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1.

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   

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Cardiac MRI function measurements are typically based on multiple breathhold 2D sequences to acquire images of the entire heart. In the present study, the feasibility of a cine 3D TrueFISP technique in which several complete volumetric measurements may be obtained during a single breathhold is demonstrated. In contrast to 3D FLASH, the TrueFISP sequence offers an excellent contrast between the myocardium and the intraventricular cavity without the use of contrast agent. An ECG-gated 3D cine TrueFISP sequence was implemented with a repetition time of 2.4-2.8 ms, which allows imaging of the complete heart within a single breathhold throughout 20-46 heartbeats with a 3D frame rate of 8-13 volumes per cardiac cycle and a spatial resolution of about 1.5 x 3.5 x 3.5 mm(3). Breathhold volumetric cine imaging with the 3D TrueFISP technique holds promise for rapid and accurate evaluation of the cardiac regional wall motion and the calculation of cardiac volume and ejection fraction.  相似文献   

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Improvements in short-axis blood-myocardium contrast in the heart with the use of four magnetization preparation schemes applied before the imaging sequence are demonstrated. Gradient-echo cine cardiac images are acquired and compared at 0.95 T incorporating T2, T1p, magnetization transfer, and double inversion (black blood) preparations in a series of volunteer studies over the first 550 ms of the cardiac cycle. T2 and T1p preparations exhibit improvements of 100% and above in image contrast. Magnetization transfer preparation exhibits improvements of 50% in image contrast, whereas an initial improvement (50%) followed by a large loss in contrast is observed using the black blood preparation. Improvements in contrast are dependent on tissue relaxation parameters and therefore are suitable for studies involving patients exhibiting poor in-flow enhancement of blood caused by poor heart function.  相似文献   

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Magnetization transfer imaging (MTI) by means of MRI exploits the mobility of water molecules in tissue and offers an alternative contrast mechanism beyond the more commonly used mechanisms based on relaxation times. A cardiac MTI method was implemented on a commercially available 1.5 T MR imager. It is based on the acquisition of two sets of cardiac‐triggered cine balanced steady‐state free precession (bSSFP) images with different levels of RF power deposition. Reduction of RF power was achieved by lengthening the RF excitation pulses of a cine bSSFP sequence from 0.24 ms to 1.7 ms, while keeping the flip angle constant. Normal volunteers and patients with acute myocardial infarcts were imaged in short and long axis views. Normal myocardium showed an MT ratio (MTR) of 33.0 ± 3.3%. In acute myocardial infarct, MTR was reduced to 24.5 ± 9.2% (P < 0.04), most likely caused by an increase in water content due to edema. The method thus allows detection of acute myocardial infarct without the administration of contrast agents. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.  相似文献   

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Accelerating cardiac cine 3D imaging using k-t BLAST.   总被引:1,自引:0,他引:1  
By exploiting spatiotemporal correlations in cardiac acquisitions using k-t BLAST, gated cine 3D acquisitions of the heart were accelerated by a net factor of 4.3, making single breathhold acquisitions possible. Sparse sampling of k-t space along a sheared grid pattern was implemented into a cine 3D SSFP sequence. The acquisition of low-resolution training data, which was required to resolve aliasing in the k-t BLAST method, was either interleaved into the sampling process or obtained in a separate prescan to allow for shorter breathhold durations in patients with heart disease. Volumetric datasets covering the heart with 20 slices at a spatial resolution of 2 x 2 x 5 mm3 were recorded with 20 cardiac phases in a total breathhold duration of 25-27 sec, or 18 sec if partial Fourier sampling was additionally employed. The feasibility of the method was demonstrated on healthy volunteers and on patients. The comparison of endocardial area derived from single slices of the 3D dataset with values extracted from separate single-slice acquisitions showed no significant differences. By shortening the acquisition substantially, k-t BLAST may greatly facilitate volumetric imaging of the heart for evaluation of regional wall motion and the assessment of ventricular volume and ejection fraction.  相似文献   

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PURPOSE: To compare balanced steady-state free precession (SSFP) and segmented fast low angle shot (FLASH) for quantification of left and right ventricular volumes and function and for left ventricular mass at high field (3 Tesla). MATERIALS AND METHODS: A total of 33 patients (19 male, mean age 54 years) with various forms of heart disease underwent ventricular function studies using cine SSFP and FLASH sequences with identical slice orientations. RESULTS: Using SSFP, left ventricular end-diastolic (+10 mL [4.7%], P < 0.001) and end-systolic volumes (+9 mL [6.1%], P < 0.001) measured larger whereas mass was considerably smaller (-23 g [-12.9%], P < 0.001) and ejection fraction (-1% [-3.2%], P < 0.01) marginally smaller. Right ventricular end-diastolic (+4 mL [2.6%], P = 0.001) and end-systolic volumes (+4 mL [5.1%], P < 0.01) were also larger, but no significant difference for right ventricular ejection fraction (P = 0.05) was found. CONCLUSION: Similar to previous results at 1.5 Tesla, at high magnetic field the cine SSFP technique led to discrete but significantly higher ventricular volume measurements and to a significantly smaller measurement of left ventricular mass in patients. The effect on left and right ventricular ejection fraction was minor, although the difference remained significant for the left ventricle.  相似文献   

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Cardiac MRI in neonates holds promise as a tool that can provide detailed functional information in this vulnerable group. However, their small size, rapid heart rate, and inability to breath‐hold, pose particular challenges that require prolonged high‐contrast and high‐SNR methods. Balanced‐steady state free precession (SSFP) offers high SNR efficiency and excellent contrast, but is vulnerable to off‐resonance effects that cause banding artifacts. This is particularly problematic in the blood‐pool, where off‐resonance flow artifacts severely degrade image quality. Methods: In this article, we explore active frequency stabilization, combined with image‐based shimming, to achieve prolonged SSFP imaging free of banding artifacts. The method was tested using 2D multislice SSFP cine acquisitions on 18 preterm infants, and the functional measures derived were validated against phase‐contrast flow assessment. Results: Significant drifts in the resonant frequency (165 ± 23Hz) were observed during 10‐min SSFP examinations. However, full short‐axis stacks free of banding artifacts were achieved in 16 subjects with stabilization; the cardiac output obtained revealed a mean difference of 9.0 ± 8.5% compared to phase‐contrast flow measurements. Conclusion: Active frequency stabilization has enabled the use of prolonged SSFP acquisitions for neonatal cardiac imaging at 3T. The findings presented could have broader implications for other applications using prolong SSFP acquisitions. Magn Reson Med 70:776–784, 2013. © 2012 Wiley Periodicals, Inc.  相似文献   

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PURPOSE: To develop and validate a three-dimensional (3D) single breath-hold, projection reconstruction (PR), balanced steady state free precession (SSFP) method for cardiac function evaluation against a two-dimensional (2D) multislice Fourier (Cartesian) transform (FT) SSFP method. MATERIALS AND METHODS: The 3D PR SSFP sequence used projections in the x-y plane and partitions in z, providing 70-80 msec temporal resolution and 1.7 x 1.7 x 8-10 mm in a 24-heartbeat breath hold. A total of 10 volunteers were imaged with both methods, and the measurements of global cardiac function were compared. RESULTS: Mean signal-to-noise ratios (SNRs) for the blood and myocardium were 114 and 42 (2D) and 59 and 21 (3D). Bland-Altman analysis comparing the 2D and 3D ejection fraction (EF), left ventricular end diastolic volume (LVEDV) and end systolic volume (LVESV), and end diastolic myocardial mass (LVEDM) provided values of bias +/-2 SD of 0.6% +/- 7.7 % for LVEF, 5.9 mL +/- 20 mL for LVEDV, -2.8 mL +/- 12 mL for LVESV, and -0.61 g +/- 13 g for LVEDM. 3D interobserver variability was greater than 2D for LVEDM and LVESV. CONCLUSION: In a single breath hold, the 3D PR method provides comparable information to the standard 2D FT method, which employs 10-12 breath holds.  相似文献   

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A 39‐year‐old female patient with thoracic syringomyelia underwent routine magnetic resonance imaging (MRI) and 3 T MRI to investigate the value of retrospectively cardiac‐gated cine steady‐state free precession (SSFP) MRI in the preoperative and postoperative diagnosis of arachnoid membranes in the spinal subarachnoid space. Therefore, 3T MRI included sagittal and transverse retrospectively cardiac‐gated cine balanced fast‐field echo (balanced‐FFE) sequences both preoperatively and after microsurgical lysis of arachnoid adhesions and expansive duraplasty. Arachnoid membranes were detected and this result was correlated with intraoperative findings and the results of routine cardiac‐gated phase‐contrast cerebrospinal fluid (CSF) flow MRI. Retrospectively cardiac‐gated cine SSFP MRI enabled imaging of arachnoid membranes with high spatial resolution and sufficient contrast to delineate them from hyperintense CSF preoperatively and postoperatively. The images were largely unaffected by artifacts. Surgery confirmed the presence of arachnoid adhesions in the upper thoracic spine. Not all arachnoid membranes that were seen on cine balanced‐FFE sequences caused significant spinal CSF flow blockages in cardiac‐gated phase‐contrast CSF flow studies. In conclusion, retrospectively cardiac‐gated cine SSFP MRI may become a valuable tool for the preoperative detection of arachnoid adhesions and the postoperative evaluation of microsurgical adhesiolysis in patients with idiopathic syringomyelia. J. Magn. Reson. Imaging 2010. © 2010 Wiley‐Liss, Inc.  相似文献   

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Previous work has shown that the use of radial GRAPPA for the reconstruction of undersampled real‐time free‐breathing cardiac data allows for frame rates of up to 30 images/s. It is well known that the spiral trajectory offers a higher scan efficiency compared to radial trajectories. For this reason, we have developed a novel through‐time spiral GRAPPA method and demonstrate its application to real‐time cardiac imaging. By moving from the radial trajectory to the spiral trajectory, the temporal resolution can be further improved at lower acceleration factors compared to radial GRAPPA. In addition, the image quality is improved compared to those generated using the radial trajectory due to the lower acceleration factor. Here, we show that 2D frame rates of up to 56 images/s can be achieved using this parallel imaging method with the spiral trajectory. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.  相似文献   

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Standard MRI cine exams for the study of cardiac function are segmented over several heartbeats and thus require a breath‐hold to minimize breathing motion artifacts, which is a current limitation of this approach. The purpose of this study was to develop a method for the measurement and correction of respiratory motion that is compatible with cine imaging. Real‐time images were used to measure the respiratory motion of heart, to allow translations, rotations, and shears to be measured and corrected in the k‐space domain prior to a final gated‐segmented reconstruction, using the same data for both purposes. A method for data rejection to address the effects of through‐plane motion and complex deformations is described (respiratory gating). A radial k‐space trajectory was used in this study to allow direct reconstruction of undersampled real‐time images, although the techniques presented are applicable with Cartesian k‐space trajectories. Corrected and uncorrected free‐breathing gated‐segmented images acquired over 18 sec were compared to the current standard breath‐hold Cartesian images using both quantitative sharpness profiles (mm?1) and clinical scoring (1 to 5 scale, 3: clinically acceptable). Free‐breathing, free‐breathing corrected, and breath‐hold images had average sharpness values of 0.23 ± 0.04, 0.38 ± 0.04, and 0.44 ± 0.04 mm?1 measured at the blood–endocardium interface, and clinical scores of 2.2 ± 0.5, 4.2 ± 0.4, and 4.7 ± 0.5, respectively. Magn Reson Med 60:709–717, 2008. © 2008 Wiley‐Liss, Inc.  相似文献   

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