bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractA 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

AbstractA 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

AbstractT1 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

AbstractTo 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

AbstractMagnetic 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

AbstractFirst‐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

AbstractParamagnetic 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

AbstractThe 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.
Pulsed magnetization transfer versus continuous wave irradiation for tissue contrast enhancement
Authors: Schneider Erika , Prost Robert W. , Glover Gary H. 
Published: March 2007

AbstractPulsed magnetization transfer and continuous wave irradiation techniques are analyzed and compared for saturation efficiency and radio‐frequency (RF) power requirements at 1.5 and 0.5 T. Binomial RF pulses transmitted on resonance are a more power‐efficient method of exciting saturation transfer and are easily implemented with any pulse sequence. Binomial pulses selectively excite all short T2 species and behave as 0° pulses for on‐resonance, long T2 species.
Overlapping section coverage in multisection imaging
Authors: Hennig Jürgen 
Published: March 2007

AbstractA method is proposed in which the section position for two‐dimensional Fourier transform multisection imaging is advanced from one phase‐encoding step to the next, so that information is sampled continuously over the total volume under observation. This “ramp scan”technique allows reconstruction of images from any arbitrary position within the sampled volume. The imaging properties depend strongly on the order of distribution of phase‐encoding steps to the different section positions. In practice, images are reconstructed at each nominal position of a multisection experiment, plus at each position halfway between sections. The volume under study is thus represented by overlapping sections. The gaps between sections that arise in conventional multisection imaging‐even with optimized pulse shapes‐are thus avoided. This approach is applicable not only to conventional spin‐echo imaging but to other techniques such as RARE (rapid acquisition with relaxation enhancement) and gradient‐echo and echo‐planar imaging.
Conventional and fast spin‐echo MR imaging: Minimizing echo time
Authors: Vinitski Simon , Mitchell Donald G. , Einstein Steven G. , Rao Vijay M. , Flanders Adam E. , Schweitzer Mark E. , Listerud John , Schnall Mitchell D. 
Published: March 2007

AbstractMagnetic resonance imaging is frequently complicated by the presence of motion and susceptibility gradients. Also, some biologic tissues have short T2s. These problems are particularly troublesome in fast spin‐echo (FSE) imaging, in which T2 decay and motion between echoes result in image blurring and ghost artifacts. The authors reduced TE in conventional spin‐echo (SE) imaging to 5 msec and echo spacing (E‐space) in FSE imaging to 6 msec. All magnetic gradients (except readout) were kept at a maximum, with data sampling as fast as 125 kHz and only ramp waveforms used. Truncated sine radio‐frequency pulses and asymmetric echo sampling were also used in SE imaging. Short TE (5.8 msec) SE images of the upper abdomen were compared with conventional SE images (TE =11 msec). Also, FSE images with short E‐space were compared with conventional FSE images in multiple body sites. Short TE significantly improved the liver‐spleen contrast‐to‐total noise ratio (C/N) (7.9 vs 4.1, n = 9, P <.01) on T1‐weighted SE images, reduced the intensity of ghost artifacts (by 34%, P <.02), and increased the number of available imaging planes by 30%. It also improved delineation of cranial nerves and reduced susceptibility artifacts. On short E‐space FSE images, spine, lung, upper abdomen, and musculoskeletal tissues appeared crisper and measured spleen‐liver C/N increased significantly (6.9 vs 4.0, n = 12, P <.01). The delineation of tissues with short T2 (eg, cartilage) and motion artifact suppression were also improved. Short TE methods can improve image quality in both SE and FSE imaging and merit further clinical evaluation.
Pulsed magnetization transfer spin‐echo MR imaging
Authors: Bruce Pike G. , Glover Gary H. , Hu Bob S. , Enzmann Dieter R. 
Published: March 2007

AbstractCross relaxation between macromolecular protons and water protons is known to be important in biologic tissue. In magnetic resonance (MR) imaging sequences, selective saturation of the characteristically short T2 macromolecular proton pool can produce contrast called magnetization transfer contrast, based on the cross‐relaxation process. Selective saturation can be achieved with continuous wave irradiation several kilohertz off resonance or short, intense 0° pulses on resonance. The authors analyze 0° binomial pulses for T2 selective saturation, present design guidelines, and demonstrate the use of these pulses in spin‐echo imaging sequences in healthy volunteers and patients. Using the phenomenologic Bloch equations modified for two‐site exchange, the authors derive the analytic expressions for water proton relaxation under periodic pulsed saturation of the macromolecular protons. This relaxation is shown to be monoexpo‐nential, with a rate constant dependent on the saturation pulse repetition rate and the individual and cross‐relaxation rates.
Coupled‐spin fast spin‐echo MR imaging
Authors: Todd Constable R. , Smith Robert C. , Gore John C. 
Published: March 2007

AbstractDistinguishing between lipid and water‐containing tissues is clinically important. Current techniques rely on the chemical shift difference between fat and water resonances or differences in relaxation times of the tissues, or a combination of both. A method is presented for separating the signals of lipid protons from those of water protons by using fast spin‐echo magnetic resonance imaging based on the principle that lipid protons behave differently from water protons in mul‐tiecho sequences. Two images are acquired with different echo train lengths and echo spacing but with identical TEs, and then subtracted to exploit differences in the behavior of lipid and water protons in mul‐tiecho sequences. The method is insensitive to B0 inhomoge‐neities or susceptibility effects and provides separate lipid and water images with a high signal‐to‐noise ratio. The advantages of the method are demonstrated with phantom studies and clinical examples.
Renal cancer staging: Comparison of contrast‐enhanced CT and gadolinium‐enhanced fat‐suppressed spin‐echo and gradient‐echo MR imaging
Authors: Semelka Richard C. , Patrick Shoenut J. , Magro Cynthia M. , Kroeker Mervyn A. , Macmahon Ross , Greenberg Howard M. 
Published: March 2007

AbstractFifty‐three consecutive patients with 61 solid or complex non‐fat‐containing renal masses compatible with renal cancer were examined with contrast‐enhanced computed tomography (CT) and magnetic resonance (MR) imaging with pre‐ and postcontrast FLASH (fast low‐angle shot) and fat‐suppressed spin‐echo sequences. CT and MR imaging were performed within a 1‐month interval. CT and MR images were prospectively interpreted. Tumor detection and staging were determined in all patients. CT and MR imaging enabled detection of 54 and 58 of 61 renal tumors, respectively. CT and MR imaging showed 34 and 35 of 38 histologically proved renal tumors, respectively, in 31 patients. Tumor size on CT and MR images demonstrated good correlation and correlated well with the size of pathologic specimens of 34 of 38 resected tumors detected with CT and MR imaging (r =.99). Of the 31 tumors in 31 patients who underwent surgical resection, 24 were correctly staged with CT and 29 with MR imaging. CT and MR imaging both enabled correct staging of four of five additional tumors with biopsy proof of tumor stage. A moderate difference in staging was observed between CT and MR imaging (P =.05). CT showed 13 and MR imaging 15 of 15 tumor thrombi. CT and MR imaging both showed 11 of 11 cases of adenopathy. The results suggest that MR imaging is moderately better than CT for the detection and staging of renal cancer.
“Keyhole” method for accelerating imaging of contrast agent uptake
Authors: Van Vaals Joop J. , Brummer Marijn E. , Thomas Dixon W. , Tuithof Hans H. , Engels Hans , Nelson Rendon C. , Gerety Brigid M. , Chezmar Judith L. , Den Boer Jacques A. 
Published: March 2007

AbstractMagnetic resonance (MR) imaging methods with good spatial and contrast resolution are often too slow to follow the uptake of contrast agents with the desired temporal resolution. Imaging can be accelerated by skipping the acquisition of data normally taken with strong phase‐encoding gradients, restricting acquisition to weak‐gradient data only. If the usual procedure of substituting zeros for the missing data is followed, blurring results. Substituting instead reference data taken before or well after contrast agent injection reduces this problem. Volunteer and patient images obtained by using such reference data show that imaging can be usefully accelerated severalfold. Cortical and medullary regions of interest and whole kidney regions were studied, and both gradientand spin‐echo images are shown. The method is believed to be compatible with other acceleration methods such as half‐Fourier reconstruction and reading of more than one line of k space per excitation.
Comparison of cerebral artery blood flow measurements with gated cine and ungated phase‐contrast techniques
Authors: Enzmann Dieter R. , Marks Michael P. , Pelc Norbert J. 
Published: March 2007

AbstractCine phase‐contrast (PC) magnetic resonance (MR) pulse sequences have been used to measure blood flow in a variety of vessels. Because the cine PC sequence is time‐consuming, this prospective study was undertaken to compare it with an ungated PC technique for measuring average blood flow in individual cerebral arteries to potentially achieve substantial time savings. The following cerebral arteries were studied in 10 healthy volunteers: carotid, basilar, middle cerebral, anterior cerebral, and posterior cerebral. Imaging planes were placed perpendicular to the vessel of interest, and velocity encoding, ranging from 40 to 250 cm/sec, was matched to individual arteries. Good correlation between cine and ungated PC blood flow measurements was obtained for both high‐ and low‐flow vessels, with an overall correlation coefficient of 978. The ungated PC sequence, because of its short imaging time, allows measurement of the blood volume flow rate in the circle of Willis in approximately 20 minutes, a clinically acceptable time.
Localized proton MR spectroscopy of the brain in children
Authors: Tzika A. Aria , Vigneron Daniel B. , Ball William S. , Dunn R. Scott , Kirks Donald R. 
Published: March 2007

AbstractSmall‐voxel (3.0–8.0 cm3), magnetic resonance (MR) imaging–guided proton MR spectroscopy was performed in 54 patients (aged 6 days to 19 years) with intracranial masses (n = 16), neurodegenerative disorders (n = 34), and other neurologic diseases (n = 4) and in 23 age‐matched control subjects without brain disease. A combined short TE (18 msec) stimulatedecho acquisition mode (STEAM) and long TE (135 and/or 270 msec) spin‐echo point‐resolved spatially localized spectroscopy (PRESS) protocol, using designed radio‐frequency pulses, was performed at 1.5 T. STEAM spectra revealed short T2 and/or strongly coupled metabolites; prominent resonances were obtained from N‐acetyl aspartate (NAA), choline‐containing compounds (Cho), and total creatine (tCr). Lactate was well resolved with the long TE PRESS sequence. Intracranial tumors were readily differentiated from cerebrospinal fluid (CSF) collections. All tumors showed low NAA, high Cho, and reduced tCr levels. Neurodegenerative disorders showed low or absent NAA levels and enhanced mobile lipid, glutamate and glutamine, and inositol levels, consistent with neuronal loss, gliosis, demyelination, and amino acid neuro‐toxicity. Preliminary experience indicates that proton MR spectroscopy can contribute in the evaluation of central nervous system abnormalities of infants and children.
First pass of an MR susceptibility contrast agent through normal and ischemic heart: Gradient‐recalled echo‐planar imaging
Authors: Wendland Michael F. , Saeed Maythem , Masui Takayuki , Derugin Nikita , Higgins Charles B. 
Published: March 2007

AbstractGradient‐recalled echo‐planar magnetic resonance (MR) imaging was used to monitor the first pass of a magnetic susceptibility contrast agent through the heart of normal rats and rats subjected to 60‐minute occlusion of the anterior branch of the left main coronary artery. Each animal (six normal and six ischemic) received four doses (0.05, 0.1, 0.15, and 0.2 mmol/kg) of Dy‐DTPA‐BMA [diethylenetriaminepentaacetic acid–bis(methylamide)] administered as a bolus volume of 1.0 mL/kg. In both normal and ischemic rats, signal intensity in nonischemic myocardium was reduced by the contrast agent in a dose‐dependent manner. Signal intensity in the ischemic zone was reduced much less, so that at a contrast agent dose of 0.1 mmol/kg or greater the ischemic zone was clearly defined as a high‐intensity zone on echo‐planar images. Plots of the change in the apparent T2* relaxation rate (ΔR2*) during the peak bolus effect versus injected dose were well fit by straight lines for normal, nonischemic, and ischemic myocardium but not for blood in the left ventricle. No difference was seen between myocardial response in normal animals and in nonischemic regions in animals with coronary artery occlusion. These findings suggest that the contrast agent–induced changes in tissue T2* are monoexponential and support the idea that data derived from contrast transit studies may be useful for calculation of myocardial blood flow.