bluuebunny/crossref_metadata_2025_split huggingface dataset:
Perfusion imaging by a flow‐sensitive alternating inversion recovery (Fair) technique: Application to functional brain imaging
Authors: Kim Seong‐Gi , Tsekos Nikolaos V. 
Published: March 2007

AbstractPerfusion is a crucial physiological parameter for tissue function. To obtain perfusion‐weighted images and consequently to measure cerebral blood flow (CBF), a newly developed flow‐sensitive alternating inversion recovery (FAIR) technique was used. Dependency of FAIR signal on inversion times (TI) was examined; signal is predominantly located in large vessels at short TI, whereas it is diffused into gray matter areas at longer TI. CBF of gray matter areas in the human brain is 71 ± 15 SD ml/100 g/min (n = 6). In fMRI studies, micro‐ and macrovessel inflow contributions can be obtained by adjusting TIs. Signal changes in large vessel areas including the scalp were seen during finger opposition at a TI of 0.4 s; however, these were not observed at a longer TI of 1.4 s. To compare with commonly used BOLD and slice selective inversion recovery techniques, FAIR and BOLD images were acquired at the same time during unilateral finger opposition. Generally, activation sites determined by three techniques are consistent. However, activation of some areas can be detected only by FAIR, not by BOLD, suggesting that the oxygen consumption increase couples with the CBF change completely. Relative and absolute CBF changes in the contralateral motor cortex are 53 ± 17% SD (n = 9) and 27 ± 11 SD ml/100 g/min (n = 9), respectively.
Reducing flow artifacts in echo‐planar imaging
Authors: Pat Gerard T. Luk , Meyer Craig H. , Pauly John M. , Nishimura Dwight G. 
Published: March 2007

AbstractEcho‐planar imaging (EPI) is very susceptible to flow artifacts. Two ways to improve its flow properties are presented. First, “partial flyback” is proposed to reduce artifacts arising from flow in the readout direction. Near the center of k‐space, only the even echoes of the EPI echo‐train are used. Partial flyback is shown to improve the readout‐flow properties at the expense of a slight worsening of the phase‐encode flow and off‐resonance properties. We recommend that the flyback region acquire 95% of the energy in k‐space. Second, “inside‐out” EPI is used to reduce artifacts arising from flow in the phase‐encode direction. Data collection begins at the center of k‐space, with separate interleaves to acquire the top and bottom halves of k‐space. Partial flyback is combined with partial‐Fourier EPI and inside‐out EPI. Partial‐flyback inside‐out EPI has worse off‐resonance properties than partial‐flyback partial‐Fourier EPI but demonstrates better flow properties and does not require partial k‐space reconstruction.
Improved intracranial lesion characterization by tissue segmentation based on a 3D feature map
Authors: Vinitski Simon , Gonzalez Carlos , Mohamed Feroze , Iwanaga Tad , Knobler Robert L. , Khalili Kamil , Mack John 
Published: March 2007

AbstractOur aim was to develop an accurate multispectral tissue segmentation method based on 3D feature maps. We utilized proton density (PD), T2‐weighted fast spin‐echo (FSE), and T1‐weighted spin‐echo images as inputs for segmentation. Phantom constructs, cadaver brains, an animal brain tumor model and both normal human brains and those from patients with either multiple sclerosis (MS) or primary brain tumors were analyzed with this technique. Initially, misregistration, RF inhomogeneity and image noise problems were addressed. Next, a qualified observer identified samples representing the tissues of interest. Finally, k‐nearest neighbor algorithm (k‐NN) was utilized to create a stack of color‐coded segmented images. The inclusion of T1 based images, as a third input, produced significant improvement in the delineation of tissues. In MS, our 3D technique was found to be far superior to that based on any combination of 2D feature maps (P < 0.001). We identified at least two distinctly different classes of lesions within the same MS plaque, representing different stages of the disease process. Further, we obtained the regional distribution of MS lesion burden and followed its changes over time. Neuropsychological aberrations were the clinical counterpart of the structural changes detected in segmentation. We could also delineate the margins of benign brain tumors. In malignant tumors, up to four abnormal tissues were identified: 1) a solid tumor core, 2) a cystic component, 3) edema in the white matter, and 4) areas of necrosis and hemorrhage. Subsequent neurosurgical exploration confirmed the distribution of tissues as predicted by this analysis.
The nature of spatiotemporal changes in cerebral hemodynamics as manifested in functional magnetic resonance imaging
Authors: Mitra Partha P. , Ogawa Seiji , Hu Xiaoping , Uǧurbil Kǎmil 
Published: March 2007

AbstractThe nature of changes in rapidly acquired magnetic resonance images of the brain was studied by using a denoising method and spectral techniques optimally suited to short time series. It was found that the stimulus related changes have a complex spatiotemporal structure even for simple visual stimuli. Apart from a low frequency window, the non‐stimulusrelated changes were found to correspond in detail to either breathing or heartbeat, although these two sources show different patterns of spatial coherence in the image. At low frequencies, oscillations with frequencies around 0.1 Hz were observed, also with nontrivial space‐time structure, which are likely to be vasomotor in origin.
Hepatic hemosiderosis in non‐human primates: Quantification of liver iron using different field strengths
Authors: Bulte Jeff W. M. , Miller Georgina F. , Vymazal Josef , Brooks Rodney A. , Frank Joseph A. 
Published: March 2007

AbstractUsing a non‐human primate model of idiopathic hemochro‐matosis, hemosiderin‐induced T2 shortening of the liver was assessed at nine different field strengths over a range of 0.05 to 1.5 Tesla. The 1/T2 values increased linearly with field strength, with all specimens having approximately the same zero‐field intercept. The slope of the field increase, termed “field‐dependent T2 proton relaxation enhancement (PRE)”, appeared to be proportional to the chemically determined tissue iron content, viz. 10.8 s−1T−1(mg Fe/g wet tissue)−1. The correlation between iron content and field‐dependent T2 PRE (r = 0.94) was better than the correlation between iron content and 1/T2 values obtained at single field strengths. For livers containing ± 2 mg Fe/g wet weight, biexponential T2 relaxation behavior emerged at higher field strengths, with the short T2 component (intracellular water) exhibiting a linear dependence of 1/T2 on field, while T2 of the long component (extracellular/sinusoidal water) was nearly field‐independent. After maceration of the specimens, all T2 relaxation curves became monoexponential, including those for high iron content at high field strengths. The present data suggest that the use of double‐field MR imaging to assess the field‐dependent T2 PRE has potential for specific quantification of (liver) tissue iron stores.
Reduction of motion artifacts in cine MRI using variable‐density spiral trajectories
Authors: Liao Jan‐Ray , Pauly John M. , Brosnan Thomas J. , Pelc Norbert J. 
Published: March 2007

AbstractDynamic cardiac imaging in MRI is a very challenging task. To obtain high spatial resolution, temporal resolution, and signalto‐noise ratio (SNR), single‐shot imaging is not sufficient Use of multishot techniques resolves this problem but can cause motion artifacts because of data inconsistencies between views. Motion artifacts can be reduced by signal averaging at some cost in increased scan time. However, for the same increase in scan time, other techniques can be more effective than simple averaging in reducing the artifacts. If most of the energy of the inconsistencies is limited to a certain region of k‐space, increased sampling density (oversampling) in this region can be especially effective in reducing motion artifacts. In this work, several variable‐density spiral trajectories are designed and tested. Their efficiencies for artifact reduction are evaluated in computer simulations and in scans of normal volunteers. The SNR compromise of these trajectories is also investigated. The authors conclude that variable‐density spiral trajectories can effectively reduce motion artifacts with a small loss in SNR as compared with a uniform density counterpart.
Quantitative diffusion imaging in implanted human breast tumors
Authors: Maier Cynthia F. , Paran Yael , Bendel Peter , Rutt Brian K. , Degani Hadassa 
Published: March 2007

AbstractQuantitative diffusion measurements were performed in tumors arising from inoculation of nude mice with two human breast cancer cell lines (MCF7 and T47D) to evaluate the specificity of this technique for characterizing solid tumors. ADC maps were compared to histology and correlated well with gross tumor morphology. Measured ADCs were highly specific for viable and necrotic tumor in the five T47D tumors included in this study (P < 0.02), while only two of the five MCF7 tumors studied developed distinguishable areas of necrosis. No statistically significant difference was observed in ADCs from viable tumor between the different cell lines (P > 0.05).
What is the optimum phased array coil design for cardiac and torso magnetic resonance?
Authors: Bottomley Paul A. , Olivieri Carlos H. Lugo , Giaquinto Randy 
Published: March 2007

AbstractTo determine the optimum configuration of a phased array MR coil system for human cardiac applications, the sensitivity of 10 flexible array designs operating under ideal conditions was calculated at 13 points circling the myocardium of a model torso whose geometry was determined from healthy volunteers. The array geometries that were evaluated included continuous strips of 2,4,6, and 10 circular coils of diameter equal to half the torso thickness wrapped laterally around the torso, 2 pairs of coils located on the left side of the chest and back, clusters of 3 coils in 2 orientations, clusters of 4 and 6 coils, and a hybrid cross of 6 coils. The 4‐, 6‐, and 10‐coil strip arrays out‐performed the other designs for a given number of coils, yielding average theoretical sensitivity improvements of 45%, 53%, and 55% relative to a single flexible coil positioned at the point closest to the anterior myocardium, compared with about 30% for 4‐ and 6‐coil clusters and the 2‐pair geometry (P < 0.02). A flexible 4‐coil strip array was constructed for a clinical 1.5 T scanner with 15‐cm diameter circular surface coils on flexible circuit board. The signal‐to‐noise ratio (SNR) of this coil at the 13 cardiac locations was measured in 15 normal volunteers and compared with the SNR measured in images acquired with standard commercial MR coils: a body coil, a flexible torso array, a general purpose flexible coil, and, in 4 subjects, a dual array coil. In the prone orientation, the average myocardial SNR improvement of the 4‐coil strip array was 650% relative to the whole body coil, compared with 310–340% for the other commercial coils (P < 0.00005). The twofold advantage over the commercial coils persisted in supine studies (P < 0.00005, n = 5). Thus, flexible circumferential phased arrays of strips of surface coils of diameter comparable with the depth of the heart generally out‐perform many other standard geometries for a given number of coils, and can yield dramatically improved SNR over coils available for general use in the torso.
A method to create an optimum current distribution and homogeneous B1 field for elliptical birdcage coils
Authors: Li Shizhe , Collins Christopher M. , Dardzinski Bernard J. , Chin Chih‐Liang , Smith Michael B. 
Published: March 2007

AbstractFor a birdcage coil with elliptical cross‐section, a sinusoidal current pattern does not provide a homogeneous B1 field. A simple theory was developed to create an optimized current distribution for elliptical birdcage coils. This optimized current pattern can create a perfectly homogeneous B1 field inside any elliptical shape. To verify the theory, a 16‐element high‐pass elliptical birdcage coil was built inside a circular RF shield. The current was optimized by using the inductance characteristics of the coil components to calculate the endring capacitances. The B1 field was theoretically calculated and experimentally mapped for the optimized elliptical birdcage coil and a nonoptimized coil. The results demonstrate that by optimizing the current distribution, a very homogeneous B1 field is produced. This method can be directly applied in design and construction of elliptical birdcage coils for imaging of the naturally occurring elliptical cross‐sectional geometries in the human body.
Oblique proton chemical shift imaging for the presurgical localization of mesial temporal epilepsy
Authors: Xue Min , Ng Thian C. , Majors Anthony , Modic Michael , Kolem Heiner 
Published: March 2007

AbstractPrecise localization of the epileptogenic zone in patients suffering from mesial temporal lobe epilepsies is a prerequisite for surgery. For this purpose, a scheme for selecting the volume of interest in an oblique plane covering the head, body, and tail of the hippocampal formation (HF) was implemented in a water‐suppressed proton chemical shift imaging (CSI) acquisition. This approach, evaluated by consecutively acquired CSI spectra of both temporal lobes, demonstrates that it can potentially be a routine technique for clinical diagnosis. Since the method produces localized spectral detail of the HF, it facilitates a convenient comparison of CSI lateralization to that assessed by HF atrophy (due to sclerosis) using the MRI‐volumetry technique.
A study of diffusion isotropy in single neurons by using NMR microscopy
Authors: Hsu Edward W. , Aiken Nanci R. , Blackband Stephen J. 
Published: March 2007

AbstractThe apparent diffusion coefficient (ADC) of water was measured in single Aplysia californica neurons by using NMR microscopy encoded in each of two perpendicular gradient directions. Comparisons of the mean ADCs of the gross nuclear and cytoplasmic compartments in five cells, and 50 subregions within these cells, showed no significant difference between the diffusion measurements in the majority of cases. Since anisotropic diffusion would make the ADC dependent on the encoding direction, the results indicate that the ADC in these single neurons is isotropic at the spatial and temporal resolutions used in these studies. Consequently, a single scalar ADC measurement is sufficient for characterizing the ADC in these cells, hence reducing the acquisition time and measurement complexity that would have been required had the ADC been anisotropic.
Limitations of temporal resolution in functional MRI
Authors: Kim Seong‐Gi , Richter Wolfgang , Uǧurbil Kǎmil 
Published: March 2007

AbstractIn fMRI, images can be collected in a very short time; therefore, high temporal resolution is possible in principle. However, the temporal resolution is limited by a blurred intrinsic hemodynamic response and a finite signal‐to‐noise ratio. To determine the upper limit of temporal resolution in a single area during repeated tasks, motor cortex activity was investigated during visually instructed finger movements. Without averaging, a sequence of four single‐finger movements with an execution time of approximately 2 s can be resolved when the delay time between consecutive sequences is at least 3 s. The hemodynamic response time is constant for each subject, but not among different subjects. The temporal resolution can be better when the signal from spatially distinct regions is examined. For a series of experiments involving a visually instructed delayed cued finger movement task with a well‐defined, independently determined, variable delay time, time courses in the motor area are distinct from each other in two experiments if the difference in delay time is as little as 2 s. The activation in the visual area due to the presentation of the task serves here as an internal time reference. By comparing a set of fMRI time courses in multiple distinct areas, serial neural processing may be investigated.
NMR “diffusion‐diffraction” of water revealing alignment of erythrocytes in a magnetic field and their dimensions and membrane transport characteristics
Authors: Kuchel Philip W. , Coy Andrew , Stilbs Peter 
Published: March 2007

Abstract“Diffusion‐diffraction” experiments on water, yielding “q‐space” plots, were conducted on suspensions of oxygenated (diamagnetic) human erythrocytes. (i) These suspensions displayed diffusion‐diffraction of water; (ii) the shape of theq‐space plots depended on the direction along which the diffusion was measured, thus implying alignment of the cells in the magnetic field of the NMR spectrometer; (iii) the diffusion anisotropy was altered in a predictable way by converting the hemoglobin to a paramagnetic form; (iv) the shapes of theq‐space plots were altered in a predictable way by inhibiting water transport; (v) the pseudo‐first order rate constant characterizing the covalent inhibition of water transport, byp‐chloromercuribenzenesulfonate (p‐CMBS), was measured; and (vi) the cell diameter and intercellular spacing were measured from the positions of the interference minima and maxima in theq‐space plots. The relevance of these findings to NMR‐based histological characterization of tissues, and the implications, for magnetic resonance imaging (MRI), of eryth‐rocyte alignment in the small vessels of the brain in particular, are noted.
3D localized in vivo1H spectroscopy of human brain by using a hybrid of 1D‐hadamard with 2D‐chemical shift imaging
Authors: Gonen Oded , Arias‐Mendoza Fernando , Goelman Gadi 
Published: March 2007

AbstractWe report acquisition of 3D image‐guided localized proton spectroscopy (1H‐MRS) in the human brain on a standard clinical imager. 3D coverage is achieved with a hybrid of chemical shift imaging (CSI) and transverse Hadamard spectroscopic imaging (HSI). 16 × 16 × 4 arrays of 3.5 and 1 ml voxels were obtained in 27 min. The spatially selective HSI 90° pulses incorporate naturally into a PRESS double spin‐echo sequence to subdivide the VOI into four partitions along its short axis. 2D CSI (16 × 16) is performed along the other long axes. Because the hybrid excites the spins in the entire VOI, a √N signal‐to‐noise‐ratio (SNR) gain per given examination time is realized compared with sequentially interleaving N 2D slices. A two‐fold gain in sensitivity is demonstrated in the brain for N = 4.
Off‐resonance pulsed magnetization transfer in clinical MR imaging: Optimization by an analysis of transients
Authors: Listerud John 
Published: March 2007

AbstractSignificant degrees of magnetization transfer (MT) have been observed in the magnetic resonance imaging of biological materials by conventional clinical imaging sequences, as well as by sequences specifically designed to enhance MT image contrast. Two aspects of these procedures distinguish them from the classic spectroscopic MT experiments using either so‐called “hard” radiofrequency (RF) pulses of short duration and high power, or continuous wave RF irradiation of low power. First, clinical sequences must make exclusive use of “soft” pulses of intermediate length and power. Second, biological materials are modeled by a two‐spin system involving magnetization transfer between a narrow and a broad homogeneous spectral component. Such materials are a relatively restricted group within the larger family of materials studied with MT by spectroscopy. The current paper addresses these two issues with a theory that gives a new transient analysis of the off‐resonance pulsed MT problem for biological materials. It leads to predictions for optimal magnetization transfer in the context of medical imaging that have been verified by computer modeling.
Spatially filtering functional magnetic resonance imaging data
Authors: Lowe Mark J. , Sorenson James A. 
Published: March 2007

AbstractWhen constructing MR images from acquired spatial frequency data, it can be beneficial to apply a low‐pass filter to remove high frequency noise from the resulting images. This amounts to attenuating high spatial frequency fluctuations that can affect detected MR signal. A study is presented of spatially filtering MR data and possible ramifications on detecting regionally specific activation signal. It is shown that absolute activation levels are strongly dependent on the parameters of the filter used in image construction and that significance of an activation signal can be enhanced through appropriate filter selection. A comparison is made between spatially filtering MR image data and applying a Gaussian convolution kernel to statistical parametric maps.
Biochemical heterogeneity in hysterectomized uterus measured by31P NMR using SLIM localization
Authors: Xu Su , Yang Yihong , Gregory Carl D. , Vary Jay C. , Liang Zhi‐Pei , Dawson M. Joan 
Published: March 2007

AbstractUltrasound and magnetic resonance imaging show contrast between the inner and outer myometrium, which is useful in the diagnosis of gynecological disorders. To determine whether the image contrast is associated with biochemical differences between these myometrial regions, phosphorus metabolite concentrations in the inner one third of the myometrium (the junctional zone; JZ) were compared with the outermost one third of the myometrium (OM) in hysterectomized uteri using31P spectral localization by imaging (SLIM). The technique was validated by comparing the results of SLIM with the results of standard Fourier‐encoded spectroscopic imaging (FSI) analysis using phantoms, and by nonlocalized spectroscopy on biopsies taken from the same hysterectomy specimens. As expected theoretically, SLIM yielded better localization than FSI, as judged by spectral intensity and leakage measurements on phantom compartments of known composition. SLIM localization revealed that the JZ has a higher intracellular phosphomonoester (PME) concentration than does the OM, which was confirmed by nonlocalized spectroscopy, and that there is very little NMR‐visible phosphorus in the cervix.
Common k‐space acquisition: A method to improve myocardial grid‐tag contrast
Authors: Doyle Mark , Walsh Edward G. , Foster Robert E. , Pohost Gerald M. 
Published: March 2007

AbstractA current limitation of many myocardial tag acquisitions employing SPAMM encoding is the relatively rapid loss of tag contrast over the cardiac cycle. Acquisition schemes that apply line tags produce prolonged tag contrast compared with directly excited grid tags. However, a grid‐tag series can be generated by combining two orthogonal line‐tag series. To be time efficient, each line‐tag series can be acquired with the read gradient oriented perpendicular to the line‐tag direction. There are several disadvantages associated with this approach, including the requirement to avoid signal fold‐over and that fat shift artifacts appear in different directions in each line‐tag series. Presented here is a method of applying separate line tags that does not require interchanging the read and phase encoding gradients and does not extend the scan time compared with a conventional grid‐tag acquisition. Additionally, the means of generating grid tags results in a doubling of the tag contrast to noise ratio compared a line‐tag set. Computer simulations are presented along with phantom and volunteer scans.