Tissue characterization

Quantitative Viscoelastic Response (QVisR): Direct Estimation of Viscoelasticity With Neural Networks

We present a machine learning method to directly estimate viscoelastic moduli from displacement time-series profiles generated by viscoelastic response (VisR) ultrasound excitations. VisR uses two colocalized acoustic radiation force (ARF) pushes to approximate tissue viscoelastic creep response and tracks displacements on-axis to measure the material relaxation. A fully connected neural network is trained to learn a nonlinear mapping from VisR displacements, the push focal depth, and the measurement axial depth to the material elastic and viscous moduli. In this work, we assess the validity of quantitative VisR (QVisR) in simulated materials, propose a method of domain adaption to phantom VisR displacements, and show in vivo estimates from a clinically acquired dataset.

The first days of diagnostic ultrasound

The Reflections series takes a look back on historical articles from The Journal of the Acoustical Society of America that have had a significant impact on the science and practice of acoustics.

Noncontact quantitative biomechanical characterization of cardiac muscle using shear wave imaging optical coherence tomography

We report on a quantitative optical elastographic method based on shear wave imaging optical coherence tomography (SWI-OCT) for biomechanical characterization of cardiac muscle through noncontact elasticity measurement. The SWI-OCT system employs a focused air-puff device for localized loading of the cardiac muscle and utilizes phase-sensitive OCT to monitor the induced tissue deformation. Phase information from the optical interferometry is used to reconstruct 2-D depth-resolved shear wave propagation inside the muscle tissue. Cross-correlation of the displacement profiles at various spatial locations in the propagation direction is applied to measure the group velocity of the shear waves, based on which the Young's modulus of tissue is quantified. The quantitative feature and measurement accuracy of this method is demonstrated from the experiments on tissue-mimicking phantoms with the verification using uniaxial compression test. The experiments are performed on ex vivo cardiac muscle tissue from mice with normal and genetically altered myocardium. Our results indicate this optical elastographic technique is useful as a noncontact tool to assist the cardiac muscle studies.

Assessment of significance of features acquired from thyroid ultrasonograms in Hashimoto's disease

INTRODUCTION

This paper concerns the analysis of the features obtained from thyroid ultrasound images in left and right transverse and longitudinal sections. In the image analysis, the thyroid lobe is treated as a texture for healthy subjects and patients with Hashimoto's disease. The applied methods of analysis and image processing were profiled to obtain 10 features of the image. Then, their significance in the classification was shown.

MATERIAL

In this study, the examined group consisted of 29 healthy subjects aged 18 to 60 and 65 patients with Hashimoto's disease. For each subject, four ultrasound images were taken. They were all in transverse and longitudinal sections of the right and left lobe of the thyroid, which gave 376 images in total.

METHOD

10 different features obtained from each ultrasound image were suggested. The analyzed thyroid lobe was marked automatically or manually with a rectangular element.

RESULTS

The analysis of 10 features and the creation for each one of them their own decision tree configuration resulted in distinguishing 3 most significant features. The results of the quality of classification show accuracy above 94% for a non-trimmed decision tree.

Ultrasonic characterization of myocardial photocoagulation lesion size in vivo during Nd:YAG laser irradiation

Endocardial coagulation lesions were created using transcatheter continuous-wave Nd:YAG laser irradiation. Ultrasound monitoring of thermal lesion dimensions was performed using 7.5-MHz and 10-MHz transducers directly from the epicardial surface in short-axis configuration (group A) or through the chest wall (group B). A total of 33 lesions were created in 10 dogs at energy levels ranging from 300 J to 1000 J. Mean histological lesion width (HW) compared with ultrasonically determined mean width (UW) showed that the differences (mean +/- standard deviation) in group A (UW - HW) was = 1.14 +/- 0.8 mm, which was not statistically significantly different from zero. In group B, (UW - HW) = 2.04 mm +/- 0.7 mm (p < .05), which was statistically significantly different from zero. Mean histological depth (HD) differentially related to ultrasound mean depth (UD) for group A and B combined showed (UD - HD) = -0.19 mm +/- 0.46 mm, not statistically significantly different from zero. The frequency distribution for width in group A showed magnitude of UW-HW > 3 mm in 32% of cases. In group B magnitude of UW-HW > 3 mm in 15%, whereas ultrasound width was larger than histology in 75% of the cases. For depth, magnitude of UD-HD > 3 mm in 15% of cases. With further refinement of the technique, ultrasonic tissue characterization may become a useful adjunct to monitoring lesion dimensions during transcatheter laser photocoagulation.

In vivo measurements of frequency-dependent attenuation in tumors of the liver

Ultrasonic frequency-dependent attenuation (FDA) coefficients of the liver obtained from selected regions of interest within the liver were determined in 106 individuals, 40 cases presumed normal based on medical histories and 66 with malignant tumors (hepatocellular carcinoma [HCC] or metastatic liver tumor) or benign tumors (hepatic hemangioma, hepatic adenoma, or focal nodular hyperplasia of the liver). All liver tumors were confirmed histopathologically by ultrasonically guided fine-needle biopsy and/or operation. Mean attenuation of normal liver was 0.53 +/- 0.03 dB/cm/MHz, 0.29 +/- 0.05 dB/cm/MHz in hepatic hemangioma, 0.43 +/- 0.05 dB/cm/MHz in HCC, and 0.41 +/- 0.12 dB/cm/MHz in metastatic liver tumor. Hepatic adenoma and focal nodular hyperplasia of the liver produced higher values, averaging 0.66 +/- 0.09 dB/cm/MHz. This difference between malignant and benign tumors was statistically significant. There was some correlation between the FDA for the hepatic tumor and the histopathology that merits further investigation.

Performance criteria for quantitative ultrasonography and image parameterisation

For the purpose of assessing and comparing the practical performance of various specific approaches to quantitative tissue characterisation, three sets of performance criteria are proposed, relating respectively to contrast resolution, spatial resolution, and speed of presentation. In each case numerical performance targets are suggested: in particular that spatial resolution should preferably be within a linear factor of three of the best achievable anatomical resolution of the associated imaging techniques and that presentation speed should be 'real time' (i.e. about 10 Hz). In the light of these criteria and performance targets the main existing approaches to ultrasonic tissue characterisation are then considered. These are classified in two groups: first those approaches based on measurements of bulk properties of tissues and secondly those related to parameters of the structural organisation of tissues. Examination of available evidence suggests that the latter group are more promising than the former. Finally it is argued that ultrasonic methods of tissue characterisation have substantial practical potential but that the realisation of such potential is contingent on achieving consensus on choice of a single, optimised and generally applicable approach that would carry with it the linked benefits of industrial standardisation and broad sharing of clinical experience.

Evolution equations and ultrasonic wave propagation in biological tissues

Fundamental research in ultrasonic diagnostics is often limited by the relatively simple models of propagation invoked in what is largely an empirical science. Careful discussion of the problem reveals the need for more sophisticated propagation theories as the basis of measurement techniques and for the interpretation of experimental results. It is thus important for dialogue between theoreticians and experimentalists in the field. The complexity of ultrasonic wave propagation in tissue arises from a combination of factors. First, there is the biochemical sophistication of the media concerned. Second, there is the variety of physical phenomena involved: the diffractive nature of the ultrasonic field, the presence of absorption, the presence of large scale inhomogeneities and small scale scatterers, and the possibility of finite amplitude propagation effects. It has tended to be the custom to deal with each of these problems on an individual basis with a second feature being introduced as a perturbation of the results obtained for the first. The present authors have been concerned to find a unified approach which will permit each of the effects to be taken into account in relation to the others. This approach is based on the application of two-dimensional evolution equations modelling ultrasonic propagation in non-cavitating soft tissues. The model incorporates all the propagation phenomena known from experimental studies, indicating a need for knowledge of nine material parameters for a complete description. It thus provides a basis for numerical investigation of the relative significance of the parameters under different conditions. This will permit identification of those that should be known experimentally with high precision and those that have a minor role in the propagation phenomena.

Ultrasonic propagation in mammalian cell suspensions based on a shell model

The interaction of ultrasonic waves with individual cells has been modelled on the basis that the cells can be represented by viscous liquid spheres surrounded by a viscoelastic shell (the membrane) immersed in a viscous fluid. The computational model includes thermal waves and requires 22 input parameters. Many of the parameters are not available in the literature and a detailed discussion is given on the procedures by which the values used in the model calculations were chosen. In spite of the arbitrariness of the choice of many of the parameter values, the computations show surprisingly good agreement with experimental measurements of ultrasonic attenuation in animal cell suspensions. The model has been used here to investigate different aspects of the interaction of ultrasound with the cells. It is found that the membrane is important only between 0.5 and 30 MHz and contributes less than 15% to the attenuation. Absorption is shown to be an important feature to include, while the scattering contribution to the attenuation is less than 1% at 3 MHz. The thermal effects are important at frequencies below 1 MHz and contribute some 65% to the attenuation at 100 MHz.

On-line two-dimensional evaluation of ultrasonic integrated backscatter

We describe an apparatus for the on-line evaluation of integrated backscatter from areas of tissue. The equipment is fully integrated into a B-mode ultrasonic system; there are therefore no new operating procedures to be learned. It provides a simultaneous display of conventional information, together with parameters of tissue characterization. The apparatus is fast and, over a broad diagnostic frequency range, may be used in conjunction with conventional equipment employing transducers.

Ultrasonic study of in vivo kinetic characteristics of human tissues

A method is described for quantifying tissue movement in vivo from the computation of correlation coefficient between pairs of A-scans with appropriate time separation. The method yields quantifiable and repeatable secondary patterns of soft tissue movement in response to primary cardiac movement in a given subject, shows consistently different results as between normal livers and a variety of abdominal tumours, and is sensitive to either progress or therapeutically-induced regression of malignant disease. While the results reported here have been obtained using somewhat simple and crude equipment, the method is well suited to implementation on a commercial real-time scanner.

Detection of myocardial scars in neonatal infants from computerized echocardiographic texture analysis

It has been demonstrated that highly reflectile echoes (HREs) on standard echocardiograms may represent foci of myocardial fibrosis, calcification, or infiltration. A pilot study of the echocardiograms of premature infants by our group has indicated the presence of HREs in many stressed infants. We have subsequently shown that these HREs correspond to myocardial scarring or necrosis.

By studying normal two-dimensional echocardiograms and those with visually observed highly reflectile echoes (HREs), we have been able to develop echo-intensity ranges for normal neonatal myocardium and suspected foci of necrosis. An amplitude analysis of the intensity levels of these highly reflectile areas (HREs) in the echocardiogram has indicated that their mean intensity was significantly higher than the surrounding healthy myocardial areas. Significant correlation was found between these highly reflectile echo zones and calcified or necrotic tissue based on postmortem pathological examination.

An objective method of quantifying the ultrasonic reflection amplitude has thereby been developed by us, based on image analysis of the echograms available from the B-scan system. Algorithms have been developed for evaluating the greylevels (or echo intensities or reflection amplitudes) of the pixels, normalizing them with respect to the reflection amplitude of the pericardium, and then printing out the grey-level distribution over an image. Appropriate software has been developed to designate scarred myocardial segments, based on the mean and standard deviation of the selected region on the echo image in comparison with these values for the pericardium.

Two-dimensional, gray-scale abdominal ultrasonography. General interpretation and abdominal masses

The techniques of and general interpretive principles of gray-scale, two-dimensional abdominal ultrasonography in small animals are described. Using case examples, commonly encountered imaging artifacts and categories of disease are integrated with a description of what was obtained by radiography. Tissue echogenicity as a basis for general assessment of organ abnormalities as well as the expectations (interpretive and prognostic) one should have of abdominal ultrasonography are presented.

Sonographic tissue characterisation in thyroid gland diagnosis. A correlation between sonography and histology

Punch biopsy was carried out in 32 cases in which thyroid gland changes were sonographically classified as being of homogeneously normal or of homogeneously low echogenicity. Mean follicle lumen size was morphometrically determined from the histological sections. This produced a significant, positive correlation between echogenicity and follicle size. The mean follicle lumen diameter in so-called echonormal structures was 67 microns (SD +/- 23 microns), and 25 microns (SD +/- 8 microns) in low-echogenic lesions. Thus normal echogenicity represented a normofollicular or macrofollicular structure, while a low echogenicity pattern indicated a microfollicular or solid tissue structure. The structure of thyroid carcinomas is not homogeneously normofollicular or macrofollicular; in exceptional cases they are such only focally. Therefore the significance of these findings lies in the exclusion of malignancy in the event of homogeneously normal echogenicity.

The dependence of myocardial ultrasonic integrated backscatter on contractile performance

We have recently shown that the cardiac cycle-dependent variation in myocardial ultrasonic integrated backscatter is blunted with regional ischemia in dogs. To determine if global and intramural regional myocardial contractile performance can be quantified by integrated backscatter, we analyzed ultrasonic responses after induction of increased and decreased contractility in five dogs. A recently developed analog data-acquisition system for measuring integrated backscatter in real time was used to sample radiofrequency signals gated from subepicardial or subendocardial regions. Base-line recordings of integrated backscatter, left ventricular pressure, left ventricular dP/dt, and wall thickness were made at 12 left ventricular sites for both intramural regions. Contractility was modified subsequently by either paired pacing or propranolol to produce significantly elevated or depressed values for maximum left ventricular dP/dt compared with baseline (1083 +/- 289 to 3001 +/- 570 mm Hg/sec; p less than .01 for all). The amplitude of the cyclic variation of integrated backscatter was 50% greater (arithmetically) in subendocardial than in subepicardial regions for all treatments (7.6 +/- 0.3 vs 6.0 +/- 0.5 dB, p less than .001). The maximum rate of change in integrated backscatter waveforms during isovolumetric contraction was faster with paired pacing and slower with propranolol than at baseline for all regions (56 +/- 6 to 74 +/- 6 to 82 +/- 5 dB/sec, p less than .005). The maximum rate of change in integrated backscatter also was greater in subendocardial than subepicardial regions (p less than .001). Thus, both regional and global differences in myocardial contractile performance are manifest quantitatively in integrated backscatter waveforms. We propose that the physiologic determinants of these differences may depend on regional and global variations in myofibril elastic characteristics.

Effects of coronary artery occlusion and reperfusion on cardiac cycle-dependent variation of myocardial ultrasonic backscatter

We have recently reported a systematic variation in integrated ultrasonic backscatter throughout the cardiac cycle in canine hearts. This study was performed to determine whether the pattern of such variation is modified systematically by ischemia. Measurements of integrated ultrasonic backscatter in selected regions of normal, ischemic, and reperfused hearts were compared in view of known differences in systolic function of myocardium in each of these regions. Integrated ultrasonic backscatter (3-7 MHz) gated to the first derivative of left ventricular pressure was measured at the apex, midwall, and base in 10 dogs and at the apex before and during transient ischemia and reperfusion in four dogs. Quantitative integrated ultrasonic backscatter was referenced to a steel reflector. Cyclic variation of integrated ultrasonic backscatter was greatest at the apex [peak to trough variation 5.5 +/- 0.9 dB (mean +/- SE)] with the maximum near end diastole (-52.9 +/- 0.9 dB) and minimum near end systole (-58.4 +/- 1.0 dB). Variation at the apex (5.5 +/- 0.9 dB) and the midwall (4.3 +/- 0.8 dB) was greater than at the base (0.5 +/- 1.0 dB) (P less than 0.01 for either region compared with base). Left anterior descending coronary occlusion for 10 minutes in four of 10 dogs reduced variation at the apex to 0.4 +/- 1.5 dB (P less than 0.02 compared with preocclusion). Reperfusion for 2 hours restored apical cyclic variation to 3.9 +/- 1.7 dB, i.e., to values not significantly different from those before occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Fibrosis, lipids, and calcium in human atherosclerotic plaque. In vitro differentiation from normal aortic walls by ultrasonic attenuation

This study was designed to determine whether attenuation of ultrasound by the aortic wall is potentially useful in characterizing the atherosclerotic lesion. Measurements were made on fresh specimens taken from a human aorta at autopsy. Four hundred different sites, 4 mm in diameter each, corresponding to the dimension of the ultrasonic beam at the focal zone, were ultrasonically analyzed and histologically studied. Attenuation of ultrasound in each site was assessed by Fourier analysis of the echo produced by a specular reflector placed behind the specimen. Two parameters were measured over the range 7-11 MHz: the integrated attenuation index (per cm), and slope (per cm per MHz) of the best fit straight line relating attenuation and frequency. Histological examination--performed for each of the 400 sites where attenuation had been measured--identified four subsets (100 samples each): normal aortic walls, fibrous plaques, fibrofatty plaques, and calcified plaques. Results obtained from ultrasonic and histological analyses showed that the integrated attenuation index was lowest in normal walls (24 +/- 2.1, mean +/- SE) and progressively increased in fibrous (32 +/- 3.1), fibrofatty (82 +/- 6.5), and calcific (185 +/- 8.7) subsets (all intergroup differences were significant, except for the normal vs. fibrous comparison). The slope value was significantly lower in the fibrous than in the normal subsets: (10(-3)) 31.9 +/- 4.5 vs. (10(-3)) 99.5 +/- 9.1, respectively. Values of fibrofatty and calcific plaques overlapped: (10(-3)) 383 +/- 21 vs. (10(-3)) 320 +/- 23, respectively. Both were significantly different from normal and fibrous groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Attenuation estimation in reflection: progress and prospects

This monograph presents a tutorial review of the current state-of-the-art in ultrasonic attenuation estimation in reflection. Clinical indications which provide the motivation for attempting in vivo attenuation estimation are discussed. Frequency and time domain techniques and their respective tradeoffs and problems are presented. Finally, current clinical results obtained with the various techniques are summarized and further areas of study are suggested.

Ultrasonic backscatter and collagen in normal ventricular myocardium

Integrated ultrasonic backscatter has been related to collagen deposition in fibrotic myocardium. The purpose of our study was to measure the integrated ultrasonic backscatter in the right and left ventricles of 10 normal freshly excised canine hearts and five normal formalin-fixed human hearts. A 2.25 MHz, 50% fractional bandwidth transducer was positioned at the transducer focal distance from the epicardium. The radio frequency backscatter signal, excluding specular reflections, was digitized, squared, and integrated to yield the integrated ultrasonic backscatter (in decibels down from a 100% reflector). The segment of myocardium corresponding to the integrated ultrasonic backscatter sample volume was excised and assayed for hydroxyproline, a marker for collagen. A second purpose of our study was to evaluate the influence of fixation with formalin on the backscatter. Regional integrated ultrasonic backscatter was therefore measured in 10 freshly excised canine left ventricles, which were fixed in 10% formalin for 2 weeks. Integrated ultrasonic backscatter measurements were then repeated. In freshly excised canine hearts, the integrated ultrasonic backscatter from right ventricle was higher than that from left ventricle (-60.4 +/- 1.6 [SEM] vs -66.9 +/- 1.0 dB; p less than .001). The collagen content of right ventricle was also higher than that of left ventricle (4.40 +/- 0.26 [SEM] vs 3.58 +/- 0.13 micrograms/mg dry weight; p less than .005). Similar results were obtained in human hearts. There were no correlations between integrated ultrasonic backscatter and collagen content (r = .28 and .32 for dogs and humans, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Relation between regional echo intensity and myocardial connective tissue in chronic left ventricular disease

Cross sectional echocardiograms were recorded within one week of death in seven patients with valvular heart disease, four with coronary artery disease, and nine with congenital heart disease. Regional echo amplitude was measured from the cross sectional display by constructing histograms of pixel intensity. Parietal pericardium was used as an internal standard for setting the gain of the instrument. At necropsy myocardium was taken from the free wall of the left ventricle, the papillary muscles, and the septum. Fibrosis was assessed histologically and biochemically as hydroxyproline content. In individual samples histological and biochemical estimates were correlated. In all regions other than the septum in patients with left ventricular hypertrophy, log [collagen] correlated with median pixel intensity. The amplitude of reflected echoes from the hypertrophied septum was significantly higher than that from other samples but was similarly correlated with collagen content. Agreement between echo amplitude and histological grade was significantly less good. Thus in chronic left ventricular disease myocardial collagen content appears to be the major determinant of regional echo intensity. Reproducibility of measurements and more rigorous definition of tissue abnormalities will, however, require further study.

Echocardiographic features of tropical endomyocardial disease in South India

Fifteen patients with tropical endomyocardial disease which had been proved angiographically were studied using M-mode and cross-sectional echocardiography to determine the extent to which specific features of this disease could be recognised by these non-invasive methods. Tethering of the posterior mitral valve leaflet to the ventricular wall in combination with areas of echo-dense material in the posterior left ventricular wall and associated papillary muscle appeared to be a constant diagnostic feature of this disease. Colour coding of regional echo amplitude showed high intensity echoes in a distribution corresponding closely to that of the fibrosis known to occur in this condition. Though M-mode echocardiography did not contribute diagnostic information, it was useful in defining the functional consequences of myocardial or mitral valve disease. Digitisation of records allowed a restrictive pattern of left ventricular filling to be observed. It was concluded that cross-sectional echocardiography, particularly when supplemented by colour coded amplitude processing, can make a confident non-invasive diagnosis of tropical endomyocardial disease and so could be useful in assessing its progression or response to treatment.

Range- and azimuth-dependent variability of image texture in two-dimensional echocardiograms

Regional two-dimensional (2D) echocardiographic amplitude patterns, or image texture, may be of diagnostic importance. Echocardiographic image texture is due in part to acoustic speckle, a complex pattern of interference of reflections from many small scatterers in tissue. The regional speckle pattern appears to be altered in several disorders associated with abnormalities in myocardial structure but also may be altered by a variety of characteristics of the scanning instrument. We hypothesized that quantitative measures of regional 2D echocardiographic image texture would vary as a function of position in range and azimuth within the field of view, even when imaging a uniform ensemble of scatterers. We tested this hypothesis by imaging a tissue-equivalent phantom with two phased-array scanners and two different methods of digitization. We analyzed the texture in several regions of interest separated in range and azimuth and found significant differences in quantitative texture measures as a function of position of the region of interest in the sector field of view (p values .006 to .0001 by multivariate analysis of variance). We found significant regional variability in texture with both scanners and both methods of digitization. We conclude that regional quantitative image texture in 2D echocardiograms varies as a function of range and azimuth, even when imaging a uniform ensemble of scatterers. This variability is related to several physical and instrument-related phenomena and precludes interpreting all regional texture alterations as indicating tissue structural abnormalities.

High resolution ultrasonic imaging by controlled averaging of backscattered signals

A new synthetic aperture technique for obtaining ultrasonic images with a high resolution is described. The attained resolution is in the order of the ultrasonic wavelength and, when using a 5 MHz unfocussed beam, amounts to 0.3 +/- 0.1 mm, i.e. it is much smaller than the diameter of the sound beam. Measurements have been performed on a model specimen consisting of a two-dimensional array of threads. The distance between the threads were chosen to approximate to the macroscopic fibre spacing of 1.5 mm +/- 0.3 mm in human muscle.

Quantitative texture analysis in two-dimensional echocardiography: application to the diagnosis of experimental myocardial contusion

We postulated that the analysis of regional image texture in two-dimensional (2D) echocardiograms would be an accurate method to differentiate normal from abnormal myocardial structure. We tested this hypothesis with quantitative texture measures to study the regional, spatial distribution of echo amplitudes in 2D echocardiograms performed before and immediately after blunt left chest trauma was induced in six anesthetized dogs. After trauma the contused region of myocardium appeared brighter and exhibited an altered myocardial texture. By use of a set quantitative texture measures, we found no significant differences in pretrauma images when normal regions were compared with regions to be contused. Also, we found no difference when we compared the normal regions in each animal in pretrauma vs posttrauma images. Twelve measures, however, differentiated normal from contused regions within the posttrauma images (p values ranged from .0057 to .0001 by multivariate analysis of variance). These texture measures were capable of differentiating normal from abnormal tissue only when texture along the azimuthal (lateral) direction was calculated. We conclude that regions of myocardial contusion exhibit visibly altered local echo-amplitude patterns (altered image texture) and that these image texture alterations may be quantified with digital image analysis techniques. These findings suggest that quantitative texture calculations may be a useful approach to ultrasound tissue characterization.

Ultrasound velocity in fixed human liver: empirical anova and regression modelling on histologically assessed abnormalities

Anova and "dummy variables" least squares regression methods are used to investigate the dependence of ultrasound propagation velocity on the presence or absence of fat and on the rank ordered level of cirrhosis in fixed human liver. Cirrhosis is found to affect velocity in a nonlinear fashion, while fat depresses the velocities toward lower values. Quantifications of these effects and statistical analyses of their magnitudes are presented. The results represent a contribution toward the empirical understanding of the effects of tissue abnormalities on the velocity of ultrasound propagation in fixed human tissues.

Myocardial texture characterization by two-dimensional echocardiography

Twenty-four normal subjects and 181 patients with various cardiac disorders (36 autopsies) were studied by 2-dimensional echocardiography. In vitro echocardiographic studies were performed on 26 of 36 autopsied hearts utilizing an ultrasonically visible metallic probe to correlate myocardial echo patterns with histopathologic features. All normal subjects and the majority of patients with ventricular hypertrophy due to valvular or hypertensive lesions showed a uniformly speckled or an echolucent appearance of the myocardium (type I texture). No autopsied heart with this texture had gross fibrosis (visible to the naked eye) or infiltrative disease. All patients with infiltrative disorders (amyloidosis, 7 of 7; Pompe's disease, 4 of 4) had multiple, discrete, and small (3 to 5 mm) highly refractile echoes (HREs) in the myocardium involving the ventricle or ventricles completely (type IIA texture) or partly (type IIB texture). However, this finding was non-specific and was observed in many other conditions such as left heart hypoplastic syndrome (10 of 10), hypertrophic cardiomyopathy (19 of 26), and chronic renal failure (4 of 9). In the noninfiltrative group, HREs in the autopsied cases were shown to result from gross fibrosis or endocardiofibroelastosis utilizing in vitro echocardiographic studies and metallic probe-guided biopsies, while HREs in the autopsied cases with cardiac amyloidosis could be correlated only with amyloid deposits since fibrosis was absent. Larger HREs (greater than 5 mm) presenting as broad patches or long linear echoes in the myocardium (type IIC texture) was seen in old myocardial infarctions (9 of 21) and congestive cardiomyopathy (4 of 26) and were correlated with large areas of myocardial fibrosis. Two-dimensional echocardiographic studies of myocardial texture help identify various infiltrative and degenerative processes in the heart.

Echocardiographic features of eosinophilic endomyocardial disease

Nine patients with eosinophilic endomyocardial disease who had undergone angiocardiography with histological staging of their disease, were studied by M-mode and two dimensional echocardiography to determine the extent to which specific features of the disease could be evaluated by these non-invasive methods. In seven patients, amplitude processed two dimensional echocardiography showed regions where the relative intensity of endomyocardial echoes was greater than normal, and their distribution corresponded to known areas of fibrosis. Standard two dimensional echocardiography was normal in all but three patients. In eight patients M-mode echocardiography showed only non-specific abnormalities, but appeared to be useful in assessing the functional consequences of myocardial or mitral valve disease. After digitisation a reduction in the duration and an increase in the peak rate of dimension increase during filling was prolonged. It was concluded that amplitude processed two dimensional echocardiography might be useful in diagnosing the extent and severity of endomyocardial disease in patients with hyperosinophilia. These noninvasive techniques may thus provide a means for the early diagnosis of endomyocardial fibrosis and could be useful in assessing in progression or response to treatment.

Some scientific and technical aspects of medical ultrasonics

The development of diagnostic applications of ultrasound has tended to follow the evolution of electric technology, and while this development as resulted in benefit to the patient, the relatively unsophisticated scientific ideas have been adequate. The present paper reviews briefly some elements of the development of diagnostic imaging relation to their scientific bases. The discussion is particularly concerned with the popular grey-scale pulse-echo systems and the philosophy behind future developments that may lead to successful pursuance of tissue differentiation, and the optimisation of instrumentation. Of necessity, the discussion touches the more fundamental areas of measurement of the ultrasonic parameters of tissues, the development of tissue models, the measurement of transducer field characteristics, the studies in visual perception; and is briefly linked to biological effects and therapy.