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Biomedical subjects

S M Collins

Publications and source records attributed to S M Collins.

At least 181 records · Page 10Linked to original sources
PubMed1985

Myocardial infarct size threshold for two-dimensional echocardiographic detection: sensitivity of systolic wall thickening and endocardial motion abnormalities in small versus large infarcts.

This study evaluated the ability of 2-dimensional echocardiography to detect myocardial infarcts of varying sizes. Echocardiography was performed in 29 closed-chest, conscious dogs 2 days after circumflex coronary artery occlusion, and the ultrasonic recordings were analyzed for regional abnormalities in either wall thickening or endocardial motion. Acute myocardial infarct (AMI) size and extent were assessed by morphologic examination. In 5 dogs, coronary occlusion failed to produce AMI; in these dogs wall thickening analysis showed no abnormalities (100% specificity), and endocardial motion analysis yielded 1 false-positive result (80% specificity). In 24 dogs an AMI developed; infarcts larger than 18% of left ventricular mass uniformly resulted in echocardiographically detectable contraction abnormalities. When the AMI was small (1 to 6% of left ventricular mass) and primarily subendocardial, the sensitivity of echocardiography was poor: Only 3 of 10 of the dogs with a small AMI had abnormalities by wall thickening, and only 1 of 10 by endocardial motion. Thus, in this canine model of AMI, 2-dimensional echocardiography was insensitive to small, subendocardial AMI. If this is so in humans as well, it is a potential limitation of the clinical use of echocardiography in the detection of AMI.

Animals↗
PubMed1985

Digital signal and image processing in echocardiography. The American Society of Echocardiography.

Digital signal and image processing techniques are acquiring an increasingly important role in the generation and analysis of cardiac images. This is particularly true of 2D echocardiography, in which image acquisition, manipulation, and storage within the echocardiograph, as well as quantitative analysis of echocardiographic data by means of "off-line" systems, depend upon digital techniques. The increasing role of computers in echocardiography makes it essential that echocardiographers and technologists understand the basic principles of digital techniques applied to echocardiographic instrumentation and data analysis. In this article, we have discussed digital techniques as applied to image generation (digital scan conversion, preprocessing, and postprocessing) as well as to the analysis of image data (computer-assisted border detection, 3D reconstruction, tissue characterization, and contrast echocardiography); a general introduction to off-line analysis systems was also given. Experience with other cardiac imaging methods indicates that digital techniques will likely play a dominant role in the future of echocardiographic imaging.

Echocardiography↗
PubMed1985

Role of oropharyngeal stimulation in cholecystokinin-induced satiety in the sham feeding rat.

The belief that oropharyngeal stimulation potentiates the satiety produced by cholecystokinin (CCK) is based on the demonstration that the ability of 20% pure CCK to suppress feeding is enhanced the closer it is injected to a meal. The increase efficacy of CCK with closer temporal proximity to a meal might simply reflect increased peptide levels at the time of feeding. Further, since oropharyngeal synergy has never been demonstrated with pure CCK, studies were performed to evaluate the role of oropharyngeal stimulation in CCK-induced satiety. Rats equipped with gastric fistulae were injected IP with CCK-8 15 min before a test sham feed. In one condition, rats sham fed for 15 min prior to CCK injection; in the other, they did not. CCK-8 suppressed eating in only those cases when its administration was accompanied by oropharyngeal stimulation. Thus, oropharyngeal cues enhance the satiety action of exogenous CCK. A second experiment examined whether oropharyngeal synergy requires oropharyngeal stimulation prior to peptide delivery. CCK-8 was injected into rats coincident with the initation of a test sham feed. Rats had either sham fed, or not sham fed, for 15 min prior to CCK administration. Both conditions produced similar and significant suppressions of eating during the test sham feed. Thus, oropharyngeal cues enhance the action of CCK and oropharyngeal amplification needs only contiguous pairings of oropharyngeal stimulation and feeding.

Animals↗
PubMed1985

Artifactual regional gray level variability in contrast-enhanced two-dimensional echocardiographic images: effect on measurement of the coronary perfusion bed.

The purpose of this study was to determine the extent of regional variability of image echocardiographic amplitude (expressed as gray level variability) in contrast-enhanced two-dimensional echocardiographic images, and to assess the effect of such baseline gray level variability on quantitation of the coronary perfusion bed. In 10 anesthetized closed chest dogs, short-axis papillary muscle echocardiographic images were obtained during control preinjection conditions and during injection of three contrast agents into the left main coronary artery with and without circumflex artery occlusion. Regional echocardiographic amplitude variation was measured by computer-based videodensitometric analysis of mean gray levels in four myocardial regions after cavity (background) gray level subtraction. To determine the effect of regional gray level variability on quantitation of the coronary perfusion bed, the contrast-enhanced left anterior descending artery perfusion bed was measured by two methods. The circumferential method ignored myocardial contrast inhomogeneity by measuring the circumferential extent of contrast enhancement, whether or not the enhancement by contrast medium extended transmurally. The exact method measured only the area of myocardium actually enhanced by contrast medium, which often did not extend transmurally. The perfusion beds determined by the two echocardiographic methods were compared with the anatomic perfusion bed determined by postmortem barium-gelatin coronary arteriography. Regional gray levels varied qualitatively and quantitatively in the control state (before contrast injection), with lateral regions being less bright than axial regions. After injection of contrast medium, brightness increased in all regions, the axial regions brightening most.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Endogenous cholecystokinin and intestinal satiety.

The role of endogenous cholecystokinin (CCK) as a mediator of intestinal satiety is examined. We used rats equipped with a chronic gastric fistula and an indwelling duodenal catheter to assess the effects of direct duodenal stimulation on sham feeding. To evaluate the contribution of endogenous CCK to intestinal satiety we used a specific competitive antagonist of the satiety action of CCK, proglumide. Intraduodenal infusion of 11 or 5 ml liquid diet suppressed sham feeding. Administration of proglumide caused a partial reversal of the suppression of feeding produced by the 11-ml, but not the 5-ml, intraduodenal infusion. Administration of proglumide alone did not influence sham feeding but completely abolished the suppression of sham feeding induced by a maximal dose of exogenous CCK. These results indicate that CCK contributes to intestinal satiety under specific test conditions only. Moreover, since that component of suppression reversed by proglumide was small in comparison with the overall inhibition of eating, these results indicate that factors other than CCK are important in intestinal satiety.

Analysis of Variance↗
PubMed1985

Assessment of fibrosis in infarcted human hearts by analysis of ultrasonic backscatter.

In animal hearts, the magnitude of integrated ultrasonic backscatter is increased in fibrotic myocardium. Our purpose in this study was to quantitate the relationship between ultrasonic backscatter and collagen deposition in 10 excised human hearts with old infarcts. A 2.25 MHz, 50% fractional bandwidth transducer was positioned at the transducer focal distance from the epicardium of each specimen. The radio frequency backscatter signal was digitized, squared, and integrated to yield the integrated ultrasonic backscatter, which was referenced to the backscatter from a water/steel interface. The interrogated myocardium was then excised and divided into two portions. One portion was assayed for hydroxyproline, a marker for collagen. A second portion was sectioned, stained with Masson's trichrome, and studied with the use of a computer-assisted image analysis system. There was a linear correlation between the magnitude of integrated backscatter and myocardial collagen content estimated by hydroxyproline assay (r = .78). Quantitative histologic analysis revealed a variable relationship between the transmural distribution of collagen and the corresponding transmural pattern of the backscatter signal. In two specimens exhibiting a discrete layer of subendocardial fibrosis, the backscatter amplitude was also increased in the subendocardial region. In specimens with other patterns of fibrosis, the local backscatter amplitude did not correspond to the transmural pattern of collagen distribution. We conclude that the quantitative analysis of ultrasonic backscatter shows promise for the noninvasive evaluation of myocardial fibrosis after infarction.

Collagen↗
PubMed1985

Determination of left ventricular mass in dogs with rapid-acquisition cardiac computed tomographic scanning.

The development of left ventricular hypertrophy in patients with heart disease often has far-reaching clinical implications with respect to overall morbidity and mortality. Approaches used to assess left ventricular mass include electrocardiography, echocardiography, contrast ventriculography, single photon-emission tomography, and conventional computed tomography. However, all of these modalities suffer from some major draw back that precludes widespread application to all patients. In this study we assessed the accuracy of determinations of left ventricular mass in 22 dogs by rapid-acquisition (50 msec) computed axial tomography (RACAT), an ultrafast computed tomographic (CT) instrument. Electrocardiographically triggered, end-diastolic, short-axis cardiac scans were obtained from apex to base during administration of intravenous iodinated contrast. Myocardial edges were determined for each tomographic scan by two methods: the regional half-contour method (the CT density half way between that of the left ventricular myocardium and adjacent ventricular cavities or lung) and "interactive plateau thresholding" of the cardiac borders. Left ventricular mass by RACAT was calculated as the sum of the mass of each individual scan from apex to base (modified Simpson's rule). Postmortem left ventricular mass ranged from 58 to 160 g. The correlation between true left ventricular mass and tomographically determined mass was excellent (r = .99), with the slope and y intercept not statistically different from 1 and 0, respectively. The standard error of the estimate was 4.1 g. Interobserver and intraobserver variability for determining left ventricular mass demonstrated excellent agreement (r = .99 and r = .99, respectively). We conclude that quantitative assessment of left ventricular mass can be accurately and reproducibly performed in dogs by rapid acquisition CT scanning. It is likely that this technique will be readily transferable to the clinical settings and prove to be an important method for quantifying left ventricular mass in patients.

Animals↗
PubMed1985

Two-dimensional echocardiographic image texture analysis: reduction of regional variability using polar coordinates.

Factors inherent to the ultrasound imaging system can influence quantitative ultrasound image texture and may produce changes that mask or mimic those due to alterations in tissue structure. In this study, we assessed the effect of the method of image data acquisition and analysis on the variations in quantitative texture measures that occurred solely due to the position of a region of interest (ROI) within the field of view. When ROI's, which varied in range and azimuth within the image of a tissue equivalent phantom (of uniform composition), were assessed by conventional analysis of scan-converted (rectangular coordinate) data, over 50 percent of all texture measures showed significant differences. Pseudo polar analysis reduced the number of texture measures showing regional variation by 80 percent (p less than 0.01) and true polar coordinate data analysis reduced the number by 74 percent (p less than 0.01). True polar analysis completely abolished differences in texture measures between ROI's separated in azimuth. Acquisition and analysis of tissue texture data using polar coordinates should allow a more definitive identification of abnormal tissue.

Echocardiography↗
PubMed1985

New directions in cardiac imaging.

Cardiac imaging is among the most commonly used diagnostic techniques in cardiovascular medicine. Conventional imaging modes (chest roentgenography, echocardiography, radionuclide imaging, and angiography) allow delineation of cardiac morphology, coronary anatomy, ventricular and valvular function, and cardiac shunts, and permit qualitative evaluation of myocardial perfusion. Four new imaging procedures (digital subtraction angiography, rapid acquisition x-ray computed tomography, emission computed tomography, and magnetic resonance imaging) promise to expand diagnostic capabilities by permitting quantitative analysis of myocardial perfusion, evaluation of myocardial metabolism, and characterization of cardiac tissue composition. These techniques differ widely in cost, availability, and in the additional information they offer. Optimal use will be achieved only through carefully controlled comparative clinical trials directed at specific diagnostic questions.

Angiography↗
PubMed1984

Computer-assisted edge detection in two-dimensional echocardiography: comparison with anatomic data.

Four methods of computer-based edge detection were evaluated for identification of endocardial and epicardial borders on 2-dimensional echocardiograms of excised hearts. A method was also evaluated for observer identification of cardiac borders in the same hearts. The accuracy of computer-derived borders and of observer-derived borders were determined by comparison to anatomic borders measured from photographs of slices of the excised hearts. Echocardiographic borders were compared with anatomic borders by calculation of segmental cavity areas and wall thickness. Each of the methods tested (computer and observer) identified endocardial borders accurately, resulting in cavity segment areas that correlated well with the corresponding anatomic data (r = 0.90 to 0.92). Regional wall thicknesses correlated less well with anatomic data (r = 0.74 to 0.80), suggesting that endocardial borders were identified more accurately than were epicardial borders. Thus, the methods of computer-assisted echocardiographic border detection tested identified the endocardium and epicardium as accurately as a trained observer evaluating unprocessed echocardiograms. Computer-based methods of border detection may be useful in the automated analysis of clinical echocardiograms.

Animals↗
PubMed1984

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)

Animals↗
PubMed1984

Rethrombosis after reperfusion with streptokinase: importance of geometry of residual lesions.

We tested the hypothesis that lesion rethrombosis after streptokinase reperfusion is related to luminal size of the residual stenosis. Two independent techniques of analyzing coronary angiograms, quantitative coronary angiography and computer-based videodensitometry, were used to estimate the size of the residual lumen immediately after discontinuation of streptokinase. These techniques were selected because they provide independent estimates of cross-sectional area of a lesion with high degrees of reproducibility and minimal observer variability. Twenty-four patients who had undergone successful reperfusion with streptokinase were studied. Seven patients had lesion rethrombosis documented either on a repeat angiogram, at autopsy, or, in one case, by the fact that the patient had an acute transmural infarction resulting in death. Vessel patency was documented by repeat coronary angiography 8 to 14 days after initial streptokinase reperfusion in the other 17 patients. As assessed by quantitative coronary angiography, seven of 13 patients (54%) with minimal luminal cross-sectional areas of less than 0.4 mm2 had rethrombosis. None of the 11 patients with lumens greater than 0.4 mm2 had rethrombosis. In the 17 patients with vessels that remained patent the size of the residual lesion at repeat catheterization was compared with its size immediately after reperfusion with streptokinase. Over the intervening 8 to 14 day interval, an average percentage increase in minimal cross-sectional area of 116 +/- 34% was observed. In seven patients minimal luminal cross-sectional area more than doubled. Integrated optical density, an index of the severity of coronary stenosis derived from computer-based videodensitometry, was also useful in identifying a subgroup of patients at high risk for rethrombosis of lesion.(ABSTRACT TRUNCATED AT 250 WORDS)

Computers↗
PubMed1984

Variation of left ventricular myocardial gray level on two-dimensional echocardiograms as a result of cardiac contraction.

Integrated ultrasonic backscatter from normal myocardium has been shown to vary with the phase of cardiac contraction (decreasing from end-diastole to end-systole) in previous studies of open-chest dogs. If confirmed, this finding would have important implications for clinical application of ultrasonic tissue characterization. Our hypothesis was that a cardiac cycle-dependent variation in regional average gray level would be detected on analysis of digitized two-dimensional echocardiograms. We analyzed echocardiographic images from 16 subjects in whom normal, technically good studies were obtained with a commercial phased-array scanner and a 2.25 MHz transducer. Images from six subjects were digitized from stop-frame photographs and those from 10 subjects were obtained directly in digital format from the scanner. Average gray level was measured in a portion of the left ventricular posterior wall in parasternal long-axis images obtained at end-diastole and end-systole by both photographic and digital-image acquisition. In seven of the subjects from whom digital images were acquired, left ventricular posterior wall gray level and ventricular septal gray level were also evaluated on parasternal short-axis images. In images digitized by the photographic technique, mean posterior wall gray level decreased significantly from end-diastole (175 +/- 5.8 SEM) to end-systole (167 +/- 5.1, p less than .05). Similarly, in images digitized directly, mean posterior wall gray level in the long-axis view decreased from end-diastole (71 +/- 3.4) to end-systole (59 +/- 2.5, p less than .005).(ABSTRACT TRUNCATED AT 250 WORDS)

Data Display↗
PubMed1984

Computer-assisted quantitation of myocardial fibrosis in histologic sections.

Histologic characterization of the myocardium may require estimation of the collagen content of the specimen. A computer-assisted method can be used to determine collagen content from histologic sections. Full-thickness segments of normal or fibrotic left ventricular myocardium from ten human hearts were divided into portions for hydroxyproline assay and for trichrome staining of histologic sections. The sections were digitized using a computerized video analysis system and were segmented into collagen and muscle regions using a gray-level threshold technique that yielded an estimate of the percent of collagen. A wide range of collagen content, from normal (5 micrograms of hydroxyproline per milligram of dry weight) to fibrotic (38 micrograms/mg) myocardium, was studied. The percentage of collagen from analysis of histologic sections strongly correlated with the hydroxyproline level, with excellent intraobserver and interobserver concordance. Results were unaffected by variations in histochemical staining.

Adolescent↗
PubMed1983

Relations between 2-dimensional echocardiographic wall thickening abnormalities, myocardial infarct size and coronary risk area in normal and hypertrophied myocardium in dogs.

Systolic wall thickening abnormalities are sensitive indicators of ischemia and infarction. One purpose of this investigation was to assess the relation between coronary risk area, infarct size and wall thickening abnormalities (dyskinesia) using 2-dimensional echocardiography (2-D echo) in a closed-chest conscious dog model of acute myocardial infarction. The second purpose was to study the effects of systemic hypertension (SH) and left ventricular (LV) hypertrophy on these relations. Our hypothesis was that the infarct size and the extent of 2D echocardiographic dyskinesia would be quantitatively different in SH-LV hypertrophy, a condition in which coronary vascular reserve is diminished. Permanent circumflex coronary occlusion was performed in 15 conscious normal dogs and in 14 dogs with LV hypertrophy secondary to renal hypertension. Two-dimensional echocardiograms were obtained before, 20 minutes after and 2 days after coronary occlusion. The systolic wall thickening along 12 equidistant radii was analyzed in short-axis images. Percent dyskinesia on 2-D echo was defined as the percentage of radii showing systolic thinning. Infarct size was determined pathologically and risk area was determined angiographically. For a given risk area, coronary occlusion resulted in a larger infarction in dogs with SH-LV hypertrophy than in normal dogs (p less than 0.05). Two-dimensional echocardiographic dyskinesia correlated well with infarct size both at 20 minutes (r = 0.92) and 2 days (r = 0.94); dyskinesia modestly overestimated the infarct size and underestimated the risk area. The relations were similar in both normal and SH-LV hypertrophy groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗