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ABSTRACT: PURPOSE: To evaluate the feasibility of diffusion tensor imaging (DTI) for the medial and lateral rectus extraocular muscle (EOM) evaluation, to investigate the normal DTI parameters of the medial and lateral rectus EOM, and to compare with other skeletal muscle. MATERIALS AND METHODS: Seven multiple sclerosis patients and five normal subjects (M:F = 5:7, mean age = 31.6 ± 9.2) without EOM disorder were included. The orbital DTIs using 2D-ss-IMVI-DWEPI were scanned with b = 500 s/mm(2) and 12 directions. The mean diffusivity (MD) and fractional anisotrophy (FA) of medial and lateral rectus EOMs in both orbits, and temporalis muscles were measured in regions of interest on two consecutive axial slices. Student t-test was performed to compare the mean apparent diffusion coefficient and FA values between medial and lateral rectus EOMs, and between EOMs and temporalis muscles. RESULTS: The MDs in medial (0.58 ± 0.18 × 10(-3) mm(2) /s) and lateral rectus EOMs (0.71 ± 0.18 × 10(-3) mm(2) /s) were significantly lower than temporalis muscle (0.84 ± 0.14 × 10(-3) mm(2) /s) (P < 0.001, respectively). The MD in medial rectus EOM was significantly lower than lateral rectus EOM (P = 0.001). The FAs in medial (0.40 ± 0.05) and lateral rectus EOMs (0.40 ± 0.05) were significantly higher than temporalis muscle (0.25 ± 0.05) (P < 0.001, respectively). There was no significant difference between the FAs in medial and lateral rectus EOMs (P > 0.05). CONCLUSION: The MDs of EOMs were lower and the FAs were higher than those of skeletal muscle. These are well correlated to the unique characteristics of EOMs. J. Magn. Reson. Imaging 2013. © 2013 Wiley Periodicals, Inc.
Journal of Magnetic Resonance Imaging 04/2013; · 2.70 Impact Factor
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Young-Hoon Sung,
Deborah A Yurgelun-Todd,
Xian-Feng Shi,
Douglas G Kondo,
Kelly J Lundberg,
Erin C McGlade,
Tracy L Hellem,
Rebekah S Huber,
Kristen K Fiedler,
Renee E Harrell,
Bethany R Nickerson, Seong-Eun Kim,
Eun-Kee Jeong,
Perry F Renshaw
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ABSTRACT: BACKGROUND: Mitochondria-related mechanisms have been suggested to mediate methamphetamine (METH) toxicity. However, changes in brain energetics associated with high-energy phosphate metabolism have not been investigated in METH users. Phosphorus-31 ((31)P) magnetic resonance spectroscopy (MRS) was used to evaluate changes in mitochondrial high energy phosphates, including phosphocreatine (PCr) and β-nucleoside triphosphate (β-NTP, primarily ATP in brain) levels. We hypothesized that METH users would have decreased high-energy PCr levels in the frontal gray matter. METHODS: Study participants consisted of 51 METH (age=32.8±6.7) and 23 healthy comparison (age=31.1±7.5) subjects. High-energy phosphate metabolite levels were compared between the groups and potential gender differences were explored. RESULTS: METH users had lower ratios of PCr to total pool of exchangeable phosphate (PCr/TPP) in the frontal lobe as compared to the healthy subjects (p=.001). The lower PCr levels in METH subjects were significantly associated with lifetime amount of METH use (p=.003). A sub-analysis for gender differences revealed that female METH users, who had lower daily amounts (1.1±1.0g) of METH use than males (1.4±1.7g), had significantly lower PCr/TPP ratios than male METH users, controlling for the amount of METH use (p=.02). CONCLUSIONS: The present findings suggest that METH compromises frontal lobe high-energy phosphate metabolism in a dose-responsive manner. Our findings also suggest that the abnormality in frontal lobe high-energy phosphate metabolism might be more prominent in female than in male METH users. This is significant as decreased PCr levels have been associated with depressive symptoms, and poor responses to antidepressant treatment have been reported in those with decreased PCr levels.
Drug and alcohol dependence 10/2012; · 3.60 Impact Factor
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ABSTRACT: The purpose of this work was to design and construct a multichannel receive-only radiofrequency coil for 3T magnetic resonance imaging of the human carotid artery and bifurcation with optimized signal-to-noise ratio (SNR) in the carotid vessels along the full extent of the neck. A neck phantom designed to match the anatomy of a subject with a neck representing the body habitus often seen in subjects with carotid arterial disease was constructed. Sixteen circular coil elements were arranged on a semirigid fiberglass former that closely fit the shape of the phantom, resulting in a 16-channel bilateral phased array coil. Comparisons were made between this coil and a typical 4-channel carotid coil in a study of 10 carotid vessels in five healthy volunteers. The 16-channel carotid coil showed a 73% average improvement in SNR at the carotid bifurcation. This coil also maintained an SNR greater than the peak SNR of the 4-channel coil over a vessel length of 10 cm. The resulting increase in SNR improved vessel depiction of the carotid arteries over an extended field of view, and demonstrated better image quality for higher parallel imaging reduction factors compared to the 4-channel coil. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.
Magnetic Resonance in Medicine 07/2012; · 2.96 Impact Factor
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ABSTRACT: Magnetization prepared rapid acquisition gradient echo (3D MPRAGE) has been shown to be a sensitive method to image carotid intraplaque hemorrhage. As the MPRAGE sequence used to identify potential intraplaque hemorrhage does not utilize cardiac gating, it is difficult to optimize the inversion times due to the dynamic nature of flowing blood. As a result, a best fit inversion time is often determined experimentally and then used for in vivo clinical examination. This results in compromised blood suppression and occasional hemorrhage mimicking flow artifacts. We demonstrate that a retrospective cardiac correlated reconstruction can be applied to the conventional MPRAGE sequence (CineMPRAGE) to more accurately identify blood signal. This CineMPRAGE reconstruction uses the data from a standard nongated MPRAGE sequence to generate a full sequence of cardiac correlated images throughout the cardiac cycle and, therefore, provides a dynamic view of the carotid artery and a better ability to discern blood signal from potential intraplaque hemorrhage. In our preliminary study of 35 patients, signal from potential hemorrhage was constant over the cardiac cycle, whereas any signal from blood flow artifact was observed as an oscillating signal over the cardiac cycle. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.
Magnetic Resonance in Medicine 07/2012; · 2.96 Impact Factor
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ABSTRACT: Carotid intraplaque hemorrhage has been associated with symptomatic stroke and can be accurately detected with magnetization-prepared rapid acquisition with gradient-echo (MPRAGE). Currently, there are no studies analyzing carotid MPRAGE signal and territorial ischemic events defined by diffusion restriction in the acute setting. Our aim was to determine the association of carotid MPRAGE signal with acute territorial ischemic events using carotid MPRAGE and brain diffusion tensor imaging.
After the addition of the MPRAGE sequence to the neck MR angiographic protocol, 159 patients with suspected acute stroke were evaluated with both brain diffusion tensor imaging and carotid MPRAGE sequences over 2 years, providing 318 carotid artery and paired brain images for analysis. Forty-eight arteries were excluded due to extracarotid sources of brain ischemia and 4 were excluded due to carotid occlusion. Two hundred sixty-six arteries were eligible for data analysis. Carotid MPRAGE-positive signal was associated with an acute cerebral territorial ischemic event with a relative risk of 6.4 (P<0.001). The relative risk of a diffusion tensor imaging-positive territorial ischemic event with carotid MPRAGE-positive signal was increased in mild, moderate, and severe stenosis categories (10.3, P<0.001; 2.9, P=0.01; and 2.2, P=0.01, respectively).
In the workup of acute stroke, carotid MPRAGE-positive signal was associated with an increased risk of territorial cerebral ischemic events as detected objectively by brain diffusion tensor imaging. The relative risk of stroke was increased in all carotid stenosis categories but was most elevated in the mild stenosis category.
Circulation Cardiovascular Imaging 04/2012; 5(3):376-82. · 5.94 Impact Factor
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Christi M Terry,
Li Li,
Huan Li,
Ilya Zhuplatov,
Donald K Blumenthal, Seong-Eun Kim,
Shawn C Owen,
Eugene G Kholmovski,
Kirk D Fowers,
Ramesh Rathi,
Alfred K Cheung
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ABSTRACT: Synthetic arteriovenous (AV) hemodialysis grafts are plagued by hyperplasia resulting in occlusion and graft failure yet there are no clinically available preventative treatments. Here the delivery and degradation of a sirolimus-laden polymer gel were monitored in vivo by magnetic resonance imaging (MRI) and its efficacy for inhibiting hyperplasia was evaluated in a porcine model of AV graft stenosis. Synthetic grafts were placed between the carotid artery and ipsilateral jugular vein of swine. A biodegradable polymer gel loaded with sirolimus (2.5mg/mL) was immediately applied perivascularly to the venous anastomosis, and reapplied by ultrasound-guided injections at one, two and three weeks. Control grafts received neither sirolimus nor polymer. The lumen cross-sectional area at the graft-vein anastomosis was assessed in vivo by non-invasive MRI. The explanted tissues also underwent histological analysis. A specifically developed MRI pulse sequence provided a high contrast-to-noise ratio (CNR) between the polymer and surrounding tissue that allowed confirmation of gel location after injection. Polymer signal decreased up to 80% at three to four weeks after injection, slightly faster than its degradation kinetics in vitro. The MR image of the polymer was confirmed by visual assessment at necropsy. On histological assessment, the mean hyperplasia surface area of the treated graft was 52% lower than that of the control grafts (0.43mm(2) vs. 0.89mm(2); p<0.003), while the minimum cross-sectional lumen area, as measured on MRI, was doubled (5.3mm(2) vs 2.5mm(2); p<0.05). In conclusion, customized MRI allowed non-invasive monitoring of the location and degradation of drug delivery polymer gels in vivo. Perivascular application of sirolimus-laden polymer yielded a significant decrease in hyperplasia development and an increase in lumen area at the venous anastomosis of AV grafts.
Journal of Controlled Release 03/2012; 160(3):459-67. · 5.73 Impact Factor
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ABSTRACT: To develop and test a hybrid radial (stack of stars) acquisition and compressed sensing reconstruction for efficient late gadolinium enhancement (LGE) imaging of the left atrium.
Two hybrid radial acquisition schemes, kx-ky-first and kz-first, are tested using the signal equation for an inversion recovery sequence with simulated data. Undersampled data reconstructions are then performed using a compressed sensing approach with a three-dimensional total variation constraint. The data acquisition and reconstruction framework is tested on five atrial fibrillation patients after treatment by radio-frequency ablation. The hybrid radial data are acquired with free breathing without respiratory navigation.
The kz-first radial acquisition gave improved image quality as compared to a kx-ky-first scheme. Compressed sensing reconstructions improved the overall quality of undersampled radial LGE images. An image quality metric that takes into account the signal, noise, artifact, and blur for the radial images was 35% (±17%) higher than the corresponding Cartesian acquisitions. Total acquisition time for 36 slices with 1.25 × 1.25 × 2.5 mm(3) resolution was under 3 min for the proposed scheme.
Hybrid radial LGE imaging of the LA with compressed sensing is a promising approach for obtaining images efficiently and offers more robust image quality than Cartesian acquisitions that were acquired without a respiratory navigator signal.
Journal of Magnetic Resonance Imaging 12/2011; 34(6):1465-71. · 2.70 Impact Factor
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ABSTRACT: To determine the apparent diffusion coefficient (ADC) values of lipid and hemorrhage in atherosclerotic plaque in human carotid arteries in vivo and compare the values obtained from ex vivo carotid endarterectomy specimens.
In vivo diffusion-weighted imaging (DWI) of carotid plaques was performed using a 2D single shot Interleaved Multislice Inner Volume Diffusion Weighted Echo Planar Imaging (2D ss-IMIV DWEPI) on 8 subjects who subsequently underwent carotid endarterectomy. A total of 32 slices used to construct the ADC maps were reviewed for the measurement of the mean ADC values in vessel wall, hemorrhage, and lipid necrotic core. The 8 endarterectomy specimens were scanned using by three-dimensional ms-IV-DWEPI. After the ADC maps were created, the mean ADC values in the same locations selected for in vivo values were calculated.
The mean ADC values obtained from in vivo DWI in normal vessel wall, lipid rich core, and hemorrhage were 1.27 ± 0.16, 0.38 ± 0.1, and 0.98 ± 0.25 × 10(-3) mm(2)/s, respectively. The mean ADC values in ex vivo lipid necrotic core, and hemorrhage were 0.33 ± 0.08, 1.28 ± 0.10 × 10(-3) mm(2)/s, respectively. These components mean ADC values obtained from in vivo and ex vivo ADC maps were compared.
ADC values of the carotid plaque components in vivo are consistent with values obtained from ex vivo endarterectomy specimens. The ability to obtain consistent plaque ADC values in vivo indicates that this technique could be an integral part of the basis for plaque component identification in conjunction with other MRI techniques.
Journal of Magnetic Resonance Imaging 09/2011; 34(5):1167-75. · 2.70 Impact Factor
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ABSTRACT: High-energy phosphate metabolism, which allows the synthesis and regeneration of adenosine triphosphate (ATP), is a vital process for neuronal survival and activity. In particular, creatine kinase (CK) serves as an energy reservoir for the rapid buffering of ATP levels. Altered CK enzyme activity, reflecting compromised high-energy phosphate metabolism or mitochondrial dysfunction in the brain, can be assessed using magnetization transfer (MT) MRS. MT (31)P MRS has been used to measure the forward CK reaction rate in animal and human brain, employing a surface radiofrequency coil. However, long acquisition times and excessive radiofrequency irradiation prevent these methods from being used routinely for clinical evaluations. In this article, a new MT (31)P MRS method is presented, which can be practically used to measure the CK forward reaction rate constant in a clinical MRI system employing a volume head (31)P coil for spatial localization, without contamination from the scalp muscle, and an acquisition time of 30 min. Other advantages associated with the method include radiofrequency homogeneity within the regions of interest of the brain using a volume coil with image-selected in vivo spectroscopy localization, and reduction of the specific absorption rate using nonadiabatic radiofrequency pulses for MT saturation. The mean value of k(f) was measured as 0.320 ± 0.075 s(-1) from 10 healthy volunteers with an age range of 18-40 years. These values are consistent with those obtained using earlier methods, and the technique may be used routinely to evaluate energetic processes in the brain on a clinical MRI system.
NMR in Biomedicine 08/2011; 24(7):765-70. · 3.21 Impact Factor
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ABSTRACT: High-resolution turbo spin echo (TSE) images have demonstrated important details of carotid artery morphology; however, it is evident that pulsatile blood and wall motion related to the cardiac cycle are still significant sources of image degradation. Although ECG gating can reduce artifacts due to cardiac-induced pulsations, gating is rarely used because it lengthens the acquisition time and can cause image degradation due to nonconstant repetition time. This work introduces a relatively simple method of converting a conventional TSE acquisition into a retrospectively ECG-correlated cineTSE sequence. The cineTSE sequence generates a full sequence of ECG-correlated images at each slice location throughout the cardiac cycle in the same scan time that is conventionally used by standard TSE sequences to produce a single image at each slice location. The cineTSE images exhibit reduced pulsatile artifacts associated with a gated sequence but without the increased scan time or associated nonconstant repetition time effects.
Magnetic Resonance in Medicine 06/2011; 66(5):1286-92. · 2.96 Impact Factor
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Journal of Cardiovascular Magnetic Resonance. 01/2011;
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ABSTRACT: High-energy phosphate metabolism, which allows the synthesis and regeneration of adenosine triphosphate (ATP), is a vital process for neuronal survival and activity. In particular, creatine kinase (CK) serves as an energy reservoir for the rapid buffering of ATP levels. Altered CK enzyme activity, reflecting compromised high-energy phosphate metabolism or mitochondrial dysfunction in the brain, can be assessed using magnetization transfer (MT) MRS. MT (31)P MRS has been used to measure the forward CK reaction rate in animal and human brain, employing a surface radiofrequency coil. However, long acquisition times and excessive radiofrequency irradiation prevent these methods from being used routinely for clinical evaluations. In this article, a new MT (31)P MRS method is presented, which can be practically used to measure the CK forward reaction rate constant in a clinical MRI system employing a volume head (31)P coil for spatial localization, without contamination from the scalp muscle, and an acquisition time of 30 min. Other advantages associated with the method include radiofrequency homogeneity within the regions of interest of the brain using a volume coil with image-selected in vivo spectroscopy localization, and reduction of the specific absorption rate using nonadiabatic radiofrequency pulses for MT saturation. The mean value of k(f) was measured as 0.320 ± 0.075 s(-1) from 10 healthy volunteers with an age range of 18-40 years. These values are consistent with those obtained using earlier methods, and the technique may be used routinely to evaluate energetic processes in the brain on a clinical MRI system. Copyright © 2010 John Wiley & Sons, Ltd.
NMR in Biomedicine 12/2010; · 3.21 Impact Factor
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ABSTRACT: This article systematically examines arterial spin labeling (ASL) as a flow quantification technique through theoretical simulation, in vitro, and in vivo experiment. The authors present a novel imaging pulse sequence design consisting of a single ASL magnetization preparation followed by Look-Locker-like image readouts. Bloch-equation-based modeling has been developed and validated using a hemodialyzer as a tissue-mimicking flow phantom.
After the single in-plane slice-selective double inversion magnetization preparation, multiple TFL readouts are acquired with linear k-space ordering, causing a signal variation that depends on through-slice flow velocity. Computer simulations were performed to assess the behavior of the flow-dependent ASL signal as a function of varying imaging parameters. The signal was optimized by choosing imaging parameters that maximize the simulated flow-sensitive signal. Furthermore, a hemodialyzer which mimics blood flow in human tissues was tested with a wide range of flow rates. An exponential curve fitting of the flow-sensitive dynamics to the model derived from Bloch equations provides a method to estimate through-slice velocity for varying flow rates on the hemodialyzer and in vivo human brain.
The flow dependency of the ASL signal and the sensitivity of the ASL signal to imaging parameters were demonstrated. Experimental results from a hemodialyzer when fitted with a Bloch-equation-based model provide flow measurements that are consistent with ground truth velocities. Human brain velocity mapping was obtained as well.
The results provide evidence that the proposed pulse sequence design is an effective technique to measure total fluid flow through image voxels. The unique combination of the two main features, multiple-image readout after a single ASL preparation and linear acquisition ordering in the phase encoding direction in TFL imaging, make this technique an appealing flow imaging method to quantify through-plane flow in a time-efficient manner.
Medical Physics 11/2010; 37(11):5801-10. · 2.83 Impact Factor
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ABSTRACT: Many MRI applications such as dynamic contrast-enhanced MRI of the breast require high spatial and temporal resolution and can benefit from improved gradient performance, e.g., increased gradient strength and reduced gradient rise time. The improved gradient performance required to achieve high spatial and temporal resolution for this application may be achieved by using local insert gradients specifically designed for a target anatomy. Current flat gradient systems cannot create an imaging volume large enough to accommodate both breasts; further, their gradient fields are not homogeneous, dropping off rapidly with distance from the gradient coil surface. To attain an imaging volume adequate for bilateral breast MRI, a planar local gradient system design has been modified into a superellipse shape, creating homogeneous gradient volumes that are 182% (Gx), 57% (Gy), and 75% (Gz) wider (left/right direction) than those of the corresponding standard planar gradient. Adding an additional field-modifying gradient winding results in an additional improvement of the homogeneous gradient field near the gradient coil surface over the already enlarged homogeneous gradient volumes of the superelliptical gradients (67%, 89%, and 214% for Gx, Gy, and Gz respectively). A prototype y-gradient insert has been built to demonstrate imaging and implementation characteristics of the superellipse gradient in a 3 T MRI system.
Magnetic Resonance in Medicine 10/2010; 65(3):863-72. · 2.96 Impact Factor
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ABSTRACT: The conventional stimulated-echo NMR sequence only measures the longitudinal component while discarding the transverse component, after tipping up the prepared magnetization. This transverse magnetization can be used to measure a spin echo, in addition to the stimulated echo. Two-dimensional single-shot spin- and stimulated-echo-planar imaging (ss-SESTEPI) is an echo-planar-imaging-based single-shot imaging technique that simultaneously acquires a spin-echo-planar image and a stimulated-echo-planar image after a single radiofrequency excitation. The magnitudes of the spin-echo-planar image and stimulated-echo-planar image differ by T(1) decay and diffusion weighting for perfect 90 degrees radiofrequency and thus can be used to rapidly measure T(1). However, the spatial variation of amplitude of radiofrequency field induces uneven splitting of the transverse magnetization for the spin-echo-planar image and stimulated-echo-planar image within the imaging field of view. Correction for amplitude of radiofrequency field inhomogeneity is therefore critical for two-dimensional ss-SESTEPI to be used for T(1) measurement. We developed a method for amplitude of radiofrequency field inhomogeneity correction by acquiring an additional stimulated-echo-planar image with minimal mixing time, calculating the difference between the spin echo and the stimulated echo and multiplying the stimulated-echo-planar image by the inverse functional map. Diffusion-induced decay is corrected by measuring the average diffusivity during the prescanning. Rapid single-shot T(1) mapping may be useful for various applications, such as dynamic T(1) mapping for real-time estimation of the concentration of contrast agent in dynamic contrast enhancement MRI.
Magnetic Resonance in Medicine 09/2010; 64(3):734-42. · 2.96 Impact Factor
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Journal of Cardiovascular Magnetic Resonance. 01/2010;
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ABSTRACT: To determine if 2D single-shot interleaved multislice inner volume diffusion-weighted echo planar imaging (ss-IMIV-DWEPI) can be used to obtain quantitative diffusion measurements that can assist in the identification of plaque components in the cervical carotid artery.
The 2D ss-DWEPI sequence was combined with interleaved multislice inner volume region localization to obtain diffusion weighted images with 1 mm in-plane resolution and 2 mm slice thickness. Eleven subjects, six of whom have carotid plaque, were studied with this technique. The apparent diffusion coefficient (ADC) images were calculated using DW images with b = 10 s/mm(2) and b = 300 s/mm(2).
The mean ADC measurement in normal vessel wall of the 11 subjects was 1.28 +/- 0.09 x 10(-3) mm(2)/s. Six of the 11 subjects had carotid plaque and ADC measurements in plaque ranged from 0.29 to 0.87 x 10(-3) mm(2)/s. Of the 11 common carotid artery walls studied (33 images), at least partial visualization of the wall was obtained in all ADC images, more than 50% visualization in 82% (27/33 images), and full visualization in 18% (6/33 images).
2D ss-IMIV-DWEPI can perform diffusion-weighted carotid magnetic resonance imaging (MRI) in vivo with reasonably high spatial resolution (1 x 1 x 2 mm(3)). ADC values of the carotid wall and plaque are consistent with similar values obtained from ex vivo endarterectomy specimens. The spread in ADC values obtained from plaque indicate that this technique could form a basis for plaque component identification in conjunction with other MRI/MRA techniques.
Journal of Magnetic Resonance Imaging 11/2009; 30(5):1068-77. · 2.70 Impact Factor
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ABSTRACT: The tradeoff between gradient performance factors, size of the imaging region, and physiological factors such as nerve stimulation typically leads to compromises in gradient design and ultimately suboptimal imaging performance. Local gradient systems can add some performance flexibility, but are cumbersome to set up and remove. In nearly all conventional MRI systems, the use of local gradients precludes the use of the more homogeneous whole body gradients. This paper presents the concept of dynamically selectable composite gradient systems where local gradients and whole body gradients can be selected independently and simultaneously. The relative performance of whole body, insert, and composite gradients is predicted for echoplanar (EPI), turbo spin echo (TSE), and steady state free precession (SSFP). A realization of the concept is presented.
Concepts in Magnetic Resonance Part B Magnetic Resonance Engineering 04/2009; 35(2):89-97. · 0.79 Impact Factor
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ABSTRACT: Diffusion-weighted and diffusion tensor MR imaging (DWI, DTI) techniques are generally performed with signal averaging of multiple measurements to improve the signal-to-noise ratio (SNR) and the accuracy of the diffusion measurement. Any discrepancy in the images between different averages causes errors which reduce the accuracy of the diffusion MRI measurements. In this report, a motion artifact reduction scheme with a real-time self-gated (RTSG) data acquisition for diffusion MRI using two-dimensional echo planar imaging (2D EPI) is described. A subject's translational and rotational motions during application of the diffusion gradients induce an additional phase term and a shift of the echo-peak position in the k-space, respectively. These motions also reduce the magnitude of the echo-peak. Based on these properties, we present a new scheme which monitors the position and the magnitude of the largest echo-peak in the k-space. The position and the magnitude of each average is compared to those of early averaging shot to determine if the differences are within or beyond the given threshold values. Motion corrupted data are reacquired in real time. Our preliminary results using RTSG indicate an improvement of both SNR and the accuracy of diffusion MRI measurements.
NMR in Biomedicine 03/2009; 22(5):545-50. · 3.21 Impact Factor
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ABSTRACT: Chronic hemodialysis requires a vascular access that provides high blood-flow rates for the extracorporeal recirculation of blood. Synthetic arteriovenous (AV) grafts often fail because of clotting caused by underlying hyperplasia formation. The authors report the use of magnetic resonance (MR) imaging (MRI) without contrast agent to monitor tissue hyperplasia formation as well as luminal area in a porcine model of AV graft stenosis.
Expanded reinforced polytetrafluoroethylene grafts were surgically placed between the common carotid artery and the external jugular vein, bilaterally, in pigs. Animals underwent MRI in a 3-T scanner at 3, 4, or 6 weeks after graft placement, followed by euthanasia and the collection of grafts and adjacent tissues for histologic analysis. Two animals underwent sequential scanning at 1, 2, 3, 5, and 7 weeks after graft placement, followed by histologic analysis.
Measurements of hyperplasia obtained from the MR images were compared with, and correlated well with, measurements obtained from the histologic cross-sections (r = 0.932, P = .02). The MR images provided a more complete view of the venous hyperplasia throughout the graft compared with histology. The MR images could be examined from multiple angles and were unaffected by histologic preparation artifacts.
Unlike histology, MRI provided longitudinal 3-dimensional views of hyperplasia within the AV grafts. This ability of MRI to more completely identify the geometry of hyperplasia and to quantify the tissue volume in vivo could provide benefits over histologic analysis in assessing the pathology of AV graft failure and the efficacy of antihyperplasia interventions.
Academic radiology 02/2009; 16(1):96-107. · 2.09 Impact Factor
