bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intravascular contrast agent improves magnetic resonance angiography of carotid arteries in minipigs
Authors: Lin Weili , Abendschein Dana R. , Celik Azim , Dolan Robert P. , Lauffer Randall B. , Walovitch Richard C. , Haacke E. Mark 
Published: March 2007

AbstractThis study was designed to optimize three‐dimensional (3D) time‐of‐flight (TOF) magnetic resonance angiography (MRA) sequences and to determine whether contrast‐enhanced MRA could improve the accuracy of lumen definition in stenosed carotid arteries of minipigs. 3D TOF MRA was acquired with use of either an intravascular (n = 13) and/or an extravascular contrast agent (n = 5) administrated at 2 to 4 weeks after balloon‐induced injury to a carotid artery in 16 minipigs. Vascular contrast, defined as signal intensity differences between blood vessels and muscle normalized to the signal intensity of muscle, was compared before and after the injection of each contrast agent and between the two agents. Different vascular patencies were observed among the animals, including completely occluded vessels (n = 5), stenotic vessels (n = 3), and vessels with no visible stenosis (n = 8). Superior vascular contrast improvement was observed for small arteries and veins and for large veins with the intravascular contrast agent when compared with the extravascular contrast agent. In addition, preliminary studies in two of the animals showed a good correlation for the extent of luminal stenosis defined by digital subtraction angiography compared with MRA obtained after administration of the intravascular contrast agent (R2 = .71, with a slope of .96 ± .04 by a linear regression analysis). We concluded that use of an intravascular contrast agent optimizes 3D TOF MRA and may improve its accuracy compared with digital subtraction angiography.
Use of k‐space segmentation in MR velocity mapping for rapid quantification of CSF flow
Authors: Ståhlberg Freddy , Nitz Wolfgang , Nilsson Christer , Holtås Stig 
Published: March 2007

AbstractIn this work, a k‐space segmentation technique for quantitative studies of pulsatile cerebrospinal fluid (CSF) flow is suggested. Three k‐space lines are sampled for each of two interleaved gradient‐echo sequences (velocity‐compensated and velocity‐encoded) within each repetition interval. Nine cardiac phases are obtained at a heart rate of 60 bpm with maintained nominal resolution and a factor of 3 in reduction of acquisition time relative to our conventional nonsegmented flow quantification protocol. Segmented and conventional sequences were compared in phantoms, in healthy volunteers, and in two patients with clinically suspected normal pressure hydrocephalus. Good agreement between flow curves obtained with the two sequences was demonstrated in vitro as well as in vivo. A slight underestimation of flow values in volunteers was attributed to data filtering when using the segmented sequence. Because the CSF circulation is complex and tightly connected to the vascular circulation, specific clinical applications may require flow studies at multiple positions and with different velocity encoding. In such cases, the proposed sequence can be used to gain time, but alternatively, the segmentation technique can be used to further increase spatial resolution within reasonable examination times.
MRI for the evaluation of regional myocardial perfusion in an experimental animal model
Authors: Lombardi Massimo , Jones Richard A. , Westby Jørgen , Kvaærness Jørn , Torheim Geir , Michelassi Claudio , L'Abbate Antonio , Rinck Peter A. 
Published: March 2007

AbstractMyocardial perfusion was assessed in nine pigs using ultrafast gradient‐echo MRI (.5 T, 15‐mT/m gradients) at different levels of myocardial blood flow (range, .005–1.84 ml/min/g), generated either by adenosine infusion or by a mechanical occluder, and measured independently using radiolabeled microspheres. Sixty‐four consecutive, ECG‐triggered, diastolic, short axis images of the left ventricle were obtained during intravenous bolus injections (y = 30) of .05 mmol/kg of gadopentetate dimeglumine. Relative changes in peak intensity, time to peak intensity, washin slope, correlation coefficient, and cross‐correlation coefficient were computed from the time‐intensity curves obtained from four regions of interest, namely septal, anterior, lateral, and inferior walls. The values from the inferior wall acted as reference for evaluating relative changes in the other three regions. The cross‐correlation coefficient (P < .001, r = 60) and the peak intensity (P < .001, r = .72) showed the best correlation with myocardial blood flow. The washin slope showed a weak positive trend (P < .05), but the low value of r (r = .28) indicated that the use of this parameter to predict flow was invalid; the correlation coefficient and time to peak intensity were not correlated ( P = ns). In conclusion, this study shows that it is possible to evaluate relative myocardial perfusion after the first pass of a an intravenously injected bolus of gadopentetate dimeglumine, using dynamic MRI on a conventional medium field MRI system. The cross‐correlation coefficient and the peak intensity resulted in more efficient parameters to evaluate relative inhom‐ogeneity of regional myocardial perfusion.
High resolution, short echo time sodium imaging of articular cartilage
Authors: Insko E. K. , Reddy Ravinder , Leigh J. S. 
Published: March 2007

AbstractThe sodium present in articular cartilage interacts with the negatively charged proteoglycan aggregates in the matrix of the cartilage. Sodium images of short echo time may be useful for detecting changes that occur in the proteoglycan content of the cartilage. Such changes are indicative of early osteoarthritic damage, for example. Using an asymmetric short echo technique, sodium images of high resolution and signal‐to‐noise ratio that demonstrate anatomic features of the cartilage are presented. These images were obtained with echo times as short as 1 msec, at an inplane resolution of 39 microns by 117 microns and signal‐to‐noise ratios of up to 40:1.
Brain atrophy progression measured from registered serial MRI: Validation and application to alzheimer's disease
Authors: Fox Nick C. , Freeborough Peter A. 
Published: March 2007

AbstractIn this paper, we validate the brain boundary shift integral (BBSI) as a measure of brain atrophy and demonstrate its application in Alzheimer's disease (AD). Nineteen normal subjects and nine patients with AD underwent serial three‐dimensional MRI (6‐ to 30‐month scan intervals). Repeat studies were registered to the baseline studies. The accuracy of the BBSI was assessed by comparison with simulated atrophy and with segmentation; it was also tested for reproducibility, linearity, and its ability to discriminate patients with AD from healthy controls. The BBSI correlated closely with simulated volumes of atrophy (r = 1.000). The mean absolute difference between repeat measures was 1.51 ml or .13% of mean brain volume. Rates of atrophy from all 18 AD scan pairs were widely separated from those of all 31 control pairs. In matched subgroups, the mean (SD) annual rate of brain atrophy in nine controls was .24% (.32%), compared with 2.78% (.92%) in nine patients with AD. We conclude that the BBSI is a linear and highly reproducible measure of atrophy with potential uses in the early diagnosis and measurement of progression in Alzheimer's disease.
Dynamic imaging of intracranial lesions using fast spin‐echo imaging: Differentiation of brain tumors and treatment effects
Authors: Hazle John D. , Jackson Edward F. , Schomer Don F. , Leeds Norman E. 
Published: March 2007

AbstractThe purpose of this study was to develop a technique for differentiating between recurrent brain tumors and treatment‐related changes, such as radiation necrosis, using dynamic MRI. Ninety‐five patients with intracranial mass lesions were evaluated using T1‐weighted fast spin‐echo (FSE) MRI at 1.5 T. Pathologies included treatment‐related changes (n = 32), primary tumors (n = 41), metastatic tumors (n = 5), meningiomas (n = 4), and mixed primary/treatment related changes (n = 13). Signal enhancement‐time curves were analyzed by fitting to a sigmoidal‐exponential function. Maximal enhancement rates were calculated as the first derivative of the fitted curve. Based on the maximal enhancement rates, treatment‐related changes could be differentiated from primary tumors, metastatic tumors, and meningiomas at the P < .05 confidence level. Lesions of mixed tumor and treatment‐related change had intermediate values. Dynamic MRI can be used to differentiate treatment‐related changes from primary tumors in previously treated patient populations based on maximal enhancement rates. Individual case studies demonstrate the clinical significance of these findings.
Fuzzy clustering of gradient‐echo functional MRI in the human visual cortex. Part I: Reproducibility
Authors: Baumgartner Richard , Scarth Gordon , Teichtmeister Claudia , Somorjai Ray , Moser Ewald 
Published: March 2007

AbstractReproducibility of human functional MRI (fMRI) studies is essential for clinical and neuroresearch applications of this new human brain mapping method. Based on a recently presented study on reproducibility of gradient‐echo fMRI in the human visual cortex (Moser et al. Magn Reson Imaging 1996; 14:567–579), comparing the performance of three different threshold strategies for correlation analysis, we demonstrate that (a) fuzzy clustering is a robust, model‐independent method to extract functional information in time and space; (b) intertrial reproducibility of cortical activation is significantly improved by the capability of fuzzy clustering to separate signal contributions from larger vessels, running perpendicular to the slice orientation, from activation apparently close to the primary visual cortex; and (c) for repeated single subject studies, SDs of <20% for signal enhancement in approximately 80% of the studies and SDs of <30% for activated area size in approximately 65% of the studies are obtained. This, however, depends also on signal‐to‐noise ratio, (motion) artifacts, and subject cooperation.
Fuzzy clustering of gradient‐echo functional MRI in the human visual cortex. Part II: Quantification
Authors: Moser Ewald , Diemling Markus , Baumgartner Richard 
Published: March 2007

AbstractFuzzy cluster analysis (FCA) is a new exploratory method for analyzing fMRI data. Using simulated functional MRI (fMRI) data, the performance of FCA, as implemented in the software package Evident, was tested and a quantitative comparison with correlation analysis is presented. Furthermore, the fMRI model fit allows separation and quantification of flow and blood oxygen level dependent (BOLD) contributions in the human visual cortex. In gradient‐recalled echo fMRI at 1.5 T (TR = 60 ms, TE = 42 ms, radiofrequency excitation flip angle [ϑ] = 10°–60°) total signal enhancement in the human visual cortex, ie, flow‐enhanced BOLD plus inflow contributions, on average varies from 5% to 10% in or close to the visual cortex (average cerebral blood volume [CBV] = 4%) and from 10% to 20% in areas containing medium‐sized vessels (ie, average CBV = 12% per voxel), respectively. Inflow enhancement, however, is restricted to intravascular space (= CBV) and increases with increasing radiofrequency (RF) flip angle, whereas BOLD contributions may be obtained from a region up to three times larger and, applying an unspoiled gradient‐echo (GRE) sequence, also show a flip angle dependency with a minimum at approximately 30°. This result suggests that a localized hemodynamic response from the microvasculature at 1.5 T maybe extracted via fuzzy clustering. In summary, fuzzy clustering of fMRI data, as realized in the Evident software, is a robust and efficient method to (a) separate functional brain activation from noise or other sources resulting in time‐dependent signal changes as proven by simulated fMRI data analysis and in vivo data from the visual cortex, and (b) allows separation of different levels of activation even if the temporal pattern is indistinguishable. Combining fuzzy cluster separation of brain activation with appropriate model calculations allows quantification of flow and (flow‐enhanced) BOLD contributions in areas with different vascularization.
Discrimination of Metabolite from Lipid and Macromolecule Resonances in Cerebral Infarction in Humans Using Short Echo Proton Spectroscopy
Authors: Saunders Dawn E. , Howe Franklyn A. , Boogaart Aad Van Den , Griffiths John R. , Brown Martin M. 
Published: March 2007

AbstractShort‐echo proton spectroscopy allows the noninvasive study of metabolites, lipids, and macromolecules in stroke patients, but spectra are difficult to interpret and quantify because narrow metabolite peaks are added to a broad background of lipid and macromolecule peaks. “Metabolite nulling” was used to distinguish the lactate peak from underlying lipid and macromolecule peaks. Increases in the lipid and macromolecule peaks were initially observed within the region of infarction in all patients, and further increases in lipid peaks were seen in five of the six patients during the following 6 weeks. The initial high lactate concentration decreases during the first 2 weeks after stroke, whereas lipid and macromolecule signals show a persistent elevation during the same period. Differences in the time courses of the observed changes suggest that lipid, macromolecule, and lactate signals arise from more than one source.
Centric ordering is superior to gradient moment nulling for motion artifact reduction in EPI
Authors: Jaffer Farouc A. , Wen Han , Jezzard Peter , Balaban Robert S. , Wolff Steven D. 
Published: March 2007

AbstractEcho‐planar imaging (EPI) is sensitive to motion despite its rapid data acquisition rate. Compared with traditional imaging techniques, it is more sensitive to motion or flow in the phase‐encode direction, which can cause image artifacts such as ghosting, misregistration, and loss of spatial resolution. Consequently, EPI of dynamic structures (eg, the cardiovascular system) could benefit from methods that eliminate these artifacts. In this paper, two methods of artifact reduction for motion in the phase‐encode direction are evaluated. First, the k‐space trajectory is evaluated by comparing centric with top‐down ordered sequences. Next, velocity gradient moment nulling (GMN) of the phase‐encode direction is evaluated for each trajectory. Computer simulations and experiments in flow phantoms and rabbits in vivo show that uncompensated centric ordering produces the highest image quality. This is probably due to a shorter readout duration, which reduces T2* relaxation losses and off‐resonance effects, and to the linear geometry of phantoms and vessels, which can obscure centric blurring artifacts.
Volume MRI and MRSI techniques for the quantitation of treatment response in brain tumors: Presentation of a detailed case study
Authors: Nelson Sarah J. , Huhn Stephen , Vigneron Daniel B. , Day Mark R. , Wald Lawrence L. , Prados Michael , Chang Susan , Gutin Philip H. , Sneed Penny K. , Verhey Lynn , Hawkins Randall A. , Dillon William P. 
Published: March 2007

AbstractPatients with primary brain tumors may be considered for several different treatments during the course of their disease. Assessments of disease progression and response to therapy are typically performed by visual interpretation of serial MRI examinations. Although such examinations provide useful morphologic information, they are unable to reliably distinguish active tumor from radiation necrosis. This poses a particular problem in the assessment of response to localized radiation therapies such as gamma knife radiosurgery. In this paper, we present methodology for evaluating changes in tissue morphology and metabolism based on serial volumetric MRI and magnetic resonance spectroscopic imaging (MRSI) examinations. Registration and quantitative analysis of these data provide measurements of the temporal and spatial distributions of gadolinium enhancement and of N‐acetylasparate, choline, creatine, and lactate/lipid. The key features of this approach and the potential clinical benefits are illustrated by a detailed analysis of six serial MRI/MRSI examinations and three serial 1‐[F‐18] fluoro‐2‐deoxy‐D‐glucose (FDG) positron emission tomography (PET) studies on a patient with a recurrent anaplastic astrocytoma.
Detection of primary breast cancer in women with known adenocarcinoma metastatic to the axilla: Use of MRI after negative clinical and mammographic examination
Authors: Brenner R. James , Rothman Barry J. 
Published: March 2007

AbstractThe purpose of this study was to evaluate the ability of MRI to identify a primary site of malignancy in the breast of patients who present clinically with ipsilateral lymph nodes containing metastatic carcinoma but whose physical and mammographic examination are negative. MRI of the breast was performed on four patients using a variety of imaging parameters, all with and without gadolinium contrast. All patients had biopsy‐proven adenocarcinoma of the ipsilateral axilla, with negative physical and mammographic examinations. Foci of enhancement assessed visually on precontrast and postcontrast scans (n = 1) and on substraction studies (n = 3) were considered suspicious under the clinical circumstances defined for this study. Lesions identified on MRI were re‐identified on ultrasound examination and either preoperative localization for excisional biopsy or tissue sampling was performed. Surgery was performed and histopathologic correlation was obtained in all cases. Primary sites of breast carcinoma were identified in all four patients, with multiple sites of malignancy identified in three of four patients. Breast conservation therapy was made possible for three of four patients based on the results of the MRI study showing sites of malignancy and no features of cancer elsewhere in the breast. Follow‐up data of 1, 2, and 5 years of these patients show no evidence of recurrent disease. MRI of the breast is a useful technique for identifying primary sites of malignancy in patients presenting with ipsilateral lymph nodes positive for metastatic adenocarcinoma when the physical and mammographic examinations are negative.
Elimination of nyquist ghosts in MRI by using fast linogram imaging
Authors: Gai Neville , Axel Leon 
Published: March 2007

AbstractTiming inaccuracies between the even and odd echoes lead to the formation of Nyquist ghosts in conventional (blipped) echo‐planar imaging (EPI). A fast radial scanning method based on the linogram sampling geometry was designed and implemented. No ghosting effects are seen with this scheme, and correction for timing inaccuracies is performed using simple postprocessing steps before reconstruction.
The effect of mechanical deformation on magnetic properties and MRI artifacts of type 304 and type 316L stainless steel
Authors: Bendel Lee P. , Shellock Frank G. , Steckel Mark 
Published: March 2007

AbstractThe purpose of this study was to evaluate the influence of composition and deformation of biomedical stainless steels on mechanical properties, magnetic properties, and MRI artifacts. Type 304 and Type 316L samples were prepared using standard wire‐drawing techniques. Mechanical properties were determined using standard test methods. The amount of ferromagnetic phase present was estimated using a Severn Gage and x‐ray diffraction. Magnetic field attraction and artifacts were determined using previously described techniques. The strength of both steels increased significantly with increasing deformation. None of the type 316L wires transformed to the magnetic phase. The amount of magnetic phase in the type 304 wires increased with increasing deformation. There was no magnetic field attraction, and artifacts were minimal for all of type 316L wires and the undeformed type 304 wire. Deflection and artifacts were significant for the deformed type 304 stainless steel. These results provide guidance regarding the use of type 304 and type 316L stainless steels for bioimplants. In this regard, type 316L stainless steel seems to be a more acceptable material with respect to MR compatibility.
Invited. Compatible instrumentation for intraoperative MRI: Expanding resources
Authors: Jolesz Ferenc A. , Morrison Paul R. , Koran Susan J. , Kelley Ray J. , Hushek Steve G. , Newman Robert W. , Fried Marvin P. , Melzer Andreas , Seibel Rainer M. M. , Jalahej Heyam 
Published: March 2007

AbstractSteadfast progress has been made from biopsy to surgery with interventional MRI (iMRI). Such image‐guided interventions require specialized instrumentation due to the unusual elements of the MR environment. Suppliers/manufacturers of MR‐compatible instrumentation were few in 1994, but now there are more than 50. We present fundamental issues of MR compatibility and a list of known suppliers/manufacturers.
Invited. MR systems for image‐guided therapy
Authors: Hinks R. Scott , Bronskill Michael J. , Kucharczyk Walter , Bernstein Mark , Collick Bruce D. , Henkelman R. Mark 
Published: March 2007

AbstractThe use of MRI to guide and monitor interventional procedures requires the merging of surgical and MRI environments. The ideal magnet shape for homogeneity and efficiency is spherical, but this design provides no access. Opening the sphere to provide both patient and surgeon access suggests cylindrical or biplanar magnets. Cylindrical magnets have poor surgical access but provide good imaging capabilities, which can be used in conjunction with a neighboring but distinct surgical environment. Biplanar magnets provide more and better approaches to the patient, but generally with lower field strength. Vertical biplanar systems allows surgical approaches from above but reduce the access of support staff to the patient. A hybrid magnet design, which combines the benefits of both cylindrical and biplanar magnets, can provide increased access with simultaneous approach from two sides of the patient. Application‐specific magnets can target a smaller region, leading to compact magnet designs that greatly expand access for both surgical intervention as well as patient support. As the field of interventional MRI matures, the suitability of each design to specific applications will be better understood, leading to more integrated system designs tailored to the needs of imageguided therapy.