bluuebunny/crossref_metadata_2025_split huggingface dataset:
STAR‐HASTE: Perfusion imaging without magnetic susceptibility artifact
Authors: Chen Qun , Siewert Bettina , Bly Benjamin Martin , Warach Steven , Edelman Robert R. 
Published: March 2007

AbstractA novel magnetic resonance imaging technique (STAR‐HASTE) based on pulsed arterial spin labeling using a single shot acquisition method is described for perfusion imaging. The method is similar to EPISTAR in using STAR (Signal Targeting with Alternating Radiofrequency) technique for pulsed radiofrequency labeling of inflowing blood, but uses a half‐Fourier single shot turbo spin‐echo (HASTE) sequence for data acquisition instead of echo‐planar imaging (EPI). Our preliminary studies show that STAR‐HASTE permits perfusion imaging to be performed without many of the artifacts encountered with other imaging methods based on EPI acquisition. The novel method not only provides similar perfusion information to that obtained by EPISTAR, as demonstrated in the functional brain imaging study, but also eliminates magnetic susceptibility artifacts and image distortion commonly observed in EPI images. Furthermore, this technique can be readily implemented in MR systems without EPI capability.
Quantitative measurements of regional cerebral blood volume using MRI in rats: Effects of arterial carbon dioxide tension and mannitol
Authors: Lin Weili , Paczynski Richard P. , Kuppusamy Karthikeyan , Hsu Chung Y. , Haacke E. Mark 
Published: March 2007

AbstractA three‐dimensional (3D) T1‐weighted sequence was used to acquire high spatial resolution whole brain images in rats before and after the injection of an intravascular contrast agent. These T1‐weighted images were used to estimate regional cerebral blood volume (rCBV) as a percentage of blood volume in each voxel. Ventilation was manipulated to investigate the effects of altered arterial carbon dioxide tension (PaCO2) on rCBV. In addition, different doses of a hypertonic mannitol solution were used to investigate the sensitivity of the proposed method in a serial monitoring paradigm. An rCBV of 2.40% ± 0.34% was obtained before any physiological manipulation, in good agreement with literature values using alternative techniques. Using this method, it was found that there exists a linear relationship between PaCO2 and rCBV (R2 = 0.77) and that rCBV increased in a dose and time dependent fashion in mannitol‐treated rats. High signal‐to‐noise was available due to the substantial increase in blood signal from the intravascular contrast agent.
Quantification and reduction of ghosting artifacts in interleaved echo‐planar imaging
Authors: Reeder Scott B. , Atalar Ergin , Bolster Bradley D. , McVeigh Elliot R. 
Published: March 2007

AbstractA mathematical analysis of ghosting artifacts often seen in interleaved echo‐planar images (EPI) is presented. These artifacts result from phase and amplitude discontinuities between lines of k‐space in the phase‐encoding direction, and timing misregistrations from system filter delays. Phase offsets and time delays are often measured using “reference” scans, to reduce ghosting through post‐processing. From the expressions describing ghosting artifacts, criteria were established for reducing ghosting to acceptable levels., Subsequently, the signal‐to‐noise ratio (SNR) requirements for estimation of time delays and phase offsets, determined from reference scans, was evaluated to establish the effect of estimation emor on artifact reduction for interleaved EPI. Artifacts resulting from these effects can be reduced to very low levels when appropriate reference scan estimation is used. This has important implications for functional MRI (fMRI) and applications involving small changes in signal intensity.
Noise suppression digital filter for functional magnetic resonance imaging based on image reference data
Authors: Buonocore Michael H. , Maddock Richard J. 
Published: March 2007

AbstractThe central decision in every functional magnetic resonance imaging (fMRI) experiment is whether pixels in brain tissues are showing activation in response to neural stimulus or as a result of noise. Images are degraded not only by random (e.g., thermal) noise, but also by structured noise due to MR system characteristics, cardiac and respiratory pulsations, and patient motion. A novel digital filter has been developed to suppress cardiac and respiratory structured noise in fMRI images, using estimates of structured and random noise power spectra obtained directly from the images. It is an adaptive filter based on stationary noise statistics, and is equivalent in form to a Wiener filter. A mathematical model of the filtering process was developed to understand how the strength and distribution of structured and random noise power influenced filter performance. The filter was tested using images from an auditory activation study in ten subjects. In subjects whose structured noise power was localized to a relatively narrow frequency range, a strong relationship was found, both experimentally (R = 0.975, P < 0.0004 for Ho: R = 0) and using the model, between filter performance and the level of structured noise power contaminating the experiment frequency. The filter significantly reduced the rate of false‐positive activations in the subset of subjects whose experiment frequency was relatively heavily contaminated by structured noise. Notch filters, that simply eliminate unwanted frequencies, performed poorly in all subjects. Unlike the proposed Wiener filter, these filters did not suppress structured noise power at the experiment frequency that contributes to false‐positive activations.
Dynamic shimming for multi‐slice magnetic resonance imaging
Authors: Morrell Glen , Spielman Daniel 
Published: March 2007

AbstractDynamic shimming has been implemented in three pulse sequences on a commercial GE Signa 1.5‐T imaging system. Multi‐slice field maps are acquired before the imaging sequence, and linear shim terms and center frequencies are calculated for each slice. During the imaging scan, the linear shim terms and center frequency are set before each pulse sequence repetition according to the current slice. Acquisition of multi‐slice field maps and calculation of shim terms and center frequency for each slice are accomplished in a matter of seconds. Pulse sequences require only minimal modification to add dynamic shimming capability. Results are shown for a fat saturation spin‐echo sequence, a single‐shot echo‐planar gradient‐recalled echo sequence, and a spiral acquisition gradient‐recalled echo sequence. In all cases, dynamic shimming with shim currents and center frequency optimized for each slice is shown to give better results than constant shim currents and a single center frequency optimized for the entire volume of interest.
Estimating test‐retest reliability in functional MR imaging I: Statistical methodology
Authors: Genovese Christopher R. , Noll Douglas C. , Eddy William F. 
Published: March 2007

AbstractA common problem in the analysis of functional magnetic resonance imaging (fMRI) data is quantifying the statistical reliability of an estimated activation map. While visual comparison of the classified active regions across replications of an experiment can sometimes be informative, it is typically difficult to draw firm conclusions by inspection; noise and complex patterns in the estimated map make it easy to be misled. Here, several statistical models, of increasing complexity, are developed, under which “test‐retest” reliability can be meaningfully defined and quantified. The method yields global measures of reliability that apply uniformly to a specified set of brain voxels. The estimates of these reliability measures and their associated uncertainties under these models can be used to compare statistical methods, to set thresholds for detecting activation, and to optimize the number of images that need to be acquired during an experiment.
Estimating test‐retest reliability in functional MR imaging II: Application to motor and cognitive activation studies
Authors: Noll Douglas C. , Genovese Christopher R. , Nystrom Leigh E. , Vazquez Alberto L. , Forman Steven D. , Eddy William F. , Cohen Jonathan D. 
Published: March 2007

AbstractFunctional magnetic resonance imaging (fMRI) using blood oxygenation contrast has rapidly spread into many application areas. In this paper, a new statistical model is used to evaluate the reliability of fMRI activation in a finger opposition motor paradigm for both within‐session and between‐session data and in a working memory paradigm for between‐session data. A slice prescription procedure for between‐session reproducibility is introduced. Estimates are made for the probabilities of correctly and falsely classifying voxels as active or inactive and receiver operator characteristic curves are generated. In the motor paradigm, estimated between‐session reliability was found to be somewhat reduced relative to within‐session reliability; however, this includes additional sources of variation and may not reflect intrinsically lower reliability. After matching false‐positive classification probabilities, between‐session reliability was found to be nearly identical for both motor and cognitive activation paradigms.
Half‐fourier BURST imaging on a clinical scanner
Authors: Jakob Peter M. , Griswold Mark A. , Lovblad Karl O. , Chen Qun , Edelman Robert R. 
Published: March 2007

AbstractA modified BURST imaging technique with a nearly twofold reduction in acquisition time, improved signal‐to‐noise ratio and clear improvement of the image quality is introduced. The method applies half‐Fourier reconstruction and can be implemented on a standard clinical scanner. This approach allows the collection of single‐shot magnetization prepared images of the human brain with a matrix size of 112 × 128 within 86‐250 ms. The signal‐to‐noise properties of the pulse sequence are analyzed and compared with a standard BURST experiment.
Regional measurement of the Gd‐DTPA tissue partition coefficient in canine myocardium
Authors: Harris Paul A. , Lorenz Christine H. , Holburn George E. , Overholser Knowles A. 
Published: March 2007

AbstractQuantifiable MRI perfusion studies using the contrast agent Gd‐DTPA require measurement or estimation of the tissue partition coefficient (λ) for tracer kinetic modeling. Radiotracer techniques were used to obtain regional λ measurements from the left ventricles of five dogs. Measurements were analyzed to determine whether spatial heterogeneity was a major component of λ variability. No systematic variations were identified in terms of radial position, short‐axis slice location, or wall position. The high λ variability seen in this study and in cited data of others may be due in part to tissue heterogeneity in interstitial volume, plasma volume, and perfusate hematocrit.
Slice profile effects in adiabatic inversion: Application to multislice perfusion imaging
Authors: Frank Lawrence R. , Wong Eric C. , Buxton Richard B. 
Published: March 2007

AbstractImperfections in the slice profile of the adiabatic inversion induced by relaxation effects are shown to cause signal variations in pulsed arterial tagging schemes on the order of magnitude of perfusion changes, and result in gross errors in perfusion quantitation. Significant improvement can be made with minor modifications to the inversion pulse which facilitate the acquisition of quantitative, multislice perfusion images, as demonstrated in both a phantom and a normal human volunteer.
Classification of 1H MR spectra of biopsies from untreated and recurrent ovarian cancer using linear discriminant analysis
Authors: Wallace J. C. , Raaphorst G. P. , Somorjai R. L. , Ng C. E. , Fung Fung M. Kee , Senterman M. , Smith Ianc. P. 
Published: March 2007

AbstractProton (1H) magnetic resonance (MR) spectra of ex vivo biopsy samples of ovarian cancers provided biochemical information that was used to discriminate cancer from normal ovarian tissue. Possible differences present in intrinsically resistant tumors or changes in biochemistry after the induction of resistance were identified. Using multivariate techniques, in particular linear discriminant analysis (LDA), ovarian cancer was distinguished from normal ovarian tissue with a sensitivity of 100%, a specificity of 95% and an accuracy of 98%. Moreover, LDA was able to distinguish untreated ovarian cancer from recurrent ovarian cancer with a sensitivity of 92%, a specificity of 100%, and an accuracy of 97%; removal of the single “fuzzy” specimen increased the accuracy to 100%. Applications of this knowledge to in vivo measurements could lead to noninvasive diagnosis of ovarian cancer.
SPLICE: Sub‐second diffusion‐sensitive MR imaging using a modified fast spin‐echo acquisition mode
Authors: Schick Fritz 
Published: March 2007

AbstractRecent human studies for measuring of the apparent diffusion coefficient in tissue by magnetic resonance imaging have been conducted by time‐consuming standard spin‐echo acquisition sequences and phase correction with navigator echoes. Diffusion‐weighted echo‐planar sequences have been shown to be rapid alternatives for brain imaging. Both methods show inherent disadvantages in applications on thoracic or abdominal sites. A new approach combining single‐shot diffusion‐weighted imaging with a modified fast spin‐echo acquisition mode is reported here. The modification is necessary, because normal fast spin‐echo acquisition requires a particular phase relation between the magnetization and the refocusing pulses. Unfortunately, this phase relation is not provided after diffusion sensitive preparation. Therefore, the split echo acquisition mode was developed and is shown to be insensitive to the phase of the magnetization. The advantages of both fast spin‐echo acquisition and diffusion weighting can be combined in the SPLICE sequence (split aqcuisition of fast spin‐echo signals for diffusion imaging). The applicability of the new technique is shown by series of sub‐second diffusion‐weighted images from different parts of the body.
Effects of diffusion anisotropy on lesion delineation in a rat model of cerebral ischemia
Authors: Lythgoe Mark F. , Busza Albert L. , Calamante Fernando , Sotak Christopher H. , King Martin D. , Bingham Anna C. , Williams Stephen R. , Gadian David G. 
Published: March 2007

AbstractThe effects of white and gray matter diffusion anisotropy on ischemic lesion delineation have been studied in the rat model of middle cerebral artery occlusion. Apparent diffusion coefficient (ADC) maps obtained by conventional pulsed gradient spin echo diffusion‐weighted imaging (PGSE‐DWI) were compared with maps of the trace of the diffusion tensor in both normal and occluded animals. Diffusion tensor trace maps were derived from the average of the ADC maps from three separate experiments with diffusion weighting along three orthogonal axes, and also from a single‐scan method. A marked degree of diffusion anisotropy was observed in both cortical gray matter and white matter from ADC maps of the control animals. In the occluded animals, the systematic effects of anisotropy on ADC and lesion area influenced the delineation of the ischemic territory in the PGSE‐DWI ADC maps. However, the two trace methods eliminated these effects and gave consistent ischemic lesion depiction, despite the use of differing diffusion times in the two measurements.
An in vivo model for functional MRI in cat visual cortex
Authors: Jezzard Peter , Rauschecker Josef P. , Malonek Dov 
Published: March 2007

AbstractA protocol is described for obtaining functional magnetic resonance images in anesthetized cat brain based on the blood oxygenation level dependent (BOLD) contrast mechanism. A visual stimulus was used, which consisted of a high‐contrast drifting grating, whose speed and spatial frequency was optimized for cat area 18 (V2). Experiments were conducted at 4.7 Tesla using a gradient echo EPI sequence with a 29‐ms echo time, yielding signal changes of between 0.7% and 2% in area 18.
Measurement of the point spread function in MRI using constant time imaging
Authors: Robson Matthew D. , Gore John C. , Constable R. Todd 
Published: March 2007

AbstractThe point spread function is a fundamental property of magnetic resonance imaging methods that affects image quality and spatial resolution. The point spread function is difficult to measure precisely in magnetic resonance even with the use of carefully designed phantoms, and it is difficult to calculate this function for complex sequences such as echo‐planar imaging. This report describes a method that measures the point spread function with high spatial resolution at each pixel in samples of uniform intensity distribution. This method uses additional phase encoding gradients before the echo‐planar acquisition that are constant in length but vary in amplitude. The additional gradients are applied to image the contents within each individual voxel. This method has been used to measure the point spread function for echo‐planar imaging to demonstrate the effects of limited k‐space sampling and transverse relaxation, as well as the effects of object motion. By considering the displacement of the point spread function, local distortions due to susceptibility and chemical shift effects have been quantified and corrected. The method allows rapid assessment of the point spread function in echo‐planar imaging, in vivo, and may also be applied to other rapid imaging sequences that can be modified to include these additional phase encoding gradients.
Isotropic diffusion‐weighted and spiral‐navigated interleaved EPI for routine imaging of acute stroke
Authors: Butts Kim , Pauly John , De Crespigny Alex , Moseley Michael 
Published: March 2007

AbstractAn interleaved echo‐planar imaging (EPI) technique is presented for the rapid acquisition of isotropic diffusion‐weighted images of stroke patients. Sixteen isotropic diffusion‐weighted images at three b values are acquired in less than 3 min. A spiral navigator echo is used to measure the constant and linear phase shifts across the head in both the x and y directions which result from motion during the isotropic diffusion‐ sensitizing gradients. The measured k‐space errors are corrected during a gridding reconstruction. The gridding kernel has a constant width in kx and a variable width in ky which eliminates variable data‐density ghosts. The resulting isotropic diffusion‐weighted images have excellent lesion‐to‐normal brain contrast, very good spatial resolution, and little sensitivity to susceptibility effects in the base of the brain. Examples of diffusion‐weighted images and ADC maps from several stroke patients are shown.
Noninvasive comprehensive characterization of renal artery stenosis by combination of STAR angiography and EPISTAR perfusion imaging
Authors: Prasad Pottumarthi V. , Kim Ducksoo , Kaiser Andreas M. , Chavez David , Gladstone Steven , Li Wei , Buxton Richard B. , Edelman Robert R. 
Published: March 2007

AbstractIn a small fraction of patients with hypertension, the cause is stenosis of the renal artery. To date, there is no established noninvasive screening technique available to identify this population, for whom treatment with a surgical procedure or percutaneous transluminal angioplasty is often possible. In this study, the sensitivity and specificity of STAR angiography and EPISTAR perfusion imaging in characterizing renal artery stenosis were evaluated in an animal model. Qualitatively, STAR provided projection angiograms that were comparably sensitive to x‐ray angiograms but obtained noninvasively. The sensitivity for detecting the stenosis was 100%. The specificity varied according to the definition of the threshold for significance, which varied 78–94%, depending on whether >70% or >50% diameter reduction was considered. Improvements in specificity will depend upon use of shorter echo times and higher spatial resolution. Our preliminary data indicate that EPISTAR provides sensitivity and specificity of 100% for characterizing stenosis with diameter reductions of >70%.
A simplified sequence for observing deoxymyoglobin signals in vivo: Myoglobin excitation with dynamic unexcitation and saturation of water and fat (MEDUSA)
Authors: Noyszewski Elizabeth A. , Chen Enn‐Ling , Reddy Ravinder , Wang Zhiyue , Leigh John S. 
Published: March 2007

AbstractThis paper describes a new, simplified pulse sequence for observing NMR signals from deoxymyoglobin in vivo. Paramagnetically shifted resonances from deoxymyoglobin can be exploited to noninvasively calculate intracellular oxygen tension in striated muscle. However, special sequences are required to observe these weak signals against the larger water and fat signals encountered in vivo. The pulse sequence described here, which is based on inversion recovery sequences, efficiently suppresses both water and fat resonances and can be implemented with short repetition rates. Moreover, it is perfectly suited for studies with surface coils, where RF inhomogeneities render other popular suppression sequences ineffective.
Statistical methods in functional magnetic resonance imaging with respect to nonstationary time‐series: Auditory cortex activity
Authors: Gaschler‐Markefski Birgit , Baumgart Frank , Tempelmann Claus , Schindler Frank , Stiller Detlet , Heinze Hans‐Jachen , Scheich Henning 
Published: March 2007

AbstractIn awake animal and human auditory cortices, it is a common experience with electrophysiological and suitable imaging methods for responses to steady stimulation to be strongly state‐dependent and to exhibit nonstationarities, even over short periods of observation. If such nonstationary behavior is also reflected by hemodynamic responses in the human auditory cortex, conventional methods of analysis of fMRI data, although applicable for instance to largely stationary responses in visual and other cortices, may be misleading in attempts to parcellate auditory cortex into fields and to demonstrate functional maps. Time‐Windows, described in this article as a convenient tool for the detection and analysis of time‐variant brain activities, solves some of these problems. Time‐Windows demonstrates that activity is evoked reliably in three separate territories of human auditory cortex, parts of which may show nonstationary behavior, depending on the auditory stimuli and tasks.
Implementation and evaluation of frequency offset corrected inversion (FOCI) pulses on a clinical MR system
Authors: Payne Geoffrey S. , Leach Martin O. 
Published: March 2007

AbstractFOCI pulses are a variant of hyperbolic secant pulses in which the RF amplitude, RF frequency, and gradient waveform are all modulated by the same function A(t). This increases the usable gradient amplitude without requiring a corresponding increase in RF amplitude. In this paper the implementation and inversion profiles of FOCI pulses on a clinical MR system are described, showing improved slice definition and chemical‐shift offset behavior. Their adiabatic behavior is confirmed, and their use with an ISIS sequence for localized MRS is illustrated. Finally the effects of waveform digitization are considered, and the implications for SAR and db/dt are discussed.
Improvements on an in Vivo automatic shimming method (FASTERMAP)
Authors: Shen Jun , Rycyna Robert E. , Rothman Douglas L. 
Published: March 2007

AbstractImprovements on a localized, automatic shimming method described by Gruetter and Boesch (J. Magn. Reson. 96, 323–334 (1992)) and Gruetter (Magn. Reson. Med. 29, 804–811 (1993)) are presented. A spin‐echo sequence employing a double sech refocusing scheme is used to acquire a field map along linear projections that improves the signal‐to‐noise ratio by at least a factor of two over the stimulated echo sequence previously used. To further improve the reliability of shim adjustments, a variance‐weighted polynomial regression analysis is performed. This also extends the scope of application of this technique to global shimming. Localized 1H spectra of human brain shimmed by this method are presented.