bluuebunny/crossref_metadata_2025 huggingface dataset:
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

Localized 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.
Migration and Accumulation of Silicone in the Liver of Women with Silicone Gel‐Filled Breast Implants
Authors: Pfleiderer Bettina , Garrido Leoncio
Published: March 2007

1H NMR localized spectroscopy (STEAM), combined with echocardiography (ECG), respiratory gating, and water and fat suppression, was used to quantify silicone concentrations in the liver of women with silicone gel‐filled breast implants. Localized spectroscopy was performed on 15 patients with silicone gel‐filled breast prostheses and on eight volunteers with no implants. The 1H spectra in the liver of patients showed silicone resonances from 0.3 to −0.8 ppm, attributable to protons in the methyl groups of silicone. The presence of silicone in the liver could first be detected 3–4 years after breast prostheses implantation. No correlation between silicone concentrations and implantation times was observed. However, our results indicated that silicone concentrations may reflect implant integrity: detectable silicone concentrations in the liver appeared to be higher when the implants were ruptured than when the implants appeared intact. Moreover, new resonances in the range of −2.6 to −4 ppm were observed in most patients after long‐term implantation. As these species increase with implantation time, the new resonances may reflect chemically changed silicone (paramag‐netically shifted silicon complexes bound to iron) accumulated over time. The sensitivity of 1H NMR localized spectroscopy is sufficient to detect silicon concentrations as low as 0.20 mM. Results from one patient whose implants had been removed 14 months prior to the NMR examination showed no detectable silicone in the liver, indicating that it may have been excreted via bile or degraded to silica and high coordinated silicon complexes. Quantitative 1H localized spectroscopy of the liver in women with silicone gel‐filled breast implants may provide valuable information concerning silicone accumulation and degradation in vivo, as well as about the kinetics of its elimination from the body after implant removal.
Spatial Encoding and Reconstruction in MRI with Quadratic Phase Profiles
Authors: Pipe James G.
Published: March 2007

Application of a slice‐selective frequency modulated radio‐frequency excitation pulse in a magnetic resonance (MR) imaging experiment creates a quadratic phase profile along the direction of slice selection. This quadratic phase profile inherently localizes the signal contribution to its vertex, which can be shifted with the application of a linear magnetic field gradient. Different methods for reconstruction of the spatial profile are discussed. The point spread functions of these reconstructions are similar to that of conventional Fourier transforms; one important difference is the elimination of aliasing at the expense of MR signal amplitude when performing ‘local,’ or limited, reconstruction. Limited reconstruction together with spatially limited excitation combines some of the advantages of both three‐dimensional phase‐encoded and two‐dimensional multislice techniques in appropriate situations. Applications discussed are three‐dimensional gradient echo experiments applied to time of flight MR angiography and T2‐weighted data collection.
High Speed 1H Spectroscopic Imaging in Human Brain by Echo Planar Spatial‐Spectral Encoding
Authors: Posse Stefan , Tedeschi Gioacchino , Risinger Robert , Ogg Robert , Bihan Denis Le
Published: March 2007

We introduce a fast and robust spatial‐spectral encoding method, which enables acquisition of high resolution short echo time (13 ms) proton spectroscopic images from human brain with acquisition times as short as 64 s when using surface coils. The encoding scheme, which was implemented on a clinical 1.5 Tesla whole body scanner, is a modification of an echo‐planar spectroscopic imaging method originally proposed by Mansfield Magn. Reson. Med. 1, 370–386 (1984), and utilizes a series of read‐out gradients to simultaneously encode spatial and spectral information. Superficial lipid signals are suppressed by a novel double outer volume suppression along the contours of the brain. The spectral resolution and the signal‐to‐noise per unit time and unit volume from resonances such as N‐acetyl aspartate, choline, creatine, and inositol are comparable with those obtained with conventional methods. The short encoding time of this technique enhances the flexibility of in vivo spectroscopic imaging by reducing motion artifacts and allowing acquisition of multiple data sets with different parameter settings.
Proton Transverse Nuclear Magnetic Relaxation in Oxidized Blood: a Numerical Approach
Authors: Gillis Pierre , Petö Stéphane , Moiny Francis , Mispelter Joël , Cuenod Charles‐André
Published: March 2007

When red blood cells are deoxygenated, hemoglobin, which is then transformed into deoxyhemoglobin or methemoglobin, becomes paramagnetic. The transverse nuclear magnetic relaxation rate of water protons is considerably enhanced by this chemical transformation. A general agreement exists about the origin of the phenomenon—local field inhomogene‐ities induced by paramagnetic centers randomly distributed within the cell—but the localization of the region that dominates the relaxation is unclear. We addressed this problem with a computer simulation devoted to the determination of transverse magnetic relaxation of water protons in the presence of superparamagnetic MRI contrast agent candidates. The simulation confirms an earlier experimental result that shares equitably the responsibility for the observed relaxation between intracellular and extracellular water.
Three‐Point Phase‐Contrast Velocity Measurements with Increased Velocity‐to‐Noise Ratio
Authors: Lee Adrian T. , Bruce Pike G. , Pelc Norbert J.
Published: March 2007

We describe a technique to increase the velocity‐to‐noise ratio (VNR) of phase‐contrast magnetic‐resonance velocity images based on making three measurements/flow encoding axis rather than the usual two. A phase‐aliased high first moment data set and a nonaliased low first moment data set are acquired, and the high‐moment data are phase unwrapped using the low‐moment data. The VNR of the resulting measurement is given by that of the high‐moment measurement and increases linearly with the first moment. A factor of 4 gain in VNR was observed with only a 50% increase in scan time. Thus, this method is a much more efficient way to increase VNR than simple averaging.
Effects of Myocardial Water Exchange on T1 Enhancement during Bolus Administration of MR Contrast Agents
Authors: Judd Robert M. , Atalay Michael K. , Rottman Gerald A. , Zerhouni Elias A.
Published: March 2007

Interpretation of first‐pass myocardial perfusion studies employing bolus administration of T1 magnetic resonance (MR) contrast agents requires an understanding of the relationship between contrast concentration and image pixel intensity. The potential effects of myocardial water exchange rates among the intravascular, interstitial, and cellular compartments on this relationship are controversial. We directly studied these issues in isolated, nonbeating canine interventricular septa. Myocardial T1 was measured three times/s during bolus transit of intravascular (albumin‐Gd‐DTPA and poly‐lysine‐Gd‐DTPA) and extracellular (gadoteridol) contrast agents. For polylsine‐Gd‐DTPA, the peak changes in myocardial 1/T1 (ΔR1) scaled nonlinearly with perfusate contrast concentration whereas a linear relationship would be expected for fast water exchange among the vascular, interstitial, and cellular compartments. For all agents, the peak ΔR1 were much smaller than the values expected on the basis of fast myocardial water exchange. The data demonstrate that in isolated myocardial tissue, myocardial T1 enhancement during bolus administration of contrast can be strongly affected by myocardial water exchange for both intravascular and extracellular MR contrast agents.
Anomalous Transverse Relaxation in 1H Spectroscopy in Human Brain at 4 Tesla
Authors: Posse Stefan , Cuenod Charles Andre , Risinger Robert , Bihan Denis Le , Balaban Robert S.
Published: March 2007

Longitudinal (T1) and apparent transverse relaxation times (T2) of choline‐containing compounds (Cho), creatine/phospho‐creatine (Cr/PCr), and N‐acetyl aspartate (NAA) were measured in vivo in human brain at 4 Tesla. Measurements were performed using a water suppressed stimulated echo pulse sequence with complete outside volume presaturation to improve volume localization at short echo times. T1‐values of Cho (1.2 ± 0.1 s), Cr (1.6 ± 0.3 s), and NAA (1.6 ± 0.2 s) at 4 Tesla in occipital brain were only slightly larger than those reported in the literature at 1.5 Tesla. Thus, TR will not adversely affect the expected enhancement of signal‐to‐noise at 4 Tesla. Surprisingly, apparent T2‐values of Cho (142 ± 34 ms), Cr (140 ± 13 ms), and NAA (185 ± 24 ms) at 4 Tesla were significantly smaller than those at 1.5 Tesla and further decreased when increasing the mixing interval TM. Potential contributing factors, such as diffusion in local susceptibility related gradients, dipolar relaxation due to intracellular paramagnetic substances and motion effects are discussed. The results suggest that short echo time spectroscopy is advantageous to maintain signal to noise at 4 Tesla.
Solid State Phosphorus‐31 Magnetic Resonance Imaging of Bone Mineral
Authors: Moore James R. , Garrido Leoncio , Ackerman Jerome L.
Published: March 2007

Chemically selective solid state phosphorus‐31 nuclear magnetic resonance (NMR) imaging of the mineral phase of bone and synthetic calcium phosphate models for bone mineral is demonstrated with microscopy‐scale (about 5 mm field of view) apparatus at 6.0 T magnetic field strength. Pixel‐by‐pixel linear combination of image data from multiple radio frequency (RF) pulse sequences, chosen to develop contrast between chemical constituents of interest in the mineral, generates derived images showing the distribution of individual constituents. The technique combines the noninvasive character of magnetic resonance imaging (MRI) with the ability of solid state NMR spectroscopy to characterize subtle chemical variations in bone mineral, as well as to measure the amount of mineral. These methods are, in principle, extensible to larger dimensional scales suitable for live animal subjects or human limbs.
Optimized Ultra‐Fast Imaging Sequence (OUFIS)
Authors: Zha Leping , Lowe Irving J.
Published: March 2007

The DUFIS sequence can make ultra‐fast images (˜10 ms) without the use of rapidly switched gradients. The RF excitation sequence is spatially selective so that only a small fraction of the magnetization in each imaging pixel is used which produces a poor imaging signal to noise ratio (SNR). We have developed several alternative RF sequences that use RF pulses with multiple phases, and also with just 0° and 180° phases to excite almost all the magnetization in a pixel and greatly improve the SNR. The optimization of these pulse sequences (now called OUFIS) have been conducted both analytically and by numerical searches, with various linear and nonlinear models. Both theoretical and computational methods used in the optimizations are described in detail. Preliminary experimental results are briefly presented with several possible applications of the OUFIS excitation sequences suggested.
Motionless Movies of Myocardial Strain‐Rates using Stimulated Echoes
Authors: Wedeen Van J. , Weisskoff Robert M. , Reese Timothy G. , Beache Garth M. , Poncelet Brigitte P. , Rosen Bruce R. , Dinsmore Robert E.
Published: March 2007

We present methods to acquire and analyze NMR movies of myocardial strain rates in which cardiac motion is suppressed and the histories of strain rates are accurately defined for each voxel of myocardial tissue. By means of stimulated echoes, the myocardial strain‐rate tensor is phase‐encoded at progressive delays in the cardiac cycle while the slice‐select and spatial encoding of the image acquisition are performed at a constant cardiac delay. In these data, every image shows the identical myocardial tissue, and the anatomic configuration of the heart appears motionless. The myocardial strainrate data, however, indicate the state of motion which existed in this slice at the time of the velocity phase‐encoding, and these data evolve with the progressive delay as a movie. Using echo‐planar MRI, motionless movies of myocardial strain rate of four to eight cardiac delays are obtained in a breath‐hold. As an application, a quantitative characterization of cardiac mechanical synchrony is accomplished by principal component analysis (PCA) of the time series of strain rates.
Proton NMR Observation of the Antineoplastic Agent Iproplatin In Vivo by Selective Multiple Quantum Coherence Transfer (Sel‐MQC)
Authors: He Qiuhong , Bhujwalla Zaver M. , Maxwell Ross J. , Griffiths John R. , Glickson Jerry D.
Published: March 2007

We have noninvasively detected the proton signal of an antineoplastic agent Iproplatin in vivo by selective multiple quantum coherence transfer (Sel‐MQC). Without isotopic labeling or chemical modification, the Sel‐MQC method labels Iproplatin by its intrinsic proton multiple quantum coherences and, hence, differentiates the Iproplatin signal from the intensive overlapping resonances of lipid and lactate. This proton NMR method should also be applicable to study other drugs with appropriate spin coupling patterns.
Pharmacokinetic Mapping of the Breast: A New Method for Dynamic MR Mammography
Authors: Hoffmann Ulf , Brix Gunnar , Knopp Michael V. , Heβ Thomas , Lorenz Walter J.
Published: March 2007

A dynamic contrast‐enhanced MRI technique for whole breast examinations is presented. The fast kinetics of tissue response during and after constant‐rate intravenous infusion of gadolinium diethylenetriaminopentaacetic acid was resolved using a strongly T1‐weighted saturation recovery TurboFLASH sequence that makes it possible to acquire signal‐time courses sequentially from 15 adjacent slices with a temporal sampling rate of 21 s. On the basis of the mathematically established and experimentally verified linear relationship between the measured saturation recovery TurboFLASH signal variation and the gadolinium diethylenetriaminopentaacetic acid concentration in the tissue, the signal‐time courses were analyzed within the framework of pharmacokinetic modeling. In our study, the tissue response was parameterized adequately using an open linear two‐compartment model. With this approach, the tissue specific information contained in the signal‐time course can be described using only two parameters: an amplitude A, reflecting the degree of MR signal enhancement, and an exchange parameter k21, characterizing vascular permeability and perfusion of the tissue. A clearly arranged representation of the large amount of data (480 saturation recovery TurboFLASH breast images/examination) was accomplished by means of color coding of the computed parameters, resulting in one color‐coded pharmacokinetic parameter map/cross‐section.
A Velocity k‐Space Analysis of Flow Effects in Echo‐Planar and Spiral Imaging
Authors: Nishimura Dwight G. , Irarrazabal Pablo , Meyer Craig H.
Published: March 2007

A velocity k‐space formalism facilitates the analysis of flow effects for imaging sequences involving time‐varying gradients such as echo‐planar and spiral. For each sequence, the velocity k‐space trajectory can be represented by kv (k)r; that is, its velocity‐frequency (kr) position as a function of spatial‐frequency (kr) position. In an echo‐planar sequence, kr is discontinuous and asymmetric. However, in a spiral sequence, kr is smoothly varying, circularly symmetric, and small near the kr origin. To compare the effects of these trajectory differences, simulated images were generated by computing the k‐space values for an in‐plane vessel with parabolic flow. Whereas the resulting echo‐planar images demonstrate distortions and ghosting that depend on the vessel orientation, the spiral images exhibit minimal artifacts.
Deuterium Magnetic Resonance Imaging of Rabbit Eye in Vivo
Authors: Obata Takayuki , Ikehira Hiroo , Koga Masahisa , Yoshida Katsuya , Kimura Fukuko , Tateno Yukio
Published: March 2007

We used deuterium magnetic resonance imaging (2H MRI) to visualize water movement in the rabbit eye. Dynamic 2H MRI was obtained every 3.5 min at 2 tesla by FLASH pulse sequence (TR, 300 ms; TE, 10 ms; α = 90°) with a slice thickness of 10 mm using a surface coil (4 cm in diameter). After topical administration (0.2 ml D2O), only the aqueous chamber was imaged, and the signals decreased mono‐exponentially. The flow rate was 0.113/min, in agreement with that already reported. After intravenous administration of deuterated saline (3 ml/kg), the aqueous chamber became visible first during imaging, then by the vitreous body. The signals around the lens were only faintly detected. Thus, deuterium MRI was determined to be useful for visualizing water movement in the eye.
Echo‐Time‐Encoded Burst Imaging (EBI): A Novel Technique for Spectroscopic Imaging
Authors: Jakob Peter M. , Ziegler Anne , Doran Simon J. , Décorps Michel
Published: March 2007

A new technique for rapid spectroscopic imaging is presented. The proposed experiment enables a complete mapping of the two‐dimensional reciprocal space kx, ko, and thus the acquisition of a 1D spectroscopic image in a single scan. The properties of the pulse sequence, based on the use of a burst of low flip angle pulses, are analyzed in the framework of linear response theory, and it is shown that chemical shift information may be introduced into the spatially encoded echoes. First experimental results are presented demonstrating that 32 x 32 proton spectroscopic images may be acquired within less than 1 min with a conventional imaging system.
Central nervous system trans‐synaptic effects of acute axonal injury: a 1h magnetic resonance spectroscopy study
Authors: Rango Mario , Spagnoli Diego , Tomei Giustino , Bamonti Fabrizia , Scarlato Guglielmo , Zetta Lucia
Published: March 2007

N‐acetylaspartate (NAA) has previously been proposed as a neuronal marker. 1H magnetic resonance spectroscopy (MRS) is able to detect NAA in brain, and decreases of NAA have been documented after brain injury. The reason for this decrease is not fully understood and neuron loss damage and “dysfunction” have all been proposed. It is hypothesized that acute central nervous system (CNS) deafferentation causes a trans‐synaptic NAA decrease and that high resolution 1H MRS is able to detect such a decrease. To test this hypothesis, an experimental model was used in which axonal lesions were obtained by stretch injury in guinea pig right optic nerve (95–99% crossed fibers). The trans‐synaptic concentration of NAA, total creatine (Cr), and the NAA/Cr ratio in lateral geniculate bodies (LGB) and superior colliculi (SC) sample extracts were measured 72 h later by high resolution 1H MRS. In the left LGB/SC, which is where right optic nerve fibers project, reductions of NAA and NAA/Cr were found whereas Cr levels were normal. NAA, NAA/Cr, and Cr values were all normal in the right LGB/SC. Histology and EM findings revealed no abnormalities. At 7 days, left LGB/SC NAA and NAA/Cr values were in the normal range. It was concluded that 1) acute deafferentation in the CNS causes a trans‐synaptic decrease of NAA levels that can be detected by 1H MRS and 2) NAA decrease may be due to changes of NAA metabolism caused by functional neuronal inactivity rather than neuronal loss, injury or “dysfunction.” 1H MRS is a potential tool for the study of functional effect of CNS lesions in vivo.
Magnetostimulation in MRI
Authors: Irnich Werner , Schmitt Franz
Published: March 2007

In national and international bodies, there is active discussion of appropriate safety regulations of levels of magnetic field strength in MRI. Present limits are usually expressed in terms of the switching rate dB/dt, but the validity of this is open to debate. Application of the fundamental law of electrostimulation is well‐established, both on theoretical and experimental grounds. Application of this law, in combination with Maxwell's law, yields a very simple equation that we call the fundamental law of magnetostimulation. This law has the hyperbolic form of a strength‐duration curve and allows an estimation of the lowest possible value of the magnetic flux density capable of stimulating nerves and muscles. Calculations prove that the threshold for heart excitation is much higher than those for nerve and muscle stimulations. Experimental results from us and other authors confirm the correctness of the derived laws for magnetostimulation. In light of these findings, proposed safety limits should be reconsidered.
Fast Three Dimensional Magnetic Resonance Imaging
Authors: Irarrazabal Pablo , Nishimura Dwight G.
Published: March 2007

To reduce the scan time in three‐dimensional (3D) imaging, the authors consider alternative trajectories for traversing k‐space. They differ from traditional 3D trajectories, such as 3DFT, in that they employ time‐varying gradients allowing longer readouts and in turn a reduced scan time. Some of these trajectories reduce by an order of magnitude the number of excitations compared with 3DFT and provide flexibility for trading off signal‐to‐noise ratio for scan time. Other concerns are the minimum echo time and flow/motion properties. As examples, the authors show two applications: A 3D data set of the head (field of view of 30 x 30 x 7.5 cm and resolution of 1.5 x 1.5 x 1.5 mm) acquired in 56 s using a stack of spirals in 3D k‐space; and a 3D movie of the heart (20 x 20 x 20 cm field of view, 2 x 2 x 2 mm resolution, and 16 time frames per cardiac cycle) acquired in 11 min using a cones trajectory.
Proton MRS of Gadolinium‐enhancing MS Plaques and Metabolic Changes in Normal‐Appearing White Matter
Authors: Roser Werner , Hagberg Gisela , Mader Irina , Brunnschweiler Heiner , Radue Ernst Wilhelm , Seelig Joachim , Kappos Ludwig
Published: March 2007

Localized short echo time (TE = 20 ms), stimulated echo acquisition mode, and double spin echo (TE = 135 ms) proton spectroscopy were performed in clearly defined, acute Gadolinium (Gd)‐enhancing multiple sclerosis (MS) plaques of 22 patients with clinically definite MS. The resonances of N‐acetylated metabolites (NA), creatine/phosphocreatine (Cr), choline‐containing compounds (Cho), glycine/myo‐inositol (Ino), and lactate were evaluated. The ratios of NA/Cr and NA/Cho were significantly decreased, Cho/Cr increased, and Ino/Cr remained unchanged. No marker peaks or elevated lactate levels were found. The measured metabolic changes were practically independent of the relative plaque size within the volume of interest (8 ml). Thus, the spectral changes measured with 1H MRS in acute Gd‐enhancing MS plaques originate not only from the lesion as depicted by MRI, but also from the surrounding normal‐appearing white matter.
NMR Relaxometric Investigation on Human Methemoglobin and Fluoromethemoglobin. An Improved Quantitative in Vitro Assay of Human Methemoglobin
Authors: Aime Silvio , Fasano Mauro , Paoletti Silvia , Arnelli Aldo , Ascenzi Paolo
Published: March 2007

Longitudinal water proton relaxation rates of methemoglobin solutions show a strong dependence on temperature and pH. The increase of the relaxation rates with temperature is associated with shortened exchange lifetime of the coordinated water molecule. An accurate measurement of the relaxation rate of methemoglobin solutions thus requires careful control of the experimental temperature. This observation prompted the authors to look for an improved version of the relaxometric in vitro determination of methemoglobin. The method is based on transforming methemoglobin into the corresponding fluoromethemoglobin derivative, which shows both a higher relaxivity and a negligible dependence on temperature. The proposed method has been found to be in good agreement with data from spectrophotometric assays.
The Estimation of Local Brain Temperature by in Vivo1H Magnetic Resonance Spectroscopy
Authors: Cady Ernest B. , D'Souza Patricia C. , Penrice Juliet , Lorek Ann
Published: March 2007

Brain temperature may be important for investigating pathology and cerebroprotective effects of pharmaceuticals and hypothermia. Two methods for estimating temperature using 1H magnetic resonance spectroscopy are described: a partially water‐suppressed binomial sequence and non‐water‐suppressed point‐resolved spectroscopy. Relative to N‐acetylaspartate (Naa), water chemical shift (θH2O‐Naa) in piglet brain depended linearly on temperature from 30° to 40°C: temperature was 286.9–94.0 θH2O‐Naa ° C. Thalamic temperature in six normal infants was 38.1° ± 0.4° C indicating that local brain temperature could be estimated with adequate sensitivity for studying pathologic and therapeutic changes.
Lactate production by human monocytes/macrophages determined by proton mr spectroscopy
Authors: López‐Villegas Dolores , Lenkinski Robert E. , , Wehrli Suzanne L. , Ho Wen‐Zhe , Douglas Steven D.
Published: March 2007

Elevated brain lactate has been observed by in vivo proton MRS in different pathological situations. The origin of this lactate remains controversial. The possibility that it was produced by the metabolism of phagocytic cells has been proposed. To investigate this hypothesis, the authors have employed high‐resolution proton MRS to monitor changes in glucose, lactate, and other metabolites in the medium used to culture human monocyte‐derived macrophages in vitro. Results show that the differentiation of human monocytes/macrophages in the presence of physiological stimulating factors (M‐CSF or GM‐CSF) was associated with an increase in lactate production and glucose utilization. The present results are consistent with the hypothesis that lactate detected by proton MRS in vivo may be produced by the metabolism of macrophages when infiltrates of these cells are present. The possible extrapolation of the authors' finding to the in vivo situation and its relevance are discussed.
Three‐dimensional spatial EPR imaging of the rat heart
Authors: Kuppusamy Periannan , Wang Penghai , Zweier Jay L.
Published: March 2007

While instrumentation capable of performing three‐dimensional EPR imaging of free radicals in whole tissues and isolated organs has been developed at L‐band, important questions remain regarding the resolution and image quality that can be obtained in practice using the presently available free radical labels. Therefore, studies were performed applying three‐dimensional spatial EPR imaging at L‐band to image the distribution of free radical labels in the isolated heart and in phantoms of similar size. With nitroxide labels the obtainable resolution is limited by the presence of hyperfine structure in the EPR absorption function that in turn limits the maximum applicable gradient. The authors observed that with the nitroxide labels, resolutions in the range of 1–2 mm are possible, while with a single line glucose char label, resolutions of 0.2 mm are obtained. With the nitroxides, images were of sufficient resolution to resolve the overall global shape of the heart and the location of the left and right ventricular cavities; however, finer structures could not be resolved. With the glucose char much finer resolution could be obtained enabling visualization of the ventricles, aortic root, and proximal coronary arteries.
Double‐echo three‐point‐dixon method for fat suppression MRI
Authors: Szumowski Jerzy , Coshow William , Li Fang , Coombs Bernard , Quinn Stephen F.
Published: March 2007

A double‐echo two‐excitation pulse sequence encoding fat and water signals for a phase‐sensitive three‐point Dixon‐type analysis (DE‐3PD) was developed and implemented on a 1.5 T MR imager. Data processing was performed using a previously developed two‐dimensional (2D) region‐growing algorithm, adapted to use double‐echo data. Density‐, T1, and T2‐weighted fat suppression images were obtained from six volunteers using the new fat suppression method. The images were compared with corresponding images obtained using frequency‐selective excitation fat suppression (FAT‐SAT) and a single‐echo three‐point‐Dixon method (SE‐3PD). The results demonstrate that the DE‐3PD sequence shortens the imaging time by one‐third compared with the SE‐3PD method, without loss in image quality. The data also show that a 2D region‐growing algorithm effectively unwraps the phase of DE‐3PD data sets, and that results of DE‐3PD fat signal suppression are consistently better than those obtained using a standard FATSAT method. The authors conclude that the double‐echo sequence provides density‐, T1, and T2‐weighted images that appear to be promising for routine clinical applications.
Quantitative analysis of regional left ventricular function after myocardial infarction in the pig assessed with cine magnetic resonance imaging
Authors: Holman Eduard R. , Vliegen Hubert W. , Van Geest Rob J. Der , H. C. Reiber Johan , Van Dijkman Paul R. M. , Laarse Arnoud Van Der , Roos Albert De , Van Wall Ernst E. Der
Published: March 2007

To assess the accuracy of quantitative analysis of global and regional wall motion and wall thickening of the left ventricle with cine magnetic resonance (MR), images obtained in eight pigs before and after myocardial infarction were compared with those obtained using gadolinium diethylenetriaminepen‐taacetic acid (Gd‐DTPA)‐enhanced multislice spin‐echo MR imaging and determination of pathology. The region with abnormal wall motion and wall thickening, as determined with cine MR imaging, identified the same region of infarction as indicated by Gd‐DTPA‐enhanced spin‐echo MR imaging and pathology. Within the infarcted region wall motion and wall thickening analyzed with the centerline method were significantly reduced. We conclude that the use of quantitative analysis of cine MR images accurately determines localization and extent of regional left ventricular dysfunction in the infarcted heartin vivo. This analysis using dedicated software including the centerline method allows sequential assessment of regional left ventricular function in normal and infarcted hearts.
Measurement of fluid‐shear rate by fourier‐encoded velocity imaging
Authors: Frayne Richard , Rutt Brian K.
Published: March 2007

A new technique for estimating the blood fluid shear rate at the vessel wall is presented. The technique uses Fourier‐encoded velocity imaging to determine the velocity distribution within a spatial element (voxel) that straddles the bloodvessel wall interface. By appropriate processing, the velocity distribution (1) can determine the location of the wall‐blood interface within the voxel and (2) estimate the velocity profile across the spatial extent of the voxel. From this information, accurate estimates of fluid shear rate may be obtained. Simulations are presented to illustrate this technique and to show the effects of various error sources, including differences in proton densities between blood and wall tissues and flow‐related signal changes. Experimental evidence obtained for steady flow in straight tubes is also presented in support of the technique. The mean error in the experimental shear rate estimates found using the proposed technique was ‐15%. This represents a significant improvement over estimates obtained by extrapolation of the velocity profile over multiple voxels (mean error of ‐73%).
Magnetic resonance fluoroscopy using spirals with variable sampling densities
Authors: Spielman Daniel M. , Pauly John M. , Meyer Craig H.
Published: March 2007

The imaging of dynamic processes in the body is of considerable interest in interventional examinations as well as kinematic studies, and spiral imaging is a fast magnetic resonance imaging technique ideally suited for such fluoroscopic applications. In this manuscript, magnetic resonance fluoroscopy pulse sequences in which interleaved spirals are used to continuously acquire data and reconstruct one movie frame for each repetition time interval are implemented. For many applications, not all of k‐space needs to be updated each frame, and nonuniform k‐space sampling can be used to exploit this rapid imaging strategy by allowing variable update rates for different spatial frequencies. Using the appropriate reconstruction algorithm, the temporal updating rate for each spatial frequency is effectively proportional to the corresponding k‐space sampling density. Results from a motion phantom as well as in in vivo gadolinium diethylenetriaminopentaacetic acid (Gd‐DTPA) bolus tracking studies in a rat model demonstrate the high temporal resolution achievable using these techniques as well as the tradeoffs available with nonuniform sampling densities. This paper focuses on the acquisition of real‐time dynamic information, and all images presented are reconstructed retrospectively. The issues of real‐time data reconstruction and display are not addressed.
Proton spectroscopic imaging of the human brain using phased array detectors
Authors: Wald Lawrence L. , Moyher Susan E. , Day Mark R. , Nelson Sarah J. , Vigneron Daniel B.
Published: March 2007

Two and four‐coil phased array detectors have been developed to increase the sensitivity of proton spectroscopic imaging of the human brain. These include a quadrature figure‐8 coil for the study of the vertex, several arrays of 2‐4 small overlapping (6‐8 cm diameter) circular coils and a combination figure‐8 coil plus circular coil. These were constructed in our laboratory and tested to assess their utility for brain spectroscopy. Methods for optimally combining the data from the independent receivers based on the analytical coil maps or measured signal to noise ratios (SNRs) of the data were investigated. High spatial resolution (0.2‐0.4 cm3 voxel size) two‐ or three‐dimensional chemical shift images of normal brain were obtained in 17‐minute acquisitions. These spatial resolutions are comparable to those previously obtained with conventional small surface coils, but the specialized detectors allow this sensitivity to be achieved for a larger region or for previously inaccessible areas such as the top of the head. The coverage and SNR increases demonstrated are similar to those obtained in magnetic resonance phased array imaging.
Error in MR volumetric flow measurements due to ordered phase encoding in the presence of flow varying with respiration
Authors: Wolf Ronald L. , Hangiandreou Nicholas J. , Felmlee Joel P. , Rossman Phillip J. , Julsrud Paul R. , Riederer Stephen J. , Ehman Richard L.
Published: March 2007

Respiratory ordered phase encoding is often employed in MRI studies to reduce image artifacts due to breathing motion. The purpose of this work was to evaluate error caused by the use of respiratory ordering of phase encoding in MR cine phase‐contrast (CPC) volumetric flow measurements when the flow rate is sensitive to respiration. It was hypothesized that this effect is due to the systematic biasing of a respiratory‐induced phase modulation function in k‐space. A theoretical model for the effects of respiration was developed and then tested in flow phantom studies and in normal volunteer studies. In phantom experiments, the use of respiratory ordering induced an error of as much as 13% in CPC volumetric flow measurements. In preliminary volunteer studies, error was as high as 26% in superior vena cava flow measurements versus less than 1% error in the ascending aorta. It is concluded that a potential for error exists in CPC volumetric flow measurements obtained with the use of respiratory ordering schemes. Volunteer studies with larger numbers are warranted. Clinical applications in which this effect may be important include flow measurements in vessels subject to variations in flow due to respiration, such as the venae cavae, pulmonary vasculature, and portal vein.
Quantitative nmr microscopy of multicellular tumor spheroids and confrontation cultures
Authors: Brandl Matthias , Tonn JÖRg‐Christian , Kotitschke Klaus , Goldbrunner Roland , Kerkau Siglinde , Haase Axel
Published: March 2007

In cancer research, tumor spheroids are a well established system to study tumor metabolism resembling the situation in vivo more closely cell monolayers. Spherical aggregates of malignant melanoma cells (MV3) and their invasion into rat brain aggregates have been investigated by quantitative NMR microscopy. Relaxation times (T1, T2) and diffusion parameter images were acquired with an in‐plane resolution of 14 × 14 μm2. The authors were able to demonstrate that the morphology of the spheroids can be visualized on these NMR maps. The contrast was mainly manifested in relaxation maps, where average relaxation times T1 = 1.94 ± 0.17 s and T2 = 42.8 ± 6.3 ms were obtained for proliferating cells, and T1 = 2.49 ± 0.31 s and T2 = 104.3 ± 29.4 ms for the necrobiotic center. The mean diffusion coefficients were 0.59 ± 0.12 μm2/ms and 0.85 ± 0.14 μm2/ms, respectively. The authors could follow the dynamic process of tumor cell invasion in the investigated co‐culture system. Knowledge about tumor cell migration and tumor cell invasion is essential for the understanding of cancer and its therapy. Quantitative NMR microscopy can study this dynamic process noninvasively and therefore may help to assess the influence of therapy on the micromilieu of these spheroids.
The role of Na+/K+ ATPase activity during low flow ischemia in preventing myocardial injury: A 31P, 23Na and 87Rb NMR spectroscopic study
Authors: Cross Heather R. , Radda George K. , Clarke Kieran
Published: March 2007

An increase in intracellular Na+ during ischaemia has been associated with myocardial injury. In this study, we determined whether inhibition of Na+/K+ ATPase activity contributes to this increase and whether Na+/K+ ATPase activity can be maintained by provision of glucose to perfused rat hearts during low flow, 0.5 ml/min, ischemia. We used 31P NMR spectroscopy to determine changes in myocardial energetics and intracellular and extracellular volumes. 23Na NMR spectroscopy, with DyTTHA3‐ present as a shift reagent, was used to measure changes in intracellular Na+ and 87Rb NMR spectroscopy was used to estimate Na+/K+ ATPase activity from Rb+ influx rates, Rb+ being an NMR‐sensitive congener of K+. In hearts provided with 11 mM glucose throughout ischemia, glycolysis continued and ATP was twofold higher than in hearts without glucose. In the glucose‐hearts, Rb+ influx rate was threefold higher, intracellular Na+ was fivefold lower at the end of ischemia and functional recovery during reperfusion was twofold higher. We propose that continuation of glycolysis throughout low flow ischemia allowed maintenance of sufficient Na+/K+ ATPase activity to prevent the increase in intracellular Na+ that would otherwise have led to myocardial injury.
Reversible decreases in N‐acetylaspartate after acute brain injury
Authors: Stefano Nicola De , Matthews Paul M. , Arnold Douglas L.
Published: March 2007

N‐Acetylaspartate (NAA), which constitutes the major proportion of the dominant resonance in proton MR spectra of brain, is localized in mature brain exclusively in neurons and neuronal processes. A decrease in NAA has been observed in many cerebral pathologies and has usually been interpreted as an index of irreversible neuronal loss. The authors report a follow‐up study of six patients with acute brain damage (four from demyelinating lesion and two from mitochondrial encephalopathy with lactic acidosis and stroke‐like episodes [MELAS]). All patients underwent serial MR spectroscopy examinations. The four patients with acute demyelinating lesions initially showed decreases in NAA in the centers of the lesions that ranged between 34‐72% of values from homologous brain volumes in the other hemisphere. All four patients subsequently showed substantial recovery of NAA as their clinical status improved. The two patients with MELAS syndrome had large decreases of NAA signal (50% and 20% of normal values, respectively) from their occipital lobe lesions during the acute stroke‐like episodes. After the acute phase of the illness a progressive increase of NAA in the same volumes was seen in both patients (to 76% and 60% of normal values, respectively). These results demonstrate that significant recovery of NAA can occur after acute brain damage. The potential contribution of reversible neuronal dysfunction (as well as neuronal loss) must be considered in the interpretation of decreases in the NAA resonance associated with acute brain pathology.
Locally focused mri
Authors: Cao Yue , Levin David N. , Yao Lian
Published: March 2007

Conventional magnetic resonance images are reconstructed by Fourier transformation and have uniform spatial resolution across the entire field of view (FOV). This paper describes a way of creating MR images that have higher spatial resolution in some areas than in others. High resolution imaging can be confined to just those areas where it is necessary to resolve strong edges without truncation artifact. Such locally focused images can be acquired in less scan time than that required to image the entire FOV with uniformly high resolution. Images are reconstructed from a subset of the usual phase‐encoded signals required to create a uniformly well‐resolved image. The measured signals are usually nonuniformly scattered ink‐space. Functional and interventional imaging may benefit from this technique, which makes it possible to acquire a rapid series of dynamical images that have high resolution in areas of expected change and lower resolution elsewhere. Spectroscopic images may be improved by using high resolution in the neighborhood of sharp edges (e.g., scalp lipids) that might otherwise cause truncation artifacts.
Local RBF‐FD solutions for steady convection–diffusion problems
Authors: Chandhini G. , Sanyasiraju Y. V. S. S.
Published: March 2007

This paper describes the application of radial basis function (RBF) based finite difference type scheme (RBF‐FD) for solving steady convection–diffusion equations. Numerical studies are made using multiquadric (MQ) RBF. By varying the shape parameter in MQ, the accuracy of the solution is seen to be highly improved for large values of Reynolds' numbers. The developed scheme has been compared with the corresponding finite difference scheme and found that the solutions obtained using the former are non‐oscillatory. Copyright © 2007 John Wiley & Sons, Ltd.
Sport for all?
Authors: Hardy K J , Kenyon R , Gillmsc G V
Published: March 2007

Hypoglycaemia may complicate exercise in insulin‐treated diabetic patients. An exercise‐induced fall in blood glucose has been well documented in the laboratory, but little has been published on the prevalence of clinically significant exercise‐induced hypoglycaemia. We studied the prevalence of exercise‐induced hypoglycaemia in patients attending our adolescent diabetes clinic by means of a questionnaire. Of the 55 respondents (mean age 16.9±1.6 years and mean diabetes duration 7.2±3.9 years), 45 took regular exercise. Only four (9%) patients were troubled by hypoglycaemia: one had proven factitious hypoglycaemia and three had better blood glucose control than the group as a whole (mean glycated haemoglobin (HbA1) for the hypoglycaemic patients 8.4±1.4 v 10.3±2.3% for the group as a whole). Forty‐two (93%) of the patients took precautions against hypoglycaemia: 31 altered their diet, three altered insulin and eight altered both. The diabetic patients performed as much sport as their non‐diabetic peers (4.2±3.1 v 4.4±3.7 hours/week). We conclude that exercise‐induced hypoglycaemia is uncommon in adolescent diabetic patients with satisfactory blood glucose control and that hypoglycaemia need not limit exercise in these young people provided appropriate precautions have been taken.
Metabolic control during Ramadan fasting
Authors: Beshyah S A , Jowett N I , Burden A C
Published: March 2007

Fifteen diabetic Muslim patients were studied to assess diabetic control during the fasting of Ramadan and the changes in the various haematological and biochemical blood parameters. No specific instructions were given to adjust their medications during the fast: six considered their diabetic control unchanged; seven improved; and two worsened. Mean weight fell from 69.1 to 68 kg (NS). Six mild episodes of hypoglycaemia were reported. No patient showed ketonuria and none needed admission to hospital. Plasma glucose and serum triglycerides fell with fasting, serum fructosamine and cholesterol levels did not alter significanly.

Conclusions: most diabetics can safely fast but more medical attention to adjust their medication by increased dosage in the evening to combat hyperglycaemia and reduced dosage in early morning to prevent hypoglycaemia.
A new semiquantitative rapid test for screening for microalbuminuria
Authors: Agardh Carl‐David
Published: March 2007

Microalbuminuria is a predictor for later development of clinical nephropathy in both Type 1 and Type 2 diabetes mellitus, and therefore important to screen for.

In this study, a new semiquantitative test‐strip (Micral‐Test®) method was compared with the results measured with a quantitative laboratory method in urine samples from 117 diabetic patients attending an out‐patient ward. When 20mg/I was chosen as the cut‐off point for pathological albumin concentration as determined by the laboratory method, pathological urinary concentrations were recorded by Micral‐Test® with a sensitivity of 87.8% and specificity of 97.4%. At higher readings, the comparison method tended to show higher values.

It is concluded that the semiquantitative method tested can be used for screening for the presence of microalbuminuria. When microalbuminuria occurs, a quantitative method is recommended.
Capillary blood sampling: How much pain is necessary?. Part 2: Relation between penetration depth and puncture pain
Authors: Fruhstorfer H , Müller T , Scheer E
Published: March 2007

The relation between penetration depth and puncture pain was studied in 30 healthy subjects with a lancing device which allowed adjustment of depth (0.3–1.1mm). Pain was linearly related to depth as was the blood volume obtained. In about half of the individuals tested, an actual penetration depth of less than 1.0 mm provided sufficient blood for a glucose test.
Fatal cardiac arrest following acute hypoglycaemia in a diabetic patient
Authors: Frier BM , Barr StCG , Walker JD
Published: March 2007

A patient is described who had long‐standing insulin‐dependent diabetes with multiple diabetic complications, and also had known coronary heart disease. While receiving treatment for acute severe hypoglycaemia he sustained a cardiac arrest and died. The haemodynamic effects and the risk of inducing cardiac arrhythmia imposed by acute hypoglycaemia is discussed. Measurement of capillary blood glucose is advised in any insulin‐treated diabetic patient presenting with an acute cardiac event.