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1.
Jingsi Xie BS Peng Lai PhD Himanshu Bhat MS Debiao Li PhD 《Journal of magnetic resonance imaging : JMRI》2010,31(5):1230-1235
Purpose
To evaluate the feasibility of improving 3.0T steady‐state free precession (SSFP) whole‐heart coronary magnetic resonance angiography (MRA) using short‐TR (repetition time) VIPR (vastly undersampled isotropic projection reconstruction).Materials and Methods
SSFP is highly sensitive to field inhomogeneity. VIPR imaging uses nonselective radiofrequency pulses, allowing short TR and reduced banding artifacts, while achieving isotropic 3D resolution. Coronary artery imaging was performed in nine healthy volunteers using SSFP VIPR. TR was reduced to 3.0 msec with an isotropic spatial resolution of 1.3 × 1.3 × 1.3 mm3. Image quality, vessel sharpness, and lengths of major coronary arteries were measured. Comparison between SSFP using Cartesian trajectory and SSFP using VIPR trajectory was performed in all volunteers.Results
Short‐TR SSFP VIPR resulted in whole‐heart images without any banding artifacts, leading to excellent coronary artery visualization. The average image quality score for VIPR‐SSFP was 3.12 ± 0.42 out of four while that for Cartesian SSFP was 0.92 ± 0.61. A significant improvement (P < 0.05) in image quality was shown by Wilcoxon comparison. The visualized coronary artery lengths for VIPR‐SSFP were: 10.13 ± 0.79 cm for the left anterior descending artery (LAD), 7.90 ± 0.91 cm for the left circumflex artery (LCX), 7.50 ± 1.65 cm for the right coronary artery (RCA), and 1.84 ± 0.23 cm for the left main artery (LM). The lengths statistics for Cartesian SSFP were 1.57 ± 2.02 cm, 1.54 ± 1.93 cm, 0.94 ± 1.17 cm, 0.46 ± 0.53 cm, respectively. The image sharpness was also increased from 0.61 ± 0.13 (mm?1) in Cartesian‐SSFP to 0.81 ± 0.11 (mm?1) in VIPR‐SSFP.Conclusion
With VIPR trajectory the TR is substantially decreased, reducing the sensitivity of SSFP to field inhomogeneity and resulting in whole‐heart images without banding artifacts at 3.0T. Image quality improved significantly over Cartesian sampling. J. Magn. Reson. Imaging 2010; 31:1230–1235. © 2010 Wiley‐Liss, Inc.2.
Yunhong Shu PhD Matt A. Bernstein PhD John Huston III MD Dan Rettmann BS 《Journal of magnetic resonance imaging : JMRI》2009,30(5):1101-1109
Purpose:
To evaluate the feasibility of applying the shells trajectory to single‐phase contrast‐enhanced magnetic resonance angiography.Materials and Methods:
Several methods were developed to overcome the challenges of the clinical implementation of shells including off‐resonance blurring (eg, from lipid signal), aliasing artifacts, and long reconstruction times. These methods included: 1) variable TR with variable readout length to reduce fat signal and off‐resonance blurring; 2) variable sampling density to suppress aliasing artifacts while minimizing acquisition time penalty; and 3) an online 3D gridding algorithm that reconstructed an 8‐channel, 2403 image volume set. Both phantom and human studies were performed to establish the initial feasibility of the methods.Results:
Phantom and human study results demonstrated the effectiveness of the proposed methods. Shells with variable TR and readout length further suppressed the fat signal compared to the fixed‐TR shells acquisition. Reduced image aliasing was achieved with minimal scan time penalty when a variable sampling density technique was used. The fast online reconstruction algorithm completed in 2 minutes at the scanner console, providing a timely image display in a clinical setting.Conclusion:
It was demonstrated that the use of the shells trajectory is feasible in a clinical setting to acquire intracranial angiograms with high spatial resolution. Preliminary results demonstrate effective venous suppression in the cavernous sinuses and jugular vein region. J. Magn. Reson. Imaging 2009;30:1101–1109. © 2009 Wiley‐Liss, Inc. 相似文献3.
Youngkyoo Jung PhD Alexey A. Samsonov PhD Walter F. Block PhD Mariana Lazar PhD Aiming Lu PhD Jing Liu PhD Andrew L. Alexander PhD 《Journal of magnetic resonance imaging : JMRI》2009,29(5):1175-1184
Purpose
To obtain diffusion tensor images (DTI) over a large image volume rapidly with 3D isotropic spatial resolution, minimal spatial distortions, and reduced motion artifacts, a diffusion‐weighted steady‐state 3D projection (SS 3DPR) pulse sequence was developed.Materials and Methods
A diffusion gradient was inserted in a SS 3DPR pulse sequence. The acquisition was synchronized to the cardiac cycle, linear phase errors were corrected along the readout direction, and each projection was weighted by measures of consistency with other data. A new iterative parallel imaging reconstruction method was also implemented for removing off‐resonance and undersampling artifacts simultaneously.Results
The contrast and appearance of both the fractional anisotropy and eigenvector color maps were substantially improved after all correction techniques were applied. True 3D DTI datasets were obtained in vivo over the whole brain (240 mm field of view in all directions) with 1.87 mm isotropic spatial resolution, six diffusion encoding directions in under 19 minutes.Conclusion
A true 3D DTI pulse sequence with high isotropic spatial resolution was developed for whole brain imaging in under 20 minutes. To minimize the effects of brain motion, a cardiac synchronized, multiecho, DW‐SSFP pulse sequence was implemented. Motion artifacts were further reduced by a combination of linear phase correction, corrupt projection detection and rejection, sampling density reweighting, and parallel imaging reconstruction. The combination of these methods greatly improved the quality of 3D DTI in the brain. J. Magn. Reson. Imaging 2009;29:1175–1184. © 2009 Wiley‐Liss, Inc. 相似文献4.
Hsu‐Lei Lee PhD Ajit Shankaranarayanan PhD Gerald M. Pohost MD Krishna S. Nayak PhD 《Journal of magnetic resonance imaging : JMRI》2010,31(5):1224-1229
Purpose:
To suppress off‐resonance artifacts in coronary artery imaging at 3 Tesla (T), and therefore improve spatial resolution.Materials and Methods:
Wideband steady state free precession (SSFP) sequences use an oscillating steady state to reduce banding artifacts. Coronary artery images were obtained at 3T using three‐dimensional navigated gradient echo, balanced SSFP, and wideband SSFP sequences.Results:
The highest in‐plane resolution of left coronary artery images was 0.68 mm in the frequency‐encoding direction. Wideband SSFP produced an average SNR efficiency of 70% relative to conventional balanced SSFP and suppressed off‐resonance artifacts.Conclusion:
Wideband SSFP was found to be a promising approach for obtaining noncontrast, high‐resolution coronary artery images at 3 Tesla with reliable image quality. J. Magn. Reson. Imaging 2010;31:1224–1229. © 2010 Wiley‐Liss, Inc. 相似文献5.
Victoria Parish BMBS Tarique Hussain MBBS Philip Beerbaum MD Gerald Greil MD Eike Nagel MD Reza Razavi MD Tobias Schaeffter PhD Sergio Uribe PhD 《Journal of magnetic resonance imaging : JMRI》2010,31(4):838-844
Purpose:
To evaluate the feasibility of a single breath‐hold 3D cine balanced steady‐state free precession (b‐SSFP) sequence after gadolinium diethylenetriamine penta‐acetic acid (Gd‐DTPA) injection for volumetric cardiac assessment.Materials and Methods:
Fifteen adult patients routinely referred for cardiac magnetic resonance imaging (MRI) underwent quantitative ventricular volumetry on a clinical 1.5T MR‐scanner using a 32‐channel cardiac coil. A stack of 2D cine b‐SSFP slices covering the ventricles was used as reference, followed by a single breath‐hold 3D cine balanced SSFP protocol acquired before and after administration of Gd‐DTPA. The acquisition was accelerated using SENSE in both phase encoding directions. Volumetric and contrast‐to‐noise data for each technique were assessed and compared.Results:
The 3D cine protocol was accomplished within one breath‐hold (mean acquisition time 20 sec; spatial resolution 2.1 × 2.1 × 10 mm; temporal resolution 51 msec). The contrast‐to‐noise ratio between blood and myocardium was 234 determined for the multiple 2D cine data, and could be increased for the 3D acquisition from 136 (3D precontrast) to 203 (3D postcontrast) after injecting Gd‐DTPA. In addition the endocardial definition was significantly improved in postcontrast 3D cine b‐SSFP. There was no significant difference for left and right ventricular volumes between standard 2D and 3D postcontrast cine b‐SSFP. However, Bland–Altman plots showed greater bias and scatter when comparing 2D with 3D cine b‐SSFP without contrast.Conclusion:
3D cine b‐SSFP imaging of the heart using 32 channel coil technology and spatial undersampling allows reliable volumetric assessment within a single breath‐hold after application of Gd‐DTPA. J. Magn. Reson. Imaging 2010;31:838–844. ©2010 Wiley‐Liss, Inc. 相似文献6.
Kim A. Connelly MBBS PhD Jay S. Detsky PhD John J. Graham MBBS Gideon Paul MBBS Ram Vijayaragavan MD Alexander J. Dick MD Graham A. Wright PhD 《Journal of magnetic resonance imaging : JMRI》2009,30(4):771-777
Purpose
To determine the accuracy of multicontrast late enhancement imaging (MCLE) in the assessment of myocardial viability and wall motion compared to the conventional wall motion and viability cardiac magnetic resonance imaging (MRI) pulse sequences.Materials and Methods
Forty‐one patients with suspected myocardial infarction were studied. Patients underwent assessment of cardiac function with cine steady‐state free‐precession (SSFP), followed by late gadolinium enhancement (LGE) imaging using inversion recovery gradient echo scanning (IR‐GRE) sequence and MCLE. MCLE was compared to cine SSFP in the assessment of wall motion, ejection fraction (EF), left ventricular (LV) mass, LV end‐diastolic volume (EDV), and to IR‐GRE for measuring infarct size.Results
MCLE, IR‐GRE, and SSFP imaging demonstrated excellent agreement in the assessment of EF, LV infarct size, and LV mass (r > 0.95, P < 0.001 for all measures), as well as in the assessment of wall motion (κ statistic 0.75).Conclusion
MCLE provided coregistered images for the assessment of viability and wall motion without loss of accuracy in the assessment of quantitative cardiac parameters. MCLE provides accurate quantitative cardiac assessment with reduced scan times compared to the conventional sequences and thus may be used as an alternative to conventional cine SSFP and IR‐GRE imaging. J. Magn. Reson. Imaging 2009;30:771–777. © 2009 Wiley‐Liss, Inc. 相似文献7.
Shuowen Hu BS Olumide Olulade MS Gregory G. Tamer Jr. PhD Wen‐Ming Luh PhD Thomas M. Talavage PhD 《Journal of magnetic resonance imaging : JMRI》2009,29(5):1234-1239
Purpose
To assess and model signal fluctuations induced by non‐T1‐related confounds in variable repetition time (TR) functional magnetic resonance imaging (fMRI) and to develop a compensation procedure to correct for the non‐T1‐related artifacts.Materials and Methods
Radiofrequency disabled volume gradient sequences were effected at variable offsets between actual image acquisitions, enabling perturbation of the measurement system without perturbing longitudinal magnetization, allowing the study of non‐T1‐related confounds that may arise in variable TR experiments. Three imaging sessions utilizing a daily quality assurance (DQA) phantom were conducted to assess the signal fluctuations, which were then modeled as a second‐order system. A modified projection procedure was implemented to correct for signal fluctuations arising from non‐T1‐related confounds, and statistical analysis was performed to assess the significance of the artifacts with and without compensation.Results
Assessment using phantom data reveals that the signal fluctuations induced by non‐T1‐related confounds was consistent in shape across the phantom and well‐modeled by a second‐order system. The phantom exhibited significant spurious detections (at P < 0.01) almost uniformly across the central slices of the phantom.Conclusion
Second‐order system modeling and compensation of non‐T1‐related confounds achieves significant reduction of spurious detection of fMRI activity in a phantom. J. Magn. Reson. Imaging 2009;29:1234–1239. © 2009 Wiley‐Liss, Inc. 相似文献8.
Keigo Kawaji MS Thanh D. Nguyen PhD Zhitong Zou MD Beatriu Reig MD Priscilla A. Winchester MD Andrew Shih MD Pascal Spincemaille PhD Martin R. Prince MD PhD Yi Wang PhD 《Journal of magnetic resonance imaging : JMRI》2011,34(3):696-701
Purpose:
To examine the feasibility of flow‐independent T2‐prepared inversion recovery (T2IR) black‐blood (BB) magnetization preparation for three‐dimensional (3D) balanced steady‐state free precession (SSFP) vessel wall MRI of the popliteal artery, and to evaluate its performance relative to flow‐dependent double inversion recovery (DIR), spatial presaturation (SPSAT), and motion‐sensitizing magnetization preparation (MSPREP) BB techniques in healthy volunteers.Materials and Methods:
Eleven subjects underwent 3D MRI at 1.5 Tesla with four techniques performed in a randomized order. Wall and lumen signal‐to‐noise ratio (SNR), wall‐to‐lumen contrast‐to‐noise ratio (CNR), vessel wall area, and lumen area were measured at proximal, middle, and distal locations of the imaged popliteal artery. Image quality scores based on wall visualization and degree of intraluminal artifacts were also obtained.Results:
In the proximal region, DIR and SPSAT had higher wall SNR and wall‐to‐lumen CNR than both MSPREP and T2IR. In the middle and distal regions, DIR and SPSAT failed to provide effective blood suppression, whereas MSPREP and T2IR provided adequate black blood contrast with comparable wall‐to‐lumen CNR and image quality.Conclusion:
The feasibility of 3D SSFP imaging of the popliteal vessel wall using flow‐independent T2IR was demonstrated with effective blood suppression and good vessel wall visualization. Although DIR and SPSAT are effective for thin slab imaging, MSPREP and T2IR are better suited for 3D thick slab imaging. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc. 相似文献9.
Daniela Föll MD Bernd Jung PhD Felix Staehle MS Elfriede Schilli Christoph Bode MD Jürgen Hennig PhD Michael Markl PhD 《Journal of magnetic resonance imaging : JMRI》2009,29(5):1043-1052
Purpose
To apply high‐temporal‐resolution tissue phase mapping (TPM) to derive a detailed representation of normal regional myocardial motion in a large cohort of 58 normal subjects (three age groups) and one patient with dilated cardiomyopathy.Materials and Methods
Analysis included transformation of the acquired myocardial velocities into radial, circumferential, and long‐axis motion components representing left ventricular (LV) function with a spatiotemporal resolution of 1.3 × 2.6 × 8 mm3 and 13.8 msec, respectively. To compare multidirectional regional myocardial velocities between groups of subjects, a multisegment and multislice visualization model was employed. Regional myocardial motion was mapped onto the visualization model to display the current status of myocardial motion from base to apex as in‐plane velocity vector fields in conjunction with color‐coded long‐axis plane motion. Moreover, correlation analysis was used to investigate regional differences in myocardial dynamics.Results
Age‐related changes in LV myocardial velocities resulted in significant differences of peak and time‐to‐peak velocities in the radial and long‐axis directions. Correlation analysis revealed clearly visible regional differences in the temporal evolution of long‐axis and circumferential velocities, particularly between the youngest and oldest age groups. Comparison of pathological LV motion with age‐matched volunteers indicated marked regional alterations in myocardial velocities and dynamics.Conclusion
High‐temporal‐resolution TPM in combination with a schematic visualization model and correlation analysis permits the identification of local changes in myocardial velocities associated with different age groups and a common LV pathology. J. Magn. Reson. Imaging 2009;29:1043–1052. © 2009 Wiley‐Liss, Inc. 相似文献10.
Ashish A. Tamhane MS Mark A. Anastasio PhD Minzhi Gui PhD Konstantinos Arfanakis PhD 《Journal of magnetic resonance imaging : JMRI》2010,32(1):211-217
Purpose:
To investigate an iterative image reconstruction algorithm using the nonuniform fast Fourier transform (NUFFT) for PROPELLER (Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction) MRI.Materials and Methods:
Numerical simulations, as well as experiments on a phantom and a healthy human subject were used to evaluate the performance of the iterative image reconstruction algorithm for PROPELLER, and compare it with that of conventional gridding. The trade‐off between spatial resolution, signal to noise ratio, and image artifacts, was investigated for different values of the regularization parameter. The performance of the iterative image reconstruction algorithm in the presence of motion was also evaluated.Results:
It was demonstrated that, for a certain range of values of the regularization parameter, iterative reconstruction produced images with significantly increased signal to noise ratio, reduced artifacts, for similar spatial resolution, compared with gridding. Furthermore, the ability to reduce the effects of motion in PROPELLER‐MRI was maintained when using the iterative reconstruction approach.Conclusion:
An iterative image reconstruction technique based on the NUFFT was investigated for PROPELLER MRI. For a certain range of values of the regularization parameter, the new reconstruction technique may provide PROPELLER images with improved image quality compared with conventional gridding. J. Magn. Reson. Imaging 2010;32:211–217. © 2010 Wiley‐Liss, Inc. 相似文献11.
Akihiko Kanki MD Katsuyoshi Ito MD Tsutomu Tamada MD Yasufumi Noda MD Akira Yamamoto MD Daigo Tanimoto MD Tomohiro Sato MD Atsushi Higaki MD 《Journal of magnetic resonance imaging : JMRI》2013,37(5):1178-1181
Purpose:
To assess whether noncontrast‐enhanced steady‐state free precession (SSFP) magnetic resonance imaging (MRI) with time‐spatial labeling inversion pulse (Time‐SLIP) can improve the visibility of corticomedullary differentiation of the normal kidney.Materials and Methods:
A series of noncontrast‐enhanced SSFP MRI with Time‐SLIP were performed in 20 patients by using various inversion times (TIs); 500–1800 msec in increments of 100 msec. In‐phase (IP) and opposed‐phase (OP) MR images were also obtained. The signal intensity (SI) of the renal cortex and medulla was measured to calculate corticomedullary contrast ratio (SI of cortex/medulla). Additionally, the visibility of corticomedullary differentiation was visually categorized using a four‐point scale.Results:
In SSFP with Time‐SLIP, corticomedullary contrast ratio was highest with TI of 1200 msec in eight subjects (40%), followed by 1100 msec in seven (35%) and 1000 msec in three (15%). The corticomedullary contrast ratio in SSFP with optimal Time‐SLIP (4.93 ± 1.25) was significantly higher (P < 0.001) than those of IP (1.46 ± 0.12) and OP (1.43 ± 0.14). The visibility of corticomedullary differentiation was significantly better (P < 0.001) in SSFP images with Time‐SLIP (averaged grade = 4.0) than in IP images (averaged grade = 2.63) and OP images (averaged grade = 2.05).Conclusion:
SSFP MRI with Time‐SLIP can improve the visibility of renal corticomedullary differentiation without using contrast agents. J. Magn. Reson. Imaging 2012;37:1178–1181. © 2012 Wiley Periodicals, Inc. 相似文献12.
Catherine J. Moran MS Frederick Kelcz MD PhD Youngkyoo Jung PhD Ethan K. Brodsky PhD Sean B. Fain PhD Walter F. Block PhD 《Journal of magnetic resonance imaging : JMRI》2009,30(1):135-144
Purpose
To assess a 3D radial balanced steady‐state free precession (SSFP) technique that provides submillimeter isotropic resolution and inherently registered fat and water image volumes in comparison to conventional T2‐weighted RARE imaging for lesion characterization in breast magnetic resonance imaging (MRI).Materials and Methods
3D projection SSFP (3DPR‐SSFP) combines a dual half‐echo radial k‐space trajectory with a linear combination fat/water separation technique (linear combination SSFP). A pilot study was performed in 20 patients to assess fat suppression and depiction of lesion morphology using 3DPR‐SSFP. For all patients fat suppression was measured for the 3DPR‐SSFP image volumes and depiction of lesion morphology was compared against corresponding T2‐weighted fast spin echo (FSE) datasets for 15 lesions in 11 patients.Results
The isotropic 0.63 mm resolution of the 3DPR‐SSFP sequence demonstrated improved depiction of lesion morphology in comparison to FSE. The 3DPR‐SSFP fat and water datasets were available in a 5‐minute scan time while average fat suppression with 3DPR‐SSFP was 71% across all 20 patients.Conclusion
3DPR‐SSFP has the potential to improve the lesion characterization information available in breast MRI, particularly in comparison to conventional FSE. A larger study is warranted to quantify the effect of 3DPR‐SSFP on specificity. J. Magn. Reson. Imaging 2009;30:135–144. © 2009 Wiley‐Liss, Inc. 相似文献13.
Christian T. Stoeck MSc Yuchi Han MD Dana C. Peters PhD Peng Hu PhD Susan B. Yeon MD Kraig V. Kissinger BS RT Beth Goddu RT Lois Goepfert RN MS Warren J. Manning MD Sebastian Kozerke PhD Reza Nezafat PhD 《Journal of magnetic resonance imaging : JMRI》2009,29(6):1293-1299
Purpose
To compare two coronary vein imaging techniques using whole‐heart balanced steady‐state free precession (SSFP) and a targeted double‐oblique spoiled gradient‐echo (GRE) sequences in combination with magnetization transfer (MT) preparation sequence for tissue contrast improvement.Materials and Methods
Nine healthy subjects were imaged with the proposed technique. The results are compared with optimized targeted MT prepared GRE acquisitions. Both quantitative and qualitative analyses were performed to evaluate each imaging method.Results
Whole‐heart images were successfully acquired with no visible image artifact in the vicinity of the coronary veins. The anatomical features and visual grading of both techniques were comparable. However, the targeted small slab acquisition of the left ventricular lateral wall was superior to whole‐heart acquisition for visualization of relevant information for cardiac resynchronization therapy (CRT) lead implantation.Conclusion
We demonstrated the feasibility of whole‐heart coronary vein MRI using a 3D MT‐SSFP imaging sequence. A targeted acquisition along the lateral left ventricular wall is preferred for visualization of branches commonly used in CRT lead implantation. J. Magn. Reson. Imaging 2009;29:1293–1299. © 2009 Wiley‐Liss, Inc. 相似文献14.
Ashish A. Tamhane PhD Konstantinos Arfanakis PhD Mark Anastasio PhD Xiaodong Guo PhD Michael Vannier MD Jia‐Hong Gao PhD 《Journal of magnetic resonance imaging : JMRI》2012,36(5):1241-1247
Purpose:
To develop a technique that is able to reduce acquisition time and remove uneven blurring in reconstructed image for PROPELLER MRI. By using under‐sampling and iterative reconstruction, this proposed technique will be less sensitive to subject motion.Materials and Methods:
Numerical simulations, as well as experiments on a phantom and healthy human subjects were performed to demonstrate advantages of a combination of under‐sampled acquisition and iterative reconstruction. Method of motion correction was modified to increase accuracy of motion correction for the under‐sampled PROPELLER acquisition.Results:
It was demonstrated that the proposed approach achieved substantial acceleration of PROPELLER acquisition while maintaining its motion correction advantage.Conclusion:
An effective method for reducing imaging time in PROPELLER was introduced in this study, which minimizes typical under‐sampling artifacts without uneven spatial resolution and maintains the ability of motion correction. J. Magn. Reson. Imaging 2012;36:1241–1247. © 2012 Wiley Periodicals, Inc. 相似文献15.
Markus Barth Heiko Meyer Stephan A. R. Kannengiesser Jonathan R. Polimeni Lawrence L. Wald David G. Norris 《Magnetic resonance in medicine》2010,63(4):1015-1020
In this study, the sensitivity of the S2‐steady‐state free precession (SSFP) signal for functional MRI at 7 T was investigated. In order to achieve the necessary temporal resolution, a three‐dimensional acquisition scheme with acceleration along two spatial axes was employed. Activation maps based on S2‐steady‐state free precession data showed similar spatial localization of activation and sensitivity as spin‐echo echo‐planar imaging (SE‐EPI), but data can be acquired with substantially lower power deposition. The functional sensitivity estimated by the average z‐values was not significantly different for SE‐EPI compared to the S2‐signal but was slightly lower for the S2‐signal (6.74 ± 0.32 for the TR = 15 ms protocol and 7.51 ± 0.78 for the TR = 27 ms protocol) compared to SE‐EPI (7.49 ± 1.44 and 8.05 ± 1.67) using the same activated voxels, respectively. The relative signal changes in these voxels upon activation were slightly lower for SE‐EPI (2.37% ± 0.18%) compared to the TR = 15 ms S2‐SSFP protocol (2.75% ± 0.53%) and significantly lower than the TR = 27 ms protocol (5.38% ± 1.28%), in line with simulations results. The large relative signal change for the long TR SSFP protocol can be explained by contributions from multiple coherence pathways and the low intrinsic intensity of the S2 signal. In conclusion, whole‐brain T2‐weighted functional MRI with negligible image distortion at 7 T is feasible using the S2‐SSFP sequence and partially parallel imaging. Magn Reson Med 63:1015–1020, 2010. © 2010 Wiley‐Liss, Inc. 相似文献
16.
Bernd Jung Matthias Honal Peter Ullmann Jürgen Hennig Michael Markl 《Magnetic resonance in medicine》2008,60(5):1169-1177
The purpose of this study was to combine a recently introduced spatiotemporal parallel imaging technique, PEAK‐GRAPPA (parallel MRI with extended and averaged generalized autocalibrating partially parallel acquisition), with two‐dimensional (2D) cine phase‐contrast velocity mapping. Phase‐contrast MRI was applied to measure the blood flow in the thoracic aorta and the myocardial motion of the left ventricle. To evaluate the performance of different reconstruction methods, fully acquired k‐space data sets were used to compare conventional parallel imaging using GRAPPA with reduction factors of R = 2–6 and PEAK‐GRAPPA as well as sliding window reconstruction with reduction factors R = 2–12 (net acceleration factors up to 5.2). PEAK‐GRAPPA reconstruction resulted in improved image quality with considerably reduced artifacts, which was also supported by error analysis. To analyze potential blurring or low‐pass filtering effects of spatiotemporal PEAK‐GRAPPA, the velocity time courses of aortic flow and myocardial tissue motion were evaluated and compared with conventional image reconstructions. Quantitative comparisons of blood flow velocities and pixel‐wise correlation analysis of velocities highlight the potential of PEAK‐GRAPPA for highly accelerated dynamic phase‐contrast velocity mapping. Magn Reson Med 60:1169–1177, 2008. © 2008 Wiley‐Liss, Inc. 相似文献
17.
Lan Ge Aya Kino Mark Griswold Charles Mistretta James C. Carr Debiao Li 《Magnetic resonance in medicine》2009,62(4):835-839
First‐pass perfusion MRI is a promising technique for detecting ischemic heart disease. However, the diagnostic value of the method is limited by the low spatial coverage, resolution, signal‐to‐noise ratio (SNR), and cardiac motion‐related image artifacts. In this study we investigated the feasibility of using a method that combines sliding window and CG‐HYPR methods (SW‐CG‐HYPR) to reduce the acquisition window for each slice while maintaining the temporal resolution of one frame per heartbeat in myocardial perfusion MRI. This method allows an increased number of slices, reduced motion artifacts, and preserves the relatively high SNR and spatial resolution of the “composite images.” Results from eight volunteers demonstrate the feasibility of SW‐CG‐HYPR for accelerated myocardial perfusion imaging with accurate signal intensity changes of left ventricle blood pool and myocardium. Using this method the acquisition time per cardiac cycle was reduced by a factor of 4 and the number of slices was increased from 3 to 8 as compared to the conventional technique. The SNR of the myocardium at peak enhancement with SW‐CG‐HYPR (13.83 ± 2.60) was significantly higher (P < 0.05) than the conventional turbo‐FLASH protocol (8.40 ± 1.62). Also, the spatial resolution of the myocardial perfection images was significantly improved. SW‐CG‐HYPR is a promising technique for myocardial perfusion MRI. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc. 相似文献
18.
Hsu‐Lei Lee Ajit Shankaranarayanan Gerald M. Pohost Krishna S. Nayak 《Magnetic resonance in medicine》2010,63(6):1716-1722
Cine balanced steady‐state free precession (SSFP) is the most widely used sequence for assessing cardiac ventricular function at 1.5 T because it provides high signal‐to‐noise ratio efficiency and strong contrast between myocardium and blood. At 3 T, the use of SSFP is limited by susceptibility‐induced off‐resonance, resulting in either banding artifacts or the need to use a short‐sequence pulse repetition time that limits the readout duration and hence the achievable spatial resolution. In this work, we apply wideband SSFP, a variant of SSFP that uses two alternating pulse repetition times to establish a steady state with wider band spacing in its frequency response and overcome the key limitations of SSFP. Prospectively gated cine two‐dimensional imaging with wideband SSFP is evaluated in healthy volunteers and compared to conventional balanced SSFP, using quantitative metrics and qualitative interpretation by experienced clinicians. We demonstrate that by trading off temporal resolution and signal‐to‐noise ratio efficiency, wideband SSFP mitigates banding artifacts and enables imaging with approximately 30% higher spatial resolution compared to conventional SSFP with the same effective band spacing. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc. 相似文献
19.
Silke Potthast MD Lee Mitsumori MD Luana A. Stanescu MD Michael L. Richardson MD Kelley Branch MD Theodore J. Dubinsky MD Jeffrey H. Maki PhD 《Journal of magnetic resonance imaging : JMRI》2010,31(1):177-184
Purpose:
To compare nongated three‐dimensional (3D) contrast‐enhanced magnetic resonance angiography (CE‐MRA) with 3D‐navigated cardiac‐gated steady‐state free‐precession bright blood (3D‐nav SSFP) and noncontrast 2D techniques for ascending aorta dimension measurements.Materials and Methods:
Twenty‐five clinical exams were reviewed to evaluate the ascending aorta at 1.5T using: breathhold cine bright blood (SSFP), cardiac‐triggered T2 black blood (T2 BB), axial 3D‐nav SSFP, and nongated 3D CE‐MRA. Three radiologists independently measured aortic size at three specified locations for each sequence. Means, SDs, interobserver correlation, and vessel edge sharpness were statistically evaluated.Results:
Measurements were greatest for 3D‐nav SSFP and 3D CE‐MRA and smallest for T2 BB. There was no significant difference between 3D‐nav SSFP and 3D CE‐MRA (P = 0.43–0.86), but significance was observed comparing T2 BB to all sequences. Interobserver agreement was uniformly >0.9, with T2 BB best, followed closely by 3D‐nav SSFP and 2D cine SSFP, and 3D CE‐MRA being the worst. Edge sharpness was significantly poorer for 3D CE‐MRA compared to the other sequences (P < 0.001).Conclusion:
If diameter measurements are the main clinical concern, 3D‐nav SSFP appears to be the best choice, as it has a sharp edge profile, is easy to acquire and postprocess, and shows very good interobserver correlation. J. Magn. Reson. Imaging 2010;31:177–184. © 2009 Wiley‐Liss, Inc. 相似文献20.
Vuissoz PA Odille F Fernandez B Lohezic M Benhadid A Mandry D Felblinger J 《Journal of magnetic resonance imaging : JMRI》2012,35(2):340-351