Magnetic resonance imaging
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The apparent diffusion coefficient (ADC) of water is a sensitive indicator of water and ion homeostasis of brain. Resuscitation of the brain after cardiac arrest, the most frequent reason for global cerebral ischemia under clinical conditions, depends critically on the reversal of disturbances of water and ion homeostasis. We, therefore, investigated whether ADC imaging can be used to monitor the development and reversal of ischemic brain injury during and after cardiac arrest. ⋯ Failure of cardiac resuscitation prevented ADC normalization and led to its further decline to below 50% of control. Postcardiac arrest normalization of ADC maps correlated with homogeneous return of ATP, glucose, and lactate to near normal, whereas failure of ADC normalization was associated with depletion of ATP and glucose and severe lactate accumulation. In conclusion, our data indicate, that normalization of ADC is a reliable indicator of cerebral recovery after resuscitation from cardiac arrest.
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Comparative Study
Localized 2D J-resolved 1H MR spectroscopy: strong coupling effects in vitro and in vivo.
A two-dimensional (2D) J-resolved MR spectroscopy sequence (2D J-PRESS), fully localized in three dimensions, has been implemented on a whole-body MR scanner. A modified PRESS sequence with [90 degrees-180 degrees-t1/2-180 degrees-t1/2-acquisition] was used for voxel localization. An incremental delay (t1/2) was added to the intervals before and after the last slice-selective 180 degree RF pulse to monitor the J-evolution in a localized 2D MR spectrum. ⋯ In conformity with previously reported results, additional cross-peaks due to strong coupling were monitored in many metabolites. A brain phantom was developed to mimic the gray matter of human brain with the metabolites at physiological concentrations (0.5-12 mM). In vivo 2D J-PRESS spectra (n = 18) of healthy human brain were in conformity with those recorded from the brain phantom.
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Comparative Study
The pulmonary artery acceleration time determined with the MR-RACE-technique: comparison to pulmonary artery mean pressure in 12 patients.
The goal of our study was to evaluate a rapid noninvasive MR technique for quantification of the pulmonary artery acceleration time (PAT) and other parameters of pulmonary hemodynamics and to correlate with pulmonary artery mean pressure (mPAP). The PAT known as "time-to-peak" out of Doppler echocardiographic measurements normally shows significant inverse correlation with mPAP. With the MR-RACE-Technique (RACE: Real time ACquisition and Evaluation of motion) blood velocity measurements can be obtained with a total acquisition time of a few seconds. ⋯ To explore the relationship between PAT and mPAP, right heart catheterization and MR-RACE measurements were performed in 12 patients with different pulmonary vascular abnormalities. Results of MR-RACE were compared with those of mPAP measured by right heart catheter and showed significant inverse correlation (r = -0.82, p = .0011, n = 12). The ability of MR-RACE to enable measurements of blood flow with profiles may be important for characterizing pulmonary and cardiovascular abnormalities.
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Time of flight, reduced matrix (64 x 256) MR angiography of the neck veins was performed in four normal subjects and four patients with neck vein thrombosis, either from indwelling catheters (n = 3) or intravenous drug abuse (n = 1). In each case, satisfactory images were acquired. Typical examination times of 3-6 min were required. MR angiography of neck veins gives a unique display of venous anatomy, including collateral veins and occlusions.
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Short echo time, single voxel localized proton spectroscopy was accomplished using a stimulated echo (STEAM) sequence running on a Siemens 1.5-T system with a head coil incorporating the Z and Y gradients. Spectra from the temporal lobe, the cerebellum and mid brain were acquired from a group of normal volunteers using the following parameters: voxel size = 8 ml, TE = 22 msec, 512 signal averages and TR = 1.7 sec. STEAM spectra acquired with the small diameter gradients showed significantly fewer artifacts at short TE, allowing the observation of glutamate/glutamine, GABA, taurine, and inositol in addition to the prominent resonance of choline, creatine/phosphocreatine and N-acetylaspartate (NAA). The levels of chlorine, creatine and NAA were found to be significantly different in the three regions of the brain examined.