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.     

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.     

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)     

Is post-systolic shortening a reliable indicator of myocardial viability? An MR tagging and late-enhancement study.

PURPOSE: In ischemic myocardium systolic strain is reduced and followed by a deformation after systole, the so-called post-systolic shortening. The presence of post systolic shortening is therefore considered a marker of viability even though its mechanism remains unclear. The hypothesis was tested whether post-systolic shortening might be a passive recoil phenomenon and therefore not uniquely associated with viability. METHODS: Five patients with a history of myocardial infarctions and fully transmural scars in late enhancement imaging and five age-matched healthy volunteers underwent a tagging study to analyze systolic and post-systolic deformation in transmurally infarcted and contra-lateral non-infarcted myocardium. From CSPAMM myocardial tagging data, mid-wall circumferential fiber shortening, radial displacement, and rotation parameters were semi-automatically extracted by harmonic phase (HARP). RESULTS: In transmurally infarcted myocardium, a post systolic shortening of 6.2 +/- 1.8% was present occurring in early diastole (time to maximum circumferential fiber shortening increased versus both, contralateral myocardium and corresponding sectors in healthy volunteers, p < 0.01). Maximum radial displacement was decreased in scar tissue (p < 0.001 versus contra-lateral), but time to maximum radial displacement did not differ. Rotation did not discriminate between infarcted and non-infarcted myocardium. CONCLUSIONS: The pure finding of post-systolic shortening is not sufficient for the diagnosis of residual myocardial viability. Post-systolic shortening may be explained in part by passive recoil, which releases energy stored in the scar tissue during systolic intra-ventricular unloading. Circumferential fiber shortening appears best suited for characterization of regional deformation, whereas radial displacement and rotation are more dependent on tethering effects, and thus, are more likely to reflect global chamber mechanics.     

应变成像评价犬左心室急性心肌缺血边缘区跨壁力学状态

目的 应用应变成像观察犬左室急性心肌缺血边缘区不同层次心肌径向峰值应变及应变达峰时间,评价其跨壁力学特征.方法 9只Beagle犬开胸结扎左冠状动脉前降支建立心肌缺血模型,分别于基础状态、缺血状态采集连续3个心动周期的左室心尖二维短轴观图像存于TDI-Q工作站,在脱机状态下应用软件衍生M型组织多普勒速度图,采样分析基础状态、缺血后边缘区的节段整体、心内膜下心肌、中层心肌及心外膜下心肌(subepicardium,subepi)的径向峰值应变(S)及达峰时间(T).统计数据分析采用两独立样本t检验和配对t检验以及直线相关分析.结果 边缘区心内膜下心肌峰值应变较基础状念值降低(P<0.05),中层心肌峰值应变与基础状态值相比无明显差异(P>0.05),心外膜下心肌峰值应变较基础状态值增高(P<0.05);节段整体达峰时间以及各层次达峰时间延长(P<0.05);同时观察到基础状态心内膜下层心肌及中层心肌分别与其节段整体的峰值应变有较好的相关性(r=0.617,r=0.556,P均<0.01),而梗死边缘区这种相关性消失(r=0.287,r=0.243.P均>0.05).结论 急性心肌缺血后,边缘区呈心内膜下层心肌峰值应变降低、心外膜下层心肌峰值应变增高和各层次达峰时间延长,该跨壁力学状态是缺血区域和非缺血区域不同层次心肌力学机制相互作用的结果.推测此力学状态是决定心室重构进程以及最终向缺血性心肌病演变的重要触发机制之一.     

背向散射积分技术评价PTCA术前后左室肌回声与收缩功能

目的：用超声背向散射积分(IBS)评价经皮冠状动脉成形术(PTCA)前后左室肌回声及收缩功能变化。方法：对33例择期行PTCA 支架术的冠心病患者用HP 5500型超声诊断仪，于PTCA术前及术后3天、1～3个月对胸骨旁乳头肌短轴切面的前间壁、下壁、后壁、侧壁行二维超声心动图(2DE)检测各节段的室壁运动情况、声学密度一背向散射积分(AD-IBS)检测心肌背向散射积分平均值及其标化值，心肌整层及心内外膜下心肌层的周期变化幅度并计算跨壁梯度指数。结果：左室存活心肌背向散射积分参数值于术后3天就有了改善，与术前相比有统计学意义；术后1～3个月检测，左室存活心肌回声及收缩功能均有明显改善。结论：PTCA能够有效地挽救存活心肌，背向散射积分技术能够为早期检测存活心肌及早期评价或预测PTCA疗效提供敏感指标。     

Quantitative comparison of myocardial fiber structure between mice,rabbit, and sheep using diffusion tensor cardiovascular magnetic resonance

Background

Accurate interpretations of cardiac functions require precise structural models of the myocardium, but the latter is not available always and for all species. Although scaling or substitution of myocardial fiber information from alternate species has been used in cardiac functional modeling, the validity of such practice has not been tested.

Methods

Fixed mouse (n = 10), rabbit (n = 6), and sheep (n = 5) hearts underwent diffusion tensor imaging (DTI). The myocardial structures in terms of the left ventricular fiber orientation helix angle index were quantitatively compared between the mouse rabbit and sheep hearts.

Results

The results show that significant fiber structural differences exist between any two of the three species. Specifically, the subepicardial fiber orientation, and the transmural range and linearity of fiber helix angles are significantly different between the mouse and either rabbit or sheep. Additionally, a significant difference was found between the transmural helix angle range between the rabbit and sheep. Across different circumferential regions of the heart, the fiber orientation was not found to be significantly different.

Conclusions

The current study indicates that myocardial structural differences exist between different size hearts. An immediate implication of the present findings for myocardial structural or functional modeling studies is that caution must be exercised when extrapolating myocardial structures from one species to another.     

Quantitative Parameters of High-Frame-Rate Strain in Patients with Echocardiographically Normal Function

Recently, we developed a high-frame-rate echocardiographic imaging system capable of acquiring images at rates up to 2500 per second. High imaging rates were used to quantify longitudinal strain parameters in patients with echocardiographically normal function. These data can serve as a baseline for comparing strain parameters in disease states. The derived timing data also reveal the propagation of mechanical events in the left ventricle throughout the cardiac cycle. High-frame-rate echocardiographic images were acquired from 17 patients in the apical four-chamber view using Duke University's phased array ultrasound system, T5. B-Mode images were acquired at 500–1000 images per second by employing 16:1 or 32:1 parallel processing in receive, a scan depth ≤14 cm and an 80° field of view with a 3.5-MegaHertZ (MHz), 96-element linear array. The images were analyzed using a speckle tracking algorithm tailored for high-frame-rate echocardiographic images developed at Aalborg and Duke University. Four specific mechanical events were defined using strain curves from six regions along the myocardial contour of the left ventricle. The strain curves measure the local deformation events of the myocardium and are independent of the overall cardiac motion. We observed statistically significant differences in the temporal sequence among different myocardial segments for the first mechanical event described, myocardial tissue shortening onset (p < 0.01). We found that the spatial origin of tissue shortening was located near the middle of the interventricular septum in patients with echocardiographically normal function. The quantitative parameters defined here, based on high-speed strain measurements in patients with echocardiographically normal function, can serve as a means of assessing degree of contractile abnormality in the myocardium and enable the identification of contraction propagation. The relative timing pattern among specific events with respect to the Q wave may become an important new metric in assessing cardiac function and may, in turn, improve diagnosis and prognosis.     

Proof of Concept of 3-D Backscatter Tensor Imaging Tomography for Non-invasive Assessment of Human Breast Cancer Collagen Organization

Tumor growth, similarly to several other pathologies, tends to change the structural orientation of soft tissue fibers, which can become relevant markers for diagnosis. Current diagnosis protocols may require a biopsy for histological analysis, which is an invasive, painful and stressful procedure with a minimum turnaround time of 2 d. Otherwise, diagnosis may involve the use of complex methods with limited availability such as diffusion tensor imaging (magnetic resonance diffusion tensor imaging), which is not widely used in medical practice. Conversely, advanced methodologies in ultrasound imaging such as backscatter tensor imaging (BTI) might become a routine procedure in clinical practice at a limited cost. This method evaluates the local organization of soft tissues based on the spatial coherence of their backscattered ultrasonic echoes. Previous work has proven that BTI applied with matrix probes enables measurement of the orientation of soft tissue fibers, especially in the myocardium. The aims of the study described here were (i) to present for the first time a methodology for performing BTI in a volume on ex vivo human breast tumors using a linear probe and (ii) to display a first proof of concept of the link between BTI measurements and the orientation of collagen fibers.     

Temporal 3D Lagrangian strain from 2D slice-followed cine DENSE MRI

A quantitative analysis of myocardial mechanics is fundamental to the understanding of cardiac function, diagnosis of heart disease and assessment of therapeutic intervention. In clinical practice, most cardiac imaging analyses are performed in 2D because of the limited scan time available. However, the obtained information from a 2D measurement is limited. This study presents a method to obtain temporal evolutions of transmural 3D Lagrangian strains from two intersecting 2D planes of slice-followed cine displacement encoding with stimulated echoes (DENSE) data using a bilinear-cubic polynomial element to resolve strain from the displaced myocardial positions. The method was validated against an analytical standard and has been applied to in vivo data acquired on a 3 T magnetic resonance system from a healthy volunteer to quantify systolic strains at the anterior-basal region of left ventricular myocardium. The method demonstrates accurate results when validated in the analytical model, and the in vivo results agree within experimental accuracy with values reported in the literature. Even with a short scan time, this method provides the full 3D Lagrangian strain tensor from two 2D DENSE measurements.     

Modelling passive diastolic mechanics with quantitative MRI of cardiac structure and function

The majority of patients with clinically diagnosed heart failure have normal systolic pump function and are commonly categorized as suffering from diastolic heart failure. The left ventricle (LV) remodels its structure and function to adapt to pathophysiological changes in geometry and loading conditions, which in turn can alter the passive ventricular mechanics. In order to better understand passive ventricular mechanics, a LV finite element (FE) model was customized to geometric data segmented from in vivo tagged magnetic resonance images (MRI) data and myofibre orientation derived from ex vivo diffusion tensor MRI (DTMRI) of a canine heart using nonlinear finite element fitting techniques. MRI tissue tagging enables quantitative evaluation of cardiac mechanical function with high spatial and temporal resolution, whilst the direction of maximum water diffusion in each voxel of a DTMRI directly corresponds to the local myocardial fibre orientation. Due to differences in myocardial geometry between in vivo and ex vivo imaging, myofibre orientations were mapped into the geometric FE model using host mesh fitting (a free form deformation technique). Pressure recordings, temporally synchronized to the tagging data, were used as the loading constraints to simulate the LV deformation during diastole. Simulation of diastolic LV mechanics allowed us to estimate the stiffness of the passive LV myocardium based on kinematic data obtained from tagged MRI. Integrated physiological modelling of this kind will allow more insight into mechanics of the LV on an individualized basis, thereby improving our understanding of the underlying structural basis of mechanical dysfunction under pathological conditions.     

A Dual-Chamber,Thick-Walled Cardiac Phantom for Use in Cardiac Motion and Deformation Imaging by Ultrasound

Determination of the mechanical properties of the myocardium is crucial for cardiac diagnosis. Cardiac strain and strain rate imaging may enable such quantification. To further develop these methodologies, an experimental setup allowing the recording of ultrasonic deformation data in a reproducible manner is necessary. Such setup with biventricular polyvinyl alcohol heart phantoms has been built. To test this setup, segmental longitudinal, radial and circumferential displacement, velocity, strain and strain rate in the phantoms were measured using a clinical ultrasound scanner and commercially available deformation imaging algorithms (based on both tissue velocity imaging and speckle tracking). The model deformation was close to that observed in the human left ventricular wall and was highly reproducible (e.g., the average peak longitudinal strain for the mid- and apical phantom segments equals −15.32 ± 0.53% and −19 ± 6% for the ventricle wall). The experimental setup is a valuable source of data for the development of algorithms for deformation estimation. (E-mail: b.lesniak-plewinska@mchtr.pw.edu.pl)     

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。     

组织追踪MR技术评价正常人左室形变功能的临床研究

目的：采用心脏磁共振（cardiac magnetic resonance，CMR）电影序列的组织追踪技术探讨正常人左室应变。方法：随机入组2018年于复旦大学附属中山医院行CMR检查的健康志愿者39例，将影像学Dicom资料存盘后，应用CVI软件的组织追踪模块分析CMR电影序列图像，比较左室心肌形变指标基底段、中间段与心尖段的差别；内膜下与外膜下的差别；性别间、年龄分组间的差别。结果：39例健康志愿者左室内膜下、外膜下及整体心肌应变自基底段至心尖段递增；自心内膜下至心外膜下左室心肌应变递减，差异有统计学意义（P<0.05）；性别对左室应变无明显影响。结论：组织追踪MR可定量分析左室整体、节段与内膜下、外膜下心肌形变功能，为临床评价心脏功能提供新的依据。     

超声组织定征对顿抑心肌各层损伤程度的实验研究

目的：探讨超声组织定征对顿抑心肌各层损伤程度的意义。方法：使用HP 5500型彩超仪及S8探头,各项设置在试验中保持一致,犬13条,麻醉后开胸,结扎冠状动脉左前降支近端,15min后再灌注,检测基础状态。结扎 15min,再灌注后心内,外膜下心肌的背向散射积分周期变化幅芳和室壁增厚率的变化。结果：结扎15min后,周期变化幅度均减少或消失,尤以心内膜下心肌为显著,室壁增厚率明显降低;再灌注后,心外膜下心肌的周期变化幅度恢复最快,心仙膜下心肌次之,室壁增厚率最慢,结论：顿抑心肌各层的损伤程度不一样,心内膜下心肌损伤较重。     

Quantitative tagged magnetic resonance imaging of the normal human left ventricle

Magnetic resonance imaging with tissue tagging is a noninvasive technique for measuring three-dimensional motion and deformation in the human heart. Tags are regions of tissue whose longitudinal magnetization has been altered before imaging so that they appear dark in subsequent magnetic resonance images. They then move with the underlying tissue and serve as easily identifiable landmarks within the heart for the detailed detection of motion. Many different motion and strain parameters can be determined from tagged magnetic resonance imaging. Strain components that are based on a high density of tag data, such as circumferential and longitudinal shortening, or parameters that are combinations of multiple strain components, have highest measurement precision and tightest normal ranges. The pattern of three-dimensional motion and strain in the heart is important clinically, because it reflects the basic mechanical function of the myocardium at both local and global levels. Localized abnormalities can be detected and quantified if the pattern of deformation in a given heart is compared to the normal range for that region, because normal motion and strain in the left ventricle is spatially heterogeneous. Contraction strains typically are greatest in the anterior and lateral walls and increase toward the apex. The direction of greatest contraction lies along a counter clockwise helix from base to apex (viewed from the base) and approximates the epicardial muscle fiber direction. This fiber geometry also results in long-axis torsion during systole. Ejection is accomplished primarily by radially inward motion of the endocardium and by descent of the base toward the apex during systole.     

构建急性心肌梗死模型犬梗死区的跨壁力学变化

背景：急性心肌梗死起病急,病情凶险,但目前对超急性期的辅助诊断主要靠心电图,实验主要利用组织多普勒应变成像的优点,对急性心肌梗死的早期诊断提供帮助。 目的：应用组织多普勒应变成像技术观测犬急性心肌梗死前、后心内膜下层心肌、中层心肌、心外膜下层心肌径向峰值应变及应变达峰时间,分析其力学变化特征。 方法：16只Beagle犬,开胸结扎左冠状动脉前降支的第一对角支建立急性心肌缺血模型。同步记录心电图,在组织速度成像模式下,分别在急性心肌梗死前、后采集标准心尖短轴切面的连续5个完整心动周期内的二维动态组织多普勒速度图像,存于TDI-Q工作站。分别观测梗死区缺血前、后局部及心内膜下层心肌、中层心肌、心外膜下层心肌径向峰值应变及应变达峰时间。 结果与结论：急性心肌梗死后,梗死区局部以及心内膜下层心肌、中层心肌、心外膜下层心肌的峰值应变较梗死前明显降低（P〈0.05）;梗死区心肌各层次间峰值应变梯度消失;梗死区局部以及各层次心肌达峰时间均较缺血前延长（P〈0.05）。同时观察到梗死区基础状态心内膜下心肌及中层心肌分别与其局部心肌的峰值应变呈正相关（r=0.617,P〈0.01;r=0.556,P〈0.01）,而与梗死区则无相关性（r=0.338,P〉0.05;r=0.218, P 〉0.05）。提示急性心肌梗死后,梗死区不同层次心肌间峰值应变梯度消失,局部及不同层次心肌峰值应变明显减低,而达峰时间明显延长,是梗死区心肌结构异常、功能障碍的反映,从而导致心脏整体运动不协调,引起心脏整体的非同步化运动,是触发心力衰竭的重要力学机制之一。     

Echocardiographic Tissue Characterization Demonstrates Differences in the Left and Right Sides of the Ventricular Septum

The left and right ventricular function of the heart are influenced by the complex structure of the ventricular septum. The cyclic variation of ultrasonic backscatter over the cardiac cycle is known to be sensitive to both structural and functional characteristics of the myocardium. The objective of this study was to investigate differences in the measured magnitude and normalized delay of cyclic variation between the left and right sides of the ventricular septum in normal adult subjects (N = 31). The measured mean magnitudes of cyclic variation were found to be 4.9 ± 0.4 dB and 2.4 ± 0.3 dB (mean ± SE; p < 0.0001) and the corresponding normalized delay values were found to be 0.94 ± 0.05 and 1.59 ± 0.12 (mean ± SE; p < 0.0001) for the left and right sides, respectively. These results show significant differences in the measured magnitude and normalized delay of cyclic variation between the left and right sides of the ventricular septum in normal subjects that appear consistent with predictions based on previously described models of cyclic variation of backscatter and reported measurements of transmural differences in strain properties of the septum. (E-mail: mrh@wuphys.wustl.edu)     

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.     

超声组织定征对犬顿抑心肌的实验研究

目的 探讨超声背向散射积分组织技术检测顿抑心肌的价值。方法 HP5500型彩超仪及S8探头,各项设置在试验中保持一致,杂种犬19种,麻醉后开胸,结扎冠状动脉左前降支近端,15min后再灌注,检测基础状态、结扎15min、再灌注后 心肌的平均背向散射积分值、背向散射积分周期变化幅度、室壁增厚率的变化。结果 结扎15min后,平均背向散射积分值增加,周期变化幅度次之,室壁增厚率的恢复最慢,结论 超声背向散射积分值增加,周期变化幅度减小或消失。心肌的增厚率明显降低,再灌注后,上述各项指标逐渐恢复,平均背向散射积分值恢复最快,周期变化幅度次之,室壁增厚率的恢复最慢。结论 超声背向散射组织定征技术能早期、快速、准确地检测顿抑心肌。