bluuebunny/crossref_metadata_2025_split huggingface dataset:
Signal‐to‐noise ratio effects in quantitative cerebral perfusion using dynamic susceptibility contrast agents
Authors: Smith Michael R , Lu Hong , Frayne Richard 
Published: January 2003

AbstractTheoretical and simulation evidence is presented in support of the idea that the optimal manner of determining blood flow from MR perfusion studies is not necessarily obtained by setting experimental conditions to maximize either the arterial input or the measured tissue concentration level for a particular echo time (TE). The noise power in the contrast concentration curve is associated with its peak because of the nonlinear relationship between the contrast concentration and MR signal intensity curves. The optimum signal‐to‐noise ratio (SNR), SNRC, for a particular contrast concentration curve can be obtained when the experimental concentration level and TE are adjusted to produce an MR intensity curve whose signal loss is 63% of the precontrast MR signal intensity. It is demonstrated that the stability of the singular valued decomposition (SVD) deconvolution approach to determine blood flow parameters is increased when the tissue curve maximum signal loss is in the range of 40–80%. The accuracy and stability of the SVD‐determined blood flow parameters are affected by deviations from these optimum conditions in a manner that depends on the mean transit time (MTT) associated with the residue function. It is recommended that the experimental TE value be set so that neither the tissue nor the arterial curves are placed a region of rapidly deteriorating SNRC. Magn Reson Med 49:122–128, 2003. © 2003 Wiley‐Liss, Inc.
Correlation between BOLD‐fMRI and EEG signal changes in response to visual stimulus frequency in humans
Authors: Singh Manbir , Kim Sungheon , Kim Tae‐Seong 
Published: January 2003

AbstractThe correlation between signals acquired using electroencephalography (EEG) and fMRI was investigated in humans during visual stimulation. Evoked potential EEG and BOLD fMRI data were acquired independently under similar conditions from eight subjects during stimulation by a checkerboard flashed at frequencies ranging from 2–12 Hz. The results indicate highly correlated changes in the strength of the EEG signal averaged over two occipital electrodes and the BOLD signal within the occipital lobe as a function of flash frequency for 7/8 subjects (average linear correlation coefficient of 0.76). Both signals peaked at approximately 8 Hz. For one subject the correlation coefficient was 0.20; the EEG signal peaked at 6 Hz and the BOLD signal peaked at 10 Hz. Overall, the EEG and BOLD signals, each averaged over 40‐sec stimulation periods, appear to be coupled linearly during visual stimulation by a flashing checkerboard. Magn Reson Med 49:108–114, 2003. © 2003 Wiley‐Liss, Inc.
Reduction of transient signal oscillations in true‐FISP using a linear flip angle series magnetization preparation
Authors: Deshpande Vibhas S. , Chung Yiu‐Cho , Zhang Qiang , Shea Steven M. , Li Debiao 
Published: January 2003

AbstractAn electrocardiogram (ECG)‐triggered, magnetization‐prepared, segmented, 3D true fast imaging with steady‐state precession (true‐FISP) sequence with fat saturation was recently proposed for coronary artery imaging. A magnetization preparation scheme consisting of an α/2 radiofrequency (RF) pulse followed by 20 constant flip angle dummy RF cycles was used to reduce signal oscillations in the approach to steady state. However, if large resonance offsets on the order of 70–100 Hz are present, significant magnetization oscillations will still occur during data acquisition, which will result in image ghosting and blurring. The goal of this work was to validate that a linear flip angle (LFA) series can be used during magnetization preparation to reduce these image artifacts. Computer simulations, phantom studies, and coronary artery imaging in healthy volunteers were performed to compare this magnetization preparation scheme with that of an α/2 pulse followed by constant flip angle dummy RF cycles. The results demonstrated substantial reduction in the apparent image artifacts when using linearly increasing flip angles during magnetization preparation. Magn Reson Med 49:151–157, 2003. © 2003 Wiley‐Liss, Inc.
Investigating the BOLD effect during infusion of Gd‐DTPA using rapid T mapping
Authors: Pears J.A. , Francis S.T. , Butterworth S.E. , Bowtell R.W. , Gowland P.A. 
Published: January 2003

AbstractThis work aimed to investigate the effects of administering Gd‐DTPA on the BOLD effect, and to determine the feasibility of using this approach to measure fractional changes in blood volume and blood oxygenation on neuronal activation during a visual paradigm. A linear relationship between cortical R and the intravascular concentration of Gd‐DTPA was demonstrated. The change in R in the visual cortex on activation at 3 T (in the absence of Gd‐DTPA) was found to be 1.38 ± 0.31 s−1 (N = 4). The fractional change in total blood volume during visual activation was calculated to be 28% ± 7% (N = 4). The absolute increase in venous blood oxygenation on activation (ΔY) was estimated to be 21% ± 4% (N = 4) (assuming HCT = 0.4, resting blood oxygenation = 60%, fraction of volume change that was venous = 36%, and the resting venous fraction of the blood volume = 70%). Simulations showed that the estimated change in venous blood oxygenation was sensitive to the assumed venous blood fraction, and that the estimated fractional change in blood oxygenation was insensitive to whether the change in blood volume occurred in the arterial or venous network. Magn Reson Med 49:61–70, 2003. © 2003 Wiley‐Liss, Inc.
Comparison of quantitative shear wave MR‐elastography with mechanical compression tests
Authors: Hamhaber U. , Grieshaber F.A. , Nagel J.H. , Klose U. 
Published: January 2003

AbstractThe mechanical properties of in vivo soft tissue are generally determined by palpation, ultrasound measurements (US), and magnetic resonance elastography (MRE). While it has been shown that US and MRE are capable of quantitatively measuring soft tissue elasticity, there is still some uncertainty about the reliability of quantitative MRE measurements. For this reason it was decided to determine in vitro how MRE measurements correspond with other quantitative methods of measuring characteristic elasticity values. This article presents the results of experiments with tissue‐like agar–agar gel phantoms in which the wavelength of strain waves was measured by shear wave MR elastography and the resultant shear modulus was compared with results from mechanical compression tests with small gel specimens. The shear moduli of nine homogeneous gels with various agar–agar concentrations were investigated. The elasticity range of the gels covered the elasticity range of typical soft tissues. The systematic comparison between shear wave MRE and compression tests showed good agreement between the two measurement techniques. Magn Reson Med 49:71–77, 2003. © 2003 Wiley‐Liss, Inc.
Congenital myasthenic syndromes: Progress over the past decade
Authors: Engel Andrew G. , Ohno Kinji , Sine Steven M. 
Published: January 2003

AbstractCongenital myasthenic syndromes (CMS) stem from defects in presynaptic, synaptic basal lamina, and postsynaptic proteins. The presynaptic CMS are associated with defects that curtail the evoked release of acetylcholine (ACh) quanta or ACh resynthesis. Defects in ACh resynthesis have now been traced to mutations in choline acetyltransferase. A basal lamina CMS is caused by mutations in the collagenic tail subunit (ColQ) of the endplate species of acetylcholinesterase that prevent the tail subunit from associating with catalytic subunits or from becoming inserted into the synaptic basal lamina. Most postsynaptic CMS are caused by mutations in subunits of the acetylcholine receptor (AChR) that alter the kinetic properties or decrease the expression of AChR. The kinetic mutations increase or decrease the synaptic response to ACh and result in slow‐ and fast‐channel syndromes, respectively. Most low‐expressor mutations reside in the AChR ϵ subunit and are partially compensated by residual expression of the fetal type γ subunit. In a subset of CMS patients, endplate AChR deficiency is caused by mutations in rapsyn, a molecule that plays a critical role in concentrating AChR in the postsynaptic membrane. Muscle Nerve 27: 4–25, 2003
Expression of matrix metalloproteinases, inhibitor, and acid phosphatase in muscles of immobilized hindlimbs of rats
Authors: Reznick Abraham Z. , Menashe Ofir , Bar‐Shai Marina , Coleman Raymond , Carmeli Eli 
Published: January 2003

AbstractExternal fixation procedures of limb immobilization provide excellent experimental models to study mechanisms involved in muscle disuse atrophy and recovery. Female Wistar rats (7–8 months old) had their right hindlimbs immobilized by an external fixation procedure for 5, 10, 21, and 30 days. Muscle mass of the gastrocnemius and quadriceps muscles was reduced by 41–46% in comparison with contralateral nonimmobilized legs. Acid phosphatase activities were significantly increased after 21 and 30 days of hindlimb immobilization. Histochemical staining for acid phosphatase activities increased in myofibers after the external fixation and also in macrophages in the adjacent extracellular matrix. Matrix metalloproteinase (MMP‐2 and MMP‐9) activities assessed by gel zymography and also a tissue inhibitor of metalloproteinases (TIMP‐1) assessed by Western blot were elevated in the immobilized hindlimb muscles. Our study demonstrated that metalloproteinases are expressed relatively late after limb immobilization and appear to be responsible to a large degree for degradation of the extracellular matrix in experimental disuse atrophy. Muscle Nerve 27: 51–59, 2003
Are voluntary muscle activation deficits in older adults meaningful?
Authors: Stevens Jennifer E. , Stackhouse Scott K. , Binder‐Macleod Stuart A. , Snyder‐Mackler Lynn 
Published: January 2003

AbstractThe relationship between the central activation ratio (CAR) and contraction force is curvilinear, not linear as was previously believed. Voluntary quadriceps femoris muscle activation from previously collected data sets in 46 older adults (64–84 years) and 46 young adults (18–32 years) were therefore reexamined using a curvilinear model of the voluntary muscle activation–percent maximum voluntary force relationship. This method revealed lower voluntary muscle activation in older adults (0.868 ± 0.018) than younger subjects (0.978 ± 0.005). The mean difference between older and younger adults was 11%, which may be more meaningful than previous reports of 2–4% because it could explain the greater rate of strength loss as compared to loss of muscle mass as humans age. Muscle Nerve 27: 99–101, 2003
Effect of training on contractile and metabolic properties of wrist extensors in spinal cord–injured individuals
Authors: Hartkopp Andreas , Harridge Stephen D. R. , Mizuno Masao , Ratkevicius Aivaras , Quistorff Björn , Kjær Michael , Biering‐Sörensen Fin 
Published: January 2003

AbstractParetic human muscle rapidly loses strength and oxidative endurance, and electrical stimulation training may partly reverse this. We evaluated the effects of two training protocols on the contractile and metabolic properties of the wrist extensor in 12 C‐5/6 tetraplegic individuals. The wrist extensor muscles were stimulated for 30 min/day, 5 days/week, for 12 weeks, using either a high‐resistance (Hr) or a low‐resistance (Lr) protocol. Total work output was similar in both protocols. The nontrained arm was used as a control. Maximum voluntary torque increased in the Hr (P < 0.05) but not the Lr group. Electrically stimulated peak tetanic torque at 15 HZ, 30 HZ, and 50 HZ were unchanged in the Lr group and tended to increase only at 15 HZ (P < 0.1) in the Hr group. Resistance to fatigue, however, increased (P < 0.05) in both Hr (42%) and Lr (41%) groups. Muscle metabolism was evaluated by 31P nuclear magnetic resonance spectroscopy (31P‐NMRS) during and following a continuous 40‐s 10‐HZ contraction. In the Hr group the cost of contraction decreased by 38% (P < 0.05) and the half‐time of phosphocreatine (PCr) recovery was shortened by 52% (P < 0.05). Thus, long‐term electrically induced stimulation of the wrist extensor muscles in spinal cord injury (SCI) increases fatigue resistance independent of training pattern. However, only the Hr protocol increased muscle strength and was shown to improve muscle aerobic metabolism after training. Muscle Nerve 27: 72–80, 2003
Consensus criteria for the diagnosis of multifocal motor neuropathy
Authors: Olney Richard K. , Lewis Richard A. , Putnam Timothy D. , Campellone Joseph V. 
Published: January 2003

AbstractAt this time, there are no widely accepted criteria for the diagnosis of multifocal motor neuropathy. Furthermore, there is insufficient empirical data to define clinical and laboratory features that may reliably separate certain lower motor neuron syndromes with overlapping features as distinct. The AAEM therefore developed five criteria through a formal consensus process that are described in this document to act as a guide for diagnosing multifocal motor neuropathy with a high level of confidence (definite multifocal motor neuropathy) or with a moderate level of confidence (probable motor neuropathy). In brief, the diagnosis requires clinical weakness without objective sensory loss or upper motor neuron signs in the distribution of two or more named nerves that is due to conduction block in two or more motor nerves outside of common entrapment sites. Furthermore, normal results are required for sensory nerve conduction studies. Muscle Nerve 27:117–121, 2003
Optimal rectangular partitions
Authors: Calheiros Felipe C. , Lucena Abilio , de Souza Cid C. 
Published: January 2003

AbstractAssume that a rectangle R is given on the Euclidean plane together with a finite set P of points that are interior to R. A rectangular partition of R is a partition of the surface of R into smaller rectangles. The length of such a partition equals the sum of the lengths for the line segments that define it. The partition is said to be feasible if no point of P is interior to a partition rectangle. The Rectangular Partitioning Problem (RPP) seeks a feasible rectangular partition of R with the least length. Computational evidence from the literature indicates that RPPs with noncorectilinear points in P, denoted NCRPPs, are the hardest to solve to proven optimality. In this paper, some structural properties of optimal feasible NCRPP partitions are presented. These properties allow substantial reductions in problem input size to be carried out. Additionally, a stronger formulation of the problem is also made possible. Based on these ingredients, a hybrid Lagrangian Relaxation—Linear Programming Relaxation exact solution algorithm is proposed. Such an algorithm has proved capable of solving NCRPP instances more than twice as large as those found in the literature. © 2002 Wiley Periodicals, Inc.
Are calcium isotopes a reliable monitor of trophic level in marine settings?
Authors: Clementz M. T. , Holden P. , Koch P. L. 
Published: February 2003

AbstractRecent research has shown that calcium isotopes are fractionated by metabolic processes, leading to a decrease in 44Ca/40Ca ratio with increasing trophic level. If so, calcium isotopes could provide information on trophic relationships within foodwebs millions of years older than what we have been able to study thus far with alternative methods (i.e., nitrogen isotopes (δ15N), Sr/Ca). To explore whether δ44Ca values provided marine trophic level information, we measured the δ44Ca composition of tooth enamel and bone from modern marine mammals representing a 2.5 order range in trophic level. Marine mammal enamel δ44Ca values clustered into two groups—mammals foraging on vegetation or invertebrates exhibited higher δ44Ca values than those foraging on fish or other marine mammals. We next examined whether this correlation was preserved in the fossil record by examining a 15 Ma marine fauna from southern California and observed that the relationship between δ44Ca values of specimens followed the same pattern as observed in modern faunas, but the mean δ44Ca values were significantly different from modern δ44Ca values for mammals of similar trophic level. We conclude that the relative spacing of δ44Ca values amongst fossil taxa can serve as a valuable tool for defining trophic level of extinct organisms and can provide critical information on relationships within ancient foodwebs. Copyright © 2003 John Wiley & Sons, Ltd.
Expression of the dietary isotope signal in the compound‐specific δ13C values of pig bone lipids and amino acids
Authors: Howland M. R. , Corr L. T. , Young S. M. M. , Jones V. , Jim S. , Van Der Merwe N. J. , Mitchell A. D. , Evershed R. P. 
Published: February 2003

AbstractPigs were raised on six isotopically controlled diets to examine the dietary macronutrients used in the synthesis of bulk bone biochemical components (apatite, collagen and lipids) and individual compounds (bone fatty acids, cholesterol and amino acids from collagen). δ13C values of apatite and bulk bone lipids reflected those of the whole diet, with Δ13Capatite‐wholediet = 10.2 ± 1.3‰ and Δ13Cbonelipids‐wholediet = −2.4 ± 0.7‰. A wide variation observed in the Δ13Ccollagen‐wholediet values (0.5 to 6.1‰) was hypothesized to reflect the relative importance of (i) the direct incorporation of essential amino acids, and (ii) the balance between direct incorporation and de novo synthesis of non‐essential amino acids. Linear regression (n = 6) was used to assess the relationship between the δ13C values of whole diet and bulk bone components and individual compounds. Whole diet δ13C values showed a strong correlation with those of bone cholesterol (R2 = 0.81) and non‐essential fatty acids (0.97 ≤ R2 ≤ 0.99). Not surprisingly, bone linoleic acid δ13C values correlated well with dietary linoleic acid (R2 = 0.95). Mass balance calculations using the δ13C values of single amino acids accurately predicted the δ13C value of whole collagen. The δ13C values of whole diet were well correlated with those of the non‐essential amino acids, alanine (R2 = 0.85) and glutamate (R2 = 0.96) in collagen. The essential amino acids leucine (Δ13Ccollagenleu‐dietleu = 0.5 ± 1.2‰) and phenylalanine (Δ13Ccollagenphe‐dietphe = −0.6 ± 0.6‰) showed little isotopic fractionation between diet and bone collagen. Copyright © 2003 John Wiley & Sons, Ltd.
Effect of mixing conditions on the morphology and properties of polystyrene/polyethylene blends compatibilized with styrene–butadiene block copolymers
Authors: Fortelný I. , Hlavatá D. , Mikešová J. , Michálková D. , Potroková L. , Šloufová I. 
Published: February 2003

AbstractThe effect of mixing conditions on the morphology, molten‐state viscoelastic properties, and tensile impact strength of polystyrene/polyethylene (80/20) blends compatibilized with styrene–butadiene block copolymers containing various numbers and lengths of blocks was studied. Under all mixing conditions, an admixture of a styrene–butadiene block copolymer led to a finer phase structure and to an increase in the dynamic viscosity, storage modulus, and tensile impact strength. The effects were stronger for S–B diblock with a short styrene block than for S–B–S–B–S pentablock with long styrene blocks (where S represents styrene and B represents butadiene). For all blends mixed longer than 2 min, the mixing time had only a small effect on their morphology and properties. Surprisingly, the localization of S–B diblock copolymers was strongly dependent on the rate of mixing. The mixing rate had a nonnegligible effect on the viscoelastic properties of the compatibilized blends. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 609–622, 2003
Modelling alpine permafrost distribution based on energy‐balance data: a first step
Authors: Stocker‐Mittaz Catherine , Hoelzle Martin , Haeberli Wilfried 
Published: January 2003

AbstractThe computer model PERMEBAL (which stands for Permafrost and Energy Balance) simulates the persistence of snow cover and daily ground surface temperatures of snow‐free gridpoints. It was developed for high‐mountain conditions. The model describes different vertical energy fluxes at the surface. With meteorological and site‐specific input data, PERMEBAL delivers daily ground surface temperatures of snow‐free gridpoints. Special emphasis is given to simulation of snow‐cover development (snow fall, snow redistribution, snowmelt). The resulting ground surface temperature data are intended for use as input data for future ground heat flux simulations. The aim is to model ground thermal conditions and thus permafrost distribution. The model was applied to the Corvatsch‐Furtschellas area (16 km2, Engadin, eastern Switzerland). The results show that the area could be divided into three classes of mean annual sums of daily ground surface temperatures of snow‐free pixels, similar to ‘permafrost probable’, ‘permafrost possible’ and ‘permafrost improbable’ classifications used in earlier empirical permafrost distribution models. Copyright © 2002 John Wiley & Sons, Ltd.
Bone induction by BMP‐2 transduced stem cells derived from human fat
Authors: Dragoo Jason L. , Choi Joon Y. , Lieberman Jay R. , Huang Jerry , Zuk Patricia A. , Zhang Jeffery , Hedrick Marc H. , Benhaim Prosper 
Published: February 2003

AbstractPurpose: We have isolated pluripotent mesenchymal progenitor cells in large numbers from liposuction aspirates (processed lipoaspirate cells or PLAs). This study examines the osteogenic potential of PLAs and bone marrow aspirate cells (BMAs), when exposed to either recombinant human bone morphogenetic protein (BMP)‐2 (rh‐BMP‐2) or adenovirus containing BMP‐2 cDNA (Ad‐BMP‐2).Methods: Liposuction aspirates underwent proteolytic digestion to obtain PLAs. After exposure to exogenous rh‐BMP‐2 or Ad‐BMP‐2 for four or seven days, PLAs and BMAs were assessed by histochemistry, spectrophotometry and RT‐PCR. Western blotting and ELISA confirmed BMP gene transduction. Results were compared to osteoblasts and cells in osteogenic media only. PLA‐Ad‐BMP‐2 cells were seeded on matrices and implanted in the hind limbs of SCID mice.Results: Analysis of quantified bone precursor assays including extracellular ALP histomorphometry, intracellular ALP spectrophotometry, and calcified extracellular matrix (von Kossa) histomorphometry revealed that PLAs treated with exogenous rh‐BMP‐2 or transduced with a BMP‐2 containing adenovirus (PLA‐Ad‐BMP‐2) produced more bone precursors than osteoblasts (p = 0.001). PLAs treated with exogenous rh‐BMP‐2 or PLA‐Ad‐BMP‐2 also produced more bone precursors than BMAs (p = 0.001), except for day 7 ALP histomorphometry (p = 0.343). ELISA confirmed successful BMP‐2 production by both progenitor cell groups transduced with Ad‐BMP‐2. H&E sections from collagen I matrices seeded with PLA‐Ad‐BMP‐2 cells confirmed bone formation at six weeks.Conclusions: Liposuction aspirates contain PLAs that can be transfected with the BMP‐2 gene, with rapid induction into the osteoblast phenotype at a rate comparable to rh‐BMP‐2 and osteoblast groups. Transduced PLAs produce more bone precursors with faster onset of calcified extracellular matrix than transduced BMAs. PLAs may be an ideal source of mesenchyme‐lineage stem cells for gene therapy and tissue engineering. © 2003 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved.