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Biomedical subjects

R M Peshock

Publications and source records attributed to R M Peshock.

At least 37 records · Page 2Linked to original sources
PubMed1996

Relationship of generalized and regional adiposity to insulin sensitivity in men with NIDDM.

Abdominal obesity, particularly excess intraperitoneal fat, is considered to play a major role in causing insulin resistance and NIDDM. To determine if NIDDM patients accumulate excess intraperitoneal fat, and whether this contributes significantly to their insulin resistance, 31 men with mild NIDDM with a wide range of adiposity were compared with 39 nondiabetic, control subjects for insulin sensitivity (measured using euglycemic-hyperinsulinemic clamp technique with [3-3H]glucose turnover) and total and regional adiposity (assessed by hydrodensitometry and by measuring subcutaneous abdominal, intraperitoneal, and retroperitoneal fat masses using magnetic resonance imaging [MRI], and truncal and peripheral skinfold thicknesses using calipers). MRI analysis revealed that intraperitoneal fat was not increased in NIDDM patients compared with control subjects; in both groups it averaged 11% of total body fat. NIDDM patients, however, had increased truncal-to-peripheral skinfolds thickness ratios. In NIDDM patients, as in control subjects, amounts of truncal subcutaneous fat showed a stronger correlation with glucose disposal rate than intraperitoneal or retroperitoneal fat; however, NIDDM patients were more insulin resistant at every level of total or regional adiposity. Further, no particular influence of excess intraperitoneal fat on hepatic insulin sensitivity was noted. We conclude that NIDDM patients do not have excess intraperitoneal fat, but that their fat distribution favors more truncal and less peripheral subcutaneous fat. Moreover, for each level of total and regional adiposity, NIDDM patients have a heightened state of insulin resistance.

Adipose Tissue↗
PubMed1996

Quantitative MR imaging of the heart.

MR imaging cardiac quantitation is accurate, highly reproducible, and feasible using equipment available in most hospitals. For determination of myocardial mass, evaluation of RV function, and quantitative measurements of flow in the great vessels and peripheral vasculature, MR imaging is the reference method. Availability of methods for rapid scanning and analysis will lead to increased use of cardiac MR imaging in quantifying cardiac function.

Heart↗
PubMed1995

Magnetic resonance imaging assessment of the severity of mitral regurgitation. Comparison with invasive techniques.

BACKGROUND: In the patient with mitral regurgitation who is being considered for valvular surgery, cardiac catheterization is usually performed to quantify the severity of regurgitation and to determine its influence on left ventricular volumes and systolic function. Magnetic resonance imaging (MRI) potentially provides a rapid, noninvasive method of acquiring these data. Thus, this study was done to determine whether MRI can reliably measure the magnitude of mitral regurgitation and evaluate the effect of regurgitation on left ventricular volumes and systolic function. METHODS AND RESULTS: Twenty-three subjects (14 women and 9 men 15 to 72 years of age) with (n = 17) or without (n = 6) mitral regurgitation underwent MRI scanning followed immediately by cardiac catheterization. The presence (or absence) of valvular regurgitation was determined, and left ventricular volumes and regurgitant fraction were quantified during each procedure. There was excellent correlation between invasive and MRI assessments of left ventricular end-diastolic (r = .95) and end-systolic (r = .95) volumes and regurgitant fraction (r = .96). All MRI examinations were completed in < 28 minutes. CONCLUSIONS: In the patient with mitral regurgitation, MRI compares favorably with cardiac catheterization for assessment of the magnitude of regurgitation and its influence on left ventricular volumes and systolic function.

Adolescent↗
PubMed1995

Quantitation of cardiac output with velocity-encoded, phase-difference magnetic resonance imaging.

Velocity-encoded, phase-difference magnetic resonance imaging (MRI) previously has been used to measure flow in the aorta, as well as in the pulmonary, carotid, and renal arteries, but these measurements have not been validated against currently accepted invasive techniques. To determine the accuracy of velocity-encoded, phase-difference MRI measurements of cardiac output, 23 subjects (11 men and 12 women, aged 15 to 72 years) underwent velocity-encoded, phase-difference MRI measurements of cardiac output in the proximal aorta, followed immediately by cardiac catheterization, with measurement of cardiac output by the Fick principle and by thermodilution. For MRI, Fick, and thermodilution measurements, stroke volume was calculated by dividing cardiac output by heart rate. The magnetic resonance images were acquired in 1 to 3 minutes. For all patients, the agreement between measurements of stroke volume was 3 +/- 9 ml for MRI and Fick, -3 +/- 11 ml for MRI and thermodilution, and 0 +/- 8 ml for MRI and the average of Fick and thermodilution. Compared with standard invasive measurements, velocity-encoded, phase-difference MRI can accurately and rapidly determine cardiac output.

Adolescent↗
PubMed1995

Assessment of left-to-right intracardiac shunting by velocity-encoded, phase-difference magnetic resonance imaging. A comparison with oximetric and indicator dilution techniques.

BACKGROUND: Velocity-encoded, phase-difference magnetic resonance imaging (MRI) has been shown to provide an accurate assessment of shunt magnitude in patients with large atrial septal defects, but its ability to determine shunt magnitude in patients with intracardiac left-to-right shunts of various locations and sizes has not been evaluated in a prospective and blinded manner. The objective of the present study was to determine whether velocity-encoded, phase-difference MRI can assess the magnitude of intracardiac left-to-right shunting in humans. METHODS AND RESULTS: Twenty-one subjects (15 women and 6 men; age range, 15 to 72 years) underwent velocity-encoded, phase-difference MRI measurements of flow in the proximal aorta and pulmonary artery, followed immediately by cardiac catheterization. The presence of left-to-right intracardiac shunting was assessed with hydrogen inhalation, after which shunt magnitude was measured by the oximetric and indocyanine green techniques. Of the 21 patients, 12 had left-to-right intracardiac shunting detected by hydrogen inhalation. There was a good correlation (r = .94) between the invasive and MRI assessments of shunt magnitude. In comparison to oximetry and indocyanine green, MRI correctly identified the 12 patients with a ratio of pulmonary to systemic flow (Qp/Qs) of < 1.5 (9 without intracardiac shunting and 3 with small shunts) and the 9 patients with a Qp/Qs of > or = 1.5 (6 with atrial septal defect, 1 with ventricular septal defect, 1 with patent ductus arteriosus, and 1 with both atrial septal defect and patent ductus arteriosus). CONCLUSIONS: Compared with measurements obtained during cardiac catheterization, velocity-encoded, phase-difference MRI measurements of flow in the proximal great vessels can reliably assess the magnitude of intracardiac left-to-right shunting.

Adult↗
PubMed1995

Measurement of absolute epicardial coronary artery flow and flow reserve with breath-hold cine phase-contrast magnetic resonance imaging.

BACKGROUND: Noninvasive measurement of absolute coronary arterial flow and coronary flow reserve would be of considerable use in the diagnosis and management of patients with coronary artery disease. Phase-contrast magnetic resonance imaging (MRI) has been used to measure flow in a variety of vessels. The goal of the present study was to determine if MRI measurements of coronary artery flow in a single breath-hold can be used to determine flow reserve and the severity of pericardial stenosis. METHODS AND RESULTS: In eight mongrel dogs, a closed chest model of partial left anterior descending coronary artery (LAD) occlusion was created. Coronary flows in the left circumflex artery (LCx) and LAD were measured at rest and during adenosine infusion using velocity-encoded, breath-hold MRI and perivascular ultrasound (US) flowmeters. MRI measurements of absolute coronary flow and coronary flow reserve were highly correlated with US (r = .96 and .94, respectively). Flow reserve measured in the constricted LAD was significantly lower than that in the unconstricted LCx by both US (P = .002) and MRI (P = .011). CONCLUSIONS: MRI measurements of coronary flow and flow reserve were in good agreement with US measurements. In addition, MRI measurements of coronary flow reserve successfully discriminated stenotic from normal vessels. These results indicate that MRI is a useful method for the noninvasive assessment of coronary flow and stenosis.

Adenosine↗
PubMed1995

Noninvasive determination of infarct artery patency by cine magnetic resonance angiography.

BACKGROUND: In survivors of myocardial infarction, restoration of antegrade flow in the infarct artery reduces morbidity and mortality. At present, coronary artery patency must be assessed invasively with contrast angiography. A noninvasive method of evaluating infarct artery patency would be useful in managing survivors of infarction. This study was performed to determine whether magnetic resonance (MR) imaging could reliably assess infarct artery patency in this patient population. METHODS AND RESULTS: Eighteen survivors of myocardial infarction (11 men and 7 women, aged 35 to 74 years) who were consecutively referred for cardiac catheterization underwent contrast coronary angiography and cine MR coronary angiography. Sequential overlapping images of the infarct artery were acquired with cine MR during 15- to 20-second periods of breath-holding. In each study, proximal, middle, and distal segments of infarct arteries were classified as having antegrade, collateral, or no flow. The infarct artery was the left anterior descending in 10 patients, the right anterior descending in 7, and the circumflex in 1. When compared with the results of contrast angiography, MR imaging correctly identified the presence or absence of antegrade flow in the infarct artery of all 18 patients. In addition, cine MR coronary angiography with presaturating pulses correctly established the presence or absence of collateral filling of the distal portion of occluded arteries in 6 of 7 subjects. CONCLUSIONS: In survivors of myocardial infarction, cine MR coronary angiography can reliably determine the patency and direction of flow in the infarct artery.

Adult↗
PubMed1995

Magnetic resonance imaging of the heart and its role in current cardiology.

Magnetic resonance imaging has been demonstrated to be useful in the assessment of aortic and pericardial disease, cardiac masses, and congenital heart disease. Recently, developments in rapid imaging, assessment of regional function, evaluation of intracardiac shunts and valvular regurgitation, and magnetic resonance coronary angiography have been achieved, indicating an increasing role for magnetic resonance techniques in clinical cardiology.

Aortic Diseases↗
PubMed1995

Relationships of generalized and regional adiposity to insulin sensitivity in men.

The relative impacts of regional and generalized adiposity on insulin sensitivity have not been fully defined. Therefore, we investigated the relationship of insulin sensitivity (measured using hyperinsulinemic, euglycemic clamp technique with [3-3H]glucose turnover) to total body adiposity (determined by hydrodensitometry) and regional adiposity. The latter was assessed by determining subcutaneous abdominal, intraperitoneal, and retroperitoneal fat masses (using magnetic resonance imaging) and the sum of truncal and peripheral skinfold thicknesses. 39 healthy middle-aged men with a wide range of adiposity were studied. Overall, the intraperitoneal and retroperitoneal fat constituted only 11 and 7% of the total body fat. Glucose disposal rate (Rd) and residual hepatic glucose output (rHGO) values during the 40 mU/m2.min insulin infusion correlated significantly with total body fat (r = -0.61 and 0.50, respectively), subcutaneous abdominal fat (r = -0.62 and 0.50, respectively), sum of truncal skinfold thickness (r = -0.72 and 0.57, respectively), and intraperitoneal fat (r = -0.51 and 0.44, respectively) but not to retroperitoneal fat. After adjusting for total body fat, the Rd and rHGO values showed the highest correlation with the sum of truncal skinfold thickness (partial r = -0.40 and 0.33, respectively). We conclude that subcutaneous truncal fat plays a major role in obesity-related insulin resistance in men, whereas intraperitoneal fat and retroperitoneal fat have a lesser role.

Adipose Tissue↗
PubMed1995

Measurement of blood-retinal barrier breakdown in endotoxin-induced endophthalmitis.

PURPOSE: Endophthalmitis is a severe inflammatory disorder with profound visual consequences. Treatment of this disorder has been limited by the lack of quantitative information regarding retinal responses to severe inflammation. The purpose of this study was to measure the effect of endotoxin-induced endophthalmitis on blood-retinal barrier (BRB) function in vivo using contrast-enhanced magnetic resonance imaging (MRI). METHODS: Endophthalmitis was produced by injecting Escherichia coli endotoxin into the midvitreous of pigmented rabbits. Contrast-enhanced MRI was performed at selected intervals thereafter. In all cases, a clinical grading system was used to assess the severity of inflammation before imaging. In a dose-response experiment, total vitreous protein was measured from vitreous specimens obtained 1 day after endotoxin injection and immediately after the imaging procedure. RESULTS: At 1 day after injection, endotoxin produced a selective breakdown of the inner BRB at all doses evaluated (0.01 microgram to 500 micrograms). Permeability-surface area product normalized to the area of leaky retina (PS') increased from 1.35 +/- 0.78 x 10(-4) cm/minute (mean +/- SEM, n = 4 eyes) at a dose of 0.01 microgram to 8.15 +/- 2.22 x 10(-4) cm/minute n = 4) eyes) at a dose of 10 micrograms. Inner BRB integrity was restored by day 28 after injection. In general, changes in PS', blood-aqueous barrier leakage, mean clinical score, and vitreous protein concentration were found, but the correlation between any two of these parameters was poor. CONCLUSION: Leakage of contrast appears early in the course of endotoxin-induced endophthalmitis and is a self-limited process. In future studies, these quantifiable changes in BRB permeability should prove useful in the assessment of various therapeutic interventions.

Animals↗
PubMed1994

Transcorneal oxygenation of the preretinal vitreous.

OBJECTIVE: Transcorneal oxygenation is a promising approach to the treatment of various anterior ocular diseases, but its effect on the vitreous and retina is uncertain. The purpose of this study was to evaluate the ocular conditions necessary to permit transcorneal oxygenation of the preretinal vitreous in the rabbit eye. METHODS: Oxygen at atmospheric pressure was supplied via a goggle to the eye while preretinal oxygen tensions were measured with a minimally invasive technique: fluorine-19 (19F) nuclear magnetic resonance spectroscopy of a small preretinal droplet of perfluorotributylamine. Experiments were performed on lensectomized eyes with intact posterior lens capsules (group 1) or in eyes that had also undergone posterior capsular discission (group 2) and mechanical vitrectomy (group 3). To better understand the results of the oxygenation studies, a water-soluble, freely diffusible contrast agent was applied topically to the cornea, and its penetration into the aqueous and vitreous was studied using T1-weighted magnetic resonance imaging. RESULTS: Preretinal PO2 was significantly increased after 30 minutes of transcorneal oxygenation in group 3 eyes (P = .002). In contrast, no change was observed in the other groups despite 30 minutes (group 1) or 3 hours (group 2) of oxygen exposure. The imaging studies demonstrated that contrast penetration of the vitreous was uniform and rapid in eyes in group 3, consistent with a fluid flow-dominated process. A much slower process of anterior and midvitreous enhancement was observed in groups 1 and 2 that was consistent with contrast diffusion. CONCLUSIONS: Because of bulk fluid movement, transcorneal oxygenation of the retina is feasible in single-compartment (vitrectomized, lensectomized) eyes within a reasonable period (30 minutes). This finding could prove useful in the treatment of retinal diseases in which hypoxia may play a role.

Animals↗
PubMed1994

Effect of vitreous fluidity on the measurement of blood-retinal barrier permeability using contrast-enhanced MRI.

Breakdown of the blood-retinal barrier (BRB), frequently an early clinical sign in retinopathy, can be accurately determined using contrast-enhanced MRI. However, increased vitreous fluidity with age and disease may affect the accuracy of the MRI method. We compared the permeability surface area product per area of leaky retina in eyes with normal vitreous (5.42 +/- 0.48 x 10(-4) cm/min, mean +/- SEM, n = 5) to the contralateral gas-compressed vitrectomized eyes (5.41 +/- 0.54 x 10(-4) cm/min, n = 5). The effect of vitrectomy was not significant (P = 0.325) using a Wilcoxon matched pairs signed rank test on the signed differences of the PS' values.

Animals↗
PubMed1994

Pulmonary embolism: comparison of MR images with radionuclide and angiographic studies.

PURPOSE: To assess the accuracy and potential of magnetic resonance (MR) imaging in evaluation of patients in whom pulmonary embolism is suspected. MATERIALS AND METHODS: Blinded, prospective interpretations of multiphasic, cardiac-gated spin-echo MR images were compared with retrospective chart review in 86 patients in whom pulmonary embolism was suspected. In 64 patients, the presence or absence of pulmonary emboli was established with x-ray angiography (n = 34) or ventilation-perfusion (V-P) scans and concurrent clinical impression (n = 30). RESULTS: In the subgroup with angiographic proof, MR imaging had a sensitivity of 90%, specificity of 77%, positive predictive value of 86%, and negative predictive value of 83%. In 21 patients with intermediate probability of pulmonary embolism on V-P scans and angiograms, MR images enabled diagnosis of pulmonary embolism in 12 of 12 patients (sensitivity, 100%) and absence of pulmonary embolism in seven of nine patients (specificity, 78%). CONCLUSION: MR imaging reliably depicts large and medium-size pulmonary emboli, regardless of infiltrates or effusion; hence, it may clarify findings on V-P scans that show intermediate probability of pulmonary embolism or are at variance with the clinical impression.

Adult↗
PubMed1994

Estimation of adipose tissue mass by magnetic resonance imaging: validation against dissection in human cadavers.

The evaluation of adipose tissue distribution has become an essential component of investigations on the complications of obesity. However, a major limitation is lack of methodology for accurate estimation of adipose tissue mass in the different regions of the body. Therefore, we have tested the accuracy and precision of magnetic resonance imaging (MRI) as a method to measure adipose tissue mass in regions of the body not accessible with standard anthropometric methods. The mass of subcutaneous and intraabdominal adipose tissue estimated by MRI was compared with that obtained by direct weighing of the same adipose tissue compartments after dissection in human cadavers. MRI was performed on three unembalmed cadavers (two males, one female) who were subsequently dissected to isolate intraperitoneal, retroperitoneal, and subcutaneous adipose tissues. These same components were delineated by MRI. The results of the two methods were highly congruent. For the various compartments, the mean of the difference between the two methods was only 0.076 kg (95% confidence interval + 0.005 kg and + 0.147 kg). The "limits of agreement" between the two techniques were -0.066 kg and +0.218 kg. Multiple repeated estimates of mass of adipose tissue compartments were made to determine reproducibility of the MRI measurement; the coefficient of variation for repeated measures was below 14%. The results of this study show that MRI is an accurate and precise technique to evaluate adipose tissue mass in subcutaneous and intraabdominal compartments. Furthermore, MRI was found to be a valid method to separately evaluate the mass of intraabdominal subcompartments of intraperitoneal and retroperitoneal adipose tissue.

Abdomen↗
PubMed1993

Echo planar imaging of perfluorocarbons.

Emulsions of perfluorotributylamine (FTBA) and perflubron were evaluated for their utility in 19F echo planar imaging. Fluorine images of the emulsions were obtained in a phantom and two mice that had been predosed. Both agents, but particularly perflubron, show potential for fluorine echo planar studies because of the long spin-spin relaxation times of the CF3 resonances. High resolution thin slice images obtained in as little as 26.6 ms are presented.

Animals↗
PubMed1993

Low resolution spin echo: a simple timesaving technique for MRI liver exams.

MR evaluation of the liver at mid-field strength requires relatively lengthy T2-weighted sequences (T2W) for differentiation of benign cavernous hemangiomas from malignant lesions. A short duration T2W, which maintains standard signal-to-noise ratio and also contrast relationships, can be easily implemented by increasing the pixel size in the phase-encoding direction (thus reducing spatial resolution) and proportionally decreasing the number of phase-encoding steps in the matrix (thus reducing acquisition time). Blinded interpretations of a quick (4 min), low resolution (3.4 mm x 1.7 mm pixel) T2W sequence (matrix 64 x 256, FOV 21.7 cm phase x 43.5 cm frequency) were compared to the 17 min standard resolution (1.7 mm x 1.7 mm) T2W sequence (256 x 256 matrix, FOV 43 x 43 cm) in 25 patients suspected of having liver metastasis. Lesions felt to be cavernous hemangiomas showed a 100% (24/24) agreement for interpreter "A" and 96% (22/23) agreement for interpreter "B" when 4 min low resolution T2W was compared to the standard 17 min sequence. Sensitivity (for all types of lesions) of the low resolution T2W sequence ranged from 100% (31/31) for interpreter "A" to 80% (28/35) for interpreter "B." Missed lesions (interpreter "B") were either partially obscured by excessive fat (wrap around) (N = 4), less than 1 cm in size (N = 2), or degraded by motion artifact (N = 1). Thus in many situations low resolution T2 may provide a substantial timesaving alternative to standard T2W particularly where T2W is used primarily for lesion classification in normal sized patients.

Adult↗
PubMed1993

Lumbar muscle usage in chronic low back pain. Magnetic resonance image evaluation.

Methods for detecting recruitment patterns of the lumbar muscles during exercise in patients with chronic low back pain are limited. This article discusses the use of magnetic resonance imaging with Roman chair extension exercise to examine lumbar muscle usage in five normal volunteers, five chronic low back pain patients without surgery, and five chronic low back pain patients with surgery. Changes in signal intensities of psoas, multifidus, and longissimus/iliocostalis with graded exercise were measured at three lumbar disc levels. At rest, there was a difference between multifidus and longissimus/iliocostalis signal intensity in chronic low back pain subjects without surgery (P = 0.0162) and in chronic low back pain subjects with surgery (P = 0.0036), but not in normal subjects. At peak exercise, there was a difference in signal intensities between multifidus and longissimus/iliocostalis in all groups (normal volunteers, P = 0.0069; chronic low back pain patients without surgery, P = 0.0125; chronic low back pain patients with surgery, P = 0.0060). The exercise response was attenuated in chronic low back pain patients with surgery. Thus, MRI demonstrates static and dynamic differences in lumbar paraspinal musculature in chronic low back pain subjects compared to normal subjects.

Exercise↗