bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simultaneous multislice acquisition with arterial‐flow tagging (SMART) using echo planar imaging (EPI)
Authors: Kao Yi‐Hsuan , Wan Xin , MacFall James R. 
Published: March 2007

AbstractArterial spin tagging techniques have been used to image tissue perfusion in MR without contrast injection or ionizing radiation. Currently, spin tagging studies are performed primarily using single‐slice imaging sequences, which are time consuming. This note reports a multislice echo‐planar arterial spin tagging technique (Simultaneous Multislice Acquisition with aRterial‐flow Tagging, or “SMART”). Multiband RF encoding (Hadamard) is used to provide simultaneous multislice acquisition capability for spin tagging techniques (such as echo planar imaging signal targeting with alternating radio frequency and flow‐sensitive alternative inversion recovery). The method is illustrated with a two‐slice pulse sequence that was implemented using the FAIR technique to generate two perfusion weighted images simultaneously. Compared with single‐slice sequences, this two‐slice sequence provided similar image quality, signal‐to‐noise ratio, and twice the spatial coverage compared with the single‐slice technique within the same scan time.
FID‐based lung MRI at 0.5 T: Theoretical considerations and practical implications
Authors: Schmidt Maria A. , Yang Guang‐Zhong , Gatehouse Peter D. , Firmin David N. 
Published: March 2007

AbstractPulse sequences based on FID signals and projection reconstruction (PR) were investigated for lung MRI at 0.5 T and evaluated for artifacts caused by: (1) k‐space mismapping due to either delay or distortion of the readout gradient waveform, (2) cardiac motion and pulsatile flow, and (3) respiratory motion. Nonstructured artifacts were described, simulated, and experimentally confirmed for the first time. Nonstructured artifacts did not impair the demonstration of structures of high signal‐to‐noise ratio (SNR) but generated quantitative errors in the image intensity analysis over the lung parenchyma. The use of FID‐based PR techniques for lung MRI is not justified at 0.5 T.
Time‐course imaging of rat embryos in utero with magnetic resonance microscopy
Authors: Smith Bradley R. , Shattuck Mark D. , Hedlund Laurence W. , Johnson G. Allan 
Published: March 2007

AbstractMagnetic resonance (MR) microscopy was used to noninvasively investigate the development of live rat embryos in utero. The difficulty in making sequential observations of a developing mammalian embryo has frustrated developmental biologists for many years. Most current technologies analyze normal and abnormal development by observing end point phenotypes (in fixed specimens) rather than investigating the live embryo. MR microscopy was adapted to allow rat litters to be scanned three times each (at 1‐ to 3‐day intervals) and has produced images of live developing embryos. It was demonstrated that repeated anesthesia and imaging protocols produced no gross malformations in the rat pups that were subsequently delivered and observed. Three‐dimensional projection encoding with phase re‐winders produced isotropic (2563) image data sets in about 30 minutes with excellent tissue contrast arising from steady‐state effects in the amniotic fluid.
Encapsulation and perfusion of mitochondria in agarose beads for functional studies with 31P‐NMR spectroscopy
Authors: Doliba Nicolai M. , Wehrli Suzanne L. , Babsky Andriy M. , Doliba Nataliya M. , Osbakken Mary D. 
Published: March 2007

AbstractAn NMR method to study on‐line mitochondrial function was developed. Mitochondria were maintained in a stable physiologic state in agarose beads that were continuously superfused with oxygenated buffer at 28°C. Oxidative function of both heart and liver mitochondria was evaluated with 31P NMR at 9.4 T using pyruvate plus malate as substrate. This method allows clear resolution of adenosine triphosphate‐γ (ATPγ) and adenosine diphosphate‐β (ADPβ) phosphate signals, whereas a signals of ATP and ADP overlap. ATP production by mitochondria was documented to be very sensitive to different interventions (hypoxia, ischemia, carbonyl cyanide p‐(tri‐fluoromethoxy)phenylhydrazone (FCCP)) and depended on the ADP concentration in supervision medium. These data demonstrate that the new application of NMR to study mitochondrial function can discriminate, on‐line, between several physiologic and biochemical processes in intact physiologically stable mitochondria.
Blood oxygen saturation assessment in vivo using T2 * estimation
Authors: Li Debiao , Wang Yi , Waight David J. 
Published: March 2007

AbstractThe feasibility of noninvasively assessing hemoglobin oxygen saturation of deep blood vessels in vivo by measuring blood T2* is investigated. Techniques for blood T2* measurements in major arteries and veins in the presence of pulsatile blood flow are presented and validated using a flow phantom. Images of multiple TEs were collected in a paired fashion. Cardiac triggering was used to eliminate image artifacts caused by pulsatile arterial blood flow. Using these techniques, it was found that the T2* of arterial blood (199 ± 8 ms) is significantly greater than that of venous blood (108 ± 6 ms) in 10 volunteers, consistent with the fact that the oxygen saturation level of arterial blood is much larger than that of venous blood. Various oxygen saturation levels were created in vivo in a pig and the blood T2* was shown to increase with oxygen saturation levels over a wide range. Preliminary results of this study indicate that it is feasible to assess local oxygen saturation by measuring blood T2* using the proposed techniques.
Timing algorithm for bolus chase MR digital subtraction angiography
Authors: Wang Yi , Lee Howard M. , Avakian Rosalynn , Winchester Priscilla A. , Khilnani Neil M. , Trost David 
Published: March 2007

AbstractAcquire multiple longitudinal locations in the lower extremity after a single contrast injection, appropriate table translation and contrast injection are required. An approximate model based on constant bolus velocity was developed to describe the space‐time course of a contrast bolus in the lower extremity. This model was verified in dynamic MR angiograms acquired in a group of patients using time‐resolved 2D MR digital subtraction angiography (MRDSA). From this contrast bolus passage model, a timing algorithm for table translation and contrast injection was developed for bolus chase MRDSA, subsequently validated in bolus chase 2D MRDSA experiments. All targeted major peripheral arteries were well depicted in bolus chase 2D MRDSA using this timing algorithm and a single 15‐ml contrast dose.
Quantitative imaging of perfusion using a single subtraction (QUIPSS and QUIPSS II)
Authors: Wong Eric C. , Buxton Richard B. , Frank Lawrence R. 
Published: March 2007

AbstractIn the pulsed arterial spin labeling (ASL) techniques EPISTAR, PICORE, and FAIR, subtraction of two images in which inflowing blood is first tagged and then not tagged yields a qualitative map of perfusion. An important reason this map is not quantitative is that there is a spatially varying delay in the transit of blood from the tagging region to the imaging slice that cannot be measured from a single subtraction. We introduce here two modifications of pulsed ASL (QUIPSS and QUIPSS II) that avoid this problem by applying additional saturation pulses to control the time duration of the tagged bolus, rendering the technique relatively insensitive to transit delays and improving the quantitation of perfusion.
Simultaneous multislice acquisition using rosette trajectories (SMART): A new imaging method for functional MRI
Authors: Noll Douglas C. , Peltier Scott J. , Boada Fernando E. 
Published: March 2007

AbstractA new acquisition technique for rapid, whole‐brain functional MRI is presented. In this technique, several slices are simultaneously acquired using rosettek‐spacetrajectories and a gradient‐induced frequency modulation. This modulation together with the spectral properties of the rosette acquisition allow all slices to be reconstructed individually. In functional MRI studies, acquisition rates of 16.7 to 25 images/s were achieved, a threefold improvement over single‐slice acquisitions. The raw images showed some increase in noise. However, because this increase is mostly stationary, the functional activation maps showed only a slight increase in noise (8%).
Heuristic optimization algorithms applied to the quantification of spectroscopic data
Authors: Weber Oliver M. , Duc Corinne O. , Meier Dieter , Boesiger Peter 
Published: March 2007

AbstractThe quantification of in vivo MR spectra imposes severe problems because of low spectral resolution and poor signal‐to‐noise ratio. Maximum likelihood methods are often applied. However, with conventional spectrum analysis procedures, the search for a global minimum in a multidimensional space often terminates in only a local minimum. Heuristic optimization procedures are able to circumvent this difficulty. Two approaches, the genetic algorithm and the simulated annealing, have been adapted to the quantification of MR spectra. For evaluation purposes, the procedures have been applied to synthetic and in vivo spectra with different noise levels. They both allowed a reliable spectrum quantification. The areas of most peaks were quantified reproducibly, although in some cases, the discrimination between spectroscopically almost identical metabolites (e.g., glutamate and glutamine) was not completely satisfactory. The two algorithms are found to be valuable alternative methods in the quantification of in vivo MR spectra.
Assessment of glucosylifosfamide mustard biodistribution in rats with prostate adenocarcinomas by means of in vivo31P NMR and in vitro uptake experiments
Authors: Haberkorn Uwe , Krems Boris , Gerlach Ludwig , Bachert Peter , Morr Iris , Wiessler Manfred , van Kaick Gerhard 
Published: March 2007

AbstractA combined in vitro/in vivo study was performed to evaluate the possible application of phosphorus (31P) NMR spectros‐copy for therapy monitoring and to investigate glucosylifos‐famide mustard (Glc‐IPM) transport and biodistribution by radiotracer techniques. Dynamic in vivo 31P NMR measurements were performed in rats with prostate adenocarcinoma after iv injection of 1 mmol/kg body weight (bw) of ifosfamide (IFO) (n = 4) and 1 mmol/kg bw (n = 4) or 2.15 mmol/kg bw (n = 9) of Glc‐IPM. In a biodistribution study with 14C‐labeled Glc‐IPM and a final dose of 0.8 mmol Glc‐IPM/kg bw, the animals were killed 5, 30, 60, and 120 min after drug administration, an ethanol extraction was performed from several tissues, and the dose per g tissue was calculated. The same tumor cell line was used in saturation and competition experiments to further elucidate the transport mechanism. The 31P NMR signals of IFO and Glc‐IPM showed no overlap with the endogenous phosphorus peaks. A rapid washout with a half‐life between 25.9 ± 5.6 min for the lower dose and 34.3 ± 4.2 min for the higher dose of Glc‐IPM was observed in the tumor. No statistically significant change of the pH value was observed during the examination period. The β‐nucleoside 5′‐triphosphate (NTP)/inorganic phosphate (Pi) signal intensity ratio showed a tendency to decrease but without statistical significance. A rapid elimination was demonstrated by both the noninvasive NMR technique and the biodistribution study. No saturation was found in vitro for the Glc‐IPM uptake, even at the concentration of 5 m/W. Furthermore, the Glc‐IPM uptake was not inhibited by the presence of 2‐deoxyglucose and vice versa. The data show that the pharmacokinetics of Glc‐IPM in the tumor can be followed in vivo by 31P NMR. The results presented are evidence for diffusion as the transport mechanism for Glc‐IPM in this tumor model. However, the better visualization of Glc‐IPM as compared to ifosfamide may be due to metabolic trapping of a negatively charged metabolite after deglycosylation.
Characterization of and correction for eddy current artifacts in echo planar diffusion imaging
Authors: Jezzard Peter , Barnett Alan S. , Pierpaoli Carlo 
Published: March 2007

AbstractMagnetic resonance diffusion imaging is potentially an important tool for the noninvasive characterization of normal and pathological tissue. The technique, however, is prone to a number of artifacts that can severely affect its ability to provide clinically useful information. In this study, the problem of eddy current‐induced geometric distortions that occur in diffusion images acquired with echo planar sequences was addressed. These geometric distortions produce artifacts in computed maps of diffusion parameters and are caused by misalignments in the individual diffusion‐weighted images that comprise the diffusion data set. A new approach is presented to characterize and calibrate the eddy current effects, enabling the eddy current distortions to be corrected in sets of Interleaved (or snapshot) echo planar diffusion images. Correction is achieved by acquiring one‐dimensional field maps in the read and phase encode direction for each slice and each diffusion step. The method is then demonstrated through the correction of distortions in diffusion images of the human brain. It is shown that by using the eddy current correction scheme outlined, the eddy current‐induced artifacts in the diffusion‐weighted images are almost completely eliminated. In addition, there is a significant improvement in the quality of the resulting diffusion tensor maps.
Versatile frequency domain fitting using time domain models and prior knowledge
Authors: Slotboom Johannes , Boesch Chris , Kreis Roland 
Published: March 2007

AbstractAn iterative nonlinear least‐squares fitting algorithm in the frequency domain using time domain models for quantification of complex frequency domain MR spectra is presented. The algorithm allows incorporation of prior knowledge and has both the advantage of time‐domain fitting with respect to handling the problem of missing data points and truncated data sets and of frequency‐domain fitting with respect to multiple frequency‐selective fitting. The described algorithm can handle, in addition to Lorentzian and Gaussian line‐shapes, Voigt and nonanalytic lineshapes. The program allows the user the design of his own fitting strategy to optimize the probability of reaching the global least‐squares minimum. The application of the fitting program is illustrated with examples from in vivo 1H– 31P‐, and 13C‐MR spectroscopy.
Temporal characteristics of oxygenation‐sensitive MRI responses to visual activation in humans
Authors: Fransson Peter , Krüger Gunnar , Merboldt Klaus‐Dietmar , Frahm Jens 
Published: March 2007

AbstractSeries of single‐shot blipped echo‐planar images with spin‐density weighting and T2* sensitivity (2.0 T, TR = 400 ms, TE = 54 ms, flip angle = 30°) were used to study the temporal response profiles to repetitive visual activation (5 Hz, reversing black and white checkerboard versus darkness) for protocols comprising multiple cycles of a 1.6‐s stimulus in conjunction with a 8.4‐s or 90‐s recovery phase and a 10‐s stimulus with a 20‐s or 90‐s recovery phase. Analysis of the real‐time data from all activated pixels resulted in a strong positive MRI response (mean values 3‐6%) as well as a marked poststimulus undershoot (mean values 1‐2%, duration 60‐90 s) for all paradigms. Repetitive protocols with insufficient recovery periods of 8.4 s or 20 s gave rise to a wraparound effect when analyzing time‐locked averages from multiple activation cycles. This problem may lead to an early signal decrease that originates from the ongoing undershoot of preceding activations folded back into the initial latency phase of a subsequent activation. When ensuring complete decoupling of responses to successive stimuli by using a 90‐s recovery period, the wraparound effect vanished and an initial dip was observed in one of seven subjects for a 10‐S/90‐S protocol.
Automatic segmentation of gadolinium‐enhanced multiple sclerosis lesions
Authors: Bedell Barry J. , Narayana Ponnada A. 
Published: March 2007

AbstractAutomatic detection and quantitation of contrast‐enhanced lesions on MRI is expected to be useful in characterizing the disease state in multiple sclerosis (MS). The enhancing structures such as cerebral vasculature and regions with no blood‐brain barrier complicate automated analysis of lesion enhancement. A pulse sequence that incorporates both stationary and marching saturation bands and gradient dephasing is described for suppressing the enhancements within the cerebral vasculature. A postprocessing technique based on automatic image segmentation is implemented for eliminating enhancing structures such as choroid plexus. All MS lesions larger than 5 mm3 have been successfully identified. The automated analysis produced no false‐positives or false‐negative lesions above this volume in 13 patients with MS who were evaluated using the acquisition and evaluation techniques described.
Relaxation anisotropy in cartilage by NMR microscopy (μMRI) at 14‐μm resolution
Authors: Xia Yang 
Published: March 2007

AbstractTo study the structural anisotropy and the magic‐angle effect in articular cartilage,T1, andT2images were constructed at a series of orientations of cartilage specimens in the magnetic field by using NMR microscopy (μMRI). An isotropic T1, and a strong anisotropic T2were observed across the cartilage tissue thickness. Three distinct regions in the microscopic MR images corresponded approximately to the superficial, transitional, and radial histological zones in the cartilage. The percentage decrease ofT2follows the pattern of the curve of (3cos2θ − 1)2at the radial zone, where the collagen fibrils are perpendicular to the articular surface. In contrast, little orientational dependence of T2was observed at the transitional zone, where the collagen fibrils are more randomly oriented. The result suggests that the interactions between water molecules and proteoglycans have a directional nature, which is somehow influenced by collagen fibril orientation. Hence, T2anisotropy could serve as a sensitive and noninvasive marker for molecular‐level orientations in articular cartilage.
GRASE imaging at 3 Tesla with template interactive phase–encoding
Authors: Jovicich Jorge , Norris David G. 
Published: March 2007

AbstractA new method for ordering the phase‐encoding gradient is proposed, and an application for short effective TE gradient‐and spin‐echo (GRASE) imaging is demonstrated. The proposed method calculates the phase‐encoding order from the signal decay of a template scan (hence “template interactive phase‐encoding” or TIPE). Computer simulations are used to compare the point spread functions of different phase‐encoding orders giving short effective echo times (kb centric GRASE, centric GRASE, centric TIPE). The conventional centric phase‐encoding order is also considered for GRASE. The conventional centric method is sensitive to both amplitude and phase modulation of the signal in K‐space. The centric TIPE method gives the least amplitude modulation artifacts but is vulnerable to phase artifacts. The TIPE experiment was implemented on a 3 Tesla system. To the best of our knowledge, we present the first in vivo GRASE images at this field strength.
Measurement of chemical shifts and coupling constants for glutamate and glutamine
Authors: Govindaraju Varanavasi , Basus Vladimir J. , Matson Gerald B. , Maudsley Andrew A. 
Published: March 2007

AbstractProton chemical shifts and coupling constants were obtained for glutamate and glutamine in water (D2O) at pH = 6.6. Initial chemical shift and coupling constant values obtained from experimental spectra were refined using a spectral simulation and optimization program to get a complete set of values that could not otherwise be measured directly from the experimental spectra due to strong spin‐spin couplings. These values are essential for automated spectral fitting procedures that require a priori information.
Arterial phase carotid and vertebral artery imaging in 3D contrast‐enhanced MR angiography by combining fluoroscopic triggering with an elliptical centric acquisition order
Authors: Wilman Alan H. , Riederer Stephen J. , Huston John , Wald John T. , Debbins Josef P. 
Published: March 2007

AbstractArterial‐phase three‐dimensional (3D) contrast‐enhanced MR angiograms of the carotid and vertebral arteries from their origins through the carotid bifurcations were obtained in 20 patients using acquisition times over 30 sec by using an MR fluoroscopy‐triggered pulse sequence with elliptical centric view order. The typical pixel size was 0.8 mm (x) × 1.6 mm (y) × 1.5 mm (z), and 32–48 coronal slices were acquired. The fluoroscopic monitoring of bolus arrival was effective in 18 of the 20 cases; two failures were attributed directly to a poor choice of RF coil. To exploit peak arterial‐to‐venous contrast, the central 3D views were acquired first in the most compact time period possible for the given TR. For the 18 successfully triggered cases, arterial‐phase 3D images were obtained with excellent venous suppression as demonstrated by an average internal jugular vein to common carotid signal enhancement ratio of only 0.05 ± 0.04.
Proton NMR spectroscopy of solvent‐saturable resonances: A new approach to study pH effects in Situ
Authors: Mori Susumu , Eleff Scott M. , Pilatus Ulrich , Mori Noriko , van Zijl Peter C. M. 
Published: March 2007

AbstractIt is shown that the effect of pH changes can be measured in proton NMR spectra through the pH sensitivity of the signal intensities of metabolite protons exchanging with water. To observe this phenomenon, pulse sequences must be used that can sensitively observe these exchangeable protons under physiological conditions, which is achieved by avoiding magnetization transfer signal losses due to water saturation for solvent suppression purposes. These methods provide an order‐of‐magnitude enhancement of many signals between 5 and 10 ppm, containing both N‐bound protons as well as aromatic C‐H protons coupled to them, the intensity of which is influenced by exchange‐relayed saturation. As a first application, the effects of pH change on these resonances are studied ex vivo (perfused cells) and in vivo (cat brain).
Hyperpolarized 3He NMR Lineshape Measurements in the Live Guinea Pig Lung
Authors: Chen X. Josette , Chawla Mark S. , Cofer Gary P. , Hedlund Laurence W. , Moller Harald E. , Johnson G. Allan 
Published: March 2007

AbstractSpatially localized lineshapes of hyperpolarized (HP) 3He in guinea pig lungs have been measured in vivo. Three different axial slice locations, each containing different compositions of airway sizes and orientations, were studied. Gas peaks from major bronchi (2 ppm) and alveoli (‐2 ppm) were distinguished. The gas phase spectra show structural features that are a result of frequency shifts caused by bulk magnetic susceptibility. For a given slice, the spectral lineshapes reflect the airway composition within the slice location, according to theory. The peak assignments given here also agree with previous studies done by Wagshul et at. with HP 129Xe. At each of the slice locations, data were acquired during two phases of the breathing cycle, resulting in a relative frequency shift of ∼0.3 ppm in the superior slices. Spectra obtained over a number of breaths show the dynamics of the gas buildup in the lung and provide further evidence supporting the peak assignments.