Integrated Backscatter Research Articles

Echolucency of Carotid Plaque Is Useful for Assessment of Residual Cardiovascular Risk in Patients With Chronic Coronary Artery Disease Who Achieve LDL-C Goals on Statin Therapy

Ultrasound assessment of either intima-media thickness (IMT) or plaque echolucency of the carotid artery provides prognostic information on coronary events. This study examined the hypothesis that IMT and plaque echolucency of the carotid artery may remain useful for prediction of coronary events in patients with coronary artery disease (CAD) after achievement of LDL-C goals on statin therapy. Ultrasound assessment of carotid maximum IMT (maxIMT) and plaque echolucency with integrated backscatter (IBS) analysis was performed in 357 chronic CAD patients with LDL-C <100mg/dl on statin therapy. All patients were prospectively followed up until the occurrence of one of the following coronary events: cardiac death, non-fatal myocardial infarction, or unstable angina pectoris requiring unplanned revascularization. During a mean follow-up of 32±18 months, 33 coronary events occurred. On multivariate Cox proportional hazards analysis, plaque echolucency (lower IBS value) was a significant predictor of coronary events (HR, 0.44; 95% CI: 0.29-0.73; P=0.009), whereas maxIMT was not. The addition of plaque echolucency to traditional risk factors improved net reclassification improvement (NRI) and integrated discrimination improvement (IDI; NRI, 0.59; P=0.0013; and IDI, 0.075; P=0.0009). Measurement of echolucency of the carotid artery was useful for assessment of residual coronary risk in CAD patients after LDL-C goal attainment on statin treatment.

TCT-638 Plaque Characteristics and Local Release of C-reactive Protein: An Integrated Backscatter Intravascular Ultrasound Study

Local release of C-reactive protein (CRP) in human coronary arterial plaque was reported to be greater in acute coronary syndrome than in the stable plaque. Recently, integrated backscatter intravascular ultrasound (IB-IVUS) based tissue characterization has been reported to be useful to detect

Quantitatively Assessed Spontaneous Echo Contrast Density Predicts Left Atrial Thrombus Formation in Patients with Rheumatismal Mitral Stenosis: An Integrated Backscatter Analysis Study

PP-395 In patients with rheumatismal mitral stenosis (MS), visually assessed left atrial (LA) spontaneous echo contrast (SEC) density is an independent and important risk factor for development of LA thrombus. Integrated backscatter analysis (IBS) provides the quantitative analysis of LA SEC

Prognostic impact of lipid contents on the target lesion in patients with drug eluting stent implantation

Background: Regardless of the imaging modality, lipid-rich coronary plaques have been associated with adverse prognostic factors, but there have been few studies on the relationship between long-term adverse outcome and target lesion morphology. Purpose: We sought to determine the morphologic predictors of Major Adverse Cardiac Events (MACEs) after successful Percutaneous Coronary Intervention (PCI) with Drug Eluting Stents (DES), using Integrated Backscatter Intravascular Ultrasound (IB-IVUS). Methods: Conventional and IB-IVUS were performed in 260 consecutive patients who underwent PCI with DES. Three-dimensional analyses were performed to determine plaque volume and the volume of each plaque component (lipid, fibrous, and calcification). Patients were divided into 2 groups according to the median Lipid Volume (LV) in the target lesion. Results: MACEs were defined as death, nonfatal myocardial infarction, and any repeat revascularization. The median follow-up interval was 1285 days. MACEs were observed in 64 patients (24.6%). Patients having a larger LV compared to their counterparts had worse long-term clinical outcomes regarding mortality (3.8% vs. 0%, p=0.02) and MACEs (31.5% vs. 17.7%, p=0.008) by log-rank test. After adjustment for confounders, diabetes (Odds Ratio (OR), 1.69; 95% CI 1.01-2.82, p=0.04) was significantly and independently associated with MACEs. In order to additional consideration about target lesion plaque morphology, large LV (OR, 1.95; 95% CI 1.14-3.33, p=0.02) was significantly and independently associated with MACEs. Conclusion: The assessment of coronary plaque characteristics in the target lesion may be useful to predict long-term outcome following successful coronary intervention.

GW24-e2422 Quantification of the aortic valve calcification by Echocardiographic integrated backscatter in aortic stenosis patients

ObjectivesAortic valve calcifications (AVC), mostly observed in the ageing population, can progress to become severe enough to induce aortic stenosis and may result in a postoperative relevant paravalvular leak in...

GW24-e2475 Relationship between intravascular ultrasonic plaque morphology and quantitative acoustic densitometry of carotid plaque in patients with coronary artery disease

ObjectivesThis study was designed to investigate the relationship between intravascular ultrasonic plaque morphology and quantitative acoustic densitometry by integrated backscatter (IBS) of carotid plaque in patients with coronary artery disease.MethodsIntravascular...

Effect of selected signals of interest on ultrasonic backscattering measurement in cancellous bones

This study examined how the signals of interest (SOI) effect on the backscattering measurement numerically based on 3-D finite-difference time-domain (FDTD) method. High resolution microstructure mappings of bovine cancellous bones provided by micro-CT were used as the input geometry for simulations. Backscatter coefficient (BSC), integrated backscatter coefficient (IBC) and apparent integrated backscatter (AIB) were calculated with changing the start (L1) and duration (L2) of the SOI. The results demonstrated that BSC and IBC decrease as L1 increases, and AIB decreases more rapidly as L1 increases. The backscattering parameters increase with fluctuations as a function of L2 when L2 is less than 6 mm. However, BSC and IBC change little as L2 continues to increase, while AIB slowly decreases as L2 continues to increase. The results showed how the selections of the SOI effect on the backscattering measurement. An explicit standard for SOI selection was proposed in this study and short L1 (about 1.5 mm) and appropriate L2 (6 mm–12 mm) were recommended for the calculations of backscattering parameters.

Fibrosis and cardiac function in obesity: a randomised controlled trial of aldosterone blockade

ObjectivesAs myocardial fibrosis might be an important contributor to the association of obesity with left ventricular (LV) dysfunction and heart failure, we investigated the effects of spironolactone on LV function...

067: Prognostic significance of calibrated integrated backscatter in patients with heart failure and preserved ejection fraction

Calibrated integrated backscatter (CIB), a surrogate for myocardial fibrosis, is deteriorated in hypertrophic, ischemic cardiomyopathy or in systolic heart failure (HF). Whether CIB may differentiate patients with heart failure and preserved ejection fraction (HFPEF) at risk of death or HF reoccurrence has never been investigated. 34 patients admitted for HFPEF (Framingham criteria, EF >50% and BNP level >100 pg/ml) were imaged by echocardiography 2 months following an acute decompensation. We measured left ventricular function, atrial dimensions and calibrated Integrated Backscatter (CIB) which was obtained from parasternal long axis by subtracting pericardial CIB intensity from myocardial CIB intensity of the LV anteroseptal and posterior walls (figure). Measurements of calibrated CIB, expressed in decibels, were performed at QRS complex onset. The primary endpoint was the occurrence of death or hospitalization for HF at 12-month F/U. 11 patients reached the primary endpoint (3 deaths and 8 hospitalizations for HF). In this group at risk, patients had more chronic obstructive pulmonary disease (p=0.03) and coronary artery bypass (p=0.008). Despite similar EF (55,7±7,3 vs. 61,5±10,8 p=0,25), we observed larger left atrial diameter (49.5 mm±6.6 vs. 44.2 mm±7.0 p=0.05) and area (28.8±6.2 cm 2 vs. 24.5±5.1 cm 2 , p=0.044) in patients with endpoint vs. no endpoint. Patients with clinical endpoint showed more anteroseptal and posterior wall myocardial ultrasound reflectivity (−12.8 dB±7.4 vs. −22.7 dB± 8.1 p=0.0017 and −14.8±5.7 vs. 21.3+/-8.0 p=0.021) as compared with event-free patients. Our data support the hypothesis that calibrated CIB, a surrogate for myocardial fibrosis, identifies HFPEF patients at risk of death or HF hospitalization. Figure (abstract 067) – Integrated backscatter measurement

A comparison between 40 MHz intravascular ultrasound iMap imaging system and integrated backscatter intravascular ultrasound

BackgroundiMap is a newly developed intravascular ultrasound (IVUS) tissue characterization system based on pattern recognition of the radio frequency (RF) signals. PurposeThe purpose of this study was to compare tissue characterization between iMap and another previously validated tissue characterization system, integrated backscatter (IB)-IVUS in vivo and to clarify similarities and differences between these two methods. MethodsA total of 31 lesions from 16 patients with ischemic heart disease were studied. IVUS imaging was performed using 40MHz IVUS catheter. RF signals from each lesion were then exported to analyze tissue characterization using both iMap and IB-IVUS. By iMap, coronary plaque was classified into four categories, fibrotic, lipidic, necrotic, or calcified. By IB-IVUS, coronary plaque was classified into four categories, fibrosis, lipid pool, dense fibrosis, or calcification. After the images were acquired, IB-IVUS and iMap images were compared at exactly the same cross-sections. Because severe calcification is a perfect reflector, dense calcification lesions (>20%) were excluded. ResultsBoth fibrotic and calcified by iMap correlated well with fibrosis and calcification by IB-IVUS (fibrotic vs. fibrosis: r2=0.522, p<0.001, calcified vs. calcification: r2=0.560, p<0.001). Although lipidic by iMap did not correlate with lipid pool by IB-IVUS, necrotic by iMap correlated well with lipid pool by IB-IVUS (r2=0.480, p<0.001). ConclusionAlthough tissue types classified by iMap correlated well with corresponding tissue type by IB-IVUS, some discrepancy presented between the two systems. These results may call for careful interpretation of the tissue types obtained by the different IVUS tissue characterization systems.

Abstract 18548: Validation of a New Imaging Parameter, Ultrasonic Intensity of Blood Speckles, Measured by Intravascular Ultrasound for Assessment of Coronary Stenosis Severity Comparing with Fractional Flow Reserve

Background : Little is known regarding intravascular ultrasound (IVUS) criteria to determine functional severity of coronary stenosis. Ultrasonic intensity of blood speckles (IBS) increases as blood flow decreases below coronary stenosis in clinical observation of gray-scale IVUS. The present study was conducted to determine IVUS parameters indicating functional significance of intermediate coronary stenotic lesions. Methods and Results : Thirty consecutive patients with angiographically single intermediate stenotic lesion in left anterior descending coronary artery were enrolled in this study. They were evaluated by means of IVUS and intracoronary pressure measurements. In IVUS analysis conventional gray-scale images were recorded and averaged integrated backscatter (IB) values of blood speckles were measured in cross-sectional vessel lumens at left main trunk (proximal) and 5 mm distal of targeted lesion (distal) using Terumo radiofrequency IVUS (RF-IVUS) system. IBS was defined as difference of IB values between the proximal and the distal sites (distal IB - proximal IB). Fractional flow reserve (FFR) was measured at maximal hyperemia induced by intravenous adenosine infusion. FFR &lt; 0.80 at maximum hyperemia was seen in 19 (63%) of total 30 lesions. IBS had significantly negative correlation with FFR (r = - 0.57, p = 0.001). The optimal cutoff value of IBS for FFR &lt; 0.80 was 10.0 which was obtained from receiver operating characteristic curve (area under curve 0.88; p = 0.001) (Figure). Sensitivity and specificity at the cutoff were 85 % and 70 %, respectively. Also, IBS wasan independent determinant of FFR (H.R. 1.23; 95% confidence interval [CI], 0.008 to 0.031; p = 0.008) in multivariate analysis. Conclusion : IBS, a brand-new IVUS parameter, obtained by RF-IVUS analysis showed a significant correlation to FFR values and can be a predictor for functional significance of epicardial coronary stenosis.

Ultrasonic Tissue Characterization of Carotid Plaque Improves the Prediction of Cardiovascular Events in Diabetic Patients

OBJECTIVEThe aim of this study is to evaluate whether noninvasive ultrasonic tissue characterization of carotid plaque using integrated backscatter (IBS) analysis can be a predictor of future cardiovascular events (CVE) in asymptomatic type 2 diabetic patients.RESEARCH DESIGN AND METHODSWe prospectively evaluated the association between Calibrated-IBS value, an ultrasonic marker for tissue characteristics of carotid plaque, and CVE in 85 asymptomatic type 2 diabetic patients with carotid plaque.RESULTSThe median follow-up period was 7.9 years, and there were 20 new CVE. The risk of CVE was significantly higher in the subjects with low Calibrated-IBS values (<−17.1 dB; n = 42) as compared with those with high values (≥−17.1 dB; n = 43) (P = 0.004, log-rank test). Cox proportional hazards regression analysis revealed that both Calibrated-IBS value (hazard ratio [HR] 0.802 [95% CI 0.710–0.906]; P < 0.0001) and plaque thickness (1.938 [1.170–3.213]; P = 0.010) were independently associated with CVE, even after adjustment for the 10-year risk for a general cardiovascular disease estimated by Framingham risk scoring (FRS). Time-dependent receiver operating characteristic curve analysis for CVE at 10 years after the baseline examinations revealed that area under the curve for Calibrated-IBS was 0.76 (0.60–0.90) and substantially higher than those for plaque thickness (0.60 [0.45–0.79]) and FRS (0.60 [0.40–0.78]). These analyses also revealed that the addition of both plaque thickness and Calibrated-IBS value to conventional risk factors significantly improved the event prediction.CONCLUSIONSCalibrated-IBS value could improve the risk prediction of CVE in asymptomatic type 2 diabetic patients with carotid plaque.

Early detection of doxorubicin myocardial injury by ultrasonic tissue characterization in an experimental animal model

In the clinical setting, the early detection of myocardial injury induced by doxorubicin (DXR) is still considered a challenge. To assess whether ultrasonic tissue characterization (UTC) can identify early DXR-related myocardial lesions and their correlation with collagen myocardial percentages, we studied 60 rats at basal status and prospectively after 2mg/Kg/week DXR endovenous infusion. Echocardiographic examinations were conducted at baseline and at 8,10,12,14 and 16 mg/Kg DXR cumulative dose. The left ventricle ejection fraction (LVEF), shortening fraction (SF), and the UTC indices: corrected coefficient of integrated backscatter (IBS) (tissue IBS intensity/ phantom IBS intensity) (CC-IBS) and the cyclic variation magnitude of this intensity curve (MCV) were measured. The variation of each parameter of study through DXR dose was expressed by the average and standard error at specific DXR dosages and those at baseline. The collagen percent (%) was calculated in six control group animals and 24 DXR group animals. CC-IBS increased (1.29±0.27 x 1.1±0.26-basal; p=0.005) and MCV decreased (9.1± 2.8 x 11.02±2.6-basal; p=0.006) from 8 mg/Kg to 16mg/Kg DXR. LVEF presented only a slight but significant decrease (80.4±6.9% x 85.3±6.9%-basal, p=0.005) from 8 mg/Kg to 16 mg/Kg DXR. CC-IBS was 72.2% sensitive and 83.3% specific to detect collagen deposition of 4.24%(AUC=0.76). LVEF was not accurate to detect initial collagen deposition (AUC=0.54). In conclusion: UTC was able to early identify the DXR myocardial lesion when compared to LVEF, showing good accuracy to detect the initial collagen deposition in this experimental animal model.

Prediction of preclinical myocardial damage utilizing cardiac biomarkers and ultrasound myocardial tissue characterization by integrated backscatter in patients with breast cancer treated with postoperative adjuvant radiotherapy.

169 Background: To evaluate whether cardiac biomarkers, ultrasonic integrated backscatter (IBS) can predict early myocardial damage in breast cancer patients treated with postoperative adjuvant radiotherapy. Methods: Forty-eight left-sided breast cancer patients treated with modified radical mastectomy and non-anthracycline containing chemotherapy regimen were examined. Baseline blood samples were drawn for cardiac markers analysis, including Troponin T (TnT), C-reactive protein (CRP), and brain natriuretic peptide (BNP). Calibrated myocardial IBS (CMIBS, assessed by comparison of the anterior wall (AW), inferior wall (IW), anteroseptum (AS) and posterior wall (PW) with pericardial IBS intensity), cyclic variation of IBS (CVIBS) and conventional echocardiography parameters (LVIDd: the left ventricular internal diameter at end-diastole; IVSTd: the intraventricular septal thickness at end-diastole; PWTd: the posterior wall thickness at end-diastole; LVDs: the left ventricular end-systolic dimension; EF: the left ventricular ejection fraction; FS: the left ventricular fractional shortening. The peak velocity of early (E) and late ventricular filling (A) were also determined for calculating the ratio E/A) were investigated before the initiation of radiotherapy (group A), during (group B, 3 weeks after the initiation, the cumulative dose was about 30Gy) and after radiotherapy (group C, 5 weeks, the cumulative dose was about 50Gy). At each time point, blood was drawn to measure TnT, CRP, and BNP. Results: TnT, CRP, and BNP did not change over time. CMIBS of AW and AS were significantly increased after radiotherapy both during (group B, p&lt;0.05) and at the end of treatment (group C, p&lt;0.01) and meanwhile CVIBS and E/A were decreased significantly throughout the treatment period (group B, p&lt;0.05 for both; group C, p&lt;0.01 for both) compared with the beginning (group A). Conclusions: Myocardial IBS offers a promising approach for early clinical detection and characterization of evolution of cardiomyopathy induced by radiotherapy in breast cancer patients.

High-frequency rapid B-mode ultrasound imaging for real-time monitoring of lesion formation and gas body activity during high-intensity focused ultrasound ablation

The goal of this study was to examine the ability of high-frame-rate, high-resolution imaging to monitor tissue necrosis and gas-body activities formed during high-intensity focused ultrasound (HIFU) application. Ex vivo porcine cardiac tissue specimens (n = 24) were treated with HIFU exposure (4.33 MHz, 77 to 130 Hz pulse repetition frequency (PRF), 25 to 50% duty cycle, 0.2 to 1 s, 2600 W/cm(2)). RF data from B-mode ultrasound imaging were obtained before, during, and after HIFU exposure at a frame rate ranging from 77 to 130 Hz using an ultrasound imaging system with a center frequency of 55 MHz. The time history of changes in the integrated backscatter (IBS), calibrated spectral parameters, and echo-decorrelation parameters of the RF data were assessed for lesion identification by comparison against gross sections. Temporal maximum IBS with +12 dB threshold achieved the best identification with a receiver-operating characteristic (ROC) curve area of 0.96. Frame-to-frame echo decorrelation identified and tracked transient gas-body activities. Macroscopic (millimeter-sized) cavities formed when the estimated initial expansion rate of gas bodies (rate of expansion in lateral-to-beam direction) crossed 0.8 mm/s. Together, these assessments provide a method for monitoring spatiotemporal evolution of lesion and gas-body activity and for predicting macroscopic cavity formation.

Detection of Progressive Myocardial Tissue Injury by Ultrasonic Integrated Backscatter Immediately After Coronary Reperfusion

Myocardial reperfusion following ischemia may paradoxically cause additional injury, including microvascular damage and edema. These structural alterations augment tissue echogenicity, which is measurable by ultrasonic integrated backscatter (IB). We sought to characterize alterations in myocardial IB in an ischemic and reperfused region of the rat heart. Myocardial IB of the regions of interest in 12 adult male Sprague-Dawley rats was studied at baseline, during ischemia, and chronologically after coronary reopening, using an ultrasound frequency of 8 MHz. IB did not significantly change between baseline and ischemia. However, within 1 min of reperfusion, IB significantly increased and continued to increase until 10 min of reperfusion, when a plateau was reached. Areas of high echogenicity were comparable to infarcted areas on gross pathologic slices and had edema with extravasation of red blood cells. Myocardial reperfusion following ischemia significantly augments tissue echogenicity. A continuing increase of IB suggests a rapid progression of reperfusion injury.

Evaluation of Rate of Change in Thickness of Heart Wall by Measuring Time Variation of Ultrasonic Integrated Backscatter during a Cardiac Cycle

Integrated backscatter (IB) from the heart wall is gaining attention as a quantitative tissue characterization method and the cyclic variation (CV) in IB during a cardiac cycle offers potential for the evaluation of myocardial contractility. Since there is large motion in the heart wall owing to the heartbeat, in the conventional method, the position of the region of interest (ROI) for calculating the IB is manually assigned in each frame during one cardiac cycle. Moreover, the change in the size of the ROI during contraction and relaxation of the myocardium is not considered. In this study, the phased tracking method was applied to multiple points in the heart wall for automatic tracking of the position and size of the ROI and, then, IB in the same site of the heart wall was measured in each frame by improving temporal resolution and spatial resolution in the axial direction. As a result, cyclic variations, which differed site by site, were found. Furthermore, the rate of change in thickness was estimated by using the interference cycle obtained by applying the discrete Fourier transform (DFT) to IB signals. According to the results, the rate of change in thickness estimated using the interference cycle of IB was in good agreement with that estimated by the phased tracking method. These results indicate the possibility of estimating the rate of change in thickness using the IB signal.

Evaluation of Rate of Change in Thickness of Heart Wall by Measuring Time Variation of Ultrasonic Integrated Backscatter during a Cardiac Cycle

Evaluation of Rate of Change in Thickness of Heart Wall by Measuring Time Variation of Ultrasonic Integrated Backscatter during a Cardiac Cycle

Left atrial pathological degeneration assessed by integrated backscatter transesophageal echocardiography as a predictor of progression to persistent atrial fibrillation: Results from a prospective study of three-years follow-up

BackgroundIt is recognized that one of the causes of atrial fibrillation (AF) is pathological degeneration of the left atrium (LA). However, prospective study that elucidated the relationship between the incidence of persistent AF and pathological degeneration has not been performed. The purpose of this study was to elucidate the usefulness of integrated backscatter (IBS) values for the prediction of progression from paroxysmal AF (PAF) to persistent AF.MethodsWe measured IBS values of the entire LA wall at 5 mm intervals (except the posterior wall) in 27 patients with paroxysmal AF and evaluated progression to persistent AF for three years. IBS values were acquired with transesophageal echocardiography (TEE) using a 4–7 MHz transducer. IBS values were calculated as the average power of the backscattered signal from regions of interest (ROI). Each IBS value was color-coded to construct three dimensional maps.ResultsAverage IBS values of total voxels in color-coded maps in the persistent AF group were significantly greater than those in the non-persistent AF group (25.8 ± 5.0 dB vs. 17.4 ± 10.2 dB, p = 0.047), whereas there was no significant difference in LA diameter between the persistent AF and the non-persistent AF group. There was significant difference in persistent AF-free survival after the baseline measurements in the subjects stratified by IBS value (<20 dB versus ≥20 dB) (univariate Cox regression analysis: hazard ratio: 8.74, p =0.046).ConclusionUsing IBS values measured by TEE, we can identify an increase in atrial degeneration that may predict the occurrence of persistent AF before LA dilation.

Quantitative assessment on the orientation and distribution of carbon fibers in a conductive polymer composite using high-frequency ultrasound

Conductive polymer composites, typically fabricated from a mix of conductive fillers and a polymer substrate, are commonly applied as bipolar plates in a fuel cell stack. Electrical conductivity is a crucial property that greatly depends on the distribution and orientation of the fillers. In this study, a 50-MHz ultrasound imaging system and analysis techniques capable of nondestructively assessing the properties of carbon fibers (CFs) in conductive polymer composites were developed. Composite materials containing a mix of polycarbonate substrates and 0 to 0.3 wt% of CFs were prepared using an injection molding technique. Ultrasonic A-line signals and C-scan images were acquired from each composite sample in regions at a depth of 0.15 mm beneath the sample surface (region A) and those at a depth of 0.3 mm (region B). The integrated backscatter (IB) and the Nakagami statistical parameter were calculated to quantitatively assess the samples. The area ratio, defined as the percentage of areas composed of CF images normalized by that of the whole C-scan image, was applied to further quantify the orientation of CFs perpendicular to the sample surface. Corresponding to the increase in CF concentrations from 0.1 to 0.3 wt%, the average IB and Nakagami parameter (m) of the composite samples increased from -78.10 ± 2.20 (mean ± standard deviation) to -72.66 ± 1.40 dB and from 0.024 ± 0.012 to 0.048 ± 0.011, respectively. The corresponding area ratios were respectively estimated to be 0.78 ± 0.35%, 2.33 ± 0.66%, and 2.20 ± 0.60% in region A of the samples; those of CFs with a perpendicular orientation were 0.04 ± 0.03%, 0.08 ± 0.02%, and 0.12 ± 0.05%. The area ratios in region B of the samples were calculated to be 1.19 ± 0.54%, 2.81 ± 0.42%, and 2.64 ± 0.76%, and those of CFs with a perpendicular orientation were 0.07 ± 0.04%, 0.12 ± 0.04%, and 0.14 ± 0.03%. According to the results of the orientations and ultrasonic images, CFs tended to distribute more uniformly in the deeper regions of the samples. This study validates that the distribution and orientation of CFs in conductive polymer composites could be sensitively and quantitatively assessed by high-frequency ultrasound in conjunction with current analysis methods.