bluuebunny/crossref_metadata_2025_split huggingface dataset:
Automatic plaque characterization employing quantitative and multicontrast MRI
Authors: Sun Binjian , Giddens Don P. , Long Robert , Taylor W. Robert , Weiss Diana , Joseph Giji , Vega David , Oshinski John N. 
Published: October 2007

AbstractMulticontrast magnetic resonance imaging (MRI) has shown promise in identifying and characterizing atherosclerotic plaques. One of the limitations of this technique is the lack of a practical automated plaque characterization scheme. In the current study, a prior‐information‐enhanced clustering (PIEC) technique that utilizes both multicontrast MR images and quantitative T2 maps is proposed to characterize atherosclerotic plaque components automatically. The PIEC algorithm was assessed on computationally simulated images and multicontrast MRI data of coronary arteries. Multicontrast (T1‐, T2‐, partial T2‐, and proton density‐weighted) MR images were acquired from freshly excised human coronary arteries using a 4.7T small‐animal scanner. The T2 distribution for each plaque constituent was measured by exponentially fitting the signal from multiple MR images with different TEs and the same TR. The calculated T2 distributions were used as the a priori information and combined with the Fuzzy C‐Means (FCM)‐based clustering algorithm to characterize plaque constituents. The proposed PIEC technique appears to be a promising algorithm for accurate automated plaque characterization. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
Intrinsic signal amplification in the application of 2D SENSE parallel imaging to 3D contrast‐enhanced elliptical centric MRA and MRV
Authors: Riederer Stephen J. , Hu Houchun Harry , Kruger David G. , Haider Clifton R. , Campeau Norbert G. , Huston John 
Published: October 2007

AbstractThe relative signal‐to‐noise ratio (SNR) provided by 2D sensitivity encoding (SENSE) when applied to 3D contrast‐enhanced MR angiography (CE‐MRA) is studied. If an elliptical centric phase‐encoding order is used to map the waning magnetization of the contrast bolus to k‐space, the application of SENSE will reduce the degree of k‐space signal modulation, providing a signal amplification A over corresponding nonaccelerated acquisitions. This offsets the SNR loss in R‐accelerated SENSE due to

and the geometry (g) factor. The theoretical bound on A is R and is reduced from this depending on the properties of the bolus profile and the duration over which it is imaged. In this work a signal amplification of 1.14–1.23 times that of nonvascular background tissue is demonstrated in a study of 20 volunteers using R = 4 2D SENSE whole‐brain MR venography (MRV). The effects of a nonuniform g‐factor and inhomogeneity of background tissue are accounted for. The observed amplification compares favorably with the value of 1.31 predicted numerically from a measured bolus curve. Magn Reson Med 58:855–864, 2007. © 2007 Wiley‐Liss, Inc.
Vessel‐encoded arterial spin‐labeling using pseudocontinuous tagging
Authors: Wong Eric C. 
Published: October 2007

AbstractA new signal‐to‐noise ratio (SNR) efficient method is introduced for the mapping of vascular territories based on pseudocontinuous arterial spin labeling (ASL). A pseudocontinuous tagging pulse train is modified using additional transverse gradient pulses and phase cycling to place some arteries in a tag condition, while others passing through the same tagging plane are in a control condition. This is combined with a Hadamard or similar encoding scheme such that all vessels of interest are fully inverted or relaxed for nearly all of the encoding cycles, providing optimal SNR. The relative tagging efficiency for each vessel is measured directly from the ASL data and is used in the decoding process to improve the separation of vascular territories. High SNR maps of left carotid, right carotid, and basilar territories are generated in 6 min of scan time. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
MRI using a concentric rings trajectory
Authors: Wu Hochong H. , Lee Jin Hyung , Nishimura Dwight G. 
Published: October 2007

AbstractThe concentric rings two‐dimensional (2D) k‐space trajectory provides an alternative way to sample polar data. By collecting 2D k‐space data in a series of rings, many unique properties are observed. The concentric rings are inherently centric‐ordered, provide a smooth weighting in k‐space, and enable shorter total scan times. Due to these properties, the concentric rings are well‐suited as a readout trajectory for magnetization‐prepared studies. When non‐Cartesian trajectories are used for MRI, off‐resonance effects can cause blurring and degrade the image quality. For the concentric rings, off‐resonance blur can be corrected by retracing rings near the center of k‐space to obtain a field map with no extra excitations, and then employing multifrequency reconstruction. Simulations show that the concentric rings exhibit minimal effects due to T modulation, enable shorter scan times for a Nyquist‐sampled dataset than projection‐reconstruction imaging or Cartesian 2D Fourier transform (2DFT) imaging, and have more spatially distributed flow and motion properties than Cartesian sampling. Experimental results show that off‐resonance blurring can be successfully corrected to obtain high‐resolution images. Results also show that concentric rings effectively capture the intended contrast in a magnetization‐prepared sequence. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
Short echo time 1H‐MRSI of the human brain at 3T with minimal chemical shift displacement errors using adiabatic refocusing pulses
Authors: Scheenen Tom W. J. , Klomp Dennis W. J. , Wijnen Jannie P. , Heerschap Arend 
Published: October 2007

AbstractThe chemical shift displacement error (CSDE) is an often‐underestimated problem in slice selection for localized proton spectroscopy at higher fields. With the proposed semi‐localized by adiabatic selective refocusing (LASER) pulse sequence, this problem is dealt with by using RF pulses with bandwidths in the order of 5 kHz. A combination of conventional nonadiabatic slice‐selective excitation of proton spins, together with double slice‐selective refocusing of the spins by two pairs of adiabatic full‐passage (APF) pulses, produces a spin echo in a volume of interest (VOI) at an echo time down to 30 ms. An illustration of the CSDE of conventional point‐resolved spectroscopy (PRESS) and the semi‐LASER sequence is shown with a measurement of the brain of a volunteer at 3T. With one application of the technique to a patient with a glioblastoma multiforme (GBM), its clinical functionality is demonstrated. With sharp selection profiles and a small CSDE, voxels close to the edge of the VOI can also be used for evaluation. With the additional advantage of being relatively insensitive for B1 inhomogeneities, the semi‐LASER technique can be viewed as a superior substitute for conventional PRESS MR spectroscopic imaging (MRSI) at 3T and beyond. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
High‐resolution contrast‐enhanced MRI of atherosclerosis with digital cardiac and respiratory gating in mice
Authors: Alsaid Hasan , Sabbah Maher , Bendahmane Zakaria , Fokapu Odette , Felblinger Jacques , Desbleds‐Mansard Catherine , Corot Claire , Briguet André , Crémillieux Yannick , Canet‐Soulas Emmanuelle 
Published: October 2007

AbstractAtherosclerosis initially develops predominantly at the aortic root and carotid origin, where effective visualization in mice requires efficient cardiac and respiratory gating. The present study sought to first compare the high‐resolution MRI gating performance of two digital gating strategies using: 1) separate cardiac and respiratory signals (double‐sensor); and 2) a single‐sensor cardiorespiratory signal (ECG demodulation), and second, to apply an optimized processing technique to dynamic contrast‐enhanced (CE) carotid origin vessel‐wall imaging in mice. High‐resolution MR mouse heart and aortic arch images were acquired by ECG signal detection, digital signal processing, and gating signal generation modeled using Simulink (MathWorks, USA). Double‐sensor gating used a respiratory sensor while single‐sensor gating used breathing‐modulated ECG to generate a demodulated respiratory signal. Pre‐ and postcontrast T1‐weighted images were acquired to evaluate vessel‐wall enhancement with a gadolinium blood‐pool agent (P792; Guerbet, France) at the carotid origin in vivo in ApoE−/− and C57BL/6 mice, using the optimized cardiorespiratory gating processing technique. Both strategies provided images with improved spatial resolution, less artifacts, and 100% correct transistor‐to‐transistor logic (TTL) signals. Image quality allowed vessel‐wall enhancement measurement in all the ApoE−/− mice, with maximal (32%) enhancement 27 min postinjection. The study demonstrated the efficiency of both cardiorespiratory gating strategies for dynamic contrast‐enhanced vessel‐wall imaging. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
Multiple reference tissue method for contrast agent arterial input function estimation
Authors: Yang Cheng , Karczmar Gregory S. , Medved Milica , Stadler Walter M. 
Published: October 2007

AbstractA precise contrast agent (CA) arterial input function (AIF) is important for accurate quantitative analysis of dynamic contrast‐enhanced (DCE)‐MRI. This paper proposes a method to estimate the AIF using the dynamic data from multiple reference tissues, assuming that their AIFs have the same shape, with a possible difference in bolus arrival time. By minimizing a cost function, one can simultaneously estimate the parameters and underlying AIF of the reference tissues. The method is computationally efficient and the estimated AIF is smooth and can have higher temporal resolution than the original data. Simulations suggest that this method can provide a reliable estimate of the AIF for DCE‐MRI data with a moderate signal‐to‐noise ratio (SNR) and temporal resolution, and its performance increases significantly as the SNR and temporal resolution increase. As demonstrated by its clinical application, sufficient reference tissues can be easily obtained from normal tissues and subregions segmented from a tumor region of interest (ROI), which suggests this method can be generally applied to cancer‐based DCE‐MRI studies to estimate the AIF. This method is applicable to general kinetic models in DCE‐MRI, as well as other CE imaging modalities. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
Three‐dimensional spiral technique for high‐resolution functional MRI
Authors: Hu Yanle , Glover Gary H. 
Published: October 2007

AbstractFor high‐resolution functional MRI (fMRI) studies, signal‐to‐noise ratio (SNR) plays an important role. Any method that results in an improvement in SNR will be able to improve the quality of activation maps. Three‐dimensional (3D) acquisition methods in general can provide higher SNR than that of 2D methods due to volume excitation. To demonstrate the superiority of 3D methods for high‐resolution fMRI scans, a comparison study between 3D and 2D spiral methods was performed using a contrast‐reversing checkerboard visual stimulus. A 3‐inch surface coil was used to limit the in‐plane FOV to 14 cm × 14 cm so that 32 1‐mm slices with an in‐plane voxel size of 1.1 mm × 1.1 mm could be acquired within 5.76 seconds. Results showed that average numbers of activated voxels were 407 and 841 for 2D and 3D methods, respectively (P < 0.01). Therefore, the 3D technique may be a useful alternative to the conventional 2D method for high resolution fMRI studies. Magn Reson Med 58:947–951, 2007. © 2007 Wiley‐Liss, Inc.
Using adiabatic inversion pulses for long‐T2 suppression in ultrashort echo time (UTE) imaging
Authors: Larson Peder E. Z. , Conolly Steven M. , Pauly John M. , Nishimura Dwight G. 
Published: October 2007

AbstractUltrashort echo time (UTE) imaging is a technique that can visualize tissues with sub‐millisecond T2 values that have little or no signal in conventional MRI techniques. The short‐T2 tissues, which include tendons, menisci, calcifications, and cortical bone, are often obscured by long‐T2 tissues. This paper introduces a new method of long‐T2 component suppression based on adiabatic inversion pulses that significantly improves the contrast of short‐T2 tissues. Narrow bandwidth inversion pulses are used to selectively invert only long‐T2 components. These components are then suppressed by combining images prepared with and without inversion pulses. Fat suppression can be incorporated by combining images with the pulses applied on the fat and water resonances. Scaling factors must be used in the combination to compensate for relaxation during the preparation pulses. The suppression is insensitive to RF inhomogeneities because it uses adiabatic inversion pulses. Simulations and phantom experiments demonstrate the adiabatic pulse contrast and how the scaling factors are chosen. In vivo 2D UTE images in the ankle and lower leg show excellent, robust long‐T2 suppression for visualization of cortical bone and tendons. Magn Reson Med 58:952–961, 2007. © 2007 Wiley‐Liss, Inc.
Diffusion properties of NAA in human corpus callosum as studied with diffusion tensor spectroscopy
Authors: Upadhyay Jaymin , Hallock Kevin , Erb Kelley , Kim Dae‐Shik , Ronen Itamar 
Published: October 2007

AbstractIn diffusion tensor imaging (DTI) the anisotropic movement of water is exploited to characterize microstructure. One confounding issue of DTI is the presence of intra‐ and extracellular components contributing to the measured diffusivity. This causes an ambiguity in determining the underlying cause of diffusion properties, particularly the fractional anisotropy (FA). In this study an intracellular constituent, N‐acetyl aspartate (NAA), was used to probe intracellular diffusion, while water molecules were used to probe the combined intra‐ and extracellular diffusion. NAA and water diffusion measurements were made in anterior and medial corpus callosum (CC) regions, which are referred to as R1 and R2, respectively. FA(NAA) was found to be greater than FA(Water) in both CC regions, thus indicating a higher degree of anisotropy within the intracellular space in comparison to the combined intra‐ and extracellular spaces. A decreasing trend in the FA of NAA and water was observed between R1 and R2, while the radial diffusivity (RD) for both molecules increased. The increase in RD(NAA) is particularly significant, thus explaining the more significant decrease in FA(NAA) between the two regions. It is suggested that diffusion tensor spectroscopy of NAA can potentially be used to further characterize microscopic anatomic organization in white matter. Magn Reson Med 58:1045–1053, 2007. © 2007 Wiley‐Liss, Inc.
Improved suppression of plaque‐mimicking artifacts in black‐blood carotid atherosclerosis imaging using a multislice motion‐sensitized driven‐equilibrium (MSDE) turbo spin‐echo (TSE) sequence
Authors: Wang Jinnan , Yarnykh Vasily L. , Hatsukami Thomas , Chu Baocheng , Balu Niranjan , Yuan Chun 
Published: October 2007

AbstractIn this study, a turbo spin‐echo (TSE) based motion‐sensitized driven‐equilibrium (MSDE) sequence was used as an alternative black‐blood (BB) carotid MRI imaging scheme. The MSDE sequence was first optimized for more efficient residual blood signal suppression in the carotid bulb of healthy volunteers. Effective contrast‐to‐noise ratio (CNReff) and residual signal‐to‐noise ratio (SNR) in the lumen measured from MSDE images were then compared to those measured from inflow saturation (IS) and double inversion‐recovery (DIR) images. Statistically significant higher CNReff and lower lumen SNR were obtained from MSDE images. To assess MSDE sequence in a clinical carotid protocol, 42 locations from six subjects with 50% to 79% carotid stenosis by duplex ultrasound were scanned with both MSDE and multislice DIR. The comparison showed that MSDE images present significantly higher CNR and lower lumen SNR compared to corresponding multislice DIR images. The vessel wall area and mean wall thickness measurements in MSDE images were slightly but significantly lower than those obtained with other blood suppression techniques. In conclusion, in vivo comparisons demonstrated that MSDE sequence can achieve better blood suppression and provide a more accurate depiction of the lumen boundaries by eliminating plaque mimicking artifacts in carotid artery (CA) imaging. Magn Reson Med 58:973–981, 2007. © 2007 Wiley‐Liss, Inc.
Sparse MRI: The application of compressed sensing for rapid MR imaging
Authors: Lustig Michael , Donoho David , Pauly John M. 
Published: October 2007

AbstractThe sparsity which is implicit in MR images is exploited to significantly undersample k‐space. Some MR images such as angiograms are already sparse in the pixel representation; other, more complicated images have a sparse representation in some transform domain–for example, in terms of spatial finite‐differences or their wavelet coefficients. According to the recently developed mathematical theory of compressed‐sensing, images with a sparse representation can be recovered from randomly undersampled k‐space data, provided an appropriate nonlinear recovery scheme is used. Intuitively, artifacts due to random undersampling add as noise‐like interference. In the sparse transform domain the significant coefficients stand out above the interference. A nonlinear thresholding scheme can recover the sparse coefficients, effectively recovering the image itself. In this article, practical incoherent undersampling schemes are developed and analyzed by means of their aliasing interference. Incoherence is introduced by pseudo‐random variable‐density undersampling of phase‐encodes. The reconstruction is performed by minimizing the ℓ1 norm of a transformed image, subject to data fidelity constraints. Examples demonstrate improved spatial resolution and accelerated acquisition for multislice fast spin‐echo brain imaging and 3D contrast enhanced angiography. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
Coronary magnetic resonance vein imaging: Imaging contrast, sequence, and timing
Authors: Nezafat Reza , Han Yuchi , Peters Dana C. , Herzka Daniel A. , Wylie John V. , Goddu Beth , Kissinger Kraig K. , Yeon Susan B. , Zimetbaum Peter J. , Manning Warren J. 
Published: October 2007

AbstractRecently, there has been increased interest in imaging the coronary vein anatomy to guide interventional cardiovascular procedures such as cardiac resynchronization therapy (CRT), a device therapy for congestive heart failure (CHF). With CRT the lateral wall of the left ventricle is electrically paced using a transvenous coronary sinus lead or surgically placed epicardial lead. Proper transvenous lead placement is facilitated by the knowledge of the coronary vein anatomy. Cardiovascular MR (CMR) has the potential to image the coronary veins. In this study we propose and test CMR techniques and protocols for imaging the coronary venous anatomy. Three aspects of design of imaging sequence were studied: magnetization preparation schemes (T2 preparation and magnetization transfer), imaging sequences (gradient‐echo (GRE) and steady‐state free precession (SSFP)), and imaging time during the cardiac cycle. Numerical and in vivo studies both in healthy and CHF subjects were performed to optimize and demonstrate the utility of CMR for coronary vein imaging. Magnetization transfer was superior to T2 preparation for contrast enhancement. Both GRE and SSFP were viable imaging sequences, although GRE provided more robust results with better contrast. Imaging during the end‐systolic quiescent period was preferable as it coincided with the maximum size of the coronary veins. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
Correction for artifacts induced by B0 and B1 field inhomogeneities in pH‐sensitive chemical exchange saturation transfer (CEST) imaging
Authors: Sun Phillip Zhe , Farrar Christian T. , Sorensen A. Gregory 
Published: October 2007

AbstractChemical exchange saturation transfer (CEST) imaging provides an indirect detection mechanism that allows quantification of certain labile groups unobservable using conventional MRI. Recently, amide proton transfer (APT) imaging, a variant form of CEST imaging, has been shown capable of detecting lactic acidosis during acute ischemia, providing information complementary to that of perfusion and diffusion MRI. However, CEST contrast is usually small, and therefore, it is important to optimize experimental conditions for reliable and quantitative CEST imaging. In particular, CEST imaging is sensitive to B0 and B1 field, while on the other hand; field inhomogeneities persist despite recent advances in magnet technologies, especially for in vivo imaging at high fields. Consequently, correction algorithms that can compensate for field inhomogeneity‐induced measurement errors in CEST imaging might be very useful. In this study, the dependence of CEST contrast on field distribution was solved and a correction algorithm was developed to compensate for field inhomogeneity‐induced CEST imaging artifacts. In addition, the proposed algorithm was verified with both numerical simulation and experimental measurements, and showed nearly complete correction of CEST imaging measurement errors caused by moderate field inhomogeneity. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
Positive contrast visualization of iron oxide‐labeled stem cells using inversion‐recovery with ON‐resonant water suppression (IRON)
Authors: Stuber Matthias , Gilson Wesley D. , Schär Michael , Kedziorek Dorota A. , Hofmann Lawrence V. , Shah Saurabh , Vonken Evert‐Jan , Bulte Jeff W.M. , Kraitchman Dara L. 
Published: October 2007

AbstractIn proton magnetic resonance imaging (MRI) metallic substances lead to magnetic field distortions that often result in signal voids in the adjacent anatomic structures. Thus, metallic objects and superparamagnetic iron oxide (SPIO)‐labeled cells appear as hypointense artifacts that obscure the underlying anatomy. The ability to illuminate these structures with positive contrast would enhance noninvasive MR tracking of cellular therapeutics. Therefore, an MRI methodology that selectively highlights areas of metallic objects has been developed. Inversion‐recovery with ON‐resonant water suppression (IRON) employs inversion of the magnetization in conjunction with a spectrally‐selective on‐resonant saturation prepulse. If imaging is performed after these prepulses, positive signal is obtained from off‐resonant protons in close proximity to the metallic objects. The first successful use of IRON to produce positive contrast in areas of metallic spheres and SPIO‐labeled stem cells in vitro and in vivo is presented. Magn Reson Med 58:1072–1077, 2007. © 2007 Wiley‐Liss, Inc.