bluuebunny/crossref_metadata_2025 huggingface dataset:
Treatment strategy and risk of functional decline and mortality after nursing‐home acquired lower respiratory tract infection: two prospective studies in residents with dementia
Authors: van der Steen Jenny T. , Mehr David R. , Kruse Robin L. , Ribbe Miel W. , van der Wal Gerrit
Published: March 2007

Background

Although lower respiratory tract infections (LRI) cause considerable morbidity and mortality among nursing home residents with dementia, the effects of care and treatment are largely unknown. Few large prospective studies have been conducted.

Methods

We pooled data from two large prospective cohort studies in 61 Dutch nursing homes and 36 nursing homes in the state of Missouri, United States. We included 551 US residents and 381 Dutch residents with dementia and LRI. Main outcome measures were 3‐month mortality and decline in activities of daily living (ADL) function after 3 months compared with pre‐illness status. Using multivariable multinomial logistic regression to control for confounding, we assessed associations of restraint use and antibiotic type (oral compared with parenteral), with outcomes of lower respiratory tract infection (LRI). Survival without ADL decline was the reference category.

Results

After multivariable adjustment, restraint use was associated with ADL decline (OR 1.9, 95% CI 1.1–3.3). Oral antibiotics were not associated with 3‐month mortality (OR 0.83; 95% CI 0.56–1.2). Severe dementia was the strongest independent predictor of decline; mortality was most strongly associated with male gender.

Conclusions

Among Dutch and US nursing home residents with dementia and LRI, restrained residents suffered more decline. Parenteral antibiotic treatment was not associated with better outcome in residents at low to moderate risk of mortality. Aggressive treatment strategies may provide little benefit for the majority of nursing home residents with dementia and LRI. Copyright © 2007 John Wiley & Sons, Ltd.
Hybrid molecular dynamics‐quantum mechanics simulations of solute spectral properties in the condensed phase: Evaluation of simulation parameters
Authors: Zwier Matthew C. , Shorb Justin M. , Krueger Brent P.
Published: March 2007

We have explored the impact of a number of basic simulation parameters on the results of a recently developed hybrid molecular dynamics‐quantum mechanics (MD‐QM) method (Mercer et al., J Phys Chem B 1999, 103, 7720). The method utilizes MD simulations to explore the ground‐state configuration space of the system and QM evaluation of those structures to yield the time‐dependent electronic transition energy, which is transformed into the optical line‐broadening function using the second‐order cumulant expansion. Both linear and nonlinear optical spectra can then be generated for comparison to experiment. The dependence of the resulting spectra on the length of the MD trajectory, the QM sampling rate, and the QM model chemistry have all been examined. In particular, for the system of oxazine‐4 in methanol studied here, at least 20 ps of MD trajectory are needed for qualitative convergence of linear spectral properties, and > 100 ps is needed for quantitative convergence. Surprisingly, little difference is found between the 3‐21G and 6‐31G(d) basis sets, and the CIS and TD‐B3LYP methods yield remarkably similar spectra. The semiempirical INDO/s method yields the most accurate results, reproducing the experimental Stokes shift to within 5% and the FWHM to within 20%. Nonlinear 3‐pulse photon echo peak shift (3PEPS) decays have also been simulated. Decays are generally poorly reproduced, though the initial peak shift which depends on the overall coupling of motions to the solute transition energy is within 15% of experiment for all model chemistries other than those using the STO‐3G basis. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007
Molecular structures of the two most stable conformers of free glycine
Authors: Kasalová Veronika , Allen Wesley D. , Schaefer Henry F. , Czinki Eszter , Császár Attila G.
Published: March 2007

The equilibrium molecular structures of the two lowest‐energy conformers of glycine, Gly‐Ip and Gly‐IIn, have been characterized by high‐level ab initio electronic structure computations, including all‐electron cc‐pVTZ CCSD(T) geometry optimizations and 6‐31G* MP2 quartic force fields, the latter to account for anharmonic zero‐point vibrational effects to isotopologic rotational constants. Based on experimentally measured vibrationally averaged effective rotational constant sets of several isotopologues and our ab initio data for structural constraints and zero‐point vibrational shifts, least‐squares structural refinements were performed to determine improved Born‐Oppenheimer equilibrium (re) structures of Gly‐Ip and Gly‐IIn. Without the ab initio constraints even the extensive set of empirical rotational constants available for 5 and 10 isotopologues of Gly‐Ip and Gly‐IIn, respectively, cannot satisfactorily fix their molecular structure. Excellent agreement between theory and experiment is found for the rotational constants of both conformers, the rms residual of the final fits being 7.8 and 51.6 kHz for Gly‐Ip and Gly‐IIn, respectively. High‐level ab initio computations with focal point extrapolations determine the barrier to planarity separating Gly‐IIp and Gly‐IIn to be 20.5 ± 5.0 cm−1. The equilibrium torsion angle τ(NCCO) of Gly‐IIn, characterizing the deviation of its heavy‐atom framework from planarity, is (11 ± 2)°. Nevertheless, in the ground vibrational state the effective structure of Gly‐IIn has a plane of symmetry. © 2007 Wiley Periodicals, Inc. J Comput Chem 2007
Molecular dynamics simulation in the grand canonical ensemble
Authors: Eslami Hossein , Müller‐Plathe Florian
Published: March 2007

An extended system Hamiltonian is proposed to perform molecular dynamics (MD) simulation in the grand canonical ensemble. The Hamiltonian is similar to the one proposed by Lynch and Pettitt (Lynch and Pettitt, J Chem Phys 1997, 107, 8594), which consists of the kinetic and potential energies for real and fractional particles as well as the kinetic and potential energy terms for material and heat reservoirs interacting with the system. We perform a nonlinear scaling of the potential energy parameters of the fractional particle, as well as its mass to vary the number of particles dynamically. On the basis of the equations of motion derived from this Hamiltonian, an algorithm has been proposed for MD simulation at constant chemical potential. The algorithm has been tested for the ideal gas, for the Lennard–Jones fluid over a wide range of temperatures and densities, and for water. The results for the low‐density Lennard–Jones fluid are compared with the predictions from a truncated virial equation of state. In the case of the dense Lennard–Jones fluid and water our predicted results are compared with the results reported using other available methods for the calculation of the chemical potential. The method is also applied to the case of vapor‐liquid coexistence point predictions. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007
MR imaging of the central nervous system in divers
Authors: Rinck Peter A. , Svihus Rasmus , de Francisco Patricia
Published: March 2007

A group of 70 professional divers and 47 healthy control subjects who had never dived were examined with magnetic resonance (MR) imaging to determine the prevalence of focal white matter changes in the brain. Spots of high signal intensity in white matter on proton density‐and/or T2‐weighted spin‐echo images were detected in 42% of the control subjects and in 34% of the divers. In the control subjects, the prevalence of more than three changes was related to smoking, use of alcohol, head trauma, age of more than 35 years, and a combination of several cerebrovas‐cular risk factors. This relationship was not present in the divers. The prevalence of changes in divers was inversely related to diving depth, amount of diving, participation in “unsafe diving,” and decompression sickness. The reasons for these results could not be ascertained. The results are compared with those of MR imaging studies of white matter changes recently presented by other research groups.
MR imaging shoulder injuries in professional baseball players
Authors: Burk D. Lawrence , Torres Jorge L. , Marone Phillip J. , Mitchell Donald G. , Rifkin Matthew D. , Karasick David
Published: March 2007

Magnetic resonance (MR) imaging was used to evaluate the shoulders of 10 symptomatic professional baseball players and one asymptomatic player, with surgical correlation in six cases and arthrographic correlation in two cases. Seven small rotator cuff tears measuring 0.5–1 cm were identified on MR images, with arthrographic and surgical confirmation of these findings in two patients and surgical confirmation only in three patients. Cortical irregularity and/or subchondral cyst formation at the posterior aspect of the greater tuberosity near the insertion site of the infraspinatus tendon was found in five of the seven players with rotator cuff tears. Similar findings were noted in the asymptomatic volunteer and in one of the three players without cuff tear, who also had irregular thickening of the posterior capsule. These findings are believed to represent chronic avulsive changes resulting from the deceleration stresses of the follow‐through motion.
Phase‐contrast MR angiography with reduced acquisition time: New concepts in sequence design
Authors: Hausmann Richard , Lewin Jonathan S. , Laub Gerhard
Published: March 2007

A new acquisition scheme for three‐dimensional (3D) phase‐contrast MR angiography reduces by 33% the measurement time for a data set sensitive to flow in all three orthogonal directions. Background suppression is achieved by acquiring a flow‐compensated data set and three data sets flow encoded in the three orthogonal directions, with subsequent complex subtraction. The data are acquired in an interleaved fashion, eliminating misregistration artifacts due to patient motion between measurements sensitive to different flow directions. A standard maximum‐intensity‐projection algorithm is applied to the combined 3D data set to obtain angiographic projections sensitive to all three orthogonal flow directions. The theory and implementation of the method are described and examples of its application to the intracranial and abdominal circulation are provided.
Polymeric gastrointestinal MR contrast agents
Authors: Tilcock Colin , Unger Evan C. , Ahkong Quet Fah , Fritz Tom , Koenig Seymour H. , Brown Rodney D.
Published: March 2007

Combining either paramagnetic (gadolinium chelatea) or superparamagnetic (ferrite) contrast agents with polymers such as polyethylene glycol or cellulose, or with simple sugars such as dextrose, results in mixtures that exhibit improved T1 and/or T2 relaxivity compared with that of the contrast agent alone. It is suggested that the addition of such inexpensive and nontoxic polymers or saccharides may improve the effectiveness and decrease the cost of enteric contrast agents.
Atypical appearance of lipomatous tumors on MR images: High signal intensity with fat‐suppression STIR sequences
Authors: Murphy William D. , Hurst Gregory C. , Duerk Jeffrey L. , Feiglin David H. , Christopher Mark , Bellon Errol M.
Published: March 2007

Lipomatous tumors generally have signal characteristics that allow them to be diagnosed with great accuracy by means of magnetic resonance imaging. These tumors usually have signal intensities similar to those of subcutaneous fat on both T1‐ and T2‐weighted spin‐echo images. Previous reports have not, to the authors' knowledge, described the appearance of lipomatous tumors on images obtained with a short‐inversion‐time inversion‐recovery (STIR) sequence, which can be used to suppress signal from fat. Three lipomatous tumors (two liposarcomas and one lipoma) with signal characteristics unlike those of normal subcutaneous fat at all pulse sequences are presented.
Ineffectiveness of averaging for reducing motion artifacts in half‐fourier MR imaging
Authors: Wood Michael L.
Published: March 2007

Two data sets for half‐Fourier imaging (HFI) can be collected in the same time as one data set for conventional full Fourier imaging (FFI). The hypothesis is that averaging twice as much data in HFI does not make ghost artifacts caused by motion have less signal intensity than in FFI. This hypothesis was tested with images of a human subject by measuring the standard deviation within regions of interest containing ghosts. The control experiment involved measuring the standard deviation on images from the same data reconstructed with FFI. The images were formed after averaging of one to eight data sets from a collection of nine data sets acquired sequentially. Background ghosts or those in other regions of low intensity were less intense on images from HFI after twice as much averaging as in FFI, but this was not the case for ghosts superimposed on anatomic structures. This observation is explained by showing that an image obtained by means of FFI can be expressed in terms of two images obtained by means of HFI applied to the top and bottom halves of the data. The use of HFI to allow twice as much averaging without prolonging data acquisition time is not advantageous for reducing ghost artifacts caused by motion.
Primary nasal amelanotic melanoma: MR appearance
Authors: Crowley John J. , Lupetin Anthony R. , Wang Scott E.
Published: March 2007

The appearance on magnetic resonance (MR) images of a primary amelanotic malignant melanoma of the nasopharynic is reported. The factors affecting the MR appearance of melanomas of the head and neck are reviewed. The case is compared with a previously reported case of primary nasopharyngeal melanotic melanoma, and the importance of considering the tumor in all nasophargyngeal neoplasms is emphasized.
Motion artifact reduction with three‐point ghost phase cancellation
Authors: Xiang Qing‐San , Henkelman R. Mark
Published: March 2007

A novel method for “ghost” artifact suppression is introduced. It suppresses ghosts induced by motion in any direction, as well as other types of quasi‐periodic signal modulation. Because it requires neither special hardware nor intensive data processing, it can be easily implemented on conventional magnetic resonance (MR) imagers. The method is based on the concept of decomposition of a ghosted complex image into a ghost mask and ideal image. A set of deliberately designed acquisitions are used to generate a set of ghosted complex images in which the ghost components are related in a simple manner. With use of equations describing image decomposition and ghost correlation, the ideal image can be calculated pixel by pixel. The ideal image obtained (representing the time‐averaged spin‐density distribution) is shown to be a truer representation of physical reality than the ghost‐free image obtained with ordered phase encoding. In this technique, both interview and intraview effects are taken into account. The technique is also useful in simultaneously suppressing ghosts from multifrequency signal modulations such as respiratory and cardiac motions. The method was successfully tested with three time‐interleaved, phase‐encoding‐order‐shifted acquisitions. Experimental results have shown that it is a simple but effective technique.
Comparison of phase‐difference and complex‐difference processing in phase‐contrast MR angiography
Authors: Bernstein Matt A. , Ikezaki Yoshikazu
Published: March 2007

The two main phase‐contrast reconstruction methods are phase difference and complex difference. The signal‐to‐noise ratio properties and relative advantages of the two techniques are discussed. It is argued that each processing method has applications in which it is superior, and guidelines are provided to determine those applications. It is demonstrated theoretically and experimentally that only the complex‐difference method is well suited for processing phase‐contrast slabs with use of a projection dephaser gradient.
The trouble with spectroscopy papers
Authors: Bottomley Paul A.
Published: March 2007

Writing a critique and guide for authors of clinical spectroscopy research papers is a likely way of ensuring that one never sees another of one's own papers published in this field. Nevertheless, it is disappointing, though perhaps predictable, that despite its historical foundations in quantitative spectroscopy, the field has its fair share of findings that are not so obviously reconciled. Here is the view of one author, one referee, and one spectroscopy protagonist about what might be expected of a clinical spectroscopy paper. In addition to novelty, the fundamental criteria for acceptance should be that the conclusions are supported by properly and objectively quantified results, and that sufficient experimental detail is provided so that one skilled in the art could reproduce the study and its findings.
Efficacy of nonionic low‐osmolar gadodiamide injection in animals with intracranial mass lesions
Authors: Carvlin Mark J. , Rajan S. Sunder , Rosa Louis , Muraki Alan S. , Francisco John , Rocklage Scott M.
Published: March 2007

Gadodiamide injection is a nonionic, low‐osmo‐lar formulation of a paramagnetic metal chelate complex consisting of gadodiamide and caldia‐mide sodium. The efficacy of gadodiamide injection as a magnetic resonance (MR) imaging enhancement medium was evaluated by imaging intracranial 9L‐glioma lesions induced in rats and naturally occurring lesions in dogs. T1‐ and T2‐weighted spin‐echo images were obtained before and after administration of gadodiamide injection at doses of 0.1 and 0.2 mmol/kg. On the precontrast T1‐weighted images, the intracranial lesions were not well seen, appearing isoin‐tense to normal brain parenchyma. Although the presence of disease was shown unequivocally on the T2‐weighted images, the margins of the masses could not be delineated. Postcontrast T1‐weighted images were characterized by marked enhancement of the tumor, with no change in signal intensity in the surrounding edematous brain tissue. Gadodiamide injection was efficacious in identifying areas of blood‐brain barrier breakdown associated with intracranial masses.
MR imaging appearance of intraperitoneal gelatin sponge in mice
Authors: Hoeffner Ellen G. , Crowley Michael G. , Soulen Renate L.
Published: March 2007

Intraperitoneal gelatin sponge can mimic a mass lesion on magnetic resonance (MR) images. To determine the MR imaging characteristics of gelatin sponge over time, a 15 × 10 × 4‐mm piece of gelatin sponge soaked in saline was surgically implanted in the peritoneal cavity of 14 mice. Two mice underwent a sham operation. Contiguous axial spin‐echo images of the abdomen were obtained with T1‐weighted, spin‐density, and T2‐weighted sequences preoperatively and over a 6‐week period postoperatively. Gelatin sponge initially appears as a heterogeneous mass of low signal intensity on T1‐weighted images and increasing intensity on spin‐density and T2‐weighted images, containing multiple round foci of very low signal intensity, attributable to air, at all sequences. Over time, signal intensity further increases and becomes more homogeneous on spin‐density and T2‐weighted images, although foci of air persist to 3 weeks. By 2‐4 weeks, the mass is no longer discrete. Foci of air should help differentiate gelatin sponge from tumor and add gelatin sponge to the differential diagnosis of abscess.
Effects related to temperature changes during MR imaging
Authors: Panych Lawrence P. , Hrovat Mirko I. , Bleier Alan R. , Jolesz Ferenc A.
Published: March 2007

Magnetic resonance (MR) imaging has been proposed as a method of monitoring the interstitial laser heating of tissue for the clinical treatment of tumors (laser hyperthermia). The treatment causes considerable temperature changes over the time that image data are acquired, and therefore an analysis of the time‐dependent effects of heating is required. The problem is expressed mathematically, and computer‐simulated images are compared with those obtained from experimental heating and imaging of gel phantoms. Results show that at the rates of heating typical for laser hyperthermia and even with the relatively slow standard imaging techniques used, generation of artifact is not a major concern. It is also shown that a spatial spin signal magnitude distribution, evolving in time, is effectively sampled at the time to when the low‐numbered phase‐encoding steps are collected at to. It is noted, however, that substantial temperature changes during image data acquisition make accurate temperature determination difficult and place limits on MR imaging for quantitative spatial temperature mapping.
Quantitative MR signal behavior in cardiac cine loops as a function of heart rate
Authors: Duewell Stefan , Koch Manola , Wüthrich Ruedi , Stöhr Susanne , Jenni Rolf , von Schulthess Gustav K.
Published: March 2007

To evaluate the heart cycle‐dependent signal intensity changes in the cardiac chambers, the aorta, and the pulmonary artery, five healthy volunteers were studied with gradient‐echo magnetic resonance cine loops at different heart rates. Quantitative evaluation of signal intensity on each side of the cardiac valves showed that there were changes in signal intensity due to section‐entry and spin‐phase phenomena but none due to the increase in heart rate. The authors conclude that there is no heart rate‐dependent signal loss in healthy persons that simulates valvular dysfunction, thus suggesting that signal intensity change can be used as an indicator for this disease, independent of heart rate.
Comparison of MR imaging after barium administration with CT in pelvic disease
Authors: Langmo Lisa , Ros Pablo R. , Torres Gladys M. , Erquiaga Eugenio
Published: March 2007

The use of magnetic resonance (MR) imaging for evaluating the abdomen and pelvis has been limited by the lack of a suitable contrast agent. The purpose of this study was to compare axial MR imaging after rectal barium administration with computed tomography (CT) for delineation of normal anatomy and lesions of the pelvis. MR images and CT scans of 11 patients were studied retrospectively and independently by four radiologists. No substantial differ‐ences in the visualization of normal bowel, iliac vessels, lymph nodes, bladder, prostate, seminal vesicles, uterus, and cervix and in detection of abnormalities were seen between CT scans and axial MR images obtained after barium administration. This preliminary study suggests that axial MR imaging with rectal barium is a useful alternative to CT in evaluating pelvic disease.
Dynamic study of the upper airway with ultrafast spoiled GRASS MR imaging
Authors: Shellock Frank G. , Schatz Charles J. , Julien Peter M. , Silverman Jeffrey M. , Steinberg Fred , Foo Tom K. F. , Hopp Martin L. , Westbrook Philip R.
Published: March 2007

Dynamic magnetic resonance (MR) imaging of the upper airway was not possible previously because of poor temporal resolution. Recently, a rapid technique has been developed that provides the means to obtain multiple images at different section locations with sufficient image quality and temporal resolution to allow a comprehensive, dynamic study of the upper airway. The authors describe an ultrafast spoiled GRASS (gradient‐recalled acquisition in the steady state) pulse sequence for dynamic studies of the upper airway. The authors believe that this procedure has potential for identifying and characterizing upper airway abnormalities such as nonfixed occlusions and/or narrowings that may exist in patients with obstructive sleep apnea.
Phantom limb pain induced in amputee by strong magnetic fields
Authors: Yuh William T. C. , Fisher David J. , Shields Richard K. , Ehrhardt James C. , Shellock Frank G.
Published: March 2007

An amputee (traumatic) experienced increased phantom limb pain when exposed to the magnetic fields of two magnetic resonance imagers. With a visual analog scale used to measure pain, electric stimulation studies demonstrated that the residual limb was unusually sensitive to subthreshold (for muscle twitch) levels of current. The painful symptoms produced mimicked those experienced in the presence of the imagers.
An electrocardiograph‐respiration gating device for MR studies
Authors: Wong Wai‐Fan , Rokey Roxann , Wendt Richard E. , Wesley Vick G.
Published: March 2007

A versatile gating device for magnetic resonance (MR) spectroscopy and imaging is presented. The device uses electrocardiograph (ECG) and respiration signals as input, applies appropriate signal conditioning, and generates control signals for ECG, respiration, or combined gating studies. In the combined ECG and respiration mode, in conjunction with a proper MR pulse program, one can acquire MR data gated by the ECG signal within a selected window of the respiration cycle, while maintaining a steady level of magnetization saturation during the remainder of the respiration cycle, by gating the radio‐frequency excitation with the ECG while inhibiting data acquisition.
Gadolinium‐enhanced high‐resolution MR angiography with adaptive vessel tracking: Preliminary results in the intracranial circulation
Authors: Lin Weili , Haacke E. Mark , Smith Alison S. , Clampitt Mark E.
Published: March 2007

To overcome problems associated with poor contrast between vessels and background tissue in time‐of‐flight magnetic resonance angiography, the role of intravenous gadopentetate dimeglumine in conjunction with a postprocessing adaptive vessel tracking scheme was studied. Vessel tracking makes it possible to discriminate arteries from veins, to prevent problems associated with other bright tissues on maximum‐intensity projections, and to increase the signal‐to‐noise ratio. Short, asymmetric, velocity‐compensated field echoes were used in conjunction with high‐resolution imaging techniques to spatially discriminate between adjacent vessels and stationary background tissue. Gadopentetate dimeglumine was shown to be useful for visualization of small vessels, aneurysms, and regions of slow flow, when used with this post processing scheme.
MR angiography of lower‐extremity arterial disease: Preliminary experience
Authors: Yucel E. Kent , Dumoulin Charles L. , Waltman Arthur C.
Published: March 2007

Nineteen patients underwent magnetic resonance (MR) angiography for evaluation of lower‐extremity arterial disease. The underlying conditions included atherosclerotic occlusive disease in 12 patients, femoral or popliteal aneurysms in four, and bypass graft stenoses or occlusion in four. In the patients with occlusive disease, the iliac and femo‐ropopliteal vessels were classified as patent, moderately stenotic, severely stenotic, or occluded. Fifteen of 16 occlusions (accuracy = 94%) were correctly classified. In the one missed case, there was a long delay between MR angiography and x‐ray angiography and it is likely that the occlusion occurred during the interval. Three of five severe stenoses were correctly classified with MR angiography. In two cases of iliac artery stenosis, there was a signal void at the point of maximal stenosis, which on the basis of anatomic features could be recognized as severe stenosis rather than an occlusion. Three of four moderate stenoses were correctly classified. Correlation with x‐ray angiography or surgery demonstrated the ability of MR angiography to accurately depict the status of runoff vessels.
Quantitation of total metastatic tumor volume in the rat liver: Correlation of MR and histologic measurements
Authors: Mahmood Umar , Devitt Mary L. , Kocheril Paul G. , Sutanto‐Ward Erika , Ballon Douglas , Sigurdson Elin R. , Koutcher Jason A.
Published: March 2007

Assessing tumor response to chemotherapy in the liver has always been difficult. Most investigators estimate tumor volume as either a product of the two perpendicular diameters of a tumor nodule, or, in animal studies, simply count surface tumor nodules. The authors evaluated magnetic resonance (MR) imaging as a technique for determining absolute tumor volume in the liver in an animal model. Specifically, histologic volumetric and MR imaging measurements of tumor and liver volumes were quantitatively compared over a wide range of tumor burdens in a rat model of hepatic metastasis of a colorectal carcinoma. Twenty‐three rats were imaged, with two different section thicknesses used in each animal. Both section thicknesses showed highly significant correlations between MR and histologic measurements for both tumor and liver volumes (P <.001). MR imaging may be useful for noninvasively quantifying tumor burden and temporal response of metastatic disease in the liver to novel antineoplastic regimens.
Thin‐section MR imaging of rat brain at 4.7 T
Authors: Ting Yen‐Ling , Bendel Peter
Published: March 2007

The brains of anesthetized 7‐month‐old male hooded rats were imaged in coronal, sagittal, and horizontal planes at 4.7 T. Images were obtained with a section thickness of 0.6 mm and in‐plane pixel size of 0.18‐0.20 mm, resulting in finer combined spatial and contrast resolution than in most previously published reports. This allowed detailed anatomic assignment of many brain structures on the basis of comparison with a histologic brain atlas. T1, apparent T2, and water proton density values of gray matter, white matter, and cerebrospinal fluid (CSF) were derived from saturation‐recovery and multiecho measurements. These values were used to calculate expected contrast‐to‐noise ratios as a function of TR and TE in spin‐echo imaging sequences. The optimal simultaneous contrast between gray and white matter and between CSF and gray matter was obtained on images with moderate T2 weighting, with a TR of 3.6 seconds and a TE of 45 msec. The use of thin sections was found to be essential for resolving many fine structures, and the improved sensitivity provided by the high magnetic field strength was crucial for imaging such thin sections at adequate signal‐to‐noise ratios.
Gadolinium‐enhanced magnetization transfer contrast imaging of intracranial tumors
Authors: Kurki Timo J. I. , Niemi Pekka T. , Lundbom Nina
Published: March 2007

The magnetization transfer contrast (MTC) technique was used in low‐field‐strength (0.1 T) magnetic resonance (MR) imaging of 28 patients with intracranial tumors. MTC images were generated with an off‐resonance, low‐power radio‐frequency pulse applied during the interpulse delay period of a gradient‐echo partial‐saturation sequence (TR msec/TE msec = 200/20). Images in the presence and absence of the MTC pulse were concurrently acquired before and after injection of gadopen‐tetate dimeglumine at a dose of 0.1 mmol/kg. The contrast agent enhanced 27 of 28 tumors. Application of the MTC pulse improved the contrast‐to‐noise ratio (C/N) between tumor and normal white matter in 26 of 28 cases on the preinjection images and in 25 of 28 cases on the postinjection images. On the gadolinium‐enhanced images, the mean C/N was 2.6 ± 1.7 without the MTC pulse and 3.2 ± 1.9 with the MTC pulse. The greatest contrast improvement with the MTC technique was obtained in tumors showing the strongest paramagnetic enhancement. The results indicate that MTC can improve contrast between normal brain and some intracranial neoplasms. The use of gadopentetate dimeglumine generally intensified this effect.
Mechanisms of flow‐induced signal loss in MR angiography
Authors: Urchuk Steven N. , Plewes Donald B.
Published: March 2007

Mechanisms of signal loss in magnetic resonance angiography were studied with a stenotic flow phantom. The results indicate that while signal loss induced by mean fluid motions is localized about the stenosis, the fluctuating component of fluid motion induces signal loss over a much larger region, primarily distal to the stenosis. For both motion components, use of gradient moment nulling (GMN) above first order was found to be an ineffective means of reducing signal loss. In contrast, shortened gradient durations were found to reduce signal loss substantially. However, though a zeroth‐order gradient is generally of the shortest duration, use of a slightly longer, first‐order gradient was found to be the most robust means of reducing signal loss.
Monitoring of laser and freezinginduced ablation in the liver with T1‐weighted MR imaging
Authors: Matsumoto Reiko , Oshio Koichi , Jolesz Ferenc A.
Published: March 2007

During both interstitial laser ablation therapy and cryoablation therapy for liver tumors, real‐time monitoring is necessary for assessment of ongoing thermal effects in tissue. With single‐section images obtained every 30 seconds with a T1‐weighted RARE (rapid acquisition with relaxation enhancement) sequence, signal intensity changes in both ex vivo and in vivo animal liver were readily seen. The reversible loss of signal intensity that took place during laser irradiation and the increased intensity at the beginning of cooling can be explained mainly by altered T1 due to temperature change. The frozen area was seen as a sudden decrease in signal intensity at O°C due to a T2 decrease. This preliminary work showed that the protocol provides enough temporal and temperature resolution to accurately depict the extent of thermal damage, as confirmed at histologic examination. Signal intensity decreased Iinearly with temperature in the range 10°C–50°C, yielding a pixel‐to‐pixel temperature resolution of 5.37°C.
Chemical shift artifact along the section‐select axis
Authors: Wachsberg Ronald H. , Mitchell Donald G. , Rifkin Matthew D. , Vinitski Simon , Tasciyan Talin A.
Published: March 2007

Chemical shift artifact (CSA), familiar to radiologists along the frequency‐encoding axis, also occurs along the section‐select axis. The authors observed a case in which CSA mimicked a renal mass. Subsequent retrospective analysis of 50 abdominal magnetic resonance (MR) imaging studies was performed to assess occurrence of CSA adjacent to the upper and lower renal poles. CSA along the section‐select axis was observed in 76% of cases and adjacent to 39% of all renal poles imaged. CSA along the section‐select axis is common in abdominal MR imaging and may occasionally mimic disease.
Effects of acceleration on the accuracy of MR phase velocity measurements
Authors: Oshinski John N. , Ku David N. , Bohning Daryl E. , Pettigrew Roderic I.
Published: March 2007

Acceleration in blood flow can affect the accuracy of phase velocity measurements. Convective acceleration is due to changes in flow geometry and is independent of the time‐varying acceleration caused by flow pulsatility. To analyze the effects of convective acceleration on flow velocity measurements, phase velocity measurements were obtained in steady laminar flow in the convergent segment of a 90%, hourglass‐shaped stenosis phantom at a Reynolds number of 1,500. Measurements at the stenosis indicated that convective acceleration caused the measured values of average cross‐sectional velocity to deviate as much as 37% from the theoretical values. The magnitude of the error could be accounted for by including the convective acceleration term in the phase shift equation. Convective acceleration effects should not be ignored in flow velocity measurements through stenoses, even when time‐dependent acceleration due to flow pulsatility can be neglected.
Dynamic image reconstruction: MR movies from motion ghosts
Authors: Xiang Qing‐San , Henkelman R. Mark
Published: March 2007

It has been previously shown that an image with motion ghost artifacts can be decomposed into a ghost mask superimposed over a ghost‐free image. The present study demonstrates that the ghost components carry useful dynamic information and should not be discarded. Specifically, ghosts of different orders indicate the intensity and phase of the corresponding harmonics contained in the quasi‐periodically varying spin‐density distribution. A summation of the ghosts weighted by appropriate temporal phase factors can give a time‐dependent dynamic image that is a movie of the object motion. This dynamic image reconstruction technique does not necessarily require monitoring of the motion and thus is easy to implement and operate. It also has a shorter imaging time than point‐by‐point imaging of temporal variation, because the periodic motion is more efficiently sampled with a limited number of harmonics recorded in the motion ghosts. This technique was tested in both moving phantoms and volunteers. It is believed to be useful for dynamic imaging of time‐varying anatomic structures, such as in the cardiovascular system.
Improved cine MR imaging of left ventricular wall motion with gadopentetate dimeglumine
Authors: Pennell Dudley J. , Richard Underwood S. , Longmore Donald B.
Published: March 2007

The assessment of left ventricular wall motion with cine magnetic resonance imaging in the cardiac long axes is useful; however, image quality is limited by reduced signal intensity due to saturation of blood flowing predominantly in plane. Twenty subjects were studied to evaluate the effects of gado‐pentetate dimeglumine on contrast between blood and myocardium. Contrast improved significantly on contrast agent –‐ enhanced images in the long axes, at both end‐systole (vertical axis, +62%, P <.0001; horizontal axis, +67%, P <.0001) and end‐diastole (vertical axis, +50%,P <.0001; horizontal axis, +26%, P <.004). The increase in the short axis was less and significant only at end‐systole (+25%, P <.0001). Subjective scoring of the cines also showed a significant and clinically useful improvement in the long axes (P <.0001 for both) on contrast‐enhanced images. Improved contrast was most evident for 10 minutes after injection, but persisted for up to 20 minutes at end‐systole in the long axes. Gadopentetate dimeglumine is useful for cine imaging of left ventricular wall motion when saturation effects prevent adequate clinical assessment.
Contribution of oral magnetic particles in MR imaging of the abdomen with spin‐echo and gradient‐echo sequences
Authors: Boudghëne Frank P. , Bach‐Gansmo Torre , Grange Jean‐Didier , Lame Samuel , Nantois Christine , Wallays Claudy , Bigot Jean‐Michel
Published: March 2007

An open phase III clinical trial of the oral contrast agent OMP (oral magnetic particles) was performed in 35 patients undergoing abdominal magnetic resonance (MR) imaging at 1.5 T with axial spin‐echo and gradient‐echo sequences. The diagnostic efficacy of OMP was examined by comparing pre‐ and postcontrast images. Bowel loops and abdominal organs were more easily recognizable after OMP ingestion, and the general quality of the images was improved because of fewer bowel‐related artifacts. The diagnostic value of the postcontrast abdominal MR examination was superior or equal to that of the precontrast study, and additional information was obtained in 44% of the cases. Postcontrast gradient‐echo sequences increased confidence in the MR examination in 18% of cases. OMP was well tolerated and increased the quality and amount of diagnostic information acquired during the examination. Gradient‐echo imaging was found to be a useful complement, but the need for a reduction in susceptibility artifacts was apparent and indicates that a decrease in TE or the use of rapid spin‐echo sequences might be advantageous.
Status of liposomes as MR contrast agents
Authors: Unger Evan C. , Shen De‐Kang , Fritz Thomas A.
Published: March 2007

Recent work on the development of liposomal magnetic resonance (MR) contrast agents has yielded structures with higher overall relaxivity than that of other nanoparti‐cles of similar diameter. Liposomes incorporating membrane‐bound complexes of manganese (“memsomes”) produce greater hepatic enhancement per micromole of metal ion than either ferrite particles or paramagnetic chelates. Memsomes also hold promise for targeting of sites outside the liver. Work is in progress to take these agents into clinical trials.
Cirrhosis: Multiobserver analysis of hepatic MR imaging findings in a heterogeneous population
Authors: Mitchell Donald G. , Lovett Karen E. , Hann Hie‐Won L. , Ehrlich Saundra , Palazzo Juan , Rubin Raphael
Published: March 2007

To investigate the magnetic resonance (MR) imaging findings of hepatic cirrhosis and the potential of MR imaging in differentiating cirrhosis from other hepatic abnormalities, three observers with different levels of expertise in MR imaging (specialist, experienced radiologist, and novice with special training) reviewed hepatic MR imaging examinations of 52 patients with biopsy‐proved presence (n = 29) or absence (n = 23) of cirrhosis. All examinations included motion‐compensated T1‐weighted, T2‐weighted, and flow‐sensitive gradientecho images. For all three observers, linear signal irregularity was more accurate than other findings. For the final diagnosis of cirrhosis, the specialist was most sensitive (76% at high threshold, 97% at low threshold), followed by the novice with special training (31% and 79%, respectively). Specificity was 100% for all observers at high threshold and 78%, 96%, and 87% for expert, experienced, and trained novice observers, respectively, at low threshold. Sensitivity did not vary regardless of severity of fibrosis, as determined independently by a hepatopathologist. MR imaging has the potential of offering a comprehensive noninvasive evaluation of patients with suspected cirrhosis, but considerable expertise is required at present.
Optimization of submillimeter‐resolution MR imaging methods for the inner ear
Authors: Schmalbrock Petra , Brogan Martha A. , Chakeres Donald W. , Hacker Vicky A. , Ying Kui , Clymer Bradley D.
Published: March 2007

Submillimeter‐resolution magnetic resonance (MR) imaging of the inner ear is valuable for diagnosis and treatment planning. Its main advantage for investigations of underlying disease is that it can directly depict the fluid spaces of the membranous labyrinth rather than define only the bony canal, as does computed tomography. A systematic evaluation of factors influencing high‐resolution three‐dimensional (3D) gradient‐echo imaging of the inner ear with a standard clinical MR system is presented. This includes the evaluation of various radio‐frequency coils, the design of steady‐state pulse sequences, and the optimization of acquisition parameters. A quantitative analysis was facilitated by computer simulations and image processing. The highest signal‐to‐noise ratio for the membranous labyrinth was obtained with a single 3‐inch (7.6‐cm) receiver coil and a 3D GRASS (gradient‐recalled acquisition in the steady state) sequence with the minimal achievable TR msec/TE msec of 25/7 and a 40°–60° flip angle, which yielded acceptable images with minimal voxel volumes of 0.1 mm3 in 14 minutes.
MR imaging of blood oxygenation‐dependent changes in focal renal ischemia and transplanted liver tumor in rat
Authors: Vexler Vladimir S. , De Crespigny Alexander J. S. , Wendland Michael F. , Kuwatsuru Ryonei , Mühler Andreas , Brasch Robert C. , Moseley Michael E.
Published: March 2007

The potential of using fast magnetic resonance (MR) imaging in conjunction with apnea‐induced blood deoxygenation for the noninvasive monitoring of relative perfusion in the rat abdomen has been studied with two experimental models: glycer‐ol‐induced focal renal ischemia and transplanted liver tumor. Gradient‐echo echo‐planar imaging (GRE‐EPI) (TE of 20 msec at 2 T) of liver and kidney was performed before, during, and after a 60‐second apnea episode and then was followed in the same rat by contrast‐enhanced (a) GRE‐EPI and (b) T1‐weighted spin‐echo imaging (TR msec/TE msec = 200/6) with polylysine‐(gadolmium‐DTPA [diethylenetriaminepentaacetic acid]). The results indicate that a noninvasive vascular challenge due to apnea can be used for the detection of focal tissue perfusion abnormalities in rat kidney and liver tumor.
MR imaging of Ho:YAG laser diskectomy with histologic correlation
Authors: Phillips Jeffrey J. , Kopchok George E. , Peng Shi‐Kaung , Mueller Mark P. , White Rodney A.
Published: March 2007

Twelve cadaveric vertebral specimens were imaged after holmium yttrium aluminum garnet (Ho:YAG) laser diskectomy to determine the usefulness of magnetic resonance (MR) imaging in evaluating treatment outcome. The Ho:YAG laser was operated at 1.0‐2.0 J per pulse, 5 Hz, and 250‐usec pulse width. The total energy varied between 600 and 2,700 J. Two distinct patterns emerged on MR images. Tissue ablation at higher power (1.5 and 2.0 J per pulse) produced discrete signal voids that correlated with areas of laser‐induced ablation identified at gross inspection. More subtle changes, characterized by a high‐signal‐intensity ring, were seen in the specimens lased at 1.0 J per pulse. The latter appearance corresponded to incomplete vaporization of diskal tissue, a broader zone of minimal thermal injury, and sparing of adjacent vertebral endplates. Total mass loss did not appear to be affected by the choice of power setting (1.0 vs 1.5 J per pulse), with total laser energy held constant.
Semiautomated method for noise reduction and background phase error correction in MR phase velocity data
Authors: Walker Peter G. , Cranney Gregory B. , Scheidegger Markus B. , Waseleski Gena , Pohost Gerald M. , Yoganathan Ajit P.
Published: March 2007

Background phase distortion and random noise can adversely affect the quality of magnetic resonance (MR) phase velocity measurements. A semiauto‐mated method has been developed that substantially reduces both effects. To remove the background phase distortion, the following steps were taken: The time standard deviations of the phase velocity images over a cardiac cycle were calculated. Static regions were identified as those in which the standard deviation was low. A flat surface representing an approximation to the background distortion was fitted to the static regions and subtracted from the phase velocity images to give corrected phase images. Random noise was removed by setting to zero those regions in which the standard deviation was high. The technique is demonstrated with a sample set of data in which the in‐plane velocities have been measured in an imaging section showing the left ventricular outflow tract of a human left ventricle. The results are presented in vector and contour form, superimposed on the conventional MR angiographic images.
Characterization of focal fatty change in the liver with a fat‐enhanced inversion‐recovery sequence
Authors: Kane Arthur G. , Redwine Michael D. , Cossi Alda F.
Published: March 2007

A T1‐weighted inversion‐recovery (IR) sequence was used to study 15 patients with possible fatty change in the liver. The inversion time (TI) was calculated for optimal suppression of normal liver signal (t‐null). Conventional spin‐echo (SE) and short TI IR (STIR) sequences were also performed. For seven documented benign focal fatty liver lesions, the T1‐weighted IR (fatenhanced)sequence clearly enabled differentiation of normal from fat‐infiltrated liver, whereas three of these lesions were isointense to normal liver with all other sequences. The livers of the other nine patients (two normal, one with diffuse fatty change, two with metastatic disease, one with hemangioma, one with focal nodular hyperplasia, one with simple cyst, and one with micronodular cirrhosis) showed homogeneous reduction of liver signal with the fat‐enhanced IR sequence.
MR imaging of muscle and tender points in fibromyalgia
Authors: Kravis Marc M. M. , Munk Peter L , McCain Glenn A. , Dale Vellet A. , Levin Morris F.
Published: March 2007

Fibromyalgia is a syndrome manifested by chronic, diffuse muscu‐loskeletal aching and soreness, palpable muscle tender points, and other symptoms. Standardized clinical diagnostic criteria have recently been developed. Skeletal muscle has been postulated as the end organ in this disease. Biochemical, histologic, electromyographic, and conventional radiographic studies have demonstrated no definitive abnormality. This study sought to establish whether magnetic resonance (MR) imaging could demonstrate any abnormality in these patients. Eighteen patients were entered in the study, 14 of whom were able to complete their examinations. T1 ‐weighted, T2‐weighted, gradient‐echo, and STIR (short‐tau inversion‐recovery) sequences were performed in all patients, with selected patients examined with T1weighted, gadopentetate dimeglu‐mine‐enhanced sequences. The trapezius and suboccipital regions were imaged in patients who, clinically, had active fibro‐myalgia. No abnormalities could be detected. The authors conclude that the conventional MR imaging used in this study was unable to depict any primary skeletal muscle abnormality in fibromyalgia.