bluuebunny/crossref_metadata_2025 huggingface dataset:
In vivo phosphorus polarization transfer and decoupling from protons in three‐dimensional localized nuclear magnetic resonance spectroscopy of human brain
Authors: Gonen Oded , Mohebbi Afsaneh , Stoyanova Radka , Brown Truman R.
Published: March 2007

Refocused insensitive nucleus enhancement by polarization transfer (RINEPT) from protons (1H) to a J‐coupled phosphorus (31P) has been incorporated into three‐dimensional (3D) chemical‐shift‐imaging (CSI) sequence on a clinical imager. The technique is demonstrated on a phantom and in in vivo human brain. The polarization‐transfer efficiency (∼1.2) is lower than the theoretical maximum of γ1H/γ31P≈ 2.4 resulting from 1H‐1H homonuclear J couplings of similar magnitude competing with the 1H →31P transfer. Nevertheless, compared with direct 31P Ernst‐angle excitation, signal gains of up to × 1.8 were obtained mainly as a result of T1 differences between 31P and the 1H. Spectral interpretation is simplified by editing out all non‐proton‐coupled 31P signals. The duration, ∼50 min, and power deposition, ∼1 W · kg−1, make the application suitable for human studies.
Application of a 3D volume 19FMR imaging protocol for mapping oxygen tension (pO2) in perfluorocarbons at low field
Authors: Pratt Ronald G. , Zheng Jie , Stewart Brent K. , Shiferaw Yoseph , McGoron Anthony J. , Samaratunga Ranasinghage C. , Thomas Stephen R.
Published: March 2007

A limited flip angle gradient‐echo 3D volume acquisition imaging protocol for mapping partial pressure of oxygen (pO2) in perfluorocarbon compounds (PFCs) at low field (0.14 T) is presented. The pO2 measurement method is based on the paramagnetic effect of dissolved molecular oxygen (O2) which reduces the PFC 19F T1− Specific objectives related to imaging of PFCs through use of the protocol include improved image signal‐to‐noise characteristics and elimination of 19F chemical shift artifacts. A parametric Wiener deconvolution filtering algorithm is used for suppression of 19F chemical shift artifacts. Application of the protocol is illustrated in a series of calculated pO2 maps of a gas equilibrated, multi‐chamber phantom containing perfluorotributylamine (FC‐43). The utility of the protocol is demonstrated in vivo through images of a commercially available perfluorocarbon based blood substitute emulsion containing FC‐43 sequestered in the liver and spleen of a rat.
Polyvinyl alcohol cryogel: An ideal phantom material for MR studies of arterial flow and elasticity
Authors: Chu Kenneth C. , Rutt Brian K.
Published: March 2007

The authors present a unique application of polyvinyl alcohol (PVA) cryogel as an anthropomorphic, elastic, vascular phantom material that can be used in MR imaging. The composition consists of two nontoxic ingredients: water and PVA. The biomechanical and MR properties can be adjusted to be similar to those of excised porcine aortas by varying the number of freeze‐thaw cycles to which the PVA solution is exposed. The authors present the T1, T2, shrinkage, and tensile properties of PVA cryogel tubes as a function of freeze‐thaw cycles. MR images of a dual elastic aortic phantom undergoing pulsatile motion are shown.
Proton‐decoupled 19F spectroscopy of 5‐FU catabolites in human liver
Authors: Murphy‐Boesch Joseph , Li Libo He Chun‐Wei , Padavic‐Shaller Kristin A. , Negendank William , Brown Truman R.
Published: March 2007

An RF network and a dual‐tuned surface coil are described for obtaining proton‐decoupled, NOE enhanced 19F spectra from a whole body clinical imager operating at 1.5 Tesla. The network removes 19F frequency noise from the decoupler transmitter and prevents preamplifier saturation from high‐level decoupling signals. Proton decoupling of 19F spectra was optimized using a sample of urine containing 5‐fluorouracil (5‐FU) and its catabolite fluoro‐β‐alanine (FBAL). Protondecoupled 19F spectroscopy in vivo is demonstrated by obtaining both nonlocalized spectra and spectra localized with three‐dimensional chemical shift imaging from the liver of patients undergoing 5‐FU chemotherapy.
In vivo detection of GABA in human brain using a localized double‐quantum filter technique
Authors: Keltner John R. , Wald Lawrence L. , Frederick Blaise De B. , Renshaw Perry F.
Published: March 2007

A proton MR spectral editing technique employing a spatially localized, double‐quantum filter (DQF) was used to measure γ‐aminobutyric acid (GABA) in the human brain at 1.5 T. The double‐quantum method provided robust, single‐shot suppression of uncoupled resonances from choline, creatine, and NAA and allowed detection of the γCH2 GABA (3.0 ppm) resonance with 30% efficiency. Spatial localization of the GABA measurement was achieved by incorporating PRESS localization within the double‐quantum excitation and detection sequence. A calibration technique was developed to adjust the relative phases of the RF pulses to maximize the in vivo double‐quantum detection efficiency for an arbitrary voxel location. The sequence efficiency, degree of suppression of uncoupled resonances, and characterization of the in vivo DQF technique was examined in phantom experiments and in a study of the occipital lobe of 10 normal subjects. The ratio of the 3.0‐ppm GABA resonance to the 3.0‐ppm creatine resonance was found to be 0.20 ± 0.05 (SD).
Differentiation between cortical atrophy and hydrocephalus using 1H MRS
Authors: Bluml Stefan , McComb J. Gordon , Ross Brian D.
Published: March 2007

Quantitative 1H MRS to determine cerebral metabolite patterns and MRI to determine CSF flow were applied to 12 patients with ventricular dilation—Group A, cortical atrophy (N = 5); or Group B, hydrocephalus (N = 7)—and in 9 normal controls. While mean brain water (Group A = 80% ± 6; Group B = 86% ± 5; normal = 85% ± 4) did not differ between the two groups of patients and controls, 1H MRS distinguished those patients with cortical atrophy (Group A) (N‐acetylaspartate/creatine (NAA/Cr) = 0.69 ± 0.17, versus normal = 1.06 ± 0.16; P < 0.002; [NAA] = 5.9 ± 1.3 mmoles/kg, versus normal 8.0 ± 1.4; P < 0.02) from those with hydrocephalus (Group B) (NAA/Cr = 1.16 ± 0.11; [NAA] = 9.2 ± 1.2; P > 0.13 and P > 0.07). Lactate levels were elevated in 3/5 patients with cortical atrophy, but in 0/7 of those with hydrocephalus. Mean absolute concentrations (mmoles/kg) of the five major cerebral osmolytes were 41 ± 4 (Group A), 43 ± 6 (Group B), and 42 ± 4 (normal), so that despite massive brain deformation, constant osmolality was maintained. 1H MRS may directly benefit surgical planning in hydrocephalus infants by clearly identifying those with cortical atrophy who do not require CSF diversion. Thinning of the cortical mantle in hydrocephalus may result from osmotically driven reduction in individual cell volumes, (shrinkage), rather than brain‐compression.
Electric current density imaging of mice tumors
Authors: Serša Igor , Beravs Katarina , Dodd Nick J. F. , Zhao Sha , Miklavčič Damijan , Demsar Franci
Published: March 2007

The use of electric current density imaging (CDI) to map spatial distribution of electric currents through tumors is presented. Specifically, a method previously tested on phantoms was implemented in vivo and in vitro for mapping electric current pulses of the same order of magnitude (j ∽ 2500 A/m2) as in electrochemotherapy through T50/80 mammary carcinomas, B‐16 melanomas and SA‐1 sarcomas. A technically simplified method of electric current density imaging is discussed as well. Three geometries of electrodes (flat‐flat, point‐point, point‐flat) indicate altered electric current distribution for the same tumor. This indicates that the method can be used for monitoring the effects of electrochemotherapy as a function of electrode geometry.
Automatic cardiac MR image segmentation using edge detection by tissue classification in pixel neighborhoods
Authors: Singleton H. Ross , Pohost Gerald M.
Published: March 2007

A highly sensitive edge detector has been developed that uses tissue classification of pixels based on analysis of data in their local neighborhoods. In conjunction with recursive region growing, it has been used successfully to define regions of interest (ROI) when applied specifically to gradient echo MR images of the heart. The detector adapts to nonuniformity by carrying out an independent analysis at each location. If two tissues are present in a neighborhood and the pixel at that location cannot be classified with the seed pixel, a region edge has been crossed and recursion is stopped. No geometric assumptions relating to object shape such as definition of a region center and radial search are required. The detector was applied to multi‐slice, multi‐phase images of the heart from 26 subjects. A segmentation strategy specified slice processing order, graded ROIs, and used successfully detected ROIs to guide subsequent detection. Segmentation of all images resulted in a 90.3% median edge pixel detection efficiency.
Alterations in T1 of normal and reperfused infarcted myocardium after Gd‐BOPTA versus GD‐DTPA on inversion recovery EPI
Authors: Wendland Michael F. , Saeed Maythem , Lauerma Kirsi , Derugin Nikita , Mintorovitch Jan , Cavagna Friedrich M. , Higgins Charles B.
Published: March 2007

This study tested whether Gd‐BOPTA/Dimeg or Gd‐DTPA exerts greater relaxation enhancement for blood and reperfused infarcted myocardium. Relaxivity of Gd‐BOPTA is increased by weak binding to serum albumin. Thirty‐six rats were subjected to reperfused infarction before contrast (doses = 0.05, 0.1, and 0.2 mmol/kg). ΔR1 was repeatedly measured over 30 min. Gd‐BOPTA caused greater ΔR1 for blood and myocardium than did Gd‐DTPA clearance of both agents from normal and infarcted myocardium was similar to blood clearance; plots of ΔR1myocardium/ΔR1blood showed equilibrium phase contrast distribution. Fractional contrast agent distribution volumes were approximately 0.24 for both agents in normal myocardium, 0.98 and 1.6 for Gd‐DTPA and Gd‐BOPTA, respectively, in reperfused infarction. The high value for Gd‐BOPTA was ascribed to greater relaxivity in infarction versus blood. It was concluded that Gd‐BOPTA/Dimeg causes a greater ΔR1 than Gd‐DTPA in regions which contain serum albumin.
Observer performance methodologies for evaluating blood vessel visibility in MR angiograms using accurate geometric registration to high resolution x‐ray angiograms
Authors: Chapman Brian E. , Sanderson Allen R. , Goodrich K. Craig , Alexander Andrew L. , Blatter Duane D. , Parker Dennis L.
Published: March 2007

Receiver operator characteristic (ROC) and two alternative forced choice (2AFC) methodologies for quantitatively assessing vessel visibility in MR angiography (MRA) were examined using x‐ray angiography images as truth. The methodologies required MRA projection images with the same orientation and magnification as the x‐ray images. Geometric distortions limited the quality of the registration. The observer performance measurements were compared to vessel contrast‐to‐noise ratio (CNR) measurements. Receiver bandwidth (RBW) and magnetization transfer (MT) effects in 3D time‐offlight MRA were evaluated. Overall, applying MT significantly increased all three measurements while decreasing the RBW significantly improved the 2AFC and CNR measurements. The relative importance of both effects on the 2AFC measure increased as vessel diameter decreased, although statistical significance was limited by small samples for diameters less than approximately 0.7 mm. These results demonstrate the usefulness of these observer performance methodologies for MRA technique assessment.
Two methods for peak RF power minimization of multiple inversion‐band pulses
Authors: Goelman Gadi
Published: March 2007

Two novel methods to minimize peak RF power for high order longitudinal Hadamard encoding are described and demonstrated experimentally. The first method uses the fact that the choice of a reference phase in an inversion process does not affect the final frequency response. In this method, the different single inversion‐band pulses are added together, each with a different reference phase. For a proper phase choice, minimization of the peak RF power is obtained. Scaling laws are defined allowing the use of a given phase‐set in multiple cases. In the second method, single inversion‐band pulses are added together, each partially shifted in time. This results in a significant reduction in peak power with only a moderate increase in pulse length. Theoretical conditions outlining the optimal addition order are defined. Experimental results verify the theoretical conditions and demonstrate that the frequency response is not affected by the peak power minimization process. With the new low peak RF power, longitudinal Hadamard encoding of 8TH (or 16TH) order can be performed in any clinical setting.
A new diffusion SSFP imaging technique
Authors: Zur Yuval , Bosak Elyakim , Kaplan Noam
Published: March 2007

In this paper a new diffusion sensitive steady‐state free precession (SSFP) pulse sequence with a reduced sensitivity to physiological brain motion is presented. The signal attenuation due to diffusion in this SSFP sequence is derived theoretically and confirmed experimentally with a phantom. It is shown that for brain tissue this signal attenuation is approximately independent of T1 and T2, but depends only on the pulse sequence used, i.e., the timing and the size of the RF and the gradient pulses. On this basis the diffusion constant can be calculated for any region in the image. Diffusion sensitive images of the brain obtained with our pulse sequence are presented and shown to be superior over an image obtained with a “conventional” diffusion sensitive SSFP sequence.
Quantitative magnetic resonance imaging of capillary water permeability and regional blood volume with an intravascular MR contrast agent
Authors: Schwarzbauer Christian , Morrissey Sean P. , Deichmann Ralf , Hillenbrand Claudia , Syha Jutta , Adolf Holger , Nöth Ulrike , Haase Axel
Published: March 2007

A novel method is presented to simultaneously measure the permeability surface area product of water (PS), also known as capillary diffusion capacity, and the regional blood volume (RBV). It is based on magnetic resonance imaging of the longitudinal relaxation times of tissue and blood at different concentrations of an intravascular MR contrast agent. PS and RBV were measured in vivo in different regions of the brain and the skeletal muscle of the rat. The average PS values (n = 5) obtained in cerebral cortex, corpus callosum, hippocampus, thalamus, jaw muscle, and tongue muscle were 3.31 ± 0.20, 1.81 ± 0.25, 3.37 ± 0.36, 3.68 ± 0.44, 10.6 ± 1.1, and 14.1 ± 2.51 ml ± min−1 ± g−1, respectively. The corresponding average RBV values were 1.63 ± 0.18,1.22 ± 0.25,3.30 ± 0.37, 3.03 ± 0.36, 1.66 ± 0.30, and 1.38 ± 0.33 ml ± 100g−1. These results are in good agreement with previously reported literature values obtained by means of autoradiography.
Improved sensitivity to overlapping multiplet signals in in vivo proton spectroscopy using a multiecho volume selective (CPRESS) experiment
Authors: Hennig Jürgen , Thiel Thorsten , Speck Oliver
Published: March 2007

A method for volume selective proton spectroscopy is presented based on a multiecho sequence with short refocusing interval tcp. It is demonstrated, that by appropriate choice of tcp on the order of 4–6 ms, signals from overlapping multiplets like the glutamine and glutamate (Glu/Gln) resonances in spectra of the human brain are considerably increased compared with a conventional PRESS volume selection scheme. Thus proton spectra from J‐coupled multiplet signals can be acquired with TE on the order of 20–30 ms avoiding the baseline problems arising at shorter echo times due to broad resonances. This allows to selectively acquire spectra from substances with longer T2 without the confounding effects from J‐coupling occurring in conventional volume selection techniques.
Effects of severe global ischemia on N‐acetylaspartate and other metabolites in the rat brain
Authors: Higuchi Toshihiro , Graham Steven H. , Fernandez Erik J. , Rooney William D. , Gaspary Heidi L. , Weiner Michael W. , Maudsley Andrew A.
Published: March 2007

N‐acetylaspartate (NAA) is found exclusively in neurons and their processes in the adult brain. Since the regional distribution of NAA may be imaged using magnetic resonance spectroscopic imaging (1H‐MRSI), a regional measure of neuronal density may be noninvasively obtained. The technique may be particularly useful in the diagnosis of diseases where neurons are selectively injured, since these diseases do not result in definitive changes on conventional imaging studies. The goal of this study was to determine whether 1H‐MRSI measurement of NAA detects neuronal loss following global ischemia. 1H‐MRSI was performed in rats 24 h after global ischemia was induced by bilateral carotid occlusion plus hypotension. 1H‐MRSI showed that NAA was decreased by 29–74% in vulnerable regions, including the cortex, striatum, hippocampus, and, to a lesser extent, the thalamus. No change was observed in the brain stem or cerebellum. Regions where 1H‐MRSI observed NAA was decreased also had histological evidence of selective neuronal necrosis and showed marked increase of lactate and alanine. These results show that 1H‐MRSI detected loss of NAA in brain regions with selective neuronal loss, suggesting that 1H‐MRSI measurements of NAA could detect neuronal loss in a variety of disease states where there is selective neuronal necrosis.
Improved vessel visualization in MR angiography by nonlinear anisotropic filtering
Authors: Orkisz Maciej M. , Bresson Christine , Magnin Isabelle E. , Champin Olivier , Douek Philippe C.
Published: March 2007

This paper deals with a preprocessing technique of magnetic resonance angiography (MRA) images, applied before maximum‐intensity‐projection (MIP). The purpose was to recover small low‐intensity vessels, visible in individual slices, but lost in MIP images that usually have higher background level than the individual slices. The authors have developed a nonlinear three‐dimensional spatial filtering technique (called HD filter) based on anisotropic smoothing. The filter first searches for the local orientation of the vessel. It then performs a nonlinear smoothing in the vessel's local direction so as to avoid blurring its boundaries. Noise level reduction, contrast enhancement, and improved small vessel visibility achieved by this filter are illustrated on dynamic contrast‐enhanced subtraction MRA images of the lower limbs.
Reduction of geometric and intensity distortions in echo‐planar imaging using a multireference scan
Authors: Wan Xin , Gullberg Grant T. , Parker Dennis L. , Zeng Gengsheng L.
Published: March 2007

Echo‐planar imaging (EPI) is very sensitive to patient‐induced field inhomogeneity caused by susceptibility changes between different anatomical regions. This results in geometric and intensity distortions in the image, especially near tissue/ air and tissue/bone interfaces. A new approach is presented to reduce geometric and intensity distortions in EPI. A phaseencoded multireference scan is used to estimate the amplitude and phase errors in the measured signals due to the field inhomogeneity. The EPI data is corrected using both the amplitude and phase of the measured errors. This technique has been evaluated using EPI pulse sequences implemented with conventional gradients and implemented with imaging systems that have special resonating gradients and fast analog to digital converters. The results in both phantom and human studies show that in the absence of object motion the new correction technique can effectively reduce the geometric and intensity distortions.
Catheter tracking using continuous radial MRI
Authors: Rasche Volker , Holz Dietrich , Köhler Jürgen , Proksa Roland , Röschmann Peter
Published: March 2007

The guidance of minimally invasive procedures may become a very important future application of MRI. The guidance of interventions requires images of the anatomy as well as the information of the position of invasive devices used. This paper introduces continuous radial MRI for the simultaneous acquisition of the anatomic MR image and the position of one or more small RF‐coils (μ‐coils), which can be mounted on invasice devices such as catheters or biopsy needles. This approach allows the in‐plane tracking of an invasive device without any prolongation of the overall acquisition time. The extension to three‐dimensional position tracking is described. Phantom studies are presented demonstrating the capability of this technique for real‐time automatic adjustment of the slice position to the current catheter position with a temporal resolution of 100 ms. Simultaneously the in‐plane catheter position is depicted in the actually acquired MR image during continuous scanning.
Integrated RF coil with stabilization for fMRI human cortex
Authors: Fitzsimmons Jeffrey R. , Scott James D. , Peterson David M. , Wolverton Bryan L. , Webster Charles S. , Lang Peter J.
Published: March 2007

Functional brain imaging of the human cortex is limited by poor contrast to noise ratio (CNR) and image degradation due to subject motion during the acquisition period. The work described here combines the use of closely coupled phased array receiver coils with a stabilization system to address these needs. Several phased array designs are evaluated and compared with the conventional “birdcage” design. Coil performance is reported in terms of relative SNR and fMRI results. Relative improvements of up to 360% are obtained for the occipital region and 180% in the temporal region. More modest gains of 10–30% were obtained for a “dome”‐shaped birdcage volume coil covering the entire cortex.
MRI and NMR spectroscopy of the lipids of atherosclerotic plaque in rabbits and humans
Authors: Trouard Theodore P. , Altbach Maria I. , Hunter Glenn C. , Eskelson Cleamond D. , Gmitro Arthur F.
Published: March 2007

The early stages of atherosclerosis are characterized by the deposition of cholesteryl esters and triglycerides into the arterial wall. In the excised human atherosclerotic plaque these lipids are in a liquid‐like state at body temperature and observable via MRI and NMR spectroscopy. To assess the ability of MRI to quantitatively image the lipids of atherosclerotic plaque in vivo, we have investigated eight New Zealand White rabbits fed atherogenic diets (2 weight (wt)% cholesterol, 1 wt% cholesterol + 6 wt% peanut oil, and 1 wt% cholesterol + 6 wt% corn oil). Postmortem examination indicated that all rabbits developed atherosclerosis in the aorta. Except for one animal, magnetic resonance angiography showed no noticeable obstruction in the aorta. MRI was carried out in an attempt to image atherosclerotic plaque lipids directly, but no signal was detected in vivo. However, a plaque lipid signal was observed from excised tissue using a small diameter RF coil. 1H NMR spectroscopy of the atherosclerotic plaque from excised aortas indicated that the major fraction of plaque lipids in rabbits is not in a liquid state at physiological temperature and are only marginally MRI‐visible compared to human plaque lipid. The differences in the MRI characteristics of rabbit and human plaque are due to differences in the fatty acid profile of the cholesteryl esters, chiefly a decrease of linoleic acid in rabbit lesions.
Acceleration mapping by fourier acceleration‐encoding: in vitro study and initial results in the great thoracic vessels
Authors: Tasu Jean‐Pierre , Jolivet Odile , Mousseaux Elie , Delouche Annie , Diebold BenoǐT , Bittoun Jacques
Published: March 2007

Acceleration mapping can be conducted by replacing the bipolar gradient pulse of a velocity mapping sequence by a tripolar pulse. However, since the acceleration encoding pulse is longer, the image quality is altered by the requirement of a long echo time. Since Fourier encoding velocity imaging has been shown to be robust, this velocity mapping method was transformed into an acceleration mapping method. Four steps of the tripolar acceleration encoding gradient pulse were applied successively; acceleration was then obtained by Fourier transform after zero‐filling. The accuracy of the method was assessed with a phantom giving a pulsatile flow. Acceleration maps of the ascending aorta and pulmonary artery were obtained in 10 healthy volunteers. The acceleration values measured were in the range of known physiologic values. The feasibility of Fourier encoding acceleration imaging was also demonstrated in four patients.
Catheter visualization using locally induced, actively controlled field inhomogeneities
Authors: Glowinski Arndt , Adam Gerhard , Bücker Arno , Neuerburg Jörg , van Vaals Joop J. , Günther Rolf W.
Published: March 2007

A new technique for visualization of interventional devices using MR is presented. A prototype catheter was equipped with a thin copper wire loop, leading from the proximal end to the tip and back. A small current (10‐150 mA) through these two parts of a wire induces a local magnetic field along the catheter. Introduction of this catheter into the main magnetic field of the MR imager locally disturbs the homogeneity of the magnetic field. Image locations within the locally induced fields appear dark due to signal loss, and the extent of this effect can be varied during the procedure by simply adjusting the current. Different dedicated wire configurations allow visualization of the catheter in its whole length or in parts, i.e., with markers for balloons. Fast gradient echo sequences that provide a bright signal from inflowing blood are used for rapid imaging.
Triple quantum sodium imaging of articular cartilage
Authors: Reddy Ravinder , Insko Erik K. , Leigh John S.
Published: March 2007

Triple quantum (TQ) sodium imaging of bovine articular cartilage is presented. True triple quantum imaging sequence was modified to incorporate asymmetric echo acquisition. Triple quantum signal expression in the presence of residual quadrupolar interaction is presented. The filtering capability of the sequence is first demonstrated on an agarose phantom. Both single and triple quantum images of articular cartilage are compared. The TQ image shows non‐zero signal intensity solely from cartilage, indicating complete suppression of signals from bone marrow and saline. The advantages of TQ imaging of articular cartilage, its feasibility in in vivo situations and further improvements in SNR are described.
Reduction of carcinogenic chromium(vi) on the skin of living rats
Authors: Liu Ke Jian , Mäder Karsten , Shi Xianglin , Swartz Harold M.
Published: March 2007

The reduction of chromate (Cr(VI)) on the skin of living rats was investigated using the technique of in vivo electron paramagnetic resonance (EPR) spectroscopy with a surface coil resonator. Topical application of aqueous solution of Cr(VI) on the skin of rats generated the transient species, Cr(V). Partial removal of the stratum corneum increased the rates of formation and decay of Cr(V), as well as Cr(V) signal intensity. The results demonstrate that skin represents one route for chromium to enter into animals and humans. The generation of reactive Cr(V) species in the reduction of Cr(VI) by the skin may play an important role in the mechanism of Cr(VI)‐induced skin cancer. These findings indicate the potential for in vivo EPR spectroscopy for studying the metabolism of paramagnetic reactive species in chemical and biochemical reactions occurring in/on the skin of both small and large animals, and possibly humans.
A multinuclear MR study of Gd‐EOB‐DTPA: Comprehensive preclinical characterization of an organ specific MRI contrast agent
Authors: Elst Luce Vander , Maton Frédéric , Laurent Sophie , Seghi Frédéric , Chapelle Florence , Muller Robert N.
Published: March 2007

The characterization of the hepatobiliary contrast agent Gd‐EOB‐DTPA (gadolinium 3, 6, 9‐triaza‐3, 6, 9‐tris(carboxymethyl)‐4‐(4‐ethoxybenzyl)‐undecandicarboxylic acid) in various media (water solution, protein containing solution, phosphorylated metabolites solution, and excised and perfused liver) was performed using different NMR approaches: water 1H nuclear magnetic relaxation dispersion profiles, 2H NMR longitudinal and transverse relaxation rates of labeled complex, water 17O transverse relaxation rates and chemical shifts, 31P relaxation rates and peak area of phosphorylated metabolites. The higher proton relaxivity of Gd‐EOB‐DTPA in water compared with Gd‐DTPA is related to a shorter distance (r) between the water proton and the gadolinium ion and to a longer rotational correlation time (TR) of the hydrated complex. Although the thermodynamic stability of Gd‐EOB‐DTPA is identical to the one of Gd‐DTPA, its kinetic stability in solutions containing phosphorylated metabolites (ATP, phosphocreatine, and inorganic phosphate) as measured by 31P relaxation rates analysis is higher than for the parent compound. Gd‐EOB‐DTPA binds noncovalently to serum proteins. Its interaction with human serum albumin is characterized by a dissociation constant of 1‐4.1 mM as calculated from proton and deuterium relaxation rates and equilibrium dialysis. This noncovalent interaction involves the subdomain IIA of human serum albumin. 31P spectroscopy of the excised and perfused rat livers was used to monitor the uptake of Gd‐EOB‐DTPA by the hepatocytes where it enhances the nuclear relaxation of the intracellular metabolites without impairing the adenosine triphosphate metabolism of the cells.
Improved activation maps via the elimination of motion effects through time‐domain mixing of data in conventional gradient echo functional MRI
Authors: Constable R. Todd
Published: March 2007

To date, most functional imaging centers have relied on ultra‐fast imaging approaches such as echo‐planar imaging (EPI) techniques for acquiring functional brain activation data. These methods require specialized hardware and are not yet installed widely on clinical MR imagers, thus limiting the application of functional MR imaging at many sites. EPI is used to limit motion artifacts and to collect multiple images under different task paradigms in order to distinguish reliably true signal changes from noise. However, it suffers from poor signal to noise ratio because of the high sampling bandwidth employed. This work presents an approach for increasing the efficiency of functional studies that use conventional gradient echo imaging. In this approach, small numbers of image data sets are acquired and recombined to generate composite datasets with minimized motion artifacts. The technique is introduced, and several algorithms for combining the data are explored. A receiver operator characteristic analysis and in vivo studies are performed to examine the efficacy of this approach for improving functional MR imaging studies.
High relaxivity linear Gd(DTPA)‐polymer conjugates: The role of hydrophobic interactions
Authors: Kellar Kenneth E. , Henrichs P. Mark , Hollister Robert , Koenig Seymour H. , Eck Jennifer , Wei Donna
Published: March 2007

A series of linear copolymers of DTPA‐class Gd3+ conjugates, linked by α,ω‐alkyldiamides with a varying number (n) of methylenes separating the amide function, were synthesized. Surprisingly, their relaxivities at all fields increased with increasing n. At MRI fields and 35°C, the relaxivities of the n = 10 and n = 12 polymers were unexpectedly high, similar to those of rigid dendrimer‐based Gd3+ chelates. The magnetic field dependence of solvent proton 1/T1 was measured for aqueous urea‐free and urea‐containing polymer solutions. The results for urea‐free solutions imply an increase of rigidity (required for high relaxivities) with increasing n, arising from hydrophobic interactions of the methylene groups with solvent. This hypothesis is supported by a large decrease in the relaxivities upon addition of urea, which is known to weaken hydrophobic interactions. The relaxivities are also independent of polymer concentration, indicating that the hydrophobic interactions are intramolecular.
MR microimaging of the lung using volume projection encoding
Authors: Shattuck Mark D. , Gewalt Sally L. , Glover Gary H. , Hedlund Laurence W. , Johnson G. Allan
Published: March 2007

Radial acquisition (RA) techniques have been extended to produce isotropic, three‐dimensional images of lung in live laboratory animals at spatial resolution down to 0.013 mm3 with a signal‐to‐noise ratio of 30:1. The pulse sequence and reconstruction algorithm have been adapted to allow acquisition of image matrices of up to 2563 in less than 15 min. Scan‐synchronous ventilation has been incorporated to limit breathing motion artifacts. The imaging sequence permits randomizing and/or discarding selected views to minimize the consequences of breathing motion. The signal in lung parenchyma was measured as a function of flip angle (α) for different repetition times and found to follow the predictions for which there is an optimum excitation (Ernst) angle. A single T1, relaxation value of 780 ± 54 ms fits all data from six guinea pigs at 2.0 T. This T1, value parameterizes the signal and allows for a priori optimization, such as calculation of the Ernst angle appropriate for lung imaging.
Phase alignment of multiple surface coil data for reduced bandwidth and reconstruction requirements
Authors: Debbins Josef P. , Felmlee Joel P. , Riederer Stephen J.
Published: March 2007

Multiple element surface coils are often used in clinical MRI to increase the image signal‐to‐noise ratio (S/N). Use of multicoils typically requires increased net sampling bandwidth and data processing for each coil element. A phase‐alignment technique is described which combines the signals from all coil elements before image reconstruction, greatly relaxing the technical requirements of the standard multicoil methods. Hardware and software implementations allow reduction of the reconstruction requirement to that of a single coil. The hardware implementation additionally allows a significant reduction in the net sampling bandwidth. The method is applicable to high speed MRI techniques, as demonstrated in phantoms and volunteers.
MR microscopy of lung airways with hyperpolarized 3He
Authors: Chen X. Josette , Chawla Mark S. , Hedlund Laurence W. , Möller Harald E. , Macfall James R. , Johnson G. Allan , G. Elaine
Published: March 2007

A technique using hyperpolarized (HP) 3He to image the small airways of the lung by using moderate flip angles and a short scanning period during early inspiration is demonstrated. Flip angles (α) ranging from 10–90° were used in guinea pig experiments with scanning during the entire inspiration period. A second series acquired data throughout a short window of the ventilatory cycle with α= 45°. The success of the animal studies has motivated implementation of similar imaging techniques in the clinical arena. Human studies involved imaging over the total inspiration period with α ≈︁ 10°. The first series of guinea pig experiments demonstrated that larger flip angles (50‐90°) destroy the magnetization before it reaches the smaller airways. At moderate flip angles (20‐40°), airway branching down to the fourth generation was apparent. Fifth‐order branchings were seen in the images of the second series. The trachea down to fourth generation pulmonary airway branching, along with some distal air spaces, was seen in the human lung images.
Automatic probe tuning and matching
Authors: Hwang F. , Hoult D. I.
Published: March 2007

The problem of automatically tuning and matching a probe is considered, and attention is drawn to the main cause of difficulty: the interaction of tuning and matching mechanisms. The use of a doubly resonant, inductively coupled probe is therefore advocated, for to first order, tuning, and matching are then orthogonal for small perturbations. It is shown that when such a probe is equipped with negative feedback control of tuning and matching elements, driven by error signals derived from a bridge and the NMR spectrometer, stable and rapid automatic tuning and matching are achieved. The importance of approximately correct phasing of the error signals is emphasized, but the restriction of having to have specific cable lengths to achieve this task is removed. The effects of small errors of phasing are then considered and shown to be unimportant for the chosen probe, in contrast to the situation for other, nonorthogonal probe types. Suggestions for orthogonalization of two common capacitively coupled probe designs are made, and a practical instrument design is then given that, with the addition of external components, can also be used if the NMR receiver cannot be pressed into service.
Tissue‐independent MR tracking of invasive devices with an internal signal source
Authors: Erhart Peter , Ladd Mark E. , Steiner Paul , Heske Norbert , Dumoulin Charles L. , Debatin Jöorg F.
Published: March 2007

An improved MR tracking coil design is described that provides more robust tracking performance. It is shown theoretically and experimentally that a coil equipped with an internal spin source increases the signal‐to‐noise ratio in comparison to a coil system without internal source. The tracking behavior is stable even in air, which is important for laparoscopic work, in which the device has to be placed inside the inflated abdomen. Two types of coil windings were tested: one with the windings perpendicular to the coil axis and the other one with the windings tilted relative to this axis. The experiments showed no significant effect on the signal‐to‐noise ratio between the two types. The improved MR‐tracking coil design with internal source was successfully used in cholecystosto‐mies and in laparoscopic interventions; both procedures were performed on swine.
Effects of the acoustic noise of the gradient systems on fMRI: A study on auditory, motor, and visual cortices
Authors: Cho Zang‐Hee , Chung Soon‐Chul , Lim Dae‐Woon , Wong Edward K.
Published: March 2007

MR acoustic, or sound, noise due to gradient pulsing has been one of the problems in MRI, both in patient scanning as well as in many areas of psychiatric and neuroscience research, such as brain fMRI. Especially in brain fMRI, sound noise is one of the serious noise sources that obscures the small signals obtainable from the subtle changes occurring in oxygenation status in the cortex and blood capillaries. Therefore, we have studied the effects of acoustic, or sound, noise arising in fMR imaging of the auditory, motor, and visual cortices. The results show that the effects of acoustic noise on motor and visual responses are opposite. That is, for motor activity, there is an increased total motor activation, whereas for visual stimulation, the corresponding (visual) cortical activity is diminished substantially when the subject is exposed to a loud acoustic sound. Although the current observations are preliminary and require more experimental confirmation, it seems that the observed acoustic‐noise effects on brain functions, such as in the motor and visual cortices, are new observations and could have significant consequences in data observation and interpretation in future fMRI studies.
Functional MRI of somatosensory activation in rat: Effect of hypercapnic tip‐regulation on perfusion‐ and BOLD‐imaging
Authors: Bock Christian , Schmitz Bernd , Kerskens Christian M. , Gyngell Michael L. , Hossmann Konstantin‐Alexander , Hoehn‐Berlage Mathias
Published: March 2007

Functional activation of somatosensory cortex was studied in α‐chloralose anesthetized rats by functional magnetic resonance imaging (fMRI), using both perfusion–weighted and T2*–weighted (blood oxygenation level dependent, BOLD) imaging. The sensitivity of functional activation was altered by ventilating animals for 3 minutes with 6% CO2. Before hyper–capnic conditioning, electrical stimulation of the left forepaw at a frequency of 3 Hz led to an increase of signal intensity (relative to the unstimulated baseline condition) in the right somatosensory cortex by 6 ± 2% (means ± SD) in T2*–weighted images and by 45% ± 48% in perfusion–weighted images. After hypercapnic conditioning the signal intensity increase in perfusion–weighted images doubled to 91% ± 62% (P = 0.034), whereas that of T2*–weighted images only marginally increased to 7 ± 4% (not significant). This different behavior in both imaging modalities is interpreted as evidence for an increased flow response in combination with a higher oxygen extraction. Thus, the fMRI data reflect hypercapniainduced resetting of the functional–metabolic coupling of the tissue during activation.
Fast imaging of phosphocreatine using a RARE pulse sequence
Authors: Greenman Robert L. , Elliott Mark A. , Vandenborne Krista , Schnall Mitchell D. , Lenkinski Robert E.
Published: March 2007

A technique is described for acquiring phosphocreatine (PCr) images of skeletal muscle using a rapid acquisition with relaxation enhancement (RARE) pulse sequence. All of the phosphorus metabolites other than PCr are forced to dephase within the first few echoes, whereas the Carr‐Purcell Mei‐boom‐Gill (CPMG) pulse sequence maintains a high PCr signal long enough to acquire 64 echoes in a single shot. Axial PCr images of a human forearm with a signal‐to‐noise ratio of 9 were acquired in 2 min. The effect of the refocusing pulse section profile on the ratio of desired to undesired metabolite signal is demonstrated.
Dynamics of blood flow and oxygenation changes during brain activation: The balloon model
Authors: Buxton Richard B. , Wong Eric C. , Frank Lawrence R.
Published: March 2007

A biomechanical model is presented for the dynamic changes in deoxyhemoglobin content during brain activation. The model incorporates the conflicting effects of dynamic changes in both blood oxygenation and blood volume. Calculations based on the model show pronounced transients in the deoxyhemoglobin content and the blood oxygenation level dependent (BOLD) signal measured with functional MRI, including initial dips and overshoots and a prolonged post‐stimulus undershoot of the BOLD signal. Furthermore, these transient effects can occur in the presence of tight coupling of cerebral blood flow and oxygen metabolism throughout the activation period. An initial test of the model against experimental measurements of flow and BOLD changes during a finger‐tapping task showed good agreement.
MRI of hyperpolarized 3He gas in human paranasal sinuses
Authors: Rizi Rahim R. , Dimitrov Ivan E. , Thompson Alan , Jones Gordon , Gentile Tom R. , Ishii Masaru , Reddy Ravinder , Schnall Mitchell D. , Leigh John S.
Published: March 2007

In this study, MRI of hyperpolarized 3He gas in human para‐nasal sinuses is presented. Helium images were obtained at 1.5 T, using a surface coil and a 2D, fast gradient‐echo sequence with a nominal constant flip angle of 12°. Coronal images of 20‐mm thick slices were generated and compared with proton images of the corresponding sections. The images enable visualization of the paranasal sinuses and the nasal cavity, suggesting a potential use of this method not only in identifying the anatomical configuration of these pneumatic spaces, but also in assessing sinus ventilation.
Temporal and regional changes during focal ischemia in rat brain studied by proton spectroscopic imaging and quantitative diffusion NMR imaging
Authors: Dreher Wolfgang , Kühn Bernd , Gyngell Michael L. , Busch Elmar , Niendorf Thoralf , Hossmann Konstantin‐Alexander , Leibfritz Dieter
Published: March 2007

The early development of focal ischemia after permanent occlusion of the right middle cerebral artery (MCA) was studied in six rats using interleaved measurements by diffusion‐weighted NMR imaging (DWI) of water and two variants of proton spectroscopic imaging (SI), multiecho SI (TE: 136, 272, 408 ms) and short TE SI (TE: 20 ms). Measurements on a 4.7‐T NMR imaging system were performed between the control phase and approximately 6 h postocclusion. In the center of the ischemic lesion of all rats, the apparent diffusion coefficient (ADC) decreased rapidly to 84.4 ± 4.2% (mean ± SD) of the control values approximately 2 min postocclusion. Approximately 6 h postocclusion, the ADC was reduced to 67.1 ± 5.9%. In contrast, large differences between the animals were observed for the temporal increase of lactate (Lac) in the ipsilateral hemisphere. The maximum Lac signal was reached in four rats after 0.5‐1.5 h, and in two rats was not reached even after 6 h postocclusion. Six h postocclusion, SI spectra measured at a TE of 136 ms revealed a decrease in the CH3 signal of N‐acetylaspartate (NAA) to 67 ± 13% of the control values. Differences were observed between the spatial regions of decreased NAA and increased Lac. In the lesions, a T2 relaxation time of Lac of 292 ± 40 ms, considering a J‐cou‐pling constant of 6.9 Hz, was measured. Furthermore, a prolongation of the T2 of the CH3 signal of creatine/phosphocre‐atine (Cr/PCr) was observed in the lesion, from 163 ± 22 ms during control to 211 ± 41 ms approximately 6 h postocclusion. The experiments proved that DWI and proton SI are valuable tools to provide complementary information on processes associated with brain infarcts.
A quantitative method for fast diffusion imaging using magnetization‐prepared turboFLASH
Authors: Thomas David L. , Pell Gaby S. , Lythgoe Mark F. , Gadian David G. , Ordidge Roger J.
Published: March 2007

For the in vivo measurement of the apparent diffusion coefficient (ADC), it is desirable for the total imaging time to be as short as possible. One technique is based on a TurboFLASH acquisition in which the diffusion gradients are inserted into a driven equilibrium Fourier transform (DEFT) combination of hard pulses. However, this sequence has the disadvantage that eddy current‐induced inhomogeneities lead to incomplete refocusing of the magnetization during the diffusion preparation and to incorrect ADC values. A modification to the sequence is suggested that eliminates this error by phase‐cycling the second 90° pulse of the preparation. This study also investigates the effect of a reduced delay time between acquisitions on the accuracy of the measurement. The quality of the TurboFLASH sequence is demonstrated by experimental validation on an agar phantom and in vivo on the rat brain using a high‐field (8.5 T) system. Reduction of the interexperiment delay time is shown to be achievable to a certain degree without compromising the measurement accuracy.
Volumetric analysis of white matter, gray matter, and CSF using fractional volume analysis
Authors: Bedell Barry J. , Narayana Ponnada A.
Published: March 2007

Quantitative cerebral tissue volumes may be useful for an objective assessment of pathological changes in brain. Accurate determination of tissue volumes is complicated, however, by the partial volume averaging (PVA) effect. We have, therefore, developed a new pulse sequence that minimizes the PVA through the use of inversion‐recovery (IR) and double inversion‐recovery (DIR) techniques. This pulse sequence simultaneously acquires four different sets of images to provide the necessary information for volumetric analysis and reduces potential spatial misregistration of images due to patient motion. The image sets acquired from the proposed pulse sequence are 1) gray matter visible, 2) white matter visible, 3) FLAIR, and 4) fast spin‐echo proton‐density weighted images. An algorithm has been implemented to correct for differential T1‐weighting and for tissue quantitation.
Optimal design of gradient coils in MR imaging: Optimizing coil performance versus minimizing cost functions
Authors: Du Yiping P. , Parker Dennis L.
Published: March 2007

The “forward” method of an optimal gradient coil design provides a coil that has the minimal cost function value. It is shown in this study that the solution obtained by minimizing the cost function is directly dependent on the specified cost function and generally results in a deviation from the most desirable coil design. In this paper, a gradient coil design approach for obtaining the best achievable coil performance for pre‐determined imaging applications is presented. Through this approach, all intermediate coil performance values calculated during an optimization process, using a simulated annealing algorithm, are stored and presented in a three‐dimensional data set. Using this three‐dimensional data set, a coil designer is able to make a balance between different coil performance parameters and to select a coil that is the most desirable for the pre‐determined imaging applications.