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Biomedical subjects

C B Higgins

Publications and source records attributed to C B Higgins.

At least 307 records · Page 17Linked to original sources
PubMed1986

MR imaging of the dilated biliary tract.

The magnetic resonance (MR) examinations of 18 patients with dilated bile ducts were reviewed retrospectively to determine the capability of MR to demonstrate biliary dilatation, assess MR appearance of the dilated biliary tract using spin-echo techniques, and define the optimal MR imaging parameters (repetition time [TR] and echo time [TE]) for its demonstration. On images with short TR (0.5 sec) and TE (28 msec), the dilated intrahepatic and intrapancreatic bile ducts usually had lower signal intensity compared with the surrounding liver or pancreas; on images with long TR (2.0 sec) and TE (56 msec), they had higher signal intensity. Because of the observed variation in percentage of contrast between dilated bile ducts and surrounding liver and pancreas, two imaging sequences are recommended to obtain reliable demonstration of dilated intrahepatic and intrapancreatic bile ducts. The dilated common bile duct at the level of the hepatic hilus is best seen with a short TR and TE.

Adolescent↗
PubMed1986

Coarctation of the aorta: MR imaging.

Thirteen patients, aged 3-31 years, with coarctation of the thoracic aorta were examined by magnetic resonance (MR) imaging (total of 14 studies). Eight studies were performed preoperatively and six postoperatively. Catheterization data were available on 12 patients for verification of MR imaging findings. Electrocardiographically gated sagittal and left anterior oblique images best depicted the coarctations; however, involvement of arch vessels was best evaluated on transaxial images. MR imaging readily identified all coarctations but one, their site and extent, and involvement of the arch vessels. In addition, MR images depicted poststenotic dilatation and dilated collateral vessels. In patients studied postoperatively, restenosis could be evaluated, and complications such as postoperative aneurysm and perianastomotic hematoma were identified. MR imaging provides excellent anatomic detail of coarctation of the aorta, potentially obviating the need for angiography.

Adolescent↗
PubMed1986

Differentiation of reversible and irreversible myocardial injury by MR imaging with and without gadolinium-DTPA.

The current study evaluated the capability of magnetic resonance (MR) imaging to distinguish myocardium subjected to reversible and irreversible ischemic injury. Nine dogs underwent left anterior descending coronary arterial occlusion for 15 minutes (reversible injury) and nine for 1 hour (irreversible injury), followed by reperfusion for 24 hours in both groups. Six dogs from each group received 0.5 mmol/kg of gadolinium-DTPA intravenously; the remaining dogs received no contrast media. In the dogs with irreversible injury but no contrast media, there were prolonged T1 and T2 of the infarcted myocardium and adequate visualization of the infarct. The percentage of contrast between normal and infarcted myocardium was greatest on T2-weighted images. In the group with irreversible injury and contrast media, Gd-DTPA produced significant T1 shortening of injured myocardium, with resultant high signal intensity of the infarct, and significantly enhanced contrast compared with the group that did not receive Gd-DTPA. In the dogs with reversible injury, there were no regional differences in intensity or relaxation times. MR has the capability to distinguish myocardium with irreversible injury from that with reversible injury. The difference of T1 between normal and reperfused infarcted myocardium is increased by Gd-DTPA; thus, contrast between these two is enhanced on MR images.

Animals↗
PubMed1986

Early-phase myocardial infarction: evaluation by MR imaging.

In vivo gated magnetic resonance (MR) imaging was performed in 12 dogs immediately after occlusion of the left anterior descending coronary artery and serially up to 5 hours and again between 4 and 14 days. This was done to evaluate the appearance of acute myocardial infarcts and to determine how soon after coronary artery occlusion MR imaging can demonstrate the site of acute myocardial ischemia. In nine dogs with postmortem evidence of myocardial infarction, regional increase of signal intensity of the myocardium was present by 3 hours after coronary artery occlusion and conformed to the site of myocardial infarct found at autopsy. The signal intensity on T2-weighted images of the infarcted myocardium was significantly greater than that of normal myocardium at 3, 4, and 5 hours after occlusion. The T2 (spin-spin) relaxation time was significantly prolonged in the region of myocardial infarct at 3, 4, and 5 hours postocclusion compared with normal myocardium. Myocardial wall thinning and increased intracavitary flow signal were found in six dogs with comparable pre- and postocclusion images in late systole.

Animals↗
PubMed1986

Influence of physiologic motion on the appearance of tissue in MR images.

Studies were performed to determine the possible influence of physiologic motion on the parenchymal intensity of organs in magnetic resonance (MR) images. It is known that periodic motion associated with respiration and cardiac function causes characteristic artifacts in spin-warp images. The present study shows that bulk motion can also cause striking intensity changes at velocities equivalent to the craniocaudal respiratory excursion of organs in the upper abdomen. The magnitude of the effect depends on the velocity and direction of motion with respect to the three orthogonal axes of the imager and on the technical details of the imager and pulse sequence. Large systematic errors in calculated tissue relaxation times are possible due to this phenomenon. The findings have important implications for clinical imaging because motion can cause artifactual changes in the gray-scale relationships among tissues. Some pulse sequences are much less sensitive to these effects. These results provide guidance for selecting MR techniques that reduce the detrimental effect of respiratory and other physiologic motion on examinations of the upper abdomen and thorax.

Abdomen↗
PubMed1986

Occlusive and reperfused myocardial infarcts: effect of Gd-DTPA on ECG-gated MR imaging.

In vivo magnetic resonance (MR) imaging was performed to determine the effect of gadolinium-DTPA on MR intensity and relaxation times of occlusive and reperfused acute myocardial infarcts. In 18 dogs the left anterior descending (LAD) coronary artery was ligated. Five hours after LAD artery occlusion, six dogs in group 1 received intravenous Gd-DTPA, 0.5 mmol/kg, and 6 dogs in group 2 received 0.1 mmol/kg. The myocardia of the remaining six dogs (group 3) were reperfused after 1 hour of coronary artery occlusion; these dogs received 0.1 mmol/kg Gd-DTPA intravenously 5 hours later. MR imaging was performed before (control) and 5 minutes after Gd-DTPA administration. Intravenous administration of 0.1 mmol/kg Gd-DTPA significantly improved contrast between infarcted and normal myocardium on T1-weighted spin echo images in group 3. In all groups, T2-weighted precontrast images provided contrast between infarcted and normal myocardium equivalent or better than that provided by T1-weighted postcontrast images. Thus, Gd-DTPA did not improve contrast between ischemically injured and normal myocardium in the early hours after coronary artery occlusion.

Animals↗
PubMed1986

Magnetic resonance imaging of cardiac transplants: the evaluation of rejection of cardiac allografts with and without immunosuppression.

The purpose of this study was to evaluate the potential of magnetic resonance imaging (MRI) in vivo for the characterization of tissue changes associated with acute myocardial rejection after cardiac transplantation. Of 15 dogs that underwent heterotopic cardiac transplantation, six served as untreated controls, and nine received immunosuppressive therapy (25 mg/kg/day cyclosporine, 1 mg/kg/day prednisone). Serial electrocardiographically gated MRI (spin-echo technique) and histologic examinations of allograft biopsy samples were performed for each dog at 2 to 3, 7 to 10, 14 to 17, and 26 to 29 days after transplantation and immediately after animals were killed. Untreated allografts showed a significant increase (p less than .01) in T2 (spin-spin) relaxation time (T2 = 66 +/- 8 msec) and intensity values compared with values in the native hearts (T2 = 44 +/- 6 msec) as early as 1 week after transplantation. The significant difference in T2 values could be observed in vivo as well as on postmortem examination and corresponded to histologic progression of the rejection process. There was no significant difference in T1, T2, or intensity values in cyclosporine-treated allografts and native hearts except in two dogs in which T2 relaxation times and signal intensity in the transplanted hearts increased simultaneously with histologic evidence of rejection, indicating failure of immunosuppressive therapy. There was a significant correlation between histologic grading of severity of rejection and T2 relaxation times of the cardiac transplants (r = .72). Likewise, there was a significant linear relationship between T2 values in vivo and percent water content when the differences between native hearts and allografts were compared (r = .92, p less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Evaluation of the hereditary Syrian hamster cardiomyopathy by 31P nuclear magnetic resonance spectroscopy: improvement after acute verapamil therapy.

The relation between metabolic and functional derangement in various cardiomyopathies has not been well characterized. This information was specifically sought in a spontaneous cardiomyopathic model. Metabolic and hemodynamic parameters were obtained in glucose-perfused beating hearts of 180-200-day-old cardiomyopathic Syrian hamsters and age-matched healthy animals. This period in the cardiomyopathic hamster lifetime is intermediary between the necrotic phase and the appearance of heart failure. We used 31P nuclear magnetic resonance spectroscopy to analyze energy metabolites and intracellular pH. Cardiomyopathic hamsters had significantly higher mole fraction values for inorganic phosphate, lower phosphocreatine mole fraction as well as lower phosphocreatine/inorganic phosphate and adenosine triphosphate/inorganic phosphate ratios. Analysis of pH indicated the presence of regions of increased acidity within the heart of myopathic hamsters. Cardiomyopathic hamsters also had significantly lower left ventricular pressure, coronary flow, and myocardial oxygen consumption. Separate groups of normal and myopathic hamsters were given verapamil for 24 hours (one injection of 4 mg/kg s.c. followed by 1.2 g/l in drinking water). Verapamil-treated myopathic hamsters had evidence of markedly improved mitochondrial function when compared with untreated animals. Left ventricular pressure and coronary flow rose to normal levels. Replacing glucose by pyruvate in the perfusate of myopathic hamsters results in a marked increase in left ventricular pressure, coronary flow, and oxygen consumption with a moderate rise in phosphocreatine. Thus, 180-200-day-old cardiomyopathic hamster heart is characterized by evidence of decreased mitochondrial function, by areas of increased acidity within the heart, and by reduced left ventricular function.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1986

Magnetic resonance imaging of chronic myocardial infarcts in man.

To evaluate the magnetic resonance imaging (MRI) features of chronic myocardial infarction (MI), 22 patients and several normal volunteers were studied with a 0.35-T cryogenic imaging system. The MIs were 9 months to 16 years old. The patients also had either left ventriculography (17 patients) or two-dimensional echocardiography (17 patients). At least one abnormality indicative of prior infarction was demonstrated on MRI in 20 of the 22 patients. Wall thinning was seen in 20 patients; in six of these, the thinning resulted in aneurysm formation. The other 14 patients had sufficient residual wall thickness to permit measurement of T2 relaxation times and MR signal intensity in the infarcted region. Ten of these 14 patients demonstrated low intensity and shortened T2 of the thinned segments (mean T2 = 28.7 msec) compared to adjacent normal myocardium (mean T2 = 45.4 msec) and to the myocardium of volunteers (mean T2 = 41.3 msec). The percentage of difference in intensity between thinned and normal myocardium was greater on 56-msec-TE images (98.2%) than on 28-msec-TE images (46.1%). In the other four patients, no difference in intensity of the myocardium was perceptible in the thinned region of the myocardial wall. Thus MRI shows regional wall thinning at the site of prior MI. In some patients, the chronic infarct is characterized as decreased spin-echo signal intensity and shortened T2 consistent with replacement of myocardium by fibrous scar.

Adult↗
PubMed1986

Overview of MR of the heart--1986.

Experience in the first few years of using MR for evaluation of cardiovascular disease indicates that it can provide information about cardiovascular anatomy, cardiovascular function, myocardial tissue characterization, and myocardial metabolism. Only the first capability is now being used for clinical diagnosis. MR imaging is evolving as a technique for the definitive diagnosis of pericardial disease, paracardiac and intracardiac masses, and thoracic aortic disease. It also shows considerable promise for the evaluation of congenital and ischemic heart disease and cardiomyopathies. The capabilities of MR displayed in animal studies extend beyond anatomic observations. Considerably more research and optimism for early progress are justified in the effort to harness its multiple capabilities for the evaluation of cardiovascular disease.

Animals↗
PubMed1986

Estimation of pulmonary vascular resistance by MRI in patients with congenital cardiovascular shunt lesions.

The intensity of the magnetic resonance signal in the pulmonary arteries was assessed in 15 patients with congenital left to right shunts and in 10 normal volunteers, using an ECG-gated multislice spin-echo technique. In normal subjects, magnetic resonance signal was only observed in great vessels of the thorax on images acquired near end-diastole; they disappeared in systole. Among the group of 15 patients, 10 had severe pulmonary hypertension (systolic pressures greater than 80 mm Hg) with severe elevation of pulmonary vascular resistances (greater than 787 dynes cm sec-1). The magnetic resonance signal persisted in systole in all 10 patients, and its intensity could be quantitatively assessed. On the other hand, in one other patient with high pulmonary artery pressure but only moderate elevation of pulmonary vascular resistance, and in patients with moderate pulmonary hypertension and normal pulmonary vascular resistance, the intravascular signal was minimal and no different from the signal recorded in normal subjects. A direct linear relationship was found between the pulmonary vascular resistance and the intensity of the magnetic resonance signal in the right pulmonary artery during systole (r = 0.84). An even closer correlation was found for the linear relationship between the ratio pulmonary vascular resistance/systemic resistance and the magnetic resonance signal in the right pulmonary artery (r = 0.93). Thus, magnetic resonance, with its sensitivity to slow-flow conditions, can potentially provide physiological information in congenital cardiovascular disease.

Adolescent↗
PubMed1986

MRI of reperfused myocardial infarct in dogs.

The current study evaluated the capability of magnetic resonance imaging (MRI) to detect acutely injured myocardium in the first 5 hr after a 1-hr period of occlusion followed by reperfusion of the coronary artery and to determine if magnetic relaxation times could be used to differentiate injured from normal myocardium. Fourteen dogs underwent left anterior descending coronary arterial occlusion for 1 hr, followed by reperfusion. Electrocardiographic gated MRI was performed before and during coronary artery occlusion and immediately after reperfusion, and serially up to 5 hr postreperfusion. In all dogs with postmortem evidence of myocardial infarction (n = 7), regional increase of signal intensity was observed in the anterior wall of the left ventricle as early as 30 min after reestablishing blood flow to the jeopardized myocardium. The area of increased signal intensity in the myocardium conformed to the site of myocardial infarction found at autopsy. The signal intensities of the jeopardized myocardium were significantly (p less than 0.01) greater than those of normal myocardium at 30 to 300 min postreperfusion. The T2 (spin-spin) relaxation time was significantly (p less than 0.05-p less than 0.01) prolonged in the region of the reperfused myocardial infarct at 30 min (59.6 +/- 13.1 msec) and remained prolonged up to 300 min (62.6 +/- 12 msec) postreperfusion compared with the T2 of normal myocardium (40.6 +/- 5.2 msec). Of the remaining seven dogs, four developed fatal arrhythmias during the reperfusion procedure and three dogs had no evidence of myocardial infarction at pathologic examination. Signal intensities and T2 relaxation times in these three dogs did not change during the experiment. Thus, acutely infarcted and reperfused myocardium can be detected by in vivo gated MRI, using the spin-echo technique, as early as 30 min after reperfusion. The jeopardized myocardium is characterized by a prolonged T2 relaxation time and, therefore, best visualized on T2-weighted images.

Animals↗
PubMed1986

MRI of blood flow: correlation of image appearance with spin-echo phase shift and signal intensity.

Phase-sensitive imaging was used to correlate signal distribution with phase shift and velocity distribution in spin-echo magnetic resonance imaging (MRI). Flow-dependent, changing intensity patterns that were seen in a constant-flow phantom study were explained by the simultaneous effects of inflow signal enhancement, first-echo dephasing, and outflow signal loss occurring during laminar flow. In clinical studies, first-echo dephasing was shown during laminar flow in the inferior vena cava. Turbulent flow was demonstrated in the descending thoracic aorta during late systolic flow, and turbulent dephasing-rephasing was shown in the abdominal aorta.

Aorta, Thoracic↗
PubMed1986

MRI of the normal pericardium.

The visibility and thickness of the pericardium, as depicted by MRI, and the changes of these parameters over the cardiac cycle were determined in 18 normal subjects. Gated, cycled, multisection images were obtained in the transaxial orientation. Using a score-point system for quantification, there was better visualization of the low-intensity pericardial line during systole as compared with diastole (p less than 0.005). Pericardial thickness was 1.2 +/- 0.5 mm in diastole and 1.7 +/- 0.5 mm in systole (p less than 0.001) as measured in a midventricular section in front of the right ventricle; both values exceeded the thickness of 0.4 to 1.0 mm reported for anatomic measurements of pericardial thickness. The layer of normal pericardial fluid present in the pericardial space should also have low intensity, and it likely contributes to the overall pericardial thickness as visualized by MRI. Since MRI is sensitive to the small amount of normal pericardial fluid and depicts its anatomic distribution, it should be valuable in detection and quantification of even small pericardial effusions.

Adult↗
PubMed1986

MRI of the abnormal pericardium.

To evaluate the use of MRI in the diagnosis of pericardial disease, 63 patients with pericardial abnormalities or clinically suspected pericardial disease were studied retrospectively. Twenty-three patients had pericardial effusion, 19 patients had pericardial thickening, and 11 patients were referred for evaluation of masses with possible pericardial involvement. The other 10 patients were referred for differentiation of constrictive pericarditis from restrictive cardiomyopathy and eventually were found to have pericardial hematoma or normal pericardium as assessed by MRI. The calculated size of pericardial effusion by MRI showed a good correlation with semiquantitative echocardiographic estimations. MRI could demonstrate fibrinous adhesions in patients with uremic pericarditis. It was also of great value in the differential diagnosis of constrictive pericarditis vs restrictive cardiomyopathy. Pericardial thickness of more than 4 mm was found in patients with constrictive pericarditis. Normal pericardial thickness was demonstrated by MRI in the three patients with restrictive cardiomyopathy. MRI diagnosed hemopericardium correctly as the cause of constrictive symptoms in two patients. Pericardial thickening in patients after cardiac surgery was commonly found by MRI and usually was not associated with clinical signs of constrictive pericarditis. MRI proved to be useful in the diagnosis of pericardial cysts and in the evaluation of paracardiac masses with possible pericardial involvement. MRI is an important technique in the evaluation of the pericardium. It can provide important additional information when diagnosis cannot be made adequately by other noninvasive imaging techniques.

Adolescent↗
PubMed1986

MRI of perivalvular infectious pseudoaneurysms.

MRI demonstrated perivalvular infectious pseudoaneurysms in three patients who had infective endocarditis that complicated cardiac surgery. In each case the infectious pseudoaneurysm, or abscess cavity, demonstrated absence of MR signal, consistent with the free flow of blood between it and the vessel lumen. Cardiac-gated MR images showed the precise location of the three infectious pseudoaneurysms in relation to the cardiac chambers: One was between the aortic root and left atrium; another was in the outflow portion of the ventricular septum; and the third surrounded the Rastelli conduit. Noninvasiveness, independence from the need for IV contrast material, precision in determining the site of the infectious pseudoaneurysm, and the lack of image artifacts produced by prosthetic valves make MRI a useful technique for detecting infectious cardiac pseudoaneurysms.

Adolescent↗
PubMed1986

MR imaging of the thyroid.

The thyroid gland was evaluated with MR imaging in six normal subjects and 32 patients with thyroid disease. The purpose was to evaluate signal characteristics of normal and diseased thyroid tissue; determine the contrast between normal and diseased tissue on T1- and T2-weighted images; compare relaxation times of normal thyroid, adenomas, and carcinoma; and assess the capability of MR for showing the extent of large thyroid masses. Adenomas and carcinomas were frequently isointense with normal thyroid tissue on T1-weighted images but had markedly higher intensity on T2-weighted images. The mean T1 (1202 +/- 717 msec) and T2 (118 +/- 48 msec) relaxation times of adenomas were markedly longer than the T1 (721 +/- 97 msec) and T2 (59 +/- 10 msec) times of normal thyroid tissue. Likewise, the T1 and T2 values of carcinomas were markedly prolonged compared with normal thyroid but the values overlapped with those of the adenomas. Sagittal and coronal images effectively depicted the extent of large goiters, adenomas, and carcinomas and indicated extension below the cervicothoracic junction. The marked prolongation of relaxation times associated with thyroid disease causes excellent contrast of lesions with normal thyroid and surrounding structures. The large field of view possible with coronal and sagittal images is useful for assessing extensive thyroid masses. These attributes indicate the potential clinical utility of MR for evaluating thyroid disease.

Adenoma↗