bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic field map estimation using a spiral‐in/spiral‐out acquisition
Authors: Sutton Bradley P. , Noll Douglas C. , Fessler Jeffrey A. 
Published: May 2004

AbstractThe long readout times of single‐shot acquisitions and the high field strengths desired for functional MRI (fMRI) using blood oxygenation level‐dependent (BOLD) contrast make functional scans sensitive to magnetic field inhomogeneity. If it is not corrected during image reconstruction, field inhomogeneity can cause geometric distortions in the images when Cartesiank‐space trajectories are used or blurring with spiral acquisitions. Many traditional methods to correct for field inhomogeneity distortions rely on a static field map measured with the use of images that are themselves distorted. In this work, we employ a regularized least‐squares approach to jointly estimate both the undistorted image and field map at each acquisition using a spiral‐in/spiral‐out pulse sequence. Simulation and phantom studies show that this method is accurate and stable over a time series. Human functional studies show that the jointly estimated field map may be more accurate than standard field map estimates in the presence of respiration‐induced phase oscillations, leading to better detection of functional activation. The proposed method measures a dynamic field map that accurately tracks magnetic field drift and respiration‐induced phase oscillations during the course of a functional study. Magn Reson Med 51:1194–1204, 2004. © 2004 Wiley‐Liss, Inc.
Efficiency of flow‐driven adiabatic spin inversion under realistic experimental conditions: A computer simulation
Authors: Trampel Robert , Jochimsen Thies H. , Mildner Toralf , Norris David G. , Möller Harald E. 
Published: May 2004

AbstractContinuous arterial spin labeling (CASL) using adiabatic inversion is a widely used approach for perfusion imaging. For the quantification of perfusion, a reliable determination of the labeling efficiency is required. A numerical method for predicting the labeling efficiency in CASL experiments under various experimental conditions, including spin relaxation, is demonstrated. The approach is especially useful in the case of labeling at the carotid artery with a surface coil, as consideration of the experimental or theoretical profile of the B1 field is straightforward. Other effects that are also accounted for include deviations from a constant labeling gradient, and variations in the blood flow velocity due to the cardiac cycle. Assuming relevant experimental and physiological conditions, maximum inversion efficiencies of about 85% can be obtained. Magn Reson Med 51:1187–1193, 2004. © 2004 Wiley‐Liss, Inc.
Single‐shot two‐echo technique for simultaneous measurement of GABA and creatine in the human brain in vivo
Authors: Choi In‐Young , Lee Sang‐Pil , Merkle Hellmut , Shen Jun 
Published: May 2004

AbstractA single‐shot, two‐echo method for the simultaneous detection of multiple‐quantum (MQ)‐filtered γ‐aminobutyric acid (GABA) and creatine (Cr) was developed and demonstrated in the human brain in vivo at 3 Tesla. The simultaneously measured Cr singlet served as a navigator for the spectral phase of GABA and any frequency shift during measurements due to drift in the static magnetic field (B0) or subject movement, as well as an internal concentration reference. In addition, the use of a double‐band frequency‐selective MQ filter for C3 and C4 methylene protons of GABA provided a very robust measurement of GABA, with excellent suppression of overlapping metabolites such as Cr and glutathione (GSH) in each single scan. Contamination from overlapping macromolecules was also demonstrated to be negligible with this method. The GABA‐to‐Cr ratio was 0.09 ± 0.03 (mean ± SD, N = 17) and the estimated concentration of GABA in the frontoparietal region of the human brain in vivo was 0.66 ± 0.19 μmol/g (mean ± SD, N = 17) with the internal reference method, and 0.69 ± 0.18 μmol/g (mean ± SD, N = 17) with the external reference method. The observed pattern of GABA doublet was consistent among all subjects, with a frequency separation of ∼13 Hz. Magn Reson Med 51:1115–1121, 2004. © 2004 Wiley‐Liss, Inc.
Quantitative proton magnetic resonance spectroscopy of the cervical spinal cord
Authors: Cooke F.J. , Blamire A.M. , Manners D.N. , Styles P. , Rajagopalan B. 
Published: May 2004

AbstractProton MR spectroscopy (1H‐MRS) provides indices of neuronal damage in the central nervous system (CNS); however, it has not been extensively applied in the spinal cord. This work describes an optimized proton spectroscopy protocol for examination of the human cervical spinal cord. B0 field mapping of the cord revealed periodic inhomogeneities due to susceptibility differences with surrounding tissue. By combining field maps and experimental data, we found that the optimum voxel size was 9 × 7 × 35 mm3 placed with the inferior end of the voxel above vertebral body C2. Metabolite concentrations were determined in the cervical cord in six healthy controls by short‐echo point‐resolved spectroscopy (PRESS) volume localization. The results were compared with metabolite concentrations in the brainstem, cerebellum, and cortex in the same individuals. The concentrations in the cervical cord were as follows: N‐acetyl‐aspartate (NAA) 17.3 ± 0.5, creatine (Cr) 9.5 ± 0.9, and choline 2.7 ± 0.5 mmol/l. The NAA concentration was significantly lower in the cord than in the brainstem (Mann‐Whitney, P < 0.025), and higher than in the cortex (P < 0.005) and cerebellum (P < 0.005). Cr was significantly lower in the cord than in the cerebellum (P < 0.05). There were no significant differences between Cr concentrations in the spinal cord compared to the cortex and brainstem. Magn Reson Med 51:1122–1128, 2004. © 2004 Wiley‐Liss, Inc.
Method for spatially interleaving two images to halve EPI readout times: Two reduced acquisitions interleaved (TRAIL)
Authors: Priest Andrew N. , Carmichael David W. , De Vita Enrico , Ordidge Roger J. 
Published: May 2004

AbstractA new MRI method is presented that can generate images using half the normal readout time or, more usefully, half the number of phase‐encode steps, combining two readouts per excitation. However, the corresponding data are interleaved in image space—not in k‐space, as in many other fast techniques. This gives a resilience to the phase‐related artifacts that can occur in many other techniques due to subject motion. A modified stimulated‐echo experiment is used to create two low‐resolution images from a single sequence. The magnetization that contributes to these images is nonuniformly distributed within each pixel, forming two sinusoidal waves in quadrature, with an oscillation period of exactly two pixels. Since only half of each pixel contributes significant signal, the two images can be interleaved to create a full image with twice as many pixels and double the resolution. When the technique is used in the phase‐encode direction, the effective imaging time is halved, though with two readouts per TR period. When two half‐length echo‐planar readouts are used, the method can also reduce blurring and distortion by halving the effective readout time for echo‐planar imaging (EPI). For even further improvements, the technique can be combined with partial Fourier or parallel imaging. Magn Reson Med 51:1212–1222, 2004. © 2004 Wiley‐Liss, Inc.
MR‐trackable intramyocardial injection catheter
Authors: Karmarkar P.V. , Kraitchman D.L. , Izbudak I. , Hofmann L.V. , Amado L.C. , Fritzges D. , Young R. , Pittenger M. , Bulte J.W.M. , Atalar E. 
Published: May 2004

AbstractThere is growing interest in delivering cellular agents to infarcted myocardium to prevent postinfarction left ventricular remodeling. MRI can be effectively used to differentiate infarcted from healthy myocardium. MR‐guided delivery of cellular agents/therapeutics is appealing because the therapeutics can be precisely targeted to the desired location within the infarct. In this study, a steerable intramyocardial injection catheter that can be actively tracked under MRI was developed and tested. The components of the catheter were arranged to form a loopless RF antenna receiver coil that enabled active tracking. Feasibility studies were performed in canine and porcine myocardial infarction models. Myocardial delayed‐enhancement (MDE) imaging identified the infarcted myocardium, and real‐time MRI was used to guide left ventricular catheterization from a carotid artery approach. The distal 35 cm of the catheter was seen under MRI with a bright signal at the distal tip of the catheter. The catheter was steered into position, the distal tip was apposed against the infarct, the needle was advanced, and a bolus of MR contrast agent and tissue marker dye was injected intramyocardially, as confirmed by imaging and postmortem histology. A pilot study involving intramyocardial delivery of magnetically labeled stem cells demonstrated the utility of the active injection catheter system. Magn Reson Med 51:1163–1172, 2004. © 2004 Wiley‐Liss, Inc.
Optimized interleaved whole‐brain 3D double inversion recovery (DIR) sequence for imaging the neocortex
Authors: Boulby P.A. , Symms M.R. , Barker G.J. 
Published: May 2004

AbstractFor a substantial number of individuals with neurological disorders, a conventional MRI scan does not reveal any obvious etiology; however, it is believed that abnormalities in the neocortical gray matter (GM) underlie many of these disorders. Attempts to image the neocortex are hindered by its thin, convoluted structure, and the partial volume (PV) effect. Therefore, we developed a 3D version of the double inversion recovery (DIR) sequence that incorporates an optimized interleaved (OIL) strategy to improve efficiency and allow high‐quality, high‐resolution imaging of GM. Magn Reson Med 51:1181–1186, 2004. © 2004 Wiley‐Liss, Inc.
Referenceless PRF shift thermometry
Authors: Rieke Viola , Vigen Karl K. , Sommer Graham , Daniel Bruce L. , Pauly John M. , Butts Kim 
Published: May 2004

AbstractThe proton resonance frequency (PRF) shift provides a means of measuring temperature changes during minimally invasive thermotherapy. However, conventional PRF thermometry relies on the subtraction of baseline images, which makes it sensitive to tissue motion and frequency drift during the course of treatment. In this study, a new method is presented that eliminates these problems by estimating the background phase from each acquired image phase. In this referenceless method, a polynomial is fit to the background phase outside the heated region in a weighted least‐squares fit. Extrapolation of the polynomial to the heated region serves as the background phase estimate, which is then subtracted from the actual phase. The referenceless method is demonstrated on a phantom during laser heating, 0° temperature rise images of in vivo human liver, interstitial laser ablation of porcine liver, and transurethral ultrasound ablation of canine prostate. A good correlation between temperature maps reconstructed with the referenceless and subtraction methods was found. Magn Reson Med 51:1223–1231, 2004. © 2004 Wiley‐Liss, Inc.
Magnetic resonance electrical impedance tomography at 3 tesla field strength
Authors: Oh Suk H. , Lee Byung I. , Park Tae S. , Lee Soo Y. , Woo Eung J. , Cho Min H. , Seo Jin K. , Kwon Ohin 
Published: May 2004

AbstractMagnetic resonance electrical impedance tomography (MREIT) is a recently developed imaging technique that combines MRI and electrical impedance tomography (EIT). In MREIT, cross‐sectional electrical conductivity images are reconstructed from the internal magnetic field density data produced inside an electrically conducting object when an electrical current is injected into the object. In this work we present the results of electrical conductivity imaging experiments, and performance evaluations of MREIT in terms of noise characteristics and spatial resolution. The MREIT experiment was performed with a 3.0 Tesla MRI system on a phantom with an inhomogeneous conductivity distribution. We reconstructed the conductivity images in a 128 × 128 matrix format by applying the harmonic Bz algorithm to the z‐component of the internal magnetic field density data. Since the harmonic Bz algorithm uses only a single component of the internal magnetic field data, it was not necessary to rotate the object in the MRI scan. The root mean squared (RMS) errors of the reconstructed images were between 11% and 35% when the injection current was 24 mA. Magn Reson Med 51:1292–1296, 2004. © 2004 Wiley‐Liss, Inc.
TRIM: TR independent multislice imaging
Authors: Fautz Hans‐Peter , Paul Dominik , Scheffler Klaus , Hennig Jürgen 
Published: May 2004

AbstractThis article introduces a novel concept to overcome the dependence of image contrast on spatial positioning parameters such as the number of slices and slice separation in multislice measurements: TR‐independent multislice (TRIM) acquisition allows the number of slices in a single measurement to remain independent of the repetition time TR. Ramped TRIM (rTRIM) allows the distance between the sections excited in each repetition to remain independent of the distance between the reconstructed slices. Even images from overlapping slices can be acquired without crosstalk between the images of adjacent slices due to spatially overlapping excitation profiles. This concept is based on a special reordering scheme: Within a single TR acquisition, steps are only taken from a fraction of all slices. This necessitates attribution of different phase‐encoding steps to different slices within each repetition cycle. The reordering scheme can be derived by the use of a design matrix. The imaging properties of the technique are discussed theoretically and illustrated by a point spread function analysis based on simulations and phantom measurements. Potential sources of artifacts are identified and methods for their prevention are developed. Optimized implementations with different T1‐weighted sequences such as spin echo (SE), turbo spin echo (TSE), and spoiled gradient echo acquisitions are shown on normal volunteers with imaging parameters used in routine diagnosis. Magn Reson Med 51:1239–1246, 2004. © 2004 Wiley‐Liss, Inc.
Improved magnetization preparation for navigator steady‐state free precession 3D coronary MR angiography
Authors: Nguyen Thanh D. , Spincemaille Pascal , Wang Yi 
Published: May 2004

AbstractThe purpose of this work was to investigate a new magnetization preparation scheme for navigator steady‐state free precession (SSFP) 3D coronary MR angiography (MRA) that executes the navigator and fat saturation pulses in steady state after the dummy RFs in order to minimize the delay between the magnetization preparation and the image echoes. Compared to the previous preparation scheme that executes the navigator and fat saturation pulses before the dummy RFs, the new scheme was found to provide more effective motion suppression, significantly improved blood‐to‐myocardium contrast‐to‐noise ratio (46%, P < 0.001) at slightly but insignificantly decreased blood signal‐to‐noise ratio (SNR) (2%, P = 0.73), significantly reduced fat SNR (32%, P < 0.001), and better overall image quality (P = 0.05; Wilcoxon paired sample signed rank test). Magn Reson Med 51:1297–1300, 2004. © 2004 Wiley‐Liss, Inc.
Quantitation of erythrocyte pentose pathway flux with [2‐13C]glucose and 1H NMR analysis of the lactate methyl signal
Authors: Delgado Teresa C. , Castro M. Margarida , Geraldes Carlos F. , Jones John G. 
Published: May 2004

AbstractA simple and sensitive NMR method for quantifying excess 13C‐enrichment in positions 2 and 3 of lactate by 1H NMR spectroscopy of the lactate methyl signal is described. The measurement requires neither signal calibrations nor the addition of a standard and accounts for natural abundance 13C‐contributions. As a demonstration, the measurement was applied to ∼3 μmol of lactate generated by erythrocyte preparations incubated with [2‐13C]glucose to determine the fraction of glucose metabolized by the pentose phosphate pathway (PP). PP fluxes were estimated from the ratio of excess 13C‐enrichment in lactate carbon 3 relative to carbon 2 in accordance with established metabolic models. Under baseline conditions, PP flux accounted for 7 ± 2% of glucose consumption while in the presence of methylene blue, a classical activator of PP activity, its contribution increased to 27 ± 10% of total glucose consumption (P < 0.01). Magn Reson Med 51:1283–1286, 2004. © 2004 Wiley‐Liss, Inc.
Microsphere‐induced embolic stroke: An MRI study
Authors: Mayzel‐Oreg Orna , Omae Tsuyoshi , Kazemi Mark , Li Fuhai , Fisher Marc , Cohen Yoram , Sotak Christopher H. 
Published: May 2004

AbstractDespite the many studies of the middle cerebral artery occlusion (MCAO) model, efficient therapy for stroke is still lacking, emphasizing the need for further development and characterization of experimental stroke models. In the present study, the rather unexplored multifocal microsphere‐induced stroke model in rats was characterized by multiparametric MRI. We induced microembolic infarction in a group of Sprague‐Dawley rats by injecting a dose of about 1000 50‐μm polyethylene microspheres intracranially from the external carotid artery. Diffusion‐, perfusion‐, and T2‐weighted MRI were used to evaluate the infarct development during and following the first 3 hr after microsphere injection (N = 20). The animals were also imaged at 12‐hr (N = 8), 24‐hr (N = 17), and 48‐hr (N = 5) time points. After the final imaging time point, the brains were removed and sectioned into 2‐mm‐thick slices, and infarct volumes were measured by 2,3,4‐triphenyltetrazolium chloride (TTC) staining. From calculated apparent diffusion coefficient (ADC) maps, a volume of reduced ADC appeared 0.5–1.0 hr postinjection, and by the 3‐hr time point the volume of ADC reduction had increased to a size of 5% ± 1% (mean ± SEM) of the brain hemisphere. The lesion volume increased significantly (P < 0.01) to 16% ± 2% of the hemisphere volume at the 12‐hr time point, while at 24 hr the lesion (15% ± 2% of the hemisphere) was also significantly larger (P < 0.001) than at 3 hr. The perfusion deficit resulting from the microsphere injection was immediate, going from a cerebral blood flow index (CBFi) of 74% ± 3% at the time of microsphere injection to 68% ± 2% of the contralateral mean at 3 hr (P < 0.05), to 55% ± 4% of the contralateral values at 12 hr (P < 0.05), and to 57% ± 2% of the contralateral mean at 24 hr (P < 0.001). The lesion development in the microsphere‐induced stroke model was found to be slower than in the MCAO model, and continued up to the 24–48‐hr time point. Magn Reson Med 51:1232–1238, 2004. © 2004 Wiley‐Liss, Inc.
High‐resolution fast spin echo imaging of the human brain at 4.7 T: Implementation and sequence characteristics
Authors: Thomas David L. , De Vita Enrico , Roberts Steven , Turner Robert , Yousry Tarek A. , Ordidge Roger J. 
Published: May 2004

AbstractIn this work, a number of important issues associated with fast spin echo (FSE) imaging of the human brain at 4.7 T are addressed. It is shown that FSE enables the acquisition of images with high resolution and good tissue contrast throughout the brain at high field strength. By employing an echo spacing (ES) of 22 ms, one can use large flip angle refocusing pulses (162°) and a low acquisition bandwidth (50 kHz) to maximize the signal‐to‐noise ratio (SNR). A new method of phase encode (PE) ordering (called “feathering”) designed to reduce image artifacts is described, and the contributions of RF (B1) inhomogeneity, different echo coherence pathways, and magnetization transfer (MT) to FSE signal intensity and contrast are investigated. B1 inhomogeneity is measured and its effect is shown to be relatively minor for high‐field FSE, due to the self‐compensating characteristics of the sequence. Thirty‐four slice data sets (slice thickness = 2 mm; in‐plane resolution = 0.469 mm; acquisition time = 11 min 20 s) from normal volunteers are presented, which allow visualization of brain anatomy in fine detail. This study demonstrates that high‐field FSE produces images of the human brain with high spatial resolution, SNR, and tissue contrast, within currently prescribed power deposition guidelines. Magn Reson Med 51:1254–1264, 2004. © 2004 Wiley‐Liss, Inc.
Observation of significant signal voids in images of large biological samples at 11.1 T
Authors: Beck Barbara L. , Jenkins Kelly , Caserta Jim , Padgett Kyle , Fitzsimmons Jeffrey , Blackband S.J. 
Published: May 2004

AbstractProton MRI of large biological samples were obtained on an 11.1 T / 40 cm instrument. Images were obtained of a fixed human brain and a large piece of fresh beef. The proton MR images demonstrate severe distortions within these conductive samples, indicative of shortened electrical wavelengths and wave behavior within the sample. These observations have significant implications with respect to the continuing evolution of MR to higher magnetic field strengths on large samples, particularly on humans. Magn Reson Med 51:1103–1107, 2004. © 2004 Wiley‐Liss, Inc.
Navigator gating and volume tracking for double‐triggered cardiac proton spectroscopy at 3 Tesla
Authors: Schär Michael , Kozerke Sebastian , Boesiger Peter 
Published: May 2004

AbstractRespiratory motion compensation based on navigator echoes for double‐triggered cardiac proton spectroscopy at 3.0T is presented. The navigators measure the displacement of the liver–lung interface during free breathing. This information allows for double triggering on a defined window within the respiratory cycle and on a defined trigger delay after the R‐wave based on the ECG. Furthermore, it allows the excitation volume to be shifted by the determined respiratory displacement within the defined window in real‐time (volume tracking). Static and motion phantom experiments were performed in this study, and it was demonstrated that volume tracking permits the suppression of signal from tissue next to the localized volume. However, triggering on a defined respiratory position is still necessary to achieve high spectral quality, because shimming and water suppression calibration are only optimal for a small window of the respiratory cycle. Single‐volume spectra obtained in the myocardial septum of healthy subjects are presented. Magn Reson Med 51:1091–1095, 2004. © 2004 Wiley‐Liss, Inc.
Method for reduced SAR T1ρ‐weighted MRI
Authors: Wheaton Andrew J. , Borthakur Arijitt , Corbo Matthew , Charagundla Sridhar R. , Reddy Ravinder 
Published: May 2004

AbstractA reduced specific absorption rate (SAR) version of the T1ρ‐weighted MR pulse sequence was designed and implemented. The reduced SAR method employs a partial k‐space acquisition approach in which a full power spin‐lock pulse is applied to only the central phase‐encode lines of k‐space, while the remainder of k‐space receives a low‐power spin‐lock pulse. Acquisition of high‐ and low‐power phase‐encode lines are interspersed chronologically to minimize average power deposition. In this way, the majority of signal energy in the central portion of k‐space receives full T1ρ‐weighting, while the average SAR of the overall acquisition can be reduced, thereby lowering the minimum safely allowable TR. The pulse sequence was used to create T1ρ maps of a phantom, an in vivo mouse brain, and the brain of a human volunteer. In the images of the human brain, SAR was reduced by 40% while the measurements of T1ρ differed by only 2%. The reduced SAR sequence enables T1ρ‐weighted MRI in a clinical setting, even at high field strengths. Magn Reson Med 51:1096–1102, 2004. © 2004 Wiley‐Liss, Inc.