bluuebunny/crossref_metadata_2025_split huggingface dataset:
Expression and localization of P‐, K‐, and OB‐cadherin in the prepubertal rat ovary
Authors: Machell Naomi H. , Blaschuk Orest W. , Farookhi Riaz 
Published: August 2002

AbstractClassical and atypical cadherins mediate calcium‐dependent cell adhesion and play an important role in morphogenetic processes. We have shown, previously, N‐ and E‐cadherin expression in the rat ovary. This expression, however, was not associated with specific follicle‐restructuring events such as antrum formation and segregation of mural from cumulus granulosa cells suggesting that other cadherins may serve this function. In this study, RT‐PCR and immunostaining techniques showed that three other cadherins are expressed throughout prepubertal ovarian development in the rat: one classical (P‐) cadherin, and two atypical (K‐ and OB‐) cadherins. RT‐PCR analysis of isolated ovarian tissue compartments (granulosa cells and the residual ovarian tissue) agreed with the immunostaining results. Immunostaining showed P‐ and K‐cadherin expression by granulosa, as well as thecal/interstitial cells, and also in oocytes of primordial follicles. P‐cadherin expression was absent in oocytes of follicles in later stages of development compared to K‐cadherin, which was found in oocytes at all stages of folliculogenesis. P‐, K‐, and OB‐cadherin were expressed by the ovarian surface epithelial cells of neonatal animals but only P‐ and OB‐cadherin expression were maintained in these cells in 25 day‐old animals. Cellular OB‐cadherin staining was absent in follicles at all stages of development and its expression was restricted to the ovarian hilar region and portions of the stroma. In summary, cadherin expression and distribution profiles changed during ovarian growth and folliculogenesis suggesting a role for cadherins in organizational and morphogenetic processes within the developing rat ovary. Mol. Reprod. Dev. 61: 142–154, 2002. © 2002 Wiley‐Liss, Inc.
Perinatal infection, fetal inflammatory response, white matter damage, and cognitive limitations in children born preterm
Authors: Dammann Olaf , Kuban Karl C. K. , Leviton Alan 
Published: August 2002

AbstractOnly sparse information is available about a possible association between antenatal infection outside the brain and subsequent cognitive limitations among preterm infants. Based on published studies, we provide a theoretical schema that links them via the fetal inflammatory response and neonatal white matter damage. We conclude that the relationship between antenatal infection and cognitive limitations deserves much further attention by researchers interested in the prevention of this undesirable outcome of prematurity. MRDD Research Reviews 2002;8:46–50. © 2002 Wiley‐Liss, Inc.
Neurological and developmental effects of HIV and AIDS in children and adolescents
Authors: Mitchell Wendy 
Published: August 2002

AbstractHIV‐related encephalopathy is an important problem in vertically infected children with HIV. Infected infants may manifest early, catastrophic encephalopathy, with loss of brain growth, motor abnormalities, and cognitive dysfunction. Even without evidence of AIDS, infected infants score lower than serorevertors on developmental measures, particularly language acquisition. Children with perinatal or later transfusion‐related infection generally are roughly comparable developmentally to their peers until late in their course. Symptoms similar to adult AIDS dementia complex are occasionally seen in adolescents with advanced AIDS, including dementia, bradykinesia, and spasticity. Opportunistic CNS infections such as toxoplasmosis and progressive multifocal leukoencephalopathy are less common in children and adolescents than in adults. Increasing evidence suggests that aggressive antiretroviral treatment may halt or even reverse encephalopathy. Neuroimaging changes may precede or follow clinical manifestations, and include early lenticulostriate vessel echogenicity on cranial ultrasound, calcifying microangiopathy on CT scan, and/or white matter lesions and central atrophy on MRI. Differential diagnosis of neurological dysfunction in an HIV‐infected infant includes the effects of maternal substance abuse, other CNS congenital infections, and other causes of early static encephalopathy. Initial entry of HIV into the nervous system occurs very early in infection. The risk of clinical HIV encephalopathy increases with very early age of infection and with high viral loads. Virus is found in microglia and brain derived macrophages, not neurons. The neuronal effect of HIV is probably indirect, with various cytokines implicated. Apoptosis is the presumed mechanism of damage to neurons by HIV. MRDD Research Reviews 2001;7:211–216. © 2001 Wiley‐Liss, Inc.
Scan time reduction in proton magnetic resonance spectroscopic imaging of the human brain
Authors: Golay Xavier , Gillen Joseph , van Zijl Peter C.M. , Barker Peter B. 
Published: August 2002

AbstractA simple technique is described for scan time reductions in proton magnetic resonance spectroscopic imaging (MRSI) of the human brain. Scan time is reduced by approximately 35% while preserving spatial resolution by reducing the field of view (FOV) and number of phase‐encoding steps in the transverse direction of the brain. A multislice MRSI of the brain is demonstrated which takes approximately 20 min with a square FOV, and 13 min with a reduced FOV. The signal‐to‐noise ratio (SNR) in the reduced FOV scan was measured to be 15% lower than that of the full FOV scan, which is close to the expected theoretical value of 19% based on the square root of the scan time. The method can be applied with any sequence, and requires minimal software and no hardware modifications. Scan time in MRSI is minimized in this method by using FOVs no larger than the dimensions of the object to be imaged. The method may also be combined with other fast MRSI techniques to provide further scan time reductions. Magn Reson Med 47:384–387, 2002. © 2002 Wiley‐Liss, Inc.
Signal recovery in free induction decay imaging using a stimulated spin echo
Authors: Hsu Jung‐Jiin , Lowe Irving J. 
Published: August 2002

AbstractA novel pulse sequence for acquiring a stimulated spin echo (SSE) is devised and implemented to recover the initial portion of the signal that is usually blanked or distorted in MRI using free induction decays (FIDs). The receiver‐phase offset, center of the k‐space, and time frame coordinates of the FID data points can be accurately determined from the SSE. A simple numerical method of signal recovery is formulated which can merge the FID and the SSE data for higher extrapolation accuracy. The application of the signal recovery method is demonstrated using the rotating ultrafast imaging sequence (RUFIS). The result shows the importance of experimentally finding the correct time origin of the FID signal. Magn Reson Med 47:409–414, 2002. © 2002 Wiley‐Liss, Inc.
Combined MR proton lung perfusion/angiography and helium ventilation: Potential for detecting pulmonary emboli and ventilation defects
Authors: Zheng Jie , Leawoods Jason C. , Nolte Mark , Yablonskiy Dmitriy A. , Woodard Pamela K. , Laub Gerhardt , Gropler Robert J. , Conradi Mark S. 
Published: August 2002

AbstractThree‐dimensional (3D) perfusion imaging allows the assessment of pulmonary blood flow in parenchyma and main pulmonary arteries simultaneously. MRI using laser‐polarized 3He gas clearly shows the ventilation distribution with high signal‐to‐noise ratio (SNR). In this report, the feasibility of combined lung MR angiography, perfusion, and ventilation imaging is demonstrated in a porcine model. Ultrafast gradient‐echo sequences have been used for 3D perfusion and angiographic imaging, in conjunction with the use of contrast agent injections. 2D multiple‐section 3He imaging was performed subsequently by inhalation of 450 ml of hyperpolarized 3He gas. The MR techniques were examined in a series of porcine models with externally delivered pulmonary emboli and/or airway occlusions. With emboli, perfusion deficits without ventilation defects were observed; airway occlusion resulted in matched deficits in perfusion and ventilation. High‐resolution MR angiography can unambiguously reveal the location and size of the blood emboli. The combination of the three imaging methods may provide complementary information on abnormal lung anatomy and function. Magn Reson Med 47:433–438, 2002. © 2002 Wiley‐Liss, Inc.
Multishot EPI‐SSFP in the heart
Authors: Herzka Daniel A. , Kellman Peter , Aletras Anthony H. , Guttman Michael A. , McVeigh Elliot R. 
Published: August 2002

AbstractRefocused steady‐state free precession (SSFP), or fast imaging with steady precession (FISP or TrueFISP), has recently proven valuable for cardiac imaging because of its high signal‐to‐noise ratio (SNR) and excellent blood–myocardium contrast. In this study, various implementations of multiecho SSFP or EPI‐SSFP for imaging in the heart are presented. EPI‐SSFP has higher scan‐time efficiency than single‐echo SSFP, as two or more phase‐encode lines are acquired per repetition time (TR) at the cost of a modest increase in TR. To minimize TR, a noninterleaved phase‐encode order in conjunction with a phased‐array ghost elimination (PAGE) technique was employed, removing the need for echo time shifting (ETS). The multishot implementation of EPI‐SSFP was used to decrease the breath‐hold duration for cine acquisitions or to increase the temporal or spatial resolution for a fixed breath‐hold duration. The greatest gain in efficiency was obtained with the use of a three‐echo acquisition. Image quality for cardiac cine applications using multishot EPI‐SSFP was comparable to that of single‐echo SSFP in terms of blood–myocardium contrast and contrast‐to‐noise ratio (CNR). The PAGE method considerably reduced flow artifacts due to both the inherent ghost suppression and the concomitant reduction in phase‐encode blip size. The increased TR of multishot EPI‐SSFP led to a reduced specific absorption rate (SAR) for a fixed RF flip angle, and allowed the use of a larger flip angle without increasing the SAR above the FDA‐approved limits. Magn Reson Med 47:655–664, 2002. Published 2002 Wiley‐Liss, Inc.
Quantification of myocardial blood flow and blood flow reserve in the presence of arterial dispersion: A simulation study
Authors: Schmitt Melanie , Viallon Magalie , Thelen Manfred , Schreiber Wolfgang G. 
Published: August 2002

AbstractMyocardial blood flow (MBF) can be quantified using dynamic T1‐weighted MRI of diffusible tracers and a mathematical model of underlying vasculature. Quantification of MBF by means of T1‐ weighted MRI requires knowledge of the arterial input function (AIF). The AIF can be estimated from the left ventricular (LV) cavity. However, dispersion may occur between the LV and the tissue of interest because of the laminar blood flow profiles, branching of venules, and because of stenosis. To evaluate the influence of dispersion on the results of MBF quantification, a simulation study was performed. The dispersion was described as a convolution of the AIF with an exponential residue function. Synthetic tissue and AIF curves were analyzed and the derived parameters fit to the simulated parameters. The results show that an unaccounted dispersion may result in a systematic underestimation of MBF up to approximately 50%. Underestimation increases with increasing dispersion and with increasing MBF. Assuming equal dispersion at rest and during hyperemia, myocardial perfusion reserve (MPR) estimates are also susceptible to underestimation of approximately 20%. An unaccounted dispersion therefore can lead to systematic underestimation of both blood flow and perfusion reserve. Magn Reson Med 47:787–793, 2002. © 2002 Wiley‐Liss, Inc.
Differential fMRI‐BOLD signal response to apnea in humans and anesthetized rats
Authors: Kannurpatti Sridhar S. , Biswal Bharat B. , Hudetz A.G. 
Published: August 2002

AbstractBlood oxygenation level dependent (BOLD) signal intensity (SI) and regional cerebral blood flow (CBF) during a 20‐s apnea stimulus in awake humans and pentobarbital‐anesthetized rats were measured to assess the usefulness of apnea in estimating cerebral vasodilatory capacity for functional MRI (fMRI) experiments. Rats were ventilated with either room air or 100% O2. While breathing room air, apnea for 20 s increased the BOLD SI in humans but decreased it in rats. However, in rats ventilated with 100% O2, BOLD SI increased upon apnea for 20 s. CBF measurements in rats using laser Doppler flowmetry (LDF) showed a 45% ± 8% increase during apnea with room air ventilation, and a 10% ± 3% increase with 100% O2. Arterial blood oxygen saturation fell from 96% ± 1% to 29% ± 5%, and cerebral tissue PO2 decreased from 15 ± 3 mmHg to 6 ± 2 mmHg by the end of 20‐s apnea in rats breathing room air. However, with 100% O2 respiration, apnea produced no change in the arterial blood oxygen saturation, which remained at 99%, but increased tissue PO2 from 35 ± 9 mmHg to 39 ± 10 mmHg. From the results obtained in rats ventilated with room air, it is concluded that apnea induces hypoxia that results in a decrease in fMRI‐BOLD signal. The signal decrease occurred despite an increase in PaCO2 and CBF. This BOLD response is the opposite of that observed in humans, who presumably do not develop hypoxia within the applied apnea period. These studies highlight the importance of the choice of ventilating gas mixture on the outcome of BOLD experiments during systemic perturbations. Magn Reson Med 47:864–870, 2002. © 2002 Wiley‐Liss, Inc.
Calculations of B1 distribution, SNR, and SAR for a surface coil adjacent to an anatomically‐accurate human body model
Authors: Collins Christopher M. , Smith Michael B. 
Published: August 2002

AbstractCalculations of the radiofrequency magnetic (B1) field, SAR, and SNR as functions of frequency between 64 and 345 MHz for a surface coil against an anatomically‐accurate human chest are presented. Calculated B1 field distributions are in good agreement with previously‐published experimental results up to 175 MHz, especially considering the dependence of field behavior on subject anatomy. Calculated SNR in the heart agrees well with theory for low frequencies (nearly linear increase with B0 field strength). Above 175 MHz, the trend in SNR with frequency begins to depend largely on location in the heart. At all frequencies, present limits on local (1 g) SAR levels are exceeded before limits on whole‐body average limits. At frequencies above 175 MHz, limits on SAR begin to be an issue in some common imaging sequences. These results are relevant for coils and subjects similar to those modeled here. Magn Reson Med 45:692–699, 2001. © 2001 Wiley‐Liss, Inc.
Proton magnetic resonance spectroscopy of Sjögren‐Larsson syndrome heterozygotes
Authors: Kaminaga Tatsuro , Mano Toshiyuki , Ono Jiro , Kusuoka Hideo , Nakamura Hironobu , Nishimura Tsunehiko 
Published: August 2002

AbstractA deficit of fatty alcohol:NAD+ oxidoreductase complex (FAO) activity has been detected in patients with the Sjögren‐Larsson syndrome (SLS). A moderate decrease in FAO activity has also been reported in heterozygote SLS subjects. Abnormal peaks were detected with proton magnetic resonance spectroscopy (1H‐MRS) in homozygote SLS subjects. The purpose of this study was to examine whether 1H‐MRS can be used to detect metabolic and/or pathological abnormalities in heterozygote SLS subjects. Four SLS heterozygotes were examined using 1H‐MRS. A moderate decrease in FAO activity was demonstrated in two of the four heterozygotes. Abnormal peaks were detected at 0.9 ppm in the spectrum from cerebral hemispheres of every heterozygote. 1H‐MRS was able to detect an abnormal accumulation of fatty alcohols and lipids, which is expected to increase due to an decrease in FAO activity or dysmyelination in heterozygote SLS subjects. Thus, 1H‐MRS is suggested to be a powerful tool in the screening of SLS heterozygotes. Magn Reson Med 45:1112–1115, 2001. © 2001 Wiley‐Liss, Inc.
Compartmentation of intracellular water in multicellular tumor spheroids: Diffusion and relaxation NMR
Authors: Smouha Eitzik , Neeman Michal 
Published: August 2002

AbstractDiffusion and relaxation of water in C6 glioma and MLS human ovarian carcinoma spheroids were measured from 1D projections acquired using a 2D diffusion‐relaxation correlation pulse sequence and processed by non‐negative least‐square (NNLS) analysis. Systematic underestimation of Is and ADCs were observed for Is/(Is + If) < 0.001. In the presence of spheroids, two apparent diffusion coefficient (ADC) compartments were observed, where ADCf, ADCs, and If, Is are the respective ADCs and signal intensities of the fast and slow compartments. These compartments differed also in their T2 relaxation (ADCs = 0.5–0.74 × 10–5 cm2/s, T2 = 36–45 ms; and ADCf = 2.2–2.8 × 10–5 cm2/s, T2 = 280–316 ms). The two ADC compartments and the slow T2 compartment were consistent with slow exchange. The fast T2 compartment showed a drift with diffusion weighting, suggesting that it represents water exchanging between compartments that differ in their ADC and T2. Both ADCs and Is were markedly attenuated with increasing diffusion time (Δ) for Δ < 100 ms, and increased at longer Δ. These results are consistent with restricted diffusion and fast relaxation of intracellular water for short diffusion time (T1′ = 46.6 ms), and with predominant extracellular contribution to ADCs at longer diffusion times. Magn Reson Med 46:68–77, 2001. © 2001 Wiley‐Liss, Inc.
Artifact due to B0 fluctuations in fMRI: Correction using the k‐space central line
Authors: Durand Emmanuel , van de Moortele Pierre‐François , Pachot‐Clouard Mathilde , Le Bihan Denis 
Published: August 2002

AbstractMagnetic resonance experiments require the main magnetic field, B0, to remain very stable. Several external sources, such as moving ferromagnetic objects and/or changing electromagnetic fields, can significantly change the value of B0 over time. This work describes an apparent displacement along the phase‐encoding axis caused by a variation in B0. This artifact was observed in fMRI images acquired with EPI. The effect was characterized and tested using an immobile phantom. The image displacement motion along the phase‐encoding axis closely followed the changes in B0. The phase of the central line in the Fourier space was successfully used to correct this artifact. Fluctuations in B0 may result in artifacts that mimic subject head motion, and must be appropriately corrected. Magn Reson Med 46:198–201, 2001. © 2001 Wiley‐Liss, Inc.
Cerebral perfusion during anesthesia with fentanyl, isoflurane, or pentobarbital in normal rats studied by arterial spin‐labeled MRI
Authors: Hendrich Kristy S. , Kochanek Patrick M. , Melick John A. , Schiding Joanne K. , Statler Kimberly D. , Williams Donald S. , Marion Donald W. , Ho Chien 
Published: August 2002

AbstractThe influence of anesthetic agents on cerebral blood flow (CBF) was tested in normal rats. CBF is quantified with arterial spin‐labeled MRI in rats anesthetized with either an opiate (fentanyl), a potent inhalation anesthetic agent (isoflurane), or a barbiturate (pentobarbital) using doses commonly employed in experimental paradigms. CBF values were found to be about 2.5–3 times lower in most regions analyzed during anesthesia with either fentanyl (with N2O/O2) or pentobarbital vs. isoflurane (with N2O/O2), in agreement with findings utilizing invasive measurement techniques. CBF was heterogeneous in rats anesthetized with isoflurane (with N2O/O2), but relatively homogeneous in rats anesthetized with either fentanyl (with N2O/O2) or pentobarbital, also in agreement with studies using other techniques. Magn Reson Med 46:202–206, 2001. © 2001 Wiley‐Liss, Inc.
Effect of graded hypo‐ and hypercapnia on fMRI contrast in visual cortex: Quantification of T changes by multiecho EPI
Authors: Posse Stefan , Kemna Lars J. , Elghahwagi Barbara , Wiese Stefan , Kiselev Valerij G. 
Published: August 2002

AbstractThe sensitivity of functional magnetic resonance imaging (fMRI) in visual cortex to graded hypo‐ and hypercapnia was quantified in 10 normal subjects using single‐shot multiecho echo‐planar imaging (Turbo‐PEPSI) with eight equidistant echo times (TEs) between 12 and 140 ms. Visual stimulation was combined with controlled hyperventilation and carbon dioxide inhalation to perform fMRI at six levels of end‐expiratory pCO2 (PETCO2) between 20 and 70 mm Hg. T in visual cortex during baseline conditions (light off) increased nonlinearly from 20 to 70 mm Hg, from 61.1 ± 4.2 ms to 72.0 ± 4.6 ms. Changes in T due to visual stimulation increased 2.1‐fold, from 1.2 ± 0.6 ms at 20 mm Hg to 2.5 ± 0.7 ms at 50 mm Hg. An almost complete loss of functional contrast was measured at 70 mm Hg. The model of MR signal dephasing by Yablonskiy and Haacke (Mag Reson Med 1994;32:749–763) was used to predict changes in cerebral blood flow (CBF), which were found to be consistent with results from previous positron emission tomography (PET) studies. This study further emphasizes that global CBF changes (due to PETCO2 changes even in the physiological range) strongly influence fMRI contrast and need to be controlled for. Magn Reson Med 46:264–271, 2001. © 2001 Wiley‐Liss, Inc.
A comparison between human magnetostimulation thresholds in whole‐body and head/neck gradient coils
Authors: Chronik Blaine A. , Rutt Brian K. 
Published: August 2002

AbstractGradient coil magnetostimulation thresholds were measured in a group of 20 volunteers in both a whole‐body gradient coil and a head/neck gradient coil. Both coils were operated using both x and y axes simultaneously (xy oblique mode). The waveform applied was a 64‐lobe trapezoidal train with 1‐ms flat‐tops and varying rise times. Thresholds were based on the subjects' perception of stimulation, and painful sensations were not elicited. Thresholds were expressed in terms of the total gradient excursion required to cause stimulation as a function of the duration of the excursion. Thresholds for each subject were fit to a linear model, and values for the threshold curve slope (SRmin) and vertical axis intercept (ΔGmin) were extracted. For the body coil, the mean values were: SRmin = 62.2 mT/m/ms, ΔGmin = 44.4 mT/m. For the head/neck coil, the mean values were: SRmin = 87.3 mT/m/ms, ΔGmin = 78.9 mT/m. These curve parameters were combined with calculated values for the induced electric field as a function of position within the coil to yield the tissue specific parameters Er (electric field rheobase) and τc (chronaxie). For tissue stimulated within the body coil, the mean values were: Er = 1.8 V/m, τc = 770 μs. For tissue stimulated within the head/neck coil, the mean values were: Er = 1.3 V/m, τc = 1100 μs. Scalar potential contributions were not included in the calculation of induced electric fields. The mean threshold curves were combined with the gradient system performance curves to produce operational limit curves. The operational limit curves for the head/neck coil system were verified to be higher than those of the whole‐body coil; however, the head/neck system was also found to be physiologically limited over a greater range of its operation than was the body coil. Subject thresholds between the two coils were not well correlated. Magn Reson Med 46:386‐394, 2001. © 2001 Wiley‐Liss, Inc.