bluuebunny/crossref_metadata_2025_split huggingface dataset:
MR imaging of flow through tortuous vessels: A numerical simulation
Authors: van Tyen Rem , Saloner David , Jou Liang‐Der , Berger Stanley 
Published: March 2007

AbstractA novel computer simulation technique is presented that allows the calculation of images from Magnetic Resonance Angiography (MRA) studies of blood flow in realistic curving and branching two‐dimensional vessel geometries. Fluid dynamic calculations provide flow streamlines through curved or branching vessels. MR simulations generate images for specific MR pulse sequence parameters. Simulations of steady flow in carotid bifurcation and carotid siphon geometries as imaged by a standard, flow‐compensated, spoiled gradient echo sequence illustrate the major features seen in clinical time of flight MRA studies. The simulations provide insight into a number of artifacts encountered in MRA such as displacement artifacts, signal pile‐up, truncation artifacts, and intravoxel phase dispersion.
Artifacts due to stimulus correlated motion in functional imaging of the brain
Authors: Hajnal Joseph V. , Myers Ralph , Oatridge Angela , Schwieso Jane E. , Young Ian R. , Bydder Graeme M. 
Published: March 2007

AbstractTo assess the effect of stimulus correlated motion on the appearance of functional magnetic resonance images, conventional visual and motor protocols were each performed by four normal volunteers and an image co‐registration technique was used to retrospectively monitor subject motion. In three studies synthetic data sets were constructed from single baseline images using the positional information obtained from the co‐registration procedure. Cumulative difference images were then created from both the synthetic and functional image sets. Stimulus correlated motion was detected in all eight studies and the synthetic cumulative difference images showed striking similarities to the equivalent functional images in each case.
Quantitative MRI of Gd‐DTPA uptake in tumors: Response to photo dynamic therapy
Authors: Kennedy S. D. , Szczepaniak L. S. , Gibson S. L. , Hilf R. , Foster T. H. , Bryant R. G. 
Published: March 2007

AbstractA partial saturation method is described for obtaining rapid images of tissue 'H spin‐lattice relaxation rates following administration of the paramagnetic contrast agent gadolinium‐diethylenetriaminepentaacetate. The paramagnetic contribution to the relaxation rates is proportional to the concentration of contrast agent, making possible quantitative studies of paramagnetic contrast agent uptake or vessel leakage. Snapshot imaging capabilities are not required. Maps of contrast agent uptake rates are made in rat borne tumors before and following photodynamic therapy, which is known to cause vascular damage. Uptake efficiency is spatially heterogenous before and after therapy. Decreases in uptake rate are observed after two photo‐irradiation protocols, which differ by a factor of four in fluence rate but deliver the same total fluence. There is no apparent fluence rate dependence for changes in the uptake rates within 5 h after therapy. Whole tumor measurements of nucleotide triphosphates, inorganic phosphate, pH, and lactate made with NMR spectroscopy indicate that, while net ATP production is inhibited, lactate concentrations are not strongly affected by photodynamic therapy. The ratio of nucleotide triphosphates to inorganic phosphate falls to 0.21 ± 0.02 of initial values 5 h after tumors are treated with the lower fluence rate protocol, and falls to 0.40 ± 0.06 in tumors treated with the higher fluence rate.
Migration and chemical modification of silicone in women with breast prostheses
Authors: Garrido Leoncio , Pfleiderer Bettina , Jenkins Bruce G. , Hulka Carol A. , Kopans Daniel B. 
Published: March 2007

AbstractStudies using magnetic resonance spectroscopy in human volunteers to evaluate their livers in vivo and to analyze their blood in vitro suggest that there are measurable amounts of silicon compounds in the blood of some women with implants and that there is migration of silicone to other organs such as the liver.
Proton NMR observation of glycogen in vivo
Authors: Chen Wei , Avison Malcolm J. , Bloch Gilles , Shulman Robert G. 
Published: March 2007

AbstractOur previous solution studies of the proton relaxation properties of glycogen H1 have shown significant dipolar cross–relaxation with intra‐ring H2 and inter‐ring H4′ protons characterized by a correlation time τc= 2.7 × 10−9 s. This leads to a significant negative Nuclear Overhauser Enhancement (NOE) of glycogen H1 following either transient or steady state perturbations of the longitudinal magnetization of dipolar coupled protons, especially H2 and H4′. Here we use the NOE to edit selectively the H1 resonance of glycogen in the rat liver in vivo using a surface coil probe. The approach shows the possibility of measuring glycogen in vivo with high sensitivity using 1H NMR.
MR temperature mapping of focused ultrasound surgery
Authors: Cline Harvey E. , Hynynen Kullervo , Hardy Christopher J. , Watkins Ronald D. , Schenck John F. , Jolesz Ferenc A. 
Published: March 2007

AbstractDeep lying soft tissue tumors may be treated by a nonincisional surgical procedure executed inside an MR imaging system using a thermal effect delivered by a focused ultrasound transducer. A prototype system is constructed to assess MRI thermal monitoring and the localization of the heat zone in muscle. The temperature distribution of the focal spot is imaged with MRI while mechanically moving the transducer with an hydraulic 3‐axis positioner. Acoustic power is applied with a spherical shell transducer using 1‐ to 10‐s duration pulses at frequencies of 1.5 MHz to selectively coagulate tissue at 60‐70°C. The procedure is monitored with a series of fast second gradient echo, T1‐weighted, temperature sensitive MR sequences. Acquisitions are optimized for high temperature sensitive images that yield the thermal diffusivity, heat flow time constant and the focal spot size in muscle. MR temperature maps of muscle provide localization and dosimetry both in the focal region and near field.
Measurement of GABA following GABA‐transaminase inhibition by gabaculine: A 1H and 31P NMR spectroscopic study of rat brain in vivo
Authors: Behar Kevin L. , Boehm Deborah 
Published: March 2007

AbstractA selective 1H NMR spin‐echo editing method was used to detect the CCH, of GABA in rat brain in vivo before and after intravenous administration of the highly selective GABA transaminase inhibitor, gabaculine (3‐amino‐2,3‐dihydrobenzoic acid‐HCl; 100 mg/kg, intravenously). The effects of the inhibitor on high energy phosphates and pH, were determined by 31P NMR. GABA levels increased approximately linearly (r = 0.81 to 0.94; P < 0.0005) from 1.9 ± 0.4 μmol/g (pre‐gabaculine; mean ± SD) to between 6 and 8 μmollg after 4 hr at rates of accumulation of 1.1 to 2.9 μmol/hr/g. 1H NMR spectroscopic measurements of cerebral GABA and its rate of turnover offers a new approach in the study of GABA‐mediated processes in vivo.
Reduction of field of view for dynamic imaging
Authors: Hu Xiaoping , Parrish Todd 
Published: March 2007

AbstractThis paper describes a simple technique that improves the temporal resolution for certain dynamic imaging applications. The technique is based on the assumption that the image to image intensity changes sought in dynamic imaging studies ire sometimes localized, and a smaller field of view can be used to reduce imaging time. Technical details and experimental results are presented. Experimental results show that this technique works reasonably well for in vivo applications.
ATP production rates as a function of force level in the human gastrocnemius/soleus using 31P MRS
Authors: Boska Michael 
Published: March 2007

AbstractNet forward adenosine triphosphate (ATP) production rates were calculated from 31P nuclear magnetic resonance spectroscopy (MRS) kinetic data collected with 1–8 s time resolution during isometric voluntary contractions of the human gastrocnemius/soleus muscle group. Volume normalized muscle output (Newtons/ml) was then divided by the calculated net ATP use (mM/s) to estimate the metabolic economy (ME) (Newtons · s/μpmol ATP). The ATP production rates from anaerobic glycolysis (An Gly) and creatine kinase (CK) reactions are approximately half of the oxidative phosphorylation ATP production rates (Ox Phos) at the end of 90 s of isometric contractions for a series of force levels. However, ME was independent of the force level in these exercises. The correlation between MVC of healthy, trained subjects, and the maximal cross‐sectional area of the gastrocnemius/soleus shows an average of 21.2 ± 4.6 Newtons/cm2 (mean ± SD, N = 15). This was measured using a foot pedal with a transducer measurement point 10.6 cm above the heel. [ADP] versus Ox Phos ATP production rate fits a Michaelis‐Menten kinetic control equation with an offset (underestimation of Ox Phos) of 0.3 m, Ws and a Km, = 27 μM for ADP and a Vmax = 1.0 mM/s. This suggests that [ADP] is the controlling factor for mitochondrial function at the end of a 90 to 120 s isometric contraction in normal subjects at any force level. Quantitative measurements of the phosphorus metabolite concentrations were obtained from 20 individuals and these data are also reported.
Development and evaluation of tracking algorithms for cardiac wall motion analysis using phase velocity MR imaging
Authors: Constable R. Todd , Rath Kristina M. , Sinusas Albert J. , Gore John C. 
Published: March 2007

AbstractPhase velocity magnetic resonance imaging (MRI) has shown considerable potential for tracking distinct regions of the myocardium throughout the cardiac cycle. Phase contrast MR imaging produces multiple images, each phase encoded for velocity in a different direction, in which individual pixels depict the local motion of the tissue. In this work we present in detail three algorithms for tracking motion based on these images. Both simulated and phantom data are used to examine some of the problems encountered in practice in tracking points based on velocity maps. Solutions to these problems are offered when possible. The impact of noise and low order phase errors in the data on each of the three tracking approaches is examined. In addition, problems due to tissue expansion and contraction, to 2D versus 3D tracking, and to round off errors from motion which is small relative to pixel size or slice thickness, are considered. An example using data obtainedin vivois included to demonstrate the efficacy of the best of the three tracking algorithms in measuring left ventricular circumferential shortening preinfarct and postinfarct in a canine model.
Observation of cardiac lipids in humans by localized 1H magnetic resonance spectroscopic imaging
Authors: den Hollander Jan A. , Evanochko William T. , Pohost Gerald M. 
Published: March 2007

AbstractDifferent approaches are being explored for the noninvasive observation of myocardial lipids in the human heart by in vivo 1H NMR spectroscopy. One approach is to measure cardiac lipids using a combination of volume selection and 2D gradient phase encoding. From these data sets lipid images can be reconstructed. By comparing these lipid images with 1H MR scout images, it is demonstrated that these signals represent epicardial and pericardial lipid. By selecting a smaller bar‐shaped volume combined with 1D phase encoding or by using single volume techniques, it is possible to avoid most of the pericardial and epicardial lipid to obtain myocardial 1H NMR spectra of the human heart showing lipid signals, as well as trimethylamine and (phospho)creatine signals. These measurements demonstrate the feasibility of obtaining 1H NMR spectra of the human myocardium.
Quantitative in vivo tissue sodium concentration maps: The effects of biexponential relaxation
Authors: Boada Fernando E. , Christensen James D. , Huang‐Hellinger Frank R. , Reese Timothy G. , Thulborn Keith R. 
Published: March 2007

AbstractThe biexponential relaxation behavior of the sodium nucleus affects the accuracy of quantitative measurement of in vivo tissue sodium concentration (TSC). Theoretical analysis and in vivo experimental results are used to demonstrate the extent of the large bias in the measured TSC that arises when the relaxation behavior in vivo differs significantly from that of the calibration standards which is when a significant fraction of the total sodium signal decays with a relaxation time much shorter than the echo time (TE) used for imaging. This bias can be as large as 20% for measurements of TSC in a normal rat brain with TE = 2 ms. Our findings indicate that shortening the echo time (TE < 0.5 ms) by projection imaging is a reliable means of obtaining accurate in vivo estimates for TSC using MR.
Thin film high temperature superconducting RF coils for low field MRI
Authors: van Heteren John G. , James Timothy W. , Bourne Lincoln C. 
Published: March 2007

AbstractWe have built and tested a thin‐film high temperature superconducting (HTS) surface coil for MRI at 0.064T. When placed as close as possible to a conductive sample, the 6.7‐cm outer diameter HTS coil had a measured signal‐to‐noise ratio (SNR) 1.8; times higher than a room temperature copper coil of similar size and location. Our results predict that in some cases, SNR gains of about a factor of 2 can be attained in low‐field MRI systems by substituting HTS surface coils for copper coils.
Turbine flow sensor for volume‐flow rate verification in MR
Authors: Frayne Richard , Holdsworth David W. , Smith Robert F. , Kasrai Reza , Larsen Jan P. T. , Rutt Brian K. 
Published: March 2007

AbstractA turbine flow sensor for MR flow experiments has been evalusted using reference volume‐flow rate measurements obtained using an electromagnetic (EM) flow meter measurements and simultaneous phase contrast (PC) MR acquisitions. After calibration, the device was found to have accuracy (compared with the EM flow meter), linearity, and precision of better than ±1%, ±3.5%, 3.5%, respectively, in constant flow mode (0 to 30 ml s−1). The frequency response of the flow sensor was flat (within ±10%) up to 13.9 Hz. Volume‐flow rate measurements on constant and simulated physiologic flow waveforms were in close agreement with both the electromagnetic (EM) flow meter and the gated MR PC estimates.
Magnetic resonance velocity imaging using a fast spiral phase contrast sequence
Authors: Pike G. Bruce , Meyer Craig H. , Brosnan Thomas J. , Pelc Norbert J. 
Published: March 2007

AbstractTime‐resolved velocity imaging using the magnetic resonance phase contrast technique can provide clinically important quantitative flow measurements in vivo but suffers from long scan times when based on conventional spin‐warp sequences. This can be particularly problematic when imaging regions of the abdomen and thorax because of respiratory motion. We present a rapid phase contrast sequence based on an interleaved spiral k‐space data acquisition that permits time‐resolved, three‐direction velocity imaging within a breath‐hold. Results of steady and pulsatile flow phantom experiments are presented, which indicate excellent agreement between our technique and through plane flow measurements made with an in‐line ultrasound probe. Also shown are results of normal volunteer studies of the carotids, renal arteries, and heart.
Quantitative MRI of spinal cord injury in a rat model
Authors: Falconer James C. , Narayana Ponnada A. , Bhattacharjee Meena B. , Liu Shi‐J. 
Published: March 2007

AbstractSequential in vivo MRI studies of experimental spinal cord injuries (SCI) were performed using a three‐dimensional implementation of the FATE (Fast low‐Angle spin echo sequence with short TE) sequence. MRI‐observed pathology was quantified using a multispectral segmentation algorithm. Neurological analysis was performed on the same animals concurrently, in addition to end‐point histology, for comparison with quantitative MRI results. These studies suggest that it is possible to use MRI to detect the onset of secondary injury in the spinal cord. The data also indicate that early detection of MRI‐visible pathology may provide the necessary markers for predicting the long‐term level of neurologic deficit.
In vivo proton magnetic resonance spectroscopy detection of human alcohol tolerance
Authors: Chiu Talc‐Ming , Mendelson Jack H. , Woods Bryan T. , Teoh Siew Koon , Levisohn Lisi , Mello Nancy K. 
Published: March 2007

AbstractAlcohol tolerance was ascertained with in vivo proton magnetic resonance spectroscopy (MRS) in men who regularly consumed either large (10–20 drinks/week) or small (2–4 drinks/week) amounts of beverage alcohol. Brain ethanol concentrations were determined by MRS, and blood ethanol levels were measured by gas chromatography after controlled ethanol administration (0.8 g/kg). Brain‐blood ethanol concentration ratios for heavy drinkers were significantly greater than ratios for occasional drinkers (P < 0.002). Inasmuch as ethanol tolerance covaries with the severity of dependence, MRS procedures may facilitate our understanding of alcohol tolerance and treatment of alcoholism.
Electrocardiogram acquisition during MR examinations for patient monitoring and sequence triggering
Authors: Felblinger Jacques , Lehmann Christoph , Boesch Chris 
Published: March 2007

AbstractWe have developed a method for measuring the electrocardiogram (ECG) continuously during MR examinations. In contrast to ECG acquisition by wires, our new method is to amplify and convert the ECG into an optical signal directly above the patient's heart. The optical signal is transmitted out of the magnet bore by optical fiber. The small and fixed dimensions of the ECG amplifier avoid interactions with the MR system because of shorter electrical structures and smaller enclosed areas. Tests of the proposed device in a 1.5 Tesla MR system show that continuous and reliable ECG monitoring and sequence triggering are possible.
Evaluation of cerebral gray and white matter metabolite differences by spectroscopic imaging at 4.1T
Authors: Hetherington Hoby P. , Mason Graeme F. , Pan Jullie W. , Ponder Steven L. , Vaughan J. Thomas , Twieg Donald B. , Pohost Gerald M. 
Published: March 2007

AbstractUsing a 4.1 T whole body system, we have acquired 1H spectroscopic imaging (SI) data of N‐acetyl (NA) compounds, creatine (CR), and choline (CH) with nominal voxel sizes of 0.5 cc (1.15 cc after filtering). We have used the SI data to estimate differences in cerebral metabolites of human gray and white matter. To evaluate the origin of an increased CWNA and CWNA ratios in gray matter relative to white matter, we measured the T1 and T2 of CR, NA, and CH in gray and white matter using moderate resolution SI imaging. In white matter the T2s of NA, CR, and CH were 233 ± 27,141 ± 18, and 167 ± 20 ms, respectively, and 227 ± 27,140 ± 16, and 189 ± 25 ms in gray matter. The T, values for NA, CR, and CH were 1267 ±141, 1487 ± 146, and 1111 ± 136 ms in gray matter and 1260 ± 154, 1429 & 233, and 1074 ± 146 ms in white matter. After correcting for T1 and T2 losses, creatine content was significantly lower in white matter than gray (P < e 0.01, t‐test), with a white/gray content ratio of 0.8, in agreement with biopsy and in vivo measurements at 1.5 and 2.0T.
Localized in vivo31P NMR spectroscopy of skin flap metabolism
Authors: Cheung Ada , Zhong Jianhui , Gore John C. , Cuono Charles B. 
Published: March 2007

AbstractWe have used a rectangular surface coil and chemical shift imaging to conduct in vivo localized 31P NMR metabolic studies in a rat dorsal skin flap model. This approach permits regional comparisons without manipulation of either coil position or subject within the magnet bore. Both the PCr:P1 ratio (reflecting ischemia insult) and the PCr:ATP ratio (reflecting phosphagen reserves) decreased as functions of time and distance from the vascular pedicle. The maximum change was nearly 6‐fold for the PCr:P, ratio, and 3‐fold for the PCr:ATP ratio. Signal contamination from subjacent muscle is constant and does not interfere with the metabolic evaluations of skin flaps. This technique may facilitate a better understanding of cutaneous metabolic derangements, such as burns and skin flaps used in reconstructive surgery, as well as studies of pharmacologic regimens developed for their treatment. It also holds potential for application in the study of congenital and neoplastic metabolic disorders of skin.
31P NMR investigation of energy metabolism in perifused MMQ cells
Authors: Goger Michael J. , Login Ivan S. , Fernandez Erik J. , Grisham Charles M. 
Published: March 2007

AbstractThe MMQ cell line is a unique prolactin‐secreting rat pituitary cell line. MMQ cells entrapped in agarose gel threads are metabolically active, as determined by the uptake and phosphorylation of creatine and the maintenance of high energy phosphates for over 15 h. Forskolin activates the catalytic subunit of adenylyl cyclase and, in MMQ cells, elevates the level of cAMP and stimulates prolactin secretion. 31P NMR spectroscopy was used to investigate the energy metabolism of the MMQ cells during stimulation by forskolin. The ability to measure small changes in the energy status of these cells was enhanced by increasing the PCr levels in the cells. Administration of forskolin to the perifused MMQ cells resulted in acute, reversible, and dose‐dependent changes in the 31P NMR spectra of the cells within 12 to 24 min of the beginning of forskolin exposure. Several lines of evidence indicate that the changes observed in the MMQ cells are the composite result of the interaction of forskolin with adenylyl cyclase and the plasma membrane glucose transporter. Also, preincubation of the MMQ cells with the dopamine agonist, bromocriptine, attenuates the forskolin‐stimulated decrease in the PCr resonance by approximately 50%. This attenuation indicates that the forskolin‐stimulated changes in energy metabolism are probably related to the prolactin secretion process.
Changes in metabolites and tissue water status after focal ischemia in cat brain assessed with localized proton MR spectroscopy
Authors: van der Toorn Annette , Verheul Hieronymus B. , van der Sprenkel Jan‐Willem Berkelbach , Tulleken Cees A. F. , Nicolay Klaas 
Published: March 2007

AbstractLocalized proton spectroscopy was used to monitor changes in metabolism and the biophysical status of tissue water in cat brain induced by occlusion of the middle cerebral artery. Changes in the intensity of N‐acetyl‐aspartate (NAA), total creatine (tCr), and lactate (Lac) signals in localized volumes of interest in the ischemic hemisphere were quantified relative to the preischemic signal. Changes in the apparent diffusion coefficient (ADC), T1‐ and T2‐relaxation times of water in those volumes were also quantified. Lactate was shown to increase rapidly in the first 0.5−2.0 h of ischemia and stabilized afterwards. The ADC of water started to decrease from 0.64 × 10−9 m2/s to 0.54 × 10−9 m2/s in the first minutes following occlusion, as was shown in two cases where ADC was measured with high temporal resolution, and stabilized after approximately 3 h at 0.38 × 10−9 m2/s (n = 6). NAA and tCr decreased by 35% (P< 0.0001) and 30% (P< 0.005), respectively, in the first 8 h of ischemia in comparison with the preischemic control levels. T1 and T2 gradually increased with 0.3 s (P< 0.0001) and 5.2 ms (P< 0.0001), respectively, during the same time span.