bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improved SNR in phase contrast velocimetry with five‐point balanced flow encoding
Authors: Johnson Kevin M. , Markl Michael 
Published: January 2010

AbstractPhase contrast velocimetry can be utilized to measure complex flow for both quantitative and qualitative assessment of vascular hemodynamics. However, phase contrast requires that a maximum measurable velocity be set that balances noise and phase aliasing. To efficiently reduce noise in phase contrast images, several investigators have proposed extended velocity encoding schemes that use extra encodings to unwrap phase aliasing; however, existing techniques can lead to significant increases in echo and scan time, limiting their clinical benefits. In this work, we have developed a novel five‐point velocity encoding scheme that efficiently reduces noise with minimal increases in scan and echo time. Investigations were performed in phantoms, demonstrating a 63% increase in velocity‐to‐noise ratio compared to standard four‐point encoding schemes. Aortic velocity measurements were performed in healthy volunteers, showing similar velocity‐to‐noise ratio improvements. In those volunteers, it was also demonstrated that, without sacrificing accuracy, low‐resolution images can be used for the fifth encoding point, reducing the scan time penalty from 25% down to less than 1%. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.
Asymmetries of the balanced SSFP profile. Part I: Theory and observation
Authors: Miller Karla L. 
Published: January 2010

AbstractThe signal in balanced steady‐state free precession has a strong sensitivity to off‐resonance, which is typically described in terms of a signal “profile” over a range of frequencies. This profile has a well‐known form for homogeneous media with a single T1, T2, and resonance frequency, which is symmetric about the on‐resonance frequency. However, a straightforward extension to this established signal model predicts that the profile may become asymmetric in the presence of inhomogeneous frequency content, as would be expected to happen in tissue due to microstructural boundaries, compartments, and chemical shift. The presence of asymmetries in the balanced steady‐state free precession profile may therefore provide a marker of tissue integrity. This manuscript describes the theory behind balanced steady‐state free precession asymmetries, a method for detecting these effects, and the first measurements of balanced steady‐state free precession asymmetries in tissue. Asymmetries are found in gray matter, white matter, and muscle, with excellent reproducibility. A companion paper considers the large white matter asymmetries in more detail. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.
High‐resolution MRS in the presence of field inhomogeneity via intermolecular double‐quantum coherences on a 3‐T whole‐body scanner
Authors: Lin Yanqin , Gu Tianliang , Chen Zhong , Kennedy Scott , Jacob Mathews , Zhong Jianhui 
Published: January 2010

AbstractSignals from intermolecular double‐quantum coherences (iDQCs) have been shown to be insensitive to macroscopic field inhomogeneities and thus enable acquisition of high‐ resolution MR spectroscopy in the presence of large inhomogeneous fields. In this paper, localized iDQC 1H spectroscopy on a whole‐body 3‐T MR scanner is reported. Experiments with a brain metabolite phantom were performed to quantify characteristics of the iDQC signal under different conditions. The feasibility of in vivo iDQC high‐resolution MR spectroscopy in the presence of large intrinsic and external field inhomogeneity (in the order of hundreds of hertz) was demonstrated in the whole cerebellum of normal volunteers in a scan time of about 6.5 min. Major metabolite peaks were well resolved in the reconstructed one‐dimensional spectra projected from two‐dimensional iDQC acquisitions. Investigations on metabolite ratios, signal‐to‐noise ratio, and line width were performed and compared with results obtained with conventional point‐resolved spectroscopy/MR spectroscopy in homogeneous fields. Metabolite ratios from iDQC results showed excellent consistency under different in vitro and in vivo conditions, and they were similar to those from point‐resolved spectroscopy with small voxel sizes in homogeneous fields. MR spectroscopy with iDQCs can be applied potentially for quantification of gross metabolite changes due to diseases in large brain volumes with high field inhomogeneity. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.
Hyperpolarized 13C spectroscopy and an NMR‐compatible bioreactor system for the investigation of real‐time cellular metabolism
Authors: Keshari Kayvan R. , Kurhanewicz John , Jeffries Rex E. , Wilson David M. , Dewar Brian J. , Van Criekinge Mark , Zierhut Matthew , Vigneron Daniel B. , Macdonald Jeffrey M. 
Published: January 2010

AbstractThe purpose of this study was to combine a three‐dimensional NMR‐compatible bioreactor with hyperpolarized 13C NMR spectroscopy in order to probe cellular metabolism in real time. JM1 (immortalized rat hepatoma) cells were cultured in a three‐dimensional NMR‐compatible fluidized bioreactor. 31P spectra were acquired before and after each injection of hyperpolarized [1‐13C] pyruvate and subsequent 13C spectroscopy at 11.7 T. 1H and two‐dimensional 1H‐1H‐total correlation spectroscopy spectra were acquired from extracts of cells grown in uniformly labeled 13C‐glucose, on a 16.4 T, to determine 13C fractional enrichment and distribution of 13C label. JM1 cells were found to have a high rate of aerobic glycolysis in both two‐dimensional culture and in the bioreactor, with 85% of the 13C label from uniformly labeled 13C‐glucose being present as either lactate or alanine after 23 h. Flux measurements of pyruvate through lactate dehydrogenase and alanine aminotransferase in the bioreactor system were 12.18 ± 0.49 nmols/sec/108 cells and 2.39 ± 0.30 nmols/sec/108 cells, respectively, were reproducible in the same bioreactor, and were not significantly different over the course of 2 days. Although this preliminary study involved immortalized cells, this combination of technologies can be extended to the real‐time metabolic exploration of primary benign and cancerous cells and tissues prior to and after therapy. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.
Slow magic‐angle coil spinning: A high‐sensitivity and high‐resolution NMR strategy for microscopic biological specimens
Authors: Wong Alan , Aguiar Pedro M. , Sakellariou Dimitris 
Published: January 2010

AbstractHigh‐resolution magic‐angle spinning has become a valuable tool to study biologic samples; however, there are only a few high‐resolution magic‐angle spinning methodologies that have been explored specifically to deal with small semisolid biomaterials such as tissues. Here, we report a novel high‐resolution 1H NMR spectroscopic approach using magic‐angle coil spinning. We demonstrate its potential for intact tissues by combining a resonant microcoil with a large‐volume commercial magic‐angle spinning rotor, where the microcoil offers incredible sensitivity and the large‐volume magic‐angle spinning rotor provides stable slow magic‐angle spinning. This approach provides high‐resolution spectra with high sensitivity and the preservation of living biologic specimens for an accurate chemical analysis. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.
Simultaneous B0‐ and B1+‐Map acquisition for fast localized shim, frequency, and RF power determination in the heart at 3 T
Authors: Schär Michael , Vonken Evert‐Jan , Stuber Matthias 
Published: January 2010

AbstractHigh‐field (≥3 T) cardiac MRI is challenged by inhomogeneities of both the static magnetic field (B0) and the transmit radiofrequency field (B1+). The inhomogeneous B fields not only demand improved shimming methods but also impede the correct determination of the zero‐order terms, i.e., the local resonance frequency f0 and the radiofrequency power to generate the intended local B1+ field. In this work, dual echo time B0‐map and dual flip angle B1+‐map acquisition methods are combined to acquire multislice B0‐ and B1+‐maps simultaneously covering the entire heart in a single breath hold of 18 heartbeats. A previously proposed excitation pulse shape dependent slice profile correction is tested and applied to reduce systematic errors of the multislice B1+‐map. Localized higher‐order shim correction values including the zero‐order terms for frequency f0 and radiofrequency power can be determined based on the acquired B0‐ and B1+‐maps. This method has been tested in 7 healthy adult human subjects at 3 T and improved the B0 field homogeneity (standard deviation) from 60 Hz to 35 Hz and the average B1+ field from 77% to 100% of the desired B1+ field when compared to more commonly used preparation methods. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.
A simulation‐based analysis of the potential of compressed sensing for accelerating passive mr catheter visualization in endovascular therapy
Authors: Yerly Jérôme , Lauzon M. Louis , Chen Henry S. , Frayne Richard 
Published: January 2010

AbstractPassive MRI is a promising approach to visualize catheters in guiding and monitoring endovascular intervention and may offer several clinical advantages over the current x‐ray fluoroscopy “gold standard.” Endovascular MRI has limitations, however, such as difficulty in visualizing catheters and insufficient temporal resolution. The multicycle projection dephaser method is a background signal suppression technique that improves the conspicuity of passive catheters by generating a sparse (i.e., catheter only) image. One approach to improve the temporal resolution is to undersample the k‐space and then apply nonlinear methods, such as compressed sensing, to reconstruct the MR images. This feasibility study investigates the potential synergies between multicycle projection dephaser and compressed sensing reconstruction for real‐time passive catheter tracking. The multicycle projection dephaser method efficiently suppressed the background signal, and compressed sensing allowed MR images to be reconstructed with superior catheter conspicuity and spatial resolution when compared to the more conventional zero‐filling reconstruction approach. Moreover, compressed sensing allowed the shortening of total acquisition time (by up to 32 times) by vastly undersampling the k‐space while simultaneously preserving spatial resolution and catheter conspicuity. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.
Parametric dependence of myocardial blood oxygen level dependent, balanced steady‐state free‐precession imaging at 1.5 T: Theory and experiments
Authors: Zhou Xiangzhi , Tang Richard , Klein Rachel , Li Debiao , Dharmakumar Rohan 
Published: January 2010

AbstractMyocardial blood oxygen level dependent, balanced steady‐state free precession (bSSFP) imaging is a relatively new technique for evaluating myocardial oxygenation changes in the presence of coronary artery stenosis. However, the dependence of myocardial bSSFP blood oxygen level dependent signal on imaging parameters has not been well studied. In this work, modeling capillaries as cylinders that act as magnetic perturbers, the Monte Carlo method was used to simulate spin relaxation via diffusion in a field variation inside and outside blood vessels. bSSFP signal changes at various levels of capillary blood oxygen saturation, for a range of pulse repetition times, flip angle, capillary blood volume fraction, vessel wall permeability, water diffusion coefficient, vessel angle to static magnetic field, and the impact of bulk frequency shifts were studied. The theoretical dependence of bSSFP blood oxygen level dependent contrast on pulse repetition times and flip angle was confirmed by experiments in an animal model with controllable coronary stenosis. Results showed that, with the standard bSSFP acquisition, optimum bSSFP blood oxygen level dependent contrast could be obtained at pulse repetition times = 6.0 ms and flip angle = 70°. Additional technical improvements that preserve the image quality may be necessary to further increase the myocardial bSSFP blood oxygen level dependent sensitivity at 1.5 T through even longer pulse repetition times. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.
Positive contrast with alternating repetition time SSFP (PARTS): A fast imaging technique for SPIO‐labeled cells
Authors: Çukur Tolga , Yamada Mayumi , Overall William R. , Yang Phillip , Nishimura Dwight G. 
Published: January 2010

AbstractThere has been recent interest in positive‐contrast MRI methods for noninvasive tracking of cells labeled with superparamagnetic iron‐oxide nanoparticles. Low‐tip‐angle balanced steady‐state free precession sequences have been used for fast, high‐resolution, and flow‐insensitive positive‐contrast imaging; however, the contrast can be compromised by the limited suppression of the on‐resonant and fat signals. In this work, a new technique that produces positive contrast with alternating repetition time steady‐state free precession is proposed to achieve robust background suppression for a broad range of tissue parameters. In vitro and in vivo experiments demonstrate the reliability of the generated positive contrast. The results indicate that the proposed method can enhance the suppression level by up to 18 dB compared with conventional balanced steady‐state free precession. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.
Asymmetries of the balanced SSFP profile. Part II: White matter
Authors: Miller Karla L. , Smith Stephen M. , Jezzard Peter 
Published: January 2010

AbstractThe signal profile measured in balanced steady‐state free precession has been shown to exhibit tissue‐dependent asymmetries that were hypothesized to relate to properties of the tissue microenvironment. It was proposed that balanced steady‐state free precession asymmetry may reflect subtle features of the frequency distribution in tissue. The present work investigates the large balanced steady‐state free precession asymmetries observed in white matter. First, maps quantifying the asymmetry are presented, which demonstrate considerable heterogeneity within white matter, with some tracts exhibiting significant asymmetry and others having a nearly symmetric profile. These maps are compared with a diffusion‐tensor atlas and indicate that the highest asymmetry is found in tracts oriented perpendicular to the main magnetic field. Measurements conducted at multiple repetition times suggest that the asymmetries are characterized by relatively small frequency shifts. These results are discussed in the context of previous work studying gradient‐recalled echo (GRE) signal behavior in white matter, and it is suggested that these two techniques are detecting closely related phenomena. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.
Non‐contrast‐enhanced pulmonary vein MRI with a spatially selective slab inversion preparation sequence
Authors: Hu Peng , Chuang Michael L. , Kissinger Kraig V. , Goddu Beth , Goepfert Lois A. , Rofsky Neil M. , Manning Warren J. , Nezafat Reza 
Published: January 2010

AbstractWe propose a non‐contrast‐enhanced, three‐dimensional, free‐breathing, electrocardiogram‐gated, gradient recalled echo sequence with a slab‐selective inversion for pulmonary vein (PV) MRI. A sagittal inversion slab was applied prior to data acquisition to suppress structures adjacent to the left atrium (LA) and PVs, thereby improving the conspicuity of the PV and LA. Compared with other MR angiography methods using an inversion pulse, the proposed method does not require signal subtraction and the inversion slab is not parallel to the imaging slab. The feasibility of the proposed method was demonstrated in healthy subjects. The inversion slab thickness and inversion time were optimized to be 60 mm and 500 ms, respectively. Compared to conventional gradient recalled echo imaging without inversion, the proposed technique significantly increased the contrast‐to‐noise ratios between the LA and the right atrium by 20‐fold (P < 0.01), increased the contrast‐to‐noise ratios between the PVs and right atrium by 10‐fold (P < 0.03), and increased the contrast‐to‐noise ratios between the PVs, LA and pulmonary artery by 4‐fold (P < 0.01 for both). The signal‐to‐noise ratios of the PVs and the LA were similar with and without the inversion slab (P > 0.3). The proposed technique greatly enhances the conspicuity of the PVs and LA without significant loss of signal‐to‐noise ratio. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.
Design and use of variable flip angle schedules in transient balanced SSFP subtractive imaging
Authors: Smith Travis , Zun Zungho , Wong Eric C. , Nayak Krishna S. 
Published: January 2010

AbstractIn subtractive imaging modalities, the differential longitudinal magnetization decays with time, necessitating signal‐efficient scanning methods. Balanced steady‐state free precession pulse sequences offer greater signal strength than conventional spoiled gradient echo sequences, even during the transient approach to steady state. Although traditional balanced steady‐state free precession requires that each excitation pulse use the same flip angle, operating in the transient regimen permits the application of variable flip angle schedules that can be tailored to optimize certain signal characteristics. A computationally efficient technique is presented to generate variable flip angle schedules efficiently for any optimization metric. The validity of the technique is shown using two phantoms, and its potential is demonstrated in vivo with a variable angle schedule to increase the signal‐to‐noise ratio (SNR) in myocardial tissue. Using variable flip angles, the mean SNR improvement in subtractive imaging of myocardial tissue was 18.2% compared to conventional, constant flip angle, balanced steady‐state free precession (P = 0.0078). Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.
Dual inversion recovery, ultrashort echo time (DIR UTE) imaging: Creating high contrast for short‐T2 species
Authors: Du Jiang , Takahashi Atsushi M. , Bae Won C. , Chung Christine B. , Bydder Graeme M. 
Published: January 2010

AbstractImaging of short‐T2 species requires not only a short echo time but also efficient suppression of long‐T2 species in order to maximize the short‐T2 contrast and dynamic range. This paper introduces a method of long‐T2 suppression using two long adiabatic inversion pulses. The first adiabatic inversion pulse inverts the magnetization of long‐T2 water and the second one inverts that of fat. Short‐T2 species experience a significant transverse relaxation during the long adiabatic inversion process and are minimally affected by the inversion pulses. Data acquisition with a short echo time of 8 μs starts following a time delay of inversion time (TI1) for the inverted water magnetization to reach a null point and a time delay of TI2 for the inverted fat magnetization to reach a null point. The suppression of long‐T2 species depends on proper combination of TI1, TI2, and pulse repetition time. It is insensitive to radiofrequency inhomogeneities because of the adiabatic inversion pulses. The feasibility of this dual inversion recovery ultrashort echo time technique was demonstrated on phantoms, cadaveric specimens, and healthy volunteers, using a clinical 3‐T scanner. High image contrast was achieved for the deep radial and calcified layers of articular cartilage, cortical bone, and the Achilles tendon. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.
MRI and localized proton spectroscopy in human leg muscle at 7 tesla using longitudinal traveling waves
Authors: Webb Andrew G. , Collins Christopher M. , Versluis Maarten J. , Kan Hermien E. , Smith Nadine B. 
Published: January 2010

AbstractUsing a small resonant loop to produce a longitudinal traveling wave on a human 7‐T system allows MR to be performed over the entire volume of the human leg. We have used this capability to perform localized proton MR spectroscopy of the lipid composition of muscle in volunteers with a coil placed ∼30 cm away from the region of interest. Spectra with a reasonable signal‐to‐noise ratio can be acquired in a clinically relevant data acquisition time of less than 5 min using the loop in transmit/receive mode, maintaining the full flexibility to acquire spectra from any part of the calf and/or thigh. If a local receive coil is used in combination with the remote transmit coil, then the signal‐to‐noise improves significantly, as expected. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.
Relationship between brain R2 and liver and serum Iron concentrations in elderly men
Authors: House Michael J. , St. Pierre Timothy G. , Milward Elizabeth A. , Bruce David G. , Olynyk John K. 
Published: January 2010

AbstractStudies of iron overload in humans and animals suggest that brain iron concentrations may be related in a regionally specific way to body iron status. However, few quantitative studies have investigated the associations between peripheral and regional brain iron in a normal elderly cohort. To examine these relationships, we used MRI to measure the proton transverse relaxation rate (R2) in 13 gray and white matter brain regions in 18 elderly men (average age, 75.5 years) with normal cognition. Brain R2 values were compared with liver iron concentrations measured using the FerriScan® MRI technique and serum iron indices. R2 values in high‐iron gray matter regions were significantly correlated (positively) with liver iron concentrations (globus pallidus, ventral pallidum) and serum transferrin saturation (caudate nucleus, globus pallidus, putamen) measured concurrently with brain R2, and with serum iron concentrations (caudate nucleus, globus pallidus) measured three years before the current study. Our results suggest that iron levels in specific gray matter brain regions are influenced by systemic iron status in elderly men. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.
Design and evaluation of a 32‐channel phased‐array coil for lung imaging with hyperpolarized 3‐helium
Authors: Meise Florian M. , Rivoire Julien , Terekhov Maxim , Wiggins Graham C. , Keil Boris , Karpuk Sergej , Salhi Zahir , Wald Lawrence L. , Schreiber Laura M. 
Published: January 2010

AbstractImaging with hyperpolarized 3‐helium is becoming an increasingly important technique for MRI diagnostics of the lung but is hampered by long breath holds (>20 sec), which are not always applicable in patients with severe lung disease like chronic obstructive pulmonary disease (COPD) or α‐1‐anti‐trypsin deficiency. Additionally, oxygen‐induced depolarization decay during the long breath holds complicates interpretation of functional data such as apparent diffusion coefficients. To address these issues, we describe and validate a 1.5‐T, 32‐channel array coil for accelerated 3He lung imaging and demonstrate its ability to speed up imaging 3He. A signal‐to‐noise ratio increase of up to a factor of 17 was observed compared to a conventional double‐resonant birdcage for unaccelerated imaging, potentially allowing increased image resolution or decreased gas production requirements. Accelerated imaging of the whole lung with one‐dimensional and two‐dimensional acceleration factors of 4 and 4 × 2, respectively, was achieved while still retaining excellent image quality. Finally, the potential of highly parallel detection in lung imaging is demonstrated with high‐resolution morphologic and functional images. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.