Chris D. Constantinides

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A method is proposed to estimate signal-to-noise ratio (SNR) values in phased array magnitude images, based on a region-of-interest (ROI) analysis. It is shown that the SNR can be found by correcting the measured signal intensity for the noise bias effects and by evaluating the noise variance as the mean square value of all the pixel intensities in a chosen(More)
PURPOSE To use sodium 23 magnetic resonance (MR) imaging to quantify noninvasively total sodium in human muscle and to apply the technique in exercise and musculoskeletal disease. MATERIALS AND METHODS Total [Na] sodium was determined from the ratio of the relaxation-corrected (23)Na signal intensities measured from short echo-time (0.4 msec) (23)Na(More)
The transport of sodium and potassium between the intra- and extracellular pools and the maintenance of the transmembrane concentration gradients are important to cell function and integrity. The early disruption of the sodium pump in myocardial infarction in response to the exhaustion of energy reserves following ischemia and reperfusion results in(More)
A new iterative extrapolation image reconstruction algorithm is presented, which enhances low resolution metabolic magnetic resonance images (MRI) with information about the bounds of signal sources obtained from a priori anatomic proton ((1)H) MRI. The algorithm ameliorates partial volume and ringing artefacts, leaving unchanged local metabolic(More)
RATIONALE AND OBJECTIVES The purpose of this study was to examine the metabolic basis for magnetic resonance (MR) spectroscopic imaging findings in focal brain lesions of patients with acquired immunodeficiency syndrome (AIDS). MATERIALS AND METHODS The authors combined MR spectroscopic imaging with [11C-methyl]thymidine positron emission tomography (PET)(More)
A prototype cardiac phased array receiver coil was constructed that comprised a cylindrical array and a separate planar array. Both arrays had two coil loops with the same coil dimensions. Data acquisition with the cylindrical array placed on the human chest, and the planar array placed under the back, yielded an overall enhancement of the signal-to-noise(More)
Despite their proven gains in signal-to-noise ratio and field-of-view for routine clinical MRI, phased-array detection systems are currently unavailable for nuclei other than protons (1H). A broadband phased-array system was designed and built to convert the 1H transmitter signal to the non-1H frequency for excitation and to convert non-1H phased-array MRI(More)
An intravascular iron-based contrast agent was used as a sodium (23Na) MRI T2 relaxant in an effort to suppress the blood signal from the ventricular cavities in normal and infarcted canine myocardium in vivo. 23Na MRI signal decreases in blood were attributed to decreases in the fast (T2f) and slow (T2s) transverse relaxation components, which were(More)
Adenosine triphosphate (ATP) is the body's basic energy currency. It provides energy for muscular contraction in the heart, and for sodium ion transport from the intra-celhflar to the extra-celhflar pools, which is basic to cell function and integrity. The ATP is supplied by oxidative phosphorylation, and, during periods of myocardial ischemia, via the(More)