bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ineffectiveness of averaging for reducing motion artifacts in half‐fourier MR imaging
Authors: Wood Michael L. 
Published: March 2007

AbstractTwo 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

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractWriting 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

AbstractGadodiamide 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

AbstractIntraperitoneal 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

AbstractMagnetic 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

AbstractTo 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

AbstractThe 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

AbstractDynamic 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

AbstractAn 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

AbstractA 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

AbstractTo 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

AbstractNineteen 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

AbstractAssessing 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

AbstractThe 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

AbstractThe 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

AbstractMechanisms 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

AbstractDuring 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

AbstractChemical 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

AbstractAcceleration 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.