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.     

Influence of attenuation on measurements of ultrasonic myocardial integrated backscatter during cardiac cycle (an in vitro study).

The purpose of this study was to investigate the dependence of ultrasonic integrated backscatter (IB) and attenuation in myocardium on wall thickness in a state of acute ischemia. Therefore, an in vitro experiment was set up in which attenuation, IB and wall thickness of a piece of freshly excised myocardium could be measured almost simultaneously. The myocardium was taken from 11 Yorkshire pigs (25–30 kg) that were killed less than 45 min before the experiment. The myocardium was placed in the far field of an ultrasound transducer (3.2–7.2 MHz) and then compressed by a stainless steel sphere. Data were processed off-line. Backscatter and attenuation were also measured as a function of frequency at 100% and 75% wall thickness, respectively. Both attenuation and IB varied during compression. Attenuation had an initial value of 2.19 ± 0.76 dB/cm and a slope of 0.015 ± 0.017 dB/cm% wall thickness. IB had an initial value of −76.9 ± 2.7 dB and a slope of −0.12 +- 0.07 dB/% wall thickness. After subtracting the influence of the attenuation from the IB the initial value of IB was −74.0 ± 2.7 dB and the slope −0.08 ± 0.07 dB/% wall thickness. Attenuation appeared to have a linear dependency on frequency. Backscatter appeared not to increase with increasing frequency without correction of the spectrum for the frequency dependent insonified volume.     

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)     

Anisotropy of apparent backscatter in the short-axis view of mouse hearts

The goals of this investigation were to measure the anisotropy of backscattered ultrasound observed in the short-axis view of mouse hearts in systole and diastole and to compare these measurements with predictions from a computer simulation. Measurements of midmyocardial apparent backscatter were obtained from analyses of the hearts of seven wild-type mice using a clinical imaging system utilizing a linear array with a nominal center frequency of 13 MHz. A computer model simulating the short-axis view was implemented based on previous measurements of the angle of insonification dependence of myocardial backscatter and attenuation. Results demonstrate that the measured backscatter was largest for those myocardial regions corresponding to approximately perpendicular insonification relative to the myofibers and the smallest for regions of approximately parallel insonification, with the minimum to maximum values of apparent backscatter differing by approximately 10 dB. The measured anisotropy of backscatter was similar for end-systole and end-diastole and was in good agreement with the predicted anisotropy obtained from the computer simulations. (E-mail: mrh@wuphys.wustl.edu)     

Ultrasonic myocardial integrated backscatter and myocardial wall thickness in animal experiments

The purpose of this study was to distinguish between normal and ischemic myocardium using ultrasonic integrated backscatter (IB) measurements and to relate IB with myocardial wall thickness. IB was measured in 9 open-chested Yorkshire pigs (24-30 kg) before, after 30 minutes of partial occlusion of the proximal left anterior descending coronary artery (LADCA), and after 60 minutes of subsequent reperfusion. The ultrasound transducer (4 MHz) was sutured onto the epicardial surface perfused by the LADCA. IB measurements were made with a repetition rate of 50 times per heart rate simultaneously with a left ventricular pressure signal. Myocardial wall thickness was measured off-line. The measurements of integrated backscatter, left ventricular pressure and wall thickness were based on mean values of ten subsequent cardiac cycles. End-systolic IB measurements were 5.3 dB higher during occlusion as compared to the reference measurements (7.1 +/- 3.2 dB versus 1.8 +/- 2.6 dB; p = 0.002). No statistically significant differences were found in end-systolic IB measurements. End-systolic wall thickness was 5 mm smaller during occlusion as compared to the reference measurements (7.2 +/- 1.4 mm versus 12.2 +/- 1.2 mm; p less than 0.001). Simple linear regression analysis showed a statistically significant inverse relationship between IB measurements and wall thickness in 21 out of the 23 sequences in which wall thickness could be measured. End-systolic IB measurements are favourable to distinguish acute ischemic myocardium from normal myocardium. There is a distinct inverse relationship between IB and myocardial wall thickness.     

The relative contributions of myocardial wall thickness and ischemia to ultrasonic myocardial integrated backscatter during experimental ischemia

The purpose of this study was to assess the empirical relationship between myocardial integrated backscatter (IB) and myocardial wall thickness (WT) in normal myocardium. A second object was to estimate the additional contribution to acute ischemic integrated backscatter levels given this relationship. Myocardial IB measurements and simultaneous myocardial WT measurements were made in 16 open-chested pigs with intact coronary circulation (normal myocardium) and 10 min after the flow in the left anterior descending coronary artery had been reduced to 20% of its baseline value (ischemic myocardium). Measurements were made 50 times during one cardiac cycle and averaged over 10 cardiac cycles. IB and WT measurements were normalized with respect to the nonischemic end-diastolic values. The relationship between IB and WT in normal myocardium was estimated in every individual pig by simple linear regression. Estimates of IB during ischemia were calculated on the basis of this relationship and the ischemic WT measurements. Differences of the estimator and the actual measurement made during ischemia depict the actual contribution of the state of acute ischemia, without the influence of WT. The slope of the relationship between IB and WT during normal myocardial contraction ranged from -0.16 to 0.03 dB/% (mean = -0.036 dB/%, SD = 0.06 dB/%). The additional contribution of ischemia ranged from -3.84 to 5.56 dB (mean = 0.31 dB, SD = 2.72 dB). It was concluded that the average contribution of ischemia to IB measurements is insignificant if the IB dependency on WT is removed from the data and that the higher level of ischemic IB measurements can be explained by the decrease in wall thickness during ischemia and not by the ischemia itself.     

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.     

背向散射技术结合多巴酚丁胺负荷试验检测不同部位冠状动脉狭窄

目的探讨背向散射技术结合多巴酚丁胺负荷试验(DSE)能否提高对不同部位冠状动脉狭窄的检测率。方法记录32例临床疑诊为冠心病的患者在不同剂量多巴酚丁胺负荷下左室乳头肌水平短轴观的背向散射积分,按冠状动脉造影结果将心肌节段分组,比较各组心肌在各剂量负荷下背向散射积分周期变异(CVIB)值的变化。结果和正常冠状动脉供血心肌节段相比,狭窄冠状动脉供血心肌节段的CVIB值在静息状态和小剂量多巴酚丁胺负荷下无显著差异,但在大剂量负荷下明显降低。以DSECVIB<4.8dB作为检测冠状动脉狭窄的阈值,对于左前降支病变,DSECVIB法可提高敏感性、特异性和准确率;对于左旋支和右冠状动脉病变,DSECVIB法未能提高检测的敏感性,而提高了特异性和准确率。结论背向散射技术与传统DSE联合应用可提高DSE对不同部位冠状动脉狭窄的检测率,尤其对于左前降支的病变。     

Transmural variation of myocardial attenuation measured with a clinical imager

The objective of this study was to quantify the transmural variation in attenuation for the septal and lateral walls of the heart. Our approach was to utilize a commercially available ultrasonic imaging system to acquire images of excised sections of eight sheep hearts with an orientation similar to that encountered in the apical four-chamber view. The measured values (mean ± SE) of the slope of attenuation for the transmural regions of the septum are: 1.40 ± 0.11, 0.99 ± 0.09, and 1.85 ± 0.16 (dB/cm/MHz) for the left subendocardial, midmyocardial, and right subendocardial zones, respectively. The analogous data from the lateral wall are: 1.42 ± 0.11, 0.83 ± 0.07, and 1.20 ± 0.16 (dB/cm/MHz) for the subendocardial, midmyocardial, and subepicardial zones, respectively. These data demonstrate that ultrasonic attenuation associated with the septum and the lateral wall, when imaged in a manner similar to that of the apical four-chamber view, is anisotropic. (E-mail: jgm@howdy.wustl.edu)     

Analysis of transmural trends in myocardial integrated backscatter in patients with progressive systemic sclerosis.

Cardiac involvement in progressive systemic sclerosis (PSS) is common and has a strong negative impact on the prognosis, especially when autoantibodies are present. To determine whether ultrasonic tissue characterization can detect early ultrastructural changes in the sclerodermal myocardium, we analyzed the transmural heterogeneity in myocardial integrated backscatter (THIB). "A-THIB" was defined as the absolute difference in integrated backscatter between the left (subendocardial) and right (subepicardial) ventricular halves of the myocardium in the septum and posterior wall, and was measured in 11 patients with PSS and 10 age- and sex-matched healthy participants. A-THIB in patients with PSS was higher than that in healthy participants (1.3 +/- 1.3 vs 4.0 +/- 1.4 dB for the septum and 1.1 +/- 0.7 dB vs 2.8 +/- 0.4 dB for the posterior wall; mean +/- SD, respectively, P <.0005). Septal A-THIB was higher in patients with PSS with than without anti-Scl70 or antinucleolar antibodies (3.2 +/- 1.1 vs 5.0 +/- 1.0 dB, P =.0165). Early changes in the myocardium of patients with PSS, possibly related to increased interstitial collagen deposition, can be detected by quantitative analysis of THIB.     

Ultrasonic propagation properties of excised human skin

Eight human skin samples were excised postmortem from the upper and lower back, chest and abdomen from two cadavers. The acoustical speed, attenuation and backscatter were measured as a function of frequency (20 to 30 MHz) at 100 positions on a uniform grid over a cross-sectional slice through each sample with the sound incident in a direction parallel to the skin surface. Measurements were made at 24 ± 0.5°C. Samples were then frozen, cut and stained for histological examination and quantification of fibrous proteins and fat content. The mean attenuation coefficients obtained for whole skin agreed well with previously published results. Employing the model = ₁ƒⁿ where is the attenuation coefficient in decibels per centimeter, ₁ is the value of the attenuation coefficient at 1 MHz and ƒ is frequency raised to the power n, mean values (±1 standard deviation) for epidermis were ₁ = 0.44 ± 0.26 and N = 1.55 ± 0.12, and for dermis ₁ = 0.264 ± 0.17 dB cm⁻¹ and N = 1.69 ± 0.084. Using a similar model the mean backscatter coefficient was defined by μ₁ = (5.01 ± 25.76) × 10⁻⁸Sr⁻¹ cm⁻¹, n = 3.77 ± 1.5 for the epidermis, and μ₁ = (1.79 ± 19.5) × 10⁻⁶ and n = 2.76 ± 1.4 for the dermis. The speed of sound values fell within the range to be found in the literature with a mean value in the epidermis of 1645 m s⁻¹ and in the dermis of 1595 m s⁻¹. Significant, strong correlation existed between the spatially averaged fibrous protein content in the epidermis and dermis and the spatially averaged integrated attenuation measurements. Likewise, strong correlation existed between integrated backscatter and fibrous protein content in the epidermis but not in the dermis. Further research is required to confirm these preliminary findings and to evaluate the role of collagen fibre orientation as a source of variation in the backscattering coefficient of dermis.     

Effect of preload reduction on sonographic myocardial integrated backscatter

PURPOSE: Sonographic myocardial tissue characterization with integrated backscatter (IBS) is affected by both structural and functional properties of the myocardium. The aim of the present study was to investigate the effect of preload reduction by hemodialysis (HD) on IBS measurements. METHODS: Fifty-two patients on maintenance HD underwent echocardiography before and after a routine HD session. Measurements included the variation of IBS during the cardiac cycle (CV-IBS) and calibrated IBS (cal-IBS). RESULTS: After HD, there were significant reductions in left ventricular end-diastolic and end-systolic dimensions and left atrial diameter. There was a reduction in stroke volume and LV ejection fraction consistent with a reduction in preload. Furthermore, CV-IBS was significantly lower after HD (7.9 +/- 2.2 versus 6.9 +/- 1.8 dB, 7.0 +/- 2.1 versus 6.2 +/- 1.9 dB, and 9.0 +/- 2.6 versus 8.1 +/- 2.0 dB [p < 0.01], respectively, in the left anterior, lateral, and inferior wall of the ventricle). Cal-IBS remained unchanged after dialysis compared with baseline. CV-IBS and ultrafiltration volume were significantly correlated. CONCLUSION: HD leads to a decrease in CV-IBS that appears to be preload-dependent. This finding is in concordance with diminished left ventricular performance during HD.     

Lumbar coupling during lateral translations of the thoracic cage relative to a fixed pelvis

Objective. To determine lumbar coupling during lateral postural translations (lumbosacral list) of the thoracic cage relative to a fixed pelvis.

Design. Digitized measurements from anteroposterior lumbar radiographs of 17 volunteers were obtained in neutral, maximal left lateral translation and maximal right lateral translation posture of the thoracic cage compared to a fixed pelvis. Subjects were constrained with two sets of clamps at the lateral borders of the pelvis and lower ribs.

Background Data. Clinically, lumbosacral list is a common posture. Range of motion and spinal coupling results have not been reported for the lumbosacral list movement.

Methods. Four vertebral body corners, mid narrow-waisted body margins, superior and inferior pedicle margins, and spinous-lamina junction of T12–L5 were digitized on 51 anterior–posterior lumbar radiographs. Using the orthogonal axes of positive x-direction to the left, vertical as positive y, and anterior as positive z, digitized points were used to measure projected segmental z-axis rotation, y-axis rotation, and segmental lateral translations of each vertebra.

Results. Using the displacement of T12, subjects could translate 35–70 mm left or right along the x-axis with an average of 53.2 mm to the left and 52.1 mm to the right. Using superior endplates to superior sacral base, lateral flexion was largest at L1 and decreased from L1 to L5, but the segmental rotation angles for lateral flexion were largest at L2–L3 (3.9°), L3–L4 (6.2°) and L4–L5 (5.7°) and were in the same direction as the main motion translation. The relative z-axis rotation of T12 was opposite to the direction of L1–L5. The coupled y-axis rotations were less than 1° and coupled segmental lateral translations were averaging less than 1 mm.

Conclusions. Thoracic cage x-axis translations compared to a fixed pelvis are significant, between 35 and 70 mm. The z-axis lumbar coupled rotation was largest at L2–L3, L3–L4 and L4–L5 and to the same side of the main motion translation in L1–L5, but opposite the main motion direction for T12. All other movements were small, averaging less than 1° or 1 mm.

Relevance

The clinically common posture of lateral translation of the thoracic cage (lumbosacral list) is often associated with disc herniation. Yet normal lumbar coupling patterns and total range of motion of this movement have not been established in the literature. Normal values for lumbar segmental coupling on anterior–posterior lumbo-pelvic radiographs during trunk list might be important for an analysis of segmental instability since segmental translations were determined to be 1 mm or less.     

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)     

尿毒症患者心肌病变的超声组织定征研究

目的应用超声组织定征背向散射积分对尿毒症患者进行检测,以探讨尿毒症心肌组织特征以及超声背向散射参数评估其心肌病变的临床价值.方法应用背向散射积分联机分析技术,对40例尿毒症患者和30例正常人进行心脏常规检查及心肌背向散射参数(IB%、CVIB)测定.结果尿毒症患者左心房明显增大,左室壁肥厚,左室舒张功能减弱,其IB%较对照组增大,而CVIB减小(P<0.05).结论尿毒症患者心肌组织特征与正常人明显不同.背向散射技术可定量客观地评价尿毒症患者心肌病变.     

小剂量多巴酚丁胺负荷下运用校正背向散射声学参数检测存活心肌

目的探讨在小剂量多巴酚丁胺负荷(LDDSE)下运用校正背向散射声学参数能否提高检测存活心肌的敏感性和特异性.方法心肌梗死患者46例,按照PTCA术后室壁运动改善状况将心肌节段分为存活心肌组和非存活心肌组,比较2组在PTCA前LDDSE下的心肌背向散射指标.结果 LDDSE下存活心肌的CVIB及校正CVIB值均高于静息状态,而非存活心肌的CVIB与校正CVIB值在两种状态下无明显差异.以CVIB＞5.0 dB和校正CVIB＞3.8 dB作为判断存活心肌的标准,敏感性、特异性、准确性分别为82.1%和85.7%、68.9%和72.4%、77.6%和81.2%.二维室壁运动评分法判断存活心肌的敏感性、特异性、准确性分别为76.9%、75.9%、76.5%.结论背向散射技术结合小剂量多巴酚丁胺负荷超声心动图能较好地定量评价存活心肌,相对于二维室壁运动评分法,是更为客观准确的评价室壁运动的方法.     

声学密度技术评价高龄高血压大鼠心肌间质纤维化

目的 探讨声学密度技术评价高龄高血压大鼠心肌间质纤维化的可靠性。方法 20月龄自发性高血压大鼠(SHR)及Wistar京都(WKY)大鼠各15只，测量室间隔、左室后壁、左室侧壁心肌的超声背向散射参数。将左室后壁校正的背向散射积分(IB％)与光镜、电镜检测的体视学定量结果对比。结果 两组间左心室各部位的背向散射积分(IBS)及室间隔、左室后壁的背向散射积分周期变化幅度(CVIB)差异有显著性意义，左室后壁IB％与光镜、电镜测得的间质胶原纤维体积百分比平均值高度相关。结论 声学密度技术可用于评价高龄高血压大鼠心肌间质纤维化程度，高龄SHR较WKY大鼠心肌间质纤维化加重。     

Evaluation of postmortem endomyocardial biopsy specimens from 38 patients with lymphocytic myocarditis: implications for role of sampling error

Among 38 hearts from autopsies in which lymphocytic myocarditis contributed to death, 10 endomyocardial specimens from the apical septal aspect of each ventricle (760 specimens) and 6 slices of ventricular myocardium (228 slices) were evaluated for myocarditis by the Dallas criteria. For each case, the number of positive biopsy samples correlated well with the mean lymphocyte counts in biopsy tissues (P less than 0.0001) and the mean number of inflammatory foci per square centimeter in myocardial slices (P less than 0.001). Right ventricular biopsy specimens, however, were positive in only 63% of the 38 cases and 17% of the 380 specimens. Similarly, left ventricular biopsy tissues were positive in only 55% of the cases and 20% of the specimens. Sampling error was somewhat more prevalent among the 11 cases with isolated myocarditis than in the 27 with myocarditis and other illnesses. Even when 10 biopsy specimens per ventricle were evaluated, the frequency of false-negative results was 45% for the left and 37% for the right ventricle. Although myocarditis was noted in 68% of the 38 septal slices, it involved the subendocardium of the right ventricle (from which biopsy specimens are usually obtained) in only 24%. Because of the mild and focal nature of the inflammatory infiltrates and involvement of regions inaccessible to the bioptome, sampling error contributes appreciably to false-negative results in endomyocardial biopsy tissue from patients with myocarditis. Thus, when myocarditis is evaluated by biopsy alone, only positive findings are considered diagnostic.     

Ultrasonic myocardial tissue characterization in the operating room: initial results using transesophageal echocardiography.

Ultrasonic tissue characterization provides quantitative assessment of myocardial function and viability. We have previously reported that normal myocardium is characterized by a diastolic-to-systolic cyclic variation of integrated backscatter (IB), whereas ischemic myocardium exhibits blunting of this pattern. To define the applicability of this measurement to characterize the left ventricular myocardium in the operating room, we studied 26 consecutive patients undergoing open heart surgery (12 coronary artery bypass graft, 13 valvular, 1 other) with 5 MHz transesophageal echocardiography. Images of the left ventricle were obtained in the short-axis plane (papillary muscle level) before cardiopulmonary bypass. M-mode acquisition of myocardial IB was attempted from the anterior and inferior segments in each patient. The cyclic variation of IB was measured in at least two consecutive cycles in addition to a qualitative assessment of wall motion. Quantitative measurement of IB was possible in 39/52 (75%) myocardial segments. Cyclic variation of IB averaged 5.7 +/- 1.4 dB (SD) in segments with normal wall motion (n = 25); no difference was noted in the cyclic variation of IB among anterior or inferior walls. Hypokinetic segments demonstrated significant reduction of the cyclic variation (3.8 +/- 1.8 dB; p less than 0.001). Difficulty with obtaining myocardial IB was related to near-field artifact or lateral displacement of the left ventricular wall during systole. Transesophageal echocardiography holds promise for the evaluation of myocardial function and its preservation during cardiac surgery.     

Changes in myocardial backscatter throughout the cardiac cycle

This investigation was performed to identify and quantify systematic variations of myocardial ultrasonic backscatter throughout the cardiac cycle. Using a broadband 5 MHz focused transducer coupled to the epicardial surface of the left ventricle in dogs, backscatter measurements were obtained from each of 7 intervals (windows) of 34 milliseconds duration evenly distributed throughout the cardiac cycle and referenced to backscatter from a steel reflector. Values of integrated backscatter obtained demonstrated a consistent and reproducible pattern throughout the cardiac cycle characterized by elevated values at end-diastole and significantly lower values at end-systole. The average maximum difference was 3.5 dB.