bluuebunny/crossref_metadata_2025_split huggingface dataset:
Three‐dimensional fast spin‐echo imaging: Pulse sequence and in vivo image evaluation
Authors: Yuan Chun , Schmiedl Udo P. , Weinberger Edward , Krueck Wolfgang R. , Rand Scott D. 
Published: March 2007

AbstractThree‐dimensional (3D) magnetic resonance imaging allows thin‐section acquisition and therefore more accurate multiplanar reconstruction than conventional two‐dimensional spin‐echo imaging. Unfortunately, addition of a third acquisition plane extends imaging time greatly. With gradient‐echo techniques, 3D acquisitions have become clinically useful. These techniques are limited, however, by susceptibility and other field inhomogeneity artifacts and decreased signal‐to‐noise ratios compared with spin‐echo techniques. The authors describe implementation of a true spin‐echo 3D technique that, by using fast spin‐echo parameters, reduces acquisition time to a clinically useful level. Potential applications of the technique are demonstrated.
MR imaging and proton spectroscopy of the brain in posttraumatic cortical blindness
Authors: Felber Stephan R. , Ettl Armin R. , Birbamer Günther G. , Luz Gaby , Aichner Franz T. 
Published: March 2007

AbstractMagnetic resonance (MR) imaging and localized proton MR spectroscopy of the occipital lobes were performed in a patient with cortical blindness following brain trauma. Computed tomography (CT) scans and MR images of the visual cortex were normal in the acute stage. Six weeks after the trauma, MR images showed cortical lesions in both occipital lobes, while the spectra showed elevated lactate and decreased N‐acetyl aspartate levels relative to those of healthy volunteers. One year later, visual acuity had improved and follow‐up studies revealed an increase in the ratios of N‐acetyl aspartate to choline and creatine. These results demonstrate that parenchymal lesions may develop in brain regions that appear normal at CT and MR imaging during the acute stage after trauma. Metabolic changes can be observed in these areas by means of localized proton MR spectroscopy.
Techniques for high‐resolution MR imaging of atherosclerotic plaque
Authors: Yuan Chun , Tsuruda Jay S. , Beach Kirk N. , Hayes Cecil E. , Ferguson Marina S. , Alpers Charles E. , Foo Thomas K. , Strandness D. Eugene 
Published: March 2007

AbstractAtherosclerotic cardiovascular disease is the most common cause of death in the United States. Investigation of atherosclerotic plaque morphology and composition is important because the findings may be useful in predicting prognosis or response to therapy. This study presents high‐resolution magnetic resonance (MR) imaging techniques developed on a 1.5‐T whole‐body imager with a custom‐built surface coil, for characterizing the composition and morphology of plaque removed at carotid endarterectomy. The initial comparison of MR imaging and histologic results showed good correlation. In conjunction with MR angiography, these techniques could be used in in vivo imaging to define the size, location, and contents of atherosclerotic plaque at the carotid bifurcation.
Hybrid RARE: Implementations for abdominal MR imaging
Authors: Mitchell Donald G. , Outwater Eric K. , Vinitski Simon 
Published: March 2007

AbstractHybrid RARE (rapid acquisition with relaxation enhancement) is a family of magnetic resonance (MR) imaging techniques whereby a set of images is phase encoded with more than one spin echo per excitation pulse. This increases the efficiency of obtaining T2‐weighted images, allowing greater flexibility regarding acquisition time, resolution, signal‐to‐noise ratio, and tissue contrast. Hybrid RARE techniques involve several important new user‐selectable parameters such as effective TE, echo train length, and echo spacing. Choices of other parameters, such as TR, sampling bandwidth, and acquisition matrix, may be different from those of comparable conventional T2‐weighted spin‐echo images. Different hybrid RARE implementations can be used for abdominal screening, with T2‐weighted or T2‐weighted and inversion‐recovery contrast, or for characterizing liver lesions or imaging the biliary system with an extremely long TE. High‐resolution images may be obtained by averaging multiple signals during quiet breathing, or images may be acquired more rapidly during suspended respiration. In this review, the authors discuss the basic principles of hybrid RARE techniques and how various imaging parameters can be manipulated to increase the quality and flexibility of abdominal T2‐weighted MR imaging.
Blood flow measurements in the aorta and major arteries with MR velocity mapping
Authors: Bogren Hugo G. , Buonocore Michael H. 
Published: March 2007

AbstractThe purpose of this study was to measure antegrade and retrograde flow in the aorta and the major arterial pathways in the body noninvasively with cine magnetic resonance (MR) velocity mapping, to determine the hemodynamic significance of retrograde flow in arteries. Two hundred forty cine velocity maps for blood flow measurements were obtained at 29 sites in the aorta and the major arteries in 31 healthy human subjects of varying age at rest. Synchronous or isolated antegrade and retrograde flow was found in the entire aorta and in arteries supplying muscles. No retrograde flow was found in arteries supplying internal organs, such as the internal carotid or splanchnic arteries. The retrograde flow in the aorta and the extremity arteries contributes substantially to supplying diastolic perfusion of internal organs such as the heart, brain, and kidneys. Antegrade flow tends to be helical in the thoracic aorta.
Retrospective registration of X‐ray angiograms with MR images by using vessels as intrinsic landmarks
Authors: Alperin Noam , Levin David N. , Pelizzari Charles A. 
Published: March 2007

AbstractConventional x‐ray angiography (XRA) images are projections of the vasculature with high spatial and temporal resolution, while magnetic resonance (MR) angiography (MRA) and MR imaging data show the three‐dimensional locations of vessels relative to brain parenchyma. The authors have developed a retrospective method of registering these studies, which makes it practical to produce multimodality displays of this complementary information. Registration was performed by matching vessels seen on both XRA and MRA images. First, the authors determined the coordinates of the center lines of a few “landmark” vessels on the XRA image and the three‐dimensional locations of the corresponding intraluminal voxels in the MRA volume. Registration was performed by rotating and translating the MRA–MR imaging volume until the perspective projection of the MRA landmark vessels matched the corresponding vessel center lines on the XRA image. Experiments with phantoms and patients indicated that the two studies were registered with an average error of less than 2 mm. A linked‐cursor display was developed to show correspondence between points on the registered XRA and MRA‐MR images.
Evaluation of loose bodies in the elbow with MR imaging
Authors: Quinn Stephen F. , Haberman Joseph J. , Fitzgerald Steven W. , Traughber Paul D. , Belkin Rod I. , Murray William T. 
Published: March 2007

AbstractThe evaluation of loose bodies in the elbow is usually done by means of clinical examination, radiography, and postarthrographic computed tomography (CT). The authors review their experience with magnetic resonance (MR) imaging in place of postarthrographic CT for the evaluation of loose bodies in the elbow. The prospective interpretation of MR studies of the elbow in 20 patients was compared with arthroscopic findings. All elbows were imaged in multiple planes with thin sections, surface coils, and combinations of T1, T2, and proton‐density weighting. The sensitivity for showing loose bodies with MR imaging was 100%, and the specificity was 67%. Because this was a nonblinded study, the results are biased and caution must be used when extrapolating these results to the general population. In this limited experience, MR imaging has reliably shown loose bodies in the elbow, and in the authors' institutions has replaced postarthrographic CT for that purpose.
Increased self‐diffusion of brain water in normal aging
Authors: Gideon Peter , Thomsen Carsten , Henriksen Ole 
Published: March 2007

AbstractWith magnetic resonance (MR) imaging, brain water self‐diffusion was measured in 17 healthy volunteers 22–76 (mean, 44.6) years old. The calculated values for the apparent diffusion coefficients (ADCs) ranged from 0.58 × 10−9 to 1.23 × 10−9 m2/sec in cerebral white matter. A significant correlation was found between the ADC in white matter and age (r =.7069, P <.01). The calculated values for ADC in cortical gray matter ranged from 1.06 × 10−9 to 1.72 × 10−9 m2/sec no correlation was found between ADCs in gray matter and age. The increased ADC in white matter may be caused by an increase in the extracellular volume due to age‐dependent neuronal degeneration or to changes in myelination. These findings have implications for future clinical investigations with diffusion MR imaging techniques in patients with neurologic diseases, and stress the importance of having an agematched group of healthy volunteers for comparison.
Ex vivo evaluation of ferromagnetism and artifacts of cardiac occluders exposed to a 1.5‐T MR system
Authors: Shellock Frank G. , Morisoli Stacy M. 
Published: March 2007

AbstractMagnetic resonance (MR) procedures are contraindicated for patients with certain ferromagnetic biomedical implants, primarily owing to the risk of movement or dislodgment of the implants by the static magnetic field. An additional concern is the amount of artifact that the implant produces, which can affect image quality and interpretation of the examination. Therefore, an ex vivo assessment of ferromagnetism and artifact was conducted for 12 different occluders used to treat patients with patent ductus arteriosus, atrial septal defects, and ventricular septal defects, in a 1.5‐T MR system. Seven of the occluders, made of 304 stainless steel, were ferromagnetic and displayed deflection forces of 248–299 dynes. Five of the implants, made of MP35n, were nonferromagnetic. Artifacts were variable and depended primarily on the type and amount of metal used to construct the implant. The authors conclude that patients with ferromagnetic cardiac occluders may undergo MR procedures approximately 6 weeks after placement of these devices, to allow tissue growth to provide additional retentive force. After this time, it is highly unlikely that the magnetic fields associated with a 1.5‐T MR system are capable of moving or dislodging any of these cardiac occluders.
Three‐dimensional steady‐state MR angiography of the lower extremities
Authors: Schmalbrock Petra , Hacker Vicky A. , Rao Anita 
Published: March 2007

AbstractVolume steady‐state black‐blood magnetic resonance imaging was evaluated as a method for depicting lower extremity vasculature. In steady‐state imaging, flow has low signal intensity because motion destroys the coherence of transverse magnetization. To optimize image contrast, computations and measurements were obtained for the three‐dimensional (3D) GRASS (gradient‐recalled acquisition in the steady state) and 3D SSFP (steady‐state free precession) sequences and a range of TRs and flip angles to determine optimal vessel‐muscle contrast. The best results were achieved with a 3D GRASS sequence with a TR msec/TE msec of 25/5 and a flip angle of 30°. Coronal images of the femoral and popliteal vessels were obtained in healthy volunteers with various fields of view and voxel sizes. Inflow of unsaturated spins from outside the image region, yielding high signal intensity, could be a potential drawback in steady‐state black‐blood imaging; however, problems can be avoided by using coronal acquisitions and large fields of view. Steady‐state black‐blood imaging depicts vessels with high accuracy and is faster and free of flow artifacts.
Prolonged positive contrast enhancement with Gd‐EOB‐DTPA in experimental liver tumors: Potential value in tissue characterization
Authors: Ni Yicheng , Marchal Guy , Yu Jie , Mühler Andreas , Lukito Gregorius , Baert Albert L. 
Published: March 2007

AbstractTo evaluate the potential of the hepatobiliary magnetic resonance (MR) imaging contrast agent gadolinium EOB‐DTPA (ethoxybenzyl diethylenetria‐minepentaacetic acid) for the characterization of hepatic tumors, 79 primary and six implanted hepatomas in 38 rats were studied. MR imaging findings after administration of Gd‐DTPA (0.3 mmol/kg) and Gd‐EOB‐DTPA (30 μmol/kg) were correlated with microangiographic and histologic findings. Gd‐EOB‐DTPA produced a strong liver enhancement, which caused prompt negative contrast enhancement (CE) in all implanted hepatomas and in 77 of 79 primary hepatomas. A positive CE that lasted up to 2 hours was found in two of 79 primary hepatomas, both of which were highly differentiated (grade I) hepatocellular carcinomas (HCCs). The rest were moderately differentiated to undifferentiated HCCs (grades II‐IV). Rim enhancement, which corresponded histologically to peritumoral malignant infiltration sequestering normal hepatocytes, was seen around all implanted and some primary hepatomas. Positive tumor CE after administration of Gd‐EOB‐DTPA in this study is much less frequent but much more specific in comparison with the results of previous studies with manganese‐DPDP (N, N′‐dipyridoxylethylenediamine‐N,N′‐diacetate 5,5′‐bis[phosphate]). These findings may help further discriminate hepatic tumors.
Measurement of renal transit of gadopentetate dimeglumine with echo‐planar MR imaging
Authors: Wolf Gerald L. , Hoop Bernard , Cannillo John A. , Rogowska Jadwiga A. , Halpern Elkan F. 
Published: March 2007

AbstractTimes of peak gadolinium concentration ([Gd]) after intravenous (IV) and left ventricular (LV) bolus injection of gadopentetate dimeglumine were determined in renal cortex and medulla in normal rabbits and in rabbits after saline load (overhydration) or hemorrhage (dehydration). Magnetic resonance images were obtained with echo‐planar inversion‐recovery sequences, and signal intensity‐versus‐time curves in cortical and medullary regions of interest were converted to [Gd]‐versus‐time curves. Cortical perfusion measured with microspheres demonstrated that the three physiologic states were significantly different. There were three separate [Gd] peaks in both the cortex and medulla as the bolus moved from one anatomic compartment to the next. The first cortical peak occurred sooner after LV than after IV bolus injection (P <.05) and later in dehydrated than in normal and overhydrated rabbits (P <.05). The first medullary peak always followed the first cortical peak by about 6–10 seconds and mirrored the cortical patterns. The second and third cortical peaks were consistent with proximal and distal tubular transit. These peaks similarly showed faster response to LV than IV injection and were delayed by hemorrhage. The authors conclude that quantitative physiologic information can be obtained with dynamic contrast‐enhanced MR imaging of the kidney.
Efficacy evaluation of gadoteridol for MR angiography of intracranial vascular lesions
Authors: McLachlan Stuart J. , Francisco John C. , Pernicone Joseph R. , Hasso Anton N. 
Published: March 2007

AbstractA phase III multicenter study was conducted in 89 patients with known intracranial vascular lesions to evaluate an extracellular gadolinium contrast agent, gadoteridol, for intracranial magnetic resonance (MR) angiography. The pre‐ and postcontrast MR angiograms of 82 patients were evaluated by the unblinded investigators and by two blinded readers (A and B) for visualization of lesions; arterial and venous anatomy; extent, size, and number of lesions; and disease classification. The unblinded readers indicated that lesions were visualized better on postcontrast images in the following categories: venous anatomy, 87 (81%) of 107 lesions; arterial anatomy, 43 lesions (40%); and extent or size of lesions, 38 lesions (36%). In 29 (35%) of 82 patients, the unblinded readers determined that enhanced MR angiography provided more diagnostic information than unenhanced MR angiography. The blinded readers determined that enhanced MR angiography provided more information for visualization of vascular anatomy in more than 60% of cases. The additional information provided with gadoteridol would have changed the diagnosis in nine (8%) of 107 lesions seen by the unblinded readers, 11 (12%) of 90 lesions seen by reader A, and three (3%) of 93 lesions seen by reader B. The results confirm that the use of gadoteridol improves the visualization of intracranial vascular lesions with MR angiography. The authors conclude that development of new postprocessing algorithms will improve the utility of contrast‐enhanced MR angiography.
Dynamic contrast‐enhanced MR imaging assessment of vascularized free fibular grafts
Authors: Lomasney Laurie M. , Madden John F. , Rizk Wagdy S. , Hedlund Lawrence W. , Martinez Salutorio , Coleman Robert E. , Richardson William J. , Sostman H. Dirk 
Published: March 2007

AbstractMagnetic resonance (MR) imaging may be a noninvasive method for assessing perfusion of vascularized bone grafts placed for treatment of avascular necrosis. One proximal femur of seven beagles was devascularized, with insertion of a vascularized fibular graft. MR imaging at 1 week (seven dogs) and 6 weeks (five dogs) after surgery included pre‐ and postcontrast spin‐echo sequences, unenhanced twodimensional time‐of‐flight (TOF) vascular imaging, and dynamic gradient‐echo imaging during infusion of gadolinium. Relative signal intensity values of selected regions obtained from the dynamic gradientecho images were plotted as percent enhancement versus time. In the operated hip, MR imaging did not show enhancement in six of seven femoral heads and greater trochanters at 1 week after surgery, with similar results after 6 weeks. MR imaging of fibular grafts 6 weeks after surgery showed an initial rapid increase in enhancement and a subsequent slower increase in five of five dogs, although no enhancement was seen in six of seven dogs at 1 week. These findings contrasted with a rapid initial increase in enhancement followed by slow decline in non‐operated hips. Two‐dimensional TOP imaging did not show the vascular pedicle of the graft in any dog. Findings of radionuclide bone scanning performed 1 week after surgery were consistent with devascularization of the operated femur and fibular graft. However, tetracycline distribution and histologic findings confirmed the viability of five of five grafts within the devascularized femurs 6 weeks after surgery. Thus, dynamic contrast‐enhanced MR imaging at 6 weeks after surgery is valuable for assessing vascular bone graft perfusion, while similar imaging at 1 week may suggest otherwise.
MR imaging of soft‐tissue masses: Role of gadopentetate dimeglumine
Authors: Benedikt Richard A. , Jelinek James S. , Kransdorf Mark J. , Moser Richard P. , Berrey B. Hudson 
Published: March 2007

AbstractTo assess the effectiveness of gadopentetate dimeglumine in the magnetic resonance (MR) imaging evaluation of soft‐tissue masses without osseous involvement, 30 patients underwent MR imaging before and after administration of contrast material (0.1 mmol/ kg) of the 30 lesions, 22 were benign and eight were malignant; histologic confirmation was available in all lesions except one benign lesion. Overall, enhancement was detected in 26 (87%) of 30 lesions: 18 (82%) of the 22 benign lesions and eight (100%) of eight malignant lesions. Enhancement was characterized as homogeneous (two [11%] benign lesions, two [25%] malignant lesions), inhomogeneous (11 [61%] benign lesions, six [75%] malignant lesions), or peripheral (five [28%] benign lesions, no malignant lesions) of the 19 lesions assessed for a change in enhancement over time, seven (37%) showed an increase and two (11%) showed a decrease in signal intensity. The authors conclude that benign and malignant soft‐tissue lesions could not be differentiated solely on the basis of enhancement (pattern, degree, or time course).
Reduction of slab boundary artifact with multiple overlapping thin slab acquisition in MR angiography of the cervical carotid artery
Authors: Robison Ronald O. , Blatter Duane D. , Parker Dennis L. , Barney William W. , Perry David M. , Goodrich Kenneth C. 
Published: March 2007

AbstractMultiple overlapping thin slab acquisition (MOTSA) is a magnetic resonance (MR) angiography technique combining advantages of two‐ and three‐dimensional time‐of‐flight techniques. The authors studied three image acquisition parameters (flip angle, TR, and the slab excitation fraction [SEF]) and a postprocessing algorithm, to evaluate their effect on MOTSA image quality, including contrast‐to‐noise ratio (C/N) and the severity of the slab boundary artifact. By increasing SEF from 0.75 to 1.10, the slab boundary artifact was reduced by 29%‐56% (P <.0001). The boundary artifact can be reduced an additional 46% by postprocessing of the overlapping section data. In the healthy volunteers studied, C/N of the cervical carotid artery could be increased sixfold (P <.0001) by increasing the flip angle from 10° to 50°, without significant worsening of the boundary artifact due to top‐of‐slab saturation. The effect of TR on image quality was not statistically significant for the range studied (52‐70 msec). We conclude that the slab boundary artifact seen with the MOTSA MR angiography technique can be reduced significantly by optimizing imaging acquisition parameters and using a postprocessing algorithm to combine overlapping section information.
MR imaging signal response to sustained stimulation in human visual cortex
Authors: Hathout Gasser M. , Kirlew Konrad A. T. , So George J. K. , Hamilton David R. , Zhang J. X. , Sinha Usha , Sinha Shantanu , Sayre James , Gozal David , Harper Ronald M. , Lufkin Robert B. 
Published: March 2007

AbstractThe response of signal intensity to transient (on‐off) motor and sensory stimulation has been well studied; however, the dependence of signal response on the duration of stimulus requires further characterization. The objective of this study was to determine the time course of signal response in the human visual cortex to prolonged, sustained stimulation and to examine possible contributory physiologic mechanisms. Nine healthy volunteers underwent magnetic resonance (MR) imaging during sustained visual stimulation with light‐proof binocular goggles. With photic stimulation, activation was observed in all subjects as an increase in signal intensity of the visual cortex. With sustained stimulation, a gradual decrease in signal intensity was subsequently observed, with progression toward an apparent steady state. Correlation with positron emission tomographic, MR spectroscopic, and visual evoked‐potential data suggests that the initial uncoupling of cerebral blood flow and oxidative metabolism with a neuronal activation burst may represent a transient phenomenon. This quick‐response phase may proceed to an equilibrium coupling of flow and oxidative metabolism, with a gradual normalization of venous deoxyhemoglobin levels and signal intensity.