bluuebunny/crossref_metadata_2025 huggingface dataset:
Adaptive blood pool segmentation in three‐dimensions: Application to MR cardiac evaluation
Authors: v. Kaushikkar Shantanu , Li Debiao , Haacke E. Mark , Dávila‐Román Victor G.
Published: March 2007

MRI is an established method of imaging the cardiac blood pool in four dimensions and evaluating global cardiac function. However, segmentation of the cardiac blood pool from the myocardial wall continues to be a time‐consuming task and is operator dependent. This has hampered the widespread use of cardiac MRI in evaluating global cardiac function. We propose the use of an adaptive threshold‐based, three‐dimensional region‐growing technique to segment the cardiac blood pool from the myocardium and to compute left ventricular blood volumes. It uses a unique double segmentation approach incorporating information from the myocardium to help better detect the edges of the blood pool. The adaptive threshold segmentation technique was evaluated on four human subjects by comparing with manual segmentation. The automated segmentation technique is fast and agreed well with manual segmentation. Further, it requires minimal operator input and is robust and user friendly. The conclusion is that adaptive thresholds and a multidimensional region‐growing approach is an appropriate method to segment the left ventricular blood pool.
Reliability and exactness of MRI‐based volumetry: A phantom study
Authors: Luft Andreas R. , Skalej Martin , Welte Dorothea , Kolb Ruppert , Klose Uwe
Published: March 2007

This study investigated the influence of slice thickness. section orientation, contrast, shape, and sequence type on the exactness of MRI‐based volumetry. Ni‐doped agarose gel phantoms (4 to 46 ml) were scanned with a T1‐weighted three‐dimensional Fourier transform (FT) fast low‐angle shot (FLASH) and a multiecho two‐dimensional FT‐Turbo spin‐echo (SE) sequence. After segmentation with a three‐dimensional region‐growing algorithm, the geometric volume was measured considering the partial volume effect. The variability coefficient (Pearson) was .7%. The volumetric error increased with slice thickness, depending on the size and form of the object. Cross sections resulted in smaller error than longitudinal sections (finger‐shaped phantoms, nonisotropic image data). Three‐dimensional FT was superior to two‐dimensional FT imaging. Results of slice thickness and section orientation experiments can be explained by the partial volume effect. Higher errors in two‐dimensional FT imaging were caused by object movements between two interleaved acquisitions. The study shows a considerable influence of the imaging parameters on the exactness, which depends on size and form of the structure of interest.
Comparison of dysprosium DTPA BMA and superparamagnetic iron oxide particles as susceptibility contrast agents for perfusion imaging of regional cerebral ischemia in the rat
Authors: Haraldseth Olav , Jones Richard A. , Müller Tomm B. , Fahlvik Anne K. , Øksendal Audun N.
Published: March 2007

The aim of the study was to compare the first‐passage profiles of dysprosium diethylenetriamine penta‐acetic acid bis(methylamide) (DTPA BMA) and the superparamagnetic iron oxide particles NSR 0430 in regions with severe and moderate cerebral ischemia. In seven rats subjected to middle cerebral artery occlusion, two dynamic MR perfusion imaging series were acquired after intravenous bolus injections of .5 mmol/kg dysprosium DTPA BMA and .06 mmolFe/kg iron oxide particles, respectively. The doses were chosen to obtain similar maximum signal change in normally perfused brain. The first‐passage profiles were compared in a region of interest (ROI) in the core area with severe ischemia and in a ROI in the penumbra area of moderate ischemia. The results were compared both as the calculated mean signal intensity versus time curves for all seven rats and statistically for an estimated mean transit time (MTT) after gamma variate fitting of the calculated concentration versus time curves. The first‐passage profiles for the two contrast agents were similar, both in the core area of severe ischemia and in the penumbra area of moderate ischemia. In this rat stroke model, dysprosium DTPA BMA and the superparamagnetic iron oxide particles NSR 0430 were found to be equally efficacious for the diagnosis of the perfusion deficit, but if safe for human investigations, iron oxide particles would have an advantage as equal susceptibility effect may be achieved with smaller injection volumes.
Atherosclerosis of the carotid artery: Evaluation by magnetic resonance angiography
Authors: Wildy Kathryn S. , Yuan Chun , Tsuruda Jay S. , Ferguson Marina S. , Wen Nuan , Subramaniam Deepa S. , Strandness D. Eugene
Published: March 2007

Carotid artery atherosclerotic plaques (APs) can lead to brain ischemia, an event shown to correlate with both the degree of stenosis and the composition of the AP. Currently, accurate estimates of stenosis can be obtained by either x‐ray angiography or three‐dimensional time of‐flight (TOF) magnetic resonance angiography (MRA). Our purpose was to determine whether three‐dimensional TOF MRA images could also provide information on plaque location, morphology, and composition. Seven pre‐endarterectomy patients underwent three‐dimensional TOF MRA. After endarterectomy, plaque histology was evaluated. Three‐dimensional TOF MRA images contained sufficient soft tissue contrast to differentiate the plaques from the surrounding tissues in all cases. Estimation of plaque morphology had 80% correlation with histology. Finally, intraplaque hemorrhage and calcification were depicted as regions of moderately high and very low intensity, respectively. These preliminary results suggest that three‐dimensional TOF MRA may be useful in studying the development and progression of carotid atherosclerosis.
Inversion recovery image reconstruction with multiseed region‐growing spin reversal
Authors: Xiang Qing‐San
Published: March 2007

A new algorithm is introduced for inversion recovery (IR) image reconstruction. The original complex image is modeled as a product of three factors: magnitude, polarity, and a smoothly changing phase factor. The simple binary polarity factor is first unified by a region‐growing spin reversal (RGSR) operation, allowing the phase factor to be extracted. Multiplying the complex conjugate of the phase factor with the original complex data yields the desired IR contrast. The RGSR process is repeated with multiple seeds distributed in the field of view (FOV), and the results are added together, enabling disconnected tissues in the FOV to be handled. The extracted phase factor is filtered to reduce noise and artifacts, without losing useful information. The method is fully automatic and has been used practically in a large number of clinical examinations. The algorithm may also be useful for phase correction in simple proton spectroscopic imaging.
Application of reduced‐encoding imaging with generalized‐series reconstruction (RIGR) in dynamic MR imaging
Authors: Chandra Sudeep , Liang Zhi‐Pei , Webb Andrew , Lee Haakil , Morris H. Douglas , Lauterbur Paul C.
Published: March 2007

Dynamic MRI has proven to be an important tool in studies of transient physiologic changes in animals and humans. High sensitivity and temporal resolution in such measurements are critical for accurate estimation of dynamic information. Fast imaging, often involving expensive hardware, has evolved for use in such cases. We demonstrate herein the possibility of accelerated data acquisition schemes on conventional machines using standard pulse sequences for dynamic studies. This is achieved by combining reduced‐encoded dynamic data (typically 30 to 40 phase encodings) with a priori high‐resolution data via a novel constrained image reconstruction algorithm. Such an approach reduces image acquisition time significantly (by a factor of 3 to 4 in the examples described here) without loss in the accuracy of information.
Image technique optimization in MR imaging of a titanium alloy joint prosthesis
Authors: Törmänen Juhani , Tervonen Osmo , Koivula Antero , Junila Juhani , Suramo Ilkka
Published: March 2007

The purpose of this study was to explore systematically the effect of the imaging parameters changeable by the user in spin‐echo (SE) imaging sequences to minimize image distortion when imaging joint prostheses. A titanium alloy hip joint prosthesis was studied at 1.0 T. The SE imaging parameters were bandwidth/pixel (BW/p), TE, strength of encoding gradients (matrix size), echo train length (ETL), and direction of phase and frequency encoding. The effect of ETL in rapid acquisition relaxation enhanced (RARE) sequences was also evaluated with a turbo‐SE sequence using a different ETL with the same TR and an effective TE. It is concluded that an optimized image quality can be achieved in SE imaging by using a high bandwidth/pixel value (at least 130 Hz/pixel), a high resolution matrix (256–512), sequences with multiple refocusing, and a frequency‐encoding axis parallel to the long axis of the prosthesis. The degree of distortion is reduced with this optimized technique.
Recent technical advances in MR imaging of the abdomen
Authors: Riederer Stephen J.
Published: March 2007

MRI of the abdomen has been under development for well over a decade. In the past, considerable work was directed toward identification and suppression of the artifacts caused by motion. However, within the last several years, image quality has further improved, particularly as various fastscan techniques have been adapted for abdominal imaging. The purpose of this work is to review these technical developments. Specific methods include adaptation of the acquisition time to breath‐holding, acquisition over multiple respiratory cycles, adjustment of the contrast of various sequences, and development of more sensitive receiver coils and faster gradient systems. Opportunities for future development are also identified, including improved slice sampling, increased in‐plane spatial resolution, real‐time means for monitoring respiration, and expanded applications. As these technical advances are implemented, it is expected that the overall sensitivity and specificity of abdominal MRI will further improve.
Importance of clot structure in gradient‐echo magnetic resonance imaging of hematoma
Authors: Taber Katherine H. , Hayman L. Anne , Herrick Richard C. , Kirkpatrick Joel B.
Published: March 2007

The MR appearance of clots with different internal structures was compared on gradient‐echo (GE) and spin‐echo (SE) images. After MR imaging, clots were submitted for histological analysis to allow direct correlation of clot structure with MR image intensity. Normal heterogeneous clots (containing entrapped serum) were hypointense compared to both unclotted blood (Hct 45) and brain on GE MR images. Homogeneous (serum‐poor) clots and settled blood were hyperintense to unclotted blood and isointense or hyperintense to brain. These results indicate that the GE technique is quite sensitive to the physical inhomogeneity created (at the voxel level) when blood forms an inhomogeneous clot containing relatively large islands of red blood cells (RBCs) surrounded by lakes of serum. The effect of the different possible clot structures on GE signal intensity thus provides an etiology for the previously unexplained observations of hemorrhage with high signal intensity on GE MR images.
Quantitative measurements with localized 1H MR spectroscopy in children with Canavan's disease
Authors: Wittsack H.‐J. , Kugel Harald , Roth B. , Heindel W.
Published: March 2007

Canavan's disease is an autosomal recessive hereditary leukodystrophy resulting from deficiency of the enzyme aspartoacylase. Two children suffering from this metabolic brain disease were examined using image‐guided localized proton spectroscopy. The absolute concentrations of metabolites were determined. These data demonstrate, for the first time, that the well known increase of the N‐Acetylaspartic acid (NAA)/Cho ratio in this disease may be not only due to a reduction of choline‐containing compounds in brain tissue but, at least in specific cases, also due to an increase of the NAA concentration, which is a result of the enzyme defect.
Fourier registration of three‐dimensional brain MR images: Exploiting the axis of rotation
Authors: Kassam Ariff , Wood Michael L.
Published: March 2007

We have developed a novel algorithm to register three‐dimensional MR images that have undergone rigid body motion. The most interesting feature of the algorithm is that it reduces a general three‐dimensional rotation to a simple planar rotation by finding the axis of rotation. The algorithm, which is a nontrivial three‐dimensional extension of existing Fourier registration algorithms, has been tested on 30 artificially misaligned MR images of a phantom, four artificially misaligned MR images of a brain, and one case of actual patient motion. The algorithm successfully registered every image. The registration error for a voxel 10 cm from the origin for the artificially misaligned phantom images was 2.8 mm at most and had a mean of 1.2 mm and standard deviation of .7 mm. The registration parameters for the images contaminated by actual patient motion were similar to that from an established image registration algorithm. The results indicate that the algorithm is accurate, reliable, and fast. The rigid body model requires the brain to be segmented from MR images of the head before registration.
Influence of model melanoidins on calcium‐dependent transport mechanisms in smooth muscle tissue
Authors: Stefanova Iliyana D. , Argirova Mariana D. , Krustev Athanas D.
Published: March 2007

Melanoidins obtained from L‐arginine and D‐glucose (MW > 3500 Da) were tested for their ability to influence the contractility of gastric smooth muscles. A study within the range 0.1–10 mg/mL revealed that at low concentrations, the melanoidins provoked concentration‐dependent contraction, whereas a muscle relaxation was registered at high concentrations. The contraction was preceded by changes in the calcium membrane current as measured by single sucrose‐gap method and significantly attenuated by the calcium channel blockers D‐600 and nifedipine. Measurements with Ca2+‐selective electrode showed that the melanoidins decreased the concentration of ionized Ca2+ in tissue bath in concentration‐dependent manner. Experiments carried out in solutions with lower than normal Ca2+ concentration and using melanoidins preliminary saturated with Ca2+ confirmed that the calcium chelation by melanoidins was a key contributing cause for the development of relaxant response. The results obtained showed that the melanoidins could influence the contractility of smooth muscles through at least two pathways: at low concentrations they caused depolarization and activation of L‐type calcium channels, stimulated the Ca2+ influx, and provoked contraction, whereas at high concentrations calcium binding by melanoidins led to significant depletion of extracellular calcium ions and contributed to the relaxation process observed.
Proteolysis of milk proteins lactosylated in model systems
Authors: Kastrup Dalsgaard Trine , Holm Nielsen Jacob , Bach Larsen Lotte
Published: March 2007

Five different milk proteins (α‐casein, β‐casein, κ‐casein, β‐lactoglobulin, and lactoferrin) and a peptide substrate were applied as substrates for the investigation of how lactosylation affected proteolysis by different proteases. After a lactosylation period of 4 days in aqueous solution, at 65°C and pH 6.8 in a protein: lactose ratio of 1000 the proteins were enzymatically hydrolyzed by the three milk relevant proteases plasmin, cathepsin D, and chymosin. Lactosylation of all substrates affected hydrolysis by plasmin negatively, with the largest effect on the globular proteins. This could be explained by modification of lysine residues, being the preferred cleavage site for plasmin, but also the residue generally preferred for lactosylation. Lactosylation of the caseins and of β‐lactoglobulin did not affect subsequent cleavage by cathepsin D and chymosin significantly, but for β‐lactoglobulin, both the secondary as well as the tertiary structure were affected by lactosylation. In contrast, decreased hydrolysis by cathepsin D and chymosin was observed for lactoferrin after lactosylation. Decreased hydrolysis may be caused by a more compact tertiary structure induced by lactosylation of lactoferrin, as indicated by fluorescence spectroscopy measurements.
Modeling of acrylamide formation and browning ratio in potato chips by artificial neural network
Authors: Serpen Arda , Gökmen Vural
Published: March 2007

The artificial neural network (ANN) modeling approach was used to predict acrylamide formation and browning ratio (%) in potato chips as influenced by time×temperature covariants. A series of feed‐forward type network models with back‐propagation training algorithm were developed. Among various network configurations, 4‐5‐3‐2 configuration was found as the best performing network topology. Four neurons in the input layer were reflecting the asparagine concentration, glucose concentration, frying temperature, and frying time. The output layer had two neurons representing acrylamide concentration and browning ratio of potato chips. The ANN modeling approach was shown to successfully predict acrylamide concentration (R = 0.992) and browning ratio (R = 0.997) of potato chips during frying at different temperatures in time‐dependent manner for potatoes having different concentrations of asparagine and glucose. It was concluded that ANN modeling is a useful predictive tool which considers only the input and output variables rather than the complex chemistry.
Inhibition of polyphenoloxidase activity by mixtures of heated cysteine derivatives with carbonyl compounds
Authors: Chériot Sophie , Billaud Catherine , Maillard Marie‐Noëlle , Nicolas Jacques
Published: March 2007

It had previously been shown that soluble Maillard reaction products (MRP) made from thiol compounds and glucose or fructose contained powerful inhibitors of various fruit and vegetable polyphenoloxidase (PPO) activity. In MRP from cysteine and glucose, the amount of hydroxymethylfurfural (HMF) formed increased with the increase in glucose concentration (0–1 M), particularly under acidic (pH 2) conditions. Using model mixtures containing a preheated cysteine‐derived compound and a carbonyl component, especially HMF, furfural and benzaldehyde, we showed that the neoformed compounds produced exhibited a stronger inhibitory potency toward PPO activity of eggplant, apple, and mushroom than former MRP. Optimal reaction conditions for the formation of inhibitory compounds when HMF reacted with preheated cysteine were investigated. It was found that a reactants molar ratio of 1:1 and a reaction time exceeding 1 h were the most efficient reaction conditions to generate inhibitory compounds. The stability of the newly formed products, evaluated during storage, showed that their inhibitory potency was globally kept at 4, 21, and 37°C for 72 h but was unstable when stored at –20°C and lost when exposed to UV radiations for 24 h.
Lung level of HMBG1 is elevated in response to advanced glycation end product‐enriched food in vivo
Authors: Bartling Babett , Fuchs Christine , Somoza Veronika , Niemann Bernd , Silber Rolf‐Edgar , Simm Andreas
Published: March 2007

High mobility group box protein 1 (HMGB1) is a ubiquitous nuclear protein that can be actively released from the cell in certain conditions thereby mediating cytokine‐like function. While nuclear HMGB1 modulates the transcriptional activity of cells, extracellular HMGB1 partially acts via binding to the receptor for advanced glycation end products (RAGE), which is highly expressed in lung tissue. Therefore, we studied the impact of food‐derived advanced glycation end products (AGEs), the Maillard reaction products, on the lung expression of HMGB1. Feeding rats with AGE‐rich diet, containing either bread crust or coffee beverage, resulted in an upregulation of HMGB1 mRNA and protein especially in those animals receiving bread crust diet. The expression of RAGE was not influenced. Moreover, we revealed a positive correlation between an increased lung AGE level and HMGB1 protein expression in both animal groups receiving either bread crust or coffee extract but not in the control group. In contrast, the ageing‐related AGE accumulation was not associated with an increased level of HMGB1 protein in lung tissue from senescent (100 wk) compared to young‐adult (24 wk) rats. Our data suggest a physiological role of food‐ but not ageing‐associated AGEs in the regulation of the HMGB1 expression in lung.
Off‐line liquid chromatography‐MALDI by with various matrices and tandem mass spectrometry for analysis of glycated human serum albumin tryptic peptides
Authors: Lapolla Annunziata , Brancia Francesco L. , Bereszczak Jessica , Fedele Domenico , Baccarin Lorenzo , Seraglia Roberta , Traldi Pietro
Published: March 2007

Advanced glycation end‐product (AGE)/peptides, arising from in vivo digestion of glycated proteins, are biologically important compounds, due to their reactivity against circulating and tissue proteins. For information on their possible structure, in vitro glycation of HSA and its further enzymatic digestion were performed. The resulting digestion product mixture was analysed directly by MALDI MS with various matrices [2,5‐dihydroxy benzoic acid (DHB) and α‐cyano‐4‐hydroxy cinnamic acid (CHCA)]. Alternatively, offline microbore LC prior to MALDI analysis was used, and showed that 63% of the free amino groups prone to glycation are modified, indicating the contemporary presence of unglycated peptides. This result proves that, regardless of the high glucose concentration employed for HSA incubation, glycation does not go to completion. Further studies showed that the collisionally activated decomposition of singly charged glycated peptides leads to specific fragmentation pathways, all related to the condensed glucose molecule. These unique product ions can be used as effective markers to establish the presence of a glucose molecule within a peptide ion.
Interactive coronary MRI
Authors: Hardy Christopher J. , Darrow Robert D. , Pauly John M. , Ken Adam B. , Dumoulin Charles L. , Hu Bob S. , Martin Kenneth M.
Published: March 2007

The acquisition of complete three‐dimensional (3D), segmented gradient‐echo data sets to visualize the coronary arteries can be both time consuming and sensitive to motion, even with use of multiple breath‐holding or respiratory gating. An alternate hybrid approach is demonstrated here, in which real‐time interactive imaging is first used to locate an optimal oblique coronary scan plane. Then, a limited number of contiguous slices are acquired around that plane within a breath‐hold with use of two‐dimensional (2D) segmented gradient‐echo imaging. Dual inversion nulling is used to suppress fat and myocardium. Finally, if needed, a limited reformat of the data is pelformed to produce images from relatively long sections of the coronaries. This approach yields relatively rapid visualization of portions of the coronary tree. Several different methods are compared for interactively moving the scan plane.
MR microscopy of transgenic mice that spontaneously acquire experimental allergic encephalomyelitis
Authors: Ahrens Eric T. , Laidlaw David H. , Readhead Carol , Brosnan Celia F. , Fraser Scott E. , Jacobs Russell E.
Published: March 2007

Pathology of fixed spinal cords from transgenic mice with a myelin basic protein (MBP) specific T cell receptor was investigated. These mice spontaneously acquire the demyelinating disease experimental allergic encephalomyelitis (EAE). Several complementary imaging modalities, all on the same tissues, were used to visualize lesions; these included high‐field (11.7‐T) microscopic diffusion tensor imaging (DTI),T‐weighted imaging, and optical microscopy on histological sections. Lesions were predominantly in white matter around meninges and vasculature and appeared hyperintense in anatomical images. DTIs showed reduced diffusion anisotropy in the same hyperintense regions, consistent with inflammation and edema. Histology in the same tissues exhibited the characteristic pathology of EAE. Two techniques for visualizing the effective diffusion tensor fields are presented, which display direction, organization, and integrity of neuronal fibers. It is shown that DTI offers intriguing possibilities for visualizing axonal organization and lesions within white matter.
Small particles of fusinite and carbohydrate chars coated with aqueous soluble polymers: Preparation and applications for in Vivo EPR oximetry
Authors: Gallez Bernard , Debuyst René , Dejehet Fernand , Liu Ke J. , Walczak Tadeusz , Goda Fuminori , Demeure Roger , Taper Henryk , Swartz Harold M.
Published: March 2007

The development of oxygen‐sensitive paramagnetic materials is being pursued actively because of their potential applications in in vivo EPR oximetry. Among these materials, several charcoals and carbohydrate chars are of special interest because of their desirable EPR properties: high sensitivity of the EPR linewidth to the partial pressure of oxygen, simple EPR spectra, and high spin density. Their potential use in humans, however, is limited by the need to demonstrate that they will not lead to deleterious effects. A strategy was used to optimize the biocompatibility of the oxygen‐sensitive materials by decreasing the size of the particles and coating them with suspending or surfactive agents such as arabic gum, polox‐amer (Pluriol 6800®), and polyvinylpyrrolidone. The coated particles of a carbohydrate char and fusinite were characterized in vitro for their size, stability, and pO2 sensitivity. The feasibility of performing pO2 measurement was examined in vivo by inducing ischemia in the gastrocnemius muscle of mice. The use of arabic gum for coating the fusinite particles preserved the pO2 sensitivity in vivo, whereas the other surfactive agents led to a loss of the pO2 sensitivity in vivo. Small particles of fusinite coated by arabic gum and intravenously administered to mice accumulated in the liver, whereas the uncoated fusinite was toxic when injected intravenously due to the large size and aggregation of the particles. Histological studies performed up to 6 months after the injection in muscles of mice did not indicate any toxicity from the materials used in the present study.
Anisotropically weighted MRI
Authors: Shrager Richard I. , Basser Peter J.
Published: March 2007

The intensity of an isotropically weighted MR image is proportional to a rotationally invariant measure of bulk diffusion, TraceD (where D is the effective diffusion tensor). Such images can be acquired from as few as two diffusion‐weighted images (DWIs). Analogously, the intensity of an anisotropically weighted MR image is proportional to a rotationally invariant measure of diffusion anisotropy derived from D, such as the variance of the principal diffusivities of D. By using linear algebra, we show that to produce an anisotropically weighted MR image requires acquiring at least seven DWls, which is also the minimum number of DWls sufficient to estimate the entire diffusion tensor, as well as the T2‐weighted amplitude image, A(b = 0), in each voxel. A general mathematical framework for constructing isotropically weighted and anisotropically weighted MR images is also provided.
29Si imaging of silicone breast implants and intraocular silicone oil
Authors: Haselhorst Reta , Scheffler Klaus , Faletti Leonardo , Kaspar Armin , Prünte Christian , Seelig Joachim
Published: March 2007

Silicon‐29 (29Si) imaging was investigated as a potential imaging modality for monitoring silicone prostheses in humans. The 29Si relaxation times of several silicone gels were measured and found to average T1 = 21.2 ± 1.5 s and T2 = 207 ± 40 ms, with no significant difference between virgin and explanted gels. A single‐shot half‐Fourier rapid acquisition with relaxation enhancement (RARE) and a refocused gradientecho sequence were used for acquiring 29Si images with 5 × 5 mm2 resolution and no slice selection. Three volunteers with silicone‐gel‐filled breast implants and one subject with an intraocular silicone oil injection were thus examined in a total acquisition time of 10–15 min per image. On all 29Si images, the shape of the silicone object was well depicted. Although at present, conventional proton images are superior in resolution and signal‐to‐noise ratio, 29Si imaging has the advantage of optimal specificity, since only the silicone itself is visible.
Fast 1H spectroscopic imaging using a multi‐element head‐coil array
Authors: Schäffter Tobias , Börnert Peter , Leussler Christoph , Carlsen Ingwer C. , Leibfritz Dieter
Published: March 2007

Fast proton magnetic resonance spectroscopic imaging (MRSI) using a multi‐element head‐coil array is examined with respect to three aspects: the coil design, the use of an appropriate signal combination method, and the design of the MRSl pulse sequence itself. An eight‐element head‐coil array has been developed to increase the signal‐to‐noise ratio (SNR) of MRSl in the human brain. The flexible wraparound design optimally fits different head sizes and thus provides high sensitivity. The signal combination of the individual coil elements is based on the approach proposed by Roemer et al. Magn. Reson. Med. 16, 192 (1990). An additional short prescan is performed to provide a good estimate of the complex coil sensitivity profiles, which are used in the signal combination procedure to correct the spectroscopic imaging data for the spatially varying intensity. The use of coil arrays in MRSI has some effect on the requirements for both water and lipid suppression. These techniques and a MRSl pulse sequence that provides a high spectroscopic resolution are described and discussed. Experimental results at 1.5 T show that metabolite maps of N‐acetylaspartate (NAA), choline (Cho), phosphocreatine (PCr)/creatine (Cr) can be obtained within a 5‐min acquisition time.
Simultaneous highly selective MR water and fat imaging using a simple new type of spectral‐spatial excitation
Authors: Schick Fritz
Published: March 2007

In a recent contribution [MRM 38:269–274 (1997)], it was reported that an excitation by a series of sinc‐shaped slice‐selective RF pulses with binomial amplitude ratios and complete spin refocusing between consecutive pulses leads to water‐ or fat‐selective images of high quality. A method for simultaneous water and fat imaging in multislice operation is presented based on the principle of alternated line scanning and linear superposition of several excitations. For example, a 1‐3‐3‐1 pulse train with suitable interpulse delays results in a water‐selective excitation, whereas a 1 ‐ 3 ‐ 3 ‐ 1 train leads to a selective excitation of fat (transmitter frequency corresponds with the Larmor frequency of water protons). Phase cycling of the excitation (1 ‐ 3 ‐ 3 ‐1 for the even line numbers in k‐space, but 1 ‐ 3 ‐ 3 ‐1 for the odd line numbers) causes a shift of n/2 lines in phase‐encode direction for the fat signals in an n × m matrix. The principle of linear superposition explains why an excitation of 2 ‐ 0 ‐ 6 ‐ 0 for the even lines and 0 ‐ 6 ‐ 0 ‐ 2 for the odd lines results in a final image with unshifted water signals and shifted fat signals. Both water and fat portions are simultaneously exhibited and separated without any signal loss. Examples recorded by a gradient‐echo sequence demonstrate the potential of the new technique that allows a reduction of up to 50% of measuring time compared with former frequency‐selective imaging methods.
Amplitude response and stimulus presentation frequency response of human primary visual cortex using BOLD EPI at 4 T
Authors: Thomas Christopher G. , Menon Ravi S.
Published: March 2007

Detailed measurement of the neural response to flicker frequency using functional MRI (fMRI) were made. The fMRl signal peaks at a flicker frequency of 8 Hz in human V1, in agreement with previous positron emission tomography (PET) and fMRl experiments. The modulation amplitude of the hemodynamic response to varying continuous periods of flicker stimulation was measured. The hemodynamic response was not observed to be modulated by neural modulation for periods shorter than 6.7 s. The resemblance between the BOLD response to the stimulus presentation frequency and the base‐line power spectra at the same frequencies suggests that the same underlying mechanism could be responsible for both curves and that the base‐line fMRl power spectrum is probably due to base‐line electrical activity in the brain. The integrals of the resting base‐line power spectrum, the background power spectrum, the respiration component, and the cardiac component were found to be linearly dependent on TE.
Visualizing blood flow patterns using streamlines, arrows, and particle paths
Authors: Buonocore Michael H.
Published: March 2007

A customized computer program (MRIView) is described for visualizing and quantifying complex blood flow patterns in major vessels, using nongated and cardiac‐gated three‐dimensional (3D) velocity data obtained with MR velocity‐encoded phase pulse sequences. Streamlines, arrows, and particle paths (collectively referred to as “paths”) can be computed interactively, using both forward and backward time integration of the velocity field. The program provides interactive cross‐sectional and 3D perspective visualization of the paths, with quantification and statistical analysis of average speed, through‐plane velocity, cross‐sectional area, and flow. Normal flow patterns in the carotid artery, basilar artery tip, ascending aorta, coronary arteries, descending aorta, and renal arteries, as well as abnormal flow patterns in basilar tip aneurysms, have been investigated. The program revealed flow patterns in these regions with features that are well known from Doppler ultrasound and other features that have not been reported previously. The association between specific abnormal flow patterns and development of atherosclerosis suggests that particle paths can be used to assess risk of plaque formation and progression, as well as to evaluate flow dynamics and vascular patency before and after vascular interventions.
Relaxometry and magnetometry of ferritin
Authors: Brooks Rodney A. , Vymazal Josef , Goldfarb Ron B. , Bulte Jeff W. M. , Aisen Phlip
Published: March 2007

By combining nuclear magnetic relaxometry on 39 ferritin samples with different iron loading with magnetometry, results were obtained that suggest a new interpretation of the core structure and magnetic properties of ferritin. These studies provide evidence that, contrary to most earlier reports, the ferritin core is antiferromagnetic (AFM) even at body temperature and possesses a superparamagnetic (SPM) moment due to incomplete cancellation of antiparallel sublattices, as predicted by Néel's theory. This moment also provides a likely explanation for the anomalous T2 shortening in ferritin solution. However, the number of SPM moments derived from this model is less than the number of ferritin molecules determined chemically, and a similar discrepancy was found by retrospectively fitting previously published magnetometry data. In other words, only a fraction of the ferritin molecules seem to be SPM. The studies also provide evidence for paramagnetic (PM) Curie‐Weiss iron ions at the core surface, where the local Néel temperature is lower; these ions are apparently responsible for the weaker T1 shortening. In fact, the conversion of uncompensated AFM lattice ions to PM ions could explain the small number of SPM particles. The apparent Curie Law behavior of ferritin thus appears to be a coincidental result of different temperature dependences of the PM and SPM components.
Functional Imaging by I0‐ and T2* ‐parameter mapping using multi‐image EPI
Authors: Speck Oliver , Hennig Jürgen
Published: March 2007

A new functional imaging method has been developed and used to measure T2*‐ and initial intensity (I0)‐parameter maps of multiple slices during activation of the cortex with high temporal resolution. Multiple echo‐planar images (EPls) are read out after a single excitation of the spin system, leading to several images with increasing effective echo times. Changes induced by primary visual stimulation in T2* and I0 were measured in eight subjects. Although stimulation‐induced increases in I0 only occurred at short repetition times, T2* increased from 57.3 to 60.9 ms on average. The method combines the high stability of a single shot EPI experiment with the high information content of a multiecho acquisition. In addition, stimulation‐induced changes in inflow can be easily separated from true blood oxygenation level dependent (BOLD) signal changes.
A new correlation‐based fuzzy logic clustering algorithm for FMRI
Authors: Golay Xavier , Kollias Spyros , Stoll Gautier , Meier Dieter , Valavanis Anton , Boesiger Peter
Published: March 2007

Fuzzy logic clustering algorithms are a new class of processing strategies for functional MRI (fMRI). In this study, the ability of such methods to detect brain activation on application of a stimulus task is demonstrated. An optimization of the selected algorithm with regard to dtfferent parameters is proposed. These parameters include (a) those defining the preprocessing procedure of the data set; (b) the definition of the distance between two time courses, considered as p‐dimensional vectors, where p is the number of sequential images in the fMRl data set; and (c) the number of clusters to be considered. Based on the assumption that such a clustering algorithm should cluster the pixel time courses according to their similarity and not their proximity (in terms of distance), cross‐correlation‐based distances are defined. A clear mathematical description of the algorithm is proposed, and its convergence is proven when similarity measures are used instead of conventional Euclidean distance. The differences between the membership function given by the algorithm and the probability are clearly exposed. The algorithm was tested on artificial data sets, as well as on data sets from six volunteers undergoing stimulation of the primary visual cortex. The fMRl maps provided by the fuzzy logic algorithm are compared to those achieved by the well established cross‐correlation technique.
Effects of acceleration, jerk, and field inhomogeneities on vessel positions in magnetic resonance angiography
Authors: Stefansic James D. , Paschal Cynthia B.
Published: March 2007

Blood flow and magnetic field inhomogeneities lead to distortions in MR angiography (MRA) images that present added risk for stereotactic neurosurgical applications. These effects are demonstrated in an MRA image of a model of cerebrovas‐culature. Analysis of the effects of velocity, acceleration, jerk, and field inhomogeneities on vessel position is presented; results are used to predict vessel shifts for several cerebral blood vessels. The actual encoded position for flowing spins is shown to be a moment‐weighted average position. Maximum shift of 3.11 mm was reduced to 0.05 mm when velocity compensation was added. Velocity compensation applied specifically in the phase‐encoding direction reduces flow‐dependent shifts to the point that they can be safely ignored even if acceleration and jerk are present. Those prescribing and using MRA images for stereotactic applications must be aware of whether compensation is actually applied along the phase‐encoding axis when a flow‐compensated sequence is used.
Chemically induced analgesic nephropathy in the rat monitored by proton‐electron double‐resonance imaging (PEDRI)
Authors: Seimenis Ioannis , Foster Margaret A. , Lurie David J. , Hutchison James M. S. , Whiting Paul H. , Payne Simon
Published: March 2007

Proton‐electron double‐resonance imaging (PEDRI) was used to assess renal function by monitoring the flow of the exogenous nitroxide free radical proxyl carboxylic acid (PCA) through normal and injured kidneys in the living rat. Kidney damage was induced by treatment with 2‐bromoethylamine (BEA), which provides a well established model for human analgesic nephropathy. PCA clearance rates for liver, abdominal blood vessels, and renal tissues were determined from serial PEDRI images of normal rats (n = 6) and rats treated with BEA (n = 21). Different groups of BEA‐treated animals were imaged on day 4 (n = 6), day 6 (n = 6), and day 9 (n = 9) after treatment. In BEA‐treated rats, there was an increase in PCA half‐life in all tissues studied. This increase was greatest in the kidney tissues and the effect progressed with time after treatment. The effect is probably due to BEA‐induced damage to the tubules in the renal cortex and may not be related to the primary lesions in the renal medulla.
Intracranial black‐blood MR angiography with high‐resolution 3D fast spin echo
Authors: Alexander Andrew L. , Buswell Henry R. , Sun Yi , Chapman Brian E. , Tsuruda Jay S. , Parker Dennis L.
Published: March 2007

Three‐dimensional fast spin‐echo (3DFSE) techniques are promising for black‐blood imaging of cerebral vessels. In this study, flow‐related signal dephasing was demonstrated as the primary mechanism for blood signal attenuation. Parameter optimization of TR (1500 to 3000 ms), receiver bandwidth (25 to 31.25 kHz), effective TE (25.7 to 30.1 ms), and ETL (7 to 8) was accomplished by making measurements of vessel‐totissue contrast‐to‐noise ratios on vessels. A comparison of high‐resolution 3DFSE and 3DTOF magnetic resonance angiography demonstrated that 3DFSE can generate images with equivalent or better small vessel detail than conventional techniques. 3DFSE black‐blood techniques may provide improved sensitivity of small arteries and veins with slow or in‐plane flow and immunity to flow‐related distortions. Future studies with optimized parameters will determine the clinical efficacy of this technique.
Single‐shot, variable flip‐angle slice‐selective excitation with four gradient‐modulated adiabatic half‐passage segments
Authors: Hsu Edward W. , Reeder Scott B. , MacFall James R.
Published: March 2007

Adiabatic pulses, although useful in generating uniform spin nutation in the presence of inhomogeneous B1 fields, are limited for NMR imaging applications due to the lack of slice‐selective excitation capability. Selective excitation techniques using gradient modulation have been introduced; however, present methods require either a minimum of two excitations or eight adiabatic segments. Here, a scheme is presented that allows single‐shot, arbitrary flip‐angle, and slice‐selective excitation with only four adiabatic half‐passage segments. The technique is demonstrated via computer simulation and experimental tests on a phantom. Furthermore, issues associated with the implementation of these gradient‐modulated adiabatic pulses are discussed.
Proton spectroscopy without water suppression: The oversampled J‐resolved experiment
Authors: Hurd Ralph E. , Gurr David , Sailasuta Napapon
Published: March 2007

A method is introduced for obtaining proton spectra in vivo with all the advantages of a full water signal. The method, based on F1 oversampled J‐resolved spectroscopy, makes it possible to separate metabolite signals from unwanted baseline artifacts. The dominant water resonance is used as a 2D reference signal for the phase‐sensitive reconstruction of the 2D J‐resolved metabolite spectra. The powerful specificity of this method is demonstrated with model compound spectra, phantoms, and in vivo examples.
A theoretical and experimental comparison of continuous and pulsed arterial spin labeling techniques for quantitative perfusion imaging
Authors: Wong Eric C. , Buxton Richard B. , Frank Lawrence R.
Published: March 2007

Under ideal conditions, continuous arterial spin labeling (ASL) techniques are higher in SNR than pulsed ASL techniques by a factor of e. Presented here is a direct theoretical and experimental comparison of continuous ASL and pulsed ASL, using versions of both that are amenable to multislice imaging and insensitive to variations in transit times (continuous ASL with a delay before imaging, and QUIPSS II (Quantitative Imaging of Perfusion Using a Single Subtraction–second version)). Perfusion image quality for comparable imaging time was nearly identical for both single‐slice and multislice imaging. The measured raw signal was approximately 25% higher with continuous ASL, but the SNR per unit time was identical.
Quantitative spectroscopic imaging of the human brain
Authors: Pan Jullie W. , Twieg Donald B. , Hetherington Hoby P.
Published: March 2007

A method to provide B1 correction and cerebrospinal fluid (CSF) referencing is developed and applied to spectroscopic imaging of the human brain at 4.1 T using a volume head coil. The B1 image allows rapid determination of the spatially dependent B1 that is then used to compensate for the B1 sensitivity of the spectroscopic sequence. The reference signal is acquired from CSF located in a lateral ventricular position using a point‐resolved echo spectroscopy (PRESS) acquisition. The CSF spectrum is also corrected for B1 dependence. Together with T2 and T1 corrections, this method is used to provide quantitative values of N‐acetylaspartate (NAA), creatine (Cr), and choline (Ch). The metabolite concentrations obtained from a spectroscopic imaging slice through the ventricles in seven normal controls are in good agreement with previously published literature values. This method is applied in a patient with secondary progressive multiple sclerosis, showing separate areas of abnormalities in both NAA and Cr.
Sodium multiple quantum spectroscopy of articular cartilage: Effects of mechanical compression
Authors: Duvvuri Umamaheswar , Kaufman Jonathan H. , Patel Saurabh D. , Bolinger Lizann , Kneeland J. Bruce , Leigh John S. , Reddy Ravinder
Published: March 2007

The effects of mechanical compression on the multiple quantum coherences generated from sodium ions in articular cartilage were investigated. Cartilage samples obtained from bovine patellae were studied during compression at 0.7 MPa (100 psi) for 1 hour. The double quantum filtered spectra showed marked lineshape changes in the compressed samples. Compression did not seem to influence the lineshapes of the single quantum and triple quantum filtered spectra significantly. We found that the residual quadrupolar interaction was reduced in the compressed samples. Changes in the ordering of collagen fibers may be responsible for the observed effect.
Quantitative assessment of improved homogeneity using higher‐order shims for spectroscopic imaging of the brain
Authors: Spielman Daniel M. , Adalsteinsson Elfar , Lim Kelvin O.
Published: March 2007

Magnetic field homogeneity is of major concern for in vivo spectroscopy, and with the increased use of volumetric chemical shift imaging (CSI) techniques, the ability to shim over a large volume of tissue is now one of the primary limiting constraints in performing these studies. In vivo shimming is routinely performed using linear shim correction terms, and although many scanners are also equipped with additional resistive shim supplies that can provide second and third‐order shim fields, they are often not used due to the additional effort and scan time required. The question as to how much improvement can be achieved using additional higher‐order shims compared with the linear shims alone was quantitatively addressed. Performance measures for both intervoxel B0 uniformity and intravoxel T2* line broadening were evaluated for 15 normal volunteers. The analysis tools developed in this study, along with the summarized data, can be useful in deciding if a given application warrants the additional time, effort, and expense (if additional hardware needs to be purchased) of Implementing higher‐order shimming routines. For CSI studies of the brain, the use of the higher‐order shims, compared with linear terms alone, yielded approximately 30% greater volume of brain tissue that could be shimmed within typical constraints for intervoxel B0 shifts and intravoxel T2* linebroadening. In addition, a regional analysis shows significant improvement in the homogeneity within specific areas of the brain, particularly those near the skull.