bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calibration of the 1H decoupling field strength and experimental evaluation of the specific RF absorption rate in 1H‐decoupled human 13C‐MRS
Authors: van den Bergh Adrianus J. , van den Boogert Hendrikusy J. , Heerschap Arend 
Published: March 2007

AbstractFor patient safety in human 1H decoupled 13C‐MRS, it is absolutely necessary to evaluate the specific RF absorption rate (SAR) of the tissue exposed to 1H frequency irradiation. With the use of surface coils, the local SAR at the body surface is of most concern due to the inherent RF field inhomogeneity. An empirical procedure to spatially calibrate the decoupler power level and to evaluate the local SAR at the body surface is described. For head, liver, muscle gastrocnemius, and muscle vastus lateralis, the SAR at the body surface was estimated for an 1HJ13C double surface coil setup. Optimized duty cycle values obtained with this procedure show that broadband 1H‐decoupled 13C‐MR spectroscopy is clinically feasible at 1.5 T for such a coil configuration within safety guidelines. Key words: SAR; decoupling; 13C‐MRS; 1.5 T.
A localized double‐quantum filter for the in vivo detection of brain glucose
Authors: Keltner John R. , Wald Lawrence L. , Ledden Patrick J. , Chen Yin‐Ching Iris , Matthews Richard T. , Küestermann Eekkehard H. G. K. , Baker John R. , Rosen Bruce R. , Jenkins Bruce G. 
Published: March 2007

AbstractA double‐quantum filter (DQF) sequence with PRESS localization was developed for in vivo detection of the glucose resonances in the 3.85‐ppm region of the brain proton spectrum. The efficiency and spectral editing characteristics were studied in phantom and animal experiments. Approximately 45% detection efficiency was achieved at 4.7 T with TE = 68 ms. Since the efficiency of the DQF method is dependent on the relative phases of the RF pulses, a phase calibration procedure was used to correct for phase shifts induced by the spatial localization. In addition to detecting the 3.85‐ppm glucose resonances with approximately 45% efficiency, the DQF sequence simultaneously detects 1.3‐ppm lactate resonance with approximately 20% efficiency. The use of the DQF technique for simultaneously monitoring both the input and output of anaerobic glycolysis in the brain was demonstrated by detecting brain glucose and lactate in the same acquisition after iv injection of glucose followed by the induction of global ischemia.
Sodium MRI of human articular cartilage in vivo
Authors: Reddy Ravinder , Insko Erik K. , Noyszewski Elizabeth A. , Dandora Rahul , Kneeland John B. , Leigh John S. 
Published: March 2007

AbstractPreliminary results from in vivo sodium MRI of human patellar articular cartilage are presented. Sodium images generated of an in vitro bovine patella clearly distinguish the region of proteoglycan depletion from the region of healthy cartilage. This provides the first evidence that sodium imaging may be used to detect changes due to osteoarthritis in vivo. The process of optimizing imaging time and signal‐to‐noise ratio, as well as potential implications in the detection of osteoar‐thritic change, are discussed.
BASE imaging: A new spin labeling technique for measuring absolute perfusion changes
Authors: Schwarzbauer Christian , Heinke Wolfgang 
Published: March 2007

AbstractA new technique for magnetic resonance imaging of absolute perfusion changes that uses magnetically labeled tissue water proton spins as a freely diffusible tracer is described. It consists of unprepared basis (BA) images that serve as a reference and selective (SE) inversion prepared images that are sensitive to perfusion changes. In the present study, the BASE technique was applied to functional neuroimaging. BA and SE images were alternatingly and repeatedly acquired during periods of visual stimulation and control. Visual stimulation was achieved with an alternating black/white checkerboard operating at a frequency of 8 Hz. Maps of the absolute cerebral blood flow changes (ACBF) were calculated from the image intensities of the corresponding BA and SE images. The individual mean values of ACBF measured in five healthy volunteers ranged from 69 ± 18 to 99 ± 26 ml/min/100 g. Since the BASE technique does not require nonselective spin inversion, it can be used with small transmit/receive head coils (e.g., surface coils). In addition, the BASE technique is robust against a mismatch of the inversion and detection slice profiles.
Three‐dimensional 31P magnetic resonance spectroscopic imaging of regional high‐energy phosphate metabolism in injured rat heart
Authors: von Kienlin Markus , Rösch Claudia , Fur Yann Le , Behr Wolfgang , Roder Fridtjof , Haase Axel , Horn Michael , Illin Barbara , Hu Kai , Ertl Georg , Neubauer Stefan 
Published: March 2007

AbstractThe purpose of this study was to measure the spatially varying 31P MR signals in global and regional ischemic injury in the isolated, perfused rat heart. Chronic myocardial infarcts were induced by occluding the left anterior descending coronary artery eight weeks before the MR examination. The effects of acute global low‐flow ischemia were observed by reducing the perfusate flow. Chemical shift imaging (CSI) with three spatial dimensions was used to obtain 31P spectra in 54‐/μl voxels. Multislice 1H imaging with magnetization transfer contrast enhancement provided anatomical information. In normal hearts (n = 8), a homogeneous distribution of high‐energy phosphate metabolites (HEP) was found. In chronic myocardial infarction (n = 6), scar tissue contained negligible amounts of HEP, but their distribution in residual myocardium was uniform. The size of the infarcted area could be measured from the metabolic images; the correlation of infarct sizes determined by histology and 31P MR CSI was excellent (P < 0.006). In global low‐flow ischemia (n = 8), changes of HEP showed substantial regional heterogeneity. Three‐dimensional 31P MR CSI should yield new insights into the regionally distinct metabolic consequences of various forms of myocardial injury.
Magnetization transfer attenuates metabolite signals in tumorous and contralateral animal brain: In vivo observations by proton NMR spectroscopy
Authors: Roell Stefan A. , Dreher Wolfgang , Busch Elmar , Leibfritz Dieter 
Published: March 2007

AbstractTumorous and contralateral rat brain was examined by in vivo single voxel proton NMR spectroscopy. Magnetization transfer (MT) experiments cause attenuation of various metabolite signals. Selective saturation of immobile metabolites was achieved by pulsed RF preirradiation. The method is compared with continuous wave MT generation. In contralateral tissue, MT attenuation is detected for both the CH3 and the CH2 protons of (phospho‐)creatine (Cr + PCr) and for a signal at 3.44 ppm ascribed to taurine. Significant attenuation is also observed for a signal at 3.78 ppm that is commonly ascribed to the αCH proton of glutamate and glutamine (Glx); however, no effect is observed for the γCH2 protons of Glx. Within implanted F98 glioma tumors, only the CH3 signal of Cr + PCr shows significant MT attenuation. Although the MT effect detected for lactate in the tumors fails to reach significance, a significant effect is observed for the lactate signal acquired during 3 to 9 min postmortem.
In‐plane motion correction for MR spectroscopic imaging
Authors: Haupt Christine I. , Kiefer Andreas P. , Maudsley Andrew A. 
Published: March 2007

AbstractA motion‐detection method is described that is specifically suited for MR spectroscopic imaging (MRSI) studies. Information on in‐plane rotation and translation of the subject was obtained using external spatial reference markers that are uniquely identified via their chemical shift. The marker locations were obtained directly from the acquired data at each encoding step, and no additional data acquisition was required. This method was applied to brain 1H MRSI studies that include subcutaneous lipid signals, which otherwise result in enhanced sensitivity to subject motion.
Recovery of the rodent brain after cardiac arrest: A functional mri study
Authors: Schmitz Bernd , Hoehn‐Berlage Mathias , Kerskens Christian M. , Bottiger Bernd W. , Hossmann Konstantin‐Alexander 
Published: March 2007

AbstractRecovery of the cerebral cortex after 10 min of cardiac arrest was studied in rat using noninvasive MRI techniques. The apparent diffusion coefficient (ADC) of brain water was imaged to document reversal of the metabolic impairment. Per‐fusion‐weighted imaging and blood oxygen level dependent (BOLD) imaging were performed to assess functional recovery. To this purpose, rats were anesthetized with α‐chloralose, and somatosensory cortex was activated by electrical stimulation of the contralateral forepaw. In sham‐operated controls, cortical ADC was 862 ±10 μm2/s, and stimulation of forepaw led to a focal increase of signal intensity in somatosensory cortex by 71 ± 22% in perfusion‐weighted images and by 6 ± 1 % in BOLD images. One hour after successful resuscitation following 10 min of cardiac arrest, ADC did not differ from control but functional activation was completely suppressed. After 3 hours of reperfusion, functional activity began to reappear but the recovery of the BOLD signal progressed faster than that of the perfusion‐weighted signal. The differences in the recovery of ADC, BOLD, and perfusion imaging are related to differences between metabolic and functional recovery on one hand and between blood flow and oxygen extraction on the other. The combination of these MRI methods thus provides detailed qualitative information about the progression of brain recovery after transient circulatory arrest.
Analysis of subcutaneous angiogenesis by gradient echo magnetic resonance imaging
Authors: Abramovitch Rinat , Frenkiel Daphna , Neeman Michal 
Published: March 2007

AbstractThe goal of this study was to develop an experimental method for noninvasive analysis of angiogenesis, namely the sprouting of capillaries from existing blood vessels. Angiogenesis was assayed in the subcutaneous vasculature of nude mice in a region of 3 × 3 cm that included in its center a defined angiogenic stimulus. Angiogenic stimuli included agarose beads containing angiogenic growth factors, multicellular tumor spheroids, and dermal incisions. Highly significant correlation (r = 0.905, P = 0.0001) was found between the apparent vessel density determined by gradient echo MRI and the density of blood‐containing vessels determined postmortem. The functionality of the neovasculature was demonstrated in mice breathing alternatingly carbogen or 95% air/5% CO2. Large signal enhancement with carbogen breathing corresponded to regions of high vessel density. The assay reported here can be applied for the study of dermal wound healing, primary vascularization of subcutaneous implants, and for measuring the activity of angiogenic and antiangiogenic agents.
Multislice imaging of quantitative cerebral perfusion with pulsed arterial spin labeling
Authors: Yang Yihong , Frank Joseph A. , Hou Lei , Ye Frank Q. , McLaughlin Alan C. , Duyn Jeff H. 
Published: March 2007

AbstractA method is presented for multislice measurements of quantitative cerebral perfusion based on magnetic labeling of arterial spins. The method combines a pulsed arterial inversion, known as the FAIR (Flow‐sensitive Alternating Inversion Recovery) experiment, with a fast spiral scan image acquisition. The short duration (22 ms) of the spiral data collection allows simultaneous measurement of up to 10 slices per labeling period, thus dramatically increasing efficiency compared to current single slice acquisition protocols. Investigation of labeling efficiency, suppression of unwanted signals from stationary as well as intraarterial spins, and the FAIR signal change as a function of inversion delay are presented. The assessment of quantitative cerebral blood flow (CBF) with the new technique is demonstrated and shown to require measurement of arterial transit time as well as suppression of intraarterial spin signals. CBF values measured on normal volunteers are consistent with results obtained from H2O15 positron emission tomography (PET) studies and other radioactive tracer approaches. In addition, the new method allows detection of activation‐related perfusion changes in a finger‐tapping experiment, with locations of activation corresponding well to those observed with blood oxygen level dependent (BOLD) fMRI.
Three‐dimensional coronary MR angiography using zonal echo planar imaging
Authors: Yang Guang Z. , Gatehouse Peter D. , Keegan Jennifer , Mohiaddin Raad H. , Firmin David N. 
Published: March 2007

AbstractUsing an adapted two‐dimensional spatially selective RF excitation scheme, a novel yet practical three‐dimensional (3D) zonal echo‐planar imaging technique for MR coronary angiography has been developed. The robustness of the technique compared with the two‐dimensional (2D) segmented fast low angle shot (FLASH) method was evaluated using the right coronary artery images of 16 asymptomatic volunteers with a 0.5‐T mobile scanner. Each 3D acquisition required multiple breath‐holds, and real‐time navigator echoes were used to ensure consistent breath‐holding. Advantages of the technique include an improved signal‐to‐noise ratio, clearer depiction of tortuous coronary vessels due to decreased partial volume effects, and reduced motion blurring by the use of a short echo‐planar readout.
An MR‐based technique for quantifying the deformation of articular cartilage during mechanical loading in an intact cadaver joint
Authors: Herberhold Christoph , Stammberger Tobias , Faber Sonja , Putz Reinhard , Englmeier Karl‐Hans , Reiser Maximilian , Eckstein Felix 
Published: March 2007

AbstractThe objective of this study was to develop an MR‐based technique for quantifying the deformation of articular cartilage during mechanical loading in an intact cadaver joint at high spatial and temporal resolution. A nonmetallic pressure device was constructed for applying loads of >1000 N to a femoro‐patellar articulation within an extremity coil of a clinical 1.5 T MRI scanner. Digital image processing methods were used to determine the location‐ and time‐dependent cartilage deformation in consecutive 2D fat‐suppressed FLASH images. Additionally, three‐dimensional reconstruction of the cartilage was performed from 3D fat‐suppressed FLASH image data. During the first 10 min of static compression, thickness changes between 10 and 30% were observed. Thickness changes greater than 50% and volume changes of 20% were recorded after 3 h. The technique permits analysis of the load and time‐dependent mechanical behavior of articular cartilage in its natural environment.
Volumetric spectroscopic imaging with spiral‐based k‐space trajectories
Authors: Adalsteinsson Elfar , Irarrazabal Pablo , Topp Simon , Meyer Craig , Macovski Albert , Spielman Daniel M. 
Published: March 2007

AbstractSpiral‐based k‐space trajectories were applied in a spectroscopic imaging sequence with time‐varying readout gradients to collect volumetric chemical shift information. In addition to spectroscopic imaging of low signal‐to‐noise ratio (SNR) brain metabolites, the spiral trajectories were used to rapidly collect reference signals from the high SNR water signal to automatically phase the spectra and to aid the reconstruction of metabolite maps. Spectral‐spatial pulses were used for excitation and water suppression. The pulses were designed to achieve stable phase profiles in the presence of up to 20% variation in the radiofrequency field. A gridding algorithm was used to resample the data onto a rectilinear grid before fast Fourier transforms. This method was demonstrated by in vivo imaging of brain metabolites at 1.5 T with 10 slices of 18 × 18 pixels each. Nominal voxel size was 1.1 cc, spectral bandwidth was 400 Hz, scan time was 18 min for the metabolite scan and 3 min for the reference scan.
Temporal and anatomical variations of brain water apparent diffusion coefficient in perinatal cerebral hypoxic‐ischemic injury: Relationships to cerebral energy metabolism
Authors: Thornton John S. , Ordidge Roger J. , Penrice Juliet , Cady Ernest B. , Amess Philip N. , Punwani Shonit , Clemence M. , Wyatt J. S. 
Published: March 2007

AbstractCerebral apparent diffusion coefficients {ADCs) were determined in nine newborn piglets before and for 48 h after transient hypoxia‐ischemia. Phosphorus MRS revealed severely reduced cerebral energy metabolism during the insult and an apparently complete recovery 2 h after resuscitation commenced. At this time, mean ADC over the imaging slice (ADCglobal) was 0.88 (0.04) × 109 m2 · s1 (mean (SD}), which was close to the baseline value of 0.92 (0.4) × 109 m2 · s1. In seven of the animals, a “secondary” failure of energy metabolism then evolved, accompanied by a decline in ADCglobal to 0.64 (0.17) × 109 m2 · s1 at 46 h postresuscitation (P < 0.001 versus baseline). For these seven animals, ADCglobal correlated linearly with the concentration ratio [phosphocreatine (PCr)][inorganic phosphate (Pi)] (0.94 r < 0.99; P > 0.001). A nonlinear relationship was demonstrated between ADCglobal, and the concentration ratio [nucleotide triphosphate (NTP)]/ [Pi + PCr + 3 NTP]. The ADC reduction commenced in the parasagittal cortex before spreading in a characteristic pattern throughout the brain. ADC seems to be closely related to cerebral energy status and shows considerable potential for the assessment of hypoxic‐ischemic injury in the newborn brain.
A simplified method to measure the diffusion tensor from seven MR images
Authors: Basser Peter J. , Pierpaoli Carlo 
Published: March 2007

AbstractAnalytical expressions of the diffusion tensor of water, D, and of scalar invariants derived from it, are given in terms of the intensities of seven diffusion‐weighted images (DWIs). These formulas simplify the post‐processing steps required in diffusion tensor imaging, including estimating D in each voxel (from the set of b‐matrices and their corresponding DWIs), and then computing its eigenvalues, eigenvectors, and scalar invariants. In a study conducted using artifact‐free DWIs with high diffusion weighting (bmax ˜ 900 s/mm2), maps of Trace(D) and the Relative and Lattice Anisotropy indices calculated analytically and by multivariate linear regression showed excellent agreement in brain parenchyma of a healthy living cat. However, the quality of the analytically computed maps degraded markedly as diffusion weighting was reduced. Although diffusion tensor MRI with seven DWIs may be useful for clinical applications where rapid scanning and data processing are required, it does not provide estimates of the uncertainty of the measured imaging parameters, rendering it susceptible to noise and systematic artifacts. Therefore, care should be taken when using this technique in radiological applications.
Cardiac MRI of the normal and hypertrophied mouse heart
Authors: Slawson Susan E. , Roman Brian B. , Williams Donald S. , Koretsky Alan P. 
Published: March 2007

AbstractWith the development of recent transgenic techniques, studies involving mice offer opportunities to increase understanding of cardiac disease. This provides motivation for the current study to perform noninvasive evaluation of the normal and hypertrophied mouse heart with MRI. By acquiring EGG and respiratory signals, the MR image acquisition was gated to both the cardiac and respiratory cycles. Combining a spin‐warp imaging sequence with an RF surface coil resulted in short‐axis images that allowed quantification of in vivo cardiac mass. Excellent agreement between MRI‐determined (y) and postmortem heart weight (x) was obtained: y = 0.991x + 1.43 (r = 0.996). Isoproterenol, at 282 μMmol/kg body weight (BW) and 573 μMmol/kg BW, induced a dose‐dependent increase in the ratio of heart weight to BW of 16.8 ± 1.09% and 24.1 ± 1.71 %, respectively, which was accurately measured by MRI. These results demonstrate the ability of MRI to non‐invasively monitor cardiac anatomy in the mouse.
In vivo measurement of T*2 and field inhomogeneity maps in the human heart at 1.5 T
Authors: Reeder Scott B. , Faranesh Anthony Z. , Boxerman Jerrold L. , McVeigh Elliot R. 
Published: March 2007

AbstractCardiac echo‐planar imaging suffers invariably from regions of severe distortion and T*2 decay in the myocardium. The purpose of this work was to perform local measurements of T*2 and field inhomogeneities in the myocardium and to identify the sources of focal signal loss and distortion. Field inhomogeneity maps and T*2 were measured in five normal volunteers in short‐axis slices spanning from base to apex. It was found that T*2 ranged from 26 ms (SD = 7 ms, n = 5) to 41 ms (SD = 11 ms, n = 5) over most of the heart, and peak‐to‐peak field inhomogeneity differences were 71 Hz (SD = 14 Hz, n = 5). In all hearts, regions of severe signal loss were consistently adjacent to the posterior vein of the left ventricle; T*2 in these regions was 12 ms (SD = 2 ms, n = 5), and the difference in resonance frequency with the surrounding myocardium was 70‐100 Hz. These effects may be caused by increased magnetic susceptibility from deoxygenated blood in these veins.
A novel k‐space trajectory measurement technique
Authors: Zhang Yantian , Hetherington Hoby P. , Stokely Ernest M. , Mason Graeme F. , Twieg Donald B. 
Published: March 2007

AbstractA new k‐space trajectory measurement technique is proposed and demonstrated. This technique measures the k‐space trajectory, in seconds, using only a few readout lines, using phase values of acquired MR signals. As a result of the technique's efficiency, k‐space trajectory measurement using patient data becomes possible. The utility of this techniques is demonstrated in phantom and human studies at 4.1 T.
Lack of effect of oral choline supplement on the concentrations of choline metabolites in human brain
Authors: Tan Jeannie , Bluml Stefan , Hoang Tuan , Dubowitz David , Mevenkamp Gregor , Ross Brian 
Published: March 2007

AbstractRecent reports suggest that oral choline supplement may alter the cerebral choline/creatine (Cho/Cr) ratio and might be used to treat neurodegenerative disorders of cholinergic transmission. Using both 1H and 31P MRS, we reexamined the Cho/Cr ratio and quantified cerebral choline and its major constituents: phosphoethanolamine (PE), phosphorylcholine (PC), glycerophosphorylethanolamine (GPE), and glycero‐phosphorylcholine (GPC). In the four brain locations examined, no significant increases in Cho/Cr, [Cho], or in its major constituents were found in response to an oral challenge of 50 mg/kg of choline bitartrate. Oral choline did not significantly affect human cerebral metabolism in the short term.
Three‐dimensional MRI of coronary arteries using an intravascular contrast agent
Authors: Li Debiao , Dolan Robert P. , Walovitch Richard C. , Lauffer Randall B. 
Published: March 2007

AbstractTo assess the effectiveness of an intravascular contrast agent, MS‐325, for enhancing the vascular signal in coronary MR angiograms, six minipigs were studied using a three‐dimensional, gradient‐echo sequence with retrospective respiratory gating. To suppress the myocardial signal, preparatory RF pulses were applied before data acquisition. With the administration of MS‐325, the blood signal‐to‐noise ratio increased by 97‐276%, depending on the region of interest in which the blood signal was measured and the precontrast imaging sequence structures. The blood/myocardium contrast‐to‐noise ratio also significantly increased. High‐resolution images (0.58 × 0.58 × 1 mm3) obtained from postmortem pig hearts demonstrated the potential delineation of coronary arteries with MS‐325. In conclusion, this study supports further evaluation of the utility of MS‐325 in improving coronary MR angiography in humans.