Scanners

Distribution by Scientific Domains
Distribution within Medical Sciences

Kinds of Scanners

  • clinical mri scanners
  • mri scanners
  • tomography scanners


  • Selected Abstracts


    Rendering: Input and Output

    COMPUTER GRAPHICS FORUM, Issue 3 2001
    H. Rushmeier
    Rendering is the process of creating an image from numerical input data. In the past few years our ideas about methods for acquiring the input data and the form of the output have expanded. The availability of inexpensive cameras and scanners has influenced how we can obtain data needed for rendering. Input for rendering ranges from sets of images to complex geometric descriptions with detailed BRDF data. The images that are rendered may be simply arrays of RGB images, or they may be arrays with vectors or matrices of data defined for each pixel. The rendered images may not be intended for direct display, but may be textures for geometries that are to be transmitted to be rendered on another system. A broader range of parameters now need to be taken into account to render images that are perceptually consistent across displays that range from CAVEs to personal digital assistants. This presentation will give an overview of how new hardware and new applications have changed traditional ideas of rendering input and output. [source]


    3D Reconstruction of Real World Scenes Using a Low-Cost 3D Range Scanner

    COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 7 2006
    Paulo Dias
    The article describes the mechanical and control issues addressed to physically achieve the 3D sensor used to acquire the data. It also presents the techniques used to process and merge range and intensity data to create textured polygonal models and illustrates the potential of such a unit. The result is a promising system for 3D modeling of real world scenes at a commercial price 10 or 20 times lower than current commercial 3D laser scanners. The use of such a system can simplify measurements of existing buildings and produce easily 3D models and ortophotos of existing structures with minimum effort and at an affordable price. [source]


    3D Image Segmentation of Aggregates from Laser Profiling

    COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 4 2003
    Hyoungkwan Kim
    Automated scanners of different designs use cameras or lasers to obtain digital images of groups of aggregate particles. To accurately determine particle size and shape parameters, each particle region in the image must be isolated and processed individually. Here, a method for segmenting a particle image acquired from laser profiling is developed using a Canny edge detector and a watershed transformation. Canny edges with rigorous and liberal threshold values are used to outline particle boundaries on a binary image and to check the validity of watersheds, respectively. To find appropriate regional minima in the watershed transformation, a varying search window method is used, where the number of neighboring pixels being compared with the pixel of interest is determined from the height value of the pixel. Test results with this method are promising. When implemented in automated systems that are designed to rapidly assess size and shape characteristics of stone particles, this technique can not only reduce the amount of time required for aggregate preparation, but also increase the accuracy of analysis results. [source]


    In vivo proton spectroscopy without solvent suppression

    CONCEPTS IN MAGNETIC RESONANCE, Issue 4 2001
    David B. Clayton
    Abstract In 1H MR spectroscopy of the human brain, it is common practice to suppress the solvent signal prior to acquisition. This reduces the large dynamic range which is otherwise required of the MR receiver and digitizer in order to detect the dilute metabolite resonances in the presence of the much larger water signal. However, complete solvent suppression is not always obtainable, particularly over large volumes and in superficial regions containing large susceptibility gradients. In this work, it demonstrated that modern commercial MR scanners possess the dynamic range necessary to adequately resolve the 1H metabolites in unsuppressed spectra. Moreover, a postacquisition method is presented which can completely remove the intact water signal and accurately quantitate the metabolite peaks. Preserving the water signal in in vivo spectroscopy has several useful benefits, such as providing a high signal-to-noise ratio internal concentration, frequency, and line shape reference. Comparison is made between suppressed and unsuppressed spectra from both a phantom and the human brain acquired at 4 T. © 2001 John Wiley & Sons, Inc. Concepts Magn Reson 13: 260,275, 2001 [source]


    Magnetic resonance microscopy of the equine hoof wall: a study of resolution and potential

    EQUINE VETERINARY JOURNAL, Issue 5 2006
    M. D. KELLER
    Summary Reasons for performing study: Obtaining magnetic resonance images of the inner hoof wall tissue at the microscopic level would enable early accurate diagnosis of laminitis and therefore more effective therapy. Objectives: To optimise magnetic resonance imaging (MRI) parameters in order to obtain the highest possible resolution of the structures beneath the equine hoof wall. Methods: Magnetic resonance microscopy (MRM) was performed in front feet from 6 cadaver horses using T2 -weighted fast spin echo (FSE-T2), and T1 -weighted gradient echo (GRE-T1) sequences. Results: In T2 weighted FSE images most of the stratum medium showed no signal, however the coronary, terminal and sole papillae were visible. The stratum lamellatum was clearly visible and primary epidermal lamellae could be differentiated from dermal lamellae. Conclusion: Most structures beneath the hoof wall were differentiated. Conventional scanners for diagnostic MRI in horses are low or high field. However this study used ultra-high field scanners currently not available for clinical use. Signal-to-noise ratio (S/N) increases as a function of field strength. An increase of spatial resolution of the image results in a decreased S/N. S/N can also be improved with better coils and the resolution of high field MRI scanners will increase as technology develops and surface array coils become more readily available. Potential relevance: Although MR images with microscopic resolution were obtained ex vivo, this study demonstrates the potential for detection of lamellar pathology as it occurs. Early recognition of the development of laminitis to instigate effective therapy at an earlier stage and may improve the outcome for laminitic horses. Clinical MR is now readily available at 3 T, while 4 T, 7 T and 9 T systems are being used for human whole body applications. [source]


    Have newer cardiovascular drugs reduced hospitalization?

    HEALTH ECONOMICS, Issue 5 2009
    Evidence from longitudinal country-level data on 20 OECD countries
    Abstract This study examines the effect of changes in the vintage distribution of cardiovascular system drugs on hospitalization and mortality due to cardiovascular disease using longitudinal country-level data. The vintage of a drug is the first year in which it was marketed anywhere in the world. We use annual data on the utilization of over 1100 cardiovascular drugs (active ingredients) in 20 OECD countries during the period 1995,2003. Countries with larger increases in the share of cardiovascular drug doses that contained post-1995 ingredients had smaller increases in the cardiovascular disease hospital discharge rate, controlling for the quantity of cardiovascular medications consumed per person, the use of other medical innovations (computed tomography scanners and magnetic resonance imaging units), potential risk factors (average consumption of calories, tobacco, and alcohol), and demographic variables (population size and age structure, income, and educational attainment). The estimates also indicate that the use of newer cardiovascular drugs has reduced the average length of stay and the age-adjusted cardiovascular mortality rate, but not the number of potential years of life lost due to cardiovascular disease before age 70 per 100,000 population. The estimates indicate that if drug vintage had not increased during 1995,2004, hospitalization and mortality would have been higher in 2004. We estimate that per capita expenditure on cardiovascular hospital stays would have been 70% ($89) higher in 2004 had drug vintage not increased during 1995,2004. Per capita expenditure on cardiovascular drugs would have been lower in 2004 had drug vintage not increased during 1995,2004. However, our estimate of the increase in expenditure on cardiovascular hospital stays is about 3.7 times as large as our estimate of the reduction in per capita expenditure for cardiovascular drugs that would have occurred ($24). Copyright © 2008 John Wiley & Sons, Ltd. [source]


    The human hippocampus at 7 T,In vivo MRI

    HIPPOCAMPUS, Issue 1 2009
    Jens M. Theysohn
    Abstract The human hippocampus plays a central role in various neuropsychiatric disorders, such as temporal lobe epilepsy (TLE), Alzheimer's dementia, mild cognitive impairment, and schizophrenia. Its volume, morphology, inner structure, and function are of scientific and clinical interest. Magnetic resonance (MR) imaging is a widely employed tool in neuroradiological workup regarding changes in brain anatomy, (sub-) volumes, and cerebral function including the hippocampus. Gain in intrinsic MR signal provided by higher field strength scanners and concomitant improvements in spatial resolution seem highly valuable. An examination protocol permitting complete, high-resolution imaging of the human hippocampus at 7 T was implemented. Coronal proton density, T2, T2*, and fluid-attenuated inversion recovery contrasts were acquired as well as an isotropic 3D magnetization-prepared rapid acquisition gradient-echo (500 ,m isotropic voxel dimension, noninterpolated). Observance of energy deposition restrictions within acceptable scan times remained challenging in the acquisition of thin, spin-echo-based sections. At the higher resolution enabled by 7 T, demarcation of the hippocampus and some internal features including gray/white matter differentiation and depiction of the hippocampal mantle becomes much more viable when compared with 1.5 T; thus, in the future, this imaging technology might help in the diagnosis of subtle hippocampal changes. © 2008 Wiley-Liss, Inc. [source]


    Assessment of the increase in variability when combining volumetric data from different scanners

    HUMAN BRAIN MAPPING, Issue 2 2009
    Santiago Reig
    Abstract In multicenter MRI studies, pooling of volumetric data requires a prior evaluation of compatibility between the different machines used. We tested the compatibility of five different scanners (2 General Electric Signa, 2 Siemens Symphony, and a Philips Gyroscan) at five different sites by repeating the scans of five volunteers at each of the sites. Using a semiautomatic method based on the Talairach atlas, and SPM algorithms for tissue segmentation (multimodal T1 and T2, or T1-only), we obtained volume measurements of the main brain lobes (frontal, parietal, occipital, temporal) and for each tissue type. Our results suggest that pooling of multisite data adds small error for whole brain measurements, intersite coefficient of variation (CV) ranging from 1.8 to 5.2%, respectively, for GM and CSF. However, in the occipital lobe, intersite CV can be as high as 11.7% for WM and 17.3% for CSF. Compared with the intersite, intrasite CV values were always much lower. Whenever possible, T1 and T2 tissue segmentation methods should be used because they yield more consistent volume measurements between sites than T1-only, especially when some of the scans were obtained with different sequence parameters and pixel size from those of the other sites. Our study shows that highest compatibility among scanners would be obtained using equipments of the same manufacturer and also image acquisition parameters as similar as possible. After validation, data from a specific ROI or scanner showing values markedly different from the other sites might be excluded from the analysis. Hum Brain Mapp, 2009. © 2007 Wiley-Liss, Inc. [source]


    Radiation exposure and the justification of computed tomography scanning in an Australian hospital emergency department

    INTERNAL MEDICINE JOURNAL, Issue 11 2009
    M. Street
    Abstract In an emergency department (ED), computed tomography (CT) is particularly beneficial in the investigation of high-speed trauma patients. With the advent of multidetector CT (MDCT) scanners, it is becoming faster and easier to conduct scans. In recent years, this has become evident with an increasing number of CT requests. Patients who have multiple CT scans during their hospital stay can receive radiation doses that have an increased theoretical risk of induction of cancer. It is essential that the clinical justification for each CT scan be considered on an individual basis and that due consideration is given to the radiation risk and possible diagnostic benefit. The current lack of a central State or Commonwealth data repository for medical images is a contributing factor to excessive radiation dosage to the population. The principles of justification and radiation risks are discussed in this study. [source]


    View planning and automated data acquisition for three-dimensional modeling of complex sites

    JOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 11-12 2009
    Paul S. Blaer
    Constructing highly detailed three-dimensional (3-D) models of large complex sites using range scanners can be a time-consuming manual process. One of the main drawbacks is determining where to place the scanner to obtain complete coverage of a site. We have developed a system for automatic view planning called VuePlan. When combined with our mobile robot, AVENUE, we have a system that is capable of modeling large-scale environments with minimal human intervention throughout both the planning and acquisition phases. The system proceeds in two distinct stages. In the initial phase, the system is given a two-dimensional site footprint with which it plans a minimal set of sufficient and properly constrained covering views. We then use a 3-D laser scanner to take scans at each of these views. When this planning system is combined with our mobile robot it automatically computes and executes a tour of these viewing locations and acquires them with the robot's onboard laser scanner. These initial scans serve as an approximate 3-D model of the site. The planning software then enters a second phase in which it updates this model by using a voxel-based occupancy procedure to plan the next best view (NBV). This NBV is acquired, and further NBVs are sequentially computed and acquired until an accurate and complete 3-D model is obtained. A simulator tool that we developed has allowed us to test our entire view planning algorithm on simulated sites. We have also successfully used our two-phase system to construct precise 3-D models of real-world sites located in New York City: Uris Hall on the campus of Columbia University and Fort Jay on Governors Island. © 2009 Wiley Periodicals, Inc. [source]


    Performance of laser and radar ranging devices in adverse environmental conditions

    JOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 9 2009
    Julian Ryde
    A comparative evaluation of millimeter-wave radar and two-dimensional scanning lasers in dust and rain conditions for sensor applications in field robotics is presented. A robust and reliable method for measuring the level of suspended dust (or other obscurant media) by determining the transmission coefficient is developed and used for quantitative assessment of sensor performance. The criteria of target acquisition reliability, precision, and accuracy under varying environmental conditions are assessed via sensor operation in a controlled environment. This environment generated dust and rain of varying densities. Sensor performance is also assessed for the potential effect on digital terrain mapping and haul truck localization due to sensor-specific behaviors in these conditions (e.g., false targets, increased noise). Trials on a research electric face shovel are conducted to test observed behaviors. It is concluded that laser scanners are suitable for environments with transmissions exceeding 92%,93%/m for targets closer than 25 m. The radar remained relatively unaffected by the generated conditions of rain (50,70 mm/h) and dust (10-m visibility); however, its accuracy (0.1 m with a corner reflector and 0.3 m on a haul truck), free-space clutter, and scan rate were insufficient for locating unmodified haul trucks for this application. © 2009 Wiley Periodicals, Inc. [source]


    High-resolution millimeter-wave radar systems for visualization of unstructured outdoor environments

    JOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 10 2006
    Graham Brooker
    This paper examines the use of millimeter-wave radar systems for visualization and navigation in unstructured outdoor environments. Three types of radar systems are described. The first is a long range, 94 GHz, frequency modulated interrupted continuous wave radar which is capable of producing two-dimensional (2D) reflectivity images to a range of more than 3 km. This is intended for use in long-range path planning. The second is a class of medium range 77 GHz frequency modulated continuous wave (FMCW) radar with two axis mirror scanners which is capable of producing high resolution threedimensional (3D) imagery out to 500 m at a reasonably slow frame rate. The final class also operates using the FMCW principle, but at 94 GHz, to produce high resolution 2D and 3D images out to about 50 m at a much higher update rate. These shorter range sensors may be used to determine the traversability of the local terrain. The outputs produced by the different classes of radar are examined and the paper considers their advantages when compared to other sensors such as vision and scanning laser. Using radar images, the final section compiles rules for interpreting radar reflectivity images from a path-planning perspective. © 2006 Wiley Periodicals, Inc. [source]


    Computer-aided detection of brain tumor invasion using multiparametric MRI

    JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2009
    Todd R. Jensen PhD
    Abstract Purpose To determine the potential of using a computer-aided detection method to intelligently distinguish peritumoral edema alone from peritumor edema consisting of tumor using a combination of high-resolution morphological and physiological magnetic resonance imaging (MRI) techniques available on most clinical MRI scanners. Materials and Methods This retrospective study consisted of patients with two types of primary brain tumors: meningiomas (n = 7) and glioblastomas (n = 11). Meningiomas are typically benign and have a clear delineation of tumor and edema. Glioblastomas are known to invade outside the contrast-enhancing area. Four classifiers of differing designs were trained using morphological, diffusion-weighted, and perfusion-weighted features derived from MRI to discriminate tumor and edema, tested on edematous regions surrounding tumors, and assessed for their ability to detect nonenhancing tumor invasion. Results The four classifiers provided similar measures of accuracy when applied to the training and testing data. Each classifier was able to identify areas of nonenhancing tumor invasion supported with adjunct images or follow-up studies. Conclusion The combination of features derived from morphological and physiological imaging techniques contains the information necessary for computer-aided detection of tumor invasion and allows for the identification of tumor invasion not previously visualized on morphological, diffusion-weighted, and perfusion-weighted images and maps. Further validation of this approach requires obtaining spatially coregistered tissue samples in a study with a larger sample size. J. Magn. Reson. Imaging 2009;30:481,489. © 2009 Wiley-Liss, Inc. [source]


    Improvement of vessel visibility in time-of-flight MR angiography of the brain

    JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2008
    Takaharu Shonai MD
    Abstract Purpose To improve vessel visibility in time-of-flight MR angiography (TOF-MRA) by careful consideration of coil choice, coil position, and frequency offset and profile of the nonspatially selective chemical shift selective (CHESS) presaturation pulse. Materials and Methods The effects of both the CHESS and the excitation radiofrequency (RF) pulses on flow signal and signals from stationary substances were evaluated by changing the spatial area where RF pulses were applied to upstream flow in a flow phantom and in human subjects. The difference between the eight-channel phased-array receive-only coil and the transmit,receive coil was evaluated. Results The CHESS pulse suppresses the flow signal over a wider frequency range than the signals from stationary substances, especially when using the body coil for transmission. Even without presaturation pulse, the excitation pulse slightly suppressed the flow signal. Adjusting the position of the transmit,receive coil relative to the head improved these TOF-MRA images. The results were better than those obtained with the eight-channel coil. Conclusion The excitation and the nonspatially selective CHESS pulses degraded the flow signal. Our results suggest that reduced spatial extent of RF pulse application to upstream flow can improve image quality of TOF-MRA. This result can be implemented on conventional scanners. J. Magn. Reson. Imaging 2008;27:1362,1370. © 2008 Wiley-Liss, Inc. [source]


    The Alzheimer's disease neuroimaging initiative (ADNI): MRI methods

    JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2008
    Clifford R. Jack Jr. MD
    Abstract The Alzheimer's Disease Neuroimaging Initiative (ADNI) is a longitudinal multisite observational study of healthy elders, mild cognitive impairment (MCI), and Alzheimer's disease. Magnetic resonance imaging (MRI), (18F)-fluorodeoxyglucose positron emission tomography (FDG PET), urine serum, and cerebrospinal fluid (CSF) biomarkers, as well as clinical/psychometric assessments are acquiredat multiple time points. All data will be cross-linked and made available to the general scientific community. The purpose of this report is to describe the MRI methods employed in ADNI. The ADNI MRI core established specifications thatguided protocol development. A major effort was devoted toevaluating 3D T1 -weighted sequences for morphometric analyses. Several options for this sequence were optimized for the relevant manufacturer platforms and then compared in a reduced-scale clinical trial. The protocol selected for the ADNI study includes: back-to-back 3D magnetization prepared rapid gradient echo (MP-RAGE) scans; B1 -calibration scans when applicable; and an axial proton density-T2 dual contrast (i.e., echo) fast spin echo/turbo spin echo (FSE/TSE) for pathology detection. ADNI MRI methods seek to maximize scientific utility while minimizing the burden placed on participants. The approach taken in ADNI to standardization across sites and platforms of the MRI protocol, postacquisition corrections, and phantom-based monitoring of all scanners could be used as a model for other multisite trials. J. Magn. Reson. Imaging 2008. © 2008 Wiley-Liss, Inc. [source]


    A practical method for 2D multiple-animal MRI

    JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2007
    Marc S. Ramirez MS
    Abstract Purpose To investigate practical methods for achieving routine simultaneous 2D MRI of multiple animals in large-bore experimental scanners. Materials and Methods Three four-element array geometries were compared against a standard single-coil configuration in terms of image quality, ease of use, and data efficiency using a four-channel, 4.7 T small animal imaging system. Results A linear arrangement of volume resonators permits unobstructed animal preparation and use of an imaging protocol that is almost identical to the single-coil configuration without requiring any image correction or other additional postprocessing. Resulting in vivo images were visually indistinguishable from those acquired through the single-coil configuration. Conclusion The efficiency of animal studies employing 2D MRI techniques can be substantially improved by using a linear array of commercially available resonators. J. Magn. Reson. Imaging 2007;26:1162,1166. © 2007 Wiley-Liss, Inc. [source]


    Comparing real-world advantages for the clinical neuroradiologist between a high field (3 T), a phased array (1.5 T) vs. a single-channel 1.5-T MR system

    JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2006
    Darren B. Orbach MD
    Abstract Purpose To evaluate signal-to-noise ratio (SNR) and neuroradiologists' subjective assessments of image quality in 3-Tesla (3-T) or phased-array MR systems that are now available for clinical neuroimaging. Materials and Methods Brain MR images of six normal volunteers were obtained on each of three scanners: a 1.5-T single-channel system, a 12-channel, phased-array system, and a 3-T single-channel system. Additionally, clinically optimized images acquired from 28 patients who underwent imaging in more than one of these systems were analyzed. SNRs were measured and image quality and artifact conspicuity were graded by two blinded readers. Results The phased-array system produced higher SNR than either the 1.5-T or the 3-T single-channel systems, and in no instance was it outperformed. Both blinded readers judged the phased-array images to be of higher quality than those produced by the single-channel systems, with significantly less artifact. The 3-T magnet produced images with high SNR, but with increased artifact conspicuity. The phased-array system markedly decreased acquisition times without introduction of artifacts. Conclusion Both quantitatively and qualitatively, the phased-array system provided image quality superior to that of the 1.5-T and 3-T single-channel systems. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source]


    Multicontrast black-blood MRI of carotid arteries: Comparison between 1.5 and 3 tesla magnetic field strengths

    JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2006
    Vasily L. Yarnykh PhD
    Abstract Purpose To compare black-blood multicontrast carotid imaging at 3T and 1.5T and assess compatibility between morphological measurements of carotid arteries at 1.5T and 3T. Materials and Methods Five healthy subjects and two atherosclerosis patients were scanned in 1.5T and 3T scanners with a similar protocol providing transverse T1 -, T2 -, and proton density (PD)-weighted black-blood images using a fast spin-echo sequence with single- (T1 -weighted) or multislice (PD-/T2 -weighted) double inversion recovery (DIR) preparation. Wall and lumen signal-to-noise ratio (SNR) and wall/lumen contrast-to-noise ratio (CNR) were compared in 44 artery cross-sections by paired t -test. Interscanner variability of the lumen area (LA), wall area (WA), and mean wall thickness (MWT) was assessed using Bland-Altman analysis. Results Wall SNR and lumen/wall CNR significantly increased (P < 0.0001) at 3T with a 1.5-fold gain for T1 -weighted images and a 1.7/1.8-fold gain for PD-/T2 -weighted images. Lumen SNR did not differ for single-slice DIR T1 -weighted images (P = 0.2), but was larger at 3T for multislice DIR PD-/T2 -weighted images (P = 0.01/0.03). The LA, WA, and MWT demonstrated good agreement with no significant bias (P 0.5), a coefficient of variation (CV) of <10%, and intraclass correlation coefficient (ICC) of >0.95. Conclusion This study demonstrated significant improvement in SNR, CNR, and image quality for high- resolution black-blood imaging of carotid arteries at 3T. Morphologic measurements are compatible between 1.5T and 3T. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source]


    Eddy-current induction in extended metallic parts as a source of considerable torsional moment

    JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2006
    Hansjörg Graf PhD
    Abstract Purpose To examine eddy-current-provoked torque on conductive parts due to current induction from movement through the fringe field of the MR scanner and from gradient switching. Materials and Methods For both cases, torque was calculated for frames of copper, aluminum, and titanium, inclined to 45° to B0 (maximum torque case). Conditions were analyzed in which torque from gravity (legal limit, ASTM F2213-02) was exceeded. Experiments were carried out on a 1.5 T and a 3 T scanner for copper and titanium frames and plates (,50 × 50 mm2). Movement-induced torque was measured at patient table velocity (20 cm/second). Alternating torque from gradient switching was investigated by holding the specimens in different locations in the scanner while executing sequences that exploited the gradient capabilities (40 mT/m). Results The calculations predicted that movement-induced torque could exceed torque from gravity (depending on the part size, electric resistance, and velocity). Two experiments on moving conductive frames in the fringe fields of the scanners confirmed the calculations. For maximum torque case parameters, gradient-switching-induced torque was calculated to be nearly 100 times greater than the movement-induced torque. Well-conducting metal parts located off center vibrated significantly due to impulse-like fast alternating torque characteristics. Conclusion Torque on metal parts from movement in the fringe field is weak under standard conditions, but for larger parts the acceptable limit can be reached with a high static field and increased velocity. Vibrations due to gradient switching were confirmed and may explain the sensations occasionally reported by patients with implants. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source]


    In vitro validation of phase-contrast flow measurements at 3 T in comparison to 1.5 T: Precision, accuracy, and signal-to-noise ratios,

    JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2005
    Joachim Lotz MD
    Abstract Purpose To evaluate the signal-to-noise ratio (SNR), precision, and accuracy of phase-contrast flow measurements at 3 T with the help of an in vitro model and to compare the results with data from two 1.5-T scanners. Materials and Methods Using an identical setup of a laminar flow model and sequence parameters, measurements were done at one 3-T and at two 1.5-T systems. Precision, accuracy, and SNR were obtained for velocity encodings ranging from 55 up to 550 cm,1. SNRs were calculated from the magnitude as well as the flow encoded images. Results Precision and accuracy for the in vitro flow model were similarly high in all scanners with no significant difference. For velocity encodings from 55 cm,1 up to 550 cm,1, the SNR in magnitude as well as phase encoded images of the 3-T measurements was approximately 2.5 times higher than the SNR obtained from the two 1.5-T systems. Conclusion Even without optimization for the 3-T environment, flow measurements show the same high accuracy and precision as is known from clinical 1.5-T scanners. The superior SNR at 3 T will allow further improvements in temporal and spatial resolution. This will be of interest for small-size vessels like coronary arteries or for slow diastolic flow patterns. J. Magn. Reson. Imaging 2005;21:604,610. © 2005 Wiley-Liss, Inc. [source]


    Simple anatomical measurements do not correlate significantly to individual peripheral nerve stimulation thresholds as measured in MRI gradient coils

    JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2003
    Blaine A. Chronik PhD
    Abstract Purpose To examine peripheral nerve stimulation (PNS) thresholds for normal human subjects in magnetic resonance imaging (MRI) gradient coils, and determine if observed thresholds could be predicted based on gross physiologic measurements. Materials and Methods PNS thresholds for 21 healthy normal subjects were measured using a whole-body gradient coil. Subjects were exposed to a trapezoidal echo-planar imaging (EPI) gradient waveform and the total change in gradient strength (,G) required to cause PNS as a function of the duration of the gradient switching time (,) were measured. Correlation coefficients and corresponding P values were calculated for the PNS threshold measurements against simple physiologic measurements taken of the subjects, including weight, height, girth, and average body fat percentage, in order to determine if there were any easily observable dependencies. Results No convincing correlations between threshold parameters and gross physiologic measurements were observed. Conclusion These results suggest it is unlikely that a simple physiologic measurement of subject anatomy can be used to guide the operation of MRI scanners in a subject-specific manner in order to increase gradient system performance while avoiding PNS. J. Magn. Reson. Imaging 2003;17:716,721. © 2003 Wiley-Liss, Inc. [source]


    Surface laser scanning to routinely produce casts for patient immobilization during radiotherapy*

    JOURNAL OF MEDICAL IMAGING AND RADIATION ONCOLOGY, Issue 2 2007
    B McKernan
    Summary Immobilization casts are used to reduce patient movement during the radiotherapy of head and neck and brain malignancies. Polyethylene-based casts are produced by first taking a Plaster of Paris ,negative' impression of the patient. A ,positive' mould is then made, which is used to vacuum form an immobilization cast. Taking the ,negative' cast can be messy, stressful for patients and labour intensive. Recently, lightweight hand-held laser surface scanners have become available. These allow an accurate 3-D representation of objects to be generated non-invasively. This technology has now been applied to the production of casts for radiotherapy. Each patient's face and head is digitized using the Polhemus FastSCAN (Polhemus, Colchester, VT, USA) scanner. The electronic data are transferred to a computer numerical controlled mill, where a positive impression is machined. The feasibility of the process was examined, the labour required and radiation therapists' satisfaction with aspects of the produced masks assessed. The scanner-based method of mask production was found to be simple, accurate and non-invasive. There was a reduction in radiation therapist labour required. Masks produced with the scanner-based method were reported to result in improved mask fitting, daily reproducibility, patient immobilization and patient comfort. [source]


    Cerebral blood flow and oxygen metabolism measured with the Kety,Schmidt method using nitrous oxide

    ACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 2 2009
    S. TAUDORF
    Background: The Kety,Schmidt method is the reference method for measuring global cerebral blood flow (CBF), cerebral metabolic rates (CMR) and flux, especially where scanners are unavailable or impractical. Our primary objective was to assess the repeatability of the Kety,Schmidt method in a variety of different approaches using inhaled nitrous oxide (N2O) as the tracer, combined with photoacoustic spectrometry. A secondary objective was to assess the impact of this tracer on the systemic vascular concentration of nitrite (NO2,). Methods: Twenty-nine healthy male volunteers underwent 61 CBF measurements by breathing a normoxic gas mixture containing 5% N2O until tension equilibrium. Paired blood samples were collected from an arterial and a jugular bulb catheter in the saturation or desaturation phase, by continuous or the discontinuous sampling. N2O concentration was measured with photoacoustic spectrometry after equilibration of blood samples with air. CBF was calculated by the Kety,Schmidt equation. CMR of oxygen (CMRO2) was determined by the Fick principle. NO2, in plasma and red blood cells (RBC) was measured by ozone-based chemiluminescence. Results: The most robust approach for CBF measurement was achieved by discontinuous sampling in the desaturation phase [CBF, 64 (95% confidence interval, 59,71 ml)] 100 g/min; CMRO2 1.8 (1.7,2.0) ,mol/g/min). The tracer did not influence plasma or RBC NO2, (P>0.05 vs. baseline). Conclusion: These findings confirm the reliability and robustness of the Kety,Schmidt method using inhaled N2O for the measurement of global CBF and CMR. At the low tracer concentration used, altered NO metabolism is unlikely to have affected cerebral haemodynamic function. [source]


    Efficient estimation of three-dimensional curves and their derivatives by free-knot regression splines, applied to the analysis of inner carotid artery centrelines

    JOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES C (APPLIED STATISTICS), Issue 3 2009
    Laura M. Sangalli
    Summary., We deal with the problem of efficiently estimating a three-dimensional curve and its derivatives, starting from a discrete and noisy observation of the curve. This problem is now arising in many applicative contexts, thanks to the advent of devices that provide three-dimensional images and measures, such as three-dimensional scanners in medical diagnostics. Our research, in particular, stems from the need for accurate estimation of the curvature of an artery, from image reconstructions of three-dimensional angiographies. This need has emerged within the AneuRisk project, a scientific endeavour which aims to investigate the role of vessel morphology, blood fluid dynamics and biomechanical properties of the vascular wall, on the pathogenesis of cerebral aneurysms. We develop a regression technique that exploits free-knot splines in a novel setting, to estimate three-dimensional curves and their derivatives. We thoroughly compare this technique with a classical regression method, local polynomial smoothing, showing that three-dimensional free-knot regression splines yield more accurate and efficient estimates. [source]


    High Power Diode Lasers for Industrial Applications

    LASER TECHNIK JOURNAL, Issue 3 2007
    Wolfgang Horn
    New wavelengths, high brightness and increasing reliability are breaking new ground for diode lasers. The higher brightness allows direct fiber coupling of several 100 W in 200 ,m and 400 ,m fibers and therefore i.e. the pumping of fiber lasers. Such high power fiber coupled laser diodes combined with fast beam deflection units (galvo scanners) have been implemented in industrial processes and used for quasi-simultaneous welding of polymers, heat treatment in the sub millimeter range or selective soldering in solar cell production. Besides pumping of solid state lasers, high power diode lasers become more and more a competitive tool for many applications in material processing. [source]


    Compressed sensing MRI with multichannel data using multicore processors

    MAGNETIC RESONANCE IN MEDICINE, Issue 4 2010
    Ching-Hua Chang
    Abstract Compressed sensing (CS) is a promising method to speed up MRI. Because most clinical MRI scanners are equipped with multichannel receive systems, integrating CS with multichannel systems may not only shorten the scan time but also provide improved image quality. However, significant computation time is required to perform CS reconstruction, whose complexity is scaled by the number of channels. In this article, we propose a reconstruction procedure that uses ubiquitously available multicore central processing unit to accelerate CS reconstruction from multiple channel data. The experimental results show that the reconstruction efficiency benefits significantly from parallelizing the CS reconstructions and pipelining multichannel data into multicore processors. In our experiments, an additional speedup factor of 1.6,2.0 was achieved using the proposed method on a quad-core central processing unit. The proposed method provides a straightforward way to accelerate CS reconstruction with multichannel data for parallel computation. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc. [source]


    In vivo 13C magnetic resonance spectroscopy of human brain on a clinical 3 T scanner using [2- 13C]glucose infusion and low-power stochastic decoupling

    MAGNETIC RESONANCE IN MEDICINE, Issue 3 2009
    Shizhe Li
    Abstract This study presents the detection of [2- 13C]glucose metabolism in the carboxylic/amide region in the human brain, and demonstrates that the cerebral metabolism of [2- 13C]glucose can be studied in human subjects in the presence of severe hardware constraints of widely available 3 T clinical scanners and with low-power stochastic decoupling. In the carboxylic/amide region of human brain, the primary products of 13C label incorporation from [2- 13C]glucose into glutamate, glutamine, aspartate, ,-aminobutyric acid, and N-acetylaspartate were detected. Unlike the commonly used alkanyl region where lipid signals spread over a broad frequency range, the carboxylic carbon signal of lipids was found to be confined to a narrow range centered at 172.5 ppm and present no spectral interference in the absence of lipid suppression. Comparison using phantoms shows that stochastic decoupling is far superior to the commonly used WALTZ sequence at very low decoupling power at 3 T. It was found that glutamine C1 and C5 can be decoupled using stochastic decoupling at 2.2 W, although glutamine protons span a frequency range of ,700 Hz. Detailed specific absorption rate analysis was also performed using finite difference time domain numerical simulation. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [source]


    Imaging single mammalian cells with a 1.5 T clinical MRI scanner

    MAGNETIC RESONANCE IN MEDICINE, Issue 5 2003
    Paula Foster-Gareau
    Abstract In the present work, we demonstrate that the steady-state free precession (SSFP) imaging pulse sequence FIESTA (fast imaging employing steady state acquisition) used in conjunction with a custom-built insertable gradient coil and customized RF coils can be used to detect individual SPIO-labeled cells using a commonly available 1.5 T clinical MRI scanner. This work provides the first evidence that single-cell tracking will be possible using clinical MRI scanners, opening up new possibilities for cell tracking and monitoring of cellular therapeutics in vivo in humans. Magn Reson Med 49:968,971, 2003. © 2003 Wiley-Liss, Inc. [source]


    In vivo measurement of brain metabolites using two-dimensional double-quantum MR spectroscopy,exploration of GABA levels in a ketogenic diet

    MAGNETIC RESONANCE IN MEDICINE, Issue 4 2003
    Zhiyue J. Wang
    Abstract A localized proton 2D double-quantum (DQ) spin-echo spectroscopy technique was implemented on 1.5 T clinical MRI scanners for the detection of ,-aminobutyrate (GABA) in the brain. The 2D approach facilitates separation of peaks overlapping with GABA in 1D DQ-filtered (DQF) spectra. This technique was applied to four normal adult volunteers and four children with intractable epilepsy. The coefficient of variation of the level of GABA and overlapping macromolecules at F2 = 3.0 ppm and F1 = 4.8 ppm was 0.08 in normal subjects. Three patients received 2D MRS scans before and after initiation of the ketogenic diet (KD): one patient showed a trend of decreasing GABA throughout the study, and two patients showed low initial GABA levels that increased over time. In addition to major metabolites and GABA, low-level metabolites (valine, leucine, and glutathione) were also identified in the 2D spectra. Magn Reson Med 49:615,619, 2003. © 2003 Wiley-Liss, Inc. [source]


    Nondestructive optical determination of fiber organization in intact myocardial wall

    MICROSCOPY RESEARCH AND TECHNIQUE, Issue 7 2008
    Rebecca M. Smith
    Abstract Mapping the myocardial fiber organization is important for assessing the electrical and mechanical properties of normal and diseased hearts. Current methods to determine the fiber organization have several limitations: histological sectioning mechanically distorts the tissue and is labor-intensive, while diffusion tensor imaging has low spatial resolution and requires expensive MRI scanners. Here, we utilized optical clearing, a fluorescent dye, and confocal microscopy to create three-dimensional reconstructions of the myocardial fiber organization of guinea pig and mouse hearts. We have optimized the staining and clearing procedure to allow for the nondestructive imaging of whole hearts with a thickness up to 3.5 mm. Myocardial fibers could clearly be identified at all depths in all preparations. We determined the change of fiber orientation across strips of guinea pig left ventricular wall. Our study confirms the qualitative result that there is a steady counterclockwise fiber rotation across the ventricular wall. Quantitatively, we found a total fiber rotation of 105.7 ± 14.9° (mean ± standard error of the mean); this value lies within the range reported by previous studies. These results show that optical clearing, in combination with a fluorescent dye and confocal microscopy, is a practical and accurate method for determining myocardial fiber organization. Microsc. Res. Tech., 2008. © 2008 Wiley-Liss, Inc. [source]