Ultrasound integrated backscatter tissue characterization of remote myocardial infarction in human subjects

Assessing engineered tissues and biomaterials using ultrasound imaging: In vitro and in vivo applications

Quantitative assessment of the structural, functional, and mechanical properties of engineered tissues and biomaterials is fundamental to their development for regenerative medicine applications. Ultrasound (US) imaging is a non-invasive, non-destructive, and cost-effective technique capable of longitudinal and quantitative monitoring of tissue structure and function across centimeter to sub-micron length scales. Here we present the fundamentals of US to contextualize its application for the assessment of biomaterials and engineered tissues, both in vivo and in vitro. We review key studies that demonstrate the versatility and broad capabilities of US for clinical and pre-clinical biomaterials research. Finally, we highlight emerging techniques that further extend the applications of US, including for ultrafast imaging of biomaterials and engineered tissues in vivo and functional monitoring of stem cells, organoids, and organ-on-a-chip systems in vitro.

Ultrasonic Assessment of Myocardial Microstructure in Hypertrophic Cardiomyopathy Sarcomere Mutation Carriers With and Without Left Ventricular Hypertrophy

BACKGROUND

The noninvasive assessment of altered myocardium in patients with genetic mutations that are associated with hypertrophic cardiomyopathy (HCM) remains challenging. In this pilot study, we evaluated whether a novel echocardiography-based assessment of myocardial microstructure, the signal intensity coefficient (SIC), could detect tissue-level alterations in HCM sarcomere mutation carriers with and without left ventricular hypertrophy.

METHODS AND RESULTS

We studied 3 groups of genotyped individuals: sarcomere mutation carriers with left ventricular hypertrophy (clinical HCM; n=36), mutation carriers with normal left ventricular wall thickness (subclinical HCM; n=28), and healthy controls (n=10). We compared measurements of echocardiographic SIC with validated assessments of cardiac microstructural alteration, including cardiac magnetic resonance measures of interstitial fibrosis (extracellular volume fraction), as well as serum biomarkers (NTproBNP, hs-cTnI, and PICP). In age-, sex-, and familial relation-adjusted analyses, the SIC was quantitatively different across subjects with overt HCM, subclinical HCM, and healthy controls (P<0.001). Compared with controls, the SIC was 61% higher in overt HCM and 47% higher in subclinical HCM (P<0.001 for both). The SIC was significantly correlated with extracellular volume (r=0.72; P<0.01), with left ventricular mass and E' velocity (r=0.45, -0.60, respectively; P<0.01 for both), and with serum NTproBNP levels (r=0.36; P<0.001).

CONCLUSIONS

Our findings suggest that the SIC could serve as a noninvasive quantitative tool for assessing altered myocardial tissue characteristics in patients with genetic mutations associated with HCM. Further studies are needed to determine whether the SIC could be used to identify subclinical changes in patients at risk for HCM and to evaluate the effects of interventions.

Review: New approaches to the assessment of left ventricular hypertrophy

In hypertension, Left ventricular hypertrophy is initially a useful compensatory process that represents an adaptation to increased ventricular wall stress; however, it is also the first step toward the development of overt clinical disease. For this reason most international guidelines recommend the assessment of cardiac target organ damage in hypertensive patients for cardiovascular risk stratification. It is therefore of great importance to keep in mind the strengths and weakness of the different available methods for LVH assessment.

Several methods are currently available for the assessment of LVH; however the various techniques differ in cost, availability, sensitivity and specificity. Due to its wide availability and its low cost, eLectrocardiography should be part of all routine assessment of subjects with high blood pressure; however, despite its good specificity, the sensitivity for LVH detection is low. Several other methods have been proposed for LVH detection. Cardiac magnetic resonance imaging allows 3D reconstruction of the heart with high spatial resolution; however its main limitation is represented by the relatively low availability and by its costs. Echocardiography certainly represents a valuable method for the detection of LVH in hypertensive patients, due to its wide availability and its relatively low cost. The main limitations of the technique are represented by the lower spatial resolution and reproducibility in comparison with magnetic resonance. The development of new matrix-array transducers and new software for 3D reconstruction with echocardiography make this approach particularly promising for the future; in the meantime, standard echocardiography, widely available and with low cost, will probably remain the most used tool for the evaluation of left ventricular structure and function in hypertension.

Efficiency of quantitative longitudinal peak systolic strain values using automated function imaging on transthoracic echocardiogram for evaluating left ventricular wall motion: new diagnostic criteria and agreement with naked eye evaluation by experienced cardiologist

PURPOSE

To evaluate the efficiency of automated function imaging (AFI) on transthoracic echocardiogram (TTE) for detecting left ventricular (LV) wall motion (LVWM) abnormalities, we compared longitudinal peak systolic strain (LPSS) measurements using AFI with naked eye TTE evaluations by experienced cardiologists and non-experienced residents.

MATERIALS AND METHODS

A total of 352 segments of LV myocardium from 22 consecutive subjects with LVWM abnormalities based on American Heart Association classifications (11 male, mean age 58 ± 14 years) on previous TTE (Vivid-7, GE) were evaluated. LPSS was measured using stored AFI data. Naked eye evaluation of LVWM was performed by 2 experienced cardiologists and 2 non-experienced residents.

RESULTS

AFI successfully tracked 342 (97%) of all segments (mean LPSS -14.8 ± 8.1%). A significant strong negative correlation was observed between LV ejection fraction using method of disks and global LPSS (R=-0.8974). Temporary AFI criteria of LPSS were normal <-12; hypokinesis -12-2; and akinesis >2. Of 342 segments, 239, 87, and 16 segments were diagnosed as normal, hypokinesis, and akinesis, respectively. Level of agreement and kappa coefficients between qualitative evaluation of LVWM by AFI temporary criteria and qualitative evaluation of LVWM by experienced cardiologist 2 (0.784 and 0.479, respectively) were inferior to those comparing experienced cardiologists (0.845 and 0.595) but superior comparing experienced cardiologist with non-experienced resident (0.696 and 0.323), and between the 2 non-experienced-residents (0.682 and 0.347).

CONCLUSION

Qualitative evaluation of LVWM using temporary AFI criteria had a 97% success rate and agreed well with findings of an experienced cardiologist. AFI can be a useful tool for training residents.

A novel power spectrum calculation method using phase-compensation and weighted averaging for the estimation of ultrasound attenuation

An estimation of ultrasound attenuation in soft tissues is critical in the quantitative ultrasound analysis since it is not only related to the estimations of other ultrasound parameters, such as speed of sound, integrated scatterers, or scatterer size, but also provides pathological information of the scanned tissue. However, estimation performances of ultrasound attenuation are intimately tied to the accurate extraction of spectral information from the backscattered radiofrequency (RF) signals. In this paper, we propose two novel techniques for calculating a block power spectrum from the backscattered ultrasound signals. These are based on the phase-compensation of each RF segment using the normalized cross-correlation to minimize estimation errors due to phase variations, and the weighted averaging technique to maximize the signal-to-noise ratio (SNR). The simulation results with uniform numerical phantoms demonstrate that the proposed method estimates local attenuation coefficients within 1.57% of the actual values while the conventional methods estimate those within 2.96%. The proposed method is especially effective when we deal with the signal reflected from the deeper depth where the SNR level is lower or when the gated window contains a small number of signal samples. Experimental results, performed at 5MHz, were obtained with a one-dimensional 128 elements array, using the tissue-mimicking phantoms also show that the proposed method provides better estimation results (within 3.04% of the actual value) with smaller estimation variances compared to the conventional methods (within 5.93%) for all cases considered.

Ultrasound image segmentation and tissue characterization

Ultrasound image segmentation deals with delineating the boundaries of structures, as a step towards semi-automated or fully automated measurement of dimensions or for characterizing tissue regions. Ultrasound tissue characterization (UTC) is driven by knowledge of the physics of ultrasound and its interactions with biological tissue, and has traditionally used signal modelling and analysis to characterize and differentiate between healthy and diseased tissue. Thus, both aim to enhance the capabilities of ultrasound as a quantitative tool in clinical medicine, and the two end goals can be the same, namely to characterize the health of tissue. This article reviews both research topics, and finds that the two fields are becoming more tightly coupled, even though there are key challenges to overcome in each area, influenced by factors such as more open software-based ultrasound system architectures, increased computational power, and advances in imaging transducer design.

Hybrid spectral domain method for attenuation slope estimation

Attenuation estimation methods for medical ultrasound are important because attenuation properties of soft tissue can be used to distinguish between benign and malignant tumors and to detect diffuse disease. The classical spectral shift method and the spectral difference method are the most commonly used methods for the estimation of the attenuation; however, they both have specific limitations. Classical spectral shift approaches for estimating ultrasonic attenuation are more sensitive to local spectral noise artifacts and have difficulty in compensating for diffraction effects because of beam focusing. Spectral difference approaches, on the other hand, fail to accurately estimate attenuation coefficient values at tissue boundaries that also possess variations in the backscatter. In this paper, we propose a hybrid attenuation estimation method that combines the advantages of the spectral difference and spectral shift methods to overcome their specific limitations. The proposed hybrid method initially uses the spectral difference approach to reduce the impact of system-dependent parameters including diffraction effects. The normalized power spectrum that includes variations because of backscatter changes is then filtered using a Gaussian filter centered at the transmit center frequency of the system. A spectral shift method, namely the spectral cross-correlation algorithm is then used to compute spectral shifts from these filtered power spectra to estimate the attenuation coefficient. Ultrasound simulation results demonstrate that the estimation accuracy of the hybrid method is better than the centroid downshift method (spectral shift method), in uniformly attenuating regions. In addition, this method is also stable at boundaries with variations in the backscatter when compared with the reference phantom method (spectral difference method). Experimental results using tissue-mimicking phantom also illustrate that the hybrid method is more robust and provides accurate attenuation estimates in both uniformly attenuating regions and across boundaries with backscatter variations. The proposed hybrid method preserves the advantages of both the spectral shift and spectral difference approaches while eliminating the disadvantages associated with each of these methods, thereby improving the accuracy and robustness of the attenuation estimation.

Measurements of the anisotropy of ultrasonic attenuation in freshly excised myocardium

Echocardiography requires imaging of the heart with sound propagating at varying angles relative to the predominant direction of the myofibers. The degree of anisotropy of attenuation can significantly influence ultrasonic imaging and tissue characterization measurements in vivo. This study quantifies the anisotropy of attenuation of freshly excised myocardium at frequencies typical of echocardiographic imaging. Results show a significantly larger anisotropy than previously reported in specimens of locally unidirectional myofibers. Through-transmission radio frequency-based measurements were performed on specimens from 12 ovine and 12 bovine hearts. Although ovine hearts are closer in size to human, the larger size of bovine hearts offers the potential for specimens in which myofibers are more nearly unidirectionally aligned. The attenuation coefficient increased approximately linearly with frequency. The mean slope of attenuation with frequency was 3-4 times larger for propagation parallel than for perpendicular to the myofibers. At perpendicular insonification, slopes between ovine and bovine myocardium were approximately equal. However, attenuation in bovine specimens was larger for angles approaching parallel. The difference in results for parallel appears consistent with what might be expected from increased myofiber curvature associated with smaller lamb hearts. Quantitative knowledge of anisotropy of attenuation may be useful in understanding mechanisms underlying the interaction of ultrasound with myocardium.

Serial assessment of myocardial properties using cyclic variation of integrated backscatter in an adriamycin-induced cardiomyopathy rat model

Although adriamycin (Doxorubicin) is one of the most effective and useful antineoplastic agents for the treatment of a variety of malignancies, its repeated administration can induce irreversible myocardial damage and resultant heart failure. Currently, no marker to detect early cardiac damage is available. The purpose of this study was to investigate whether an assessment of the acoustic properties of the myocardium could enable the earlier detection of myocardial damage after adriamycin chemotherapy. Forty Wistar rats were treated with adriamycin (2 mg/kg, i.v.) once a week for 2, 4, 6 or 8 weeks consecutively. Left ventricular ejection fraction (LVEF) was calculated using M-mode echocardiography data. The magnitude of cardiac cycle dependent variation of integrated backscatter (CVIB) of the myocardium was measured in the mid segment of the septum and in the posterior wall of the left ventricle, using a real time two dimensional integrated backscatter imaging system. LVEF was significantly lower in the adriamycin-treated 8-week group than in the controls (75+/-9 vs 57+/-8%, p<0.05). Myocyte damage was only seen in the 8-week adriamycin-treated group. However, no significant changes of CVIB were observed between baseline or during follow-up in the ADR or control group. In conclusion, serial assessment of the acoustic properties of the myocardium may not be an optimal tool for the early detection of myocardial damage after doxorubicin chemotherapy in a rat model.

Two-dimensional strain-a novel software for real-time quantitative echocardiographic assessment of myocardial function

OBJECTIVES

We sought to assess the feasibility of 2-dimensional strain, a novel software for real-time quantitative echocardiographic assessment of myocardial function.

METHODS

Conventional and a novel non-Doppler-based echocardiography technique for advanced wall-motion analysis were performed in 20 patients with myocardial infarction and 10 healthy volunteers from the apical views. Two-dimensional strain is on the basis of the estimation that a discrete set of tissue velocities are present per each of many small elements on the ultrasound image. This software permits real-time assessment of myocardial velocities, strain, and strain rate. These parameters were also compared with Doppler tissue imaging measurements in 10 additional patients.

RESULTS

In all, 80.3% of infarct and 97.8% of normal segments could be adequately tracked by the software. Peak systolic strain, strain rate, and peak systolic myocardial velocities, calculated from the software, were significantly higher in the normal than in the infarct segments. In the 10 additional patients, velocities, strain, and strain rate obtained with the novel software were not significantly different from those obtained with Doppler tissue imaging.

CONCLUSION

Two-dimensional strain can accomplish real-time wall-motion analysis, and has the potential to become a standard for real-time automatic echocardiographic assessment of cardiac function.

Microalbuminuria Is Associated with Reduced Cardiac Cyclic Variation of Integrated Backscatter Signal in Severe Hypertension

OBJECTIVE

Microalbuminuria (MA) as a marker of systemic vascular disease and left ventricular (LV) hypertrophy is associated with increased cardiovascular mortality and morbidity in patients with essential hypertension. The aim of this study was to investigate changes in cardiac cycle-dependent variation of integrated backscatter signals (CVIBS) in hypertensive patients with MA.

METHODS

Randomly selected 60 hypertensive patients (mean age 51 +/- 8) with uncontrolled blood pressure (BP) (>/=130 mmHg systolic and/or 85 mmHg diastolic) were included. All patients underwent urinary albumin excretion (UAE) measurements, 24-hour ambulatory BP monitoring, and LV echocardiographic examination. UAE was measured in two separate 24-hour urine collection and mean of two values was taken into consideration. Normotensive 20 healthy subjects served as controls. CVIBS values were obtained from mid-anteroseptal, mid-posterolateral, and mid-inferior areas at the papillary muscle level in the parasternal short-axis view. CVIBS was defined as the difference in integrated backscatter values between systole and diastole. CVIBS values in MA positive patients were compared with the values in MA negative patients and control subjects.

RESULTS

Twelve patients had MA (UAE 30 to 300 mg/day) while 48 patients had normal UAE (<30 mg/day). The wall thickness (at septum and posterior) and left ventricular mass index (LVMI) values were all significantly higher in hypertensive patients with MA (P < 0.01). The CVIBS values in MA positive group were significantly lower than the CVIBS values both in MA negative hypertensive patients and control subjects (P < 0.01).

CONCLUSION

This study demonstrates that in hypertensive patients a high LVMI is associated with reduced CVIBS values and MA appears to be a marker of hypertrophy.

Ultrasonic analysis of anthracycline-induced myocardial damage using cyclic variation of integrated backscatter

To test the feasibility of integrated backscatter (IB) for detecting anthracycline cardiotoxicity, we performed conventional echocardiography and IB analysis. For interindividual comparison, 32 patients with non-Hodgkin's lymphoma and 14 control subjects were selected. Of the patients, 10 had been treated with doxorubicin doses of </=200 mg/m(2) (low dose), 15 with </=400 mg/m(2) (moderate dose), and 7 with >400 mg/m(2) (high dose). In intraindividual comparison, 8 patients were examined before doxorubicin therapy and at a dose of 100 mg/m(2) and 8 were examined before and at a 300-mg/m(2) dose. Cyclic variation of IB (CV-IB) was obtained at the left ventricular posterior wall, using a modified, commercially available system in M-mode format. In interindividual comparison, CV-IB in high- and moderate-dose groups was smaller. In intraindividual comparison, CV-IB decreased after treatment with 300 mg/m(2) of doxorubicin. CV-IB was affected in some patients treated with a moderate dose of doxorubicin. IB analysis may be helpful for detecting early anthracycline cardiotoxicity.

Ultrasonic myocardial tissue characterization in patients with hypertrophic cardiomyopathy and pressure-overloaded hypertrophy by backscattered energy temporal analysis

This study measured integrated backscatter (IB) values in the subendocardium and subepicardium of patients with hypertrophy using the newly developed Backscattered Energy Temporal Analysis (BETA) system, and evaluated the differences of acoustic properties according to etiology. Twenty-one patients with hypertrophic cardiomyopathy (HCM), 16 with pressure-overloaded hypertrophy (POH), and 21 controls were studied. M-mode formatted IB images were obtained using BETA and the region of interest (ROI), automatically divided into epicardial and endocardial halves of the myocardium, was placed in the ventricular septum and posterior wall. Values for the cyclic variation of IB (CVIB) in the entire ROI and in each half of the ROI were obtained. CVIB significantly decreased in the ventricular septum in HCM and POH compared with normal subjects, but there were no significant differences between HCM and POH. In the posterior wall, the CVIB was less in the subendocardium than in the epicardium in POH, and was also less than in normal subjects (7.0+/-1.7 dB vs 8.6+/-1.9 dB and 8.8+/-2.1 dB, p<0.05, respectively). Separate ultrasonic tissue characterization of the subendocardium and subepicardium provides further etiological information of various heart diseases.

Enhanced method for predicting left ventricular reverse remodeling after surgical repair of aortic regurgitation: application of ultrasonic tissue characterization

To predict left ventricular (LV) reverse remodeling after surgical repair of aortic regurgitation, we examined 30 patients with aortic regurgitation accompanying LV dilatation by myocardial tissue characterization with integrated backscatter method. Before and after operation, the magnitude of cyclic variation of integrated backscatter (CVIB) was obtained from anterior septum and posterior wall, and averaged value was calculated in each patient. Before operation, LV end-diastolic dimension, fractional shortening, and LV end-diastolic pressure were not significantly different between the patients with (group GR) and without (group PR) decreased LV end-diastolic dimension after operation. Under these conditions, CVIB, which was 9.6 +/- 1.0 dB from healthy volunteers, was significantly greater in group GR, 5.7 +/- 1.4 dB, than that in group PR, 3.8 +/- 0.8 dB (P =.0003). The patients with CVIB >/= 4 before operation were expected to have reverse remodeling after operation with a sensitivity of 79%, a specificity of 82%. These data indicate that preoperative CVIB from the left ventricle provides pivotal information for predicting reverse remodeling after operation for aortic regurgitation in addition to the conventional echocardiographic parameters.

Novel ultrasonic fusion imaging method based on cyclic variation in myocardial backscatter

Quantitative ultrasonic tissue characterisation of the myocardium based on integrated backscatter (IB) has the potential of becoming an effective method for detecting and evaluating myocardial ischaemia. To facilitate IB-based clinical applications, a new imaging method has been developed that combines the anatomical information of a B-mode image with the contractile performance of a selected myocardial region. To produce such a fusion image, a region of interest (ROI) in a B-mode cardiac image was first selected by the user. Algorithms for detection of the endocardium and epicardium were developed, and the resulting mean distance between the computer-detected curve and the manually traced curve was 0.83mm for the endocardium and 0.58mm for the epicardium. The cyclic variation of IB (CVIB) of each myocardial tissue element within the ROI was then calculated over one cardiac cycle. Finally, a grey-scale B-mode image at the end of diastole was displayed as a still image, and the pixels representing the myocardial tissue in the ROI colour-coded according to the corresponding CVIB over the past heart cycle. Both the B-mode image and the colour-coded region were refreshed (up-dated) at the next end-of-diastole. Preliminary results from normal (CVIB= 10-12dB) and ischaemic (CVIB = 5-7 dB) canine hearts are presented that demonstrate the utility of this new imaging method.

A point process approach to assess the frequency dependence of ultrasound backscattering by aggregating red blood cells

To study the shear-thinning rheological behavior of blood, an acoustical measurement of the erythrocyte aggregation level can be obtained by analyzing the frequency dependence of ultrasonic backscattering from blood. However, the relation that exists among the variables describing the aggregation level and the backscattering coefficient needs to be better clarified. To achieve this purpose, a three-dimensional random model, the Neyman-Scott point process, is proposed to simulate red cell clustering in aggregative conditions at a low hematocrit (H<5%). The frequency dependence of the backscattering coefficient of blood, in non-Rayleigh conditions, is analytically derived from the model, as a function of the size distribution of the aggregates and of their mass fractal dimension. Quantitative predictions of the backscatter increase due to red cell aggregation are given. The parametric model of backscatter enables two descriptive indices of red cell aggregation to be extracted from experimental data, the packing factor W and the size factor delta. Previously published backscatter measurements from porcine whole blood at 4.5% hematocrit, in the frequency range of 3.5 MHz-12.5 MHz, are used to study the shear-rate dependence of these two indices.

Dipyridamole stress ultrasonic myocardial tissue characterization in patients with Kawasaki disease

Dipyridamole stress integrated backscatter (IBS) was used for evaluation of myocardial ischemia or damage in 31 children with coronary artery lesions caused by Kawasaki disease, in comparison with thallium-201 myocardial imaging. All patients underwent echocardiography at rest and after dipyridamole stress at the anterior interventricular septum, posterior wall (PW), and inferior wall (INF). At rest, no significant difference was seen in cyclic variation (CV) of IBS in the regions with normal or abnormal distribution on Tl-201 imaging. But in the regions showing abnormal distribution after stress, CV decreased significantly. A delayed study after stress showed the recovery of CV to the level at rest in all patients. Sensitivity of abnormal cyclic variation integrated backscatter was 75% in the PW and 91% in the INF, and specificity was 91% in the PW and 90% in the INF, compared with the results of thallium-201 imaging. Dipyridamole stress IBS can provide sensitive detection of myocardial ischemia or damage in Kawasaki disease.

Prediction of contractile reserve by cyclic variation of integrated backscatter of the myocardium in patients with chronic left ventricular dysfunction

OBJECTIVE

To clarify whether assessment of the acoustic properties of the myocardium at rest can predict contractile reserve in patients with chronic left ventricular dysfunction.

METHODS

23 patients (mean (SD) age 63 (12) years) with chronic left ventricular dysfunction were studied. The magnitude of cardiac cycle dependent variation of integrated backscatter (CVIB) of the myocardium was measured at rest in the basal and mid segment of the septum and posterior wall of the left ventricle, using a real time two dimensional integrated backscatter imaging system. The results were compared with the percentage wall thickening and the wall motion at rest and during low dose dobutamine infusion. The wall motion was graded as normal, hypokinetic, or akinetic and contractile reserve was considered present when an akinetic or hypokinetic segment improved during dobutamine infusion.

RESULTS

The CVIB at rest correlated with per cent wall thickening at rest and during dobutamine infusion (at rest, r = 0.61, p < 0.0001, during dobutamine, r = 0.76, p < 0.0001). Of the 76 segments examined, 27 showed contractile reserve. The mean CVIB at rest was significantly greater in segments with contractile reserve than in those without (p < 0.0001). CVIB above 3 dB at rest predicted segments with contractile reserve with a sensitivity and specificity of 81% and 60%, respectively (p < 0.0001).

CONCLUSIONS

CVIB reflected not only myocardial contractility but also the functional capacity of the myocardium. It predicted segmental contractile reserve in patients with chronic left ventricular dysfunction.

Ultrasonic tissue characterization with integrated backscatter during inotropic stimulation

Ultrasonic tissue characterization with integrated backscatter is an objective method to quantitatively define the physical state of the myocardium. To determine if backscatter imaging during inotropic stimulation could be used objectively to determine the myocardial viability and ischemia in patients with ischemic heart disease, the backscatter changes were examined in 23 patients with myocardial infarction during dobutamine stress two-dimensional (2-D) echocardiography. Coronary angiography was performed within 1 to 2 days after the stress test. The results of this study demonstrated that changes in backscatter variability correlated significantly with the wall motion changes in stress echocardiography during dobutamine infusion (p < 0.0001). In addition, it was shown that the backscatter changes were significantly different in various types of myocardial tissue. In 23 healthy control segments, the ultrasonic backscatter variability was preserved and unchanged during inotropic stimulation (p = NS). In 15 viable infarct zones, restoration or an increase in backscatter variability during low-dose dobutamine infusion was noted, this being lost when ischemia developing during high-dose dobutamine infusion (p < 0.01). In 9 nonviable infarct zones, the phase-weighted variation was usually < or = 0 and did not change significantly during inotropic stimulation, regardless of the patency of the infarct-related arteries. In 15 remote ischemic myocardial zones, the backscatter variability was preserved at the baseline level, did not change during low-dose dobutamine infusion, but decreased significantly during high-dose dobutamine stress (p < 0.01). In conclusion, dobutamine stress tissue characterization could offer an objective approach for the detection of myocardial viability and ischemia, and might be a useful adjunct to the conventional stress echocardiography.

Detection of residual tissue viability within the infarct zone in patients with acute myocardial infarction: ultrasonic integrated backscatter analysis versus dobutamine stress echocardiography

OBJECTIVES

The goals of this study were to analyze temporal changes in cardiac cyclic variation of integrated backscatter (CVIB) in acute myocardial infarction (AMI) and to investigate the predictive value of CVIB normalization compared with that of dobutamine stress echocardiography (DSE) in the assessment of functional recovery after revascularization.

BACKGROUND

The normal CVIB is blunted by ischemia and recovers early after reperfusion, faster than wall motion improvement. Analysis of CVIB has been widely investigated for its potential to detect viable myocardium in the early stage of infarction. No studies have compared CVIB analysis with other techniques for viability assessment in patients with acute ischemic.

METHODS AND RESULTS

Integrated backscatter images were obtained in 12 patients with AMI on days 1, 3, and 7 after admission and 1 month after revascularization. On day 7, DSE was performed in all patients. On admission, 22 of 144 segments were dyssynergic. On day 1, CVIB was abnormal in all 22 infarcted segments, on day 3, in 16, and on day 7, in only 10 infarcted segments. Eight of 10 segments nonviable by CVIB (CVIB-nonviable) were also nonrespondent by DSE; whereas 12 of 14 segments viable by DSE (DSE-viable) were also CVIB-viable. At follow-up, 10 CVIB-viable segments and 1 CVIB-nonviable segment showed functional recovery; whereas 10 of 14 DSE-viable segments showed functional recovery. Thus the positive predictive value of CVIB and DSE was 83% and 72%, respectively, with a diagnostic agreement between techniques in 77% of segments.

CONCLUSIONS

Our data suggest that the normalization in CVIB in the first week after AMI accurately predicts residual tissue viability within the infarct zone. We also observed that the initial pattern of cyclic variation may be predictive of functional recovery. Finally, we found a good correlation between the recovery of a normal CVIB in segments that were still dysfunctional and a more validated method to assess tissue viability, such as the dobutamine test.

Alterations in ultrasonic backscatter during intra-aortic balloon counterpulsation support in patients with acute myocardial infarction

Alterations of ultrasonic backscatter parameters have been evident in humans with myocardial infarction or ischemia. The backscatter variability could be restored in ischemic or stunned myocardium after reperfusion. The aims of this study were to determinate changes in regional myocardial ultrasonic backscatter during intra-aortic balloon counterpulsation (IABP) support in patients with acute myocardial infarction (AMI), and to evaluate whether backscatter imaging could be a functional guide of IABP support. A total of 9 patients with AMI were investigated during IABP support with a two-dimensional (2-D) ultrasonic backscatter imaging approach for parasternal short-axis view. Coronary angiography was performed in 6 of the 9 patients. A total of 21 vessel territories were studied in different modes of IABP support: 1:1, 1:2 and standby. Restoration of cyclic variation of backscatter after IABP support was demonstrated in 10 vessel territories. Failure of restoration of cyclic variation of backscatter after IABP support was noted in 6 vessel territories with severe coronary lesions (total or nearly total occlusion) or scar tissue. No changes of the ultrasonic backscatter were found in nonischemic vessel territories with patent coronary arteries or TIMI III coronary flow. In addition, the wall motion score did not change significantly with different IABP support. These results suggest that IABP could restore the cyclic variation of backscatter in ischemic myocardium. Myocardial anisotropy may play an influential role in the alterations of ultrasonic backscatter. We propose that ultrasonic backscatter could be a noninvasively functional guide of IABP use in patients with AMI.

[Characterization of myocardial tissue by ultrasound: backscatter]

One of the most important goals in Cardiology is to identify, noninvasively, the normal as well as pathological changes in structure and function of myocardial tissue in order to recognize their etiology and severity. Ultrasonic Tissue Characterization is an approach to define the physical state of the heart by the analysis of the pathological changes that modify cardiac tissue physical properties, therefore generating an ultrasonic signal alteration. Among the most practical types of analysis of this data is the acoustic parameters measurement, and measurements based on integrated backscatter have been utilized the most. Backscatter is the ultrasonic quantification reflected back to the transducer, therefore emanating from myocardial structures or "scatterers". This method has been used to study many patients with hypertrophy, cardiomyopathies, cardiac allograft rejection. But is the investigation of myocardial ischemia-viability one of the most clinically relevant applications because of the importance of selecting, non-invasively, and at a relatively low cost those patients with coronary artery disease in whom myocardial asynergy is noted by conventional echocardiography and/or angiography. The magnitude of alterations in backscatter measurements such as the cyclic variation of integrated backscatter are markers of myocardial viability and could better identify patients who stand to benefit the most revascularization procedures.

Real time assessment of myocardial revascularization during coronary artery bypass surgery by means of ultrasonic integrated backscatter

OBJECTIVE

The recovery of cyclic variation (CV) of ultrasonic integrated backscatter (IB) may provide a more sensitive predictor of the success of myocardial revascularization. This study was designed to elucidate the possibility of real time assessment of coronary artery bypass grafting (CABG) using CV of IB.

METHODS

We studied 10 patients (61 +/- 4 years old) with the perfused areas by stenosed or occluded LAD without myocardial infarction. There were six ischemic dysfunctional areas, and four ischemic but non-dysfunctional areas. The CV of IB was measured before and just after extracorporeal circulation (ECC). Wall motion was analyzed by segmental wall thickening during systole at the same time of the IB analysis during CABG and at 3 weeks after CABG. Those 10 areas were completely revascularized.

RESULTS

In the non-dysfunctional areas, wall thickening did not change and remained at normal values before and after ECC, and 3 weeks after CABG (31 +/- 3% 29 +/- 3% and 29 +/- 5%, respectively). The magnitude of CV of IB did not also change before and after ECC (8.0 +/- 1.6 dB and 7.8 +/- 1.3 dB). However, in the ischemic dysfunctional areas, while wall thickening did not change before and after ECC (21 +/- 5% and 20 +/- 5%), it increased and reached similar values as the non-dysfunctional regions at 3 weeks after CABG (26 +/- 7%, P < 0.01 vs. before and after ECC values). The magnitude of CV of IB increased even after ECC (3.71 +/- 0.4 dB vs. 7.4 +/- 3.5 dB, P < 0.05), and reached the same level as those in the non-dysfunctional areas. There was a significant relationship between wall thickening at 3 weeks after bypass grafting and magnitude of CV of IB after ECC (r = 0.67, P < 0.05).

CONCLUSIONS

Improvement in wall motion was gradually attained after bypass grafting. On the contrary, an increase in the magnitude of CV of IB was obtained immediately after myocardial revascularization. Our data suggest that CV of ultrasonic IB method can provide close real time information regarding the effectiveness of bypass surgery.

Dependence of "apparent" magnitude on the time delay of cyclic variation of myocardial backscatter

The goal of this study was to determine if the "apparent" magnitude of the cyclic variation, defined as the difference between the values of integrated backscatter at end-diastole and end-systole, was dependent on the corresponding time delay. We measured the cyclic variation in four myocardial segments of the parasternal short-axis view in 23 healthy subjects. The "apparent" magnitude, actual magnitude, and time delay were compared for each segment. Measured time delays were: 2.22+/-0.71 (lateral wall); 1.65+/-0.66 (inferior septum); and approximately 1.0 for the anterior septum and posterior wall. Segments exhibiting large time delays (> 1.0) resulted in a reversal in sign of the "apparent" magnitude of cyclic variation in one instance, and underestimated the true magnitude in both cases. Thus, estimates of the "apparent" magnitude of the cyclic variation are dependent on the associated time delay, whereas a properly defined magnitude is not.

Myocardial tissue characterization in heart failure by real-time integrated backscatter

OBJECTIVE

Differentiation between normal and abnormal physical state of the myocardium, not possible with conventional echocardiography, so far could be done with integrated backscatter (IBS) as a research tool only.

METHODS

This study investigates myocardial texture analysis with new commercially available real time IBS in 12 normal individuals and in 18 patients with severe left ventricular dysfunction due to coronary artery disease (CAD) in 8 and dilated cardiomyopathy (DCM) in 10 patients. Analysis of IBS amplitude and cyclic variation (dB) in the parasternal long and short axis view of the septum and the posterior wall were measured and corrected with IBS curve of the blood to get absolute values.

RESULTS

Compared to normal individuals patients with left ventricular dysfunction had a reduced myocardial cyclic variation (P<0.0001), which correlated to regional systolic wall thickening (r=0.64, P=0.001) and global shortening fraction (r=0.62, P<0.01). Although systolic wall thickening in the posterior wall was lower in CAD patients (% thickening, 11.9+/-10 vs. 21.9+/-8, P=0.004), absolute cyclic variation was reduced in both, CAD and DCM patients in the same order of magnitude. However, the higher maximal IBS amplitude in the posterior wall observed in CAD when compared to DCM patients (13.2+/-4.4 vs. 9.2+/-2.4 dB; P=0.002) indicate fibrosis or scar. The dissociation between cyclic variation and systolic wall thickening could implicate hybernating myocardium.

CONCLUSION

Real-time IBS has progressed from research to routine as a tool to obtain additional and valuable information to conventional echocardiography in daily practice.

Developments in cardiovascular ultrasound. Part 3: Cardiac applications

Echocardiography is still the principal, non-invasive method of investigation for the evaluation of cardiac disorders. Using Doppler ultrasound, indices such as coronary flow reserve and cardiac output can be determined. The severity of valvular stenosis can be determined by the area of the valve, either directly from 2D echo, from pressure half-time calculations, from continuity equations or from the proximal isovelocity surface area method. Alternatively, the severity of regurgitation can be estimated by colour or pulsed ultrasound detection of the back-projection of the high-velocity jet into the chamber. Myocardial wall abnormalities can be assessed using 2D ultrasound, M-mode or analysis from the radio-frequency-ultrasound signal. Doppler tissue imaging can be used to quantify intra-myocardial wall velocities, and 3D reconstruction of cardiac images can provide visualisation of the complete cardiac anatomy from any orientation. The development of myocardial contrast agents and associated imaging techniques to enhance visualisation of these agents within the myocardium has aided qualitative assessment of myocardial perfusion abnormalities. However, quantitative myocardial perfusion has still to be realised.

Effects of tissue anisotropy on the spectral characteristics of ultrasonic backscatter measured with a clinical imaging system

In this paper, we report the effects of inherent tissue anisotropy on the spectral properties of backscattered ultrasound when measured with a commercially-available imaging system. We insonified five specimens of bovine tendon immersed in a water tank and rotated in 10 degrees increments while being imaged with a Hewlett-Packard Sonos 1500 system. The backscattered RF signals corresponding to each angle of insonification were digitized and the spectral characteristics of the backscattered ultrasound were determined. The mean anisotropy, defined as the average difference between values at perpendicular and parallel insonification, for band-limited estimates of backscattered power, centroid frequency, upper-band to lower-band power ratio, and upper-band to total-band power ratio were found to be 24.6 +/- 1.1 dB, 142 +/- 27 kHz, 32 +/- 13%, and 22 +/- 5%, respectively (mean +/- SE). The magnitude of each of these backscatter spectral parameters was larger at perpendicular insonification compared with the corresponding values at parallel insonification, consistent with previous measurements of the inherent anisotropy of ultrasonic attenuation and backscatter in tissue.

Ultrasonic tissue characterization predicts myocardial viability in early stage of reperfused acute myocardial infarction

BACKGROUND

The aim of the present study was to characterize temporal changes in cyclic variation of ultrasonic integrated backscatter (IBS), which reflects intrinsic contractile performance, in patients with reperfused acute myocardial infarction (AMI) and to elucidate the clinical value of tissue characterization in predicting myocardial viability.

METHODS AND RESULTS

We recorded short-axis IBS images before and 3, 7, and 21 days after reperfusion in 26 patients with AMI and obtained the cyclic variation of IBS in the normal and infarct zones. When cyclic variation showed synchrony and asynchrony, we expressed its magnitude as positive and negative values, respectively, called the phase-corrected magnitude. We also measured average wall motion score (dyskinesis, 4; normal, 0) of the infarct segments. The phase-corrected magnitude was lower in the infarct zone than in the normal zone before reperfusion (0.3+/-2.5 versus 5.2+/-1.7 dB, P<.05). At day 3, the phase-corrected magnitude increased by 2.1+/-2.6 dB despite no improvement in wall motion. Improvement in wall motion was observed only at day 21. The patients with the phase-corrected magnitude of > or =2.0 dB at day 3 showed significantly lower wall motion score at day 21 than did the other patients (1.7+/-0.6 versus 2.4+/-0.5, P<.01).

CONCLUSIONS

In patients with AMI, cyclic variation of IBS is blunted during ischemia but recovers much faster after reperfusion than the improvement in wall motion. The greater phase-corrected magnitude at day 3 may be a predictor of better functional improvement.

Quantification of sonographic echogenicity with grey-level histogram width: a clinical tissue characterization

Grey-level histogram width (GLHW) values obtained by common sonographic devices were large in echogenic image and small in less echoic parts. The Aloka UIP-100 computer system, SSD-680, and Toshiba SSA-270A sonographs showed GLHW values not significantly different when tested with RMI-412 phantom with the device contrast set at the lowest level. No influence on the GLHW value was observed by the changes of device gain, STC or image depth in the range of clinical practice. Device contrast control influenced the value. Although two sonographs showed significant differences from UIP-100, they were easily corrected by a small factor. Normal ranges of GLHW values of the placenta were obtained every 2 weeks, from 20 to 41 weeks, in 222 normal pregnancies measured by old scanners. GLHW values of normal pregnancies measured by the new Aloka and Toshiba machines were distributed within the normal ranges, and those of Grannum Grade III abnormally echogenic placenta were greater than the upper normal range. GLHW is a reproducible value among commercial ultrasonic devices, and the value is useful in clinical practice. Manual and automated GLHW values were identical.

Comparison of integrated backscatter values obtained with acoustic densitometry with values derived from spectral analysis of digitized signals from a clinical imaging system

Time-domain-based integrated backscatter values obtained with the use of acoustic densitometry (AD) were compared with values determined from a spectral-based analysis of the radio-frequency (RF) signals with a modified Hewlett-Packard Sonos 1500 imaging system. Integrated backscatter images of five specimens of bovine tendon were acquired in the AD acquisition mode, and the corresponding signals related to the backscattered RF were digitized for each angle of insonification as the specimens were rotated in 10-degree increments. The integrated backscatter images were analyzed with the AD analysis package, and the corresponding values determined from the RF power spectra were obtained from the digitized ultrasonic signals. Good agreement was found between the two methods over the entire range of measured values. The mean anisotropy in the measured integrated backscatter (mean +/- standard error) was found to be 27 +/- 2 dB for time-domain-based analysis and 25 +/- 2 dB for RF spectral-based analysis.

Two-dimensional Fourier filtration of acoustic quantification echocardiographic images: improved reproducibility and accuracy of automated measurements of left ventricular performance

To determine the accuracy of Fourier filtration in removing the high-frequency component of noise from acoustic quantification (AQ) echocardiographic images, we processed 800 parasternal short-axis images obtained from 10 study subjects. M-mode tracings were also obtained and used as gold standard for correlating the results from raw AQ and Fourier-filtered images. Left ventricular short-axis diameters measured from the raw AQ and Fourier-filtered data were compared with the M-mode diameters (r = 0.91, p < 0.001 for raw AQ; and r = 0.96, p < 0.001, for Fourier filtered images). Fractional shortening showed better correlation between Fourier-filtered images and M-mode (r = 0.79, p < 0.03) versus raw AQ and M-mode (r = 0.33, p = 0.46). Best-to-beat reproducibility was also found to be better for fractional area change (r = 0.82, p = 0.01 versus r = 0.66, p = 0.77), peak area filling rate (r = 0.87, p = 0.004 versus r = 0.62, p = 0.1), and peak are emptying rate (r = 0.99, p < 0.0001 versus r = 0.19, p < 0.7) for Fourier filtered versus raw AQ. Our results indicate that Fourier filtration of AQ data results in more accurate representation of the true endocardial borders.

Viability after myocardial infarction: can it be assessed within five minutes by low-dose dynamic iodine-123-iodophenylpentadecanoic acid imaging with a multicrystal gamma camera?

Although positron emission tomography (PET) assesses myocardial viability (V) accurately, a rapid, inexpensive substitute is needed. Therefore, the authors developed a low-dose (1 mCi) Iodine-123-Iodophenylpentadecanoic Acid (IPPA) myocardial viability scan requiring analysis of only the first three minutes of data acquired at rest with a standard multicrystal gamma camera. Twenty-one patients > 2 weeks after myocardial infarction (MI) (24 MIs, 10 anterior, 14 inferoposterior, 21 akinetic or dyskinetic) had cardiac catheterization and resting IPPA imaging. V was determined by either transmural myocardial biopsy during coronary bypass surgery (12 patients, 14 MIs) or reinjection tomographic thallium scan (9 patients, 10 MIs), and 50% of MIs were viable. The IPPA variables analyzed were: time to initial left ventricular (LV) uptake in the region of interest (ROI), the ratio of three-minute uptake in the ROI to three-minute LV uptake, three-minute clearing (counts/pixel) in the ROI (decrease in IPPA after initial uptake), and three-minute accumulation (increase in IPPA after initial uptake) in the ROI. Rules for detecting V were generated and applied to 10 healthy volunteers to determine normalcy. While three-minute uptake in nonviable MIs was only 67% of volunteers (P < 0.0001) and 75% of viable MIs, uptake alone identified only 50% of viable MIs and 75% of nonviable MIs. IPPA clearing, however, was > or = 13.5 counts/pixel in 10/12 (83%) of viable MIs, and IPPA accumulation > or = 6.75 counts/pixel identified one more viable MI, for a sensitivity for V of 11/12 (92%), with a specificity of 11/12 (92%), and a 100% normalcy rate. The authors conclude low-dose IPPA (five-minute acquisition with analysis of the first three minutes of data) has potential for providing rapid, inexpensive V data after MI. Since newer multicrystal cameras are mobile, IPPA scans can be done in emergency rooms or coronary care units generating information that might be useful in decisions regarding thrombolysis, angioplasty, or bypass surgery.

Influences of ultrasonic machine settings, transducer frequency and placement of region of interest on the measurement of integrated backscatter and cyclic variation

Integrated backscatter and its cyclic variation are potentially important parameters to discriminate normal from diseased myocardium. Cyclic variation of integrated backscatter is expected to be independent of machine settings. Backscatter images of swine hearts were taken using a two-dimensional backscatter system while acoustic power was varied at different time gain control (TGC) settings. Cyclic variation was measured in vivo with various acoustic power and TGC settings using different transducer frequencies. Three different regions were analyzed. For any given TGC setting, the relationship between acoustic power and integrated backscatter in vitro was linear only over a narrow range. In vivo, cyclic variation was present at all regions studied in both long- and short-axis views. However, lower acoustic power (< 15 dB) and TGC (< 20 dB), or excessive settings of acoustic power (> 35 dB) and TGC (> 50 dB), produced minimal cyclic variation. Appropriate acoustic power (20-35 dB) and TGC (30-50 dB) produced larger and more consistent cyclic, variation at the posterior region of the left ventricle. These data indicate that each region has specific, appropriate machine settings to maximize the magnitude of cyclic variation.

Ultrasonic tissue characterization of infarcted myocardium by scanning acoustic microscopy

The purpose of this study was to ultrasonically characterize infarcted human myocardial tissue at the microscopic level by scanning acoustic microscopy. Infarcted myocardial specimens from ten cases with acute myocardial infarction were studied. Specimens were formalin fixed, paraffin embedded and sectioned to 10-micron thickness. A specially developed scanning acoustic microscope system, operating in the 100- to 200-MHz ultrasound frequency range, was used for the measurements. The values of the attenuation constant were 0.94 +/- 0.04 dB/mm/MHz in normal myocardium, 0.71 +/- 0.12 dB/mm/MHz in degenerated myocardium, 0.88 +/- 0.47 dB/mm/MHz in granulation tissue and 1.75 +/- 0.11 dB/mm/MHz in fibrosis. The values of sound speed were 1620.2 +/- 8.2 m/s in normal myocardium, 1572.4 +/- 10.6 m/s in degenerated myocardium, 1590.2 +/- 32.5 m/s in granulation tissue and 1690.3 +/- 9.1 m/s in fibrosis. The ultrasonic properties of the diseased myocardium at the microscopic level will provide important information for ultrasonic tissue characterization at the macroscopic level.

Myocardial ultrasonic tissue characterization in patients with different types of left ventricular hypertrophy: a videodensitometric approach

Although analysis of the radio frequency signal is the most accurate approach to myocardial tissue characterization, clinical diffusion has been limited because of the complex technology required. Much easier to perform, videodensitometric analysis could represent a valuable alternative. Previous works carried out on radio frequency data have shown that the absolute value of ultrasonic back scatter increases while its diastole-to-systole variation decreases in the hypertrophied myocardium. This study was aimed at clarifying whether alterations in characterization indexes of ultrasonic tissue can be detected by means of a videodensitometric approach, whether a specific type of left ventricular (LV) hypertrophy can be identified with this method, and finally what possible relationships exist between parameters of contractile function and tissue characterization indexes. Myocardial echo intensity (MEI), its cyclic variation (CV), and the dynamic relationship between myocardial signal and wall thickness variations during the cardiac cycle were assessed in 20 healthy subjects, 11 patients with essential hypertension and LV hypertrophy, 15 patients with hypertrophic cardiomyopathy, and 4 patients with primary amyloidosis. The CV was lower in the interventricular septum of patients with cardiac hypertrophy as a group, compared with that of control subjects (13.0% +/- 5.6% versus 18.8% +/- 5.5%, p < 0.001), but it was similar among patients with different types of hypertrophy. In control subjects, a significant inverse correlation was found between the progressive decrease of the myocardial signal and the parallel increase in wall thickness during systole; this correlation was lost in 60% of patients with hypertrophic cardiomyopathy and 50% of those with amyloidosis, but only in 9% of patients with essential hypertension (chi square analysis 12.68, p < 0.01). The CV was associated with systolic wall thickening (r = 0.53, p = 0.0001) and fractional shortening (r = 0.44, p = 0.0014). MEI and its CV per se cannot distinguish among different types of LV hypertrophy; however, the loss of an inverse relationship between the myocardial signal and wall thickness may suggest abnormal myocardial conditions in individual patients with the same disease or comparable wall thickness.

Cyclic variation of integrated ultrasound backscatter: normal and abnormal myocardial patterns in children

Cyclic variation of integrated backscatter (CVIBS) is altered in adults with myocardial infarction, allograft rejection, and cardiomyopathy. Its utility in children has not been tested. We studied 99 normal subjects: 16 fetuses, 13 newborns, 47 children, and 23 teenagers. Fifteen children with cardiomyopathy (13 dilated and two infiltrative) were studied to define abnormal CVIBS. CVIBS was measured in the anterior septum and the left ventricular posterior wall from a two-dimensional ultrasound image with an acoustic densitometry software package. CVIBS was similar in the anterior septum (3.7 +/- 1.9 dB) and the posterior wall (4.1 +/- 2.4 dB) of all children after birth. CVIBS was significantly lower in the fetus (septum: 2.8 +/- 1.6 dB) and in children with cardiomyopathy (septum: 0.6 +/- 1.6 dB, dilated; -1.2 +/- 4.2 dB, infiltrative; p < 0.01). Four children, studied after recovery from cardiomyopathy, had diminished CVIBS despite the return of normal systolic function. The pattern and extent of CVIBS in children is similar to that of adults. CVIBS is diminished in children with cardiomyopathy.

Dobutamine stress ultrasonic myocardial tissue characterization in patients with dilated cardiomyopathy

Although acoustic properties of the myocardium are different between patients with cardiomyopathy and normal subjects, the frequency of the abnormal properties in patients with cardiomyopathy is unknown. We assessed the frequency of abnormal acoustic properties of the myocardium detectable with integrated backscatter in patients with cardiomyopathy and attempted more sensitive ultrasonic tissue characterization by combining dobutamine stress testing in patients with cardiomyopathy with apparently normal acoustic properties of the myocardium at rest. The magnitude of cyclic variation of integrated backscatter and calibrated myocardial integrated backscatter at end diastole were measured in 36 normal subjects and 40 patients with dilated cardiomyopathy. Either one of the integrated backscatter parameters was abnormal in 30 of 40 patients with cardiomyopathy. Dobutamine stress ultrasonic tissue characterization was performed in 10 patients with cardiomyopathy with normal values of both integrated backscatter parameters and 10 normal subjects. Calibrated myocardial integrated backscatter did not change during dobutamine infusion in any subject. The magnitude of cyclic variation in integrated backscatter increased in normal subjects but did not change in patients with cardiomyopathy despite a comparative associated increase in the systolic wall thickening during dobutamine infusion. Abnormal acoustic properties are detectable at rest with myocardial integrated backscatter about in three quarters of patients with cardiomyopathy. A combination of dobutamine stress testing would provide more sensitive ultrasonic myocardial tissue characterization and may make it possible to detect subtle changes in the acoustic properties of the myocardium in patients with dilated cardiomyopathy. Therefore dobutamine stress ultrasonic tissue characterization may detect mild dilated cardiomyopathy.

Ultrasonic Tissue Characterization: Review of a Noninvasive Technique for Assessing Myocardial Viability

The determination of myocardial perfusion and myocardial viability has prognostic and therapeutic implications, particularly in the current era of percutaneous transluminal coronary angioplasty and thrombolytic therapy. Several modes of investigation, including positron emission tomography, thallium-201 scintigraphy, and nuclear magnetic resonance imaging are used to differentiate viable from nonviable myocardium. Though these noninvasive tests are useful diagnostic modalities, they are expensive, time consuming, and too cumbersome to be used in the acute setting. Expeditious distinction between viable and nonviable myocardium, during acute coronary syndromes, is of great importance since reperfusion can minimize the extent of ischemic injury and infarction. An expanding body of evidence confirms that ultrasonic tissue characterization has great potential to become a practical bedside diagnostic tool in the search for salvageable myocardium. Further clinical investigative studies would help accomplish a better understanding of the complex interaction between ultrasound and myocardium. (ECHOCARDIOGRAPHY, Volume 13, July 1996)

Integrated backscatter for quantification of left atrial spontaneous echo contrast

OBJECTIVES

This study was designed to develop a quantitative method of spontaneous echo contrast (SEC) assessment using integrated backscatter and to compare integrated backscatter SEC measurement with independent qualitative grades of SEC and clinical and echocardiographic predictors of thromboembolism.

BACKGROUND

Left atrial SEC refers to dynamic swirling smokelike echoes that are associated with low flow states and embolic events and have been graded qualitatively as mild or severe.

METHODS

We performed transesophageal echocardiography in 43 patients and acquired digital integrated backscatter image sequences of the interatrial septum to internally calibrate the left ventricular cavity and left atrial cavity under different gain settings. Patients were independently assessed as having no, mild or severe SEC. We compared intensity of integrated backscatter in the left atrial cavity relative to that in the left ventricular as well as to the independently assessed qualitative grades of SEC. Fourier analysis characterized the temporal variability of SEC. The integrated backscatter was compared with clinical and echocardiographic predictors of thromboembolism.

RESULTS

The left atrial cavity integrated backscatter intensity of the mild SEC subgroup was 4.7 dB higher than that from the left ventricular cavity, and the left atrial intensity of the severe SEC subgroup was 12.5 dB higher than that from the left ventricular cavity. The left atrial cavity integrated backscatter intensity correlated well with the qualitative grade. Fourier transforms of SEC integrated backscatter sequences revealed a characteristic dominant low frequency/high amplitude spectrum, distinctive from no SEC. There was a close relationship between integrated backscatter values and atrial fibrillation, left atrial size, left atrial appendage flow velocities and thrombus.

CONCLUSIONS

Integrated backscatter provides an objective quantitative measure of SEC that correlates well with qualitative grade and is closely associated with clinical and echocardiographic predictors of thromboembolism. The relationship between integrated backscatter measures and cardioembolic risk will be defined in future multicenter studies.

Dissociation between wall thickening of normal myocardium and cyclic variation of backscatter during inotropic stimulation

The purpose of this study was to determine the relation between increased myocardial wall thickening during inotropic stimulation and quantitative acoustic properties of normal myocardium in humans. We first validated a new 2-dimensional ultrasonic backscatter imaging approach for measurement of cyclic variation in the parasternal long-axis view against conventional M-mode integrated backscatter technique in 41 patients and controls (group A). We then performed 2-dimensional ultrasonic integrated backscatter imaging in 18 patients (group B) with normal segmental function at baseline to determine the magnitude of the cyclic variation of the septum and the posterior wall before and during infusion of dobutamine (10 and 20 microgram/kg/min). Group A patients showed a close correlation of the cyclic variation obtained by the new 2-dimensional ultrasonic integrated backscatter imaging approach and the conventional M-mode technique. Group B patients had mean values of cyclic variation that remained unchanged in the septum (4.4 +/- 1.4, 4.3 +/- 1.7, and 4.8 +/- 1.6 dB at baseline and at each dobutamine stage, respectively, p = NS) and in the posterior wall (6.4 +/- 1.7, 6.4 +/- 1.8 and 6.1 +/- 1.9 dB, respectively, p = NS) despite progressive dobutamine-induced increases in percent wall thickening (septum: 38 +/- 10% to 57 +/- 17% and 68 +/- 19%, respectively, and posterior wall 42 +/- 13% to 72 +/- 20% and 77 +/- 18%, respectively; both p <0.001 vs baseline for both walls). Thus, physical properties of normal myocardium remain unchanged during inotropic stimulation.

Quantitative three-dimensional reconstruction of left ventricular volume with complete borders detected by acoustic quantification underestimates volume

Recently a new acoustic-quantification (AQ) technique has been developed to provide on-line automated border detection with an integrated backscatter analysis. Prior studies have largely correlated AQ areas with volumes without direct comparison of volumes for agreement. By using complete AQ-detected borders as the input to a validated method for three-dimensional echocardiographic (3DE) reconstruction, we can compare an entire cavity volume measured with the aid of AQ against a directly measured volume. This would also explore the possibility of applying AQ to 3DE reconstruction to reduce tracing time and enhance routine applicability. To compare reconstructed volumes with actual values in a stable standard allowing direct volume measurement, the left ventricles of 13 excised animal hearts were studied with a 3DE system that automatically combines two-dimensional (2D) images and their locations. Intersecting 2D views were obtained with conventional scanning and AQ imaging, with gains optimized to permit 3D reconstruction by detecting the most continuous AQ borders for each view, with maximal cavity size. Reconstruction was performed with manually traced central endocardial reflections and AQ-detected borders visually reproduced the left ventricular shapes; the AQ reconstructions, however, were consistently smaller. The reconstructed left ventricular (LV) volumes correlated well with actual values by both manual and AQ techniques (r = 0.93 and 0.88, with standard errors of 2.3 cc and 2.0 cc, p = not significant [NS]). Agreement with actual values was relatively close for the manually traced borders (y = 0.93x + 0.68, mean difference = -0.8 +/-2.2 cc). AQ-derived reconstructions consistently underestimated LV volume by 39 +/- 10% (y = 0.62x-0.09, mean difference = -7.8 +/- 3.0 cc, different from manually traced and actual volumes by analysis of variance [ANOVA], F = 69, p<0.00001). The AQ-detected threshold signal was displaced into the cavity, and volume between walls and false tendons was excluded, leading to underestimation, which increased with increasing cavity volume (r = 0.76). The AQ technique can therefore be applied to 3DE reconstruction, providing volumes that correlate well with directly measured values in a stable in vitro standard, minimizing observer decisions regarding manual border placement after image acquisition. However, when the complete borders needed for 3D reconstruction are used, absolute volumes are underestimated with current algorithms that integrate backscatter and displace the detected threshold into the ventricular cavity.

Ultrasonic myocardial tissue characterization in patients with dilated cardiomyopathy: value in noninvasive assessment of myocardial fibrosis

Dilated cardiomyopathy (DCM) is usually diagnosed from the left ventricular functional viewpoint by the detection of dilated ventricular cavity and depressed myocardial contractility. Although histologic analysis of the myocardium no doubt provides clinically important information, it is possible only with microscopic examination of biopsy specimen of the myocardium. The objective of this particular study is to clarify the comparative values of the measures of ultrasonic tissue characterization, that is, calibrated myocardial integrated backscatter (IB) and the magnitude of cyclic variation in IB, with conventional echocardiographic parameters in assessing histologic condition of the myocardium. The magnitude of cyclic variation in IB and myocardial IB at end-diastole calibrate with the power of Doppler signals from the blood were measured in addition to conventional echocardiographic parameters in 14 patients with DCM. Calibrated myocardial IB was higher in patients with more fibrosis in the biopsy specimen of the heart tissue, whereas the magnitude of variation in IB or conventional echocardiographic parameters did not significantly correlate with a histologic estimate of myocardial fibrosis. Calibrated myocardial IB provides information about the myocardial fibrosis that cannot be assessable with conventional echocardiographic parameters. Calibrated myocardial IB and the magnitude of cyclic variation of IB are likely to reflect somewhat different acoustic properties of the myocardium.

Analysis of transmural trend of myocardial integrated ultrasonic backscatter in patients with old myocardial infarction

Changes in myocardial integrated backscatter (IB) reflect myocardial viability in patients with myocardial infarction. IB may be obtained separately in the subendocardial and subepicardial layers to establish a transmural trend. The purpose of this study is to examine the possibilities that the measurement of the transmural trend in myocardial IB may provide a new estimate of transmurality of infarction in patients with old myocardial infarction. A calibrated myocardial IB and its transmural trend were measured both in the septum and posterior wall in 21 normal subjects, 24 patients with anteroseptal old myocardial infarction (13 patients with Q-wave myocardial infarction and 11 patients with non-Q-wave myocardial infarction). The transmural trend in myocardial IB was assessed by measuring the acoustic parameter separately in the right and left ventricular halves of the septum, and in the endocardial and epicardial halves of the posterior wall. The magnitude of cyclic variation of IB (a difference between minimum and maximum peaks) was lower, and calibrated myocardial IB (the maximum value of myocardial IB at end diastole calibrated with the power of Doppler signals from the blood along the same ultrasound beam) was higher in patients with anteroseptal old myocardial infarction in the septum, compared with normal subjects. Among patients with myocardial infarction, the difference in these IB parameters between the right and left ventricular halves of the septum was found only in patients with non-Q-wave myocardial infarction. The transmural trend of myocardial IB was likely to reflect the transmurality of myocardial infarction. Therefore, our data give another insight into the assessment of transmural inhomogeneity of myocardial fibrosis or viability in patients with myocardial infarction.

Influence of preload, afterload, and contractility on myocardial ultrasonic tissue characterization with integrated backscatter

Influence of hemodynamic changes in preload, afterload and contractility on myocardial integrated backscatter (IB) was studied in 26 adult mongrel dogs by measuring myocardial IB calibrated with the backscatter from the blood during volume infusion (preload alteration), during aortic constriction (afterload alteration), and during dobutamine or propranolol infusion (contractility alteration). Changes in preload, afterload or contractility did not significantly affect the calibrated myocardial IB either in the septum or in the posterior wall. Changes in preload and afterload did not affect the magnitude of cyclic variation in IB. However, dobutamine produced a significant increase in the magnitude of cyclic variation in IB and propranolol significantly decreased the magnitude of cyclic variation in IB. These data indicated that the calibrated myocardial IB is independent of preload, afterload and contractility, and that the magnitude of cyclic variation in IB is influenced by contractility. We may estimate static (related to histological changes such as fibrosis, edema, necrosis, and so on) and dynamic (related to myocardial contraction such as sarcomere length, muscle fiber orientation, and so on) properties of the myocardium more precisely using myocardial IB calibrated with the backscatter from the blood in addition to the magnitude of cyclic variation in IB.

Detection of regional left ventricular dysfunction in early pacing-induced heart failure using ultrasonic integrated backscatter

BACKGROUND

It has been demonstrated that cyclic variation of ultrasonic integrated backscatter (CVIBS) may be useful in detecting altered physical conditions in the heart. However, no previous study has examined serial changes of CVIBS in the myocardium during the development of left ventricular dysfunction.

METHODS AND RESULTS

We examined alterations of CVIBS in pacing-induced cardiac dysfunction. Eight pigs (36 +/- 2 kg) were studied before and sequentially during sustained rapid ventricular pacing (225 +/- 9 beats per minute). CVIBS was measured in the IVS and left ventricular PLW before pacing and daily for 4 days after onset of pacing. Five additional pigs (35 +/- 10 kg) were examined after 14 days of pacing. Regional function and CVIBS were assessed with pacemakers inactivated. A quantitative integrated backscatter imaging system (two-dimensional format) was used. Over 4 days of pacing, the magnitude of CVIBS progressively decreased in the PLW but was unchanged in the IVS, findings that persisted at 14 days. Percent wall thickening in the PLW progressively decreased to a greater degree than percent wall thickening in the IVS. A linear relation between the magnitude of CVIBS and percent wall thickening was found. At 14 days, blood flow to the two regions was similar but regional differences in CVIBS persisted.

CONCLUSIONS

Rapid left ventricular pacing produces abnormalities of regional myocardial function within 48 hours of pacing. Regional myocardial dysfunction is accompanied by a reduction in CVIBS in the same region.