bluuebunny/crossref_metadata_2025 huggingface dataset:
The Binuclear Cyclopentadienylvanadium Carbonyls (η5‐C5H5)2V2(CO)7 and (η5‐C5H5)2V2(CO)6: Comparison with Homoleptic Chromium Carbonyls
Authors: Zhang Xiuhui , Li Qian‐shu , Xie Yaoming , King R. Bruce , Schaefer III Henry F.
Published: March 2007

The cyclopentadienylvanadium carbonyls CpV(CO)n (n = 4, 3, 2, 1), Cp2V2(CO)7, and Cp2V2(CO)6 have been studied by density functional theory using the B3LYP and BP86 functionals. The optimized structure of CpV(CO)4 is close to that found experimentally by X‐ray and electron diffraction methods. For the coordinately unsaturated CpV(CO)n (n = 3, 2, 1) the computed ν(CO) frequencies by BP86 are related to those found in low‐temperature matrix isolation experiments but show some significant differences for n = 3 and 2 in band spacings suggesting some matrix effects on the geometries. An optimized structure for Cp2V2(CO)7 is found with one symmetrical bridging carbonyl group and a V–V distance of 3.306 Å (BP86) suggesting a single bond. Energetically competitive structures for Cp2V2(CO)6 include a doubly symmetrically bridged singlet structure with only two‐electron donor carbonyl groups, a triplet doubly semibridged structure, and a singlet structure with one four‐electron donor bridging carbonyl group. Thermodynamic considerations rationalize why neither Cp2V2(CO)7 nor Cp2V2(CO)6 have yet been synthesized. Thus Cp2V2(CO)7 is predicted to be unstable with respect to dissociation into CpV(CO)4 + CpV(CO)3. Furthermore, the dissociation energy of the lowest lying singlet isomer from Cp2V2(CO)6 to Cp2V2(CO)5 is only 10.8 kcal/mol (BP86) consistent with the formation of Cp2V2(CO)5 rather than Cp2V2(CO)6 upon decomposition of the presumed CpV(CO)3H2 dihydride generated by acidification of the dianion CpV(CO)32–.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Theoretical study of the vertical excited states of benzene, pyrimidine, and pyrazine by the symmetry adapted cluster—Configuration interaction method
Authors: Li Yongjian , Wan Jian , Xu Xin
Published: March 2007

The ground state and the excited states of benzene, pyrimidine, and pyrazine have been examined by using the symmetry adapted cluster‐configuration interaction (SAC‐CI) method. Detailed characterizations and the structures of the absorption peaks in the vacuum ultraviolet (VUV), low energy electron impact (LEEI), and electron energy loss (EEL) spectra were theoretically clarified by calculating the excitation energy and the oscillator strength for each excited state. We show that SAC‐CI has the power to well reproduce the electronic excitation spectra (VUV, LEEI, and EEL) simultaneously to an accuracy for both the singlet and the triplet excited states originated from the low‐lying π → π*, n → π*, π → σ* and n → σ* excited states of the titled compounds. The present results are compared with those of the previous theoretical studies by methods, such as EOM‐CCSD(T), STEOM‐CCSD, CASPT2 and TD‐B3LYP, etc. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007
Theoretical studies on farnesyl transferase: Evidence for thioether product coordination to the active‐site zinc sphere
Authors: Sousa Sérgio Filipe , Fernandes Pedro Alexandrino , Ramos Maria João
Published: March 2007

Farnesyltransferase (FTase), an interesting zinc metaloenzyme, has been the subject of great attention in anticancer research over the last decade. However, despite the major accomplishments in the field, some very pungent questions on the farnesylation mechanism still persist. In this study, the authors have analyzed a mechanistic paradox that arises from the existence of several contradicting and inconclusive experimental evidence regarding the existence of direct coordination between the active‐site zinc cation and the thioether from the farnesylated peptide product, which include UV–vis spectroscopy data on a Co2+‐substituted FTase, two X‐ray crystallographic structures of the FTase‐product complex, and extended X‐ray absorption fine structure results. Using high‐level theoretical calculations on two models of different sizes, and QM/MM calculations on the full enzyme, the authors have shown that the farnesylated product is Zn coordinated, and that a subsequent step where this Zn bond is broken is coherent with the available kinetic results. Furthermore, an explanation for the contradicting experimental evidence is suggested. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007
Quick scheme for evaluation of atomic charges in arbitrary aluminophosphate sieves on the basis of electron densities calculated with DFT methods
Authors: Larin A. V. , Mortier W. J. , Vercauteren D. P.
Published: March 2007

It is demonstrated that unique and simple analytical functions are justified for the atomic charge dependences q of the T (T = Al, P) and O atoms of aluminophosphates (AlPOs) using DFT calculations with several basis sets, starting from STO‐3G to 3‐21G and 6‐21G**. Three internal (bonds, angles, …) coordinates for the charge dependences of the T atoms and four coordinates for the O are sufficient to reach a precision of 1.8% for the fitted q(Al), 1.0% for q(P), and 2.5% for q(O) relatively to the values calculated at any basis set level. The proposed strategy consists in an iterative scheme starting from charge dependences based on the neighbor's positions only. Electrostatic potential values are computed to illustrate the differences between the calculated and fitted charges in the considered AlPO models. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007
Imaging of diffusion and microcirculation with gradient sensitization: Design, strategy, and significance
Authors: Le Bihan Denis , Turner Robert , Moonen Chrit T. W. , Pekar James
Published: March 2007

Recent developments in the use of magnetic resonance (MR) to measure and image diffusion and blood microcirculation (“perfusion”) are summarized. After a brief description of the effects of diffusion and perfusion on the MR signal, the different methods (conventional spin‐echo, stimulated‐echo, gradient‐echo, and echo‐planar imaging) that have been proposed and used to image and measure diffusion and perfusion by gradient sensitization are presented, along with their advantages and limitations. The difficulties of diffusion/ perfusion imaging related to both hardware and software are then discussed. Special attention is given to specific problems encountered with in vivo studies and data analysis. Finally, the potential biologic and clinical applications are outlined, and some examples are presented.
Preliminary clinical trial of gadodiamide injection: A new nonionic gadolinium contrast agent for MR imaging
Authors: Kaplan Gabriela D. , Aisen Alex M. , Aravapalli S. Rao
Published: March 2007

The safety and efficacy of a newly developed intravenous formulation of the nonionic contrast agent gadolinium diethylenetriaminepentaacetic acid‐bis(methylamide), formulated as gadodia‐mide injection, was investigated. In 30 patients who underwent spin‐echo magnetic resonance (MR) imaging before and after contrast agent enhancement, the enhanced images had characteristics judged similar to those of images enhanced by means of available gadolinium compounds. In 15 patients, contrast agent administration was of major diagnostic help, either revealing lesions not apparent without enhancement or providing important lesion characterization. In 12 patients, the lack of abnormal enhancement patterns was important in excluding the presence of disease. In three patients, the contrast agent did not provide information additional to that obtained with the unenhanced T1‐ and T2‐weighted images. No clinically significant changes were observed in vital signs, neurologic status, or laboratory results. The authors conclude that, in this limited series, gadodiamide injection proved to be a safe and useful MR imaging contrast agent for evaluation of the central nervous system and surrounding structures.
MR imaging of patients with implanted drug infusion pumps
Authors: Roemeling Reinhard Von , Lanning Rosellen M. , Eames Frederick A.
Published: March 2007

The influence of magnetic resonance (MR) imaging on the integrity and function of an implantable, programmable drug infusion pump and the distortion of the image by this device were tested. Six identical pumps were tested in magnetic fields of 1.5 T. Pump memory was not affected by the procedure. The pump rotor stalled (no infusion) as long as the device was within the magnetic field. Drug delivery resumed as programmed after the pump was removed from the field. No structural damage to the electrical or mechanical pump components was detected. The pump caused a circular image artifact (a signal dropout) within 8–10 cm of the device. The authors conclude that MR imaging is accurate if the area of interest is at least 10 cm from the pump, and that with awareness of temporary infusion cessation, it is safe to perform MR imaging in patients with this implanted pump.
Direct hepatic tumor injection in rats: Can it be used for analysis of MR imaging contrast agents?
Authors: Murphy Frederick B. , del Pilar Fernandez Maria , Kossoff Marjorie B. , Dillehay Dirck L. , Malko John A. , Bernardino Michael E.
Published: March 2007

With a recently described rat model technique for direct hepatic injection of tumor cells for imaging research, there were concerns that the injection itself might produce lesions detectable with magnetic resonance (MR) imaging, thereby producing false‐positive results. To examine this possibility, the authors prospectively studied 14 Sprague‐Dawley rats after direct hepatic injection of cells from a rat hepatoma cell line. The rats were imaged with a variety of pulse sequences before and after intravenous injection of the contrast agent manganese dipyridoxal diphosphate at a dose of 8 μmol/kg. No intrahepatic lesions could be detected with MR imaging during the first 6 days after direct hepatic injection of the tumor cells. Therefore, the direct injection technique should be accurate for evaluating various MR imaging sequences and contrast agents for early hepatic tumor detection.
Interactive design of motion‐compensated gradient waveforms with a personal computer spreadsheet program
Authors: Wendt Richard E.
Published: March 2007

A personal computer spreadsheet program was used to compute the amplitudes of the gradient pulses in motion‐compensated gradient waveforms. The resulting designs for velocity‐compensated, gradient‐echo, frequency‐encoding gradients and velocity‐compensated section‐select waveforms required little or no modification when implemented on two clinical magnetic resonance imagers.
Detection with echo‐planar MR imaging of transit of susceptibility contrast medium in a rat model of regional brain ischemia
Authors: Wendland Michael F. , White David L. , Aicher Klaus P. , Tzika A. Aria , Moseley Michael E.
Published: March 2007

Gradient‐refocused echo‐planar magnetic resonance (MR) images (TE = 18 msec) were acquired in rats during bolus injection of iron oxide particles, and the first pass of the contrast agent through the brain was monitored. In control rats, contrast agent (0.1 mmol/kg iron) produced significant signal‐intensity (SI) reduction over the right hemisphere and similar declines over the left. SI loss occurred first in the cortex and basal ganglia and later in the periventricular regions, along the midline, and in the thalamic zone. Sequential volume‐localized proton spectra acquired during transit of 0.02 mmol/kg iron showed substantial reduction in SI, slight asymmetric broadening, and no change in chemical shift of the water resonance. In rats with unilateral occlusion of the middle cerebral artery, peak reduction in ischemic brain SI was to 70% ± 9% of control, while normal brain SI was reduced to 18% ± 2% (P < .01), allowing distinction of the ischemic regions. The presence and location of injury were confirmed with diffusion‐weighted imaging and postmortem vital staining. These results demonstrate abnormal transit profiles in a rat model of regional brain ischemia. Evaluation of dynamic contrast delivery patterns may provide unique information in early brain ischemia.
Lumen definition in MR angiography
Authors: Lin Weili , Haacke E. Mark , Smith Alison S.
Published: March 2007

Factors affecting blood vessel lumen definition for two‐dimensional and three‐dimensional inflow magnetic resonance (MR) imaging methods are considered. Vessel definition is affected (a) by the amount of dephasing of the blood in the vessels, both for uncompensated and velocity‐compensated gradients; (b) by the image reconstruction technique (normal Fourier reconstruction when asymmetric echoes are collected or a maximum‐intensity projection technique in postprocessing); (c) by loss of signal due to T2 de‐phasing; (d) by misregistration; (e) by vessel wall motion; and (f) by partial‐volume effects. The first two factors were found to dominate for resolution on the order of 1 mm3. To overcome these dephasing problems, the authors developed asymmetric echo, velocity‐compensated sequences with TEs as short as 4.8 msec. The data were then reconstructed with an iterative partial Fourier algorithm, enabling improved lumen definition to be obtained in phantoms and in vivo.
MR imaging—guided interstitial Nd:YAG laser phototherapy: Dosimetry study of acute tissue damage in an in vivo model
Authors: Anzai Yoshimi , Lufkin Robert B. , Castro Dan J. , Farahani Keyvan , Jabour Bradley A. , Layfield Lester J. , Udkoff Ranon , Hanafee William N.
Published: March 2007

A dosimetry study of acute tissue damage induced by interstitial application of the neodymium‐yttrium‐aluminum‐garnet (Nd:YAG) laser was performed with magnetic resonance (MR) imaging. The MR appearance of the lesion was correlated with gross and histopathologic findings. Seventy‐six lesions were induced in rabbit muscle with laser power outputs of 5–20 W and exposure times of 20–600 seconds. MR imaging was performed immediately after laser exposure. T2‐weighted spin‐echo images clearly showed the acute thermal injuries caused by laser energy deposition and correlated best with histopathologic findings. These images showed three distinct layers, corresponding to central ablation, coagulative necrosis, and interstitial edema, respectively, in the pathologic findings. Lesion diameters measured on MR images showed a linear correlation with those in gross sections. Lesion volume increased not only with increasing total energy delivered but with increasing power output for a fixed total energy delivered. MR imaging is an accurate modality for dosimetry studies of laser‐induced acute lesions.
MR imaging of head and neck vascular malformations
Authors: Gelbert François , Riche Marie Claire , Reizine Daniel , Guichard Jean‐Pierre , Assouline Eva , Hodes Jonathan E. , Merland Jean Jacques
Published: March 2007

Between 1980 and 1990, 150 patients with cervicofacial vascular malformations were studied at the authors' institution with computed tomography, plain radiography, and angiography. Since 1989, 34 of these patients have also undergone magnetic resonance (MR) imaging. Capillary‐venous hemangiomas seem to be the best indication for the adjunctive use of MR imaging. The venous pouches, characteristic of this type of lesion, cause elevated signal intensity, well seen on the T2‐weighted images. Excellent fat and muscle differentiation with MR imaging allows appreciation of the depth of extension of these lesions and their delimitation from normal tissue. Arteriovenous malformations (AVMs) are characterized by serpentine signal voids, indicative of the high flow rate of these lesions. Delimitation of the AVM nidus in the midst of the afferent and efferent dilated vessels is often difficult. Study of immature angiomas with MR imaging should be restricted to lesions in specific locations (eg, orbital, laryngeal). Lymphatic malformations showed either tissular or cystic signal intensity changes. MR imaging does not replace other studies but represents an important complementary study for the delineation and diagnosis of deep extensions of vascular malformations, allowing better planning of therapy.
Bowel disease: Prospective comparison of CT and 1.5‐T pre‐ and postcontrast MR imaging with T1‐weighted fat‐suppressed and breath‐hold FLASH sequences
Authors: Semelka Richard C. , Shoenut J. Patrick , Silverman Richard , Kroeker Mervyn A. , Yaffe Clifford S. , Micflikier Allan B.
Published: March 2007

The potential of new high‐field‐strength magnetic resonance (MR) imaging sequences to evaluate bowel disease was investigated and compared with computed tomographic (CT) studies. Thirty‐two patients were studied, 14 with known or suspected gastrointestinal tumors and 18 with known or suspected bowel inflammatory conditions. T1‐weighted fat‐suppressed spinecho and breath‐hold FLASH (fast low‐angle shot) images were obtained before and after intravenous injection of 0.1 mmol/kg gadopentetate dimeglumine. Pathologic confirmation was obtained by biopsy (n = 18), surgical excision (n = 8), or endoscopy (n = 6). CT and MR images were analyzed separately in a prospective fashion and reviewed by consensus. Information from CT and MR images was comparable in cases of confirmed bowel neoplasia. CT scans had better spatial resolution, while fat‐suppressed gadolinium‐enhanced MR images had better contrast resolution. In the 18 cases of bowel inflammation, CT scans showed concentric wall thickening in 16, while MR images showed concentric wall thickening in 14 and increased contrast enhancement in 17. Contrast enhancement was better appreciated on fat‐suppressed images than on FLASH images. The results suggest that MR imaging may play a role in the evaluation of bowel disease.
Experimental hyaline cartilage lesions: Two‐dimensional spin‐echo versus three‐dimensional gradient‐echo MR imaging
Authors: Adam Gerhard , Nolte‐Ernsting Claus , Prescher Andreas , Bühne Markus , Bruchmüller Kira , Küpper Werner , Günther Rolf W.
Published: March 2007

The value of magnetic resonance (MR) imaging, with two‐dimensional (2D) spin‐echo and FISP (fast imaging with steady‐state precession) and FLASH (fast low‐angle shot) three‐dimensional (3D) gradient‐echo sequences, for the detection of hyaline cartilage defects of the femoral condyle and the tibial plateau, was investigated in an animal model. In eight dogs, the anterior cruciate ligament was transected in one knee joint, resulting in rapid development of osteoar‐thritis with degeneration of the hyaline cartilage. At autopsy, 24 cartilage lesions were found, which were classified into four grades. The overall detection of cartilage lesions with MR imaging was poor. Only five of the 24 lesions were visible on 2D spin‐echo images, while 11 of 24 were visible on 3D FISP images and 15 of 24 were seen on 3D FLASH images. The best results were obtained in advanced stages of cartilage degeneration, involving ulceration and complete abrasion of the cartilage layer. Signal loss or signal intensity increase in the cartilage layer was seen inconsistently in grades 3 and 4 degeneration. In this animal model, 2D spin‐echo imaging was inadequate for the diagnosis of hyaline cartilage lesions, while 3D gradient‐echo imaging permitted satisfactory diagnosis in only grade 4 cartilage disease.
MR imaging of microcirculation in rat brain: Correlation with carbon dioxide‐induced changes in blood flow
Authors: Maki Jeffrey H. , Benveniste Helene , Macfall James R. , Piantadosi Claude A. , Johnson G. Allan
Published: March 2007

Considerable interest has been shown in developing a magnetic resonance (MR) imaging technique with quantitative capability in the evaluation of tissue microcirculation (“perfusion”). In the present study, the flow‐dephased/flow‐compensated (FD/FC) technique is evaluated for measuring rat cerebral blood flow (CBF) under nearly optimal laboratory conditions. Imaging was performed on a 2.O‐T system equipped with shielded gradient coils. Rat CBF was varied by manipulating arterial carbon dioxide pressure (Paco2). In parallel experiments, optimized MR imaging studies (seven rats) were compared with laser Doppler flowmetry (LDF) studies (nine rats). LDF values showed a high degree of correlation between CBF and Paco2, agreeing with results in the literature. MR imaging values, while correlating with Paco2, showed considerable scatter. The most likely explanation is unavoidable rat motion during the requisite long imaging times. Because of this motion sensitivity, the FD/FC technique cannot provide a quantitative measure of CBF. It can, however, provide a qualitative picture.
Clearance of liposomal gadolinium: In vivo decomplexation
Authors: Unger Evan C. , Fritz Thomas A. , Tilcock Colin , New Terri E.
Published: March 2007

The contrast agents gadolinium‐DTPA (diethylenetriaminepentaacetic acid), Gd‐DOTA (tetraazacyclododecanetetraacetic acid), and Gd‐HP‐DO3A (1,4,7‐tris[carboxymethyl]‐10‐[2′hydroxypropyl]‐1,4,7,10‐tetraazacyclododecane) are used in humans as extracellular contrast agents. Although free Gd+ ion is toxic, the intact Gd3+ complexes are rapidly excreted and are relatively nontoxic. Decomplexation with release of free gadolinium is a relevant clinical concern in patients with altered renal clearance. Blood pool contrast agents currently under development may have longer clearance half‐lives and be more prone to decomplexation. The present study was designed to evaluate the clearance of liposomally encapsulated Gd3+ complexes (DTPA, DOTA, and HP‐DO3A). The macrocyclic compounds had more rapid and complete clearance than DTPA (P <.05). Parallel studies with carbon‐14 and Gd‐153‐labeled complexes showed significant differences (P <.05) in the amount of these isotopes retained in the heart, kidney, lungs, and spleen, providing strong supportive evidence for in vivo decomplexation.
High‐dose gadoteridol in MR imaging of intracranial neoplasms
Authors: Runge Val M. , Kirsch John E. , Burke Vickie J. , Price Ann C. , Nelson Kevin L. , Thomas Greg S. , Dean Bruce L. , Lee Charles
Published: March 2007

Twelve patients with a high suspicion of brain metastases by previous clinical or radiologic examinations were studied in a phase III investigation with magnetic resonance (MR) imaging at 1.5 T after a bolus intravenous injection of 0.1 mmol/kg gadoteridol followed at 30 minutes by a second bolus injection of 0.2 mmol/kg gadoteridol. All lesions were best demonstrated (showed greatest enhancement) at the 0.3‐mmol/kg (cumulative) dose, with image analysis confirming signal intensity enhancement in the majority of cases after the second gadoteridol injection. More lesions were detected with the 0.3‐mmol/kg dose than with the 0.1‐mmol/kg dose, and more lesions were detected with the 0.1‐mmol/kg dose than on precontrast images. In this limited clinical trial, high‐dose gadoteridol injection (0.3‐mmol/kg cumulative dose) provided improved lesion detection on MR images specifically in intracranial metastatic disease.
Reblurred deconvolution method for chemical shift removal in F‐19 (PFOB) MR imaging
Authors: Lee H. K. , Nalcioglu Orhan
Published: March 2007

Perfluorocarbons such as perfluoroctylbromide (PFOB) can be used as contrast agents in the vascular system for fluorine‐19 magnetic resonance imaging or as synthetic oxygen carriers. F‐19 imaging has been proposed for studying the vascular system, capillary flow, tissue perfusion, and tumor oxygenation. A major difficulty is that F‐19 compounds often have complex multipeak spectra. These peaks result in chemical shift artifacts, lower signal‐to‐noise ratios, and blurred images. Each peak also excites a different section when a section‐select gradient is applied. Direct inverse filtering is the simplest deconvo‐lution method for correcting such artifacts; however, two major difficulties present themselves: functional singularity and noise amplification at high frequencies. The use of a new reblurred de‐convolution (RED) method appears to overcome these problems. Although this method is based on iterative deconvolution in the spatial domain, the computational overhead is negligible. Since the point spread function and object data are already available in the time domain as FID data, RED appears to be useful for eliminating chemical shift artifacts and suppressing noise amplification while restoring the original image without loss of resolution.
Calculation of three‐dimensional left ventricular strains from biplanar tagged MR images
Authors: Moore Christopher C. , O'Dell Walter G. , McVeigh Elliot R. , Zerhouni Elias A.
Published: March 2007

The noninvasive measurement of time‐resolved three‐dimensional (3D) strains throughout the myocardium could greatly improve the clinical evaluation of cardiac disease and the ability to mathematically model the heart. On the basis of orthogonal arrays of tagged magnetic resonance (MR) images taken at several times during systole, such strains can be determined, but only after heart motion through the image planes is taken into account. An iterative material pointtracking algorithm is presented to solve this problem. It is tested by means of mathematical models of the heart with cylindric and spherical geometries that undergo deformations and bulk motions. Errors introduced by point‐tracking interpolation were found to be negligible compared with those due to marker identification on the images. In a human heart studied with this technique, the corrected radial strains at the left ventricular base were approximately 2.5 times the two‐dimensional estimates derived from the fixed image planes. The authors conclude that material point tracking allows accurate, timeresolved 3D strains to be calculated from tagged MR images, and that prior correction for motion of the heart through image planes is necessary.
MR imaging detection of calcified intracranial lesions and differentiation from iron‐laden lesions
Authors: Gronemeyer Suzanne A. , Langston James W. , Hanna Soheil L. , Langston James W.
Published: March 2007

Magnetic susceptibility variation caused by calcium permits limited detection of intracranial calcificatios and/or their distinction from iron‐laden lesions with spin‐echo or gradient‐echo magnetic resonance (MR) techniques. The magnetic susceptibility sensitivity of phase imaging has been used to detect iron‐laden lesions. A new approach that combines the magnetic susceptibility sensitivity of both gradient‐echo and phase imaging to yield greater imaging sensitivity to calcium is presented. Two‐dimensional fast low‐angle shot (FLASH) gradient‐echo imaging with phase image reconstruction (gradient‐echo phase [GEP]) was used at 1.0 and 1.5 T. Twelve patients with computed tomography‐proved calcified intracranial lesions (≥200 HU) and seven patients with iron‐laden intracranial lesions having a characteristic appearance on T1‐and T2‐weighted and FLASH MR images were studied. The GEP imaging technique helped detect calcified intracranial lesions (≥200 HU) and helped distinguish them from iron‐laden lesions.
Detection of acute and treated lesions of hepatosplenic candidiasis: Conparison of dynamic contrast‐enhanced CT and MR Imaging
Authors: Semelka Richard C. , Patrick Shoenut J. , Greenberg Howard M. , Bow Eric J.
Published: March 2007

Dynamic contrast‐enhanced computed tomography (CT) was compared with 1.5‐T magnetic resonance (MR) imaging with FLASH (fast low‐angle shot), gadolinium‐enhanced FLASH (Gd‐FLASH), and T2‐weighted fat‐suppression (T2FS) sequences in 11 patients with hematologic malignancies, five with biopsy‐confirmed hepatosplenic candidiasis treated with antifungal chemotherapy and six with a clinical history suggestive of acute hepatosplenic candidiasis. CT and MR images were separately interpreted in a prospective fashion. MR imaging showed lesions compatible with candidiasis in the liver in six patients, the spleen in five, and the kidneys in one. CT showed candidiasis‐compatible lesions in the liver in three patients and the spleen in one; no renal lesions were shown. Differences between acute and treated candidal lesions were observed. Gd‐FLASH images showed the most liver lesions (n = 106), followed by FLASH (n = 85), T2FS (n = 20), and CT (n = 18). MR imaging performed better than CT in distinguishing candidal hepatic lesions from recurrent lymphoblastic lymphoma in one patient and from hepatic infarcts in another. The results suggest that MR imaging may be superior to CT in detecting lesions of hepatosplenic candidiasis.
Cardiovascular MR imaging: Current level of clinical activity
Authors: White Richard D. , Ehrnan Richard L. , Weinreb Jeffrey C.
Published: March 2007

Relative to other clinical magnetic resonance [MR] imaging activities, cardiovascular [CV] MR imaging has been slow to demonstrate a clinical presence. To better understand the present situation in clinical CV MR imaging, a survey of Society for Magnetic Resonance Imaging (SMRI) members was conducted. A large majority (78%) of the 90 sites responding to the survey reported clinical activity in CV MR imaging. Of these 70 sites, 46% restricted such activity to routine clinical work, while 3% restricted it to clinical research. The remaining 51% conducted both. At all clinical sites. The overall frequency of performance of clinical CV MR imaging was variable (mean, 4.2 and 13.8 cases per month at routine‐only and combined routine‐research sites, respectively]. In clinical CV studies, gated static, multilevel spin‐echo and dynamic gradient‐echo [cine] techniques were most common. At the 68 sites involved in routine clinical CV MR imaging. Primarily anatomic studies composed a much higher proportion of the total [mean, 86%) than primarily functional studies. The evaluation of acquired thoracic aortic disease, congenital cardiac malformation, and para‐or intracardiac mass were the most prevalent anatomic indications overall. Approximately half of the same sites assessed functional aspects of CV disease. The assessment of ventricular dysfunction and valvular dysfunction were the most common functional objectives. The survey indicated that the level of clinical activities in CV MR imaging was low and that most responding sites were involved in clinical CV MR imaging primarily for detection and delineation of anatomic abnormalities.
High‐speed black blood imaging of vessel stenosis in the presence of pulsatile flow
Authors: Chien Daisy , Goldmann Alexander , Edelman Robert R.
Published: March 2007

Stenosis phantoms were created to study the ability of “black blood” methods to image a vessel stenosis in the presence of pulsatile flow. Black blood images were acquired with a modified TurboFLASH (fast low‐angle shot) method that eliminates flow signal by applying a set of prepulses before segmented data acquisition. With this high‐speed approach, imaging can be completed within 16 seconds. This technique was compared with conventional spin‐echo black blood, gradient‐echo black blood, and gradient‐echo bright blood methods. Loss of flow signal, which extended beyond the site of the stenosis, was seen on the gradient‐echo bright blood images. The pattern of signal loss varied with the type of stenosis. Flow voids were achieved with spin‐echo black blood imaging: however, substantial ghosting artifacts were seen. With gradient‐echo black blood imaging, it was difficult to eliminate all flow signal, particularly for in‐plane flow. The modified TurboFLASH method produced high‐quality black blood images in a fraction of the time needed for spin‐echo imaging. It showed no ghosting artifacts even in the presence of pulsatile flow.
Effect of hypothyroidism on phosphorus metabolism in muscle and liver: In vivo P‐31 MR spectroscopy study
Authors: Hagspiel Klaus D. , Von Weymarn Constantin , McKinnon Graeme , Haldemann Regina , Marincek Borut , von Schulthess Gustav K.
Published: March 2007

Hypothyroidism is known to affect nearly every organ and organ system of the human body. The goal of the present study was to gain insight into the phosphorus metabolism and bioenergetic function of striated (calf) muscle and liver in patients with hypothyroidism before and after thyroid hormone treatment. With an ISIS (image‐selected in vivo spectroscopy) magnetic resonance (MR) technique for volume selection, phosphorus‐31 metabolism of the calf muscle in 10 patients and of the liver in seven patients with severe hypothyroidism was studied before and after treatment. In addition, spectra from the calf muscle and liver were obtained in 10 healthy volunteers. Relative to those from the healthy subjects, the P‐31 MR spectra from patients with hypothyroidism showed a significantly diminished phosphocreatine/inorganic phosphate ratio (P < .01). After thyroid hormone substitution therapy, this ratio returned to normal values within several weeks. No statistically significant changes in the spectra of liver tissue could be detected. The results support the theory that hypothyroidism induces a hormone‐dependent, fully reversible impairment of the energy metabolism of striated muscle. Changes in liver metabolism observed with biochemical methods are apparently not detectable with state‐of‐the‐art P‐31 MR spectroscopy.
Reduced‐bandwidth method for F‐19 imaging of perflubron
Authors: Lee H. K. , Nalcioglu Orhan
Published: March 2007

A reduced‐bandwidth imaging method has been developed to eliminate the chemical shift artifacts in magnetic resonance (MR) imaging of the blood substitute perflubron (PFB) and simultaneously enhance the signal‐to‐noise ratio (SNR). The two strongest spectral peaks, which have relatively long T2 values (247 and 471 msec), were used. When the receiver bandwidth is reduced substantially by increasing the data acquisition time Ts, the bandwidth across the object becomes less than the chemical shift frequency. The reduced bandwidth eliminates misregistration by displaying the images corresponding to multiple spectral peaks on the same image plane simultaneously. An additional gain due to the reduced bandwidth is the reduced thermal Gaussian noise. Unfortunately, the increased Ts results in an increased TE, which causes the signal to be attenuated by T2 relaxation. The optimum measured Ts (and TE) values for successful image separation and maximum SNR were 120 and 144 msec for the two spectral peaks, respectively. The long TE also suppresses the rest of the downfield spectral peak cluster of PFB. The degree of magnetic field inhomogeneity and tissue susceptibility across the object may cause some limitations in the application of this technique; however, a composite radio‐frequency pulse that will allow use of additional spectral lines and/or localized volume imaging techniques may be incorporated to overcome these limitations.
Rapid fat/water assessment in knee bone marrow with inner‐volume rare spectroscopic imaging
Authors: Oshio Koichi , Mulkern Robert V.
Published: March 2007

An inner‐volume modification of a spectroscopic imaging technique based on RARE (rapid acquisition with relaxation enhancement) sequences is shown to provide, in less than 1 minute, spectra suitable for fat/ water peak‐area integration from selected imaging columns containing more than 1,000 5 × 5 × 1‐mm voxels. A limitation is the unavoidable T2 weighting of the spectral peaks, which influences estimations of true fat/ water composition from the spectra. Studies obtained in the knees of healthy volunteers demonstrate the ability of the technique to enable characterization of the two major proton peaks in bone marrow. Data collected at two or more effective TEs are suitable for extrapolation of fat/water estimates to zero TE.
Routine quantitative analysis of brain and cerebrospinal fluid spaces with MR imaging
Authors: Kikinis Ron , Shenton Martha E. , Gerig Guido , Martin John , Anderson Mark , Metcalf David , Guttmann Charles R. G. , McCarley Robert W. , Jolesz Ferenc A. , Lorensen William , Cline Harvey
Published: March 2007

A computerized system for processing spin‐echo magnetic resonance (MR) imaging data was implemented to estimate whole brain (gray and white matter) and cerebrospinal fluid volumes and to display three‐dimensional surface reconstructions of specified tissue classes. The techniques were evaluated by assessing the radiometric variability of MR volume data and by comparing automated and manual procedures for measuring tissue volumes. Results showed (a) the homogeneity of the MR data and (b) that automated techniques were consistently superior to manual techniques. Both techniques, however, were affected by the complexity of the structure, with simpler structures (eg, the intracranial cavity) showing less variability and better spatial correlation of segmentation results between raters. Moreover, the automated techniques were completed for whole brain in a fraction of the time required to complete the equivalent segmentation manually. Additional evaluations included interrater reliability and an evaluation that included longitudinal measurement, in which one subject was imaged sequentially 24 times, with reliability computed from data collected by three raters over 1 year. Results showed good reliability for the automated segmentation procedures.
MR angiography with a cardiac‐phase–specific acquisition window
Authors: Selby Katherine , Saloner David , Anderson Charles M. , Chien Daisy , Lee Ralph E.
Published: March 2007

A method for cardiac‐phase–specific magnetic resonance (MR) angiography is presented. An electronics module permits incrementing of phase‐encoding gradients and storage of incoming data only during a chosen portion of the cardiac cycle. Suppression of stationary material is maintained by delivering radio‐frequency pulses at constant TR throughout the cycle. Imaging of a pulsatile flow phantom demonstrates that acquiring data only during systole substantially increases the signal intensity of flowing material. In addition, phase‐encoding ghost artifacts are eliminated from the neighborhood of the vessel. Image acquisition time is minimized by acquiring only the low‐frequency phase‐encoding lines in the cardiac‐phase–specific mode. In healthy volunteers, greatly improved MR angiograms of the lower extremities are obtained. Fat saturation and magnetization transfer further enhance vessel/background contrast. Acquiring data only during systole ensures rapid inflow for all phase‐encoding lines, permitting a near‐longitudinal section orientation without in‐plane saturation. This substantially reduces total acquisition time relative to axial acquisition.
Altered phase‐encoding order for reduced sensitivity to motion in three‐dimensional MR imaging
Authors: Korin Hope W. , Riederer Stephen J. , Bampton Anna E. H. , Ehman Richard L.
Published: March 2007

A method of reordering phase and slab encoding that can be used to address some of the inherent problems due to motion in three dimensional imaging is described and implemented. The method is shown to be more robust with respect to reducing artifacts resulting from several fundamental types of motion. It can be readily implemented on a standard magnetic resonance imager with essentially no increase in total imaging time. Results of simulations and phantom and in vivo experiments are presented.
Lumbar myelography with three‐dimensional MR imaging
Authors: Zisch Rainer J. , Artmann Wolfgang , Hollenbach Hans P.
Published: March 2007

A strongly T2*‐weighted, three‐dimensional (3D) PSIF (time‐reversed FISP (fast imaging with steady‐state precession)) gradient‐echo magnetic resonance (MR) sequence, with postprocessing of the 3D data set with a maximum‐intensity projection (MIP) algorithm, produced x‐ray myelography–equivalent images. The method was tested in 10 healthy volunteers to optimize sequence parameters and was evaluated in 30 patients with proven lumbar disk disease. MIP myelograms, unlike two‐dimensional MR images, could not show the pathologic disks themselves but clearly demonstrated the effect on the thecal sac, giving a clear overall view of its geometry and dimensions, especially when displayed in a cine loop. All 28 medial and mediolateral disk herniations could be visualized, whereas only three of eight intraforaminal disk herniations were seen on MR myelograms.
In vivo relaxometry of three brain tumors in the rat: Effect of Mn‐TPPS, a tumor‐selective contrast agent
Authors: Wilmes Lisa J. , Hoehn‐Berlage Mathias , Els Thomas , Bockhorst Kurt , Eis Manfred , Bonnekoh Petra , Hossmann Konstantin‐Alexander
Published: March 2007

T1 and T2 were determined simultaneously in vivo at 4.7 T in implanted rat brain tumors. Three different tumor cell lines were implanted in the right caudate nucleus: the F98 glioma, the E367 neuro‐blastoma, and the RN6 schwannoma. Their T1 and T2 values (mean ± standard deviation [msec]), respectively, were 1,312 ± 107 and 89 ± 3 (gli‐oma), 1,284 ± 86 and 87 ± 7 (neuroblastoma), and 1,338 ± 85 and 86 ± 9 (schwannoma). The T1 values (msec) of normal brain and muscle were 1,090 ± 59 and 1,139 ± 77, respectively, and the T2 values (msec) were 76 ± 3 and 36 ± 2, respectively. After injection of the contrast agent manganese (III) tet‐raphenylporphine sulfonate (TPPS) the T1 of all three tumors decreased by 30% and the T2 by 10%, whereas no such change in relaxivity was noted in normal brain. As a result, strong contrast enhancement of the three tumor types was seen on T1‐weighted images. The tumor was clearly delineated and correlated with findings at histologic examination. This tumor enhancement was followed up for 4 days with quantitative relaxation time measurements, and the strong, selective reduction in T1 for all three tumor types after Mn‐TPPS injection was preserved over the entire observation period.
MR imaging of hepatic iron overload in rat
Authors: Kim Il‐Young , Mitchell Donald G. , Vinitski Simon , Macke Consigny P. , Hann Hie‐Won L. , Rifkin Matthew D. , Rubin Raphael
Published: March 2007

To investigate the relationship of hepatic signal intensity and T2 with histologic grading in an animal model of oral iron overload and to determine the duration of feeding necessary to produce abnormalities detectable on magnetic resonance (MR) images, hepatic iron overload was induced in 12 rats by feeding them a diet supplemented with 4% car‐bonyl iron for 2–11 weeks. Iron overload seen on MR images was graded independently and blindly by two radiologists as normal, mild, moderate, or severe. The rats were killed, and histologic findings were graded blindly by four pathologists using a similar subjective scale. Hepatic T2 values were estimated from spin‐echo images. In the rats with iron overload, intracellular iron deposition was noted on histologic studies. On MR images, hepatic signal intensity and T2 decreased after only 2 weeks of dietary iron overload, and both continued to decrease with longer duration of feeding. There was significant correlation between iron overload duration and changes on MR images and between MR images and histologic grading (r =.92, P =.0001 for both). The mean T2 of hepatic iron overload decreased with longer duration of feeding.
Chronic pancreatitis: MR imaging features before and after administration of gadopentetate dimeglumine
Authors: Semelka Richard C. , Patrick Shoenut J. , Kroeker Mervyn A. , Micflikier Allan B.
Published: March 2007

Magnetic resonance (MR) imaging was performed in patients with a history (>1 year) of inflammatory pancreatic disease. Calcification was seen at recent computed tomographic examinations in 13 patients and was not seen in nine patients. On fat‐suppressed spin‐echo images, the signal‐to‐noise ratio of the pancreas was significantly lower (P <.001) in patients with pancreatic calcification (18.2 ± 2.5 vs 38.1 ± 6.1). On fast low‐angle shot images, the percentage of contrast enhancement was also significantly lower (P <.001) in patients with calcification (26.1% ± 5.8 vs 78.7% ± 15.9). The results suggest that MR imaging may be useful in evaluating patients with a long history of pancreatic disease for the presence of irreversible disease.
First‐pass evaluation of renal perfusion with turboflash MR imaging and superparamagnetic iron oxide particles
Authors: Trillaud Hervë , Grenier Nicolas , Degreze Philippe , Louail Catherine , Chambon Catherine , Franconi Jean‐Michel
Published: March 2007

First‐pass intrarenal hemodynamics were studied with superparamagnetic iron oxide particles and a T2‐weighted TurboFLASH (fast low‐angle shot) magnetic resonance (MR) imaging sequence. Four groups of five rabbits each were imaged after bolus injection of 40, 100, 140, and 200 μ,mol/kg iron, respectively. Images were acquired every 1.2 seconds, with an acquisition time of 700 msec. The signal intensity was measured in the cortex, outer medulla, inner medulla, and globally. In preliminary pathologic applications, two rabbits were imaged after ligation of the lumbar ureter and two after embolization of the renal artery. The reproducibil‐ity of the normal dynamics was evaluated with a cross‐correlation test. On the images, the intravas‐cular progression of the iron particles could be visualized within the cortex and the two compartments of the medulla in all cases. The maximal reduction in signal intensity in the cortex and medulla increased with the dose. The relationship between signal intensity decrease and dose was not linear, and the reproducibility of the signal intensity versus time plots was acceptable only at the 140 and 200 μ.mol/kg doses. The decrease in signal intensity was reduced and delayed in the emboli‐zed and hydronephrotic kidneys.
Proton relaxation enhancement
Authors: Wood Michael L. , Hardy Peter A.
Published: March 2007

Paramagnetic and superparamagnetic substances are used as contrast agents to enhance proton relaxation in magnetic resonance imaging. This review summarizes the physics of contrast agents, specifically the mechanisms by which contrast agents enhance T1 and T2 relaxation. The purpose is to provide a background for understanding the behavior of existing contrast agents in basic experimental and clinical studies. Terms such as magnetic dipole, dipole moment, magnetic susceptibility, diamag‐netism, paramagnetism, superparamagnetism, and ferro‐magnetism are introduced. Two important interactions between the magnetic dipole moments of paramagnetic substances and the dipole moments associated with protons are described. The Solomon‐Bloembergen‐Morgan equations and other basic relaxation theory that has been confirmed experimentally are introduced to account for the dependence of relaxation on such parameters as the Larmor frequency, magnetic moment, accessibility of water molecules to the core of a contrast agent, and frequency of molecular motions.
Efficacy and safety of gadopentetate dimeglumine in the evaluation of patients with a suspected tumor of the extracranial head and neck
Authors: Hudgins Patricia A. , Elster Allen D. , Runge Val M. , Kashanian Franciska K. , Goldstein Harold A.
Published: March 2007

The clinical efficacy and safety of gadopentetate dimeglumine as a paramagnetic contrast agent for magnetic resonance (MR) imaging of the extracranial head and neck was evaluated in a multicenter trial involving 60 patients. Patients with signs and/or symptoms of a tumor in the nasopharynx, oropharynx, hypopharynx, larynx, or neck were studied. T1‐weighted images were obtained before and after injection of gadopentetate dimeglumine, 0.1 mmol/kg, at a rate of 10 mL/min. No lesions were seen on the pre‐ or postinjection images of five of the 60 patients. Postinjection lesion enhancement was present in 53 of the remaining 55 (96%) patients. The absence of postinjection lesion enhancement in one of the two remaining patients was useful information. Postinjection impressions differed from preinjection diagnosis in 22 of 60 (37%) patients. Additional information was obtained from postinjection relative to preinjection images in 38 of 60 (63%) patients. Four adverse experiences were reported in three of 60 (5%) patients. Two mild (chest wall pain and headache) and one moderate (nausea) adverse experiences were considered by the authors to be unrelated to the studied drug. One severe adverse experience was reported. This patient had a seizure, considered by the investigator to be remotely related to the study drug and attributed to the abrupt withdrawal of anticonvulsant medications. The data indicate that gadopentetate dimeglumine is safe and efficacious in the evaluation of patients with extracranial head and neck lesions.