bluuebunny/crossref_metadata_2025_split huggingface dataset:
Peripheral nerve stimulation during MRI: Effects of high gradient amplitudes and switching rates
Authors: Ham C. L. G. , Engels J. M. L. , van de Wiel G. T. , Machielsen A. 
Published: March 2007

AbstractThe application of high gradient amplitudes and switching rates for MRI and spectroscopy, resulting in short rise times for the gradient field and high changes of the magnetic flux density in the patient, is known to possibly evoke peripheral nerve stimulation (PNS) in patients. These effects have been studied on 20 volunteers under different experimental circumstances. The results of these measurements are partially in line with earlier findings reported in the literature. New information is found for the dependence of the PNS threshold level as a function of the rise time of the gradient waveform. The PNS threshold level, expressed in terms of dB/dt, is found to be proportional with t−05, where t is the switch time for the gradients. Indications are found that |B|, the modulus of the gradient vector field, is more closely related to the PNS threshold level than Bz, the imaging component of the gradient field. From the experiments, it is furthermore concluded that only for the imaging protocols characterized by the application of long bipolar repetitive gradient pulse trains, such as echo‐planar imaging, PNS is expected at the reported threshold levels. For the protocols based on spin echo, turbo spin echo, inversion recovery, fast field echo, etc., characterized by shorter gradient pulse trains, the threshold levels are expected to be much higher.
SPIO‐enhanced 2D‐TOF MR angiography of the portal venous system: Results of an intraindividual comparison
Authors: Reimer Peter , Marx Christian , Rummeny Ernst J. , Müller Markus , Lentschig Markus , Balzer Thomas , Dietl Karl‐Heinz , Sulkowski Udo , Berns Thomas , Shamsi Kohkan , Peters Peter E. 
Published: March 2007

AbstractThe purpose of this study was to investigate whether MR angiography (MRA) of the portal venous system may be improved by means of superparamagnetic iron oxides (SPIOs) during accumulation phase imaging and to study the underlying contrast mechanisms. MRA of the portal venous system was performed on 48 patients before and after intravenous injection of a new SPIO (Resovist, Schering AG, Berlin, Germany). Resovist, as a predominantly liver parenchymal darkening agent on T2‐weighted MR images with uptake into the reticuloendothelial cell system, was administered intravenously by bolus injection of 8 to 12 μmol Fe/kg body weight. Patients were scanned with breath‐hold coronal and axial two‐dimensional (2D) time of flight (TOF) MRA (TR = 31.0 msec, TE = 9.8 msec, flip angle (FA) = 50°, and 6.9‐second acquisition time per section) sequences. Signal intensity values of liver parenchyma, the portal venous system, and background were obtained for quantitative analysis. The clinical relevance of additional plain and contrast‐enhanced MRA studies for surgical planning was assessed by independent reading of three readers. Liver signal‐to‐noise ratio (SNR) significantly decreased following iv injection of Resovist; however, SNR values of the portal veins or hepatic veins did not change significantly. Visibility of the portal venous system improved significantly (tertiary branches visible: pre in 15.2% versus post in 87.0% of patients). Resovist‐enhanced 2D‐TOF MRA may improve planning of liver resections by better demonstrating the relationship of central liver lesions and vessels on source images. The decrease in liver SNR at a constant vessel SNR after iv injection of Resovist improves MRA of the liver. SPIO‐enhanced 2D‐TOF MRA scans are superior to plain 2D‐TOF MRA studies and may be added for the workup of preoperative patients.
Coronary MR angiography during peak‐systole: Work in Progress
Authors: Duerinckx André , Atkinson Dennis P. 
Published: March 2007

AbstractThe purpose of this study is to compare the quality of images of coronary arteries obtained with two‐dimensional breath‐hold coronary MR angiography during peak systole and mid diastole. Two‐dimensional coronary MR angiography was performed in eight normal volunteers at peak systole and in mid diastole with a commercial 1.5‐T MR imager. An ultrafast gradient‐echo sequence with incremented flip angle series and k‐space segmentation was used. The image quality grade, length, and proximal diameter of each visualized coronary artery were measured. The highest quality images in systole and diastole were compared. Coronary MR angiography provided high quality images in systole and diastole in 14 of 16 coronary vessels (87.5%). In 8 of 14 vessels (57%), there was no visible coronary MR angiogram image degradation when comparing peak systolic with mid‐diastolic images. In 4 of 14 vessels (29%), there was mild MR image degradation. There was significant MR image degradation in only one case (7%). And in one case (7%), there was mild image improvement during systole. The width and length of the visualized coronary vessels did not change significantly from diastole to systole. Existing two‐dimensional breath‐hold coronary MR angiography provides MR images during peak systole and mid‐diastole with little or no perceptible difference in quality.
Novel application of breath‐hold turbo spin‐echo T2 MRI for detection of acute myocardial infarction
Authors: Lim Tae‐Hwan , Hong Myeong‐Ki , Lee Jin Seong , Mun Chi Woong , Park Seung‐Jung , Park Seong‐Wook , Ryu Jin Sook , Lee Jung Hee , Chien Daisy , Laub Gerhard 
Published: March 2007

AbstractTo assess the clinical utility of the breath‐hold turbo spin‐echo T2‐weighted MRI in patients with acute myocardial infarction, the results of MRI were compared with those of electrocardiography, coronary angiography, and thallium‐201 single photon emission tomography (SPECT) in 23 patients and 5 healthy volunteers. To compare MRI and thallium‐SPECT, the left ventricle was divided into five segments, and the presence of myocardial infarction was determined in each segment. MRI demonstrated an abnormally bright signal in 49 of 140 segments (five segments each from 23 patients and 5 volunteers); thallium‐SPECT showed a fixed perfusion defect in 52 segments, for an 85% diagnostic concordance rate. The size of the myocardial infarction measured on MRI corresponded well to that measured on thallium‐SPECT (r = .70, P < .01). Breath‐hold turbo spin‐echo T2 MRI can be used for detection of acute myocardial infarction in conjunction with thallium‐SPECT, especially when accurate localization of lesion, increased spatial resolution, and anatomic landmarks are needed.
Water‐fat imaging with direct phase encoding
Authors: Xiang Qing‐San , An Li 
Published: March 2007

AbstractA new method is Introduced for water‐fat imaging. With three acquisitions, a general direct phase encoding (DPE) of the chemical shift information is achieved. Pixels containing both water and fat are solved directly. Pixels with only a single component are resolved with local and global orientation filters, which use phase information from neighboring pixels. The fact that a single component is more likely to be water than fat in living tissues is also useful. A second pass solution yields water and fat images with superior signal‐to‐noise ratio. Unlike other methods, DPE does not rely on the error‐prone phase unwrapping; also, it easily handles disconnected tissues. Because the magnetization vectors of water and fat are sampled not only at parallel or antiparallel, they can be not only separated but also identified respectively, which is desirable for routine clinical work. DPE has been implemented on several imagers at various field strengths and has been demonstrated in a large number of clinical cases to be useful and robust in various parts of the body.
Multifeature analysis of Gd‐enhanced MR images of breast lesions
Authors: Sinha Shantanu , Lucas‐Quesada Flora Anne , Debruhl Nanette D. , Sayre James , Farria Dionne , Gorczyca David P. , Bassett Lawrence W. 
Published: March 2007

AbstractThe objective of this study was to determine whether linear discriminant analysis of different independent features of MR images of breast lesions can increase the sensitivity and specificity of this technique. For MR images of 23 benign and 20 malignant breast lesions, three independent classes of features, including characteristics of Gd‐DTPA‐uptake curve, boundary, and texture were evaluated. The three classes included five, four and eight features each, respectively. Discriminant analysis was applied both within and across the three classes, to find the best combination of features yielding the highest classification accuracy. The highest specificity and sensitivity of the different classes considered independently were as follows: Gd‐up‐take curves, 83% and 70%; boundary features, 86% and 70%; and texture, 70% and 75%, respectively. A combination of one feature each from the first two classes and age yielded a specificity of 79% and sensitivity of 90%, whereas highest figures of 93% and 95%, respectively, were obtained when a total of 10 features were combined across different classes. Statistical analysis of different independent classes of features in MR images of breast lesions can improve the classification accuracy of this technique significantly.
RARE imaging of PCr in human forearm muscles
Authors: Chao Hui , Bowers John L. , Holtzman David , Mulkern Robert V. 
Published: March 2007

AbstractRapid acquisition with relaxation enhancement (RARE) sequences have been used to map the 31P phosphocreatine (PCr) signal in human forearms at 4.7 T. Signal‐to‐noise levels of approximately 10 were achieved from the major muscle groups in 5.5‐minute scan times with a spatial resolution of 4 × 2 × 2 cm3. Exercise caused demonstrable reductions in PCr signal from activated muscles, which correlated with affected muscle groups in T2‐weighted proton images. RARE imaging of the PCr signal at 4.7 T is feasible and, with technically achievable improvements in signal‐to‐noise ratio, should prove useful in studying energy metabolism in muscle and other organs.
A segment‐interleaved motion‐compensated acquisition in the steady state (SIMCAST) technique for high resolution imaging of the inner ear
Authors: Kurucay Saban , Schmalbrock Petra , Chakeres Donald W. , Keller Paul J. 
Published: March 2007

AbstractMRI, with ever‐increasing spatial resolution, recently has depicted progressively more anatomic details of the inner ear and is playing an important role in the diagnostic evaluation of patients with sensorineural hearing loss. We present a three‐dimensional (3D) segment‐interleaved, motion‐compensated acquisition in steady state (SIMCAST) sequence that allows further increase in spatial resolution in reasonable scan times minimizing artifacts due to susceptibility and motion. The sequence uses gradient moment nulling over TR and segmented interleaved acquisition of multiple data sets with different radiofrequency (RF) phase‐cycling schemes. Combination of data from multiple acquisitions by averaging and maximum intensity projection were compared. Images of phantoms and in vivo inner ears were obtained with both full and fractional echoes and compared with other high resolution techniques such as three‐dimensional gradient‐echo and two‐dimensional (2D) and three‐dimensional fast spin‐echo (FSE) sequences. The new sequence achieves improved signal‐to‐noise ratio (SNR) and spatial resolution resulting in improved depiction of inner ear structures.
Magnetization transfer fast imaging of implanted glioma in the rat brain at 4.7 T: Interpretation using a binary spin‐bath model
Authors: Quesson Bruno , Bouzier Anne‐Karine , Thiaudiere Eric , Delalande Christophe , Merle Michel , Canioni Paul 
Published: March 2007

AbstractC6 glioma cells were implanted in the left caudate nucleus of the rat brain. Histologic studies confirmed the presence of neoplastic tissue surrounded by a thin edematous region. Proton magnetization transfer contrast (MTC) fast imaging, using continuous wave off‐resonance irradiation, was performed in vivo at 4.7 T with the rapid acquisition with relaxation enhancement (RARE) sequence. The observed MTC allowed very clear distinction of the tumoral region, in which magnetization transfer (MT) ratios were lower than in healthy tissues. Contrasts were analyzed as a function of the offset frequency and the amplitude of the radiofrequency (RF) irradiation. The contrast was higher between the contralateral basal ganglia and the tumor and lower between the tumor and the temporal lobe. Modeling of MT in the three brain regions was performed using a system including free water and a pool of protons with restricted motions. The rate of exchange between the two pools exhibited a decreasing hierarchy from the basal ganglia to the tumor. T2B values for the immobile protons ranged from 9.3 μsec in the basal ganglia to 7.5 μsec for the glioma. The acquisition conditions leading to the highest contrasts between the tumor and the healthy tissues correspond to 3,000 Hz offset frequency and 300 to 700 Hz RF irradiation amplitude.
Perfusion‐weighted MRI using gadobutrol as a contrast agent in a rat stroke model
Authors: Heiland Sabine , Benner Thomas , Reith Wolfgang , Forsting Michael , Sartor Klaus 
Published: March 2007

AbstractThe purpose of this study was to examine the new nonionic contrast agent gadobutrol in MR perfusion‐weighted imaging, including the influence of different concentrations and dosages of the agent on the sensitivity to perfusion alterations. Sixteen rats were examined within 35 to 105 minutes after endovascular occlusion of the middle cerebral artery. A fast T2*‐weighted fast low‐angle shot (FLASH) sequence was used to acquire four images before and 16 images after bolus injection of .1, .2, .3, and .4 mmol/kg gadobutrol as .5 molar and 1.0 molar formulation. From user‐defined regions, we obtained the maximum signal decrease, the relative regional cerebral blood volume, and the bolus delay. Contrast between ischemic and nonischemic regions during bolus passage increased with dose and concentration of the contrast agent. For low doses (.1 and .2 mmol/kg), the ischemic lesion could not or could barely be discerned. For higher doses (.3 and .4 mmol/kg), administration of the 1 molar contrast agent yielded a better contrast between ischemic and nonischemic tissue. Our results suggest that administration of gadobutrol at higher dosage and higher concentration increases sensitivity to perfusion alterations. These results are potentially useful for perfusion‐weighted imaging of the human brain, because the volume of contrast agent will be reduced if a solution with higher concentration is used. When using contrast agents in higher concentrations for human examinations, a significant signal decrease may be achieved also with the low doses (.1–.15 mmol/kg).
First pass MRA of the Abdomen: Ultrafast, non‐breath‐hold time‐of‐flight imaging using Gd‐DTPA bolus
Authors: Atkinson Dennis J. , Vu Bach , Chen Dar‐Yeong , Duerinckx Andre , Bradley William G. 
Published: March 2007

AbstractThe authors describe a new fast imaging sequence that can produce projection angiograms of the abdominal vessels at a rate of 2 to 3 frames per second. The result is a versatile imaging technique that can track the arrival of a bolus of contrast in major vessels. With very fast data acquisition, gross patient motion is not a problem, and routine vascular projection studies may be performed without the need for breath‐holding. This method is compatible with later high‐resolution three‐dimensional gradient echo studies using contrast agents and may, in fact, be used as an accurate timing protocol to gauge the arrival time of contrast in various segments of the abdominal vessels. Compared with echo planar imaging, this method has the advantages of avoiding susceptibility artifacts and depicting retroperitoneum and other abdominal fat‐containing landmarks and does not require extensive hardware modifications for a clinical system.
Breath‐hold R2* mapping with a multiple gradient‐recalled echo sequence: Application to the evaluation of intrarenal oxygenation
Authors: Prasad Pottumarthi V. , Chen Qun , Goldfarb James W. , Epstein Franklin H. , Edelman Robert R. 
Published: March 2007

AbstractBlood oxygenation level dependent (BOLD) MRI is sensitive to changes in regional oxygen supply versus demand and is therefore potentially useful in evaluating susceptibility to ischemic injury. Recently, we have demonstrated the use of BOLD MRI to evaluate intrarenal oxygenation using single shot echo‐planar imaging (EPI). Here, we present an alternate implementation of BOLD MRI sequence, using multiple gradient echoes, that does not require any specialized hardware.
Accessory equipment considerations with respect to MRI compatibility
Authors: Keeler Elaine K. , Casey Francis X. , Engels Hans , Lauder Elizabeth , Pirto Catherine Anne , Reisker Theodore , Rogers James , Schaefer Daniel J. , Tynes Thomas 
Published: March 2007

AbstractThe MR Section of The National Electrical Manufacturers Association (NEMA), in response to a request from the Food & Drug Administration (FDA), recently issued a position paper to address generic issues related to the compatibility of accessory equipment produced by third party equipment manufacturers or MR equipment users and intended to be used in conjunction with MR equipment or within the MR scanning room. The recommendations concern scanning accessories, such as radiofrequency (RF) coils, patient monitoring equipment and injectors, as well as patient comfort accessories and positioning devices. The following issues related to safety performance are discussed: (a) the interaction of the equipment with the MR scanner, (b) interactions of the MR scanner with the equipment, and (c) potential safety hazards for patients and staff that can be posed by accessory equipment in the MR scan environment. The recommendations are based on combined input from NEMA member companies who manufacture MR systems and MR accessories and are presented for consideration in the design of MR accessory products and incorporation of these concepts into testing plans to ensure MR compatibility of third party devices.
Malignant hepatic tumors: Changes on MRI after hepatic arterial chemoembolization – preliminary findings
Authors: Semelka Richard C. , Worawattanakul Suvipapun , Mauro Matthew A. , Bernard Stephen A. , Cance William G. 
Published: March 2007

AbstractThis study describes the MR appearances of malignant hypervascular liver lesions pre‐ and post‐hepatic‐arterial chemoembolization, with correlation to serial imaging and clinical responses. Eight patients with malignant hypervascular liver lesions underwent pretreatment and posttreatment MR examination on a 1.5‐T MR imager. MR sequences included T1‐weighted spoiled gradient echo (SGE), T2‐weighted fat‐suppressed spin echo or turbo spin echo, and dynamic gadolinium‐enhanced SGE images. All patients underwent pretreatment, initial posttreatment, and subsequent posttreatment MR studies. The histology of primary tumors included various types of hepatocellular carcinoma (HCC) (four patients: fibrolamellar HCC [one patient], HCC [two patients], mixed HCC/cholangiocarcinoma [one patient]) and liver metastases (four patients: untyped islet cell tumor [two patients], gastrinoma [one patient], carcinoid [one patient]). Response to chemoembolization was determined by three assessments: MR response, serial imaging response, and clinical response. The appearance of MR response to chemoembolization was determined based on the correlation with clinical and serial imaging response. The MR response of lesions that showed good clinical response included: increase in signal intensity on T1‐weighted images (three patients), decrease in signal intensity on T2‐weighted images (three patients), and negligible or minimal enhancement on immediate postgadolinium images (four patients) after chemoembolization. The most marked change in lesion appearance was observed in lesions < 1 cm, which had intense homogeneous enhancement on pretreatment MR studies and negligible enhancement on initial posttreatment MR examinations. MR response of lesions that showed moderate clinical response demonstrated a variety of lesion appearances from substantial change to minimal change. MR response of lesions that showed poor clinical response demonstrated no change in lesion appearances compared with the pretreatment MR study. Our results demonstrated change in appearance of liver lesions between pre‐ and post‐hepatic‐arterial chemoembolization MR studies. MR response correlated with response determined by serial imaging studies and clinical findings.
Calculated RF electric field and temperature distributions in RF thermal ablation: Comparison with gel experiments and liver imaging
Authors: Cheng Yu‐Chung N. , Brown Robert W. , Chung Yiu‐Cho , Duerk Jeffrey L. , Fujita Hiroyuki , Lewin Jonathan S. , Schuele Donald E. , Shvartsman Shmaryu 
Published: March 2007

AbstractThe present paper is a study of theoretic modeling and experimental tests of that modeling for the local heating due to radiofrequency thermal ablation. A model is developed for the current and the associated electric field produced by a radiofrequency ablation probe. The temperature distributions resulting from the induced ohmic currents in the surrounding material are considered. A comparison is made between the theoretic temperature profiles and the shapes of thermal ablation ‘lesions’ produced in a controlled gelatin sample experiment. Comparison with the contours of human thermally induced liver lesions found in MRI studies also provides a validation of the success of the modeling. Successful modeling should lead to methods for optimization of the ablation procedure, especially as it is used in interventional MRI.
Evaluation of 3D image registration as applied to MR‐guided thermal treatment of liver cancer
Authors: Wilson David L. , Carrillo Andres , Zheng Lan , Genc Ahmet , Duerk Jeffrey L. , Lewin Jonathan S. 
Published: March 2007

AbstractThere are many potential applications of three‐dimensional (3D) image registration in MR‐guided radiofrequency (RF) thermal ablation of tumors. For example, after registration of image volumes obtained before and after thermal ablation, a variety of quantitative and visual assessments of therapy were performed. For liver tumors, the accuracy of rigid body, manual registration on 19 pairs of image volumes was evaluated, almost all of which were obtained during thermal treatment sessions. Registration error was estimated as a distance between anatomical landmarks, including both internal vascular structures as well as the surface of the liver. Over all image pairs and throughout a large portion of the liver, the registration error was 3.1 mm (mean + 1 SD). From the bottom to the top of the liver, error increased on the order of 13%, probably because of liver motion and deformation resulting from respiration. Although probably insufficient for blind guidance of therapy, registration accuracy was undoubtedly sufficient for interesting applications in the planning, assessment, and optimization of interventional MR‐guided thermal treatment of liver tumors.