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J D Pearlman

Publications and source records attributed to J D Pearlman.

16 recordsLinked to original sources
PubMed1992

Real-time NMR beam-directed velocity mapping. V-mode NMR.

BACKGROUND: Currently available noninvasive techniques for measuring blood flow velocities are constrained by limited view orientations (Doppler ultrasound) or limited time resolution (magnetic resonance imaging, MRI). We describe an MRI technique for measuring flow velocities in real time at arbitrary orientations within a cylindrical volume or "beam": V-mode nuclear magnetic resonance (NMR). METHODS AND RESULTS: The technique was implemented on a standard 1.5-T clinical NMR imager with no special hardware and was tested on phantoms and human volunteers. The beam can be fired at rates up to 60 times per second, allowing measurements on a time scale that is appropriate for ungated cardiac studies. In phantoms, steady flow velocities were measured with the beam aligned along the direction of flow, and the measured velocities correlated well with the actual velocities (r > 0.99). The radial distribution of velocities in phantoms under constant flow conditions was also determined. In humans, flow of blood in the descending aortas of normal and aortic insufficiency subjects was measured. Distinctive backflow of blood because of aortic insufficiency was readily apparent. CONCLUSIONS: The V-mode NMR technique is capable of acquiring clinically relevant real-time blood flow information from any desired angle of view with no attenuation at bone or air-tissue interfaces.

Aorta, Thoracic↗
PubMed1992

Accumulation of fluoxetine and norfluoxetine in human brain during therapeutic administration.

In vivo 19fluorine nuclear magnetic resonance spectroscopy was used to measure the brain concentration of fluoxetine and norfluoxetine in five patients with obsessive-compulsive disorder and three with major depression. The mean brain:plasma ratio of the parent drug plus the metabolite was significantly elevated to 2.6 (SD = 1.0) (95% confidence interval = 1.9-3.3). This accumulation may have implications for understanding both the therapeutic and the toxic effects of fluoxetine.

Adult↗
PubMed1991

Fast MR cardiac profiling with two-dimensional selective pulses.

A rapid-profiling NMR pulse sequence has been designed to provide an interactive, real-time cardiac probe analogous to M-mode ultrasound. The pulse sequence employs a two-dimensional (2D) selective NMR pulse to excite a narrow (nominally 1-cm-diameter) cylinder of magnetization intersecting the heart. This procedure is followed by a readout gradient applied along the length of the cylinder, or "beam," to yield an M-mode type profile with a one-dimensional Fourier transform reconstruction. k-space techniques were used to design 2D pulses which excite cylinders characterized by either Gaussian or square radial excitation profiles. Images of phantoms acquired at 1.5 T confirm the predictions of the k-space analysis. The cylinder can be displaced interactively by modulating the rf excitation and the beam axis can be reoriented to any oblique direction by changing the relative mixing of the gradient waveforms. Flow compensation using bipolar gradient waveforms inverts the contrast of flowing blood and suppresses flow artifacts. A gated cardiac image is acquired as a reference to locate the excitation axis. A series of cardiac experiments was performed on several healthy volunteers. As the beam is moved and rotated to probe the myocardium, the profile plots resemble an M-mode echocardiogram. Unlike in M-mode echocardiography, however, the axis of interrogation is not limited to specific windows, and there is distinct flexibility of contrast. However, the temporal resolution is currently less than that achieved by ultrasound. NMR M-mode profiling provides a direct, fast method of measuring heart motion to assess cardiac function as part of an MR cardiac exam.

Fourier Analysis↗
PubMed1991

Nuclear magnetic resonance microscopy of atheroma in human coronary arteries.

The purpose of this study was to use direct nuclear magnetic resonance (NMR) microscopy to quantitate and image accumulations of atheroma lipids in human coronary arteries and to validate the results by comparison with histologic preparations. NMR microscopy was performed on a superconducting experimental NMR imaging system operating at 2 Tesla with a probe designed for short echo time (TE), strong B1 field strength, and small samples. Data acquisition used multiple-offset chemical encoding with offsets based on the thermotropic spectral signature of atheroma lipids within the human arterial vessel wall. Three separate channels of image data yielded color axis display of atheroma within the vessel walls. Atheroma location by histology was identified by rarefaction of stroma, as the lipids are extracted in the process of embedding in paraffin. Perimeters, areas, and a shape index (perimeter2:4 pi area) of lumen, atheroma, and outer wall were determined and compared for NMR vs histology. There was no significant difference in the measurements with the exception of luminal shape indices, which were uniformly larger by histology, attributable to flattening of the vessels during histologic preparation. NMR measurement of atheroma content of coronary artery walls agreed well with histology (r = 0.996). NMR microscopy with color axis display proved able to quantitate and image atheroma in coronary arteries, obviating the distortions and lipid removal associated with fixation, embedding, and sectioning for histology.

Adult↗
PubMed1990

Left atrial dimensions in growth and development: normal limits for two-dimensional echocardiography.

Reference values for normal left atrial dimensions have been based primarily on blind M-mode measurements, with no reports based on two-dimensional echocardiography to provide a comprehensive analysis of the two-dimensional measurements from infancy to old age. This report analyzes the left atrial dimensions from two-dimensional echocardiographic studies in 268 normal healthy subjects to determine normal limits and relations among linear, area and volume measurements of the left atrium. The group mean values change with body size, fitting well to the exponential growth model (r = 0.78 to 0.92). The variance about the mean (which determines normal limits) is represented effectively by a quadratic function of body surface area (r = 0.84 to 0.99). The variables determined by this modeling simplify evaluation of normal limits for any body size at any desired level of confidence, and the data are useful reference standards for interpretation of two-dimensional echocardiograms.

Adult↗
PubMed1990

Echocardiographic definition of the left ventricular centroid. I. Analysis of methods for centroid calculation from a single tomogram.

Quantitation of myocardial contraction requires a frame of reference. Most investigators have sought a single reference frame per image, centered in some manner with respect to the mass of myocardium. Because there is no anatomic marker for the center of the heart, many different approaches have been pursued to identify a centroid of the left ventricle. The issue of whether the reference should be fixed throughout the cardiac cycle or float from image to image has been addressed in previous studies, but the more fundamental question of how a centroid can best be defined has not been answered. This study examines this basic issue by analysis of variance from observer to observer, cycle to cycle, animal to animal and method to method. Both endocardial and epicardial borders were digitized twice by each of two observers at 1/30 s intervals spanning the cardiac cycle for each of three cardiac cycles in six normal dogs. The left ventricular centroid was calculated by six methods: center of endocardial coordinates, center of epicardial coordinates, center of mid-myocardial (average) coordinates, center of endocardial area, center of epicardial area and center of mid-myocardial (average) area. The path of each centroid was correlated between observers and correlation coefficients were transformed for analysis of variance. This analysis indicates a best approach to centroid definition through distinct minimization of the variance: the best of the six methods proved to be center of endocardial area.

Analysis of Variance↗
PubMed1990

Echocardiographic definition of the left ventricular centroid. II. Determination of the optimal centroid during systole in normal and infarcted hearts.

Although two-dimensional echocardiography is widely used in both clinical and experimental evaluations of regional cardiac wall motion, there is no established clinical method for quantitative analysis of the wall motion, not even for the normal radial motion observed in short-axis images. Measurement of radial wall motion requires determination of a centroid from which the radii emanate. Depending on its definition, the centroid is variously affected throughout systole by cardiac translation, regional wall motion and any shift of the subject position or transducer. A floating centroid is defined relative to the ventricular walls frame by frame, whereas a fixed centroid never moves with respect to the transducer. Evaluation of the best approach to definition of a centroid was previously presented (part I, this issue). The next question is how to use the centroid. This study examines which of four centroid applications provides the best reference for quantifying regional wall motion during systole. Method 1 is a floating centroid (defined separately for every image frame), method 2 uses the end-diastolic centroid as a fixed reference for all image frames, method 3 uses the end-systolic centroid as a fixed reference and method 4 uses the average as a fixed reference. Wall motion was measured with respect to each of these centroids by determining radial wall motion from end-diastole to end-systole and correlating radial motion throughout the cardiac cycle with that in normal control hearts.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Continual NMR cardiography without gating: M-mode MR imaging.

A magnetic resonance (MR) pulse sequence was designed and implemented to examine the heart continually without gating, at rates in excess of 256 images in 7 seconds. The results are analogous to those of M-mode ultrasound, allowing interactive exploration of cardiac dynamics and flow in real time with full three-dimensional freedom of view. The technique is based on designed two-dimensional excitation pulses in which the magnetic field gradient is not constant, as in section-selection pulses, but varies in time to define a trajectory that results in a specified (eg, cylindric) region of excitation. The technique was implemented on a 1.5-T clinical imager with no special hardware and was tested on phantoms and volunteers. In human subjects, details of valve motion, intracardiac flow, and wall motion could be observed from moment to moment along optimal lines of sight selected interactively, with or without flow compensation and without gating. The momentary physiologic changes in chamber volumes and blood pool replenishment that occur during rhythm disturbances, the Valsalva maneuver, and simple breathing and breath-holding were readily demonstrated.

Adult↗
PubMed1989

Prevalence and mechanisms of mitral regurgitation in the absence of intrinsic abnormalities of the mitral leaflets.

Two hundred nineteen consecutive patients referred for echocardiography were analyzed to determine the occurrence of mitral regurgitation (MR) in the absence of intrinsic abnormalities of the mitral leaflets. MR was assessed by means of the pulsed-Doppler technique. There was a higher incidence of MR associated with absence of mitral leaflet abnormalities compared to the presence of these abnormalities (59% vs 41%, p less than 0.01). The most common causes of MR were mitral annular calcification (MAC) and incomplete mitral leaflet closure (IMLC). The extent of calcific deposit in patients with MAC and the distance from the mitral leaflet coaptation point to the mitral annular plane in systole patients with IMLC correlated well with the severity of MR by Doppler technique (rho = 0.91 and 0.71, respectively). To determine the mechanisms of MR in these two conditions, 29 consecutive patients with MAC and 28 with IMLC were referred to the echocardiography laboratory, and 10 age-matched control subjects were prospectively analyzed. Patients with MAC had a 50% reduction in the sphincteric action of the mitral anulus in systole compared to control subjects. All patients with IMLC had poor left ventricular systolic function; most had left ventricular, mitral annular, and left atrial dilation, and only eight had regional wall motion abnormalities. When discriminant function analysis was used, poor left ventricular systolic function was the principal variable that separated patients with IMLC from normal subjects (F = 81.6, p less than 0.0001). We conclude that: (1) MR in adults occurs most commonly in the absence of intrinsic abnormalities of the mitral leaflets, primarily those resulting from MAC and IMLC; (2) MR in patients with MAC results from a reduced sphincteric action of the mitral anulus in systole; and (3) IMLC results from poor left ventricular systolic function, irrespective of the cause.

Aged↗
PubMed1988

Diagnostic value for coronary artery disease of chest pain during dipyridamole-thallium stress testing.

Intravenous dipyridamole with thallium imaging permits stress testing for coronary artery disease (CAD) without exercise. Chest pain may occur with dipyridamole-thallium testing, but its diagnostic significance is uncertain. Forty-five patients who had coronary angiography, no revascularization and chest pain during dipyridamole-thallium testing were identified. These patients were matched blindly by sex and age to 45 patients who had coronary angiography, no revascularization and no chest pain reported during the dipyridamole-thallium test. In the groups with versus without chest pain, 9 versus 24% had no CAD, 16 versus 16% had 1-vessel disease, 38 versus 29% had 2-vessel CAD and 38 versus 29% had 3-vessel CAD. These differences did not achieve statistical significance. Also, there were no evident differences in the severity of angiographic CAD by vessel or by percent of stenosis (p greater than 0.50). There was only a moderate association with ischemic ST changes (40 versus 16%, p less than 0.02). Chest pain with concurrent ischemic ST changes also failed to predict any difference in distribution or severity of angiographic stenoses. We conclude that chest pain during dipyridamole-thallium testing is not closely related to the severity of CAD and has little diagnostic value.

Adult↗
PubMed1988

High-resolution 1H NMR spectral signature from human atheroma.

Coronary artery disease due to atherosclerosis takes the lives of approximately 550,000 Americans each year--an enormous toll. Put in economic terms, the cost to the United States alone has been estimated to exceed 60 billion dollars annually. We have found that well-resolved proton (1H) NMR spectra can be obtained from human atheroma (fatty plaque), despite its macroscopic solid appearance. The fraction of the total spectral intensity corresponding to the sharp 1H NMR signals is temperature dependent and approaches unity at body temperature (37 degrees C). Studies of the total lipids extracted from atheroma and cholesteryl esters were conducted to identify the chemical and physical origin of the spectral signature. The samples were characterized through assignment of their chemical shifts and by measurement of their T1 and T2 relaxation times as a function of magnetic field strength. The results suggest that the relatively sharp 1H NMR signals from human atheroma (excluding water) are due to a mixture of cholesteryl esters, whose liquid-crystalline to isotropic fluid phase transition is near body temperature. Preliminary applications to NMR imaging of human atheroma are reported, which demonstrate early fatty plaque formation within the wall of the aorta. These findings offer a basis for noninvasive imaging by NMR to monitor early and potentially reversible stages of human atherogenesis.

Aorta↗
PubMed1988

Limits of normal left ventricular dimensions in growth and development: analysis of dimensions and variance in the two-dimensional echocardiograms of 268 normal healthy subjects.

The majority of studies generating normal echocardiographic reference values for left ventricular dimensions have been based on blindly performed M-mode measurements, and there are no previous reports based on two-dimensional echocardiography that provide a comprehensive analysis of the two-dimensional measurements from infancy to old age. This report presents the results of analyzing the left ventricular internal dimensions from cross-sectional echocardiographic studies on 268 normal healthy subjects (none were hospitalized for any reason) whose ages ranged from 6 days to 76 years. The mean data are reported as functions of body surface area and, in addition, the variance is modeled as a function of body surface area to provide an accurate and clinically useful determination of normal limits and to model changes in the cardiac dimensions and in their variance representing normal growth and development. The data fit well to the exponential growth model (r values 0.85 to 0.95). Variance about the central values also depended significantly on body size; that relation is represented effectively by a quadratic function of body surface area (r values 0.82 to 0.98). The model parameters allow calculation of normal limits at any desired level of confidence. Areas determined by hand planimetry have significantly greater variance compared with variance of linear dimensions, and also compared with variance of cross-sectional area using ellipses generated from the anteroposterior and mediolateral dimensions. This implies that either biologic variations in the amount of infolding or errors in freehand planimetry constitute a significant source of variance; this may be remedied by filtering out high frequency oscillations of contour. There is no significant difference in midnormal values and confidence limits for corresponding dimensions measured from orthogonal views. Furthermore, the anteroposterior and mediolateral dimensions of the left ventricle superimpose at each body size, consistent with circular cross section for normal subjects throughout growth and development. The data presented should comprise a useful set of reference standards for interpretation of cross-sectional echocardiograms.

Adolescent↗
PubMed1987

High-resolution proton NMR spectra of human arterial plaque.

Well-resolved proton (1H) NMR spectra of solid human arterial plaque can be acquired. Studies have been carried out of human fatty plaque obtained postmortem (ex vivo), the total lipids extracted from human atheroma, and a model mixture of cholesteryl esters whose lipid composition resembles that of human atheroma. In each case, well-resolved 1H NMR spectra were obtained at body temperature (37 degrees C), with little or no underlying broad signal. Such sharp 1H NMR spectra are typical of isotropic fluids, whereas solid and liquid-crystalline materials give rise to much broader spectral lines. The results suggest the sharp 1H NMR spectra of human atheromatous lesions at body temperature are due largely to the presence of intracellular and extracellular droplets of cholesteryl esters in the isotropic liquid phase. These findings provide a necessary basis for use of 1H NMR techniques to image quantitatively the lipid constituents of human atheroma in vivo, and to study their chemical and physical properties.

Adult↗
PubMed1987

Doppler measurement of left atrial depressurization and mitral valve area in patients with suspected mitral stenosis: validation of a new method.

Atrial depressurization time measurement by Doppler ultrasound can be used to quantify stenotic mitral valve area. In this report, we present the results of a blinded trial comparing the standard Doppler method for "pressure half-time" (A) and another Doppler method we devised (B) for measurement of atrial depressurization time. Both methods were tested against valve area data from catheterization performed within 24 hours after Doppler echocardiography. Ten readers analyzed each of 10 Doppler profiles by methods A and B, in random order. After decoding, each of the 200 Doppler readings was compared to the catheterization result. Method B proved more accurate than method A by repeated measures analysis of variance (p less than 0.0001). Furthermore, method B took less than half as long to perform (p less than 0.0001). The methods presented herein provide a simple alternative means to follow the progression of mitral stenosis noninvasively and to determine optimal timing for surgery.

Heart Atria↗
PubMedDate not supplied

Rapid NMR cardiography with a half-echo M-mode method.

A real-time NMR cardiac profiling pulse sequence has been developed that incorporates two-dimensional (2D) selective excitation and a half-echo readout. The time resolution has been improved by a factor of two relative to the previous flow-compensated, full-echo version. The technique produces a 2D plot of "beam"-axis position versus time, analogous to M-mode echocardiography. In human subjects, details of valve leaflet motion, intracardiac flow, wall motion, and wall thickening may be observed along optimal lines of sight selected interactively. The pulse sequence uses a low-tip-angle 2D selective-excitation pulse derived from a spiral k-space trajectory to excite a narrow cylinder of magnetization, followed by a half-echo readout gradient oriented along the axis of the cylinder. One-dimensional Fourier transformation of the acquired signal results in a magnetization profile along the length of the cylinder, or beam. The pulse sequence is effectively flow compensated without any additional gradient lobes, because the rapid oscillation in the gradient wave forms of the 2D excitation pulse produces relatively small net gradient moments, and the shortened readout gradient has minimal first-order moment relative to center echo. The signal from moving blood can alternatively be velocity encoded by the addition of bipolar gradients along any of the three axes, producing Doppler-like traces of intracardiac blood flow.

Echocardiography↗