bluuebunny/crossref_metadata_2025 huggingface dataset:
Epikatonic acid from Austroplenckia populnea: structure elucidation by 2D NMR spectroscopy and X‐ray crystallography
Authors: Silva G. D. F. , Duarte L. P. , Vieira Filho S. A. , Doriguetto A. C. , Mascarenhas Y. P. , Ellena J. , Castellano E. E. , Cota A. B.
Published: August 2002

From the chloroform extract of Austroplenckia populnea, epikatonic acid, friedelin, populnonic acid, abruslactone A, salaspermic acid and 22β‐epi‐maytenfolic acid were isolated. The structure and stereochemistry of epikatonic acid were established by two‐dimensional NMR spectroscopic techniques (HMQC, HMBC and NOESY) and later confirmed by single crystal X‐ray diffraction as 3β‐hydroxy‐olean‐12‐en‐29‐oic acid, which unambiguously established the configuration of the hydroxyl group at C‐3 as 3β‐OH and the carboxyl group at C‐20 as 20α‐COOH. The crystal structure shows two independent molecules in the asymmetric unit. The crystal packing is stabilized by four O–H·O intermolecular hydrogen bonds, which give rise to infinite double chains along the c axis. Copyright © 2002 John Wiley & Sons, Ltd.
A 1H NMR and molecular modelling investigation of diastereotopic methylene hydrogen atoms
Authors: Tormena Cláudio F. , Freitas Matheus P. , Rittner Roberto , Abraham Raymond J.
Published: August 2002

The 1H NMR spectra of methyl 3‐bromo‐2‐methylpropionate (1a) and the corresponding chloro compound (2a) show no long‐range coupling between the methyl and methylene protons. In contrast, in the analogous dihalocompounds, methyl 2,3‐dibromo‐2‐methylpropionate (1b) and methyl 2,3‐dichloro‐2‐methylpropionate (2b), one of the methylene protons exhibits a large 4JHH coupling (0.8 Hz) to the methyl group, but the other proton shows no observable splitting. This can be explained quantitatively by calculations of the conformational preferences in these compounds combined with the known orientation dependence of the 4JHHcouplings. One conformer predominates in the dihalo compounds 1b and 2b, and this is responsible for the 4JHH coupling. In 1a and 2a all three conformers are populated and the 4JHH couplings average to zero. The technique is a potentially general method of unambiguously assigning diastereotopic methylene protons. Copyright © 2002 John Wiley & Sons, Ltd.
Heterogeneity of surface colour centres on alkaline earth metal oxides as revealed through EPR/ENDOR spectroscopy
Authors: Purnell Ian J. , Chiesa Mario , Farley Robert D. , Murphy Damien M. , Rowlands Christopher C. , Cristina Paganini Maria , Giamello Elio
Published: August 2002

A variety of surface anion vacancies, or point defects, are created by high‐temperature activation of a series of polycrystalline alkaline earth metal oxides (MgO, CaO and SrO). Subsequent UV irradiation of the activated oxide under a hydrogen atmosphere results in the generation of surface colour centres [FS+(H)], by electron trapping at these anion vacancies. The paramagnetic properties of these colour centres were studied by EPR and ENDOR spectroscopy. 1H ENDOR spectroscopy revealed that a well defined heterogeneity of trapped electron species exists on each oxide surface, as characterized by the different superhyperfine couplings between the trapped electron and the nearby proton of the FS+ (H) centre. On MgO and CaO two dominant FS+ (H) centres were identified (labelled sites I and II) whereas on SrO three FS+ (H) species were found (sites I, II and III). The possible surface sites responsible for electron stabilization are discussed, and include a 3C corner mono‐vacancy, a 4C mono‐vacancy and an anion–cation di‐vacancy. The results indicate that regardless of the oxide used, a common degree of morphological similarities exists on each oxide. Copyright © 2002 John Wiley & Sons, Ltd.
Molecular motion in some radiolabelled dipeptides: a muon spin relaxation study
Authors: Rhodes Christopher J. , Dintinger Timothy C. , Morris Harry , Scott Christopher A.
Published: August 2002

Activation parameters were determined for the dynamics of radicals formed by muonium addition to glycylglycine (GlyGly; H3N+CH2CONHCH2CO2−) and the doubly protected alanylalanine derivative [Boc‐AlaAla‐Bz; ButOCONHCH(Me)CONHCH(Me)CO—O—CH2Ph]. GlyGly forms an adduct by muonium addition to the amide carbonyl group which isomerizes by flipping the muon between opposite sides of the molecule, requiring an activation energy of 20.4 kJ mol−1. In Boc‐AlaAla‐Bz, muonium addition to the benzene ring of the benzyl (—CH2Ph) group occurs, exhibiting an activation energy of 9.4 kJ mol−1, believed to be from torsion about the C—Ph bond. Copyright © 2002 John Wiley & Sons, Ltd.
Phosphoryldithioformates: Part V. Unusual linewidth variations in the ESR spectra of some spin adducts of (dimenthoxy)phosphoryl methyl dithioformate
Authors: Alberti Angelo , Benaglia Massimo , Macciantelli Dante , Hudson Andrew , Masson Serge
Published: August 2002

Unusual temperature‐dependent linewidth variations were observed in spin adducts of (dimenthoxy)phosphoryl methyl dithioformate with bulky free radicals, possibly involving a combination of restricted rotation of a methyl group and slow molecular tumbling. Copyright © 2002 John Wiley & Sons, Ltd.
Isotope‐induced chemical shifts 2Δ10/11B(29Si) in alkenylsilanes containing three‐ and four‐coordinate boron. A new tool for studying weak intramolecular boron–element bonds
Authors: Wrackmeyer Bernd , Tok Oleg L.
Published: August 2002

Numerous alkenylsilanes with silyl and boryl groups in cis ‐positions at the CC bond were studied for the first time by 29Si NMR with regard to isotope‐induced chemical shifts Δ10/11B(29Si). Such effects are transmitted across an Si—X—B bridge (X = H, OR, SR, Cl) most efficiently if the interactions in this bridge are weak. In the absence of an Si—X—B bridge, 3Δ10/11B(29Si) effects were not observed. In such cases, where, depending on the substituents, both weak and strong B—X bonding are possible, the 2Δ10/11B(29Si) effects were readily observed only for weak B—X interactions (except for X = Cl), whereas for strong B—X bonding the effects were small or not detectable. Thus, the 2Δ10/11B(29Si) values provide another tool for probing weak interactions which are not clearly reflected by other NMR data. Copyright © 2002 John Wiley & Sons, Ltd.
Fitting dynamic NMR lineshapes
Authors: Bain Alex D. , Rex Darrell M. , Smith Rashida N.
Published: August 2002

The lineshapes in an NMR spectrum, due to dynamic processes within the sample, provide an excellent way of measuring the rates of these processes. As the process speeds up, lines broaden, coalesce and finally sharpen into an average peak. Mathematical techniques for simulating these lineshapes have long been available, and rates can be extracted by fitting the calculated lineshape to the experiment. This is often done by manual iteration and visual comparison. The principal iterative program, DNMR5, is somewhat clumsy by modern standards. A recent reformulation of the theory of the lineshapes, which describes the spectrum as a sum of transitions, simplifies setting up the iterative process. This approach is described in general, and illustrated with the two‐site equally populated case. Copyright © 2001 John Wiley & Sons, Ltd.
Conformational study of the tricyclic sesquiterpene β‐panasinsene aided by ab initio calculations and simulated 1H NMR parameters†
Authors: Flores‐Sandoval César A. , Cerda‐García‐Rojas Carlos M. , Joseph‐Nathan Pedro
Published: August 2002

Ab initio calculations of the tricyclic sesquiterpene β‐panasinsene (1) provided theoretical H—C—C—H dihedral angles that allowed us to predict the corresponding 1H–1H vicinal coupling constant values, using a generalized Karplus‐type equation. These values, together with the experimental 1H chemical shifts extracted from an HMQC spectrum, were used as the initial input data for the full spectral simulation of 1, which provided an excellent correlation with the experimental 1H NMR spectrum after a few iterations. The complete assignment of the 1H NMR parameters allowed us to determine the conformation of 1 in solution. The four‐membered ring exists in a more flattened conformation than cyclobutane, with torsion angles of ∼12°. The five‐membered ring possesses a half‐chair conformation with pseudorotational parameters θm = 39.5° and P = 3.8°, while the six‐membered ring exists in a conformation close to the canonical chair, with angular variables θ = 9.2° and P2 = 15.5°, and the total puckering amplitude Q = 54.5°. Application of this procedure to β‐panasinsen‐5α‐ol (2) and β‐panasinsen‐5‐one (3) gave similar results. Copyright © 2001 John Wiley & Sons, Ltd.
Complete 1H and 13C NMR assignments of stigma‐5‐en‐3‐O‐β‐glucoside and its acetyl derivative
Authors: Faizi Shaheen , Ali Muhammad , Saleem Rubeena , Irfanullah  , Bibi Sarah
Published: August 2002

Unambiguous and complete assignments of 1H and 13C NMR chemical shifts for stigma‐5‐en‐3‐O‐β‐glucoside, isolated from Brassica rapa sb.sp. campestris and Aloe barbadensis, and its acetyl derivative are presented, based on DEPT, HETCOR, COLOC, HMBC, COSY‐45°, NOESY and J‐resolved experiments. Copyright © 2001 John Wiley & Sons, Ltd.
Dynamic and magnetic susceptibility effects on the MAS NMR linewidth of a tetrapeptide bound to different resins
Authors: Furrer Julien , Elbayed Karim , Bourdonneau Maryse , Raya Jésus , Limal David , Bianco Alberto , Piotto Martial
Published: August 2002

Under magic angle spinning, the NMR spectrum of the tetrapeptide Ala‐Ile‐Gly‐Met bound to a Wang resin, and swollen in DMF, exhibits proton and carbon linewidths that are sharp enough to allow the complete characterization of the peptide using classical liquid‐state NMR methods. The proton linewidths of the bound peptide remain, however, about three times larger than those of the free peptide in solution. The residual NMR linewidth originates essentially from incompletely averaged magnetic susceptibility effects due to the Wang resin. Replacing the aromatic Wang resin with a PEGA or POEPOP resin removes this effect. To investigate the contribution to line broadening of the peptide dynamics, relaxation studies were performed on the peptide bound to Wang and POEPOP resins. Copyright © 2001 John Wiley & Sons, Ltd.
A relationship between the half‐width of 73Ge NMR signals and hypercoordination in some phenylgermanes
Authors: Takeuchi Yoshito , Tanaka Katsumi , Aoyagi Shigenobu , Yamamoto Hiroyuki
Published: August 2002

73Ge NMR spectra of some phenylgermanes were determined. The chemical shifts and half‐widths are discussed in terms of structure and in relation to hypercoordination of germanium atoms. It appears that linewidths can be a measure of hypercoordination. Copyright © 2002 John Wiley & Sons, Ltd.
3D Heteronuclear long‐range 1H–13C scalar correlation at natural abundance: application to oligosaccharide analysis
Authors: Hernández Griselda , LeMaster David M.
Published: August 2002

A 3D 1H–13C–1H refocused INEPT transfer experiment is proposed in which the initial coherence transfer of 1H longitudinal to 13C transverse magnetization is tuned to the long‐range 1H, 13C couplings while the reverse INEPT component transfers the magnetization to the directly bonded 1H. Integration of a constant time 1H evolution period into the long‐range coherence transfer interval provides absorption mode signals for each dimension. A 13C purge component at the beginning of the sequence selects for 12C‐bound 1H magnetization that is then transferred to a 13C‐bound hydrogen, thus strongly suppressing the diagonal signals. This experiment is expected to be of particular value for situations in which resonance overlap in the 13C dimension renders 2D long‐range heteronuclear correlation data ambiguous. In combination with a diagonal‐suppressed 3D 1H–13C–1H TOCSY‐HSQC experiment, complete assignment of the ring resonances of the Lewis‐b hexasaccharide was obtained on a 4.2 mM sample using a conventional 500 MHz probe (0.1% ethylbenzene signal‐to‐noise ratio of 600), suggesting its applicability to sub‐millimolar samples using cryoprobe technology. Copyright © 2002 John Wiley & Sons, Ltd.
Structural characterization of monomeric and oligomeric arylamides by solution and solid‐state NMR spectroscopy
Authors: Cavallaro Stefano , Cum Giampietro , Gallo Raffaele , Spadaro Agatino , Visalli Giuseppe
Published: August 2002

An extensive study of both liquid‐ and solid‐state NMR spectroscopy was undertaken in order to elucidate the structural features of a phenyleneterephthalamide oligomer (OPTA) and of some related diarylamides. 1D‐ and 2D‐COSY measurements allowed us to assign completely the proton signals of the title compounds in solution, while 1D‐, 2D‐HETCOR and 2D‐COLOC measurements were used to assign 13C resonances. Solid‐state 13C NMR experiments, by conventional cross‐polarization (CP) at different contact times and with the dipolar dephased CP technique, were used to characterize these molecules in the solid state. Such techniques allowed us to differentiate among different carbon atoms; in the resulting spectra it was then possible to observe the selective appearance of signals from protonated and quaternary carbon atoms. It was also ascertained that the limited structural mobility of the insoluble OPTA, existing as a single monophasic species, can be explained in terms of hydrogen‐type bonds present in the solid state. Copyright © 2002 John Wiley & Sons, Ltd.
Aromatase plays a key role during normal and temperature‐induced sex differentiation of tilapia Oreochromis niloticus
Authors: D'cotta Helena , Fostier Alexis , Guiguen Yann , Govoroun Marina , Baroiller Jean‐Francois
Published: August 2002

In the tilapia Oreochromis niloticus, sex is determined genetically (GSD), by temperature (TSD) or by temperature/genotype interactions. Functional masculinization can be achieved by applying high rearing temperatures during a critical period of sex differentiation. Estrogens play an important role in female differentiation of non‐mammalian vertebrates. The involvement of aromatase, was assessed during the natural (genetic all‐females and all‐males at 27°C) and temperature‐induced sex differentiation of tilapia (genetic all‐females at 35°C). Gonads were dissected between 486–702 degree × days. Aromatase gene expression was analyzed by virtual northern and semi‐quantitative RT‐PCR revealing a strong expression during normal ovarian differentiation concomitant with high levels (465 ± 137 fg/g) of oestradiol‐17β (E2‐17ß). This was encountered in gonads after the onset of ovarian differentiation (proliferation of both stromal and germ cells prior to ovarian meiosis). Genetic males exhibited lower levels of aromatase gene expression and E2‐17ß quantities (71 ± 23 fg/ g). Aromatase enzyme activity in fry heads established a sexual dimorphism in the brain, with high activity in females (377.9 pmol/head/hr) and low activity in males (221.53 pmol/head/hr). Temperature induced the masculinization of genetic females to a different degree in each progeny, but in all cases repression of aromatase expression was encountered. Genetic males at 35°C also exhibited a repression of aromatase expression. Aromatase brain activity decreased by nearly three‐fold in the temperature‐masculinized females with also a reduction observed in genetic males at 35°C. This suggests that aromatase repression is required in the gonad (and perhaps in the brain) in order to drive differentiation towards testis development. Mol. Reprod. Dev. 59:265–276, 2001. © 2001 Wiley‐Liss, Inc.
Inhibiting 3‐phosphoglycerate kinase by EDTA stimulates the development of the cleavage stage mouse embryo
Authors: Lane Michelle , Gardner David K.
Published: August 2002

Addition of EDTA to the medium significantly enhances mouse embryo development in culture. Embryos cultured in the absence of EDTA exhibit abnormal increases in glycolytic activity that result in reduced development. Culture with EDTA was able to prevent this increase in glycolysis and, therefore, maintain developmental competence. EDTA was shown to inhibit the activity of the glycolytic enzyme, 3‐phosphoglycerate kinase. Additionally, the effect of EDTA on maintaining high rates of embryo development in culture could be mimicked by the addition of Cibacron blue, an inhibitor of 3‐phosphoglycerate kinase. The inhibition of 3‐phosphoglycerate kinase by EDTA could be overcome by the addition of exogenous magnesium, indicating that the effect of EDTA was to reduce the availability of this co‐factor to the glycolytic kinases. Embryos cultured with EDTA had significantly lower levels of intracellular magnesium compared to embryos cultured without EDTA. Therefore, the effect of EDTA appears to be as a chelator of divalent cations such as magnesium, that are required for normal activity of kinases such as 3‐phosphoglycerate kinase. Mol. Reprod. Dev. 60: 233–240, 2001. © 2001 Wiley‐Liss, Inc.
Distinct roles for distal‐less genes Dlx3 and Dlx5 in regulating ectodermal development in Xenopus
Authors: Luo Ting , Matsuo‐Takasaki Mami , Sargent Thomas D.
Published: August 2002

In vertebrates, there are six or more copies of genes related to the Drosophila pattern formation homeodomain gene Distal‐less. Among this family, Dlx3 and Dlx5 share extensive sequence homology and have similar, but distinctive, expression patterns, suggesting that these two factors may have substantially redundant developmental functions. Here we show that at the earliest phases of embryogenesis in Xenopus, there are significant differences between Dlx3 and Dlx5 expression and that this correlates with different functions in the restriction of neural crest and neural plate boundaries, respectively. Mol. Reprod. Dev. 60: 331–337, 2001. © 2001 Wiley‐Liss, Inc.
Spermatogenesis in the golden hamster: The role of c‐kit
Authors: Vigodner M. , Lewin L. M. , Shochat L. , Golan R.
Published: August 2002

c‐kit is related to the family of transmembrane tyrosine kinase receptors. Mutations in genes for either c‐kit or its ligand, Steel factor, result in infertility, but the role of c‐kit/SCF system in spermatogenesis is not well understood. In this study Western blot analysis together with confocal microscopy were used to follow c‐kit expression in hamsters during the first spermatogenic wave in mature animals and in old age. Three antibodies raised against different domains of c‐kit were tested on Western Blot. Confocal microscopy was performed after incubation of fixed seminiferous tubules with tested antibodies followed by binding of FITC‐labeled secondary antibody. Longitudinal sections of seminiferous tubule were observed by confocal microscopy to determine in which stages of spermatogenesis and in which cell types c‐kit was found. C‐kit bands of 80,140, and 150 kDa were observed on Western blot, indicating that c‐kit is a name related to several proteins sharing some common domains. Only the band of 150 kDa correlated with positive staining of c‐kit in tubules using confocal microscopy. We term this protein c‐kit150T (150 kDa, testis). We demonstrated that c‐kit150T appeared in differentiating hamster spermatogonia at stages VII–VIII of adult spermatogenesis and at day 13–14 during the first spermatogenic wave. It remained attached to the cell until late pachytene. This suggests that c‐kit may play a role in preparing the germinal cells to enter meiosis. In order to evaluate the effect of aging on the number of germ cells, B2 spermatogonia/Sertoli cell ratio was calculated in the group of young animals (5–7 months) compared to this ratio in older ones (20–26 months). A significant decrease (P < 0.01) in the number of B2 spermatogonia in the group of old hamsters as compared to young ones was seen. The calculated value for the B2 spermatogonia/Sertoli cell ratio was 5.6 ± 0.7 in young animals and 3.8 ± 1.2 in the 20–26 months ones. In addition, decrease in the intensity of staining for c‐kit was detected in the old hamsters. These may be the reasons for subfertility in old age and in other cases of testicular disorders. Mol. Reprod. Dev. 60: 562–568, 2001. © 2001 Wiley‐Liss, Inc.
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

Classical 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

Only 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

HIV‐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

A 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

A 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

Three‐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

Refocused 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

Myocardial 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

Blood 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

Calculations 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

A 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

Diffusion 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

Magnetic 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

The 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

The 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

Gradient 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.
Proteoglycan‐induced changes in T1ρ‐relaxation of articular cartilage at 4T
Authors: Akella Sarma V.S. , Reddy Regatte Ravinder , Gougoutas Alexander J. , Borthakur Arijitt , Shapiro Erik M. , Kneeland J. Bruce , Leigh John S. , Reddy Ravinder
Published: August 2002

Proteoglycan (PG) depletion‐induced changes in T1ρ (spin‐lattice relaxation in rotating frame) relaxation and dispersion in articular cartilage were studied at 4T. Using a spin‐lock cluster pre‐encoded fast spin echo sequence, T1ρ maps of healthy bovine specimens and specimens that were subjected to PG depletion were computed at varying spin‐lock frequencies. Sequential PG depletion was induced by trypsinization of cartilage for varying amounts of time. Results demonstrated that over 50% depletion of PG from bovine articular cartilage resulted in average T1ρ increases from 110–170 ms. Regression analysis of the data showed a strong correlation (R2 = 0.987) between changes in PG and T1ρ. T1ρ values were highest at the superficial zone and decreased gradually in the middle zone and again showed an increasing trend in the region near the subchondral bone. The potentials of this method in detecting early degenerative changes of cartilage are discussed. Also, T1ρ‐dispersion changes as a function of PG depletion are described. Magn Reson Med 46:419–423, 2001. © 2001 Wiley‐Liss, Inc.
Mixed echo train acquisition displacement encoding with stimulated echoes: An optimized DENSE method for in vivo functional imaging of the human heart
Authors: Aletras Anthony H. , Wen Han
Published: August 2002

Mixedechotrainacquisitiondisplacementencoding withstimulatedechoes (meta‐DENSE) is a phase‐based displacement mapping technique suitable for imaging myocardial function. This method has been optimized for use with patients who have a history of myocardial infarction. The total scan time is 12–14 heartbeats for an in‐plane resolution of 2.8 × 2.8 mm2. Myocardial strain is mapped at this resolution with an accuracy of 2% strain in vivo. Compared to standardstimulatedecho (STE) methods, both data acquisition speed and resolution are improved with inversion‐recovery FID suppression and the meta‐DENSE readout scheme. Data processing requires minimal user intervention and provides a rapid quantitative feedback on the MRI scanner for evaluating cardiac function. Magn Reson Med 46:523–534, 2001. Published 2001 Wiley‐Liss, Inc.
Two‐dimensional time correlation relaxometry of skeletal muscle in vivo at 3 Tesla
Authors: Saab George , Thompson R. Terry , Marsh Gregory D. , Picot Paul A. , Moran Gerald R.
Published: August 2002

A hybrid two‐dimensional relaxometry (2DR) sequence was used to simultaneously measure both the spin‐spin (R2) and spin‐lattice relaxation rates (R1) of skeletal muscle in vivo. The 2DR sequence involved a 180° inversion pulse followed by a variable delay time (30 values from 40 to 7000 ms); a projection presaturation (PP) scheme to localize a 16‐ml cylindrical voxel; and a CPMG sequence (950 even echoes, effective echo spacing = 1.2 ms, equilibrium time = 12 s). The 2DR data were collected at 3.0 Tesla from the flexor digitorum profundus of eight healthy males, 26 ± 2 years old. Analysis was performed with a 2D version of the non‐negative least‐squares algorithm and a one‐way ANOVA. All subjects exhibited at least three spin‐groups (R2 < 200 s−1), designated B, C, and D, with R2 values of 42.7, 26.5, and 8.1 s−1, and fractional volumes of 52, 35, and 7%, respectively. The R1 values of B and C were similar, ≅0.7 s−1, but different from that of D (P < 0.001), which had an R1 of 1.0 s−1. The results suggest that exchange between B and C ranges from 0.7–16.2 s−1, while exchange between either of these spin‐groups with D is slower. If the data are interpreted with a compartment model, in which spin‐groups with short and long R2 values are attributed to extra‐ and intracellular fluid, respectively, the exchange of water across the cell membrane in living skeletal muscle is slow or intermediate relative to both R1 and R2. Magn Reson Med 46:1093–1098, 2001. © 2001 Wiley‐Liss, Inc.
Motor unit number estimation in infants and children with spinal muscular atrophy
Authors: Bromberg Mark B. , Swoboda Kathryn J.
Published: August 2002

Spinal muscular atrophy (SMA) is a disease of lower motor neurons. Motor unit number estimation (MUNE) is an electrophysiologic method to estimate the number of motor neurons innervating a muscle group. We applied the multiple point stimulation technique to the ulnar nerve–hypothenar muscle group to study lower motor neuron loss in 14 SMA subjects, including those presymptomatic, and varying from newborn through 45 years of age. Preliminary data support the value of MUNE to help understand the time course of motor neuron loss in SMA. © 2002 Wiley Periodicals, Inc. Muscle Nerve 25: 000–000, 2002