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R M Peshock

Publications and source records attributed to R M Peshock.

At least 91 records · Page 5Linked to original sources
PubMed1986

Improved in vivo magnetic resonance imaging of acute myocardial infarction after intravenous paramagnetic contrast agent administration.

Gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA), a paramagnetic relaxation agent, has been used in vitro to improve the detection of acute myocardial infarction (MI) by magnetic resonance imaging (MRI). In this study, the ability of Gd-DTPA to improve in vivo magnetic resonance imaging of MI was examined. Ten dogs with MI caused by left anterior descending coronary artery ligation were imaged 1 to 5 days after infarction. Imaging was performed before and for 2 hours after intravenous administration of 0.34 mmol/kg Gd-DTPA. One to 2 days after MI, Gd-DTPA improved visualization of the infarct in 3 of 4 dogs. This effect was more prominent in dogs imaged 4 to 5 days after MI, when 6 of 6 dogs showed substantially improved infarct definition after Gd-DTPA. At both times the intensity ratio, an objective measure of contrast between infarcted and normal tissue that is defined by the ratio of image intensity of infarcted area to that of noninfarcted area, was significantly better after Gd-DTPA administration. The intensity ratio at 24 to 48 hours after infarction was 1.4 +/- 0.2 (mean +/- standard deviation) before Gd-DTPA, and 1.7 +/- 0.6 after Gd-DTPA (p = 0.03). The intensity ratio at 4 to 5 days after infarction was 1.5 +/- 0.3 before Gd-DTPA, and 1.8 +/- 0.5 after Gd-DTPA (p less than 0.001). Thus, Gd-DTPA administration improves in vivo visualization of MI by MRI.

Animals↗
PubMed1986

Nuclear magnetic resonance study of high-energy phosphate stores in models of adriamycin cardiotoxicity.

Previous studies have suggested that one of the mechanisms of adriamycin (ADR) cardiomyopathy is depletion of high-energy phosphate stores (HEP). To examine this hypothesis, we used 31P nuclear magnetic resonance to assess the adenosine triphosphate-to-phosphocreatine ratio (ATP-to-PCr ratio) in Langendorff-perfused rabbit hearts. Using either an acute (5 days of therapy at 5 mg/kg/day) or chronic model (7 to 10 weeks of therapy at 1.2 or 1.5 mg/kg twice a week), we compared isovolumetric LV systolic pressure, heart rate, ATP-to-PCr ratios, and histologic lesions between the treated and control animals in each model. In the acute model, there was a significant increase in the ATP-to-PCr ratio (P less than 0.02), without significant changes in myocardial function. Despite significant hemodynamic and histologic alterations in the chronic model, compared to controls, we were unable to identify significant differences in ATP-to-PCr ratios. We conclude that there appear to be differences in energy metabolism between the acute cardiotoxicity and the chronic cardiomyopathy of ADR in the rabbit model and the mechanism of the chronic cardiomyopathy from ADR therapy does not appear to be related to progressive impairment of cellular high-energy phosphate metabolism as measured by the ATP-to-PCr ratio.

Adenosine Triphosphate↗
PubMed1986

In vivo measurement of myocardial mass using nuclear magnetic resonance imaging.

To examine the accuracy of nuclear magnetic resonance imaging in measuring left ventricular mass, measurements of left ventricular mass made using this technique were compared with left ventricular weight in 10 mongrel dogs. Left ventricular myocardial volume was measured from five short-axis end-diastolic images that spanned the left ventricle. Left ventricular mass was calculated from left ventricular myocardial volume and compared with the left ventricular weight determined after formalin immersion-fixation. Linear regression analysis yielded the following relation in grams: left ventricular mass determined using nuclear magnetic resonance imaging = (0.94) (left ventricular weight) + 9.1 (r = 0.98, SEE = 6.1 g). The small overestimation of left ventricular weight by nuclear magnetic resonance imaging was judged to be secondary to both difficulty with proper border definition and partial volume effects. Hence, this imaging technique can be used to obtain accurate measurements of left ventricular mass in dogs in vivo.

Animals↗
PubMed1986

Venous thrombosis: clinical and experimental MR imaging.

Five venous thrombi were induced in the external jugular veins of three laboratory dogs, and were repeatedly imaged over 3 weeks using a 0.35-T magnetic resonance (MR) imager. MR magnitude and phase images, T1 and T2 relaxation times, venography, and histologic sections of these thrombi were evaluated to determine the changes in appearance on MR images with time. Venous thrombi appeared hyperintense compared with muscle on both relatively T1- and T2-weighted spin-echo sequences regardless of the age of the clot. Organization of the thrombus beyond 1 week was manifested as increased prominence of flow signal void in and around the clot. Distinction between intraluminal thrombus and flow-related artifacts was aided by phase image reconstruction. Nineteen venous thrombi locations in 13 patients revealed an MR appearance similar to that of the experimental animal model. Three patients (six thrombi locations) had serial examinations over 4 weeks. No significant change in thrombus signal characteristics was noted with time. It is concluded that MR imaging at 0.35 T cannot be used to predict the age of thrombus (up to 3 weeks) but may be helpful in following its resolution.

Animals↗
PubMed1986

Magnetic resonance imaging of acute myocardial infarction: gadolinium diethylenetriamine pentaacetic acid as a marker of reperfusion.

We examined the effects of a paramagnetic contrast agent, gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) on magnetic resonance images of acute myocardial infarction with and without reperfusion. Twenty-two dogs underwent occlusion of the left anterior descending coronary artery (LAD). In 10 dogs (group I) the LAD remained occluded for 3 hr and in the other 12 (group II) for 2 hr followed by 1 hr of reperfusion. Gd-DTPA (0.34 mM/kg) was administered to five dogs in group I at 2 hr and 5 min after occlusion and to seven dogs in group II 5 min after reperfusion. At 3 hr after ligation, the hearts were excised and imaged with spin echo and inversion recovery pulse sequences on a 0.35 Tesla magnetic resonance imager. Reperfused hearts given Gd-DTPA demonstrated a significant increase in contrast between normal and reperfused myocardium as compared with nonreperfused hearts and reperfused hearts not given Gd-DTPA. This enhancement was particularly prominent in the inversion recovery images. Studies performed in vivo in two additional dogs demonstrated similar enhancement with reperfusion with Gd-DTPA in gated spin echo images. Contrast-enhanced magnetic resonance imaging allows the detection of reperfusion early in the course of acute infarction.

Animals↗
PubMed1985

Metabolic studies of pyruvate- and lactate-perfused guinea pig hearts by 13C NMR. Determination of substrate preference by glutamate isotopomer distribution.

Guinea pig hearts perfused in vitro with 99% enriched [3-13C]pyruvate and [3-13C]lactate have been examined by 13C NMR spectroscopy at 75.45 MHz. Resonances from the intracellular metabolites, glutamate, aspartate, alanine, citrate, malate, lactate, and acetylcarnitine are detected in the [3-13C]pyruvate-perfused hearts while glutamate is the only metabolite observed in the [3-13C]lactate-perfused hearts. Extracts obtained from individual freeze-clamped hearts run under high resolution conditions show similar distributions of metabolites indicating that the intracellular concentrations of these metabolites are indeed quite dependent upon the substrate being utilized. The excellent signal to noise in the spectra of lactate-perfused hearts allows observation of spin-spin coupling between 13C-enriched nuclei in the various glutamate isotopomers within the intact heart. It is shown that the steady-state distribution of glutamate isotopomers is determined by the amount of 12C- versus 13C-enriched acetyl-CoA entering the citric acid cycle and this provides the basis for a direct determination of substrate utilization by the heart in the presence of competing substrates. Similar information may be derived from the 13C spectrum of an extract prepared from a single [3-13C]pyruvate-perfused heart. Our results indicate that lactate is preferred over glucose by the guinea pig heart even in the presence of insulin.

Acetyl Coenzyme A↗
PubMed1985

Fluorine-19 NMR spectroscopy and imaging investigations of myocardial perfusion and cardiac function.

Fluorine-19 nuclear magnetic resonance images of rabbit hearts have been obtained with the administration of a fluorinated contrast compound. The use of fluorine-labeled compounds allows differences in tissue perfusion to be demonstrated between hearts with and without coronary artery ligation. In postischemic reperfusion studies, regional hypoperfusion is also demonstrated by 19F imaging. The results of in vivo rabbit studies show that 19F NMR can be used to monitor the rate of blood pool and extravascular space dilution of a single bolus injection of either a water soluble or emulsified fluorine-labeled agent.

Animals↗
PubMed1985

Left ventricular volumes measured by MR imaging.

We assessed the potential of proton magnetic resonance (MR) imaging for accurately measuring left ventricular volumes using 15 latex casts of excised human left ventricles. The casts were submerged in water to stimulate the endocardial left ventricular cavity interface in in vivo imaging conditions. Tomographic image sections perpendicular to the long axis of the cast were obtained, spanning each cast from apex to base. Simpson's rule was used to calculate the cast volumes. Correlation between the actual cast volumes (as measured by the displacement method) and the calculated volumes using MR imaging for the 15 casts was excellent. Our data demonstrate that MR imaging accurately measures cardiac chamber volumes in this in vitro model.

Heart Ventricles↗
PubMed1984

Pathophysiologic mechanisms of cardiac tamponade and pulsus alternans shown by echocardiography.

A pericardial effusion is easily recognized by echocardiography, but the diagnosis of cardiac tamponade by echocardiography is controversial. Recently, several reports have indicated that right ventricular (RV) or right atrial (RA) diastolic collapse represent highly specific and sensitive signs of a hemodynamically significant pericardial effusion. This report evaluates the pathophysiologic significance of these findings in 3 patients. One patient had classic clinical and hemodynamic features of tamponade without typical echocardiographic features; 1 had typical echocardiographic features of tamponade without the characteristic clinical or hemodynamic features; and 1 had all the findings characteristic of tamponade, including mechanical and electrical alternans. The first patient had increased right-sided cardiac pressures and RV hypertrophy, which prevented RV or RA collapse. The second patient had low right-sided intracardiac pressures, which allowed RV and RA diastolic compression to occur during early and mid-diastole. In the third patient, severe holodiastolic impairment of right-sided filling, and presumed decreased pulmonary venous and pericardial compliance, in the setting of tamponade produced a beat-to-beat alternation of RV and left ventricular filling with associated electrical and mechanical alternans. RV or RA collapse during diastole occurs when intrapericardial pressure equals or exceeds intracardiac pressure. Increases in wall stiffness of chamber pressures may prevent diastolic collapse in the setting of tamponade. Conversely, extremely low intracardiac pressures may allow diastolic collapse to occur in the absence of overt cardiac tamponade. The extent and timing of the RA or RV collapse, rather than its mere occurrence, are important in the diagnosis of cardiac tamponade by echocardiography.

Adolescent↗
PubMed1983

Hydrogen peroxide contrast echocardiography.

Several agents are used as echocardiographic contrast agents, but their unreliability discourages routine clinical use. Studies from the early 1960s suggest that dilute hydrogen peroxide (H2O2) is a safe intravascular agent. Its use was evaluated in contrast echocardiography. To obtain dense opacification reliably, H2O2 (3%) was passed through a sterile 0.2 micron Millipore filter and diluted with heparinized saline solution to make a 0.1 to 0.2% solution. A drop of blood was withdrawn from an indwelling peripheral venous needle into a syringe containing 0.5 to 2.0 ml of the dilute H2O2 and the contents injected. Studies in dogs, normal adults and 36 patients with noncyanotic congenital and acquired cardiac disorders produced dense opacification with no complications. In vitro mixture of H2O2 (0.3%) with leukocyte-poor blood or plasma produced only a few microbubbles, while addition to whole blood or buffy coat produced many, suggesting a role for leukocyte peroxidase. H2O2 contrast echocardiography is simple, inexpensive, and reliably provides dense, sustained opacification. This study and previous studies suggest that intravenous injection of 0.2% H2O2 can be done safely. Great caution should be exercised in patients with severe pulmonary hypertension or large right-to-left shunts because little clinical experience with H2O2 is available.

Animals↗
PubMed1979

ST isopotential precordial surface maps in patients with acute myocardial infarction.

ST amplitude distributions were studied in 41 patients with acute myocardial infarction by deriving isopotential maps from a 5 x 7 electrode precordial matrix. Independent data on infarct size and localization were obtained utilizing the technetium 99m stannous pyrophosphate scintigraphic method. The locus of maximal ST elevation was stable for at least two days in 86% of 27 patients with anterior infarction. A single maximum or maximum-minimum was found in 88% but 22% of the patients had multiple maxima and/or minima in at least two maps. Areas of significant ST elevation were often excluded from the precordial matrix. The site of maximal ST elevation correlated with scintigraphic infarct site but was displaced medially in lateral infarction. The relation between infarct size and sigmaST elevation was significant and curvilinear. sigmaST underestimated size in large anterior infarction. The correlation of the size and the number of sites with ST elevation greater than or equal to 1.5 mm was weak (r = 0.56). The degree of ST abnormality in 14 patients with inferior infarction decreased significantly during the initial 24 hours. The isopotential maps were similar to those obtained in anterior infarction but the polarity was reversed. The results provide limited support for the continued exploration of ST analysis as a clinical method but suggest that sizing methods should be based on total body surface mapping, taking into account the geometry and electrical properties of the torso.

Action Potentials↗
PubMedDate not supplied

Effect of perfusion on exercised muscle: MR imaging evaluation.

An ischemic clamp model of exercise was used to evaluate the potential role of blood flow in mediating changes in the magnetic resonance imaging appearance of skeletal muscle. Proton relaxation times of muscle were serially estimated in 10 healthy subjects (a) before exercise, (b) after exercise in the presence of vascular occlusion (VO1), (c) during vascular reocclusion after 1 minute of reperfusion (VO2), and (d) after reinstitution of continuous flow. T1 and T2 of active muscles were increased during VO1. During VO2, there were additional increases in relaxation times of active muscles. Reinstitution of continuous flow was associated with a continuous decrease in the T2 of exercised muscle. Hence, blood flow was not required for increases in T1 and T2 with exercise. Additional relaxation time increases occurred after a brief period of reperfusion; however, continuous flow was associated with a decrease in T2.

Adult↗
PubMedDate not supplied

Oxygen tension mapping with F-19 echo-planar MR imaging of sequestered perfluorocarbon.

The authors used fluorine-19 inversion-recovery (IR) echo-planar imaging (EPI) to map oxygen tension on the basis of the spin-lattice relaxation rate (R1) of sequestered perfluorocarbon. R1 measured with IR-EPI varied as a linear function of oxygen tension and temperature, and the relationship agreed well with earlier spectroscopic findings. Oxygen tension maps of a mouse that had received a dose of perflubron emulsion were acquired before, during, and after the mouse breathed pure oxygen. Results showed low liver oxygen tension during air breathing, which increased during breathing of pure oxygen, with distinct regional heterogeneity, to 8-17% atm (60-130 torr [8.0-17.3 kPa]).

Animals↗
PubMedDate not supplied

Velocity-encoded, phase-difference cine MRI measurements of coronary artery flow: dependence of flow accuracy on the number of cine frames.

Phase-contrast magnetic resonance imaging (PC-MRI) can be used to produce multiframe cine flow images of the coronary arteries. Accurate coronary flow measurement requires the elimination of respiratory motion artifacts using k-space segmentation to acquire the data in a single breath-hold. However, the duration of the breath-hold is proportional to the number of cine frames. In the present study, the number of cine frames was varied and the accuracies of the coronary flow measurements were assessed using perivascular US. For the range of flows studied (2 ml/min to 147 ml/min), the correlation coefficients for PC-MRI and US increased (.70-.98) and the limits of agreement improved (+/-45 ml.min-1 to +/-10 ml.min-1) as the number of cine frames increased from one to six. The results suggest that the accuracy of breath-hold cine PC-MRI measurements of coronary artery flow improves as the number of cine frames increases.

Animals↗