Noninvasive quantitation of left ventricular wall thickening using cine magnetic resonance imaging with myocardial tagging.
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Adult↗
Biomedical subjects
R M Peshock
Publications and source records attributed to R M Peshock.
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↗
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↗
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↗
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↗
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↗
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↗
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↗
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↗
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↗
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↗
Left ventricular dimensions and mass using magnetic resonance imaging in female endurance athletes.
Few published studies of left ventricular (LV) mass in female endurance athletes have been performed with M-mode echocardiography, which involves assumptions of LV geometry. Therefore, magnetic resonance imaging, a 3-dimensional technique, was used to examine LV mass, LV end-diastolic volume and mean wall thickness in female long distance runners (n = 13; mean age 29 years), cyclists (n = 12; mean age 26 years) and cross-country skiers (n = 11; mean age 24 years), and the findings were compared with sedentary control subjects (n = 10; mean age 27 years) matched for height and body weight. The physical characteristics for all subjects included height (mean 166 cm, and body weight (mean 56 kg). The percent body fat (mean 11.7) and maximal oxygen uptake (VO2max, mean 63 ml.kg-1.min-1) were similar (p greater than 0.05) among all athletic groups, but significantly different from the control group (body fat, mean 22.5%; VO2max, mean 35 ml.kg-1.min-1). LV mass (mean 159 kg), LV end-diastolic volume (mean 122 ml), and mean wall thickness (mean 11.5 mm) were also similar among the athletic groups and significantly larger than the following control values: LV mass (mean 115 g), LV end-diastolic volume (mean 93 ml) and mean wall thickness (mean 9.8 mm). Ratios of LV mass to lean body weight were similar among all athletic groups, although athletic groups had larger ratios (p less than 0.05) than the sedentary control subjects. LV mass/LV end-diastolic volume ratio was similar (p greater than 0.05) among all groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Analysis of Variance↗
The skeleton in congenital, generalized lipodystrophy: evaluation using whole-body radiographic surveys, magnetic resonance imaging and technetium-99m bone scintigraphy.
Congenital generalized lipodystrophy (CGL) is a rare genetic disease characterized by the absence of body fat from birth. Focal bone lesions have also been reported, but their pathophysiology is poorly understood. To characterize skeletal abnormalities further in 3 patients with CGL, we employed whole-body radiographic skeletal surveys, magnetic resonance imaging (MRI, including gadolinium enhancement), and triple phase technetium-99m methylene diphosphonate bone scintigraphy. Radiographs showed numerous focal lesions within the long bones, as described in other reports. MRI showed that the entire marrow space of the long bones was abnormal and was characterized, at least in part, by the absence of marrow fat. Prolonged T1 and T2 times and marked gadolinium enhancement were observed in radiographically normal-appearing long bone. Radiographically lytic lesions occasionally demonstrated fluid-fluid levels on MRI and enhanced peripherally after gadolinium infusion. Bone scintigraphy findings such as periarticular hyperemia were relative subtle. We conclude that the appendicular skeleton of patients with CGL is diffusely abnormal and is predisposed to focal osteolysis and cyst formation.
Adult↗
Glycogenolysis, not perfusion, is the critical mediator of exercise-induced muscle modifications on MR images.
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Animals↗
MR imaging-guided muscle biopsy for correlation of increased signal intensity with ultrastructural change and delayed-onset muscle soreness after exercise.
To determine if there is a correlation between the degree of delayed increase in signal intensity (SI) of muscle after exercise on magnetic resonance (MR) images and the amount of ultrastructural (ULS) injury and delayed-onset muscle soreness (DOMS), MR imaging-guided muscle biopsy was performed to obtain tissue from the legs of nine sedentary subjects 48 hours after downhill running on a treadmill. The degree of soreness was subjectively graded. T1-weighted, spin-density, T2-weighted, and short inversion time inversion-recovery images were obtained before and after biopsy, at 48 and 96 hours after exercise, respectively. The delayed SI increase of muscle on images obtained before biopsy was subjectively graded and measured. The degree of ULS injury was determined with electron micrographs. Serum creatine kinase levels were obtained before and up to 144 hours after exercise at 24-hour intervals. The measured SI, SI grades, and DOMS grades were correlated with the degree of ULS injury. Linear regression analysis revealed poor correlation between the DOMS grades and the degree of ULS injury and good correlation between the SI grade and the degree of ULS injury.
Adult↗
Finger-specific flexor recruitment in humans: depiction by exercise-enhanced MRI.
To evaluate the spatial distribution of human forearm musculature stressed by finger-specific exercise, magnetic resonance imaging was performed in conjunction with exercise protocols designed to separately stress the flexor digitorum superficialis and flexor digitorum profundus. These muscles were shown to consist of subvolumes selectively recruited by flexion of the individual fingers. Knowledge of the finger-specific regions of muscle recruitment during finger flexion could improve sampling accuracy in electromyography, biopsy, magnetic resonance spectroscopy, and invasive vascular sampling studies of hand exercise.
Adult↗
Peculiar distribution of adipose tissue in patients with congenital generalized lipodystrophy.
Congenital generalized lipodystrophy (CGL) is a rare genetic disease with extreme paucity of fat from birth which is believed to be generalized, involving the whole body. Affected patients are characterized by severe insulin resistance. Sites of adipose tissue distribution in patients with CGL have not been studied systematically. Therefore, the fat distribution in three women (17-20 yr old) with CGL was investigated. Determination of body composition by underwater volume displacement suggested the complete absence of body fat (range, -3 to -7%; normal, 15-25%). Whole body magnetic resonance imaging, however, detected fat in particular anatomical sites, namely in orbits, palms and soles, and periarticular and epidural regions. Some fat was also localized in the tongue, breasts, vulva, and buccal area. Fat in other subcutaneous areas, intraabdominal and intrathoracic regions, and bone marrow was essentially absent. Thus, patients with CGL do not have a complete absence of body fat; of interest, fat is present in those sites where adipose tissue may be serving mainly a mechanical function. Patients with CGL, therefore, provided a unique opportunity to identify the various sites of localization of "mechanical" adipose tissue in the human body. Our study suggests that the genetic defect in CGL results in poor growth and development of metabolically active adipose tissue, whereas mechanical adipose tissue is well preserved.
Adipose Tissue↗
Automated localization and identification of lower spinal anatomy in magnetic resonance images.
Clinical interpretation of the subtle changes present in MR images in the setting of disease currently relies on subjective image analysis. Image evaluation could potentially be improved by computerized segmentation and precise quantification of the image anatomy. However, this cannot be automated unless reliable navigation within an image is established, capable of compensating for unpredictable factors such as anatomical variability, positioning of an image plane in the body, and variable image characteristics. Focusing on the lower spinal region, this paper explores the presence of image- and anatomy-invariant features which facilitate automated, unconstrained identification, and localization of basic lower spine anatomy.
Algorithms↗