Influence of data processing on cyclic variation of integrated backscatter and wall thickness in stunned porcine myocardium.

This study was performed to investigate the relationship between the cyclic variation of integrated backscatter and myocardial wall thickening in stunned myocardium. Different definitions of cyclic variation were evaluated to be able to compare with other studies. Ultrasound data were acquired from 10 open-chested Yorkshire pigs (25-33 kg) at baseline, during regional ischemia and during 30 min of stunning, using a broadband ultrasound transducer (3-7 MHz) sutured directly upon the left ventricular myocardial wall. Cyclic variation of integrated backscatter and myocardial wall thickening were calculated using three definitions obtained from the literature. Independent of the definition, cyclic variation of wall thickness and integrated backscatter were blunted during acute ischemia and returned transiently to or above baseline during the first minute of reperfusion, followed by a gradual decrease to a level under baseline during stunning. An early return of the cyclic variation of the integrated backscatter was not observed in pigs, independent of the data processing used. The relationship between integrated backscatter and wall thickness was maintained.

Reproducibility of quantitative measurements from intracoronary ultrasound images. Beat-to-beat variability and influence of the cardiac cycle.

OBJECTIVES: The purpose of this study was to determine the variability of quantitative measurements from intracoronary ultrasound images, and the influence of the cardiac cycle on this variability, as a basis for in vivo applications. METHODS: Two observers analysed 30 MHz cross-sectional images from 96 in-vivo coronary arterial sites. By computer-assisted contour tracing we determined lumen area, vessel area, lesion area (vessel area minus lumen area) and percent obstruction (100% x lesion area/vessel area). Intra- and inter-observer and beat-to-beat variability, and systolic to diastolic differences were calculated by paired analysis. RESULTS: Consistent intra- and inter-observer differences (bias) were small (< or = 0.9%). Random variations in the two direct parameters were < or = 21.1%, but for the two derived parameters they were up to 40%. For all four parameters, random inter-observer variability was significantly greater (up to 119% for vessel area: 19.3 vs 8.8%) than intra-observer variability, but consistent variability was similar. Consistent beat-to-beat differences were small (< or = 1.4%), random variations were 8.9% to 17.5%. Random beat-to-beat variability for all four parameters was greater in diastolic than in systolic frames (up to 47.0% difference (11.9 vs 17.5%) for lesion area). Vascular dimensions were significantly greater in systole (2%). We found an error of 0.24 mm (2SD) for intra-observer variability of calculated mean arterial diameters, which is similar to the error described in angiographic studies (0.22 mm). CONCLUSIONS: Quantitative measurements from intracoronary ultrasound images generally reproduce well. It is preferable to use directly measured parameters as opposed to derived parameters, as they are less subject to variability. Variability can be reduced by selecting systolic images.

An in vitro evaluation of the line pattern of the near and far walls of carotid arteries using B-mode ultrasound.

This in vitro study was executed to evaluate the double line pattern generated at both near and far walls of human carotid arteries using B-mode ultrasound. Therefore, extravascular (7.5 MHz) and intravascular (30 MHz) ultrasound imaging were performed at the same locations of the carotid artery. The thickness of the double line pattern of the extravascular image (7.5 MHz) was compared to the thickness of the intima-media complex seen on the corresponding intravascular image (30 MHz) and on the histologic section. At the far wall of the extravascular image, the measurements were executed at the leading edge of the echo. The data showed high correlation and agreement with the intravascular (r = 0.91, p < 0.001; mean(diff) = -0.01 and SDdiff = 0.12) and the histologic measurements (r = 0.87, p < 0.001; mean(diff) = -0.12 and SDdiff = 0.13). In addition, the results of the measurements of the intravascular image showed high correlations and agreement with the histologic data (r(near) = 0.86, p < 0.001; mean(diff) = -0.08 and SDdiff = 0.15, respectively, r(far) = 0.92, p < 0.001; mean(diff) = -0.12 and SDdiff = 0.12). For comparison with other studies, near wall measurements were also included. These had to be performed at the trailing edge of the echoes to be compatible with these studies. The results of the measurements of the extravascular image showed poor correlations and lack of agreement with those of the intravascular (r = 0.49, p = 0.03; mean(diff) = 0.09 and SDdiff = 0.25) and of the histologic (r = 0.37, p = 0.03; mean(diff) = 0.04 and SDdiff = 0.23) measurements. These results can easily be explained from the physical limitations of measuring at the trailing edges. We conclude that the double line pattern seen at the far wall of the extravascular image is representative of the intima-media complex.

The relationship between myocardial integrated backscatter, perfusion pressure and wall thickness during isovolumic contraction: an isolated pig heart study.

To investigate the independent effect of myocardial wall thickness and myocardial perfusion pressure on integrated backscatter, experiments were designed in which integrated backscatter of normally perfused myocardial tissue was measured while changes in wall thickness during the cardiac cycle were reduced to a minimum. In nine blood-perfused isolated pig hearts, perfusion pressure was uncoupled from left ventricular pressure generation (Langendorff method) and isovolumic contraction and relaxation were realized by inserting a noncompressible water-filled balloon into the left ventricle. In a first experiment, at constant perfusion pressure (85 mmHg), the integrated backscatter (3-7 MHz), the myocardial wall thickness and the left ventricular pressure were determined simultaneously at various balloon volumes (5-25 mL). A quasistatic increase of balloon volume by 50% resulted in an average decrease of wall thickness of 6.5% (p < 0.01) and a mean increase in the integrated backscatter level of 1.1 dB (p < 0.01). Integrated backscatter levels increased statistically significant by 0.14 +/- 0.014 dB per percent decrease of wall thickness. Measurements of percentage end-systolic myocardial wall thickening ranged from -10% to +10%, mean 0.15 +/- 4.5% (NS from zero); whereas cyclic variation of integrated backscatter ranged from -3.9 to +3.9 dB, mean 0.19 +/- 1.5 dB (NS from zero). In a second experiment, at a constant midrange balloon volume, the same parameters were determined simultaneously at various perfusion pressures (20-120 mmHg). An increase in perfusion pressure by 50% resulted in a small but statistically significant increase of 1.5% in myocardial wall thickness, which could be explained by an increase of intravascular volume. The integrated backscatter levels did not change statistically significantly. Measurements of percentage end-systolic myocardial wall thickening ranged from -8.9 to +7.8%, mean 0.13 +/- 4.0% (NS from zero); whereas cyclic variation of integrated backscatter ranged from -1.8 to +4.2 dB, mean 0.37 +/- 1.3 dB (NS from zero). The magnitude of cyclic variation of integrated backscatter of myocardial tissue in a contractile state is reduced if myocardial muscle is prevented from normal thickening. In addition, changes in intravascular volume during the cardiac cycle have a negligible influence on the absolute backscatter level or its cyclic variation. We conclude, if only wall thickness and perfusion pressure are involved, that integrated backscatter is mainly determined by myocardial wall thickness.

Histopathologic validation of intracoronary ultrasound imaging.

The purpose of this study was to validate intracoronary ultrasound imaging by correlation with histologic examination. In this in-vitro study of pressure-perfused human coronary arteries, 104 matching intracoronary ultrasound imaging images and histologic cross-sections from 12 hearts were compared to determine the diagnostic accuracy of 30 MHz commercially available intracoronary ultrasound imaging. For lipid deposits, sensitivity was 46% and specificity 97%. The smallest lipid deposit that was visualized measured 0.25 mm in axial diameter on histologic study. For calcific deposits, sensitivity was 77% and specificity 100%. The smallest calcific deposit that was visualized measured 0.25 mm in axial diameter on histologic examination. Atherosclerotic intimal thickening could not be distinguished qualitatively or quantitatively from nonatherosclerotic intimal thickening unless there were localized deposits of lipids or calcium. Intracoronary ultrasound imaging is accurate in detecting lipid and calcium deposits. Intimal thickening in intracoronary ultrasound imaging images does not prove the presence of atherosclerosis.

Dobutamine stress--Doppler echocardiography before and after coronary angioplasty.

To determine if dobutamine-induced myocardial ischaemia causes abnormalities in Doppler parameters of left ventricular ejection and filling and to assess early effects of successful coronary angioplasty (PTCA) on these parameters, dobutamine stress echocardiography and Doppler studies were performed once in 11 normal volunteers and twice in 17 patients (within 1 day pre- and post-PTCA). Dobutamine induced wall motion abnormalities, ST changes and angina in 11, five and five patients, respectively, before and three, two and one patients, respectively, after PTCA. Doppler indices of both systolic and diastolic function were comparable at rest, before and after PTCA. Dobutamine induced similar increases in peak aortic velocity and average acceleration in healthy individuals (39% and 53%) and in patients with one-vessel disease both before (38% and 39%) and after PTCA (39% and 40%). In the three patients with multivessel disease, peak aortic velocity showed a blunted response (-0.3%) before PTCA but increased by 17% after PTCA, while acceleration decreased both before (12%) and after PTCA (14%). There were significant differences (P < 0.0001) between healthy individuals and pre-PTCA patients in the effect of dobutamine on peak early (E) filling velocity (+34% vs -19%), E-acceleration (+35% vs -26%), peak early to atrial filling velocity ratio (E/A) (-0.7% vs -37%) and diastolic time velocity integral (TVI) (+34% vs -22%). After PTCA, the response of Doppler diastolic indices improved during dobutamine, as shown by the increase in E and E-acceleration (+8%, +24%), respectively) and by the decline in the reduction of E/A and TVI (-17% and -10%, respectively). Thus, the response of Doppler diastolic parameters to dobutamine stress is a sensitive indicator of significant coronary disease and is superior to changes in ejection indices. Successful PTCA resulted in an improved diastolic filling response to dobutamine stress.

Ultrasound myocardial integrated backscatter signal processing: frequency domain versus time domain.

In the literature, different forms of measuring the ultrasound power returned by myocardial tissue are reported. Frequency domain methods will give the maximum frequency information, whereas time domain methods are limited in bandwidth, but more practical to realize. It was the purpose of this study to compare the various methods of signal processing. High frequency ultrasound signals from a pig's myocardium, digitally recorded during normal contractile performance, were analyzed by six different methods of signal processing to obtain estimates of backscatter power. The myocardial tissue characterization parameters studied were the integrated power as well as its cyclic variation during the cardiac cycle. A total number of 8109 ultrasound traces obtained in 16 pigs were processed. The study included three signal processing methods in the frequency domain: frequency compensated integrated backscatter calculated over both a large (4 MHz, method 1) as well as a small frequency bandwidth (2 MHz, method 2) and uncompensated integrated backscatter (method 3), and three methods in the time domain: high frequency signal squared and integrated (method 4), mean rectified signal level (method 5) and mean signal level after logarithmic compression and envelope detection (method 6). The random measurement variation (including beat-to-beat variation) was analyzed as well as the paired differences of the backscatter parameters obtained by the respective methods as compared with the only theoretically correct method in the time domain (method 4). The magnitudes of the random measurement variation expressed as a standard deviation (SD) were comparable (range 0.93-1.2 dB) except for method 6 (0.61 dB), where the measurement variation is decreased by the logarithmic compression.(ABSTRACT TRUNCATED AT 250 WORDS)

Does the measurement of left ventricular isovolumic relaxation time allow early prediction of cardiac allograft rejection?

In order to evaluate the value of isovolumic relaxation time measurement for the diagnosis of moderate acute rejection episodes in cardiac allograft recipients a comparison was made with the histological results from the endomyocardial biopsy. A total of 202 isovolumic relaxation time measurements from 26 patients were compared to the biopsy results. The technique used to record isovolumic relaxation time was dual M-mode echocardiography. In addition a combined phonoechocardiography was used for 54 isovolumic relaxation time measurements from 17 patients. A good correlation was found between these two methods. When the biopsy results were normal the isovolumic relaxation time was 71.4 +/- 15.1 ms. When moderate acute rejection episodes were present isovolumic relaxation time decreased to 50.2 +/- 21.2 ms (p < 0.001). In spite of the close correlation detected at group level, there was a large variability of the measurements without accompanying changes in the biopsy specimen. At the same time a significant overlap was found between the measurements taken during rejection and non-rejection periods making it impossible to use these methods for clinical decision making. We conclude that isovolumic relaxation time measured with these methods is not a sufficiently sensitive parameter for the diagnosis of moderate acute rejection episodes in the individual patient, and in our experience, it is not a substitute for endomyocardial biopsy and can not be applied for clinical decision making.

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.

Backscatter directivity and integrated backscatter power of arterial tissue.

A 27 MHz transducer, mounted on an ultrasonic microscope, was used to quantify the dependence of backscatter power on the angle of incidence of arterial vessels. Due to variations in the angle of incidence significant variations in backscatter power were found in the intima, the muscular and elastic media, the adventitia and the external elastic lamina. The muscular and the elastic media show anisotropic behaviour in their angle dependence, i.e. the extent of the angle dependence depends on the direction of angle variation. This anisotropic nature is probably caused by the dominant orientation of smooth muscle cells or elastin fibers in these tissue layers. Measurements on 13 specimens of the iliac artery showed that each tissue type of the vessel has its own specific angle dependent behaviour. In the future this property might be used for quantitative tissue characterization.

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.

[Reliability of blood pressure measurements; comparison of an electronic meter and a mercury manometer in family practice]. / Betrouwbaarheid van de bloeddrukmeting; vergelijking van een elektronische meter en een kwikmanometer in de huisartspraktijk.

The Riva-Rocci indirect method of measuring the blood pressure carries a number of sources of error. A report is presented of a study of the serviceability of an electronic blood pressure meter as compared with the conventional mercury manometer. Seventy-six paired measurements were carried out in patients selected at random using an electronic blood pressure meter and a mercury manometer meeting all Health Council requirements. The systematic error and the incidental error in both measuring procedures were compared. The differences found were so slight as to be negligible in practice. It is concluded that the electronic blood pressure meter in practice constitutes an acceptable substitute for the conventional mercury manometer.

The reproducibility of continuous wave Doppler measurements in the assessment of mitral stenosis or mitral prosthetic function: the relative contributions of heart rate, respiration, observer variability and their clinical relevance.

The reproducibility of continuous wave Doppler echocardiographic measurements of transmitral diastolic flow velocity were studied in terms of bias and random error in 40 patients with either mitral stenosis or a Björk-Shiley mitral valve prosthesis. Twenty-seven patients were in sinus rhythm; 13 patients had atrial fibrillation. Intra- and interobserver differences in bias were small for the Doppler parameters studied i.e. early peak velocity (0.6% vs 3.6%), mean diastolic velocity (1.1% vs 8.6%), mean temporal velocity (2.3% vs 14.5%) and pressure half-time (2.7% vs 4.8%). The overall random error of the measurements (in terms of twice the standard deviation) was estimated separately in patients in sinus rhythm and atrial fibrillation: early peak velocity 5.6% and 9.2%, respectively, mean diastolic velocity 9.4% and 22%, mean temporal velocity 8.6% and 19% and pressure half-time 34% and 46%. The relative contributions to the overall random error of observer variation, heart rate dependency and respiratory variation were also studied. Heart rate dependency was demonstrated for both the mean diastolic velocity and the pressure half-time. Respiratory variation was found in the early peak velocity. From the results of this study the number of measurements to reduce the random error of the final average could be determined. Our results indicate that for the measurements in which a respiratory effect is present it is advisable to average the measurements taken over complete respiratory cycles.

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.

Reference ranges of left ventricular cross-sectional echocardiographic measurements in adult men.

Reference ranges for left ventricle cross-sectional echocardiographic measurements were determined in 67 healthy Dutch men. Age, weight, height, and heart rate were used as the determinants. The images were made with the apical long-axis view, and the calculations were done with the area-length method. The end-diastolic volume, end-systolic volume, stroke volume, and ejection fraction were measured for six consecutive cardiac cycles in every subject and were averaged. Data were analyzed by means of both simple linear regression and multiple linear regression after logarithmic transformation of all measurements. Weight proved to be the best predictor of the echocardiographic end-diastolic volume, end-systolic volume, and stroke volume. The left ventricular ejection fraction could be regarded as independent of the determinants studied. Nomograms of the 5th, 50th and 95th percentile limits were made of the echocardiographic parameters versus weight.

Can we assess the changes of ventricular filling resulting from acute allograft rejection with Doppler echocardiography?

We investigated the value of several Doppler echocardiographic measurements for the diagnosis of acute allograft rejection after orthotopic heart transplantation. In all, 144 transmitral flow velocity curves and 159 internal jugular venous flow velocity curves were recorded by continuous wave Doppler echocardiography, and the results were compared with the histologic findings. The recordings were evaluated with a computer-aided analysis system. The Doppler measurements did not show any significant correlation with the biopsy results. Only one recording obtained during a moderate acute rejection episode supported the hypothesis about the relation between jugular venous flow and cardiac rejection. We conclude that these Doppler echocardiographic measurements are not suitable to detect acute allograft rejection noninvasively.

In vitro cyclic AMP induced phosphorylation of phospholamban: an early marker of long-term recovery of function following reperfusion of ischaemic myocardium?

Changes in myocardial membrane biochemistry and ultrastructure, determined shortly (2 h) after reperfusion of ischaemic myocardium, were compared with the long term (4 wk) recovery of regional myocardial function. Anaesthetised pigs were subjected to 30 min (n = 14, group I) or 60 min (n = 14, group II) of left circumflex coronary artery occlusion. Seven animals of each group were studied 2 h and the others 4 weeks after flow was reinstated. After 2 h of reperfusion, regional myocardial function was absent in both groups. At 4 weeks regional function had returned to normal in group I, but was still significantly depressed in group II. Biochemical studies after 2 h of reperfusion showed that a functional index of the cardiac membrane, the in vitro cyclic AMP dependent 32P incorporation into phospholamban, was 71 (SEM 9)% compared to non-ischaemic myocardium in group I and 31 (6)% in group II (p less than 0.05). After 4 weeks this index had completely recovered in group I, 114 (13)%, but a significant decrease to 79 (2)% could still be observed in group II (p less than 0.05). After 2 h of reperfusion as well as after 4 weeks of recovery the myocytes in group II were more severely damaged than in group I. This study suggests that determination of in vitro phosphorylation of phospholamban shortly after reperfusion of ischaemic myocardium may be of value in the prediction of long term recovery of regional myocardial function.

Myocardial backscatter analysis in animal experiments.

This paper describes the instrumentation and data analysis procedures for cardiac tissue characterization by a backscatter method. Experimental results obtained with a 'button' transducer in direct contact with the myocardium are discussed.

Does echocardiography allow the monitoring of the cardiac effects of nitrates?

Echocardiography is a very useful non-invasive method of cardiac diagnosis. It has been widely used in evaluating the effects of some drugs, such as nitrates, prazosin, and propranolol, on heart and seems very successful. In this paper, the echocardiographic studies of the effects of nitrates on left ventricular dimension and volume have been reviewed and an attempt has been made to answer whether or not echocardiography can allow to monitor the effects of nitrates in patient groups and further in individual patients.

Monitoring aspects of an ultrasonic esophageal transducer. Initial experience.

A method of semi-automatic contour detection is described using a commercial (Kontron) image analysis instrument. Input data consists of high-quality transesophageal echocardiograms of short-axis left ventricular cross-sections. The purpose of the study is to evaluate the feasibility of such a method for the quantitative monitoring of the dynamic behaviour of the left ventricle during high risk surgery. From the first experience it is authors' impression that the automatically derived contour depends strongly on the selected algorithm parameters. Therefore derivation of absolute measurements from these contours seems problematic. Automatic contour detection seems much better fit for monitoring situations, where the patient acts as his own reference and there is no need to change the algorithm parameters.