In vivo ultrasonic tissue characterization of human intracardiac masses

The 'cardiac-lung mass' artifact: an echocardiographic sign of lung atelectasis and/or pleural effusion

INTRODUCTION

We conducted an ultrasound study to investigate echocardiographic artifacts in mechanically ventilated patients with lung pathology.

METHODS

A total of 205 mechanically ventilated patients who exhibited lung atelectasis and/or pleural effusion were included in this 36-month study. The patients underwent lung echography and transthoracic echocardiography, with a linear 5 to 10 MHz and with a 1.5 to 3.6 MHz wide-angle phased-array transducer, respectively. Patients were examined by two experienced observers who were blinded to each other's interpretation.

RESULTS

A total of 124 patients (60,48%) were hospitalized because of multiple trauma; 60 patients (29,26%) because of respiratory insufficiency, and 21 (10,24%) because of recent postoperative surgery. The mean duration ( +/- standard deviation) of hospitalization was 35 +/- 27 days. An intracardiac artifact was documented in 17 out of 205 patients (8.29%) by echocardiography. It was visible only in the apical views, whereas subsequent transesophageal echocardiography revealed no abnormalities. The artifact consisted of a mobile component that exhibited, on M-mode, a pattern of respiratory variation similar to the lung 'sinusoid sign'. Lung echography revealed lung atelectasis and/or pleural effusion adjacent to the heart, and a similar M-mode pattern was observed. The artifact was recorded within the left cardiac chambers in 11 cases and within the right cardiac chambers in six.

CONCLUSIONS

Lung atelectasis and/or pleural effusion may create a mirror image, intracardiac artifact in mechanically ventilated patients. The latter was named the 'cardiac-lung mass' artifact to underline the important diagnostic role of both echocardiography and lung echography in these patients.

TRIAL REGISTRATION

This trial is ISRCTN registered: ISRCTN 49216096.

Quantitation of left-ventricular asynergy by cardiac ultrasound

The clinical evaluation of regional delays in myocardial motion (myocardial asynchrony) has proved problematic, yet it remains an important functional parameter to evaluate. Prior attempts to quantify regional asynergy have met with limited success, often thwarted by the low temporal resolution of imaging-system data acquisition. If a delay in onset of motion of 30-40 msec is clinically important to measure, then data acquisition at frame rates of 50-100 per second is required. This is out of the current temporal resolution of angiographic, nuclear, or magnetic resonance studies. Only cardiac ultrasound can currently achieve the necessary frame rates. Furthermore, quantitative studies into the accuracy with which a trained observer can identify computed regional myocardial asynchrony in a left-ventricular 2-dimensional (2-D) image have shown that regional delays of < 80 msec are not normally recognized in a moving image. This may be improved to 60 msec when either training is undertaken or comparative image review is used. However, this is still out of the temporal resolution required in clinical practice. Thus, visual interpretation of asynchrony is not sufficiently accurate. Two ultrasound data sets based on either integrated backscatter or Doppler myocardial imaging data may provide the solution. Doppler myocardial imaging is a new ultrasound technique which, in either its pulsed or color Doppler format, can achieve the required temporal resolution (with temporal resolutions of 8 msec and 16 msec, respectively). In contrast, color Doppler myocardial imaging, in its curved M-mode format, can display the timing of events during the cardiac cycle for all in-plane myocardial segments. This should allow the quantitation of regional delay for all systolic and diastolic events. Potentially, asynchrony due to regional ischemia, bundle branch block, ventricular premature beats, and ventricular preexcitation could all be identified and the degree of delay quantified. This overview will aim to establish the potential role of these new ultrasound methodologies in the recognition and quantitation of left-ventricular asynergy and how they might best be introduced into clinical practice.

Differentiation of intracardiac tumors and thrombi by echocardiographic tissue characterization: comparison of an artificial neural network and human observers

The feasibility of classifying ultrasound images of intracardiac tumors and thrombi with a neural network-based algorithm was compared with the performance of experienced echocardiographers. The neural network used statistical descriptors of the apparent echocardiographic texture of the masses, and the blinded echocardiographers were given photographic prints of enlarged regions of interest without clinical data. The network classified 66% of the images correctly and the echocardiographers, 83%. The network and echocardiographers agreed in 88% of the images. Human observers usually base their classification of intracardiac masses on clinical data. The echocardiographic texture of tumors is quantitatively different from that of thrombi. This difference can be recognized by a neural network and potentially be useful in assisting with the diagnosis when clinical clues are insufficient.

Tissue Doppler Echocardiography: Future Developments

The use of color-coded tissue Doppler echocardiography has resulted in rapid technological advances in the evaluation of cardiac function. This article describes some of these exciting new advances, including curved M-mode analysis and strain rate imaging. Data from studies in animals and humans are presented to demonstrate the potential clinical use of this new echocardiographic diagnostic tool.

Pericardial Tamponade: A Manifestation of Pericardial Sac Sarcoma-A Case Report

Cardiac tamponade was manifested in a 30-year-old male with a 6-month history of fever and weight loss prior to admission. Cross-sectional echocardiography demonstrated huge pericardial effusion with a large mass in the posterior pericardial space. Pericardiocentesis revealed exudative fluid with no malignant cells. Surgery performed to determine the nature of the mass disclosed the mass originating from the posterior pericardium, invading the posterior pleural sac and adjacent structures. Histopathology identified spindle cell sarcoma. The preoperative diagnosis of the mass and its presenting features and nature are discussed. (ECHOCARDIOGRAPHY, Volume 13, May 1996)

Quantitative Echocardiography, Part 1

The quantitative applications of echocardiography in clinical practice are well known. The measurements of cardiac chamber dimensions, wall thickness, and overall performance have been uniformly adopted. An important emerging ultrasound modality known as tissue characterization of the myocardium has evolved from experimental studies to clinical investigation. The ability to quantitate myocardial acoustic properties by the measurement of integrated backscatter (in decibels) provides direct assessment of myocardial structural characteristics and contractile performance, to complement conventional two-dimensional imaging of ventricular wall motion and wall thickening. Despite the considerable amount of work that has been done, there are several areas of research that need to be further investigated before widespread clinical use of these techniques is possible. Specifically, absolute values of myocardial backscatter are not yet obtainable with the current instrumentation; only the relative change in backscatter during the cardiac cycle (cyclic variation) has been defined and employed in clinical studies. This review summarizes the principles of tissue characterization and the results of several clinical studies, specifically those carried out in patients with coronary artery disease and cardiomyopathies.

Blocked element compensation in phased array imaging

In clinical applications using large apertures, a significant number of phased array elements may be blocked due to discontinuous acoustic windows into the body. These blocked elements produce undesired beamforming artifacts, degrading spatial and contrast resolution. To minimize these artifacts, an algorithm using multiple receive beams and the total-least-squares method is proposed. Simulations and experimental results show that this algorithm can effectively reduce imperfections in the point spread function of the imager. Combined with first-and second-order scatterer statistics derived from multiple receive beams, the algorithm is modified for blocked element compensation on distributed scattering sources. Results also indicate that compensated images are comparable to full array images, and that even full array images can be improved by removing undesired sidelobe contributions. This method, therefore, can enhance detection of low contrast lesions using large phased-array apertures.

Recent experience with ultrasonic tissue characterization

The current effort in the research laboratory at Stanford University Medical Center attempts tissue characterization using the parameter of cyclic variation of integrated ultrasonic backscatter (CVIBS). This parameter is available using prototype equipment that concentrates on the relative change in ultrasonic backscatter rather than the absolute level of backscatter measured. The interobserver reproducibility is quite good. The magnitude of CVIBS is greater in the posterior wall than in the septum generally. There is a weak association of aging with the magnitude of CVIBS. Measurement of CVIBS in patients with uncomplicated pressure overload hypertrophy and those with hypertrophic cardiomyopathy shows values in the posterior wall to be similar for all groups; however, the values for the septum were significantly smaller in patients in both hypertrophy groups compared with normal subjects. Studies in human cardiac allografts for the recognition of acute rejection have been carried out using CVIBS. A decrease in the magnitude of this parameter during rejection, compared to the baseline level, was characteristically seen. Return to prerejection levels was not invariably seen. Among the different systems for ultrasonic tissue characterization, the current system using CVIBS has been successful in specific studies.

Diagnosis of malignant cardiac disease by endomyocardial biopsy

Among oncology patients, endomyocardial biopsy has been used primarily for the evaluation of anthracycline cardiotoxicity. In addition, however, endomyocardial biopsy may be useful for the detection of malignant cardiac neoplasms. Between 1982 and 1989, metastatic involvement of the heart was diagnosed by endomyocardial biopsy in seven patients at our institution. All except one of these patients were older than 50 years of age and had dyspnea as an initial symptom, and all had a known malignant lesion. Results of endomyocardial biopsy confirmed cardiac involvement by a hematologic malignant lesion in four patients and metastatic melanoma in two patients. In one patient, who had a history of breast cancer and lymphoma, a metastatic neoplasm of uncertain differentiation was observed. Myocyte damage was evident in endomyocardial biopsy specimens from two of the four patients with hematologic malignant disease. Endomyocardial biopsy was performed to confirm the possibility of metastatic involvement in five patients; in the other two, endomyocardial biopsy was performed to determine whether anthracycline cardiotoxicity was present, and metastatic involvement was unanticipated.

Characterization of acute experimental left ventricular thrombi with quantitative backscatter imaging

Two-dimensional echocardiography is an excellent technique for detecting left ventricular thrombi, however, acute clot is sometimes difficult to differentiate from adjacent myocardium and intracavitary signals. We hypothesized that quantitative assessment of the acoustic properties of acute left ventricular thrombi using a quantitative backscatter imaging system would permit the differentiation of thrombus from adjacent myocardium and intracavitary echoes. Acute, experimental left ventricular thrombi in seven dogs were evaluated with a quantitative backscatter imaging system that allowed the measurement of relative integrated backscatter and cyclic (i.e., diastolic minus systolic) variation in integrated backscatter. Coronary ligation abolished the cyclic variation in relative backscatter that occurred in normal myocardium. The end-diastolic relative backscatter in the thrombus (16.9 +/- 1.3 dB) was significantly higher than in apical myocardium (13.2 +/- 0.6 dB, p less than 0.05). There was no significant difference in the cyclic variation in relative backscatter among thrombus, ischemic myocardium, or intracavitary blood. Thus, the quantitative assessment of the acoustic properties of left ventricular thrombi can be useful in their detection and in the differentiation from myocardium and intracavitary signals.

Accessory thyroid tissue in the right ventricle

In an asymptomatic 66-year-old woman presenting a systolic murmur in the pulmonic area, echocardiography evidenced a voluminous mass in the right ventricular outflow tract resembling a cardiac tumor. Histologic finding was that of aberrant normal thyroid. Although the occurrence of ectopic thyroid tissue in the heart is rare, it should be considered in the differential diagnosis whenever a mass is located at the level of the interventricular septum and encroaches on the right ventricular outflow tract. In these cases, a thyroid scintiscan may avoid an unnecessary surgical intervention.

Diagnosis of primary cardiac sarcoma. Report of 4 cases and review of the literature

The authors report the most extensive series of malignant primitive cardiac tumours. The patients presented with pericarditis in three cases and with a ventricular rhythm disorder in one patient. The diagnosis was made by non-invasive imaging techniques in three of the four. Angiography was carried out in three cases and was the determining diagnostic procedure in one. Diagnosis of the cardiac tumour was made prior to death in all cases. A histological diagnosis was obtained surgically in two cases. From the therapeutic viewpoint, surgical excision followed by chemotherapy and/or radiotherapy may prolong life. The average survival period of our patients was 11 months. The prognosis appears to be better after early surgical intervention. In view of the variability of the clinical features of cardiac sarcomas, cardiac computed tomography scanning is a valuable complement to cross-sectional echocardiography and, in our opinion, essential for early diagnosis.

Ultrasound characterization of acoustic properties of acute intracardiac thrombi: studies in a new experimental model

Echocardiographic differentiation among intracavitary thrombus, cavity noise, and adjacent myocardium can be difficult. As an initial step toward quantitative thrombus characterization with ultrasound, 11 dogs were studied with an in vivo intracardiac thrombus model to delineate the acoustic properties of acute thrombi. The apical coronary arteries were ligated, and subsequently injections of 5% sodium rescinoleate and 1000 units of thrombin at the endocardium-blood interface created left ventricular mural thrombi. Echocardiographic images were obtained in long- and short-axis views with a digital acquisition system, and a statistical analysis of echo intensities was performed in regions of interest in the thrombus, surrounding ventricular cavity and adjacent myocardium. Statistical measurements used to evaluate echo intensities in each region of interest included mean gray level, standard deviation, skewness, and kurtosis. The results showed that thrombus could be distinguished from myocardium (by mean gray level and standard deviation) only in short-axis views, where regions of interest could be placed at similar depths of field. Mean gray level, standard deviation, and skewness all distinguished thrombus from intracavitary blood regardless of the region of interest placement. The phase of the cardiac cycle at which data were acquired did not alter the results. We conclude that acute intracardiac thrombi can be distinguished from surrounding blood and myocardium with ultrasound tissue characterization techniques that may have the potential for clinical application.

Deviations from Rayleigh statistics in ultrasonic speckle

The statistics of speckle patterns in ultrasound images have potential for tissue characterization. In "fully developed speckle" from many random scatterers, the amplitude is widely recognized as possessing a Rayleigh distribution. This study examines how scattering populations and signal processing can produce non-Rayleigh distributions. The first order speckle statistics are shown to depend on random scatterer density and the amplitude and spacing of added periodic scatterers. Envelope detection, amplifier compression, and signal bandwidth are also shown to cause distinct changes in the signal distribution.

Quantitation in echocardiography

Imaging of the heart is the predominant approach to cardiovascular diagnosis in current practice. Of the wide variety of cardiac imaging techniques available, echocardiography is one of the most widely used. Standard methods of quantitation of M-mode and two-dimensional echocardiograms yield reproducible, accurate measurements of cardiac chamber, wall, and great vessel dimensions. Qualitative analysis of valvular appearance and motion permits the diagnosis of a wide variety of valvular disorders. Doppler echocardiography yields information on blood flow velocity and pattern in the heart and great vessels. Evolving methods of quantitation in echocardiography include computerized image enhancement, computer-assisted border detection, analysis of regional left ventricular contraction, three-dimensional reconstruction, contrast-enhanced echocardiography, ultrasound myocardial tissue characterization, and intraoperative echocardiography. Echocardiography is a dynamic, evolving discipline with the potential of defining cardiac structure, function, blood flow dynamics, myocardial perfusion, and tissue characteristics. Thus, ultrasonography will continue to be of major importance in the diagnosis of cardiac disease.

Noninvasive tissue characterization: diagnosis of lipomatous hypertrophy of the atrial septum by nuclear magnetic resonance imaging

An atrial septal mass was identified by echocardiogram in a patient with multiple subcutaneous lipomas. In order to differentiate the benign condition of lipomatous hypertrophy from myxoma, thrombus and other tumors, nuclear magnetic resonance and computed tomographic imaging were performed. Both techniques identified the adipose nature of the tissue noninvasively, consistent with the diagnosis of lipomatous hypertrophy. Pathologically demonstrated lipomatous hypertrophy in a postmortem heart was similarly characterized by nuclear magnetic resonance imaging.

Ultrasonic tissue characterization: detection of acute myocardial ischemia in dogs

Ultrasonic tissue characterization is a new area of investigation in the field of cardiac ultrasound. The amplitude and frequency of the ultrasound signal are normally altered as the signal penetrates through tissue. It is assumed that the amplitude distribution and frequency shift of diseased or edematous tissue are different than those of normal tissue. A statistical approach to the analysis of the unprocessed radiofrequency signal in the amplitude domain was used to study the effect of acute myocardial ischemia on the parameter mean amplitude/standard deviation of the amplitude (MSR). Ten dogs were anesthetized and underwent left lateral thoracotomy. Baseline mean MSR from the interventricular septum was 1.99 +/- 0.05, but increased by 30 min after coronary artery occlusion and started to plateau at 1 hr (mean 2.24 +/- 0.06). Reproducibility in noninfarcted myocardium (left ventricular inferoposterior wall) was good, with a mean MSR of 2.00 +/- 0.05 at baseline and 1.98 +/- 0.04 3 to 4 hr later. There was no difference in mean MSR when data were obtained through chest wall and when they were obtained directly from the surface of the heart. We conclude that statistical analysis in the amplitude domain of the unprocessed radiofrequency signal can detect acute myocardial ischemia within 30 min after coronary artery occlusion, provides reproducible measurements, and is unaffected by chest wall filtering.

[Sarcoma of the heart. Apropos of 2 cases]

Sarcoma of the heart is a very rare condition. We present here two cases with very different clinical expression. The first patient, a 15-year old girl, presented with extremely severe ventricular arrhythmia, whereas the second patient, a 63-year old woman, mainly had signs of congestive cardiac failure. A diagnosis of cardiac tumour was made in the first case on the basis of ultrasonographic results which clearly showed the tumour developed from the walls of the left ventricle. In the second case, the tumour involved the right ventricular wall, the deformation of which was undetected by ultrasounds and only suspected at angiography. Both patients died rapidly, and the diagnosis of sarcoma was confirmed at post-mortem examination.

Effects of coronary artery occlusion and reperfusion on cardiac cycle-dependent variation of myocardial ultrasonic backscatter

We have recently reported a systematic variation in integrated ultrasonic backscatter throughout the cardiac cycle in canine hearts. This study was performed to determine whether the pattern of such variation is modified systematically by ischemia. Measurements of integrated ultrasonic backscatter in selected regions of normal, ischemic, and reperfused hearts were compared in view of known differences in systolic function of myocardium in each of these regions. Integrated ultrasonic backscatter (3-7 MHz) gated to the first derivative of left ventricular pressure was measured at the apex, midwall, and base in 10 dogs and at the apex before and during transient ischemia and reperfusion in four dogs. Quantitative integrated ultrasonic backscatter was referenced to a steel reflector. Cyclic variation of integrated ultrasonic backscatter was greatest at the apex [peak to trough variation 5.5 +/- 0.9 dB (mean +/- SE)] with the maximum near end diastole (-52.9 +/- 0.9 dB) and minimum near end systole (-58.4 +/- 1.0 dB). Variation at the apex (5.5 +/- 0.9 dB) and the midwall (4.3 +/- 0.8 dB) was greater than at the base (0.5 +/- 1.0 dB) (P less than 0.01 for either region compared with base). Left anterior descending coronary occlusion for 10 minutes in four of 10 dogs reduced variation at the apex to 0.4 +/- 1.5 dB (P less than 0.02 compared with preocclusion). Reperfusion for 2 hours restored apical cyclic variation to 3.9 +/- 1.7 dB, i.e., to values not significantly different from those before occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative echocardiographic image texture: normal contraction-related variability

Myocardial tissue characterization using ultrasound is a growing area of investigation which attempts to evaluate the structure of the myocardium by analysis of ultrasound signals. Our laboratory has been exploring the use of texture analysis for the determination of myocardial tissue properties from two-dimensional echocardiographic images. In the present study, we tested the hypothesis that echocardiographic image texture varies with cardiac contraction in normal human subjects. In 17 subjects, we obtained long-and short-axis images at end diastole and end systole. Echo image texture was assessed using three classes of quantitative texture measures: run length, gray level difference, and busyness statistics. These statistics measure various attributes of image texture. We found significant contraction-related changes in image texture for the left ventricular posterior wall. This observation is important in that future applications of texture analysis to echocardiographic image data will require that texture be measured at a consistent point in the cardiac cycle. Moreover, it is possible that alteration in the normal variation of texture with cardiac contraction may be a sensitive indicator of abnormal myocardium.

Applicability of ultrasonic tissue characterization for longitudinal assessment and differentiation of calcification and fibrosis in cardiomyopathy

Progress in tissue characterization of myocardium with ultrasound suggests that quantitative recognition of ischemic or scarred tissue will be achieved. Despite the increasing recognition and importance of cardiomyopathy, its diagnosis generally requires invasive procedures such as cardiac catheterization and biopsy. To investigate methods that permit the characterization of longitudinal cardiomyopathic changes that might ultimately be extended for noninvasive studies in patients, quantitative ultrasonic methods were utilized for in vitro tissue characterization of hearts from Syrian hamsters of selected age of either 2 to 3 or 5 to 7 months. Normal hamsters were used as controls. Myocardial sites (n = 600) from the young Syrian hamsters exhibited values (+/- standard error) of integrated ultrasonic backscatter averaging -53.87 +/- 0.26 dB, which were significantly different from values (n = 500) in age-matched control hamsters (-58.07 +/- 0.08 dB; p less than 0.001). Cardiomyopathic hearts from older animals exhibited backscatter values (n = 500 sites) averaging -50.87 +/- 0.22 dB, again significantly different from values (n = 300 sites) in age-matched control hamsters (-55.91 +/- 0.11 dB; p less than 0.001). In addition, ultrasonic attenuation was significantly different for hearts from the control and cardiomyopathic hamsters of both age ranges. The results correlated with sequential calcification and fibrosis characteristics assessed histopathologically. This study indicates that quantitative characterization of myocardium with ultrasound may permit longitudinal assessment of cardiomyopathic changes in diverse disease entities and their response to therapy.

An improved stochastic approach to rf amplitude analysis in ultrasonic cardiac tissue characterization

We carried out a series of studies to improve the reproducibility of methods for ultrasonic myocardial tissue characterization using a stochastic approach to amplitude analysis of radiofrequency signals previously reported from our laboratory. Analysis of transducer scanner characteristics, data acquisition and processing, and data display from studies in tissue phantoms permit us to define some features of a parameter for expression of tissue character. The ratio of mean to standard deviation of the amplitude histogram from our system is explored as now implemented in our laboratory for reproducible measurements. The theoretical basis for understanding the utility of this method in defining tissue architecture and pathologic conditions requires further work.

Ultrasonic characterization of blood during coagulation

Recently ultrasound has been found to be extremely useful in detecting intracardiac thrombi as well as intracranial hemorrhages in neonates. The principal criterion used for clinical diagnosis of thrombus has been an increase in the echogenicity of clotted blood. However, echogenicity is a rather nonspecific and qualitative description of tissue ultrasonic properties. A rise in echogenicity could be the result of an increase in ultrasonic backscatter, or a decrease in attenuation, or a combination of both. In order to ascertain the mechanism responsible for the clinically observed increase in echogenicity and thus put the technique on a firm foundation, we have measured serially the ultrasonic velocity, attenuation and backscatter in human blood up to 24 hours following the onset of coagulation. Preliminary results show that all three ultrasonic properties increase during this time period. At 24 hours following clotting, the mean rises in velocity, attenuation and backscatter are 3.36 +/- 0.35 X 10(3) cm/sec, 2.3 +/- 0.22 db/cm and 18.5 +/- 1.2 dB per unit volume of blood (at 7.5 MHz and a temperature of 23 degrees C), respectively. These results indicate that the increase in echogenicity of a thrombus is due to a substantial increase in ultrasonic backscatter, which is moderated to a certain extent by the accompanied increase in attenuation.

Estimation of ultrasonic attenuation and mean backscatterer size via digital signal processing

The backscattered rf signals from the lungs of fetal sheep during their last trimester of development were digitized and processed in an attempt to correlate ultrasonic parameters with measured functional parameters related to lung maturation. The broadband, post- TGC , rf signal of a commercial B-mode ultrasonic scanner was digitized at a sampling rate of 25 MHz. Sorting excluded data from regions of rib shadowing and other nonlung structures from analysis. The sorted data were used to estimate the slope of the ultrasonic attenuation coefficient with respect to frequency via linear regression on the average difference of the logarithm of power spectra from separated data segments. The power spectra were also corrected for attenuation, averaged and used to compute the power cepstrum of the backscattered signal which can be related to mean backscatterer radius. Results are presented for eight fetal sheep.