardiomyopathy with 2-dimensional contrast echocardiography

The study of transgenic mouse models of human cardiovascular disease has been limited by the small size and high heart rate of the mouse heart. Advances in digital echocardiographic imaging equipment have provided the high spatial and temporal resolution necessary for 2-dimensional (2D) in vivo imaging of the mouse heart. The goal of this study was to test the use of contrast-enhanced 2D echocardiography to quantitatively assess left ventricular (LV) size and function in normal and transgenic mice with dilated cardiomyopathy. Images were obtained with a 12-MHz broadband transducer in the parasternal short-axis view in 8 control mice and 8 transgenic mice with dilated cardiomyopathy resulting from expression of a dominant-negative CREB transcription factor in the heart. LV opacification was achieved with injections of human albumin microspheres, injectable suspension (Optison) (15 to 30 microliter bolus). LV area was measured throughout the cardiac cycle with manual frame-by-frame tracing of the endocardial boundary. End-systolic and end-diastolic areas (ESA and EDA) were measured and fractional area change (FAC) calculated in both groups at baseline and during administration of dobutamine (40 microgram/kg/min intravenously). High-quality 2D images, which yielded LV area over time waveforms, were obtained in all mice. Under baseline conditions, ESA was significantly higher and FAC lower in the transgenic mice compared with their controls. During administration of dobutamine, normal mice had significantly smaller ESA and significantly larger FAC compared with baseline conditions, whereas this trend did not reach significance in the transgenic mice. In summary, quantitative assessment of LV size and function may be achieved with contrast-enhanced 2D echocardiographic imaging. This technique promises to facilitate studies of pathophysiology in murine models of human cardiovascular disease.