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Normal Human Subjects (normal + human_subject)
Selected AbstractsDoppler Superior Vena Cava Flow Evolution and Respiratory Variation in Superior Vena Cava SyndromeECHOCARDIOGRAPHY, Issue 4 2008Fa Qin Lv M.D. Background: Superior vena cava syndrome (SVCS) is a clinical expression of obstruction of blood flow through the superior vena cava. The patterns of the Doppler flow changes of superior vena cava (SVC), especially the respiratory effects on them have not yet been fully elucidated. This study was to examine SVC Doppler flow patterns and the respiratory effects on them in healthy subjects and patients with SVCS. Methods: The SVC Doppler flow patterns of 18 normal human subjects and 22 patients with SVCS were analyzed at initial diagnosis and were followed up every 2 months for at least 11 months. Results: Among the 22 patients, 5 patients with the tumor near the right atrium oppressing the inferior segment of the SVC had clear VR- and AR-waves, while in the other 17 patients the VR- and AR-waves disappeared or their outlines were vague. The respiratory variations of the S- and D-waves as a percentage change in inspiration compared to expiration in patient group were much lower than those in control group (S-wave: 1.67 ± 3.32% vs. 15.65 ± 16.15%, P = 0.0003; D-wave: 1.80 ± 1.12% vs. 23.55 ± 37%, P = 0.0087), which gradually became larger with treatment and showed no significant difference with those in control group after 7 months. Conclusions: The Doppler flows of the patients with SVCS correlate well with the images of CT scan of them. The respiratory variation of the S- and D-velocities could be used to evaluate the severity of SVC obstruction and its therapeutic effect. [source] MRI diffusion tensor tracking of a new amygdalo-fusiform and hippocampo-fusiform pathway system in humansJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2009Charles D. Smith MD Abstract Purpose To use MRI diffusion-tensor tracking (DTT) to test for the presence of unknown neuronal fiber pathways interconnecting the mid-fusiform cortex and anteromedial temporal lobe in humans. Such pathways are hypothesized to exist because these regions coactivate in functional MRI (fMRI) studies of emotion-valued faces and words, suggesting a functional link that could be mediated by neuronal connections. Materials and Methods A total of 15 normal human subjects were studied using unbiased DTT approaches designed for probing unknown pathways, including whole-brain seeding and large pathway-selection volumes. Several quality-control steps verified the results. Results Parallel amygdalo-fusiform and hippocampo-fusiform pathways were found in all subjects. The pathways begin/end at the mid-fusiform gyrus above the lateral occipitotemporal sulcus bilaterally. The superior pathway ends/begins at the superolateral amygdala. The inferior pathway crosses medially and ends/begins at the hippocampal head. The pathways are left-lateralized, with consistently larger cross-sectional area, higher anisotropy, and lower minimum eigenvalue (D-min) on the left, where D-min assesses intrinsic cross-fiber diffusivity independent of curvature. Conclusion A previously-undescribed pathway system interconnecting the mid-fusiform region with the amygdala/hippocampus has been revealed. This pathway system may be important for recognition, memory consolidation, and emotional modulation of face, object, and lexical information, which may be disrupted in conditions such as Alzheimer's disease. J. Magn. Reson. Imaging 2009. © 2009 Wiley-Liss, Inc. [source] Simple anatomical measurements do not correlate significantly to individual peripheral nerve stimulation thresholds as measured in MRI gradient coilsJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2003Blaine A. Chronik PhD Abstract Purpose To examine peripheral nerve stimulation (PNS) thresholds for normal human subjects in magnetic resonance imaging (MRI) gradient coils, and determine if observed thresholds could be predicted based on gross physiologic measurements. Materials and Methods PNS thresholds for 21 healthy normal subjects were measured using a whole-body gradient coil. Subjects were exposed to a trapezoidal echo-planar imaging (EPI) gradient waveform and the total change in gradient strength (,G) required to cause PNS as a function of the duration of the gradient switching time (,) were measured. Correlation coefficients and corresponding P values were calculated for the PNS threshold measurements against simple physiologic measurements taken of the subjects, including weight, height, girth, and average body fat percentage, in order to determine if there were any easily observable dependencies. Results No convincing correlations between threshold parameters and gross physiologic measurements were observed. Conclusion These results suggest it is unlikely that a simple physiologic measurement of subject anatomy can be used to guide the operation of MRI scanners in a subject-specific manner in order to increase gradient system performance while avoiding PNS. J. Magn. Reson. Imaging 2003;17:716,721. © 2003 Wiley-Liss, Inc. [source] Cardiac diffusion MRI without motion effectsMAGNETIC RESONANCE IN MEDICINE, Issue 1 2002Jiangang Dou Abstract We present a method for diffusion tensor MRI in the beating heart that is insensitive to cardiac motion and strain. Using a stimulated echo pulse sequence with two electrocardiogram (ECG) triggers, diffusion-encoding bipolar gradient pulses are applied at identical phases in consecutive cardiac cycles. In this experiment, diffusion is encoded at a single phase in the cardiac cycle of less than 30 ms in duration. This encoding produces no phase shifts for periodic motion and is independent of intervening strains. Studies in a gel phantom with cyclic deformation confirm that by using this sequence we can map the diffusion tensor free of effects of cyclic motion. In normal human subjects, myocardial diffusion eigenvalues measured with the present method showed no significant change between acquisitions encoded at maximum contractile velocity (peak) vs. at myocardial standstill (end-systole), demonstrating motion independence of in vivo diffusion measurements. Diffusion tensor images acquired with the present method agree with registered data acquired with a previous cardiac diffusion MRI method that was shown to be valid in the normal heart, strongly supporting the validity of MRI diffusion measurement in the beating heart. Myocardial sheet and fiber dynamics measured during systole showed that normal human myocardial sheet orientations tilt toward the radial during systole, and fiber orientations tilt toward the longitudinal, in qualitative agreement with previous invasive studies in canines. These results demonstrate the technique's ability to measure myocardial diffusion accurately at any point in the cardiac cycle free of measurable motion effect, as if the heart were frozen at the point of acquisition. Magn Reson Med 48:105,114, 2002. © 2002 Wiley-Liss, Inc. [source] Anisotropy in high angular resolution diffusion-weighted MRI ,MAGNETIC RESONANCE IN MEDICINE, Issue 6 2001Lawrence R. Frank Abstract The diffusion in voxels with multidirectional fibers can be quite complicated and not necessarily well characterized by the standard diffusion tensor model. High angular resolution diffusion-weighted acquisitions have recently been proposed as a method to investigate such voxels, but the reconstruction methods proposed require sophisticated estimation schemes. We present here a simple algorithm for the identification of diffusion anisotropy based upon the variance of the estimated apparent diffusion coefficient (ADC) as a function of measurement direction. The rationale for this method is discussed, and results in normal human subjects acquired with a novel diffusion-weighted stimulated-echo spiral acquisition are presented which distinguish areas of anisotropy that are not apparent in the relative anisotropy maps derived from the standard diffusion tensor model. Magn Reson Med 45:935,939, 2001. Published 2001 Wiley-Liss, Inc. [source] Relaxation times of choline, creatine and N -acetyl aspartate in human cerebral white matter at 1.5 TNMR IN BIOMEDICINE, Issue 3 2002D. R. Rutgers Abstract Several studies have investigated the T1 and T2 relaxation time of choline, creatine and N -acetyl aspartate in cerebral white matter in normal human subjects. However, these studies demonstrate a large variation in T1 and T2 values. In the present study, relaxation times of choline, creatine and N -acetyl aspartate were determined in cerebral white matter in 15 control subjects (age 21,±,2 y, mean,±,SD) at 1.5 T. Using PRESS, seven or eight data points were obtained to fit the T1 and T2 relaxation curves to, respectively. The mean voxel size was 14,cm3. The T1 relaxation times of choline, creatine and N -acetyl aspartate were 1091,±,132 (mean,±,SD), 1363,±,137 and 1276,±,132,ms. The T2 relaxation times were 352,±,52, 219,±,29 and 336,±,46,ms, respectively. Copyright © 2002 John Wiley & Sons, Ltd. [source] Phonation threshold pressure estimation using electroglottography in an airflow redirection systemTHE LARYNGOSCOPE, Issue 12 2009Adam L. Rieves BS Abstract Objectives/Hypothesis: The present study proposed to estimate phonation threshold pressure (PTP) noninvasively using airflow redirection into a pneumatic capacitance system. Study Design: Prospective study. Methods: Subjects phonated into the device, which interrupts airflow mechanically and redirects the flow into a pneumatic capacitor. Five interruptions were effected per trial. PTP was estimated as the difference between subglottal pressure (SGP) and transglottal pressure at phonation offset. The novel method was tested for consistency in 20 normal human subjects at low (75 dB) and high (85 dB) sound pressure levels. The device was tested for validity on a tracheotomy patient. Results: Mean SGP was 9.02 ± 3.27 cm H2O, and mean PTP was 3.68 ± 1.41 cm H2O. Intrasubject coefficient of variation, a measure of intrasubject consistency, was 0.33 ± 0.23. Statistically significant differences existed between the means of SGP but not PTP at 75 dB and 85 dB. The correlation coefficient between accepted and experimental SGP in a tracheotomy patient was 0.947 (P < .001). Conclusions: Measurements corresponded well to previously reported values, and intrasubject variability was low, indicating the device was consistent. Testing on a tracheotomy patient demonstrated validity. More research is needed to determine the sensitivity and specificity of the device in differentiating between normal and pathological voices. This device may have clinical application as a noninvasive and reliable method of estimating PTP and indicating that laryngeal health is likely abnormal. Laryngoscope, 2009 [source] 3122: Regulation of retinal tissue oxygenationACTA OPHTHALMOLOGICA, Issue 2010CJ POURNARAS Purpose To evaluate the changes in the retinal oxygen partial pressure (PO2) following physiological stimuli. Methods Evaluation of either the preretinal and intraretina partial pressure of oxygen (PO2) distribution, using oxygen sensitive microelectrodes, in various animal models. Measurements were obtained during changes of the perfusion pressure, systemic hyperoxia, hypoxia, hypercapnia, carbogen breathing and following carbonic anydrase inhibitors use. Results The oxygen tension (PO2) in the inner half of the retina remains largely unaffected by moderate changes in perfusion pressure. The increase of the systemic PaO2 through breathing of 100% O2 (hyperoxia) induces endothelin (ET) mediated marked vasoconstriction of the inner retinal arterioles in both anesthetized animals and normal human subjects. The regulatory vasoconstriction maintains the PO2 in retinal tissue constant. A decrease in PaO2 (hypoxia) induces a vasodilation of the retinal arterioles through endothelium-derived NO release. As a result, trans-retinal PO2 profiles made during steps of systemic hypoxia have shown that the values measured in the inner retina up to half of its thickness, remain rather stable. By contrast, the PO2 values, measured close to the choroid and in the outer retina, decrease in a linear manner with the decrease of the PaO2. An increase in the PaCO2 (hypercapnia) of arteriolar blood, produces an increase in retinal blood flow and retinal tissue PO2. Intravenous injection of acetazolamide (carbonic anhydrase inhibitor) produces an increase in preretinal PO2 due to dilation of the retinal vessels Conclusion Thanks to the autoregulatory capability of the retinal circulation, the oxygen tension (PO2) in the inner half of the retina, remains largely unaffected during physiological stimuli. 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