bluuebunny/crossref_metadata_2025 huggingface dataset:
Increased brain tumor resection using fluorescence image guidance in a preclinical model
Authors: Bogaards Arjen , Varma Abhay , Collens Sean P. , Lin Aihua , Giles Anoja , Yang Victor X.D. , Bilbao Juan M. , Lilge Lothar D. , Muller Paul J. , Wilson Brian C.
Published: September 2004

Background and Objectives

Fluorescence image‐guided brain tumor resection is thought to assist neurosurgeons by visualizing those tumor margins that merge imperceptibly into normal brain tissue and, hence, are difficult to identify. We compared resection completeness and residual tumor, determined by histopathology, after white light resection (WLR) using an operating microscope versus additional fluorescence guided resection (FGR).

Study Design/Materials and Methods

We employed an intracranial VX2 tumor in a preclinical rabbit model and a fluorescence imaging/spectroscopy system, exciting and detecting the fluorescence of protoporphyrin IX (PpIX) induced endogenously by administering 5‐aminolevulinic acid (ALA) at 4 hours before surgery.

Results

Using FGR in addition to WLR significantly increased resection completeness by a factor 1.4 from 68±38 to 98±3.5%, and decreased the amount of residual tumor post‐resection by a factor 16 from 32±38 to 2.0±3.5% of the initial tumor volume.

Conclusions

Additional FGR increased completeness of resection and enabled more consistent resections between cases. Lasers Surg. Med. 35:181–190, 2004. © 2004 Wiley‐Liss, Inc.
Peripheral thermal and mechanical damage to dentin with microsecond and sub‐microsecond 9.6 μm, 2.79 μm, and 0.355 μm laser pulses
Authors: Rosa Alfredo Dela , Sarma Anupama V. , Le Charles Q. , Jones Robert S. , Fried Daniel
Published: September 2004

Background and Objectives

It is desirable to minimize peripheral thermal damage during laser irradiation, since thermal damage to collagen and mineral compromises the bond strength to restorative materials in dentin and inhibits healing and osteointegration in bone. There were two primary objectives of this study. The first objective was to measure the degree of thermal damage peripheral to incisions in dentin produced with lasers resonant to the specific absorption bands of water, collagen, and hydroxyapatite with varying pulse duration using polarized‐light microscopy (PLM). The second objective was to use synchrotron radiation infrared spectromicroscopy (SR‐FTIR) to identify the specific chemical nature of the optical changes observed under PLM in the respective zones of thermal damage peripheral to the laser incisions.

Study Design/Materials and Methods

Precise incisions were produced in 3×3 mm2blocks of human dentin using CO2(9.6 μm), Er:YSGG (2.79 μm), and Nd:YAG (355 nm) lasers with and without a computer controlled water‐spray. Optical coherence tomography (OCT) was used to obtain optical cross‐sections of each incision to determine the rate of ablation. The peripheral thermal damage zone around each incision was analyzed using PLM and SR‐FTIR.

Results

Thermally induced chemical changes to both mineral and the collagen matrix were observed with SR‐FTIR with a 10 μm spatial resolution and those changes were correlated with optical changes observed with PLM. Minimal (<10 μm) thermal damage was observed for pulse durations less than the thermal relaxation time (Tr) of the deposited laser energy, with and without applied water at 9.6 μm and with only applied water at 2.79 μm. For pulse durations greater than Tr, greater peripheral thermal damage was observed for both IR laser wavelengths with and without the water‐spray. There was minimal thermal damage for 355 nm laser pulses less than Trwith and without applied water; however, extensive mechanical damage (cracks) was observed.

Conclusions

High resolution SR‐FTIR is well suited for characterization of the chemical changes that occur due to thermal damage peripheral to laser incisions in proteinaceous hard tissues. Sub‐microsecond pulsed IR lasers resonant with water and mineral absorption bands ablate dentin efficiently with minimal thermal damage. Similar laser parameters are expected to apply to the ablation of alveolar bone. Lasers Surg. Med. 35:214–228, 2004. © 2004 Wiley‐Liss, Inc.
Laser irradiation of the guinea pig basilar membrane
Authors: Wenzel Gentiana I. , Pikkula Brian , Choi Chul‐Hee , Anvari Bahman , Oghalai John S.
Published: September 2004

Background and Objectives

The cochlea is the part of the inner ear that transduces sound waves into neural signals. The basilar membrane, a connective tissue sheet within the cochlea, is tonotopically tuned based on the spatial variation of its mass, stiffness, and damping. These biophysical properties are mainly defined by its constituent collagen fibers. We sought to assess the effect of laser irradiation on collagen within the basilar membrane using histological analysis.

Study Design/Materials and Methods

Four excised guinea pig cochleae were stained with trypan blue. From these, two were irradiated with a 600 nm pulsed dye laser and two were used as controls. Collagen organization was visualized using polarization microscopy.

Results

Laser irradiation reduced the birefringence within the basilar membrane as well as within other stained collagen‐containing structures. Larger reductions in birefringence were measured when more laser pulses were given. The effects were similar across all turns of each cochlea.

Conclusions

Laser irradiation causes immediate alterations in collagen organization within the cochlea that can be visualized with polarization microscopy. These alterations may affect cochlear tuning. Ongoing research is aimed at analyzing the effect of laser irradiation on cochlear function. It is conceivable that this technique may have therapeutic benefits for patients with high‐frequency sensorineural hearing loss. Lasers Surg. Med. 35:174–180, 2004. © 2004 Wiley‐Liss, Inc.
Laser‐assisted vascular end to end anastomosis of elastin heterograft to carotid artery with an albumin stent: A preliminary in vivo study
Authors: Xie Hua , Bendre Suhas C. , Burke Allen P. , Gregory Kenton W. , Furnary Anthony P.
Published: September 2004

Background and Objectives

Laser‐assisted end to end vascular anastomosis of an elastin heterograft to native artery may prevent problems associated with currently available vascular synthetic grafts and conventional suture anastomosis.

Study Design/Materials and Methods

A total of 21 anastomoses in the carotid arteries of 7 domestic swine were performed with an 800 nm laser and an albumin stent plus solder. There were 5 artery to artery and 16 elastin heterograft to native artery anastomoses. Operative parameters, vascular patency, and histology of the anastomoses were evaluated.

Results

Out of 21 anastomoses, 16 were patent for 3 hours. One artery to artery anastomosis was thrombosed and four elastin heterograft to artery anastomoses were excluded from the study due to heterograft burst. The average amount of applied energy was 212 J for artery to artery anastomosis and 273 J for elastin heterograft to native artery. Histology shows coagulative necrosis of the adventitia, hypereosinophilic contraction band in the media of native arteries and no changes in elastin heterografts.

Conclusions

Laser‐assisted vascular anastomosis (LAVA) of elastin heterograft to medium size vessel using an albumin stent is feasible. Chronic studies are warranted to determine long‐term patency and histology of the LAVA. Lasers Surg. Med. 35:201–205, 2004. © 2004 Wiley‐Liss, Inc.
Microarray analysis of prostate cancer progression to reduced androgen dependence: Studies in unique models contrasts early and late molecular events
Authors: Sirotnak F.M. , She Yuhong , Khokhar Nushmia Z. , Hayes Paula , Gerald William , Scher Howard I.
Published: September 2004

Three unique variants of the CWR22 human prostate cancer xenograft model (CWR22LD1, LD2, and LD3) with a decrease in dependence on androgens were selected under noncastrate conditions, i.e., by outgrowth after transplantation into male NCR (AT) nu mice without testosterone supplementation. These variants were unable to grow in castrated male mice. For comparison, a second set of variants with even less dependence on androgens (castrate‐resistant) were derived following outgrowth from CWR22 (CWR22Rv1 and RC) or CWRLD1 (CWR22RS) after transplantion in castrated male mice. The androgen receptor (AR) gene in the CWR22LD variants was transcriptionally active and was neither mutated nor significantly overexpressed compared to CWR22. Oligonucleotide microarray analysis showed distinctly different profiles of dysregulated gene expression among the CWR22LD variants. Groups of only 26–41 genes were dysregulated greater than threefold with a different proportion of up versus downregulated genes in each variant. Only one of the castrate‐resistant variants (CWR22Rv1) had a highly overexpressed AR gene but AR in this variant and the two other castrate‐resistant variants, CWR22 RS and RC, was not mutated beyond that seen in CWR22. In contrast to the CWR22LD variants, a total of 342, 295, and 222 genes were dysregulated at least threefold in CWR22Rv1, CWR22RS, and CWR22RC, respectively, differing as well in the proportion of up versus downregulated genes. Many of the genes dysregulated in CWR22LD1, LD2, and LD3 were further dysregulated in CWR22Rv1, RC, or RS. The most downregulated gene was microseminoprotein beta (MSPB). Along with cyclin D1, the most upregulated gene by an order of magnitude compared to other upregulated genes was hepatocyte growth factor (HGF) (scatter factor). These results suggest that the onset in the loss of androgen dependence in CWR22 proceeds through multiple pathways and does not require any direct change in the status of AR. However, upregulation of other survival pathways like that involving HGF in these studies could co‐activate AR signaling. The endogenous overexpression of genes regulating sterol biosynthesis also observed in castrate‐resistant CWR22 variants delineated a clinically relevant, compensatory mechanism for overcoming androgen deprivation reaffirming a central role for AR signaling in this process. © 2004 Wiley‐Liss, Inc.
Pharmacological inhibition of fatty acid synthase (FAS): A novel therapeutic approach for breast cancer chemoprevention through its ability to suppress Her‐2/neu (erbB‐2) oncogene‐induced malignant transformation
Authors: Menendez Javier A. , Mehmi Inderjit , Verma Vishal A. , Teng Poh K. , Lupu Ruth
Published: September 2004

We designed our experiments to evaluate whether fatty acid synthase (FAS), a lipogenic enzyme linked to tumor virulence in population studies of human cancer, is necessary for the malignant transformation induced by Her‐2/neu (erbB‐2) oncogene, which is overexpressed not only in invasive breast cancer but also in premalignant atypical duct proliferations and in ductal carcinoma in situ of the breast. To avoid the genetic complexities associated with established breast cancer cell lines, we employed NIH‐3T3 mouse fibroblasts engineered to overexpress human Her‐2/neu coding sequence. NIH‐3T3/Her‐2 cells demonstrated a significant upregulation of FAS protein expression, which was dependent on the upstream activation of mitogen‐activated protein kinase and phosphatidylinositol 3′‐kinase/AKT pathways. Remarkably, pharmacological FAS blockade using the mycotoxin cerulenin or the novel small compound C75 completely suppressed the state of Her‐2/neu‐induced malignant transformation by inhibiting the ability of NIH‐3T3/Her‐2 cells to grow under either anchorage‐independent (i.e., to form colonies in soft agar) or low‐serum monolayer conditions. Moreover, NIH‐3T3/Her‐2 fibroblasts were up to three times more sensitive to chemical FAS inhibitors relative to untransformed controls as determined by MTT‐based cell viability assays. In addition, pharmacological FAS blockade preferentially induced apoptotic cell death of NIH‐3T3/Her‐2 fibroblasts, as determined by an ELISA for histone‐associated DNA fragments and by the terminal deoxynucleotidyltransferase (TdT)‐mediated nick end labeling assay (TUNEL). Interestingly, the degree of Her‐2/neu oncogene expression in a panel of breast cancer cell lines was predictive of sensitivity to chemical FAS inhibitors‐induced cytotoxicity, while low‐FAS expressing and chemical FAS inhibitors‐resistant MDA‐MB‐231 breast cancer cells became hypersensitive to FAS blockade when they were engineered to overexpress Her‐2/neu. Our observations strongly suggest that inhibition of FAS activity may provide a new molecular avenue for chemotherapeutic prevention and/or treatment of Her‐2/neu‐related breast carcinomas. © 2004 Wiley‐Liss, Inc.
Resources, capabilities, and the performance of industrial firms: A multivariate analysis
Authors: Carmeli Abraham , Tishler Asher
Published: September 2004

This study uses multivariate analysis to assess the basic question asked by resource‐based view researchers: Do organizational resources and capabilities account for variations in firm performance? An analysis of survey responses of 93 industrial enterprises in Israel indicates that superiority of an industrial enterprise, in terms of four performance measures (return on sales, return on equity, market share change, and customer satisfaction), can be explained by a set of four core organizational resources and capabilities (managerial skills, organizational culture, organizational communication, and perceived organizational reputation). The results lend significant support to the premise of the resource‐based view of strategic management. Copyright © 2004 John Wiley & Sons, Ltd.
Compensating for innovation: Do small firms offer high‐powered incentives that lure talent and motivate effort?
Authors: Zenger Todd R. , Lazzarini Sergio G.
Published: September 2004

Empirical studies commonly confirm that small firms enjoy efficiency advantages in generating innovation. However, the origin of this advantage remains poorly understood. This study explores the hypothesis that small firms enjoy advantages over large firms in crafting effective, incentive‐intensive employment contracts that lure top engineering talent and motivate high effort. These hypotheses are tested using data from a sample of R&D engineers in Silicon Valley and the Route 128 area. Copyright © 2004 John Wiley & Sons, Ltd.
Redeployment of corporate resources: A study of acquisition strategies in the US defense industries, 1978–1996
Authors: Anand Jaideep
Published: September 2004

How are excess resources redeployed when an industry declines? These resources can be redeployed within the firm through diversification and across firms through a market interface. Acquisitions can play an important role in either of these mechanisms. First, acquisitions can provide new complementary resources and facilitate the redeployment of excess resources within the firm through recombination. Second, horizontal acquisitions can facilitate consolidation and disposal of excess or redundant resources that can be redeployed elsewhere through a market interface. I study both these kinds of acquisitions in the US defense industries (1978–1996), and explain the choice between the two acquisition strategies on the basis of the business environment, underlying resources of the firm, and to a lesser extent, as a consequence of agency forces within the firm. I derive implications for strategic transformation of firms, and the resource‐based and evolutionary perspectives. Copyright © 2004 John Wiley & Sons, Ltd.
Empirical evidence regarding the tension between knowledge sharing and knowledge expropriation in collaborations
Authors: Heiman Bruce A. , Nickerson Jack A.
Published: September 2004

Interfirm collaborations can raise a fundamental dilemma. To create value, collaborators may have to adopt a variety of practices to facilitate knowledge transfer. Deploying these practices may increase the likelihood that economically valuable knowledge, which is (1) beyond the scope of the collaboration, and (2) difficult to legally protect, is expropriated. How can firms manage this dilemma? The purpose of this paper is to empirically examine the veracity of a chain of propositions addressing this dilemma based on a novel joint knowledge‐based view/transaction cost economics framework. A plausible chain of relationships is briefly summarized and explored in detail empirically using unrelated datasets. The chain links two knowledge‐based attributes of collaboration—knowledge tacitness and problem‐solving complexity—to the use of knowledge management practices—high‐bandwidth communication channels and co‐specialized communication codes. These practices are economic responses to knowledge‐sharing difficulties as measured by tacitness and complexity. Increasing knowledge transparency via knowledge management practices, however, gives rise to opportunism hazards, which are safeguarded against via economizing governance choice. Our empirical effort examines the effects that two knowledge attributes of collaborations have on governance choice, first directly and then indirectly through the intervening linkages. Empirical results from both datasets indicate substantial support for the proposed chain of relationships. The results are provocative in that they offer the first preliminary evidence for a plausible reconciliation of two perspectives previously treated exclusively as adversaries. Copyright © 2004 John Wiley & Sons, Ltd.
Organizational choice in R&D alliances: Knowledge‐based and transaction cost perspectives
Authors: Sampson Rachelle C.
Published: September 2004

This study examines how firms choose organizational form for their R&D alliances. Encouraging cooperation in these alliances is often challenging, given the difficulties in knowledge sharing between partners and protecting the property rights over partner knowledge. Interestingly, knowledge‐based and transaction cost perspectives generate different hypotheses on alliance organization choice in this setting. When partner knowledge bases are very different, the risk of unintended transfer or leakage is reduced, yet the need for enhanced communication and knowledge sharing mechanisms remains undiminished. With a sample of 232 R&D alliances, I find more thorough support for the transaction cost hypothesis. Firms more likely select an equity joint venture as partner knowledge bases diverge and knowledge transfer becomes more difficult. When such knowledge bases are very different, however, firms are less likely to choose an equity joint venture over more contractual forms of alliance organization. Thus, these results provide empirical evidence on alliance organization choice and also have important implications for the fundamental question of why firms exist. Copyright © 2004 John Wiley & Sons, Ltd.
Reach out or reach within? Performance implications of alliances and location in biotechnology
Authors: Zaheer Akbar , George Varghese P.
Published: September 2004

The extensive literature on geographical clusters has argued that firms stand to gain from the knowledge spillovers and the easy availability of skills in regional agglomerations. At the same time, the research on strategic alliances, particularly in technology‐intensive industries, views alliances as vehicles for the transfer of technology and knowledge. Does membership in a geographical cluster or a network of alliances—an alliance cluster—benefit firms equally? More importantly, does it matter whether firms form alliances with firms within their geographical cluster, or do they do better by reaching out beyond their cluster? In this paper, we investigate these and other related questions in the context of technology‐intensive industries such as biotechnology and argue that the high‐level knowledge sensing and acquiring needs of firms in such industries may require combinations of both kinds of knowledge‐access mechanisms. We use the BioScan database to obtain 648 alliances for the period 1985–1998 among 248 public companies, and complement it with COMPUSTAT data to examine the effect of clustering and alliances on market value. Our results suggest that merely being part of geographical clusters is not enough, and nor is it adequate for firms to join alliance clusters. Rather, firms gain by forming alliances both within and beyond their geographical clusters, which highlights the complexities of acquiring technology‐intensive knowledge and suggests that the acquisition of knowledge in technology‐intensive settings is best achieved through mechanisms both formal and informal, both proximate and distant. Copyright © 2004 John Wiley & Sons, Ltd.
Competing in groups
Authors: Rowley Tim J. , Baum Joel A. C. , Shipilov Andrew V. , Greve Henrich R. , Rao Hayagreeva
Published: September 2004

In this study, we examine how the characteristics of clique structures affect the performance of firms embedded within the cliques. Although it is generally accepted in organization theory and strategic management that firms are embedded within ego and overarching industry networks that each affect their behavior and performance, there is little evidence on whether cliques are stable features of industry networks or affect firm behavior or performance. We theorize that the value of a clique to its members depends on (1) the network centrality of the clique and (2) the internal structure and organization (heterogeneity and inequality) of the clique. Our analysis of the Canadian investment banking industry from 1952 to 1990 provides empirical evidence of stable cliques, and indicates that while a clique's internal structure and organization materially affect firm‐level benefits of clique membership, its positional embeddedness within the industry network does not. Copyright © 2004 John Wiley & Sons, Ltd.
Vertical group formation: A social process perspective
Authors: Shanley Mark , Peteraf Margaret
Published: September 2004

Vertical groups are a common occurrence that is rarely studied as a group‐level phenomenon. This paper brings attention to the vertical group, as a collective actor, and group formation processes. We define the vertical group and describe, in brief, why they exist. We explore the issue of how they form and the social processes under which different types of groups are likely to emerge. These include trial and error learning, social learning, and social identification. We introduce a framework that shows how variation in two more fundamental enabling conditions affects both the group development process and the characteristics of the emerging groups. Copyright © 2004 John Wiley & Sons, Ltd.
Localized in vivo human 1H MRS at very short echo times
Authors: Zhong Kai , Ernst Thomas
Published: September 2004

A new point‐resolved spectroscopy (PRESS) sequence was developed that allows localized human proton MR spectra to be acquired at echo times (TEs) of 10 ms or less. The method was implemented on a 4 Tesla Varian research console and a clinical 3 Tesla Siemens Trio scanner. Human brain spectra acquired in vivo from the prefrontal cortex at TE = 8 ms showed improved signals from coupled resonances (such as glutamate, glutamine, and myo‐inositol) compared to spectra acquired at TE = 30 ms. These improvements should result in more accurate quantitation of these metabolites. Magn Reson Med 52:898–901, 2004. © 2004 Wiley‐Liss, Inc.
Ultrafast 2D NMR spectroscopy using sinusoidal gradients: Principles and ex vivo brain investigations
Authors: Sela Noa , Degani Hadassa , Frydman Lucio
Published: September 2004

A new methodology capable of delivering complete 2D NMR spectra within a single scan was recently introduced. The resulting potential gain in time resolution could open new opportunities for in vivo spectroscopy, provided that the technical demands of the methodology are satisfied by the corresponding hardware. Foremost among these demands are the relatively short switching times expected from the applied gradient‐echo trains. These rapid transitions may be particularly difficult to accomplish on imaging systems. As a step toward solving this problem, we assessed the possibility of replacing the square‐wave gradient train currently used during the course of the acquisition by a shaped sinusoidal gradient. Examples of the implementation of this protocol are given, and successful ultrafast acquisitions of 2D NMR spectra with suitable spectral widths on a microimaging probe (for both phantom solutions and ex vivo mouse brains) are demonstrated. Magn Reson Med 52:893–897, 2004. © 2004 Wiley‐Liss, Inc.
In vivo tumor lactate relaxation measurements by selective multiple‐quantum‐coherence (Sel‐MQC) transfer
Authors: Muruganandham Manickam , Koutcher Jason A. , Pizzorno Giuseppe , He Qiuhong
Published: September 2004

The frequency‐selective multiple‐quantum‐coherence (Sel‐MQC) lactate (Lac) filter offers complete lipid and water suppression in a single scan for robust in vivo detection of tumor Lac, even in the presence of abundant lipids. Conversion of the detected signal into accurate tissue concentrations of Lac requires knowledge of in vivo Lac T1 and T2 relaxation times. This work reports modifications to the Sel‐MQC pulse sequence, T1‐ and T2‐Sel‐MQC, that facilitate relaxation measurements of Lac. The T1‐Sel‐MQC sequence combines an inversion prepulse with the Sel‐MQC filter. The T2‐Sel‐MQC sequence incorporates a CH3‐selective 180° pulse during the MQ preparation period to overcome the J‐modulation effects and allow the insertion of variable echo delays. The performance of these sequences was evaluated with the use of phantoms and subcutaneous murine tumor models in vivo. The present approach will allow investigators to correct for the relaxation‐induced Lac signal loss in Sel‐MQC experiments for the quantitative mapping of in vivo tumor Lac distribution. Magn Reson Med 52:902–906, 2004. © 2004 Wiley‐Liss, Inc.
Noise‐adaptive nonlinear diffusion filtering of MR images with spatially varying noise levels
Authors: Samsonov Alexei A. , Johnson Chris R.
Published: September 2004

Anisotropic diffusion filtering is widely used for MR image enhancement. However, the anisotropic filter is nonoptimal for MR images with spatially varying noise levels, such as images reconstructed from sensitivity‐encoded data and intensity inhomogeneity‐corrected images. In this work, a new method for filtering MR images with spatially varying noise levels is presented. In the new method, a priori information regarding the image noise level spatial distribution is utilized for the local adjustment of the anisotropic diffusion filter. Our new method was validated and compared with the standard filter on simulated and real MRI data. The noise‐adaptive method was demonstrated to outperform the standard anisotropic diffusion filter in both image error reduction and image signal‐to‐noise ratio (SNR) improvement. The method was also applied to inhomogeneity‐corrected and sensitivity encoding (SENSE) images. The new filter was shown to improve segmentation of MR brain images with spatially varying noise levels. Magn Reson Med 52:798–806, 2004. © 2004 Wiley‐Liss, Inc.
Reproducibility of fMRI at 1.5 T in a strictly controlled motor task
Authors: Liu Jing Z. , Zhang Luduan , Brown Robert W. , Yue Guang H.
Published: September 2004

Reproducibility of functional MRI (fMRI) data has been controversial. This issue was examined in this study by evaluating a strictly controlled voluntary force‐matching handgrip task. Handgrip force, electromyogram (EMG), and fMRI data of brain activity were simultaneously recorded during the task performance. The task was repeated three times in each of the two experimental sessions. While force remained unchanged and EMG showed little variation across trials and sessions, the results revealed that fMRI‐measured brain signals varied significantly among individual trials. However, the averaged fMRI signals over the three trials did not show significant difference between the two sessions. Our data suggest that fMRI is better at defining brain activation qualitatively than quantitatively, i.e., the locations of the activation areas could be reproduced quite reliably while their sizes fluctuated substantially. Magn Reson Med 52:751–760, 2004. © 2004 Wiley‐Liss, Inc.
Automated rectilinear self‐gated cardiac cine imaging
Authors: Crowe Mark E. , Larson Andrew C. , Zhang Qiang , Carr James , White Richard D. , Li Debiao , Simonetti Orlando P.
Published: September 2004

ECG‐based gating in cardiac MR imaging requires additional patient preparation time, is susceptible to RF and magnetic interference, and is ineffective in a significant percentage of patients. “Wireless” or “self‐gating” techniques have been described using either interleaved central k‐space lines or projection reconstruction to obtain MR signals synchronous with the cardiac cycle. However, the interleaved, central line method results in a doubling of the acquisition time, while radial streak artifacts are encountered with the projection reconstruction method. In this work, a new self‐gating technique is presented to overcome these limitations. A retrospectively gated TrueFISP cine sequence was modified to acquire a short second echo after the readout and phase gradients are rewound. The information obtained from this second echo was used to derive a gating signal. This technique was compared to ECG‐based gating in 10 healthy volunteers and shown to have no significant difference in image quality. The results indicate that this method could serve as an alternative gating strategy without the need for external physiological signal detection. Magn Reson Med 52:782–788, 2004. © 2004 Wiley‐Liss, Inc.
Finite‐difference simulations of 3He diffusion in 3D alveolar ducts: Comparison with the “cylinder model”
Authors: Fichele Stanislao , Paley Martyn N.J. , Woodhouse Neil , Griffiths Paul D. , van Beek Edwin J.R. , Wild Jim M.
Published: September 2004

Time‐dependent measurements of 3He diffusion in the lung could provide an accurate method to quantify alveolar length scales and the progression of diseases such as emphysema. However, the apparent diffusion coefficient (ADC) presents a complex problem to model and solve analytically. Here, finite‐difference methods were used to simulate diffusion in 3D alveolar ducts. The results were compared to the only available analytical model—the “cylinder model”—from which it is possible to estimate the average radii of the alveolar ducts from in vivo data. The trend in data observed from simulations was found to agree well with the cylinder model. However, the cylinder model always overestimated the average radii of the simulated alveolar ducts. The simulations also demonstrated that the measurement of the longitudinal ADC (along the alveolar ducts) should be sensitive to early emphysematous changes, whereas the measured radii should be far less sensitive. Magn Reson Med 52:917–920, 2004. © 2004 Wiley‐Liss, Inc.
In vivo safe catheter visualization and slice tracking using an optically detunable resonant marker
Authors: Weiss Steffen , Kuehne Titus , Brinkert Florian , Krombach Gabriele , Katoh Marcus , Schaeffter Tobias , Guenther Rolf W. , Buecker Arno
Published: September 2004

The purpose of this study was to test the in vivo feasibility of safe automatic catheter tracking based on an optically detunable resonant marker installed on the catheter tip, and also to test the compatibility of this approach with guidewire materials. The design of the resonant marker and the integration into the real‐time MR environment is described. The catheter was used for real‐time MR‐guided catheterization of the aorta, left ventricle, and carotid in two swine. For in‐plane visualization, the marker was repeatedly detuned. For automatic slice tracking, a projection difference measurement including detuning was interleaved with the imaging sequence. In vitro experiments were conducted to investigate the RF‐safety of the marker and the effect of the guidewires on the signal intensity. For all orientations the marker provided excellent in vivo contrast using a radial steady‐state free‐precession sequence. Flashing of the marker by repetitive tuning/detuning further improved the in‐plane visualization. Automatic slice tracking during real‐time imaging was successfully performed. The plastic guidewires did not interfere with the marker, and detuning by guidewires containing nitinol could be compensated. In conclusion, automatic slice tracking as well as excellent in‐plane visualization can be achieved with this approach and it is safe with respect to RF transmission. Magn Reson Med 52:860–868, 2004. © 2004 Wiley‐Liss, Inc.
Inherent insensitivity to RF inhomogeneity in FLASH imaging
Authors: Wang Danli , Heberlein Keith , LaConte Stephen , Hu Xiaoping
Published: September 2004

Radiofrequency (RF) field inhomogeneity is an unavoidable problem in MRI, and it becomes severe at high magnetic fields due to the dependence of B1 on the sample. It leads to nonuniformities in image intensity and contrast, causing difficulties in quantitative interpretation and image segmentation. In this work, it is observed that with the fast low‐angle shot (FLASH) sequence, which is often used for anatomic imaging and morphometric studies, sensitivity to RF inhomogeneity can be substantially reduced when the same coil is used for both transmission and reception, and an appropriate nominal flip angle is employed. This observation can help us understand the signal behavior of FLASH in the presence of RF inhomogeneity, and provide a guide for selecting parameters in FLASH imaging. Magn Reson Med 52:927–931, 2004. © 2004 Wiley‐Liss, Inc.
Human whole‐blood relaxometry at 1.5T: Assessment of diffusion and exchange models
Authors: Stefanovic Bojana , Pike G. Bruce
Published: September 2004

Human whole‐blood relaxometry experiments were performed to allow the prediction of blood signal changes with blood oxygen saturation (Y) and refocusing interval (τ180). Such predictions are particularly relevant for spin‐echo (SE) blood oxygenation level‐dependent (BOLD) experiments and a recently proposed noninvasive fMRI method for measuring cerebral blood volume (CBV). Ensemble fitting of the entire set of T2 estimates, obtained over an extensive range of Y and τ180 values, was performed with the use of both a fast chemical exchange model and a model of diffusion in weak magnetic field inhomogeneities. The diffusion modeling resulted in a large reduction in the residual sum‐of‐squares compared to the fast exchange modeling. The longitudinal relaxation rate decreased linearly with Y, and increased with hematocrit. The results support the application of the recently reported diffusion model to describe deoxyhemoglobin (dHb)‐induced blood transverse relaxation rate enhancement at 1.5 T. Magn Reson Med 52:716–723, 2004. © 2004 Wiley‐Liss, Inc.
Measurement of compartment size in q‐space experiments: Fourier transform of the second derivative
Authors: Kuchel Philip W. , Eykyn Thomas R. , Regan David G.
Published: September 2004

Restricted diffusion in compartmentalized systems can lead to spatial coherence phenomena being observed in q‐space plots from pulsed field gradient spin‐echo (PGSE) nuclear magnetic resonance (NMR) experiments. The underlying features observed in these plots contain information on the geometry of the compartments that is otherwise difficult to obtain. A numerical procedure is proposed that accentuates these coherence features: the data are weighted with a bell‐shaped window function, interpolated with a shifting cubic spline, and then the second derivative is taken prior to Fourier transformation. The window function provides apodization of the noisy data at high q values, while it and the second derivative are equivalent to applying a high‐pass filter to remove the zero‐ or low‐frequency components in the echo‐signal attenuation. Using a combination of theory, Monte Carlo simulations, and data from PGSE NMR experiments on human red blood cells, we demonstrate this to be a valuable processing tool for delineating the underlying coherence features. It should prove particularly useful where the coherence features are poorly defined or where more than one pattern is present in a q‐space plot. Magn Reson Med 52:907–912, 2004. © 2004 Wiley‐Liss, Inc.
Quantifying the intra‐ and extravascular contributions to spin‐echo fMRI at 3 T
Authors: Jochimsen Thies H. , Norris David G. , Mildner Toralf , Möller Harald E.
Published: September 2004

Functional MRI (fMRI) by means of spin‐echo (SE) techniques provides an interesting alternative to gradient‐echo methods because the contrast is based primarily on dynamic averaging associated with the blood oxygenation level‐dependent (BOLD) effect. In this article the contributions from different brain compartments to BOLD signal changes in SE echo planar imaging (EPI) are investigated. To gain a better understanding of the underlying mechanisms that cause the fMRI contrast, two experiments are presented: First, the intravascular contribution is decomposed into two fractions with different regimes of flow by means of diffusion‐weighting gradient schemes which are either flow‐compensated, or will maximally dephase moving spins. Second, contributions from the intra‐ and extravascular space are selectively suppressed by combining flow‐weighting with additional refocusing pulses. The results indicate two qualitatively different components of flowing blood which contribute to the BOLD contrast and a nearly equal share in functional signal from the intra‐ and extravascular compartments at TE ≈ 80 ms and 3 T. Combining these results, there is evidence that at least one‐half of the functional signal originates from the parenchyma in SE fMRI at 3 T. The authors suggest the use of flow‐compensated diffusion weighting for SE fMRI to improve the sensitivity to the parenchyma. Magn Reson Med 52:724–732, 2004. © 2004 Wiley‐Liss, Inc.
Pharmacokinetics of a triarylmethyl‐type paramagnetic spin probe used in EPR oximetry
Authors: Matsumoto Ken‐ichiro , English Sean , Yoo John , Yamada Ken‐ichi , Devasahayam Nallathamby , Cook John A. , Mitchell James B. , Subramanian Sankaran , Krishna Murali C.
Published: September 2004

The paramagnetic spin probe Oxo63 is used in oximetric imaging studies based on electron paramagnetic resonance (EPR) methods by monitoring the oxygen‐dependent linewidth while minimizing the contributions from self‐broadening seen at high probe concentrations. Therefore, it is necessary to determine a suitable dose of Oxo63 for EPR‐based oxygen mapping where the self‐broadening effects are minimized while signal intensity adequate for imaging can be realized. A constant tissue concentration of spin probe would be useful to image a subject and assess changes in pO2 over time; accumulation or elimination of the compound in specific anatomical regions could translate to and be mistaken for changes in local pO2, especially in OMRI‐based oximetry. The in vivo pharmacokinetics of the spin probe, Oxo63, after bolus and/or continuous intravenous infusion was investigated in mice using a novel approach with X‐band EPR spectroscopy. The results show that the half‐life in blood was 17–21 min and the clearance by excretion was 0.033–0.040 min−1. Continuous infusion following a bolus injection of the probe was found to be effective to obtain stable plasma concentration as well as image intensity to permit reliable pO2 estimates. Magn Reson Med 52:885–892, 2004. Published 2004 Wiley‐Liss, Inc.
Assessment of axonal fiber tract architecture in excised rat spinal cord by localized NMR q‐space imaging: Simulations and experimental studies
Authors: Chin Chih‐Liang , Wehrli Felix W. , Fan Yingli , Hwang Scott N. , Schwartz Eric D. , Nissanov Jonathan , Hackney David B.
Published: September 2004

NMR q‐space imaging is a method designed to obtain information from porous materials where diffusion‐diffraction phenomena were observed from which pore size was derived. Recently, the technique has been applied to the study of biological structures as well. Although diffusive diffraction has so far not been observed in multicellular systems, displacement profiles have been used with some success as a means to estimate structure size. However, there have been no quantitative correlations of the retrieved structure sizes with histology. Clearly, the complexity of tissue architecture poses significant challenges to the interpretation of q‐space data. In this work, simulations were first performed on a two‐compartment model to demonstrate the effects of interference of the diffraction patterns arising from intra and extra‐axonal compartments and finite boundary permeability on q‐space data. Second, q‐space echo attenuation was simulated on the basis of histologic images of various rat spinal cord fiber tracts and the information obtained from the displacement profiles were compared with structural parameters computed from the histologic images. The results show that calculated mean displacements and kurtosis parallel mean axon size and axonal density. Finally, spatially localized q‐space measurements were carried out at the locations where simulations had previously been performed, resulting in displacement data that support those obtained by simulation. The data suggest the NMR q‐space approach has potential for nondestructive analysis of the axonal architecture in the mammalian spinal cord. Magn Reson Med 52:733–740, 2004. © 2004 Wiley‐Liss, Inc.
Projection imaging of the right coronary artery with an intravenous injection of contrast agent
Authors: Green Jordin D. , Schirf Brian E. , Omary Reed A. , McCarthy Richard M. , Carr James C. , Li Debiao
Published: September 2004

Contrast‐enhanced (CE) MR angiography of the right coronary artery (RCA) was performed using 2D thick‐slice projection imaging with a small (8 mL) intravenous injection of contrast agent in six volunteers. With a tight contrast bolus injection, the RCA was enhanced for a few seconds after the contrast bolus was washed out of the right ventricle. This allowed data to be acquired when only the RCA was enhanced. Using 2D thick‐slice magnetization prepared steady‐state free precession (SSFP) imaging, background signal was suppressed and a complete data set was acquired in three heartbeats. A mean vessel length of 7.1 ± 0.9 cm was depicted with a signal‐to‐noise ratio of 11.8 ± 0.7 and contrast‐to‐noise ratio of 6.1 ± 0.6. Thick‐slice 2D projection CE SSFP is a promising method to depict the RCA. Magn Reson Med 52:699–703, 2004. © 2004 Wiley‐Liss, Inc.
Large field‐of‐view real‐time MRI with a 32‐channel system
Authors: Hardy Christopher J. , Darrow Robert D. , Saranathan Manojkumar , Giaquinto Randy O. , Zhu Yudong , Dumoulin Charles L. , Bottomley Paul A.
Published: September 2004

The emergence of parallel MRI techniques and new applications for real‐time interactive MRI underscores the need to evaluate performance gained by increasing the capability of MRI phased‐array systems beyond the standard four to eight high‐bandwidth channels. Therefore, to explore the advantages of highly parallel MRI a 32‐channel 1.5 T MRI system and 32‐element torso phased arrays were designed and constructed for real‐time interactive MRI. The system was assembled from multiple synchronized scanner‐receiver subsystems. Software was developed to coordinate across subsystems the real‐time acquisition, reconstruction, and display of 32‐channel images. Real‐time, large field‐of‐view (FOV) body‐survey imaging was performed using interleaved echo‐planar and single‐shot fast‐spin‐echo pulse sequences. A new method is demonstrated for augmenting parallel image acquisition by independently offsetting the frequency of different array elements (FASSET) to variably shift their FOV. When combined with conventional parallel imaging techniques, image acceleration factors of up to 4 were investigated. The use of a large number of coils allowed the FOV to be doubled in two dimensions during rapid imaging, with no degradation of imaging time or spatial resolution. The system provides a platform for evaluating the applications of many‐channel real‐time MRI, and for understanding the factors that optimize the choice of array size. Magn Reson Med 52:878–884, 2004. © 2004 Wiley‐Liss, Inc.
Coil‐based artifact reduction
Authors: Atkinson David , Larkman David J. , Batchelor Philipp G. , Hill Derek L.G. , Hajnal Joseph V.
Published: September 2004

Multiple MRI receiver coils provide extra information and can enable the reconstruction of multiple images using data from different combinations of coils. Comparison of these images shows that artifacts due to motion or flowing blood appear with different intensities due to the differing coil sensitivities. Typically, the artifact appears amplified in regions of low coil sensitivity. An optimization routine was developed to correct for the artifact by comparing reconstructions from various coil combinations and favoring a self‐consistent solution. It is demonstrated that images artifacted by blood flowing in the aorta, or translational motion of the head, can be improved. Magn Reson Med 52:825–830, 2004. © 2004 Wiley‐Liss, Inc.
Defining a local arterial input function for perfusion MRI using independent component analysis
Authors: Calamante Fernando , Mørup Morten , Hansen Lars Kai
Published: September 2004

Quantification of cerebral blood flow (CBF) using dynamic‐susceptibility contrast MRI relies on the deconvolution of the arterial input function (AIF), which is commonly estimated from the signal changes in a major artery. However, it has been shown that the presence of bolus delay/dispersion between the artery and the tissue of interest can be a significant source of error. These effects could be minimized if a local AIF were used, although the measurement of a local AIF can be problematic. This work describes a new methodology to define a local AIF using independent component analysis (ICA). The methodology was tested on data from patients with various cerebrovascular abnormalities and compared to the conventional approach of using a global AIF. The new methodology produced higher CBF and shorter mean transit time values (compared to the global AIF case) in areas with distorted AIFs, suggesting that the effects of delay/dispersion are minimized. The minimization of these effects using the calculated local AIF should lead to a more accurate quantification of CBF, which can have important implications for diagnosis and management of patients with cerebral ischemia. Magn Reson Med 52:789–797, 2004. © 2004 Wiley‐Liss, Inc.
Simple, low‐cost multipurpose RF coil for MR microscopy at 9.4 T
Authors: Bilgen Mehmet
Published: September 2004

An inductively coupled RF coil is introduced for high‐resolution MR studies at 9.4 T. The coil offers the flexibility of use as an implantable coil for local imaging inside the body or as a surface coil for imaging below complex surfaces. Successful operation of this coil at strong magnetic field requires special design considerations. In this note, implementation issues of the coil are discussed in detail and practical solutions to overcome some of these difficulties are offered. Imaging performance of the coil and its versatility are demonstrated with images acquired from rat spinal cord when the coil is implanted, and mouse spine and brain when the coil is placed on the surface. Magn Reson Med 52:937–940, 2004. © 2004 Wiley‐Liss, Inc.
Different physiological MRI noise between cortical layers
Authors: Pelled Galit , Goelman Gadi
Published: September 2004

Significantly higher temporal fluctuations of the blood oxygenation level‐dependent (BOLD) signal in the living rat group compared to that in the dead rat group were observed in the cortex, suggesting the existence of physiological information in the signal fluctuations. A similar analysis shows significantly different fluctuations between visual cortical layers. The highest fluctuations were observed in layers 4 and 5 and the lowest in layer 1. Given the consistency with published electrophysiology studies anticipating high spontaneous activity in the deeper layers (particularly layer 4), and low activity in superficial layers, we hypothesize that the BOLD signal temporal fluctuations may reflect cortical neuronal activity. Temporal fluctuations in ultrahigh spatial resolution data of the rat brain were measured in two ways. In the first, analyses were performed according to known layer widths, and in the second equal lines of 117 μ along the cortex were selected. The second approach yielded temporal fluctuations along the cortex that resemble known neuronal density distributions including the intralayer structure, particularly within layer 5. Magn Reson Med 52:913–916, 2004. © 2004 Wiley‐Liss, Inc.