Native tissue harmonic imaging improves endocardial border definition and visualization of cardiac structures

Myocardial Viability Testing in the Management of Ischemic Heart Failure

Although major advances have occurred lately in medical therapy, ischemic heart failure remains an important cause of death and disability. Viable myocardium represents a cause of reversible ischemic left ventricular dysfunction. Coronary revascularization may improve left ventricular function and prognosis in patients with viable myocardium. Although patients with impaired left ventricular function and multi-vessel coronary artery disease benefit the most from revascularization, they are at high risk of complications related to revascularization procedure. An important element in selecting the patients for myocardial revascularization is the presence of the viable myocardium. Multiple imaging modalities can assess myocardial viability and predict functional improvement after revascularization, with dobutamine stress echocardiography, nuclear imaging tests and magnetic resonance imaging being the most frequently used. However, the role of myocardial viability testing in the management of patients with ischemic heart failure is still controversial due to the failure of randomized controlled trials of revascularization to reveal clear benefits of viability testing. This review summarizes the current knowledge regarding the concept of viable myocardium, depicts the role and tools for viability testing, discusses the research involving this topic and the controversies related to the utility of myocardial viability testing and provides a patient-centered approach for clinical practice.

Performance Evaluation of Adaptive Imaging Based on Multiphase Apodization with Cross-correlation: A Pilot Study in Abdominal Ultrasound

Degradation of image contrast caused by phase aberration, off-axis clutter, and reverberation clutter remains one of the most important problems in abdominal ultrasound imaging. Multiphase apodization with cross-correlation (MPAX) is a novel beamforming technique that enhances ultrasound image contrast by adaptively suppressing unwanted acoustic clutter. MPAX employs multiple pairs of complementary sinusoidal phase apodizations to intentionally introduce grating lobes that can be used to derive a weighting matrix, which mostly preserves the on-axis signals from tissue but reduces acoustic clutter contributions when multiplied with the beamformed radio-frequency (RF) signals. In this paper, in vivo performance of the MPAX technique was evaluated in abdominal ultrasound using data sets obtained from 10 human subjects referred for abdominal ultrasound at the USC Keck School of Medicine. Improvement in image contrast was quantified, first, by the contrast-to-noise ratio (CNR) and, second, by the rating of two experienced radiologists. The MPAX technique was evaluated for longitudinal and transverse views of the abdominal aorta, the inferior vena cava, the gallbladder, and the portal vein. Our in vivo results and analyses demonstrate the feasibility of the MPAX technique in enhancing image contrast in abdominal ultrasound and show potential for creating high contrast ultrasound images with improved target detectability and diagnostic confidence.

Effect of Transmit Beamforming on Clutter Levels in Transthoracic Echocardiography

Transmit beamforming has a strong impact on several factors that govern image quality, field-of-view, and frame-rate in ultrasound imaging. For cardiac applications, the visualization of fine structures and the ability to track their motion is equally important. Consequently, beamforming choices for echocardiography aim to optimize these trade-offs. Acoustic clutter can dramatically impact image quality and degrade the diagnostic value of cardiac ultrasound imaging. Clutter levels, however, are closely tied to the choice of beamforming configuration. This study aims to quantify the impact of transmit beamforming on clutter levels under in vivo conditions. The performance of focused as well as plane wave transmit configurations in fundamental and harmonic modes is evaluated under matched conditions. Contrast between the cardiac chambers and the interventricular septum is used as a surrogate for the level of clutter in a given imaging scenario. Under in vivo conditions, contrast was found to improve incrementally across the four beamforming configurations in the following order: fundamental-plane, fundamental-focused, harmonic-plane, and harmonic-focused. Using the fundamental-focused configuration as a reference, the harmonic-plane and harmonic-focused cases showed improvements in median contrast of 2.97 dB and 6.1 dB, respectively, while the fundamental-plane case showed a contrast deterioration of 1.23 dB. Contrast was also found to vary systematically as a function of imaging depth. Median contrast for the right ventricle (shallow chamber) was measured to be 2.96 dB lower than that in the left ventricle (deep chamber).

Hypothesis of Improved Visualization of Microstructures in the Interventricular Septum with Ultrasound and Adaptive Beamforming

In this work, in vivo ultrasound cardiac images created with Capon's minimum variance adaptive beamformer are compared with images acquired with the conventional delay-and-sum beamformer. Specifically, we provide three views of a human heart imaged through the parasternal short-axis, the parasternal long-axis and the apical four-chamber views. The minimum variance beamformer produced images with improved lateral resolution, resulting in better resolved speckle structure and improved edges, especially on close investigation of the interventricular septum. These improvements in image quality might possibly improve the visualization of microstructures in the human heart.

High-Frame-Rate Deformation Imaging in Two Dimensions Using Continuous Speckle-Feature Tracking

The study describes a novel algorithm for deriving myocardial strain from an entire cardiac cycle using high-frame-rate ultrasound images. Validation of the tracking algorithm was conducted in vitro prior to the application to patient images. High-frame-rate ultrasound images were acquired in vivo from 10 patients, and strain curves were derived in six myocardial regions around the left ventricle from the apical four-chamber view. Strain curves derived from high-frame-rate images had a higher frequency content than those derived using conventional methods, reflecting improved temporal sampling.

Harmonic imaging with fresnel beamforming in the presence of phase aberration

Fresnel beamforming is a beamforming method with a delay profile similar in shape to a physical Fresnel lens. The advantage of Fresnel beamforming is the reduced channel count, which consists of four to eight transmit and two analog-to-digital receive channels. Fresnel beamforming was found to perform comparably to conventional delay-and-sum beamforming. However, the performance of Fresnel beamforming is highly dependent on focal errors. These focal errors result in high side-lobe levels and further reduce the performance of Fresnel beamforming in the presence of phase aberration. With the advantages of lower side-lobe levels and suppression of aberration effects, harmonic imaging offers an effective solution to the limitations of Fresnel beamforming. We describe the implementation of tissue harmonic imaging and pulse inversion harmonic imaging in Fresnel beamforming, followed by dual apodization with cross-correlation, to improve image quality. Compared with conventional delay-and-sum beamforming, experimental results indicated contrast-to-noise ratio improvements of 10%, 49% and 264% for Fresnel beamforming using tissue harmonic imaging in the cases of no aberrator, 5-mm pork aberrator and 12-mm pork aberrator, respectively. These improvements were 22%, 57% and 352% for Fresnel beamforming using pulse inversion harmonic imaging. Moreover, dual apodization with cross-correlation was found to further improve the contrast-to-noise ratios in all cases. Harmonic imaging was also found to narrow the lateral beamwidth and shorten the axial pulse length by at least 25% and 21%, respectively, for Fresnel beamforming at different aberration levels. These results suggest the effectiveness of harmonic imaging in improving image quality for Fresnel beamforming, especially in the presence of phase aberration. Even though this combination of Fresnel beamforming and harmonic imaging does not outperform delay-and-sum beamforming combined with harmonic imaging, it provides the benefits of reduced channel count and potentially reduced cost and size of ultrasound systems.

Contrast echocardiography in myocardial infarction

The contrast agents used in ultrasound are approved for several clinical situations. New echocardiographic techniques, such as harmonic imaging and power pulse inversion imaging, can improve the visualization of microbubbles. In this article we discuss the early development of contrast echocardiography, new technologies that help improve image acquisition and its practical role in the assessment of myocardial infarction.

Harmonic tracking of acoustic radiation force-induced displacements

Ultrasound-based elasticity imaging methods rely upon accurate estimates of tissue deformation to characterize the mechanical properties of soft tissues. These methods are corrupted by clutter, which can bias and/or increase variance in displacement estimates. Harmonic imaging methods are routinely used for clutter suppression and improved image quality in conventional B-mode ultrasound, but have not been utilized in ultrasound-based elasticity imaging methods. We introduce a novel, fully-sampled pulse-inversion harmonic method for tracking tissue displacements that corrects the loss in temporal sampling frequency associated with conventional pulse-inversion techniques. The method is implemented with acoustic radiation force impulse (ARFI) imaging to monitor the displacements induced by an impulsive acoustic radiation force excitation. Custom pulse sequences were implemented on a diagnostic ultrasound scanner to collect spatially-matched fundamental and harmonic information within a single acquisition. B-mode and ARFI images created from fundamental data collected at 4 MHz and 8 MHz are compared with 8-MHz harmonic images created using a band-pass filter approach and the fully sampled pulse-inversion method. In homogeneous, tissue-mimicking phantoms, where no visible clutter was observed, there was little difference in the axial displacements, estimated jitter, and normalized cross-correlation among the fundamental and harmonic tracking methods. The similarity of the lower- and higher-frequency methods suggests that any improvement resulting from the increased frequency of the harmonic components is negligible. The harmonic tracking methods demonstrated a marked improvement in B-mode and ARFI image quality of in vivo carotid arteries. Improved feature detection and decreased variance in estimated displacements were observed in the arterial walls of harmonic ARFI images, especially in the pulse-inversion harmonic ARFI images. Within the lumen, the harmonic tracking methods improved the discrimination of the blood–vessel interface, making it easier to visualize plaque boundaries. Improvements in harmonic ARFI images in vivo were consistent with suppressed clutter supported by improved contrast and contrast-to-noise ratio (CNR) in the matched harmonic B-mode images compared with the fundamental B-mode images. These results suggest that harmonic tracking methods can improve the clinical utility and diagnostic accuracy of ultrasound-based elasticity imaging methods.

Effects of dual apodization with cross-correlation on tissue harmonic and pulse inversion harmonic imaging in the presence of phase aberration

Dual apodization with cross-correlation (DAX) is a relatively new beamforming technique which can suppress side lobes and clutter to enhance ultrasound image contrast. However, previous studies have shown that with increasing aberrator strength, contrast enhancements with DAX diminish and DAX becomes more prone to image artifacts. In this paper, we propose integrating DAX with tissue harmonic imaging (THI) or pulse inversion harmonic imaging (PIHI) to overcome their shortcomings and achieve higher image contrast. Compared with conventional imaging, our experimental results showed that DAX with THI allows for synergistic enhancements of image contrast with improvements of more than 231% for a 5-mm pork aberrator and 703% for a 12-mm pork aberrator. With PIHI, improvements of 238% and 890% were observed for the two pork tissue samples. Our results suggest that the complementary contrast enhancement mechanism employed by the proposed method may be useful in improving imaging of technically difficult patients in clinics.

Sources of image degradation in fundamental and harmonic ultrasound imaging: a nonlinear, full-wave, simulation study

A full-wave equation that describes nonlinear propagation in a heterogeneous attenuating medium is solved numerically with finite differences in the time domain. This numerical method is used to simulate propagation of a diagnostic ultrasound pulse through a measured representation of the human abdomen with heterogeneities in speed of sound, attenuation, density, and nonlinearity. Conventional delay-and-sum beamforming is used to generate point spread functions (PSFs) that display the effects of these heterogeneities. For the particular imaging configuration that is modeled, these PSFs reveal that the primary source of degradation in fundamental imaging is due to reverberation from near-field structures. Compared with fundamental imaging, reverberation clutter in harmonic imaging is 27.1 dB lower. Simulated tissue with uniform velocity but unchanged impedance characteristics indicates that for harmonic imaging, the primary source of degradation is phase aberration.

Coded tissue harmonic imaging with nonlinear chirp signals

Coded tissue harmonic imaging with pulse inversion (CTHI-PI) based on a linear chirp signal can improve the signal-to-noise ratio with minimizing the peak range sidelobe level (PRSL), which is the main advantage over CTHI with bandpass filtering (CTHI-BF). However, the CTHI-PI technique could suffer from motion artifacts due to decreasing frame rate caused by two firings of opposite phase signals for each scanline. In this paper, a new CTHI method based on a nonlinear chirp signal (CTHI-NC) is presented, which can improve the separation of fundamental and harmonic components without sacrificing frame rate. The nonlinear chirp signal is designed to minimize the PRSL value by optimizing its frequency sweep rate and time duration. The performance of the CTHI-NC method was evaluated by measuring the PRSL and mainlobe width after compression. From the in vitro experiments, the CTHI-NC provided the PRSL of -40.6 dB and the mainlobe width of 2.1 μs for the transmit quadratic nonlinear chirp signal with the center frequency of 2.1 MHz, the fractional bandwidth at -6 dB of 0.6 and the time duration of 15 μs. These results indicate that the proposed method could be used for improving frame rates in CTHI while providing comparable image quality to CTHI-PI.

Sources of image degradation in fundamental and harmonic ultrasound imaging using nonlinear, full-wave simulations

A full-wave equation that describes nonlinear propagation in a heterogeneous attenuating medium is solved numerically with finite differences in the time domain (FDTD). This numerical method is used to simulate propagation of a diagnostic ultrasound pulse through a measured representation of the human abdomen with heterogeneities in speed of sound, attenuation, density, and nonlinearity. Conventional delay-andsum beamforming is used to generate point spread functions (PSF) that display the effects of these heterogeneities. For the particular imaging configuration that is modeled, these PSFs reveal that the primary source of degradation in fundamental imaging is reverberation from near-field structures. Reverberation clutter in the harmonic PSF is 26 dB higher than the fundamental PSF. An artificial medium with uniform velocity but unchanged impedance characteristics indicates that for the fundamental PSF, the primary source of degradation is phase aberration. An ultrasound image is created in silico using the same physical and algorithmic process used in an ultrasound scanner: a series of pulses are transmitted through heterogeneous scattering tissue and the received echoes are used in a delay-and-sum beamforming algorithm to generate images. These beamformed images are compared with images obtained from convolution of the PSF with a scatterer field to demonstrate that a very large portion of the PSF must be used to accurately represent the clutter observed in conventional imaging.

Coded excitation for ultrasound tissue harmonic imaging

Coded excitation can improve the signal-to-noise ratio (SNR) in ultrasound tissue harmonic imaging (THI). However, it could suffer from the increased sidelobe artifact caused by incomplete pulse compression due to the spectral overlap between the fundamental and harmonic components of ultrasound signal after nonlinear propagation in tissues. In this paper, three coded tissue harmonic imaging (CTHI) techniques based on bandpass filtering, power modulation and pulse inversion (i.e., CTHI-BF, CTHI-PM, and CTHI-PI) were evaluated by measuring the peak range sidelobe level (PRSL) with varying frequency bandwidths. From simulation and in vitro studies, the CTHI-PI outperforms the CTHI-BF and CTHI-PM methods in terms of the PRSL, e.g., -43.5dB vs. -24.8dB and -23.0dB, respectively.

Tissue non-linearity

The propagation of acoustic waves is a fundamentally non-linear process, and only waves with infinitesimally small amplitudes may be described by linear expressions. In practice, all ultrasound propagation is associated with a progressive distortion in the acoustic waveform and the generation of frequency harmonics. At the frequencies and amplitudes used for medical diagnostic scanning, the waveform distortion can result in the formation of acoustic shocks, excess deposition of energy, and acoustic saturation. These effects occur most strongly when ultrasound propagates within liquids with comparatively low acoustic attenuation, such as water, amniotic fluid, or urine. Attenuation by soft tissues limits but does not extinguish these non-linear effects. Harmonics may be used to create tissue harmonic images. These offer improvements over conventional B-mode images in spatial resolution and, more significantly, in the suppression of acoustic clutter and side-lobe artefacts. The quantity B/ A has promise as a parameter for tissue characterization, but methods for imaging B/ A have shown only limited success. Standard methods for the prediction of tissue in-situ exposure from acoustic measurements in water, whether for regulatory purposes, for safety assessment, or for planning therapeutic regimes, may be in error because of unaccounted non-linear losses. Biological effects mechanisms are altered by finite-amplitude effects.

In vitro mitral chordal cutting by high intensity focused ultrasound

Mitral regurgitation, when it arises from functional restriction of mitral leaflet closure, can be relieved by surgical cutting of the mitral tendineae chordae. We hypothesized that high intensity focused ultrasound (HIFU) might be useful as a noninvasive extracorporeal technique for cutting mitral chordae. As a pilot study to test this hypothesis, we examined the in vitro feasibility of using HIFU to cut calf mitral chordae with diameters from 0.2 to 1.6 mm. Sixty-seven percent of chordae were completely cut with HIFU, operated at 4.67 MHz and 45 W acoustic power, with up to 120 pulses of 0.3-s duration at 2-s intervals. Forty-five percent were completely cut when the pulse duration was reduced to 0.2 s. The average diameter of those chordae, which were completely cut, was significantly smaller than that of incompletely cut chordae (0.59 +/- 0.30 versus 1.14 +/- 0.30 mm with a pulse duration of 0.2 s, p < 0.0001; 0.68 +/- 0.29 versus 1.32 +/- 0.20 mm with a pulse duration of 0.3 s, p < 0.0001). For each pulse duration, the number of pulses required for complete cutting exhibited a strong positive correlation with the chordae diameter. In conclusion, in vitro feasibility of mitral chordal cutting by HIFU depended on the diameter of chordae but was controllable by HIFU settings. (E-mail: abeyukio@aol.com).

Echocardiography with Tissue Harmonic Imaging in the Detection of ST Segment Elevation Myocardial Infarction: Comparison with Coronary Angiography

BACKGROUND

Tissue harmonic imaging (THI) has been used to improve endocardial border definition and cardiac structure visualization in patients with poor quality echocardiograms. However, little is known about the usefulness of THI in the detection of acute myocardial infarction.

METHODS

Ninety-eight patients with a first ST segment elevation myocardial infarction were investigated using THI and coronary angiography.

RESULTS

Using THI, adequate quality echocardiograms were obtained in 95.9% of the patients. THI detected myocardial infarction in 92.9% of the patients. The sites of myocardial infarction estimated by THI and echocardiogram were nearly consistent. The sites of myocardial infarction estimated by THI were in accordance with the territories subtended by the infarct-related artery in coronary angiography (accuracy 88.8%), among which the highest accuracy (96.8%) concerning infarcts caused by left anterior descending branch disease. Infarcts involving inferior, posterior wall, or right ventricle were commonly complicated with myocardial infarction of other location, and were more likely to be missed.

CONCLUSIONS

Echocardiography with THI is a sensitive technique for detecting ST segment elevation myocardial infarction. More attention should be paid to the observation of inferior, posterior wall, or right ventricle to avoid missing the detection of myocardial infarction involving these sites.

Potential clinical perspectives of Doppler myocardial imaging and strain rate imaging during stress echocardiography

Stress echocardiography has become a common non-invasive test in patients with chest pain and known or suspected coronary artery disease, but, as with exercise electrocardiography, it shows several major limitations. Analysis of gray-scale images based on subjective visual interpretation of wall motion and thickening has considerable variability even among experts. Doppler myocardial imaging and strain rate imaging echocardiography provides additional information in comparison with conventional echocardiography. These techniques provide quantification of regional wall motion at rest and during stress. Quantification of both systolic and diastolic myocardial function by either Doppler myocardial imaging or strain rate imaging mapping during dobutamine stress test has been shown to be a feasible, accurate, non-invasive tool that should be considered to be a sensitive alternative to the present echocardiographic and scintigraphic imaging techniques for stress tests. Time consuming off-line analysis of color images is required in the present state of technology. However, these non-invasive techniques are rapidly evolving and expanding. Further refinements in signal processing and quantitative analysis are likely in the near future.

Impact of propagation through an aberrating medium on the linear effective apodization of a nonlinearly generated second harmonic field

Techniques based on the nonlinearly generated second harmonic signal (tissue harmonic imaging) have rapidly supplanted linear (fundamental) imaging methods as the standard in two-dimensional echocardiography. Enhancements to the compactness of the nonlinearly generated second harmonic (2f) field component with respect to the fundamental (1f) field component are widely considered to be among the factors contributing to the observed image quality improvements. The objective of this study was to measure the impact of phase and amplitude aberrations resulting from propagation through an inhomogeneous tissue, on the beamwidths associated with: the fundamental (1f); the nonlinearly generated second harmonic (2f); and the linearly propagated, effective apodization signal at the same (21) frequency. Modifications to the transmit characteristics of a phased-array imaging system were validated with hydrophone measurements. Results demonstrate that the characteristics of the diffraction pattern associated with the linear-propagation effective apodization transmit case were found to be in good agreement with the detailed spatial characteristics of the nonlinearly generated second harmonic field. The effects of the abdominal wall tissue aberrators are apparent for all three of the beam profiles studied. Consistent with the improved image quality associated with harmonic imaging, the aberrated nonlinearly generated second harmonic beam was shown to remain more compact than the corresponding aberrated fundamental beam patterns in the presence of the interposed aberrator.

Comparison of transthoracic versus transesophageal echocardiography for detection of right-to-left atrial shunting using agitated saline contrast

Agitated saline contrast studies (bubble studies) can be performed with either transthoracic or transesophageal echocardiography for the detection of right-to-left atrial shunts. The echocardiograms of 94 consecutive patients who underwent saline contrast studies with transthoracic and transesophageal approaches were reviewed to compare the ability of these modalities to detect right-to-left atrial shunts.

Assessment of the tricuspid valve morphology by transthoracic real-time-3D-echocardiography

AIM

To demonstrate the feasibility of transthoracic three-dimensional real-time echocardiography (3D-TTE) supplemental to routine assessments of the tricuspid valve and to analyze interrater agreement.

METHODS

Twenty healthy subjects and 74 patients with right ventricular failure were examined with conventional 2D and additionally 3D-TTE (SONOS 7500, Philips, Netherlands). The 3D exams were performed and recorded by one of two raters. The recordings were evaluated offline and independently by both raters for visualization of morphological and functional features of the tricuspid valve according to a subjective 3-point scale. Statistical analyses were performed for interrater agreement and for comparison of imaging quality between the two study groups. In addition, we present an illustrative case report.

RESULTS

Visualization of the spatial relationship between the tricuspid valve and vicinal structures, of the commissures, the orifice, and entirety of valve depiction were better in the ventricular failure group as compared to the control group. Annular dimensions were equally assessable in both groups, leaflet thickness and mobility were not significantly different. Interrater agreement on assessability was slight for leaflet thickness, fair for leaflet mobility and orifice area, and good for the remaining features. The 3D-TTE exam including offline evaluation took 6.5 minutes on average and maximally 14 minutes.

CONCLUSION

3D-TTE of the tricuspid valve can be performed in addition to routine 2D echocardiography within a reasonable time and with high assessability of important features in patients with right ventricular failure. Interrater agreement was fair to good overall. Thus, its feasibility may encourage prospective studies on its potential for more detailed noninvasive diagnosis and preoperative planning.

Comparison between fundamental and second-harmonic imaging echocardiography for calculation of left ventricular mass in children

In adults, calculation of left ventricular mass (LVM) has been shown to give higher values when based on M-mode measurements obtained by the second-harmonic imaging (SHI) technique than with the older fundamental imaging (FI) technique. No information is available in paediatric subjects. This study, therefore, compares LVM calculated from measurements obtained with SHI and FI in 14 children, aged 6.9-13.0 years. M-mode tracings were obtained in accordance with American Society of Echocardiography (ASE) recommendations. Three experienced sonographers performed measurements on each subject with both SHI and FI. The mean value was used in all calculations. LVM was calculated according to ASE convention and indexed by body surface area. LVM mean values were 58.9 +/- 9.7 g m(-2) for SHI and 57.8 +/- 8.2 g m(-2) for FI (P = 0.45). This preliminary study in a small group of paediatric subjects demonstrates no systematic differences between FI and SHI modalities in the calculation of LVM. The likely explanation is that the left ventricular endocardial border is usually well visualized with SHI as well as with FI in children.

Contrast Echocardiography Can Save Nondiagnostic Exams in Mechanically Ventilated Patients

Patients in an intensive care unit (ICU) under mechanical ventilation (MV) are very difficult to image by transthoracic echocardiography, diminishing the beneficial information that could be obtained by this noninvasive approach. The objective of this study is to assess whether the addition of a contrast agent to fundamental imaging (FI) can improve or change the initial diagnosis in cardiac postoperative patients under mechanical ventilation by enhancing endocardial border delineation and Doppler flow signal. Thirty mechanically ventilated post-cardiac surgery patients (20 men, mean age 61 +/- 13 years) were evaluated with FI before and after intravenous injection of contrast. Left ventricular endocardial border delineation score index (EBDSI), estimated left ventricular ejection fraction (LVEF), and color and spectral Doppler were analyzed. The use of contrast resulted in a significant increase in the number of well-delineated segments, with a salvage rate of 77% of nondiagnostic studies. EBDSI was 1.62 +/- 0.61, before contrast, increasing to 2.05 +/- 0.53 after it (P < 0.001). There was a change in the LVEF estimation in 5 exams, and a new wall motion abnormality was detected in other 4 exams, after the use of contrast. Moreover, a significant change was observed in the quantification of mitral regurgitation in 5 patients, in the aortic transvalvular peak gradient in 1 patient, and measurement of tricuspid regurgitation peak flow velocity in 8 patients. It is concluded that in cardiac postoperative patients under mechanical ventilation, intravenous injection of a contrast agent using FI resulted in a high salvage rate of studies and changed the initial diagnosis in a significant number of patients.

Hand-carried ultrasound performed at bedside in cardiology inpatient setting - a comparative study with comprehensive echocardiography

Background

Hand-carried ultrasound (HCU) devices have been demonstrated to improve the diagnosis of cardiac diseases over physical examination, and have the potential to broaden the versatility in ultrasound application. The role of these devices in the assessment of hospitalized patients is not completely established. In this study we sought to perform a direct comparison between bedside evaluation using HCU and comprehensive echocardiography (CE), in cardiology inpatient setting.

Methods

We studied 44 consecutive patients (mean age 54 ± 18 years, 25 men) who underwent bedside echocardiography using HCU and CE. HCU was performed by a cardiologist with level-2 training in the performance and interpretation of echocardiography, using two-dimensional imaging, color Doppler, and simple calliper measurements. CE was performed by an experienced echocardiographer (level-3 training) and considered as the gold standard.

Results

There were no significant differences in cardiac chamber dimensions and left ventricular ejection fraction determined by the two techniques. The agreement between HCU and CE for the detection of segmental wall motion abnormalities was 83% (Kappa = 0.58). There was good agreement for detecting significant mitral valve regurgitation (Kappa = 0.85), aortic regurgitation (kappa = 0.89), and tricuspid regurgitation (Kappa = 0.74). A complete evaluation of patients with stenotic and prosthetic dysfunctional valves, as well as pulmonary hypertension, was not possible using HCU due to its technical limitations in determining hemodynamic parameters.

Conclusion

Bedside evaluation using HCU is helpful for assessing cardiac chamber dimensions, left ventricular global and segmental function, and significant valvular regurgitation. However, it has limitations regarding hemodynamic assessment, an important issue in the cardiology inpatient setting.

Anatomic m-mode, a pertinent tool for the daily practice of transthoracic echocardiography

OBJECTIVES

We sought to compare anatomic M-mode (AMM), a new echocardiographic postprocessing option, and conventional M-mode (CMM) using fundamental imaging and tissue harmonic imaging.

METHODS

Transthoracic echocardiography was performed in 15 selected patients to analyze the reproducibility of AMM and in 47 patients to assess its clinical value versus CMM. Acquisitions were performed successively: CMM fundamental imaging; CMM tissue harmonic imaging; tissue harmonic imaging cineloops for AMM; and fundamental imaging cineloops for AMM. Quantitative analysis was performed offline. The angle alpha between the CMM line and the septal endocardial interface was calculated and the expected percentage of error in measuring left ventricular diameter was derived.

RESULTS

AMM analysis was reproducible. Optimal AMM full echocardiographic definition was obtainable in 77% of the population, whereas CMM was optimal for 49% because of scan line misalignment, causing a measurement overestimation exceeding 5%.

CONCLUSION

The ability with AMM to reduce the alpha angle to 0 degrees and, thus, avoid overestimation of left ventricular dimensions might improve follow-up in several pathologic conditions.

Effect of tissue harmonic imaging and contrast upon between observer and test-retest reproducibility of left ventricular ejection fraction measurement in patients with heart failure

AIMS

To investigate the effects of tissue harmonic imaging (THI) and contrast chamber opacification (LVO) upon measurement variability and reproducibility of echocardiographic left ventricular (LV) volume and ejection fraction (EF) measurements in patients with heart failure (HF).

BACKGROUND

Echocardiography is often used in HF patients to determine LV volumes and EF. However, current echo methods are variable and may not be applicable for repeat testing in individual patients. THI and LVO have both been shown to improve endocardial visualisation, but it remains to be determined whether this results in better measurement reproducibility.

METHODS

Thirty-one HF patients and 30 control subjects underwent echocardiography on two separate days. LV volumes were measured under four different imaging conditions: fundamental, THI, LVO and LVO with ECG-triggered Power Doppler. Chamber opacification, pulmonary transit time (PTT), endocardial enhancement, reproducibility and bias were assessed.

RESULTS

Chamber opacification was inferior and the PTT longer in the HF patients. PTT was related to LV volumes, EF, jugular venous pressure and mitral filling pattern. THI improved endocardial visualisation, and although LVO improved endocardial visualisation in the controls, it offered no benefit over THI in the HF patients. LV volumes and EF were different for each method and THI was the least variable method for repeat measurements.

CONCLUSIONS

THI improved endocardial visualisation and was the least variable of the techniques. LVO offered no further advantage in patients with HF and thus cannot be routinely advocated and since LV volumes and EF were different for each, these methods are neither comparable nor interchangeable for follow-up assessments.

Comparison of Echocardiography Using Tissue Harmonics and Contrast Harmonics with Radionuclide Angiography for the Assessment of Left Ventricular Function

Background

Left ventricular ejection fraction (LVEF) is a significant predictor of morbidity and mortality; however, the optimal noninvasive modality for the quantitative determination of LVEF is not apparent.

Hypothesis

We verified the hypothesis that the various echocardiographic methods of assessing LVEF using the Method of Discs with contrast (Optison human albumin microspheres; Amersham Health, Princeton, NJ) and visual assessment of LVEF using tissue harmonics and contrast harmonics compare favorably with radionuclide angiography (RNA).

Methods

In a prospective analysis, 24 consecutive patients scheduled to undergo RNA had an echocardiogram using tissue harmonics and contrast harmonics on the same day. LVEF was assessed by RNA by an experienced, blinded reader using manual determination of the region of interest. LVEF was calculated using the Method of Discs (Simpson's Rule) by a blinded sonographer. LVEF was visually estimated by two blinded readers using echocardiography with tissue harmonics and contrast harmonics on separate occasions.

Results

By linear regression analysis, LVEF determination by echocardiography with contrast using the Method of Discs correlated well with RNA (r = .835, p < .0005). Using Bland-Altman analysis, the second echocardiogram reader had excellent agreement with RNA, whereas the first reader had a mean difference of 5.25% (CI 1.3–9.2; p = .012) with visual assessment using tissue harmonics and a mean difference of 4.67% (CI 0.4–8.8; p = .031) with visual assessment using contrast harmonics compared with RNA. Thus, a small difference in agreement between RNA and echocardiographic visual estimation was noted that appeared to be primarily reader dependent.

Conclusions

LVEF determination with echocardiography with contrast using the Method of Discs correlated well with RNA and provided agreement across a range of cardiac functions. Visual echocardiographic assessment of LVEF with both tissue harmonics and contrast harmonics correlated well with RNA, but contrast harmonics did not appear to offer an advantage over tissue harmonics alone.

Interpretation of Left Ventricular Wall Motion During Stress Testing

This article describes the obstacles to stress echocardiographic interpretation, and reviews the techniques currently available that offer a more objective approach to stress wall motion analysis than the conventional visual methodology. These techniques include Doppler-based methods, such as myocardial Doppler velocity and strain rate imaging, as well as automated border detection techniques, such as acoustic quantification and color kinesis.

Comparison of two-dimensional echocardiographic tissue harmonic imaging and gated sestamibi single-photon emission computed tomographic left ventricular ejection fraction measurements

There was good correlation between left ventricular ejection fraction (EF) measurements employing 2-dimensional echocardiography with tissue harmonic imaging and single-photon emission computed tomography using quantitative gated scintigraphy, although in most patients, echocardiographic EF was lower. There was a high degree of agreement between these 2 techniques in assignment of EF to the categories of normal, mildly, moderately, or severely decreased. However, when EF categories did differ, echocardiography always resulted in assignment to a lower category.

Spatial coherence of the nonlinearly generated second harmonic portion of backscatter for a clinical imaging system

Correlation-based approaches to phase aberration correction rely on the spatial coherence of backscattered signals. The spatial coherence of backscatter from speckle-producing targets is predicted by the auto correlation of the transmit apodization (Van Cittert-Zernike theorem). Work by others indicates that the second harmonic beam has a wider mainlobe with lower sidelobes than a beam transmitted at 2f. The purpose of this paper is to demonstrate that the spatial coherence of backscatter for the second harmonic is different from that of the fundamental, as would be anticipated from applying the Van Cittert-Zernike theorem to the reported measurements of the second harmonic field. Another objective of this work is to introduce the concept of the effective apodization and to verify that the effective apodization of the second harmonic is narrower than the transmit apodization. The spatial coherence of backscatter was measured using three clinical arrays with a modified clinical imaging system. The spatial coherence results were verified using a pseudo-array scan in a transverse plane of the transmitted field with a hydrophone. An effective apodization was determined by backpropagating these values using a linear angular spectrum approach. The spatial coherence for the harmonic portion of backscatter differed systematically and significantly from the auto correlation of the transmit apodization.

A comparison of image quality between tissue harmonic imaging and fundamental imaging with an electronic radial scanning echoendoscope in the diagnosis of pancreatic diseases

BACKGROUND

The availability of an electronic radial scanning echoendoscope has facilitated the clinical use of tissue harmonic imaging. This study compares the quality of US images acquired by tissue harmonic imaging during electronic radial scanning EUS to those acquired by fundamental imaging.

METHODS

Electronic radial scanning EUS was performed in 108 patients with pancreatic lesions (58 cystic, 50 solid). US images acquired by fundamental imaging at a frequency of 7.5 MHz were compared with those acquired by tissue harmonic imaging by using transmitting and receiving frequencies of, respectively, 4.0 and 8.0 MHz at the same scanning plane. Cystic lesions were evaluated for boundary/septum and nodules, and solid lesions, for boundary and internal structure. US images acquired by tissue harmonic imaging and fundamental imaging during electronic radial scanning EUS were compared, by using a Likert scale for the respective evaluation criteria, by two independent endoscopists.

OBSERVATIONS

For cystic lesions, tissue harmonic images were significantly clearer than fundamental images for visualizing boundary and septum (p < 0.0001, both reviewers) and nodules (p = 0.0003, Reviewer 1; p = 0.0007, Reviewer 2). For solid lesions, tissue harmonic images were significantly clearer than fundamental images for visualizing boundary (p = 0.0003, Reviewer 1; p < 0.0001, Reviewer 2) and internal structures (p = 0.0003, Reviewer 1; p = 0.0009, Reviewer 2).

CONCLUSIONS

US images acquired by tissue harmonic imaging appear to be clearer compared with those acquired by fundamental imaging.

Comparison study of harmonic imaging (HI) and fundamental imaging (FI) in fetal echocardiography

OBJECTIVES

To directly compare the quality of harmonic imaging (HI) and fundamental imaging (FI) in fetal echocardiography and to determine any differences in image quality between the two modalities.

METHODS

Fetal echocardiograms were performed with the use of FI and HI in 58 fetuses, image quality and visualization of left and right atria, left and right ventricles, mitral and tricuspid valves, aortic and pulmonary valves, left and right ventricular outflow tracts were evaluated and compared between FI and HI.

RESULTS

Mean HI scores were higher than mean FI scores (2.73 +/- 0.43 vs 2.16 +/- 0.69, P < 0.001) for all the cardiovascular structures evaluated. Compared with FI, HI improved the image quality and visualization of fetal cardiac structures in subjects with both good (2.73 +/- 0.43 vs 2.88 +/- 0.32, P < 0.001) and suboptimal (1. 65 +/- 0.41 vs 2.58 +/- 0.47, P < 0.001) echocardiographic windows. The interobserver correlation coefficient for the grading scores was 0.74 (P < 0.001).

CONCLUSIONS

harmonic imaging enhances and improves the image quality of fetal echocardiography; and has important potential role in cardiac imaging in the fetus.

Harmonic ultrasound: a review

Harmonic ultrasound is a technique based on the principle of transmitting at frequency f and receiving at frequency 2f (or 1/2f). This technology has become available through the development of wide-bandwidth transducers. Microbubble contrast media produce a large amount of harmonic signal. Contrast harmonic ultrasound provides the opportunity to image patterns of high flow vasculature and overall perfusion. Regions of poor perfusion, including necrosis or infarction, can be identified with contrast harmonic ultrasound. While proportionately lower, tissues also produce harmonic signals. Tissue harmonic ultrasound sequences often improve subjective image quality compared to fundamental ultrasound in echocardiographic and abdominal examinations. This review will discuss the physical principles of harmonic ultrasound signal generation, medical and animal research applications, and an overview of current veterinary experiences.

Pitfalls of echocardiographic measurement in tissue harmonic imaging: in vitro and in vivo study

BACKGROUND

Tissue harmonic imaging (THI) is a useful method for endocardial border detection by transthoracic echocardiography, especially in technically difficult patients, even though accuracy of this method in the echocardiographic measurement is unclear. The purpose of this study is to evaluate the accuracy of echocardiographic measurement by THI in vivo and in vitro.

METHODS

In vitro, we measured wall thickness, dimension, and volume of the excised hearts by THI. In 11 patients, we assessed the comparative accuracy of THI and fundamental imaging (FI) in determination of left ventricular (LV) wall thickness, dimension, volume, and ejection fraction.

RESULTS

In vitro, thickness measurements by THI overestimated true length, and both volume and dimension measurements by THI underestimated true values. In vivo, LV ejection fraction measurements obtained by THI exhibited excellent correlation and agreement with those obtained by FI. However, LV wall thickness determined by THI was significantly larger than that determined by FI, and the dimensions and volume of LV measured by THI were significantly smaller than those measured by FI.

CONCLUSION

Although THI is an excellent imaging technique for determination of LV ejection fraction, echocardiographic measurement by THI underestimates LV dimensions and volume, and overestimates LV wall thickness.

Noninvasive evaluation of women with coronary artery disease

Coronary artery disease (CAD) is the leading cause of death in women. More women than men die of CAD each year, and unlike men, the death rate has not declined for women but has remained stable over the last 20 years. Despite these statistics, much less is known about the prevention, diagnosis, or treatment of CAD in women. The noninvasive diagnosis of CAD in women is difficult secondary to differences in physiology, etiology, presenting symptoms, risk factor prevalence, comorbid conditions, hormonal status, and body habitus between women and men. Echocardiography and Tc-99m sestamibi single photon emission computed tomography imaging are two noninvasive imaging techniques commonly combined with exercise or pharmacologic agents (dobutamine, adenosine, dipyridamole) that have recently evolved to address these differences. These evolutions and the role of both techniques in the diagnosis and prognosis of women with CAD will be reviewed in this article.

Role of echocardiography in the diagnosis and management of infective endocarditis

Infective endocarditis is a life-threatening disease with significant morbidity and mortality. Accurate and early diagnosis for initiation of effective treatment is essential in improving patient outcome. Echocardiography is currently the primary modality for the detection of vegetations and cardiac complications that result from endocarditis. Technological advances in echocardiography, particularly the development of transesophageal echocardiography (TEE), have revolutionized the diagnosis and management of infective endocarditis. With the enhanced resolution provided by TEE, vegetations and paravalvular complications can be reliably detected. Transthoracic and transesophageal echocardiography provides complementary information for patient management and follow-up, and is best used in conjunction with clinical data. By means of its high sensitivity and negative predictive value, TEE is essential in the evaluation of prosthetic valve endocarditis and the paravalvular complications of IE. All patients with suspected infective endocarditis should undergo transthoracic echocardiography, and most of these patients should also undergo TEE evaluation. The role of new technology such as harmonic and three-dimensional imaging is yet to be determined.

Improvement in echocardiographic evaluation of left ventricular wall motion using still-frame parametric imaging

BACKGROUND

Conventional echocardiographic assessment of left ventricular wall motion is based on visual interpretation of dynamic images, which depends on readers' experience. We tested the feasibility of evaluating endocardial motion using still-frame parametric images.

METHODS AND RESULTS

In protocol 1, integrated backscatter images were obtained in 8 anesthetized pigs at baseline, 5, and 60 seconds after left anterior descending coronary occlusion and during reperfusion. Images from 1 cardiac cycle were analyzed offline to create a parametric image of local video intensity oscillations. Ischemia-induced changes were quantified by segmenting the parametric images and calculating regional pixel-intensity profiles. In protocol 2, parametric images were obtained from contrast-enhanced echocardiograms in 30 patients (18 with wall-motion abnormalities; 12 control subjects). "Gold standard" for wall motion was determined from independent interpretations of dynamic images made by 3 experienced reviewers. Dynamic images were independently classified by 3 inexperienced and 3 intermediate-level readers. Interpretation was then repeated in combination with parametric images. Parametric images showed a bright band in the area spanned by endocardial motion, which gradually decreased in brightness and thickness in the left anterior descending territory during coronary occlusion in all animals. In patients, the agreement with the gold standard correlated with the readers' experience (68% inexperienced, 87% intermediate) and significantly improved by adding parametric images (83% and 91%, respectively).

CONCLUSION

Parametric imaging provides a still-frame display of regional endocardial motion, sensitive to track ischemia-induced abnormalities. When combined with dynamic images, this technique improves the accuracy of the interpretation of wall motion, especially by less experienced echocardiographers.

Real-time MR image acquisition during high-dose dobutamine hydrochloride stress for detecting left ventricular wall-motion abnormalities in patients with coronary arterial disease

PURPOSE

To compare the accuracy of real-time magnetic resonance (MR) imaging with that of standard echo-planar MR imaging for detecting myocardial wall-motion abnormalities at rest and during dobutamine hydrochloride-induced stress in patients with coronary arterial disease.

MATERIALS AND METHODS

In 22 patients with coronary arterial disease, left ventricular wall motion was examined at rest and during dobutamine hydrochloride stress, by using echo-planar MR imaging and a new technique with real-time segmented k-space turbo gradient-echo echo-planar MR imaging (repetition time, 16.5 msec; echo time, 6.8 msec). Wall-motion abnormalities were determined visually for each perfusion territory, and Cohen kappa coefficients were calculated for real-time imaging in comparison with echo-planar imaging. Coronary angiography was performed in all patients. Sensitivity and specificity for real-time and echo-planar imaging were calculated for detecting significant coronary arterial stenosis.

RESULTS

kappa values for detecting wall-motion abnormalities at real-time imaging, in comparison with echo-planar MR imaging, were 0.97 at rest and 0.94 at maximum dobutamine hydrochloride stress. At comparison with those of angiography, the sensitivity and specificity for detecting significant coronary arterial stenosis were 88% (14 of 16 patients) and 83% (five of six patients), respectively, for echo-planar imaging and 81% (13 of 16 patients) and 83% (five of six patients), respectively, for real-time imaging.

CONCLUSION

Real-time MR imaging is possible under stress conditions and allows accurate detection of wall-motion abnormalities.

Head-to-head comparison of fundamental, tissue harmonic and contrast harmonic imaging with or without an air-filled contrast agent, levovist, for endocardial border delineation in patients with poor quality images

Recent developments in tissue harmonic imaging and intravenous contrast agents have enhanced left ventricular endocardial border delineation (EBD). In a total of 48 patients with poor quality images, apical 4- and 2-chamber views were obtained with fundamental, tissue harmonic and contrast harmonic imaging with or without intravenous Levovist, an air-filled contrast agent. The left ventricle (LV) was divided into 12 segments, and the EBD of each segment was scored: (1) not visible, (2) barely visible, (3) well delineated. The EBD index (EBDI), defined as the sum of the endocardial scores divided by 12 was obtained for each patient. Of a total of 576 LV segments, 231 were scored as 1 by fundamental imaging and that number decreased to 125 segments by tissue harmonic imaging and 116 segments by fundamental imaging with Levovist. The number of segments scored as 1 decreased to 38 segments by tissue harmonic imaging with Levovist, and to 29 segments by contrast harmonic imaging with Levovist. The EBDI by fundamental imaging was 1.85+/-0.29, which improved significantly with the addition of Levovist (2.10+/-0.36, p<0.001) and was nearly identical to that by tissue harmonic imaging (2.15+/-0.32, p=NS). Tissue and contrast harmonic imaging with Levovist further enhanced the EBDI (2.43+/-0.26, 2.51+/-0.27, respectively). Levovist enhances EBD, even in the fundamental mode, to the level obtained with tissue harmonic imaging. Tissue harmonic and contrast harmonic imaging are the best modalities for enhancing EBD after Levovist injection.

Echocardiographic and magnetic resonance methods for diagnosing hibernating myocardium

Hibernating myocardium refers to regions of impaired left ventricular function at rest due to coronary artery disease that is reversible with revascularization. The accurate identification and assessment of myocardial viability is a critical aspect of the management of the patient with coronary artery disease and left ventricular dysfunction. Several non-invasive methods exist to assist the clinician in distinguishing those patients with significant regions of hibernating myocardium from those who have non-viable scar. This is important not only to identify those patients who would most benefit from percutaneous intervention or surgery, but also to spare the latter group from the morbidity and mortality associated with a revascularization procedure that would provide little benefit. While nuclear medicine imaging is the most widely used means for evaluating myocardial viability, alternative modalities have emerged and have gained increasing acceptance in recent years. This article will review the echocardiographic and magnetic resonance imaging (MRI) methods that are currently available or under investigation to assess myocardial viability. These techniques include rest and stress echocardiography, myocardial contrast echocardiography, stress MRI, contrast-enhanced MRI and magnetic resonance spectroscopy (MRS).

Initial experiences of tissue harmonic imaging in the diagnosis of fetal cardiac tumors

The usefulness of tissue harmonic imaging in prenatal diagnosis is illustrated in two fetuses with a cardiac tumor. Tissue harmonic imaging provided more informative images than conventional B-mode imaging, enabling the detection of the site of attachment of the cardiac tumor and estimation of intracardiac blood flow. The advantages of tissue harmonic imaging over conventional B-mode imaging in prenatal diagnosis are discussed.

Pulse inversion harmonic imaging improves endocardial border visualization in two-dimensional images: comparison with harmonic imaging

Pulse inversion harmonic imaging (PIHI) is a new modality that increases the detection of harmonic echoes and myocardial contrast by cancelling linearly transmitted signals. We tested whether PIHI improved the detection of endocardial borders in noncontrast 2-dimensional echocardiography. We compared PIHI with tissue harmonic imaging (THI), which decreases linearly transmitted signals using filters. Fundamental mode (FM) was compared with THI and PIHI in 50 consecutive patients. The global and segmental endocardial visualization scores measured with FM were significantly improved by using either THI or PIHI. The improvement of the global score compared with FM was slightly higher using PIHI than THI, because of an improved visualization of the base and the anterior wall with the PIHI technique compared with THI. The ratio of myocardial-to-cavity signal was similarly increased from FM with THI and PIHI. PIHI, a new modality for detection of myocardial contrast, can also be used for endocardial border visualization. It provides an improvement relative to THI for specific regions of the endocardium.

Nonlinear acoustics in diagnostic ultrasound

The propagation of ultrasonic waves is nonlinear. Phenomena associated with the propagation of diagnostic ultrasound pulses cannot be predicted using linear assumptions alone. These include a progressive distortion in waveform, the generation of frequency harmonics and acoustic shocks, excess deposition of energy and acoustic saturation. These effects occur most strongly when ultrasound propagates within liquids with comparatively low acoustic attenuation, such as water, amniotic fluid or urine. Within soft tissues, similar effects occur, although they are limited by absorption and scattering. Nonlinear effects are of considerable importance during acoustic measurements, especially when these are used to predict in situ exposure. Harmonic generation may be used to create images. These offer improvements over conventional B-mode images in spatial resolution and, more significantly, in the suppression of acoustic clutter and side-lobe artifacts. B/A has promise as a parameter for tissue characterisation, but methods for imaging B/A have shown limited success.