bluuebunny/crossref_metadata_2025_split huggingface dataset:
In vitro assessment of flow patterns and turbulence intensity in prosthetic heart valves using generalized phase‐contrast MRI
Authors: Kvitting John‐Peder Escobar , Dyverfeldt Petter , Sigfridsson Andreas , Franzén Stefan , Wigström Lars , Bolger Ann F. , Ebbers Tino 
Published: April 2010

AbstractPurpose:To assess in vitro the three‐dimensional mean velocity field and the extent and degree of turbulence intensity (TI) in different prosthetic heart valves using a generalization of phase‐contrast MRI (PC‐MRI).Materials and Methods:Four 27‐mm aortic valves (Björk‐Shiley Monostrut tilting‐disc, St. Jude Medical Standard bileaflet, Medtronic Mosaic stented and Freestyle stentless porcine valve) were tested under steady inflow conditions in a Plexiglas phantom. Three‐dimensional PC‐MRI data were acquired to measure the mean velocity field and the turbulent kinetic energy (TKE), a direction‐independent measure of TI.Results:Velocity and TI estimates could be obtained up‐ and downstream of the valves, except where metallic structure in the valves caused signal void. Distinct differences in the location, extent, and peak values of velocity and TI were observed between the valves tested. The maximum values of TKE varied between the different valves: tilting disc, 100 J/m3; bileaflet, 115 J/m3; stented, 200 J/m3; stentless, 145 J/m3.Conclusion:The TI downstream from a prosthetic heart valve is dependent on the specific valve design. Generalized PC‐MRI can be used to quantify velocity and TI downstream from prosthetic heart valves, which may allow assessment of these aspects of prosthetic valvular function in postoperative patients. J. Magn. Reson. Imaging 2010;31:1075–1080. © 2010 Wiley‐Liss, Inc.
Modified brix model analysis of bone perfusion in subjects of varying bone mineral density
Authors: Ma Heather Ting , Griffith James F. , Yeung David K. , Leung P.C. 
Published: April 2010

AbstractPurpose:To apply pharmacokinetic modeling to the investigation of bone perfusion in subjects of varying bone mineral density.Materials and Methods:This study re‐analyzed previous experimental data. A modified pharmacokinetic model was applied to data obtained from two prior studies of dynamic contrast‐enhanced MR imaging of L3 vertebral body in 165 subjects (65 males, 100 females), classified into three groups (normal, osteopenia, and osteoporosis) according to bone mineral density. Three parameters, amplitude A, exchange rate (kep), and elimination rate (kel), were obtained by fitting the signal intensity to the pharmacokinetic model. These parameters were compared across the three groups for males and females, respectively.Results:Perfusion parameters, amplitude A was found to be reduced in osteoporotic subjects with additional, though less pronounced, reductions found in the permeability constant (A*kep) and the elimination rate (kel). Increased marrow fat content was found in osteoporotic bone, which helped to partially explain the observed reduction in interstitial space.Conclusion:By pharmacokinetic model, bone perfusion can be quantitatively analyzed with alteration in functional parameters related to microcirculation in subjects of varying bone mineral density. Developing bone marrow specific pharmacokinetic models should help to deepen knowledge of physiological and pathological perfusion changes occurring in bone. J. Magn. Reson. Imaging 2010;31:1169–1175. © 2010 Wiley‐Liss, Inc.
Ruthenium(III)‐mediated oxidation of D‐mannitol by cerium(IV) in aqueous sulfuric acid medium: A kinetic and mechanistic approach
Authors: Hosahalli Rajeshwari V. , Savanur Anita P. , Nandibewoor Sharanappa T. , Chimatadar Shivamurti A. 
Published: April 2010

AbstractThe oxidation of D‐mannitol by cerium(IV) has been studied spectrophotometrically in aqueous sulfuric acid medium at 25°C at constant ionic strength of 1.60 mol dm−3. A microamount of ruthenium(III) (10−6 mol dm−3) is sufficient to enhance the slow reaction between D‐mannitol and cerium(IV). The oxidation products were identified by spot test, IR and GC‐MS spectra. The stoichiometry is 1:4, i.e., [D‐mannitol]: [Ce(IV)] = 1:4. The reaction is first order in both cerium(IV) and ruthenium(III) concentrations. The order with respect to D‐mannitol concentration varies from first order to zero order as the D‐mannitol concentration increases. Increase in the sulfuric acid concentration decreases the reaction rate. The added sulfate and bisulfate decreases the rate of reaction. The active species of oxidant and catalyst are Ce(SO4)2 and [Ru(H2O)6]3+, respectively. A possible mechanism is proposed. The activation parameters are determined with respect to a slow step and reaction constants involved have been determined. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 440–452, 2010
In vivo near‐IR imaging of approximal dental decay at 1,310 nm
Authors: Staninec Michal , Lee Chulsung , Darling Cynthia L. , Fried Daniel 
Published: April 2010

AbstractObjectiveThe high transparency of dental enamel in the near‐IR (NIR) light at 1,310‐nm can be exploited for imaging dental caries without the use of ionizing radiation (X‐rays). We present the results of the first in vivo imaging study in which NIR images were acquired of approximal contact surfaces.MethodsNIR imaging hand‐pieces were developed and attached to a compact InGaAs focal plane array and subsequently used to acquire in vivo NIR images of 33 caries lesions on 18 test subjects. The carious lesions were discernible on bitewing radiographs, but were not visible upon clinical examination.ResultsNIR images were acquired in vivo from three directions and the majority of lesions examined were too small to require restoration, based on accepted bitewing radiograph criteria. All but one of the 33 lesions examined were successfully imaged from at least one direction.ConclusionThis first in vivo study of imaging at the 1,310‐nm wavelength region shows that NIR imaging has great potential as a screening tool for the detection of approximal lesions without the use of ionizing radiation. Lasers Surg. Med. 42:292–298, 2010. © 2010 Wiley‐Liss, Inc.
Blood flow assessment with magnetic resonance imaging after 1.9 µm diode laser‐assisted microvascular anastomosis
Authors: Leclère Franck Marie P. , Schoofs Michel , Auger Florent , Buys Bruno , Mordon Serge R. 
Published: April 2010

AbstractBackground and ObjectivesMicrovascular surgery associates intricate surgical techniques to join tiny blood vessels and help transfer large amount of tissues. Successful venous anastomosis remains the main challenge because inadequate blood flow correlates with a major risk of free flaps venous congestion and thrombosis. The aim of this study is to assess blood flow after laser‐assisted microvascular anastomosis (LAMA) using a 1.9‐µm diode laser.Study Design/Materials and MethodsLAMA was performed on a series of 10 external jugular veins of Wistar rats. Two stay sutures and a standard laser tissue welding technique (λ: 1.9 µm; power: 110 mW) were used. Similarly, a series of 10 conventional venous anastomosis were performed (CSMA). In both groups, contralateral non‐operated jugular veins were used as control. MRI was used to perform positioning, anatomical, angiographic blood flow sequences, 1 day post‐procedure and at 1, 4 and 8 weeks.ResultsVenous patency rate was 100% at the time of surgery. Mean clamping time was 7.9 minutes in the LAMA group compared to 11.4 minutes in the CSMA group. In the angiographic sequence, there were no aneurysms in both groups for all observation periods. At post‐operative day 1, mean loss of blood flow at the level of anastomosis in the LAMA group was 7% compared with 22% in the CSMA group. At 1, 4 and 8 weeks, blood flow reduction was greater in the CSMA group: 34%, 38% and 41%, respectively, compared to 12%, 15% and 16% in the LAMA group. Moreover, three cases of thrombosis were observed in the venous anastomosis performed with the conventional technique at 1 (n = 2) and 3 months (n = 1).ConclusionThe flow‐MRI further demonstrates that 1.9 µm diode LAMA is a consistent, reliable and reproducible technique, capable of improving blood flow in veins when compared to conventional surgery. Lasers Surg. Med. 42:299–305, 2010. © 2010 Wiley‐Liss, Inc.
Improving TV weather broadcasts with technological advancements: two cases from a 20 year perspective
Authors: Bech Joan , Molina Tomàs , Vilaclara Eliseu , Lorente Jeroni 
Published: April 2010

AbstractThe introduction of technological advancements in TV weather broadcasts has been a constant trend, particularly in the last 20 years. Rapidly evolving techniques, both from the point of view of new meteorological products or the use of advanced computer generated graphics, have offered a wide choice of possibilities to enhance information content and communication capability. However, despite the potential advantage of technological innovation, a case‐by‐case careful feasibility analysis is always required, including not only technical and economical aspects, but most importantly communication issues bearing in mind the education and acceptance of the audience.In this paper two specific cases of technological advances in TV weather broadcasts, seen from the perspective of the last 20 years, are examined: the introduction of weather radar images and the use of animated characters as weathercasters. These cases are illustrated from the experience acquired in TVC, the public Television of Catalonia (NE Spain). Direct access to weather radar data was first made possible within the framework of a joint collaboration agreement with the University of Barcelona and the Meteorological Service of Catalonia, which installed a new C‐band Doppler radar. The use of animated characters as weathercasters was the result of developing and advanced human‐like interface accessing an already existing database fed automatically by NWP forecasts. In each case a description of both technical aspects and also of the benefits and challenges seen from the communication point of view found in their introduction in TV weather broadcasts is provided. Copyright © 2010 Royal Meteorological Society
Public perception of and response to severe weather warnings in Nova Scotia, Canada
Authors: Silver Amber , Conrad Catherine 
Published: April 2010

AbstractHurricane Juan, which struck Atlantic Canada on 29 September, 2003, revealed the full extent of public vulnerability to severe weather events in Nova Scotia. In this study, 130 people were interviewed via a systematic sampling technique to examine their perception of severe weather warnings, and to determine what actions (if any) they are most likely to take when a warning has been posted. It was found that different target groups (e.g. the elderly, students) use different modes of media to obtain their severe weather information. It is recommended that forecast centres tailor their advisories for specific media sources so as best to reach various target groups. It was also found that respondents are generally satisfied with the weather warnings they receive, but there is a lack of awareness of the existence and extent of public vulnerability in Nova Scotia. The development of a comprehensive education campaign which will outline various facets of social vulnerability, while also offering recommendations on how best to lower existing social vulnerability, is critical. Copyright © 2010 Royal Meteorological Society
3D magnetization‐prepared imaging using a stack‐of‐rings trajectory
Authors: Wu Holden H. , Nishimura Dwight G. 
Published: April 2010

AbstractEfficient acquisition strategies for magnetization‐prepared imaging based on the three‐dimensional (3D) stack‐of‐rings k‐space trajectory are presented in this work. The 3D stack‐of‐rings can be acquired with centric ordering in all three dimensions for greater efficiency in capturing the desired contrast. In addition, the 3D stack‐of‐rings naturally supports spherical coverage in k‐space for shorter scan times while achieving isotropic spatial resolution. While non‐Cartesian trajectories generally suffer from greater sensitivity to system imperfections, the 3D stack‐of‐rings can enhance magnetization‐prepared imaging with a high degree of robustness to timing delays and off‐resonance effects. As demonstrated with phantom scans, timing errors and gradient delays only cause a bulk rotation of the 3D stack‐of‐rings reconstruction. Furthermore, each ring can be acquired with a time‐efficient retracing design to resolve field inhomogeneities and enable fat/water separation. To demonstrate its effectiveness, the 3D stack‐of‐rings are considered for the case of inversion‐recovery‐prepared structural brain imaging. Experimental results show that the 3D stack‐of‐rings can achieve higher signal‐to‐noise ratio and higher contrast‐to‐noise ratio within a shorter scan time when compared to the standard inversion‐recovery‐prepared sequence based on 3D Cartesian encoding. The design principles used for this specific case of inversion‐recovery‐prepared brain imaging can be applied to other magnetization‐prepared imaging applications. Magn Reson Med 63:1210–1218, 2010. © 2010 Wiley‐Liss, Inc.
Concatenated and parallel optimization for the estimation of T1 map in FLASH MRI with multiple flip angles
Authors: Wang Defeng , Shi Lin , Wang Yi‐Xiang J. , Yuan Jing , Yeung David K.W. , King Ann D. , Ahuja Anil T. , Heng Pheng Ann 
Published: April 2010

AbstractMost traditional methods for T1 map estimation in MRI with fast low‐angle‐shot sequences are aimed at high efficiency by compromising the fitting accuracy. In this paper, the fundamental problem of parameter estimation in fast low‐angle‐shot MRI was re‐examined, and an accurate and fast optimization approach, named concatenated optimization for parameter estimation, was proposed for the regression of data points acquired with multiple flip angles. The initial estimation of T1 was obtained from the linear regression, followed by the constrained nonlinear regression based on the initial estimates. This heterogeneous initialization strategy improves the fitting accuracy and reduces the computational time. A computationally efficient implementation of concatenated optimization for parameter estimation was achieved based on the graphic processing unit, named as concatenated optimization for parameter estimation graphic processing unit. In experimental comparison with Fram's method and the Fitter Tool in Jim, the proposed methods are capable of achieving significantly higher efficiency and more accurate estimations. Magn Reson Med 63:1431–1436, 2010. © 2010 Wiley‐Liss, Inc.
Optimum SNR data compression in hardware using an Eigencoil array
Authors: King Scott B. , Varosi Steve M. , Duensing G. Randy 
Published: April 2010

AbstractWith the number of receivers available on clinical MRI systems now ranging from 8 to 32 channels, data compression methods are being explored to lessen the demands on the computer for data handling and processing. Although software‐based methods of compression after reception lessen computational requirements, a hardware‐based method before the receiver also reduces the number of receive channels required. An eight‐channel Eigencoil array is constructed by placing a hardware radiofrequency signal combiner inline after preamplification, before the receiver system. The Eigencoil array produces signal‐to‐noise ratio (SNR) of an optimal reconstruction using a standard sum‐of‐squares reconstruction, with peripheral SNR gains of 30% over the standard array. The concept of “receiver channel reduction” or MRI data compression is demonstrated, with optimal SNR using only four channels, and with a three‐channel Eigencoil, superior sum‐of‐squares SNR was achieved over the standard eight‐channel array. A three‐channel Eigencoil portion of a product neurovascular array confirms in vivo SNR performance and demonstrates parallel MRI up toR= 3. This SNR‐preserving data compression method advantageously allows users of MRI systems with fewer receiver channels to achieve the SNR of higher‐channel MRI systems. Magn Reson Med 63:1346–1356, 2010. © 2010 Wiley‐Liss, Inc.
Phase‐field dithering for active catheter tracking
Authors: Dumoulin Charles L. , Mallozzi Richard P. , Darrow Robert D. , Schmidt Ehud J. 
Published: April 2010

AbstractA strategy to increase the robustness of active MR tracking of microcoils in low signal‐to‐noise ratio conditions was developed and tested. The method employs dephasing magnetic field gradient pulses that are applied orthogonal to the frequency‐encoding gradient pulse used in conventional point‐source MR tracking. In subsequent acquisitions, the orthogonal dephasing gradient pulse is rotated while maintaining a perpendicular orientation with respect to the frequency‐encoding gradient. The effect of the dephasing gradient is to apply a spatially dependent phase shift in directions perpendicular to the frequency‐encoding gradient. Since the desired MR signal for robust MR tracking comes from the small volume of nuclear spins near the small detection coil, the desired signal is not dramatically altered by the dephasing gradient. Undesired MR signals arising from larger volumes (e.g., due to coupling with the body coil or surface coils), on the other hand, are dephased and reduced in signal intensity. Since the approach requires no a priori knowledge of the microcoil orientation with respect to the main magnetic field, data from several orthogonal dephasing gradients are acquired and analyzed in real time. One of several selection algorithms is employed to identify the “best” data for use in the coil localization algorithm. This approach was tested in flow phantoms and animal models, with several multiplexing schemes, including the Hadamard and zero‐phase reference approaches. It was found to provide improved MR tracking of untuned microcoils. It also dramatically improved MR tracking robustness in low signal‐to‐noise‐ratio conditions and permitted tracking of microcoils that were inductively coupled to the body coil. Magn Reson Med 63:1398–1403, 2010. © 2010 Wiley‐Liss, Inc.
Separation of macrovascular signal in multi‐inversion time arterial spin labelling MRI
Authors: Chappell Michael A. , MacIntosh Bradley J. , Donahue Manus J. , Günther Matthias , Jezzard Peter , Woolrich Mark W. 
Published: April 2010

AbstractArterial spin labeling (ASL) provides a noninvasive method to measure brain perfusion and is becoming an increasingly viable alternative to more invasive MR methods due to improvements in acquisition, such as the use of a three‐dimensional GRASE readout. A potential source of error in ASL measurements is signal arising from intravascular blood that is destined for more distal tissue. This is typically suppressed using diffusion gradients in many ASL sequences. However, several problems exist with this approach, such as the choice of cutoff velocity and gradient direction and incompatibility with certain readout modules. An alternative approach is to explicitly model the intravascular signal. This study exploits this approach by using multi‐inversion time ASL data with a recently developed model‐fitting method. The method employed permits the intravascular contribution to be discarded in voxels where there is no support in the data for its inclusion, thereby addressing the issue of overfitting. It is shown by comparing data with and without flow suppression, and by comparing the intravascular contribution in GRASE ASL data to MR angiographic images, that the model‐fitting approach can provide a viable alternative to flow suppression in ASL where suppression is either not feasible or not desirable. Magn Reson Med 63:1357–1365, 2010. © 2010 Wiley‐Liss, Inc.
Optimal design of multiple‐channel RF pulses under strict power and SAR constraints
Authors: Brunner David O. , Pruessmann Klaas P. 
Published: April 2010

AbstractParallel radio frequency transmission has recently been explored as a means of tailoring the spatial response of MR excitation. In particular, parallel transmission is increasingly used to accelerate radio frequency pulses that rely on time‐varying gradient fields to achieve selectivity in multiple dimensions. The design of the underlying multiple‐channel radio frequency waveforms is mostly based on regularized least‐squares optimization in close analogy with image reconstruction in parallel imaging. However, this analogy has important limitations. Unlike image reconstruction, the design of radio frequency waveforms is subject to multiple strict constraints, which arise from technical power limits, as well as safety limits on local and global energy deposition in vivo. To optimize excitation profiles under such strict constraints, it is proposed to depart from the regularization strategy and rely on semidefinite programming instead. To render this approach fast, it is performed in a reduced search space, which is obtained by initial Lanczos iteration. The proposed algorithm is demonstrated to enable efficient pulse optimization within exactly the given constraints, including local specific absorption rate limits for multiple compartments. It is also shown that the proposed approach readily accommodates advanced forward models of the excitation process, including the effects of local off‐resonance and transverse relaxation. Magn Reson Med 63:1280–1291, 2010. © 2010 Wiley‐Liss, Inc.
Susceptibility mapping in the human brain using threshold‐based k‐space division
Authors: Wharton Sam , Schäfer Andreas , Bowtell Richard 
Published: April 2010

AbstractA method for calculating quantitative three‐dimensional susceptibility maps from field measurements acquired using gradient echo imaging at high field is presented. This method is based on division of the three‐dimensional Fourier transforms of high‐pass‐filtered field maps by a simple function that is the Fourier transform of the convolution kernel linking field and susceptibility, and uses k‐space masking to avoid noise enhancement in regions where this function is small. Simulations were used to show that the method can be applied to data acquired from objects that are oriented at one angle or multiple angles with respect to the applied field and that the use of multiple orientations improves the quality of the calculated susceptibility maps. As part of this work, we developed an improved approach for high‐pass filtering of field maps, based on using an arrangement of dipoles to model the fields generated by external structures. This approach was tested on simulated field maps from the substantia nigra and red nuclei. Susceptibility mapping was successfully applied to experimental measurements on a structured phantom and then used to make measurements of the susceptibility of the red nuclei and substantia nigra in healthy subjects at 3 and 7 T. Magn Reson Med 63:1292–1304, 2010. © 2010 Wiley‐Liss, Inc.