bluuebunny/crossref_metadata_2025_split huggingface dataset:
Noise and artifact comparison for Fourier and polynomial phase correction used with Fourier reconstruction of asymmetric data sets
Authors: Hua Jianmin , Hurst Gregory C. 
Published: March 2007

AbstractTwo processes of phase correction, Fourier phase mapping and second‐order polynomial phase fitting, are compared in combination with four different schemes for Fourier reconstruction of asymmetric data, using one‐dimensional simulations and two‐dimensional human head data. Polynomial phase correction provides systematically less image noise and is much less affected by localized phase differences caused by object edges and motion.
In vivo Na‐23 MR imaging and spectroscopy of rat brain during TmDOTP5− infusion
Authors: Bansal Navin , Germann Martha J. , Lazar Istvan , Malloy Craig R. , Sherry A. Dean 
Published: March 2007

AbstractIn vivo sodium‐23 and hydrogen‐1 magnetic resonance (MR) imaging and spectroscopy of the rat brain during infusion of the shift reagent thulium DOTP5− (1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetra[methylene phosphonate]) was performed to assign the various peaks observed during infusion and to evaluate the shift reagent in discriminating tissue compartments. Na‐23 spectra collected during the infusion showed two shifted peaks that were assigned to intravascular Na+ and extracellular muscle Na+, respectively, and one unshifted peak assigned to intra‐ and extracellular brain Na+ and cerebrospinal fluid Na+. These assignments were validated with H‐1 and Na‐23 MR imaging and Na‐23 chemical shift imaging (CSI). The H‐1 and Na‐23 images showed that a surface coil placed on a rat head can detect a substantial amount of signal from muscle surrounding the skull. Na‐23 CSI spectra from successive 1‐mm‐thick coronal sections indicated that the shift reagent did not cross the blood‐brain barrier. The study also showed that bulk susceptibility shifts are quite small with Tm‐DOTP5−. This reagent may be useful in determining compartmental Na+ concentrations and blood flow kinetics in brain and in examining the integrity of the blood‐brain barrier.
Comparison of velocity‐encoded MR imaging and fluid dynamic modeling of steady and disturbed flow
Authors: Sun Yi , Hearshen David O. , Rankin Gary W. , Haggar Allan M. 
Published: March 2007

AbstractThe contrast of flow‐encoded magnetic resonance (MR) images obtained in vivo and the accuracy of velocity measurements are complicated by the presence of complex flow states. The effects of complex flow states on MR flow‐encoded images were studied and quantitative flow information was obtained with an MR phase‐subtraction technique. Regions of complex flow, including flow stagnation and separation and laminar flow, could be clearly identified on the phase images. The MR imaging velocity measurements were validated by comparison with numerical simulation results for three‐dimensional velocity distributions. The velocity MR images and the profiles obtained from the simulation generally agreed well for flow rates of 660 and 1,680 mL/min. This agreement lends support to both the fluid dynamic model and the physical basis of the phase imaging technique and establishes the validity of flow‐encoded phase imaging as an in vivo flow quantization method, especially under low Reynolds number flow conditions.
Diagnosis of fatty liver with MR imaging
Authors: Kreft Burkhard P. , Tanimoto Akihiro , Baba Yuji , Zhao Longhai , Chen John , Middleton Michael S. , Compton Carolyn C. , Finn J. Paul , Stark David D. 
Published: March 2007

AbstractThe diagnosis of fatty liver with magnetic resonance (MR) imaging was evaluated in experimental rat models of simple fatty infiltration and fatty liver with hepatocellular injury. T1 and T2 were measured ex vivo and correlated with the histologic degree of fatty infiltration. Enhancement of fatty liver with four different cell‐specific contrast agents was studied with ex vivo relaxometry and in vivo MR imaging. Quantitative analysis of conventional and chemical shift MR images was correlated with biochemically determined fat content of the liver. Diet‐induced simple fatty infiltration of the liver caused a decrease in T1 of 15%, whereas the T1 of L‐ethionine‐induced fatty liver with hepatocellular injury increased by 12%. T2 showed a positive correlation with the degree of fatty infiltration in both models. Cell‐specific hepatobiliary contrast agents showed the same liver uptake and relaxation enhancement in fatty livers as in normal livers. Conventional T1‐weighted images and chemical shift images showed good correlation (r =.83 and.80, respectively) between signal intensity and the degree of fatty infiltration. However, only chemical shift imaging was reliable in the diagnosis of fatty liver.
Fast spin‐echo studies of contrast and small‐lesion definition in a liver‐metastasis phantom
Authors: Chien Daisy , Mulkern Robert V. 
Published: March 2007

AbstractA liver‐metastasis model was used to study the ability of fast spin‐echo (FSE) imaging to show small lesions (1 pixel in diameter) relative to conventional spin‐echo imaging. FSE images of the liver‐metastasis phantom were acquired with various phase‐encode reordering schemes to manipulate T2 contrast. The imaging time for multisection acquisitions was 27 seconds for FSE imaging and 6 minutes 48 seconds for conventional spin‐echo imaging. Computer simulations were performed to determine how the point spread function varies with the different phase‐encoding orders in FSE imaging. Contrast‐to‐noise ratios and signal profiles of the lesions were measured as a function of the effective TE and lesion size. Experimental results and theoretical simulations showed that T2‐weighted FSE imaging provides high contrast and good edge definition even for small lesions. The results indicate that FSE imaging may become a powerful method for the early detection of liver metastases.
Cerebral lactate production and blood flow in acute stroke
Authors: Henriksen Ole , Gideon Peter , Sperling Bjørn , Olsen Tom Skyhøj , Jørgensen Henrik S. , Arlien‐Søborg Peter 
Published: March 2007

AbstractEight stroke patients were examined serially in the acute phase and 1 week and 2–4 weeks after stroke with water‐suppressed proton magnetic resonance spectroscopy. The time courses of lactate level and regional cerebral blood flow were studied. A high lactate level was found in the acute phase. The lactate content decreased to barely detectable levels during the following 3 weeks, while regional blood flow increased during this period. The inverse relationship between lactate level and cerebral blood flow suggests that lactate plays no substantial role in the vasodilatation underlying the hyperemia that follows reperfusion. The amount of lactate present in the acute phase reflects the severity of ischemia in the affected region. The lactate level was still above normal in the subacute phase with hyperemia, suggesting lactate production through aerobic glycolysis. Thus, the lactate level in the subacute phase probably does not reflect the degree of anaerobic glycolysis in hypoxic neuronal tissue.
Automated local maximum‐intensity projection with three‐dimensional vessel tracking
Authors: Lin Weili , Haacke E. Mark , Smith Alison S. , Masaryk Thomas J. 
Published: March 2007

AbstractDespite the simplicity and widespread acceptance of the maximum‐intensity‐projection (MIP) technique for displaying three‐dimensional (3D) magnetic resonance angiographic data, several disadvantages are associated with MIP as it is applied to all of the 3D data. These include elevated noise level, reduced contrast between small vessels and background tissue, and the inability to distinguish arteries from veins. The authors have developed a 3D vessel tracking method combined with a local MIP around a given vessel to complement conventional MIP and alleviate these problems. The method is referred to as a traveling MIP (TMIP). TMIP was evaluated in both patients and healthy volunteers. The results indicate that TMIP provides better contrast between vessels and background tissue, better lumen definition, and better vascular visualization than either MIP or vessel tracking alone.
Why fat is bright in rare and fast spin‐echo imaging
Authors: Hardy Peter A. , Henkelman R. Mark , Bishop Jonathan E. , Poon E. Colin S. , Plewes Donald B. 
Published: March 2007

AbstractFast spin‐echo (FSE) sequences are becoming popular for T2‐weighted clinical imaging because they result in a severalfold reduction in imaging time and because they provide conventional spin‐echo contrast for most tissues. Fat, however, has been observed to have anomalously high signal intensity on FSE images. The present study shows that the brighter fat results from the multiple 180° refocusing pulses, which eliminate diffusion‐mediated susceptibility dephasing and suppress J‐coupling modulation of the echo train.
Practical T2 quantitation for clinical applications
Authors: Poon Colin S. , Henkelman R. Mark 
Published: March 2007

AbstractMany studies have investigated the use of magnetic resonance relaxation times for tissue characterization. A number have been performed in vivo with clinical whole‐body imagers. Unfortunately, the results have yet to establish the role of quantitative tissue relaxation time measurements in clinical diagnosis. One of the major problems is that the techniques used in many of these studies are error prone, making the results inconclusive. In the present study, the problems associated with clinical T2 measurements were systematically evaluated in an attempt to obtain reliable in vivo quantitation. The authors demonstrate that spoiler gradients are the most effective technique for artifact suppression but that they render ineffective radio‐frequency phase schemes such as the Meiboom‐Gill modification to the Carr‐Purcell sequence to compensate experimental imperfections. The present study results in a more reliable multiecho sequence for T2 measurement. Preliminary clinical results in brain and cervix demonstrate the performance of the new technique.
Mucinous carcinomas involving the prostate: Atypical findings at MR imaging
Authors: Outwater Eric , Schiebler Mark L. , Schnall Mitchell D. , Kressel Herbert Y. , Tomaszewski John E. 
Published: March 2007

AbstractThe magnetic resonance (MR) imaging findings in four patients with mucinous tumors involving the prostate are presented. The MR appearance of these tumors differed from that of typical prostatic adenocarci‐nomas in that the signal intensity on T2‐weighted images approximated or exceeded that of the uninvolved peripheral zone. The unusual appearance of mucinous prostate tumors may present problems in diagnosis and staging with MR imaging.
Correlation of MR changes with doppler US measurements of blood flow in exercising normal muscle
Authors: Morvan Daniel , Vilgrain Valérie , Arrivé Lionel , Nahum Henri 
Published: March 2007

AbstractMuscle data from phosphorus‐31 magnetic resonance (MR) spectroscopy and hydrogen‐1 MR imaging and popliteal artery data from duplex Doppler ultrasound were compared during an exercise test of the anterior compartment of the leg, in nine healthy volunteers. Significant variations (mean ± standard deviation) were observed at the end of exercise versus rest in intracellular pH (pHi) (6.32 ± 0.02 vs 7.02 ± 0.04, P < .001), T2 (38.2 msec ± 2.3 vs 29.5 msec ± 1.1, P < .001), and popliteal output (652 mL/min ± 232 vs 149 mL/ min ± 65, P < .001). These variables showed the following significant correlations at the end of exercise: T2 and pHi (r = −.784, P < .01), T2 and popliteal output (r = −.737, P < .03), and pHi and popliteal output (r = −.902, P < .001). However, during recovery, the T2 curve was significantly different from those of pHi and popliteal output. This suggests that even if circulatory conditions play a role in the maximum T2 variation during exercise, they do not directly explain T2 changes. Furthermore, the correlations involving pHi suggest the role of the metabolism of exercising muscle in transcapillary fluid movement.
Magnetization‐prepared MR angiography with fat suppression and venous saturation
Authors: Richardson Donna B. , Bampton Anna E. H. , Riederer Stephen J. , Macfall James R. 
Published: March 2007

AbstractMagnetization‐prepared magnetic resonance (MR) angiography (MPMRA) is an inflow‐based two‐dimensional (2D) imaging sequence in which a preparation phase precedes rapid image acquisition. For maximal blood/tissue contrast, an inversion‐recovery preparation nulls signal from static tissue. If needed, a second inversion suppresses signal from fat. Fully magnetized blood flows in after the inversion pulse (s), providing high signal intensity. The centric phase‐encoding order, which ensures that the initial contrast is reflected in the image set, requires the use of a modified venous saturation technique. The sequence is described and its performance assessed with regard to (a) depiction of in‐plane flow, (b) fat suppression, and (c) venous saturation. Phantom and volunteer studies showed good performance in all three areas. MPMRA images, acquired in just 2–4 seconds per image, had a blood/tissue contrast‐to‐noise ratio nearly twice that of standard 2D time‐of‐flight MR angiograms, acquired in 5–7 seconds. The technique is promising for restless patients and in anatomic areas plagued by motion degradation.
MR imaging with spatially variable resolution
Authors: Cao Yue , Levin David N. 
Published: March 2007

AbstractIn some situations it may be advantageous to produce “locally focused” magnetic resonance images that have nonuniform spatial resolution matching the expected local rate of spatial variation in the object. Because such an image has fewer pixels than a conventional image with uniformly high resolution, it can be reconstructed from fewer signals, acquired in less time. This can be done by using a highly convergent representation of the image as a sum of orthonormal functions with slow (fast) spatial variation in relatively homogeneous (heterogeneous) parts of the object. Since this series is shorter than a conventional truncated Fourier series, its terms can be calculated from a subset of the usual array of phase‐encoded signals. The optimal choice of these phase encodings, which are usually scattered nonuniformly in k space, results in minimization of noise in the reconstructed image. The technique is illustrated by applying it to simulated data and to data from images of phantoms.
Does memory loss occur after MR imaging?
Authors: Brockway John P. , Bream Peter R. 
Published: March 2007

AbstractIn four separate studies, the existence of specific memory loss after magnetic resonance (MR) imaging at 1.5 T was assessed by means of recognition and recall tests for faces, common objects, lexical items, and by digit span, in a pre‐post paradigm. Although specific memory loss was demonstrated, it was shown that the loss was not due to the main magnetic field of the imager or to radio‐frequency pulse sequences, but rather to probable psychological (not physical) factors. No gross or subtle memory changes could be attributed to MR imaging, because control groups showed similar patterns of memory loss.
Dual effects of gadodiamide injection in depiction of the region of myocardial ischemia
Authors: Saeed Maythem , Wendland Michael F. , Yu Kyle K. , Li Hong‐Tai , Higgins Charles B. 
Published: March 2007

AbstractThe high safety index of the nonionic magnetic resonance (MR) contrast agent gadodiamide injection permits a wide dose range without induction of he‐modynamic effects. The wide dose range might confer a diagnostic advantage by providing both T1 enhancing and magnetic susceptibility effects for demarcating pathologic regions. The dual utility of this contrast agent for T1 and T2 enhancement in creating differential contrast between normal and acutely ischemic myocardium was explored. MR imaging was initiated 20–40 minutes after occlusion of the left coronary artery in two groups of rats: Group 1 (n = 8) received 0.3 mmol/kg gadodiamide injection before and after acquisition of T1‐weighted images; group 2 (n = 10) received 0.5 mmol/kg before and after acquisition of T2‐weighted images. Postcontrast T1‐weighted images showed clear delineation of the ischemic region as a relatively low‐signal‐intensity area for 15 minutes. On postcontrast T2‐weighted images, the ischemic region appeared as a relatively high‐signal‐intensity area for 60 minutes. These effects were obtained with doses of gadodiamide injection that have safety indexes greater than those of gado‐pentetate dimeglumine.
Comparison of Gd‐EOB‐DTPA and Gd‐DTPA for contrast‐enhanced MR imaging of liver tumors
Authors: Clemént Olivier , Mühler Andreas , Vexler Vladimir S. , Kuwatsuru Ryohei , Berthezéne Yves , Rosenau Werner , Brasch Robert C. 
Published: March 2007

AbstractA new hepatobiliary contrast agent for magnetic resonance (MR) imaging, gadolinium‐ethoxybenzy1 (EOB)‐diethylemetriaminepentaacetic acid (DTPA), was compared with Gd‐DTPA to define the potential for improving tumor‐liver contrast in a rodent liver adenocarcinoma model. With a T1‐weighted spin‐echo sequence, the contrast‐to‐noise ratio (C/N) for tumor before contrast agent administration was 5 (arbitrary units), the tumor appearing slightly hypo‐intense with respect to liver parenchyma. After Gd‐DTPA injection (0.1 mmol/kg), tumor enhanced more strongly than liver, resulting in an equalization of tumor and liver signal intensities and a decline in C/N to zero at 3 minutes after injection. After Gd‐EOB‐DTPA injection (0.1 mmol/kg), liver enhanced more strongly than tumor. Five minutes after injection, C/N increased from 5 to 25 and remained above 17 for 50 minutes. The data indicate that Gd‐EOB‐DTPA yields higher and more prolonged tumor‐liver contrast than Gd‐DTPA on T1‐weighted spin‐echo images. The high liver‐tumor contrast after Gd‐EOB‐DTPA administration should prove clinically advantageous for MR imaging detection of focal hepatic masses.
Polymeric contrast agents for MR imaging of adrenal glands
Authors: Weissleder Ralph , Wang Yun Ming , Papisov Mikhail , Bogdanov Alex , Schaffer Brad , Brady Thomas J. , Wittenberg Jack 
Published: March 2007

AbstractA variety of adrenal imaging agents have been used in nuclear medicine, but no agent has been developed for magnetic resonance (MR) imaging. The authors have previously observed accumulation of aminated macromolecules in adrenal glands. They now report the synthesis of a model polymeric aminated contrast agent for enhanced MR imaging of the adrenal glands. The model agent consisted of a poly‐L‐lysine conjugate (molecular weight, 245kd) that had 70% free epsilon amino groups and 30% diethylenetriaminepentaacetic acid (DTPA)‐deriv‐atized amino groups to bind indium‐111 or gadolinium. One hour after intravenous administration of this compound, adrenal uptake was 10.1% ± 0.7 of injected dose per gram of tissue. When all free epsilon amino groups of the polylysine were completely substituted with DTPA, adrenal uptake was 3.4 times lower, indicating the importance of free amino groups for adrenal uptake. MR imaging in rats showed that a dose of 0.08 mmol of gadolinium per kilogram of the agent was sufficient to enhance the signal intensity of adrenal glands. Three hours after intravenous administration of the agent, signal intensity of the adrenal glands was 186% of precon‐trast values (liver, 165%; kidney, 91%). Fluorescence microscopy showed that the agent accumulated primarily in the cortical zona glomerulosa and in the adrenal medulla. These initial studies demonstrate the feasibility of designing contrast agents for MR imaging of the adrenal glands.
Primary ovarian cancer: Prospective comparison of contrast‐enhanced CT and pre‐and postcontrast, fat‐ suppressed MR imaging, with histologic correlation
Authors: Semelka Richard C. , Lawrence Patrick H. , Patrick Shoenut J. , Heywood Mark , Kroeker Mervyn A. , Lotocki Robert 
Published: March 2007

AbstractSixteen patients with clinically suspected malignant ovarian disease underwent contrast agent‐enhanced computed tomography (CT) and magnetic resonance (MR) imaging in a prospective comparative study. MR imaging included fat‐suppressed spin‐echo and breath‐hold FLASH (fast low‐angle shot) before and after intravenous injection of gadopentetate dimeglumine. Histologic confirmation was obtained at laparotomy (n = 13) and biopsy (n = 3). Thirteen patients had histologically proven primary ovarian cancer. MR images showed the internal architecture of ovarian tumors better than CT in nine patients and equivalently in seven. MR images showed the relationship between ovarian tumors and adjacent pelvic structures (uterus [n = 9], sigmoid colon [n = 7], bladder [n = 7], and rectum [n = 3]) better than CT in nine patients and equivalently in seven. Intraabdominal extent of disease was better defined on MR than on CT images in nine patients, equivalently in six, and worse in one. Peritoneal metastases 1–2 cm in diameter were detected on MR images and missed on CT scans in six patients. In only one case did this result in a staging error with CT. The results suggest that MR imaging is at least equivalent and may be superior to CT in the evaluation of ovarian malignancy.
Basic physics of MR contrast agents and maximization of image contrast
Authors: Hendrick R. Edward , Mark Haacke E. 
Published: March 2007

AbstractThis review summarizes the physical basis of magnetic resonance (MR) imaging contrast agents, including both T1 agents, such as gadolinium‐DTPA (diethylenetri‐aminepentaacetic acid), and T2 or T2* agents, such as superparamagnetic iron oxides. The maximization of image contrast and lesion visibility with contrast agents is described, and the use of contrast agents in MR angiogra‐phy and perfusion imaging is discussed.
Evaluation of adrenal masses with gadolinium enhancement and fat‐suppressed MR imaging
Authors: Semelka Richard C. , Patrick Shoenut J. , Lawrence Patrick H. , Greenberg Howard M. , Maycher Bruce , Madden Terrance P. , Kroeker Mervyn A. 
Published: March 2007

AbstractA study was undertaken to determine the ability to characterize benign and malignant masses with unenhanced and contrast material‐enhanced fast lowangle shot and fat‐suppressed spin‐echo magnetic resonance (MR) imaging. Thirty patients with adrenal masses detected at computed tomography (CT) underwent MR imaging within 14 days after CT. CT and MR images were interpreted in a prospective, blinded fashion. Sixteen patients had 20 benign adrenal masses, and 14 patients had 18 malignant masses. Quantitative measurements included percentage of contrast enhancement on immediate postcontrast dynamic images and periphery ‐ center signal‐to‐noise ratio (S/N) on gadolinium‐enhanced fat‐suppressed images. Qualitative evaluation included determination of the regularity of lesion margins, homogeneity of signal intensity, and local extension. MR imaging depicted all adrenal masses discovered at CT examinations. Lesions ranged in diameter from 1 to 15 (mean, 4.4) cm. No significant difference was observed in percentage of contrast enhancement between benign (90.5% ± 59.0 [standard deviation]) and malignant (110.5% ± 116.4) masses. A difference was observed between periphery ‐ center S/N for benign (−.05 ± 1.5) and malignant (7.7 ± 9.8) masses; overlap between the two, however, occurred. Qualitative evaluation allowed correct characterization of 32 of 38 masses, comparing favorably with CT, which allowed characterization of 30 lesions.