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Biomedical subjects

F H Epstein

Publications and source records attributed to F H Epstein.

342 records · Page 19Linked to original sources
PubMedDate not supplied

Improved T1-weighted two-dimensional MP-GRE imaging of the liver with variable flip angles for shaping the signal evolution.

The recently introduced method of shaping the transient signal evolution in magnetization-prepared gradient-echo (MP-GRE) imaging with variable flip angles has been applied to two-dimensional (2D) MP-GRE imaging of the abdomen. The technique was analyzed by using theoretical models and was implemented on a standard 1.5-T whole-body imager with a segmented acquisition. Theoretical models predicted that the variable-flip-angle 2D MP-GRE sequence would increase liver-spleen signal difference--to-noise ratios by 290%, 110%, and 160% compared with a 2D MP-GRE sequence with a flip angle of 10 degrees and sequential phase encoding, a 2D MP-GRE sequence with a flip angle of 30 degrees and centric phase encoding, and the fast low-angle shot sequence, respectively. Experimental measurements supported the theoretical predictions.

Algorithms↗
PubMedDate not supplied

CSF-suppressed T2-weighted three-dimensional MP-RAGE MR imaging.

Fluid-attenuated inversion recovery (FLAIR) is a pulse sequence used for acquiring T2-weighted images of the brain and spine in which the normally high signal intensity of CSF is greatly attenuated. The CSF-suppressed T2-weighted contrast of this technique may be more sensitive to a variety of disorders than that of conventional T2-weighted imaging. The primary disadvantage associated with conventional spin-echo implementations of FLAIR is the relatively limited anatomic coverage that can be achieved in a reasonable imaging time. We developed and optimized a three-dimensional magnetization-prepared rapid gradient-echo (3D MP-RAGE) pulse sequence that combines CSF-suppressed T2-weighted contrast similar to existing FLAIR techniques with anatomic coverage characteristic of 3D imaging. A preliminary evaluation of the new sequence was performed by imaging healthy volunteers and patients with multiple sclerosis.

Brain↗
PubMedDate not supplied

Using cardiac phase to order reconstruction (CAPTOR): a method to improve diastolic images.

A method is proposed to reconstruct multiphase images that accurately depicts the entire cardiac cycle. A segmented, gradient-recalled-echo sequence (FASTCARD) was modified to acquire data continuously. Images were reconstructed retrospectively by selecting views from each heartbeat based on cardiac phase rather than the time elapsed from the QRS complex. Cardiac phase was calculated using a model that compensates for beat-to-beat heart rate changes. Images collected using cardiac phase to order reconstruction (CAPTOR) depict the entire cardiac cycle and lack the temporal gap that is characteristic of prospectively reconstructed sequences. Time-volume curves of the left ventricle capture the contribution of atrial contraction to end-diastolic volume (EDV). Transmitral phase-contrast flow measurements show a second peak inflow (alpha wave) that is absent in the standard sequence. Because atrial contraction contributes to ventricular EDV, images using CAPTOR potentially may provide a more reliable measure of EDV, stroke volume, and ejection fraction than standard techniques.

Cardiac Volume↗
PubMedDate not supplied

Breath-hold R2* mapping with a multiple gradient-recalled echo sequence: application to the evaluation of intrarenal oxygenation.

Blood oxygenation level dependent (BOLD) MRI is sensitive to changes in regional oxygen supply versus demand and is therefore potentially useful in evaluating susceptibility to ischemic injury. Recently, we have demonstrated the use of BOLD MRI to evaluate intrarenal oxygenation using single shot echo-planar imaging (EPI). Here, we present an alternate implementation of BOLD MRI sequence, using multiple gradient echoes, that does not require any specialized hardware.

Echo-Planar Imaging↗
PubMedDate not supplied

[Prevention and risk factors of coronary disease in the Canton of Zürich].

An intervention study is being carried out in relation to the prevention of diseases caused by atherosclerosis, especially coronary heart disease. The purpose of the study is to test in one community whether an intensive health education program, including the media (newspapers, radio and educational materials) as well as more individual instruction (lecture, group discussions, courses, exhibitions, collaboration with organizations) can modify risk factors in the population through favorable changes in the mode of life. Another community without any programs serves as a control. Questionnaires are being sent and screening examinations are being carried out in random samples of both populations before and at the end of the educational campaign in order to evaluate its effect. The plan and methods of the study are being described and the distribution of risk factors, based on the first round of examinations, is presented. A second round of examinations is due after a 12 months interval.

Adult↗
PubMedDate not supplied

New and old perspectives on acute renal failure.

The pathophysiology, course, and treatment of acute renal failure in humans differs substantially from the ischemia/reflow model of renal injury commonly studied in rats and mice. Acute renal failure in humans is best understood as the result of an exacerbation of the usual state of hypoxia in the renal medulla and medullary rays, leading to reversible tubular dysfunction and glomerular vasoconstriction. A secondary inflammatory cascade may also play an important role, though this has not yet been clearly shown in patients.

Acute Kidney Injury↗
PubMedDate not supplied

Joint distribution of lipoprotein cholesterol classes. The Framingham study.

During the period 1971 to 1975, the cholesterol content of lipoprotein density classes were measured in 2415 male and female Framingham Heart Study participants and 4342 of their offspring and offspring spouses who were free of coronary heart disease. In this first of three papers, the univariate and bivariate distributions of high density lipoprotein cholesterol, low density lipoprotein cholesterol, and very low density lipoprotein cholesterol are presented. There are differences in the levels of lipoprotein cholesterols by age, gender, and use of hormone preparations. The bivariate cross-tabulations of the three pairs of lipoprotein cholesterol measurements exhibit properties that cannot be appreciated from univariate summary statistics and suggest the importance of joint consideration of different lipoprotein cholesterol patterns for assessing the risk of coronary heart disease.

Adolescent↗
PubMedDate not supplied

Active chloride transport powered by Na-K-ATPase in shark rectal gland.

The isolated rectal gland of the spiny dogfish is a unique model for the study of active chloride transport. The gland is stimulated to secrete chloride agains an electrical and a chemical gradient when perfused in vitro by theophylline and/or dibutyryl cyclic AMP. Chloride secretion is depressed by ouabain which inhibits Na-K-ATPase. Thiocyanate and furosemide also inhibit chloride secretion but ethoxolamide, a carbonic anhydrase inhibitor, does not. Chloride transport is highly dependent on sodium concentration in the perfusate. The intracellular concentration of chloride in intact glands exceeds the level expected at electrochemical equilibrium, suggesting active transport of chloride into the cell. These features suggest a general hypothesis for chloride secretion in which the uphill transport of chloride into the cytoplasm is coupled through a membrane carrier to the downhill movement of sodium along its electrochemical gradient. The latter is maintained by the Na-K-ATPase pump while chloride is extruded into the duct by electrical forces.

Animals↗
PubMedDate not supplied

Factors influencing the increase in Na-K-ATPase in compensatory renal hypertrophy.

An increase in Na-K-ATPase in kidney homogenates usually accompanies compensatory renal hypertrophy. While it may be evident in both the cortex and medulla of the kidney, it is most marked in the outer medulla and may be present only in that region. The increase in enzyme activity does not depend on an intact adrenal cortex and can be elicited in the absence of adrenal glucocorticoids. It is not seen in the form of renal hypertrophy produced by potassium depletion, in which the transport of sodium and potassium by the kidney is not increased. When present in compensatory renal growth, the enzyme change is correlated with an increase in the reabsorption of sodium, or the excretion of potassium, or both, per unit of renal tissue. It proceeds in the presence of either, but not in the absence of both.

Adrenalectomy↗
PubMedDate not supplied

The shark rectal gland: a model for the active transport of chloride.

The rectal gland of the spiny dogfish, Squalus acanthias, provides an easily studied model of active chloride transport powered indirectly by Na-K-ATPase. Co-transport of sodium with chloride can be demonstrated in membrane vesicles isolated from basolateral membranes of the gland. Chloride secretion is under the hormonal control of vasoactive intestinal peptide, and possibly other agents, via adenyl cyclase and cyclic AMP. A similar mechanism is probably responsible for the active transport of chloride across other biological membranes.

Animals↗
PubMedDate not supplied

The relation between sodium transport and oxygen consumption in isolated perfused rat kidney.

A non-filtering isolated perfused rat kidney model was developed to determine renal oxygen consumption in the absence of tubular reabsorption. The oxygen consumption in the absence of filtration was 3.1 +/- 0.8 micron of O2/min/g. This "basal" value was substantially higher than that of 2.0 micron of O2/min/g calculated by extrapolation of a plot of sodium reabsorption vs. oxygen consumption in filtering kidneys. It was also found that ouabain 10(-4) M decreased oxygen consumption in non-filtering kidneys and acetazolamide increased it in a dose dependent fashion. Furosemide did not change "basal" oxygen consumption. In filtering kidneys, the ratio of sodium reabsorbed to oxygen consumed averaged 36.8 muEq of Na/mumole of O2. It is concluded that basal oxygen consumption is not a fixed quantity and can be changed by experimental manipulations thereby changing the relation between transport activity and oxygen consumption.

Acetazolamide↗