bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ghost artifact reduction for echo planar imaging using image phase correction
Authors: Buonocore Michael H. , Gao Lisheng 
Published: March 2007

AbstractAn algorithm is described for reducing ghost artifacts in echo planar imaging (EPI) using phase corrections derived from images reconstructed using only even or odd k‐space lines. The N/2 ghost, that arises principally from time‐reversal of alternate k‐space lines, was significantly reduced by this algorithm without the need for a calibration scan. In images obtained in eight subjects undergoing EPI for auditory functional MRI (fMRI) experiments, N/2 ghost intensity was reduced from 10.3% – 2.1% (range: 7.9–14.1%) to 4.5% ± 0.2% (range: 4.1–4.9%) of parent image intensity, corresponding to a percent reduction in ghost intensity of 54% ± 9% (range: 43–65%), and the algorithm restored this intensity to the parent image. It provided a significant improvement in image appearance, and increased the correlation coefficients related to neural activation in functional MRI studies. The algorithm provided reduction of artifacts from all polynomial orders of spatial phase errors in both spatial directions. The algorithm did not eliminate N/2 ghost intensity contributed by field inhomogeneities, susceptibility, or chemical shift.
Double line scan diffusion imaging
Authors: Gudbjartsson Hákon , Maier Stephan E. , Jolesz Ferenc A. 
Published: March 2007

AbstractA new double line scan diffusion imaging sequence (DLSDI) is presented. In DLSDI, two lines from two separate slices are acquired in each shot. As its predecessor, LSDI, DLSDI is insensitive to motion artifacts and it can be used on conventional MR scanners. In addition, DLSDI is almost twice as fast as LSDI. Preliminary results from phantom and patient studies show excellent agreement between ADC trace maps obtained with DLSDI and LSDI. The technical and the theoretical aspects of DLSDI are studied, and it is shown how the conditional random walk model can be used as an analytical tool to derive the diffusion sensitivity in the DLSDI sequence.
Amplitude demodulation of the electrocardiogram signal (ECG) for respiration monitoring and compensation during MR examinations
Authors: Felblinger Jacques , Boesch Chris 
Published: March 2007

AbstractA method for respiration monitoring during MR‐sequences using the electrocardiogram signal (ECG) is presented. The basic principle is known in conventional patient monitoring and is based on the fact that the amplitude of the ECG‐signal varies with respiratory motion. A demodulation of this “cardio‐respiratory signal” yields a respiration curve that can be used for patient monitoring, triggering, or respiration compensation of MRI sequences. Since no drift is introduced by digital demodulation, this method is superior to analog signal processing. The proposed method was applied during MR examinations using an optically coupled ECG sensor that has the advantage of almost negligible interference due to the MR sequences (<10% of the main ECG signal). The respiration signal obtained is strongly correlated (r= 0.79 to 0.98) with the position of the diaphragm in inferior‐superior direction measured during breath‐holding MRI.
Stability constants and 1H relaxation effects of ternary complexes formed between gd‐dtpa, gd‐dtpa‐bma, gd‐dota, and gd‐edta and citrate, phosphate, and carbonate ions
Authors: Burai László , Hietapelto Vesa , Király RóBert , Tóth éva , Brücher Ernő 
Published: March 2007

AbstractFormation of ternary complexes between Gd‐DTPA, Gd‐DTPA‐BMA, and Gd‐DOTA, used as contrast enhancement agents in MRI and the endogenously available carbonate and phosphate ions, has been demonstrated. The extent of ternary complex formation and its effect on the proton relaxation, measured at 9 MHz, rates is negligible at around pH <8. The complex Gd‐EDTA forms more stable ternary complexes with carbonate and phosphate and it also strongly coordinates the terdentate citrate ligand. The formation of ternary complexes Gd‐EDTA(X) (X = CO32‐, Cit3‐) results in a significant decrease in the proton relaxation rates under physiological conditions.
A comparison of RIGR and SVD dynamic imaging methods
Authors: Hanson Jill M. , Liang Zhi‐Pei , Magin Richard L. , Duerk Jeff L. , Lauterbur Paul C. 
Published: March 2007

AbstractSeveral constrained imaging methods have recently been proposed for dynamic imaging applications. This paper compares two of these methods: the Reduced‐encoding Imaging by Generalized‐series Reconstruction (RIGR) and Singular Value Decomposition (SVD) methods. RIGR utilizes a priori data for optimal image reconstruction whereas the SVD method seeks to optimize data acquisition. However, this study shows that the existing SVD encoding method tends to bias the data acquisition scheme toward reproducing the known features in the reference image. This characteristic of the SVD encoding method reduces its capability to capture new image features and makes it less suitable than RIGR for dynamic imaging applications.
Easy fabrication of a tunable high‐pass birdcage resonator
Authors: Xu Yan , Tang Pei 
Published: March 2007

AbstractA practical design for a high‐pass birdcage resonator is presented. Precision seamless telescoping tubes were used for easy tuning of resonant frequency by adjusting the length of the coils. Three probes, of 4.4, 5.0, and 25.0 cm in diameter, respectively, were constructed and tested. An empirical formula is given that can be used to calculate the capacitance needed for a given frequency when the desired physical dimension and the number of elements of the coil are specified. A simple three‐step procedure is suggested for easy fabrication of resonators that are routinely tunable over tens of megahertz.
A new method for absolute quantitation MRS metabolites
Authors: Barantin Laurent , Pape Alain Le , Akoka Serge 
Published: March 2007

AbstractA new method for absolute of MRS spectra is presented. This method is not based on a reference peak, derived from a real NMR signal, but rather on a synthesized NMR reference produced by an electronic device, transmitted by a broad‐band antenna to avoid quality factor variations. This signal is therefore received at the same time as the sample signal. The reference line produced is stable in time (maximum variation lower than 2%) and allows precise and accurate measurement of absolute concentrations (mean error lower than 3%) in vitro and in vivo.
The effect of magnetization transfer on functional MRI signals
Authors: Zhang Rongyan , Cox Robert W. , Hyde James S. 
Published: March 2007

AbstractA magnetization transfer (MT)‐prepared echo‐planar imaging (EPI) pulse sequence was developed to study motor cortex activation, using a finger tapping paradigm. MT weighting resulted in a reduction of both the activated area and, in the majority of activated pixels, the functional MRI signal, regardless of the correlation coefficient threshold used in generating the activation map. The magnetization transfer ratio (MTR) was higher during task activation than during rest. Because the MT effect is strongly tissue‐dependent, these results support the hypothesis that incorporation of MT into functional MRI will help to understand the origin of the functional MRI signal.
Consistent fat suppression with compensated spectral‐spatial pulses
Authors: Block Walter , Pauly John , Kerr Adam , Nishimura Dwight 
Published: March 2007

AbstractReliable fat suppression is especially important with fast imaging techniques such as echo‐planar (EPI), spiral, and fast spin‐echo (FSE) T2‐weighted imaging. Spectral‐spatial excitation has a number of advantages over spectrally selective presaturation techniques, including better resilience to B0 and B1, inhomogeneity. In this paper, a FSE sequence using a spectral‐spatial excitation pulse for superior fat suppression is presented. Previous problems maintaining the CPMG condition are solved using simple methods to accurately program radio‐frequency (RF) phase. Next an analysis shows how B0 eddy currents can reduce fat suppression effectiveness for spectral‐spatial pulses designed for conventional gradient systems. Three methods to compensate for the degradation are provided. Both the causes of the degradation and the compensation techniques apply equally to gradient‐recalled applications using these pulses. These problems do not apply to pulses designed for high‐speed gradient systems. The spectral‐spatial FSE sequence delivers clinically lower fat signal with better uniformity than spectrally selective pre‐saturation techniques.
In Vivo sodium multiple quantum spectroscopy of human articular cartilage
Authors: Reddy Ravinder , Li Shuchun , Noyszewski Elizabeth A. , Kneeland J. Bruce , Leigh John S. 
Published: March 2007

AbstractThe authors report, for the first time, sodium properties of human articular cartilage in vivo using sodium multiple‐quantum‐filtered methods with a surface coil. A flip angle‐independent, phase‐cycled pulse sequence was used to obtain triple‐quantum‐filtered spectra as a function of preparation time. Biexponential relaxation rates were calculated by fitting the triple‐quantum‐filtered spectral amplitudes to a theoretical expression. Theoretical analysis of the flip angle dependence of even rank two‐quantum coherence (T22), odd rank two‐quantum coherence (T23), and triple‐quantum coherence are presented and verified against experimental results on a cartilage specimen. Sodium multiple‐quantum‐filtered spectral lineshapes obtained in vivo correlate well with those observed on in vivo specimens. Relaxation rates obtained from asymptomatic volunteers were found to be: T2rise= 1.0 ± 0.12 ms, T2decay= 12.0 ± 0.75 ms (mean ± SD). The diagnostic potential of this method in detecting early changes in articular cartilage is described.
In vivo validation of MR pulse pressure measurement in an aortic flow model: Preliminary results
Authors: Urchuk Steven N. , Fremes Stephen E. , Plewes Donald B. 
Published: March 2007

AbstractMR imaging experiments were conducted to investigate the feasibility of estimating vascular pulse pressure waveforms from measurements of blood flow rates and vessel cross‐sectional area. Blood flow waveforms were measured in the aorta's of three 25–30‐kg pigs at multiple imaging sections using phase‐contrast velocity imaging. Estimates of pulse pressure were derived from these data by evaluating a model characterizing the relationship between pressure, flow, and the cross‐sectional area of a vessel segment. Comparisons between the MR‐derived estimates of pressure and those obtained from a micromanometer pressure catheter indicate that accurate measurements (mean error ± SD = 8.2 ± 3.4, n = 6) can be obtained using conventional velocity imaging techniques. Optimization of the method will require the application of rapid imaging techniques and the development of strategies for obtaining a more localized measurement. With these improvements, our results suggest that MR‐based measurement of pulse pressure and related elastic parameters is feasible.
Determination of laser‐induced temperature distributions using echo‐shifted turboflash
Authors: Harth Thorsten , Kahn Thomas , Rassek Margarethe , Schwabe Birgit , Schwarzmaier Hans‐Joachim , Lewin Jonathan S. , Mödder Ulrich 
Published: March 2007

AbstractAn echo‐shifted TurboFLASH sequence implemented on a clinical whole body MR scanner was used to determine thermal changes in tissue. With this snapshot‐like data acquisition, temperature‐related phase shifts were measured with a temporal resolution of 1.3 s. For different types of tissue (postmortem porcine brain, liver, and muscle) the temperature coefficients of the proton chemical shift were recorded during uniform heating of the specimen in a water bath. The specific temperature‐dependent frequency shifts appeared similar to the proton chemical shift of free water (‐0.01 ppm/°C). With this method, laser‐induced ablation in postmortem porcine brain was monitored by temperature mapping. Comparison of the induced temperature profiles measured with NiCrNi‐thermocouples with the MR calculated profiles demonstrated excellent temperature sensitivity and accuracy for this method of MR thermometry, with a maximum deviation of the determined temperatures of only 1.8°C. This investigation was designed as a feasibility study for this rapid version of the phase mapping method, and no in vivo studies were performed.
Hormonally induced modulation in the phosphate metabolites of breast cancer: Analysis of in vivo31P MRS signals with a modified prony method
Authors: Viti V. , Ragona R. , Guidoni L. , Barone P. , Furman E. , Degani H. 
Published: March 2007

AbstractA modified Prony method (MPM) was applied to analyze the main signals present in spatially resolved 31P NMR spectra of MCF7 breast tumors implanted in nude mice. First, the method was tested on synthetic data to establish its limits of reliability. Its performance with respect to peak identification and quantification of signal intensities was then exploited on data from three implanted tumors during hormonal manipulation with estrogen and the antiestrogenic drug tamoxifen. The phosphomonoester peak was resolved into phosphocholine (PC) and phosphoethanolamine (PE). Treatment with tamoxifen led to a significant reduction in the PE to PE+PC peak amplitude ratio in the tumors under consideration. MPM analysis also revealed the presence of two different inorganic phosphate pools: a larger acidic pool and a smaller alkaline pool during estrogen‐induced growth and the reverse during tumor regression.
Quantitative regional brain water measurement with magnetic resonance imaging in a focal ischemia model
Authors: Lin Weili , Paczynski Richard P. , Venkatesan Ramesh , He Yong Y. , Powers William J. , Hsu Chung Y. , Haacke E. Mark 
Published: March 2007

AbstractTherapeutic approaches to cerebral edema require an understanding of both the magnitude and location of changes in brain water content. It is desirable to have a sensitive, accurate means of measuring brain water noninvasively so that effective therapies for cerebral edema in stroke, head trauma, and other conditions can be investigated. In this work, a three‐dimensional magnetic resonance imaging technique that is able to provide both spin density and T1 simultaneously is described. This method was used to quantitate regional changes in brain water content in a rat model of focal cerebral ischemia. Brain water contents estimated from both relative spin density and relative T1 measurements made in vivo were compared with ex vivo measurements of relative tissue water content based on the wet‐dry technique. Correlation coefficients of 0.95 and 0.98 were obtained between the wet‐dry measurements and magnetic resonance measurements of T1 and spin density, respectively. Notably, the slope of the relationship between T1 and tissue water content changed dramatically after the injection of a paramagnetic contrast agent while precontrast and postcontrast spin density measurements remained essentially invariant. In addition, a plot of absolute spin density (obtained by normalizing spin density from agar gelatin phantoms of different water contents to the spin density of a sample of 100% water) was linearly related to wet‐dry measurements with a slope of 0.99 (R2 = 0.99).
Improved water and lipid suppression for 3D PRESS CSI using rf band selective inversion with gradient dephasing (basing)
Authors: Star‐Lack Josh , Nelson Sarah J. , Kurhanewicz John , Huang L. Royal , Vigneron Daniel B. 
Published: March 2007

AbstractA T1 insensitive solvent suppression technique— band selective inversion with gradient dephasing (BASING)—was developed to suppress water and lipids for 1H magnetic resonance spectroscopy (MRS). BASING, which consists of a frequency selective RF inversion pulse surrounded by spoiler gradient pulses of opposite signs, was used to dephase stopband resonances and minimally impact passband metabolites. Passband phase linearity was achieved with a dual BASING scheme. Using the Shinnar‐Le Roux algorithm, a highpass filter was designed to suppress water and rephase the lactate methyl doublet independently of TE, and water/lipid bandstop filters were designed for the brain and prostate. Phantom and in vivo experimental 3D PRESS CSI data were acquired at 1.5 T to compare BASING with CHESS and STIR suppression. With BASING, the measured suppression factor was over 100 times higher than with CHESS or STIR causing baseline distortions to be removed. It was shown that BASING can be incorporated into a variety of sequences to offer improved suppression in the presence of B1 and T1 inhomogeneites.
Three‐dimensional flow‐independent peripheral angiography
Authors: Brittain Jean H. , Olcott Eric W. , Szuba Andrzej , Gold Garry E. , Wright Graham A. , Irarrazaval Pablo , Nishimura Dwight G. 
Published: March 2007

AbstractA magnetization‐prepared sequence, T2‐Prep‐IR, exploits T1, T2, and chemical shift differences to suppress background tissues relative to arterial blood. The resulting flow‐independent angiograms depict vessels with any orientation and flow velocity. No extrinsic contrast agent is required. Muscle is the dciminant source of background signal in normal volunteers. However, long‐T2 deep venous blood and nonvascular fluids such as edema also contribute background signal in some patients. Three sets of imaging parameters are described to address patient‐specific contrast requirements. A rapid, spiral‐based, three‐dimensional readout is utilized to generate high‐resolution angiograms of the lower extremities. Comparisons with x‐ray angiography and two‐dimensional time‐of‐flight angiography indicate that this flow‐independent technique has unique capabilities to accurately depict stenoses and to visualize slow flow and in‐plane vessels.
Real‐time interactive MRI on a conventional scanner
Authors: Kerr Adam B. , Pauly John M. , Hu Bob S. , Li King C. , Hardy Christopher J. , Meyer Ciraig H. , Macovski Albert , Nishimura Dwight G. 
Published: March 2007

AbstractA real‐time interactive MRI system capable of localizing coronary arteries and imaging arrhythmic hearts in real‐time is described. Non‐2DFT acquisition strategies such as spiral‐interleaf, spiral‐ring, and circular echo‐planar imaging provide short scan times on a conventional scanner. Real‐time grid‐ding reconstruction at 8–20 image is achieved by distributing the reconstruction on general‐purpose UNIX workstations. An X‐windows application provides interactive control. A six‐interleaf spiral sequence is used for cardiac imaging and can acquire six images/s. A sliding window reconstruction achieves display rates of 16–20 images/s. This allows cardiac images to be acquired in real‐time, with minimal motion and flow artifacts, and without breath holding or cardiac gating. Abdominal images are acquired at over 2.5 images/s with spiral‐ring or circular echo‐planar sequences. Reconstruction rates are 8–10 images/s. Rapid localization in the abdomen is demonstrated with the spiral‐ring acquisition, whereas peristaltic motion in the small bowel is well visualized using the circular echo‐planar sequence.
Manganese ion enhances T1‐weighted MRI during brain activation: An approach to direct imaging of brain function
Authors: Lin Yi‐Jen , Koretsky Alan P. 
Published: March 2007

AbstractPresent techniques for functional MRI rely on detecting changes in hemodynamics that result as a consequence of brain activation. It would be useful if MRI techniques could be developed that enable imaging of a parameter directly related to neuronal activity. Influx of calcium into neurons is necessary for release of neurotransmitters. Divalent manganese ions (Mn2+) can enter cells through voltage‐gated calcium channels and Mn2+ is paramagnetic. Mn2+ accumulation in brain due to activation should alter relaxation times offering an approach to sensitize MRI to calcium influx in the brain. To test this idea, T1‐weighted MRI was obtained from the rat brain in the presence of a continuous intravenous infusion of 3.6 μmol/min MnCl2. In the anesthetized rat brain, signal enhancement was detected in regions corresponding to ventricles. Activation of the brain with glutamate led to increase in MRI signal intensity in the brain to 238 ± 23% of the original. This increase in signal was dependent on the presence of MnCl2 and was not due to changes in blood flow. It was necessary to break the blood brain barrier with mannitol to make Mn2 accessible to the active sites for efficient detection. Enhancement of MRI signal in the brain was also detected with decreasing anesthesia and with somatosensory stimulation. Due to the slow clearance of Mn2+ from the stimulated region of the brain, MRI enhancement could also be detected after stimulation that occurred on awake, behaving rats outside the magnet. These data indicate that MnCl2 shows potential as a MRI contrast agent that is directly sensitive to brain activation.
Detection of dopaminergic neurotransmitter activity using pharmacologic MRI: Correlation with PET, microdialysis, and behavioral data
Authors: Chen Yin Ching I. , Galpern Wendy R. , Brownell Anna‐Liisa , Matthews Russell T. , Bogdanov Mikhail , Isacson Ole , Keltner John R. , Beal M. Flint , Rosen Bruce R. , Jenkins Bruce G. 
Published: March 2007

AbstractThe metabolic activation resulting from direct dopaminergic stimulation can be detected using auto‐radiography, positron emission tomography (PET) or, potentially, fMRI techniques. To establish the validity of the latter possibility, we have performed a number of experiments. We measured the regional selectivity of two different dopaminergic ligands: the dopamine release compound D‐amphetamine and the dopamine transporter antagonist 2β‐carbomethoxy‐3β‐(4‐fluoropheny) tropane (CFT). Both compounds led to increased signal intensity in gradient echo images in regions of the brain with high dopamine receptor density (frontal cortex, striatum, cingulate cortex ≫ parietal cortex). Lesioning the animals with unilaterally administered 6‐hydroxydopamine (6‐OHDA) led to ablation of the phMRI response on the ipsilateral side; control measurements of rCBV and rCBF using bolus injections of Gd,‐DTPA showed that the baseline rCBV and rCBF values weire intact on the lesioned side. The time course of the BOLD signal changes paralleled the changes observed by microdialyisis measurements of dopamine release in the striatum for both amphetamine and CFT; peaking at 20–40 min after injection and returning to baseline at about 70–90 min. Signal changes were not correlated with either heart rate, blood pressure or pCO2. Measurement of PET binding in the same animals showed an excellent correlation with the phMRI data when compared by either measurements of the number of pixels activated or percent signal change in a given region. The time course for the behavioral measurements of rotation in the 6‐OHDA lesioned animals correlated with the phMRI. These experiments demonstrate that phMRI will become a valuable, noninvasive tool for investigation of neurotransmitter activity in vivo. Key words: fMRI; dopamine; amphetamine; CFT.
Gradient, high‐resolution, magic‐angle spinning nuclear magnetic resonance spectroscopy of human adipocyte tissue
Authors: Millis Kevin K. , Maas Werner E. , Cory David G. , Singer Samuel 
Published: March 2007

AbstractThe recently developed technique of gradient, high‐resolution magic‐angle spinning NMR (g‐hr‐MAS‐NMR) spectroscopy was applied to the study of ex vivo human lipoma and liposarcoma tissue. Compared with conventional 1H‐NMR, the g‐hr‐MAS method yielded a large improvement in spectral resolution and permitted the detection of metabolite resonance's in a well‐differentiated liposarcoma that was not observed in spectra of similar samples obtained using nonspinning NMR methods. These findings suggest that g‐hr‐MAS‐NMR spectroscopy provides a key improvement in spectral quality for ex vivo lipoma and liposarcoma tissue thereby permitting a more precise determination of tissue metabolite composition than conventional nonspinning NMR methods. Key words: magic‐angle spinning; nuclear magnetic resonance; magnetic field gradients; sarcoma.