bluuebunny/crossref_metadata_2025_split huggingface dataset:
Patlak plots of Gd‐DTPA MRI data yield blood–brain transfer constants concordant with those of 14C‐sucrose in areas of blood–brain opening
Authors: Ewing James R. , Knight Robert A. , Nagaraja Tavarekere N. , Yee John S. , Nagesh Vijaya , Whitton Polly A. , Li Lian , Fenstermacher Joseph D. 
Published: July 2003

AbstractThe blood‐to‐brain transfer rate constant (Ki) of Gd‐DTPA was determined in MRI studies of a rat model of transient cerebral ischemia. The longitudinal relaxation rate, R1, was estimated using repeated Look‐Locker measurements. A model‐independent analysis of ΔR1, the Patlak plot, produced maps of Ki for Gd‐DTPA and the distribution volume of the mobile protons (Vp) with intravascular‐Gd changed R1's. The Ki's of Gd‐DTPA were estimated in regions of interest with blood–brain barrier (BBB) opening (regions of interest, ROIs) and compared to those of 14C‐sucrose determined shortly thereafter by quantitative autoradiography. The Ki's for both Gd‐DTPA and sucrose were much higher than normal within the ROIs (n = 7); linear regression of Ki for Gd‐DTPA vs. Ki for sucrose yielded a slope of 0.43 ± 0.11 and r2 = 0.72 (P = 0.01). Thus, Ki for Gd‐DTPA varied in parallel with, but was less than, Ki for sucrose. In the ROIs, mean Vp was 0.071 ml g−1 and much higher than mean vascular volume estimated by dynamic‐contrast‐enhancement (0.013 ml g−1) or mean Vp in contralateral brain (0.015 ml g−1). This elevated Vp may reflect increased capillary permeability to water. In conclusion, Ki can be reliably calculated from Gd‐DTPA‐MRI data by Patlak plots. Magn Reson Med 50:283–292, 2003. © 2003 Wiley‐Liss, Inc.
Measurements of cerebral perfusion and arterial hemodynamics during visual stimulation using TURBO‐TILT
Authors: Hendrikse Jeroen , Lu Hanzhang , van der Grond Jeroen , van Zijl Peter C.M. , Golay Xavier 
Published: July 2003

AbstractEstimation of cerebral blood flow (CBF) in functional perfusion imaging could benefit from a method capable of separating effects of arterial arrival time and trailing edge. To accomplish this, the transfer insensitive labeling technique (TILT) was combined with a train of 13 consecutive acquisitions, called TURBO‐TILT. Visual activation maps obtained at 13 postlabeling delay times (TI) showed a spatial shift from regions surrounding the arterial vasculature at short TI to brain parenchyma at longer delay times. High baseline CBF and short arrival times were found for the voxels with maximum activation at short TI (<1200 ms), while CBF values (43 ml / 100 g tissue/min) and its increase upon activation (55%) at longer TI were in agreement with literature data on regional cerebral perfusion. Magn Reson Med 50:429–433, 2003. © 2003 Wiley‐Liss, Inc.
Geometrical optimization of a phased array coil for high‐resolution MR imaging of the carotid arteries
Authors: Liffers A. , Quick H.H. , Herborn C.U. , Ermert H. , Ladd M.E. 
Published: July 2003

AbstractThe geometry of an RF phased‐array receiving coil for high‐resolution MRI of the carotid artery, particularly the bifurcation, was optimized with respect to signal‐to‐noise ratio (SNR). A simulation tool was developed to determine homogeneity, sensitivity, and SNR for a given imaging situation. The algorithm takes into account the coil geometry, the parameters of the measured object, and the imaging parameters of the pulse sequence. The coil with the optimum geometry was implemented as a receive‐only coil for 1.5 T and comparative SNR measurements with different coils were performed. The experimental SNR measurements verified the simulations. The optimized carotid artery phased array offered the best SNR over the desired field of view. In vivo high‐resolution MRI of the carotid arteries of healthy volunteers and patients with known stenosis was conducted with the optimized phased array coil. The capability of the phased array coil for resolving components within the carotid artery walls is demonstrated. Magn Reson Med 50:439–443, 2003. © 2003 Wiley‐Liss, Inc.
Optimization of localized 19F magnetic resonance spectroscopy for the detection of fluorinated drugs in the human liver
Authors: Klomp Dennis W.J. , van Laarhoven Hanneke W.M. , Kentgens Arno P.M. , Heerschap Arend 
Published: July 2003

AbstractFluorine MR spectroscopy (19F MRS) is an indispensable tool for assessing the pharmacokinetics of fluorinated drugs. Since the metabolism of 5‐fluorouracil (5FU), a frequently used cytotoxic drug, is expected to be different in normal liver and in tumor tissue, spatial localization is required for detection by MRS. In this study, three independent signal‐to‐noise ratio (SNR) optimizations were combined to enable chemical shift imaging (CSI) as a localization method in the detection of 5FU and its metabolites in tumor tissue. First, the hardware was optimized by using circularly polarized coils together with integrated preamplifiers. Second, the optimal pulse angle (Ernst angle) was determined on the basis of T1 relaxation time measurements of 5FU. Finally, averaging of CSI phase‐encoding steps was optimized by using the applied Hamming filter as a weighting function. The combination of these three methods enables the in vivo detection of 5FU and α‐fluoro‐β‐alanine (FBAL) by 19F MRS, localized in three dimensions in tumor and liver tissue at a time resolution of 4 min at 1.5 Tesla. Magn Reson Med 50:303–308, 2003. © 2003 Wiley‐Liss, Inc.
Detection of Alzheimer's amyloid in transgenic mice using magnetic resonance microimaging
Authors: Wadghiri Youssef Zaim , Sigurdsson Einar M. , Sadowski Marcin , Elliott James I. , Li Yongsheng , Scholtzova Henrieta , Tang Cheuk Ying , Aguinaldo Gilbert , Pappolla Miguel , Duff Karen , Wisniewski Thomas , Turnbull Daniel H. 
Published: July 2003

AbstractThe presence of amyloid‐β (Aβ) plaques in the brain is a hallmark pathological feature of Alzheimer's disease (AD). Transgenic mice overexpressing mutant amyloid precursor protein (APP), or both mutant APP and presenilin‐1 (APP/PS1), develop Aβ plaques similar to those in AD patients, and have been proposed as animal models in which to test experimental therapeutic approaches for the clearance of Aβ. However, at present there is no in vivo whole‐brain imaging method to detect Aβ plaques in mice or men. A novel method is presented to detect Aβ plaques in the brains of transgenic mice by magnetic resonance microimaging (μMRI). This method uses Aβ1‐40 peptide, known for its high binding affinity to Aβ, magnetically labeled with either gadolinium (Gd) or monocrystalline iron oxide nanoparticles (MION). Intraarterial injection of magnetically labeled Aβ1‐40, with mannitol to transiently open the blood–brain barrier (BBB), enabled the detection of many Aβ plaques. Furthermore, the numerical density of Aβ plaques detected by μMRI and by immunohistochemistry showed excellent correlation. This approach provides an in vivo method to detect Aβ in AD transgenic mice, and suggests that diagnostic MRI methods to detect Aβ in AD patients may ultimately be feasible. Magn Reson Med 50:293–302, 2003. © 2003 Wiley‐Liss, Inc.
Hyperpolarized 13C MR angiography using trueFISP
Authors: Svensson Jonas , Månsson Sven , Johansson Edvin , Petersson J. Stefan , Olsson Lars E. 
Published: July 2003

AbstractA 13C‐enriched water‐soluble compound (bis‐1,1‐(hydroxymethyl)‐1‐13C‐cyclopropane‐D8), with a 13C‐concentration of approximately 200 mM, was hyperpolarized to ∼15% using dynamic nuclear polarization, and then used as a contrast medium (CM) for contrast‐enhanced magnetic resonance angiography (CE‐MRA). The long relaxation times (in vitro: T1 ≈ 82 s, T2 ≈ 18 s; in vivo: T1 ≈ 38 s, T2 ≈ 1.3 s) are ideal for steady‐state free precession (SSFP) imaging with a true fast imaging and steady precession (trueFISP) pulse sequence. It was shown both theoretically and experimentally that the optimal flip angle was 180°. CE‐MRA was performed in four anesthetized live rats after intravenous injection of 3 ml CM. The angiograms covered the thoracic/abdominal region in two of the animals, and the head‐neck region in the other two. Fifteen consecutive images were acquired in each experiment, with a flip‐back pulse at the end of each image acquisition. In the angiograms, the vena cava (SNR ≈ 240), aorta, renal arteries, carotid arteries (SNR ≈ 75), jugular veins, and several other vessels were visible. The SNR in the cardiac region was 500. Magnetization was preserved from one image acquisition to the next using the flip‐back technique (SNRcardiac ≈ 10 in the 15th image). Magn Reson Med 50:256–262, 2003. © 2003 Wiley‐Liss, Inc.
Nonlinear phase correction for navigated diffusion imaging
Authors: Miller Karla L. , Pauly John M. 
Published: July 2003

AbstractMotion during diffusion‐weighted imaging (DWI) introduces phase errors that can cause significant artifacts in brain images. One method of correcting these errors uses additional navigator data to measure the phase corruptions. Standard navigator methods correct for rigid‐body motion but cannot correct for nonrigid deformations of the brain related to the cardiac cycle. This work derives a generalized reconstruction that corrects for nonrigid motion based on a least‐squares formulation. Since this reconstruction has the disadvantage of being computationally expensive, an approximation is presented, called a refocusing reconstruction. The refocusing reconstruction is both efficient and straightforward. Each readout is multiplied in image space by the phase conjugate of the navigator image, and these rephased readouts are then summed. The conditions under which the refocusing reconstruction is sufficient are considered and methods to improve the quality of refocused images are discussed. In particular, synchronization of the acquisition to the cardiac cycle can provide data that is well‐conditioned to the refocusing reconstruction without incurring the large time penalty traditionally associated with cardiac gating. These methods are applied to steady‐state DWI, a promising pulse sequence that is particularly sensitive to motion‐induced phase artifacts. The refocusing reconstruction is shown to significantly improve SS‐DWI over standard rigid‐body corrections. Magn Reson Med 50:343–353, 2003. © 2003 Wiley‐Liss, Inc.
Improved molecular imaging contrast agent for detection of human thrombus
Authors: Winter Patrick M. , Caruthers Shelton D. , Yu Xin , Song Sheng‐Kwei , Chen Junjie , Miller Brad , Bulte Jeff W.M. , Robertson J. David , Gaffney Patrick J. , Wickline Samuel A. , Lanza Gregory M. 
Published: July 2003

AbstractMolecular imaging of microthrombus within fissures of unstable atherosclerotic plaques requires sensitive detection with a thrombus‐specific agent. Effective molecular imaging has been previously demonstrated with fibrin‐targeted Gd‐DTPA‐bis‐oleate (BOA) nanoparticles. In this study, the relaxivity of an improved fibrin‐targeted paramagnetic formulation, Gd‐DTPA‐phosphatidylethanolamine (PE), was compared with Gd‐DTPA‐BOA at 0.05‐4.7 T. Ion‐ and particle‐based r1 relaxivities (1.5 T) for Gd‐DTPA‐PE (33.7 (s*mM)‐1 and 2.48 × 106 (s*mM)‐1, respectively) were about twofold higher than for Gd‐DTPA‐BOA, perhaps due to faster water exchange with surface gadolinium. Gd‐DTPA‐PE nanoparticles bound to thrombus surfaces via anti‐fibrin antibodies (1H10) induced 72% ± 5% higher change in R1 values at 1.5 T (ΔR1 = 0.77 ± 0.02 1/s) relative to Gd‐DTPA‐BOA (ΔR1 = 0.45 ± 0.02 1/s). These studies demonstrate marked improvement in a fibrin‐specific molecular imaging agent that might allow sensitive, early detection of vascular microthrombi, the antecedent to stroke and heart attack. Magn Reson Med 50:411–416, 2003. © 2003 Wiley‐Liss, Inc.
Deconvolution algorithm based on automatic cutoff frequency selection for EPR imaging
Authors: Deng Yuanmu , He Guanglong , Kuppusamy Periannan , Zweier Jay L. 
Published: July 2003

AbstractThe large line‐width associated with electron paramagnetic resonance imaging (EPRI) requires effective algorithms to deconvolve the true spatial profiles of spins from the measured projection data. The commonly used Fourier transform (FT) deconvolution algorithm is easy to implement but suffers from the division‐by‐zero problem. As a result, a couple of parameters are used to control the deconvolution performance. However, this is inconvenient and the deconvolution results are subject to the experience of the operators. In the present work we examined FT deconvolution for EPRI, and proposed an automatic algorithm to determine the cutoff frequency by calculating the piecewise variance of the division result of the Fourier amplitude spectra. The deconvolution algorithm and the filtered back‐projection image reconstruction algorithm were implemented and validated using 3D phantom and in vivo imaging data. It was clearly observed that the image resolution improved after deconvolution with the proposed algorithm. Magn Reson Med 50:444–448, 2003. © 2003 Wiley‐Liss, Inc.
Proton electron double resonance imaging (PEDRI) of the isolated beating rat heart
Authors: Liebgott Thibaut , Li Haihong , Deng Yuanmu , Zweier Jay L. 
Published: July 2003

AbstractProton electron double resonance imaging (PEDRI) is a double resonance technique where proton MRI is performed with irradiation of a paramagnetic solute. A low‐field PEDRI system was developed at 20.1 mT suitable for imaging free radicals in biological samples. With a new small dual resonator, PEDRI was applied to image nitroxide free radicals in isolated beating rat hearts. Experiments with phantoms showed maximum image enhancement factors (IEF) of 42 or 28 with TEMPONE radical concentrations of 2–3 mM at EPR irradiation powers of 12W or 6W, respectively. In the latter case, image resolution better than 0.5 mm and radical sensitivity of 5 μM was obtained. For isolated heart studies, EPR irradiation power of 6W provided optimal compromise of modest sample heating with good SNR. Only a small increase in temperature of about 1°C was observed, while cardiac function remained within 10% of control values. With infusion of 3 mM TEMPONE an IEF of 15 was observed enabling 2D or 3D images to be obtained in 27 sec or 4.5 min, respectively. These images visualized the change in radical distribution within the heart during infusion and clearance. Thus, PEDRI enables rapid and high‐quality imaging of free radical uptake and clearance in perfused hearts and provides a useful technique for studying cardiac radical metabolism. Magn Reson Med 50:391–399, 2003. © 2003 Wiley‐Liss, Inc.
An image‐based finite difference model for simulating restricted diffusion
Authors: Hwang Scott N. , Chin Chih‐Liang , Wehrli Felix W. , Hackney David B. 
Published: July 2003

AbstractWater diffusion in tissues is generally restricted and often anisotropic. Neural tissue is of particular interest, since it is well known that injury alters diffusion in a characteristic manner. Both Monte Carlo simulations and approximate analytical models have previously been reported in attempts to predict water diffusion behavior in the central nervous system. These methods have relied on axonal models, which assume simple geometries (e.g., ellipsoids, cylinders, and square prisms) and ignore the thickness of the myelin sheath. The current work describes a method for generating models using synthetic images. The computations are based on a 3D finite difference (FD) approximation of the diffusion equation. The method was validated with known analytic solutions for diffusion in a cylindrical pore and in a hexagonal array of cylinders. Therefore, it is envisioned that, by exploiting histologic images of neuronal tissues as input model, current method allows investigating the water diffusion behavior inside biological tissues and potentially assessing the status of neural injury and regeneration. Magn Reson Med 50:373–382, 2003. © 2003 Wiley‐Liss, Inc.
Novel nonparametric approach to canonical correlation analysis with applications to low CNR functional MRI data
Authors: Nandy Rajesh R. , Cordes Dietmar 
Published: July 2003

AbstractDetection of activation in functional MRI (fMRI) is often complicated by the low contrast‐to‐noise ratio (CNR) in the data. The primary source of the difficulty is the fact that for activities that are subtle the signal can be hidden inside the inherent noise in the data. Classical univariate methods based on t‐test or F‐test are susceptible to noise, as they fail to harness systematic correlations in evoked responses within neighboring voxels. Here the power of a multivariate statistical analysis tool known as canonical correlation analysis (CCA) in fMRI studies is demonstrated where the CNR is low. As a further illustration of the power of the method, a comparative study of CCA and ordinary correlation analysis using simulated data under various noise levels is also performed. A novel nonparametric approach is introduced to calculate the P‐values from the distribution of the complicated test statistic. The circumstances under which CCA is a better performer as well as when it is not the case are discussed. As an example, this method is applied to detect hippocampal activation from memory‐related tasks. Magn Reson Med 50:354–365, 2003. © 2003 Wiley‐Liss, Inc.
Rapid quantitation of high‐speed flow jets
Authors: Nayak Krishna S. , Hu Bob S. , Nishimura Dwight G. 
Published: July 2003

AbstractFlow jets containing velocities up to 5–7 m/s are common in patients with congenital defects and patients with valvular disease (stenosis and regurgitation). The quantitation of peak velocity and flow volume in these jets is clinically significant but requires specialized imaging sequences. Conventional 2DFT phase contrast sequences require lengthy acquisitions on the order of several minutes. Conventional spiral phase contrast sequences are faster, but are highly corrupted by flow artifacts at these high velocities due to phase dispersion and motion during the excitation and readout. A new prospectively gated method based on spiral phase contrast is presented, which has a sufficiently short measurement interval (<4 ms) to minimize flow artifacts, while achieving high spatial resolution (2 × 2 × 4 mm3) to minimize partial volume effects, all within a single breathhold. A complete single‐slice phase contrast movie loop with 22 ms true temporal resolution is acquired in one 10‐heartbeat breathhold. Simulations indicate that this technique is capable of imaging through‐plane jets with velocities up to 10 m/s, and initial studies in aortic stenosis patients show accurate in vivo measurement of peak velocities up to 4.2 m/s (using echocardiography as a reference). Magn Reson Med 50:366–372, 2003. © 2003 Wiley‐Liss, Inc.
Ifosfamide pharmacokinetics and hepatobiliary uptake in vivo investigated using single‐ and double‐resonance 31P MRS
Authors: Mancini Laura , Payne Geoffrey S. , Dzik‐Jurasz Andrzej S.K. , Leach Martin O. 
Published: July 2003

AbstractMRS has considerable potential for the measurement of drug pharmacokinetics in vivo. In this study single‐ and double‐resonance 31P MRS was used to investigate the biodistribution, pharmacokinetics, and metabolism of ifosfamide following administration of 500 mg/kg ifosfamide in guinea pigs. 1H‐decoupling was found to nearly double the signal of detected peaks. However, in contrast to studies of ifosfamide in solution, the polarization transfer sequence gave no further signal enhancements. This was attributed to significantly reduced relaxation times in vivo. Chemical shift imaging (CSI) measurements showed that significant proportions of ifosfamide‐related 31P MRS signals arose from the liver, as expected, but also from the gall bladder, which was not predicted from the current literature. Signals were observed within 5 min of the end of administration. The halflife in liver was approximately 74 min, whereas in gall bladder there was no measurable signal decay during the 2.5‐hr studies. High‐resolution 31P MRS of bile showed that the “ifosfamide” peak in vivo consists of at least two compounds. The lower‐concentration peak is ifosfamide, and an investigation is under way to identify the higher‐concentration peak. Other peaks observed in bile are tentatively assigned to carboxy‐ifosfamide and dechloroethyl‐ifosfamide. Overall, 1H‐decoupled 31P MRS has proved to be a useful tool for investigating the metabolism of ifosfamide in vivo. Magn Reson Med 50:249–255, 2003. © 2003 Wiley‐Liss, Inc.
MRI‐based monitoring of inflammation and tissue damage in acute and chronic relapsing EAE
Authors: Rausch M. , Hiestand P. , Baumann D. , Cannet C. , Rudin M. 
Published: July 2003

AbstractExperimental autoimmune encephalomyelitis (EAE) is a commonly used animal model that in several respects mimics human multiple sclerosis (MS), and can be used to design or validate new strategies for treatment of this disease. In the present study, different MRI techniques (macrophage tracking based on labeling cells in vivo by ultrasmall particles of iron oxide (USPIO), blood–brain barrier (BBB) breakdown, and magnetization transfer imaging (MTI)), as well as immunohistological staining were used to study the burden of disease in Lewis rats immunized by guinea pig myelin. The resulting imaging data was compared with behavioral readouts. Animals were studied during the acute phase and the first relapse. Activated monocytes were detected during both episodes in the brain stem or cortex. These areas coincided in part with areas of BBB breakdown. Significant changes of the magnetization transfer ratios (MTRs) of up to 35% were observed in areas of USPIO accumulation. This suggests that infiltrating monocytes are the major source of demyelination in EAE, but monocyte infiltration and breakdown of the BBB are temporally or spatially independent inflammatory processes. Magn Reson Med 50:309–314, 2003. © 2003 Wiley‐Liss, Inc.
New MRI method with contrast based on the macromolecular characteristics of tissues
Authors: Neufeld Arnon , Eliav Uzi , Navon Gil 
Published: July 2003

AbstractA new MRI method with a contrast that is derived from the macromolecular composition and spin dynamics in the tissue is described and demonstrated on excised mouse brain and rat spinal cord. In the method, magnetization is selectively excited in the macromolecules by using a double quantum filter and subsequently transferred to water. The new imaging method differs from previous methods that rely on magnetization transfer contrast (MTC) in that it enables a separate and independent control of the effect of the macromolecule characteristics, chemical exchange, and water‐related parameters on the images. Magn Reson Med 50:229–234, 2003. © 2003 Wiley‐Liss, Inc.
Assessment and compensation of susceptibility artifacts in gradient echo MRI of hyperpolarized 3He gas
Authors: Wild Jim M. , Fichele Stan , Woodhouse Neil , Paley Martyn N.J. , Swift Andrew , Kasuboski Larry , van Beek Edwin J.R. 
Published: July 2003

AbstractThe effects of macroscopic background field gradients upon 2D gradient echo images of inhaled 3He in the human lung were investigated at 1.5 T. Effective compensation of in‐slice signal loss in 3He gradient echo images was then demonstrated using a multiple acquisition interleaved single gradient echo sequence. This method restores signal dephasing through a combination of separate images acquired with different slice refocusing gradients. In vivo imaging of volunteers with the sequence shows substantial restoration of signal at the lung periphery and close to blood vessels. The technique presented may be useful when using 3He MRI for volumetric measurements of lung ventilation and in studies using 3He combined with intravenous contrast as a means of assessing lung ventilation/perfusion (V/Q). Magn Reson Med 50:417–422, 2003. © 2003 Wiley‐Liss, Inc.