Myocardial Fiber Mapping of Rat Hearts,Using Apparent Backscatter,with Histologic Validation

Myocardial fiber architecture is a physiologically important regulator of ejection fraction, strain and pressure development. Apparent ultrasonic backscatter has been shown to be a useful method for recreating the myocardial fiber architecture in human-sized sheep hearts because of the dependence of its amplitude on the relative orientation of a myofiber to the angle of ultrasonic insonification. Thus, the anisotropy of the backscatter signal is linked to and provides information about the fiber orientation. In this study, we sought to determine whether apparent backscatter could be used to measure myofiber orientation in rodent hearts. Fixed adult-rat hearts were imaged intact, and both a transmural cylindrical core and transmural wedge of the left ventricular free wall were imaged. Cylindrical core samples confirmed that backscatter anisotropy could be measured in rat hearts. Ultrasound and histologic analysis of transmural myocardial wedge samples confirmed that the apparent backscatter could be reproducibly mapped to fiber orientation (angle of the fiber relative to the direction of insonification). These data provided a quantitative relationship between the apparent backscatter and fiber angle that was applied to whole-heart images. Myocardial fiber architecture was successfully measured in rat hearts. Quantifying myocardial fiber architecture, using apparent backscatter, provides a number of advantages, including its scalable use from rodents to man, its rapid low-cost acquisition and minimal contraindications. The method outlined in this study provides a method for investigators to begin detailed assessments of how the myocardial fiber architecture changes in preclinical disease models, which can be immediately translated into the clinic.     

Effects of tissue anisotropy and contrast acoustic properties on myocardial scattering in contrast echocardiography.

In this study we explored the potential effects that tissue anisotropy, in conjunction with the acoustic properties of contrast, may have on quantitative measurements of myocardial perfusion with the use of ultrasonic contrast agents. We used a computer simulation of the parasternal short-axis view, based on previously measured values for the anisotropy of backscatter and attenuation of myocardium, to predict the backscattered energy from 18 specific regions within the heart before and after myocardial contrast perfusion. Results demonstrated a regional variation of contrast enhancement in the short-axis view and variations caused by incremental increases in contrast level for specific myocardial regions. Thus quantitative assessment of myocardial perfusion with contrast echocardiography is influenced by the anisotropic properties of the myocardium, and the resulting postcontrast image will depend on the interaction between tissue properties and contrast acoustic properties. The degree of myocardial enhancement caused by the presence of contrast may depend on the spatial position of the specific region investigated with respect to the transducer and the amount of contrast in the myocardium.     

Regional variation in the measured apparent ultrasonic backscatter of mid-gestational fetal pig hearts

The goal of this study was to characterize and compare regional backscatter properties of fetal hearts through measurements of the apparent integrated backscatter. Sixteen excised, formalin-fixed fetal pig hearts, representing an estimated 53 to 63 days of gestation, were investigated. Spatially localized measurements of integrated backscatter from these specimens were acquired using a 50 MHz single-element transducer. The apparent integrated backscatter measurements demonstrate different patterns of backscatter from the myocardium of the right ventricle compared with that of the left ventricle. These backscatter measurements appear to be consistent with the anisotropy of the fiber orientation observed in histologic assessment of the same specimens. For each of the 16 hearts, the apparent integrated backscatter from the right ventricular myocardium was larger than that from the left ventricular myocardium, exhibiting mean apparent backscatter values of –35.9 ± 2.0 dB and –40.1 ± 1.9 dB (mean ± standard deviation; n = 16; p < 0.001), respectively. This study suggests that the intrinsic ultrasonic properties of the left and right ventricular myocardium are distinct in fetal pig hearts at mid-gestation. (E-mail: mrh@wuphys.wustl.edu)     

Characterization of anisotropic myocardial backscatter using spectral slope, intercept and midband fit parameters

The specific myocardial structural components that contribute to the observed level of backscatter from the heart and its dependence on the angle of insonification have not been completely identified: The objectives of this study were to measure the anisotropy of backscatter from myocardium using the approach first introduced by Lizzi et al. [J Acoust Soc Am 73, 1366-1373 (1983)] and to use the extracted spectral parameters (spectral slope, intercept and midband fit) to characterize changes in the apparent scatterer size, spatial concentration and acoustic impedance properties as functions of the angle of insonification. Backscatter measurements were performed in vitro on eight cylindrical formalin-fixed lamb myocardial specimens using a 5 MHz focused transducer. The backscattered spectral data as a function of angle of insonification relative to the myocardial fiber direction were analyzed over the frequency range of 4 to 6 MHz. The spectral parameters describing features of backscatter were determined by applying a linear fit to attenuation-compensated normalized spectra. Results show that values of the spectral slope do not exhibit a significant dependence on the angle of insonification within uncertainties; however, the zero-frequency intercept showed clear anisotropy and was found to be a maximum for insonification perpendicular to the predominant myofiber orientation and a minimum for parallel insonification. A comparison of midband fit values at 5 MHz with attenuation-compensated integrated backscatter values showed excellent agreement for all angles of insonification. These data suggest that measurements of spectral slope, intercept, and midband fit can provide insights regarding aspects of tissue microstructure underlying the observed anisotropy of myocardial scattering properties. Measurements of the slope parameter suggest a very modest change in effective scatterer size with angle of insonification. However, the observed anisotropy in intercept and midband fit and apparent absence of anisotropy in the spectral slope suggests an angle of insonification dependence of acoustic concentration, the combination of effective spatial scatterer concentration and acoustic impedance properties, without a significant contribution from changes in effective scatterer size.     

Three-dimensional characterization of human ventricular myofiber architecture by ultrasonic backscatter.

Normal human left ventricular architecture comprises a highly aligned array of cardiac myofibers whose orientation depends on transmural location. This study was designed to determine whether measurement of integrated backscatter could be used detect the progressive transmural shift of myofiber alignment that occurs from epicardium to endocardium in human ventricular wall segments. Integrated backscatter was measured at 32 transmural levels in seven cylindrical biopsy specimens (1.4 cm diam) sampled from normal regions of six explanted fixed human hearts by insonification of samples at 180 independent angles in 2 degrees steps around their entire circumference with a 5-MHz broadband piezoelectric transducer. Histologic analysis was performed to determine fiber orientation. Integrated backscatter varied approximately as a sinusoidal function of the angle of insonification at each transmural level. Greater integrated backscatter was observed for insonification perpendicular as compared with parallel to fibers (difference = 14.5 +/- 0.6 dB). Ultrasonic analysis revealed a progressive transmural shift in fiber orientation of approximately 9.2 +/- 0.7 degrees/mm of tissue. Histologic analysis revealed a concordant shift in fiber orientation of 7.9 +/- 0.8 degrees/mm of tissue. Thus, human myocardium manifests anisotropy of ultrasonic scattering that may be useful for characterization of the intramural fiber alignment and overall three-dimensional organization of cardiac myofibers.     

Measurements of ultrasonic attenuation properties of midgestational fetal pig hearts

The objectives of this study were to measure the relative attenuation properties of the left and right ventricles in fetal pig hearts and to compare the spatial variation in attenuation measurements with those observed in previously published backscatter measurements. Approximately 1.0-mm-thick, short-axis slices of excised, formalin-fixed heart were examined from 15 midgestational fetal pigs using a 50-MHz single-element transducer. Measurements of the attenuation properties demonstrate regional differences in the left and right ventricular myocardium that appear consistent with the previously reported regional differences in apparent integrated backscatter measurements of the same fetal pig hearts. For regions of perpendicular insonification relative to the myofiber orientation, the right ventricular free wall showed larger values for the slope of the attenuation coefficient from 30-60 MHz (1.48 +/- 0.22 dB/(cm x MHz) (mean +/- SD) and attenuation coefficient at 45 MHz (46.3 +/- 7.3 dB/cm [mean +/- SD]) than the left ventricular free wall (1.18 +/- 0.24 dB/(cm x MHz) and 37.0 +/- 7.9 dB/cm (mean +/- SD) for slope of attenuation coefficient and attenuation coefficient at 45 MHz, respectively). This attenuation study supports the hypothesis that intrinsic differences in the myocardium of the left and right ventricles exist in fetal pig hearts at midgestation.     

Estimating myocardial attenuation from M-mode ultrasonic backscatter

The objective of this investigation was to determine whether measurements of myocardial attenuation can be obtained from analyses of M-mode images. We exploited the inherent anisotropy of myocardial properties as a means of systematically varying the attenuation to evaluate this M-mode image-based method for myocardial tissue characterization. A commercially available ultrasonic imaging system was used to acquire M-mode images of 24 excised cylindrical specimens from six formalin-fixed sheep hearts that were analyzed using video signal analysis. Data were compensated for the presence of bright intramural myocardial echoes, a potentially significant contributor to uncertainty in measurements of attenuation from backscattered ultrasound. The estimated attenuation coefficient in dB/cm at an effective center frequency of 2.75 MHz as a function of angle of insonification for measurements obtained from analyses of M-mode images is presented. Given a linear frequency-dependence of attenuation in myocardial tissue over frequencies ranging from 1.5 MHz to 8 MHz, as has been previously reported, M-mode image-based analyses were used to estimate the slope of attenuation. Results showed slopes of attenuation (over a -10 dB transmit bandwidth of 1.875 MHz to 3.75 MHz) ranging from 1.00 +/- 0.07 to 1.81 +/- 0.08 dB/(cm.MHz) for perpendicular and parallel insonification, respectively. These values were in good agreement with contemporaneously measured values (0.99 +/- 0.02 to 1.77 +/- 0.04 dB/(cm.MHz)) obtained over a frequency bandwidth of 4 MHz to 7 MHz using a through-transmission radio-frequency-based approach. These data suggest that robust measurements of myocardial attenuation can be obtained from analyses of M-mode images and that this method may be diagnostically feasible in the clinical setting.     

Cyclic Variation of Integrated Backscatter: Dependence of Time Delay on the Echocardiographic View Used and the Myocardial Segment Analyzed

To determine the influence of myocardial anisotropy in ultrasonic tissue characterization, we measured the time delay (and magnitude) of the cyclic variation of myocardial integrated backscatter from specific segments visualized in the 4 standard transthoracic echocardiographic views. The cyclic variation data in 10 myocardial regions were obtained from analyses of 2-dimensional integrated backscatter images from 23 healthy subjects. Resultant values (mean ± SD) for the time delay were as follows: parasternal long-axis view: 1.08 ± 0.17 (septum) and 1.00 ± 0.14 (posterior wall); parasternal short-axis view: 1.03 ± 0.16 (anterior septum), 1.03 ± 0.14 (posterior wall), 2.22 ± 0.71 (lateral wall), and 1.65 ± 0.66 (posterior septum); apical 4-chamber view: 1.08 ± 0.31 (septum) and 2.20 ± 0.79 (lateral wall); and apical 2-chamber view: 1.68 ± 0.62 (inferior wall) and 2.04 ± 0.72 (anterior wall). Hence, results of this study indicate that myocardial ultrasonic characterization that uses the cyclic variation is influenced by the echocardiographic view and the specific segment of the left ventricle. (J Am Soc Echocardiogr 2000;13:9-17.)     

Cyclic variation of ultrasound backscatter in normal myocardium is view dependent: clinical studies with a real-time backscatter imaging system

Real-time ultrasound backscatter imaging is a new method of evaluating relative integrated backscatter in a clinically applicable manner. The potential clinical utility of real-time backscatter imaging of diseased tissue depends on recognition of normal variations in cyclic backscatter when measured from different echocardiographic image orientations. The view dependence of cyclic backscatter variation was studied in normal human volunteers. In twenty normal male subjects (mean age 28 +/- 5 years) cyclic variation in integrated backscatter (diastolic minus systolic backscatter) was assessed in multiple left ventricular regions with four standard two-dimensional echocardiographic views (parasternal long-axis and short-axis views, and apical two-chamber and four-chamber views). M-mode backscatter imaging was performed from the standard parasternal long-axis view. Cyclic variation in backscatter was present in the septum only when imaged from the parasternal long-axis view (2.7 +/- 3.1 [standard deviation] decibels [dB], p less than 0.01 for diastole versus systole). The posterior wall of the left ventricle demonstrated cyclic variation of integrated backscatter when imaged from both the parasternal long-axis (4.6 +/- 1.6 dB, p less than 0.01) and short-axis views (2.8 +/- 2.2 dB, p less than 0.01). Cyclic variation in integrated backscatter was not demonstrated in inferoseptal, septal, or lateral wall regions when imaged from the parasternal short-axis view. The apical views did not demonstrate cyclic variation in integrated backscatter in any of the segments studied.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Anisotropy of high-frequency integrated backscatter from aortic valve cusps

The biaxial anisotropy of integrated backscatter from aortic valve cusps was characterized ex vivo as an initial assessment of the suitability of high-frequency ultrasound for nondestructive evaluation of fiber alignment in tissue-engineered heart valves. Apparent integrated backscatter (AIB) from eight fresh, intact porcine cusps was measured over an 80 degrees range of insonification angles using a 40-MHz ultrasound system. Angular dependence of backscatter was characterized by fitting a sinusoid to plots of AIB versus insonification angle for data acquired while rotating the transducer about the cusps in the circumferential and radial directions. Angular variations in backscatter were detected along both directions in individual specimens, although the mean amplitude of the fitted sinusoid was significantly greater for the circumferential data (12.1 +/- 2.6 dB) than the radial data (3.5 +/- 3.1 dB, p = 0.002). The higher angular variation of backscatter in the circumferential direction implies that collagen fibers in the fibrosa layer are the most prominent source of high-frequency scattering from porcine aortic valve cusps. The ability to characterize anisotropic backscattering from individual specimens demonstrates that high-frequency ultrasound can be used for nondestructive evaluation of fiber alignment in heart valve biomaterials. (E-mail: jlacefield@eng.uwo.ca).     

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.     

Diagnosis of recent myocardial infarction with quantitative backscatter imaging: preliminary studies

Acute myocardial ischemia and chronic myocardial infarction may be recognized with ultrasound tissue characterization techniques because of myocardial acoustic changes caused by reduced perfusion and/or collagen deposition. Our purpose was to study the acoustic properties of recent myocardial infarction when the predominating pathologic finding was myocardial edema and leukocytic infiltration. We used a new quantitative backscatter imaging system to study 18 patients 9 +/- 5 days after myocardial infarction (eight patients with anteroseptal myocardial infarction and 10 with inferior myocardial infarction) and 20 normal subjects. The cyclic variation of relative integrated backscatter (end-diastolic minus end-systolic) was calculated from on-line measurements. Standard parasternal long- and short-axis and apical four- and two-chamber views were obtained. In the anteroseptal myocardial infarction group, the cyclic variation of relative integrated backscatter was lower in the septum (1.5 +/- 1.6 dB) than in the posteroinferior wall (3.2 +/- 1.2 dB); however, the sample size of only three patients (of eight patients imaged) in the latter group prevented statistical comparison. The cyclic variation of relative integrated backscatter in the infarcted septum was less than the measurement obtained in the septum of the control group (4.3 +/- 2.4 dB, p less than 0.05). In the inferior infarction group, the cyclic variation of integrated backscatter in the posteroinferior wall (1.8 +/- 1.7 dB) was not significantly different from the measurement obtained in the septum (3.7 +/- 3.6 dB); however, the cyclic variation in the posteroinferior wall was significantly less than that obtained in the control group posteroinferior wall (5.7 +/- 1.7 dB, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Echocardiographic visualization of acute myocardial ischemia--in vitro study

To evaluate whether myocardial texture changes resulting from acute ischemia can be visualized with satisfactory spatial resolution, short axis compound echo images (CEI) (B-scan) were obtained from 12 excised canine hearts in vitro. Seven had myocardial ischemia produced by open chest ligation of the left anterior descending coronary artery (LAD) for 15-30 min prior to excision. The CEI were constructed by compounding 60 simple linear B-scans. Hearts were sectioned after scanning, and gross morphological changes were recorded. Microscopic comparison between grossly abnormal and normal regions were recorded. The CEI from the ischemic group revealed altered myocardial texture seen as bright coarsely granular echoes in the regions normally perfused by the ligated LAD artery. Corresponding anatomic sections revealed increased redness in these regions. Microscopically these regions revealed interstitial and intercellular edema as compared to the normal regions. Acute myocardial ischemia can be visualized in CEI and these regions have significantly increased backscatter, decreased attenuation, and decreased speed of ultrasound relative to normal regions in the same hearts. Myocardial edema is probably responsible for these changes.     

Echocardiographic-based assessment of myocardial fiber structure in individual, excised hearts

The objective of this study was to assess the feasibility of using echocardiographic imaging as an approach for determining the myocardial fiber structure of intact, individual hearts. Seven formalin-fixed, ex vivo sheep hearts were imaged using a commercially available echocardiographic imaging system, and the intrinsic fiber structure for the reconstructed short-axis cross section was determined for a specific distance from the apex of each heart. Diffusion tensor magnetic resonance (DT-MR) images of each heart were acquired and fiber maps were created for comparison with the fiber structure obtained from the corresponding reconstructed echocardiographic images. These two methods of obtaining the fiber structure showed relatively good agreement, suggesting that measurements of fiber orientation for individual hearts can be derived from echocardiographic images. Further development of this method may provide a clinically useful approach for mapping the fiber orientation in individual patients over the heart cycle.     

超声斑点追踪技术对心肌梗死患者室壁运动的二维应变研究

目的 应用超声斑点追踪技术测量心肌梗死患者梗死节段室壁的二维应变，探讨其诊断局部室壁运动异常的临床应用价值。方法30例正常人及30例心肌梗死患者，分别记录左室短轴（二尖瓣，乳头肌，心尖部）图像和心尖位四腔切面，二腔切面，左室长轴高帧频图像，应用二维应变软件测量各个节段的二维应变值。结果心肌梗死患者梗死节段共177个，其中158个节段通过超声斑点追踪技术，获得二维应变值。基底段，中间段及心尖段纵向应变值与正常对照组均明显减低，有显著性差异，P〈0．01；左室短轴（二尖瓣，乳头肌及心尖部水平）的径向应变及圆周应变与正常对照组均明显减低，有显著性差异，P〈0．05；旋转角度无统计学差异。结论超声斑点追踪技术可准确评价节段性室壁运动异常，为临床评价心肌梗死患者左心收缩功能提供无创性新方法．     

超声斑点追踪技术与多普勒组织速度显像评价心肌梗死患者左心室内不同步性

目的 评价超声斑点追踪技术在定量心肌梗死患者左心室内不同步性的价值.方法 采集30例心肌梗死患者左心室短轴切面(二尖瓣,乳头肌,心尖部)和心尖位四腔切面、二腔切面和左心室长轴的二维灰阶与组织多普勒(TVI)动态图,应用二维应变软件分别测量左心室短轴与左心长轴的各节段的径向与纵向应变收缩期达峰时间;同时用组织多普勒技术测量左心长轴的各节段的组织速度的收缩期达峰时间.如左心长轴每一节段6个壁的收缩期最早与最晚达峰时间的差值>110 ms、左心室短轴每一节段前间隔与后壁的达峰时间差值>130 ms即为左心室内收缩不同步.结果 基底部左心室短轴径向应变达峰时间明显长于组织多普勒纵向收缩期速度达峰时间(P<0.01);心尖部左心室短轴径向应变达峰时间明显长于左心室纵向应变达峰时间(P<0.01).二维应变短轴检出率高于二维应变长轴,两者均高于组织多普勒长轴.结论 超声斑点追踪技术可以较好地评价左心室内不同步性,二维应变短轴可更准确地判断心肌梗死患者心尖段的不同步性.     

Detection of remote myocardial infarction with quantitative real-time ultrasonic characterization

We have previously shown that the intrinsic properties of myocardium can be characterized quantitatively by the assessment of ultrasonic integrated backscatter. In this study we utilized a novel, real-time, two-dimensional system capable of quantitative integrated backscatter imaging to determine whether zones of remote myocardial infarction in dogs could be delineated definitively by ultrasonic tissue characterization. Detection of such zones in patients is needed as a basis for management decisions related to thrombolysis, angioplasty, and coronary surgery. Integrated backscatter was measured through the closed chest from 25 myocardial sites. Zones of infarction exhibited time-averaged integrated backscatter values approximately 10 dB (9.5 +/- 0.5 dB, standard error of the mean) greater than those in normal regions (p less than 0.001). In addition, the physiologic cardiac cycle--dependent variation of integrated backscatter was blunted significantly in zones of infarction [0.8 dB +/- 0.3 vs. 3.8 +/- 0.6 (p less than 0.01) for normal regions]. Ultrasonic results matched the histopathologic features assessed directly. Thus quantitative ultrasonic tissue characterization can differentiate infarcted tissue from normal myocardium and offers promise for quantitative detection of histopathology in vivo.     

超声分层应变成像技术对阿霉素致大鼠急性左心室心肌早期毒性损伤的评价

目的应用二维超声斑点追踪成像（2D-STI）分层应变技术,评价阿霉素致大鼠急性左心室心肌早期毒性损伤的特点。 方法选取体质量300~350 g SD雄性大鼠32只,完全随机分为阿霉素组和空白对照组,每组各16只。阿霉素组：采用浓度2 mg/ml盐酸阿霉素,按12 mg/kg给药剂量一次性腹腔注射。空白对照组：给予同等容量的0.9%氯化钠溶液一次性腹腔注射。应用常规二维灰阶采集给药前、给药后24 h和给药后48 h 3个时间点的左心室短轴乳头肌水平的超声心动图像,采用解剖M型超声技术测量左心室舒张末期内径（LVEDD）、左心室收缩末期内径（LVESD）,以及测量舒张末期室间隔（IVSd）、左心室后壁（LVPWd）厚度,计算左心室短轴缩短率（FS）和左心室射血分数（LVEF）。应用基于二维超声斑点追踪成像工作站心肌分层应变分析技术获取左心室乳头肌水平短轴切面心肌整体圆周分层应变值,比较两组大鼠3个时点的左心室FS、EF测值及左心室乳头肌水平短轴切面心内膜下心肌、中层心肌、心外膜下心肌3层圆周应变差异。完成3个时间点超声心动图检查后,两组各随机处死3只大鼠,取大鼠心脏行HE染色行常规心肌病理学检查。组内给药后24 h、48 h数据与给药前数据比较采用配对t检验,组间给药前数据比较采用成组t检验。 结果两组大鼠左心室短轴乳头肌水平整体圆周分层应变值分布均存在梯度特征：心内膜下心肌>中层心肌>心外膜下心肌。阿霉素组大鼠左心室乳头肌水平短轴心内膜下心肌圆周应变在给药48 h后减低。与给药前相比,差异有统计学意义（-25.13±10.6 vs -17.04±2.89,t=2.3,P<0.05）;对照组大鼠左心室乳头肌水平短轴切面三层心肌圆周应变参数及阿霉素组大鼠左心室乳头肌水平短轴切面中层心肌及心外膜下心肌圆周应变参数在给药前后3个时点比较,差异均无统计学意义（P均>0.05）。LVEDD、LVESD、IVSd、LVPWd、FS、LVEF在两组中给药前后3个时点比较,差异均无统计学意义（P均>0.05）。阿霉素组大鼠心脏病理改变主要是：心内膜下心肌细胞水肿,空泡样变,心肌细胞核萎缩、溶解,间质水肿,毛细血管扩张等。 结论采用超声分层应变成像技术有可能早期检出并定量分析阿霉素致SD大鼠左心室心内膜下心肌力学功能异常变化。     

背向散射积分对早期心肌缺血识别价值的实验研究

目的探讨背向散射积分对早期心肌缺血的识别价值。方法10头正常猪，开胸后通过Ameroid环套扎猪冠脉的左回旋支(LCX)，6例成功建立慢性心肌缺血模型，分别于术前、术后2周、5周乳头肌短轴切面测量左心室侧后壁的背向散射积分(IBS)指标一背向散射积分周期变异幅度(CVIB)和背向散射积分平均值(AII)，并与病理结果对照。结果AII值术后2周、5周与术前相比无显著差别，CVIB随时间总体变化趋势不明显(P=0，06)，但术后2周与术前相比CVIB值有所下降。结论CVIB和AII能否识别极早期心肌缺血尚有待于进一步研究。