[Show abstract][Hide abstract] ABSTRACT: Purpose To describe and characterize a new approach to first-pass myocardial perfusion utilizing balanced steady-state free precession acquisition without the use of saturation recovery or other magnetization preparation. TheoryThe balanced steady-state free precession sequence is inherently sensitive to contrast agent enhancement of the myocardium. This sensitivity can be used to advantage in first-pass myocardial perfusion imaging by eliminating the need for magnetization preparation. Methods
Bloch equation simulations, phantom experiments, and in vivo 2D imaging studies were run comparing the proposed technique with three other methods: saturation recovery spoiled gradient echo, saturation recovery steady-state free precession, and steady-state spoiled gradient echo without magnetization preparation. Additionally, an acquisition-reconstruction strategy for 3D perfusion imaging is proposed and initial experience with this approach is demonstrated in healthy subjects and one patient. ResultsPhantom experiments verified simulation results showing the sensitivity of the balanced steady-state free precession sequence to contrast agent enhancement in solid tissue is similar to that of magnetization-prepared acquisitions. Images acquired in normal volunteers showed the proposed technique provided superior signal and signal-to-noise ratio compared with all other sequences at baseline as well as postcontrast. ConclusionsA new approach to first-pass myocardial perfusion is presented that obviates the need for magnetization preparation and provides high signal-to-noise ratio. Magn Reson Med 71:133-144, 2014. (c) 2013 Wiley Periodicals, Inc.
Full-text · Article · Jan 2014 · Magnetic Resonance in Medicine
[Show abstract][Hide abstract] ABSTRACT: Purpose:
To evaluate the feasibility of free-breathing three-dimensional (3D) phase sensitive inversion recovery (PSIR) Turbo FLASH late gadolinium enhancement (LGE) magnetic resonance images (MRI) on left ventricular scar in patients with coronary artery disease (CAD) compared with clinically established breathhold two-dimensional (2D) PSIR Turbo FLASH images.
Materials and methods:
In 58 consecutive patients with confirmed CAD, LGE MRI using the two sequences have been acquired. Image quality was graded on a four-point scale according to the image appearance. Qualitative evaluation including the distribution area and the transmural extent of the scar based on the American Heart Association's (AHA's) 17-segment model was performed in both of 2D and 3D images. The scar volumes were compared quantitatively between 2D and 3D images.
A total of 51 individuals were used for final statistical analysis. No differences were noted in image quality (P = 0.80), scar distribution area (P = 0.17), and scar transmural extent (P = 0.20) between 3D and 2D images. There was strong correlation in scar volume between the 3D and 2D results (r = 0.940; P < 0.001; Y = 0.298 + 1.251X, R(2) = 0.876). But the scar volume derived from 3D images was significantly larger than that derived from 2D images (2D versus 3D, 20.08 ± 9.41 cm(3) versus 25.41 ± 12.57 cm(3) , t = -7.60; P < 0.001). The trend toward a larger scar volume identified by 3D method was indicated through Bland-Altman analysis.
Free-breathing 3D PSIR Turbo FLASH imaging is another feasible method to identify left ventricular myocardial scar in patients with CAD and detects more scar volume compared with breathhold 2D PSIR Turbo FLASH imaging.
No preview · Article · Jul 2013 · Journal of Magnetic Resonance Imaging
[Show abstract][Hide abstract] ABSTRACT: Magnetic resonance elastography (MRE) can noninvasively measure the stiffness of liver tissue and display this information in anatomic maps. Magnetic resonance imaging (MRI) guidance has not previously been used to biopsy segments of heterogeneous stiffness identified on MRE. Dedicated study of MRE in post-liver transplant patients is also limited. In this study, the ability of real-time MRI to guide biopsies of segments of the liver with different MRE stiffness values in the same post-transplant patient was assessed.
MRE was performed in 9 consecutive posttransplant patients with history of hepatitis C. Segments of highest and lower stiffness on MRE served as targets for subsequent real-time MRI-guided biopsy using T2-weighted imaging. The ability of MRI-guided biopsy to successfully obtain tissue specimens was assessed. The Wilcoxon signed-rank test was used to compare mean stiffness differences for highest and lower MRE stiffness segments, with α = 0.05.
MRI guidance allowed successful sampling of liver tissue for all (18/18) biopsies. There was a statistically significant difference in mean MRE stiffness values between highest (4.61 ± 1.99 kPa) and lower stiffness (3.03 ± 1.75 kPa) (P = .0039) segments biopsied in the 9 posttransplant patients.
Real-time MRI can guide biopsy in patients after liver transplantation based on MRE stiffness values. This study supports the use of MRI guidance to sample tissue based on functional information.
No preview · Article · Sep 2012 · Academic radiology
[Show abstract][Hide abstract] ABSTRACT: Quantification of myocardial T1 relaxation has potential value in the diagnosis of both ischemic and nonischemic cardiomyopathies. Image acquisition using the modified Look-Locker inversion recovery technique is clinically feasible for T1 mapping. However, respiratory motion limits its applicability and degrades the accuracy of T1 estimation. The robust registration of acquired inversion recovery images is particularly challenging due to the large changes in image contrast, especially for those images acquired near the signal null point of the inversion recovery and other inversion times for which there is little tissue contrast. In this article, we propose a novel motion correction algorithm. This approach is based on estimating synthetic images presenting contrast changes similar to the acquired images. The estimation of synthetic images is formulated as a variational energy minimization problem. Validation on a consecutive patient data cohort shows that this strategy can perform robust nonrigid registration to align inversion recovery images experiencing significant motion and lead to suppression of motion induced artifacts in the T1 map.
Full-text · Article · Jun 2012 · Magnetic Resonance in Medicine
[Show abstract][Hide abstract] ABSTRACT: Example of improved T1 mapping after motion correction. Left column: T1 maps of original modified Look-Locker inversion recovery (MOLLI) sequence images indicating smearing on the myocardium due to imperfect breath-holding. Right column: Sharp myocardial boundary is recovered after motion correction using proposed technique. These images were from three different patients from the article by Xue et al (pp 1644-1655).
Full-text · Article · Jun 2012 · Magnetic Resonance in Medicine
[Show abstract][Hide abstract] ABSTRACT: To compare different state-of-the-art T2-weighted (T2w) imaging sequences combined with late gadolinium enhancement (LGE) for myocardial salvage area (MSA) assessment by cardiac magnetic resonance (CMR). T2w imaging has been used to assess the myocardial area at risk (AAR) in acute myocardial infarction (AMI) patients, but its clinical application is challenging due to technical and physical limitations.
Thirty patients with reperfused AMI underwent complete CMR imaging 2-5 days after hospital admission. Myocardial AAR and MSA were quantified on four different T2w sequences: (a) free-breathing T2-prepared single-shot balanced steady-state free precession (T2p_ssbSSFP); (b) breathhold T2-weighted acquisition for cardiac unified T2 edema (ACUTE); (c) breathhold T2w dark-blood inversion recovery turbo-spin echo (IR-TSE) (short-term inversion recovery: STIR); and (d) free-breathing high-resolution T2 dark-blood navigated BLADE. The diagnostic performance of each technique was also assessed.
Quantitative analysis showed significant differences in myocardial AAR extent as quantified by the four T2w sequences (P < 0.05). There were also significant differences in sensitivity, specificity and overall diagnostic performance.
Detection and quantification of AAR, and thus of MSA, by T2wCMR in reperfused AMI patients varied significantly between different T2w sequences in the same clinical setting.
Full-text · Article · Feb 2012 · Journal of Magnetic Resonance Imaging
[Show abstract][Hide abstract] ABSTRACT: Three-dimensional black-blood MRI is a promising noninvasive imaging technique for the assessment of atherosclerotic carotid artery disease. However, this technique is inherently susceptible to motion. In particular, swallowing can result in considerable wall motion at the carotid bifurcations, which may induce drastic image degradation or substantial overestimation of wall thickness. Self-gating techniques have previously been shown to be capable of resolving and compensating for cardiac or respiratory motion during MRI. This work presents a self-gating-based prospective motion gating scheme that is combined with a three-dimensional variable-flip-angle turbo spin-echo sequence (SPACE) for detecting swallowing motion. Self-gating signal readouts along the superior-inferior direction during each repetition time period are used to derive the projection profiles of the imaging volume. Based on cross-correlation analysis between the projection profiles and the corresponding reference profiles, swallowing motion can be detected and the motion-contaminated data will subsequently be discarded and reacquired in the next repetition time. The self-gated SPACE sequence was validated on eight healthy volunteers and two patients and, when compared with the conventional SPACE sequence, proved to be more resistant to swallowing motion and significantly improved image quality as well as the sharpness of carotid artery wall boundaries.
Full-text · Article · Feb 2012 · Magnetic Resonance in Medicine
[Show abstract][Hide abstract] ABSTRACT: PURPOSE
The purpose of the study is to evaluate a fully automated motion corrected first pass myocardial perfusion (FPMP) MRI with semi quantitative perfusion parameter maps in patients with suspected ischemic heart disease.
METHOD AND MATERIALS
A recently introduced framework to automatically analyze cardiac first pass perfusion MR includes registration, surface coil correction and noise suppression of images as well as pixel by pixel based map generation of semi-quantitative parameters. Stress and rest FPMP images were acquired in 28 patients with suspected ischemic heart disease on 1.5T scanner (MAGNETOM Avanto, Siemens Healthcare). Three short axis slices were acquired during infusion of 0.075 mMol/kg of Gadolinium (Magnevist, Bayer HealthCare Pharmaceuticals, USA) at rate of 4 ml/sec and adenosine (Adenoscan, Astellas Pharma, USA) infusion (0.14 mg/kg/min; duration: 4 min) were administrated to induce stress. Free breathing, motion-corrected images and corresponding perfusion maps were assessed independently by 2 radiologists using the AHA 16 model and evaluated using a four point Likert scale (poor to excellent) to evaluate image quality and confidence level in presence or absence of hypo-perfusion regions. Upslope index of both free breathing and motion corrected images during stress and rest were manually calculated in non-ischemic and ischemic areas and compared to the corresponding pixel wise parameter map generated based on motion corrected images. FPMP MRI results were subsequently compared to coronary angiogram, stress echocardiography, or SPECT.
All patients were successfully scanned; perfusion defects were detected in 18 patients. The mean image quality score for motion corrected images (3.57 ± 0.42) and confidence level (3.28 ± 0.51) were significantly higher (p<0.001), than free breathing images (mean image score of 2.5 ± 0.62 and confidence level of 2.94 ± 0.39). Upslope index of non ischemic and ischemic areas and semi quantitative perfusion parameter maps values were comparable.
The feasibility of a fully integrated semi-quantitative myocardial perfusion analysis was demonstrated in patients with myocardial ischemia.
A fully automated motion corrected first pass myocardial perfusion MRI with semi quantitative perfusion parameter maps is a feasible approach for evaluation of patients with myocardial ischemia.
[Show abstract][Hide abstract] ABSTRACT: Objective: To assess the value of free-breathing 3D phase sensitive inversion recovery (PSIR) turbo FLASH for demonstrating the left ventricular myocardial scar in patients with myocardial infarction. Methods: Twenty-three patients with myocardial infarction underwent 2D and 3D phase sensitive inversion recovery (PSIR) Turbo FLASH sequences 10-15 minutes after injection of dimeglumine gadopentetate. The image quality, the area, location and volume of hyperenhanced scar were independently assessed by two experienced radiologists. Student's t test or rank sum test and Pearson linear correlation were used for the statistics. Results: There were no significant differences in the overall image quality (2.57 ± 0.59 vs 2.39 ± 0. 66, Z = -0.93, P =0.35), the area (24.48 ± 10.83 vs 29.00 ± 11.56, Z = -1.41, P=0.16) and location (16.78 ± 6.51 vs 18.87 ± 6.76, Z = - 1. 17, P = 0.24) of hyperenhanced scar between 2D and 3D PSIR sequences. The mean volume of hyperenhanced scar was significantly greater in 3D PSIR sequence than that in 2D PSIR sequence[ (23.46 ± 10.61) vs (31.65 ± 13.86) cm3, t = -2. 25, P = 0.03]. There was a good correlation in the volume of hyperenhanced scar between 2D PSIR and 3D PSIR sequences (r = 0.940, P < 0.01; y = 2.851 + 1.228x, R2 = 0.883). Conclusion: Free-breathing 3D PSIR Turbo FLASH is a promising new imaging technique for accurate assessment of myocardial scar.
[Show abstract][Hide abstract] ABSTRACT: Whole-heart coronary magnetic resonance angiography is a promising method for detecting coronary artery disease. However, the imaging time is relatively long (typically 10-15 min). The goal of this study was to implement a radial echo planar imaging sequence for contrast-enhanced whole-heart coronary magnetic resonance angiography, with the aim of combining the scan efficiency of echo planar imaging with the motion insensitivity of radial k-space sampling. A self-calibrating phase correction technique was used to correct for off-resonance effects, trajectory measurement was used to correct for k-space trajectory errors, and variable density sampling was used in the partition direction to reduce streaking artifacts. Seven healthy volunteers and two patients were scanned with the proposed radial echo planar imaging sequence, and the images were compared with a traditional gradient echo and X-ray angiography techniques, respectively. Whole-heart images with the radial EPI technique were acquired with a resolution of 1.0 × 1.0 × 2.0 mm(3) in a scan time of 5 min. In healthy volunteers, the average image quality scores and visualized vessel lengths of the RCA and LAD were similar for the radial EPI and gradient echo techniques (P value > 0.05 for all). Anecdotal patient studies showed excellent agreement of the radial EPI technique with X-ray angiography.
Full-text · Article · Jul 2011 · Magnetic Resonance in Medicine
[Show abstract][Hide abstract] ABSTRACT: The biophysical mechanisms influencing balanced steady-state free precession (bSSFP) based edema imaging in the setting of acute myocardial infarction are not well understood. To assess the various mechanisms that enable the detection of myocardial edema on bSSFP-based imaging approaches (cine bSSFP and T(2)-prepared bSSFP), experiments were conducted in canine models subjected to ischemia-reperfusion injury. Results showed that in addition to relaxation effects, the alteration in thermal equilibrium (M(0)) (including magnetization transfer) has a significant contribution to the image contrast between edematous and healthy myocardium. The relative signal-intensity ratios between edematous and healthy myocardium were: 1.51 ± 0.18 (cine bSSFP) and 1.58 ± 0.20 (T(2)-prepared bSSFP); the theoretically estimated relative relaxation and M(0) effects were: 1.17 ± 0.09 and 1.30 ± 0.19, respectively (cine bSSFP), and 1.49 ± 0.23 and 1.06 ± 0.07, respectively (T(2)-prepared bSSFP). There were no significant difference between cine bSSFP and T(2)-prep bSSFP relative signal-intensity ratios. However, the relative relaxation effect in cine bSSFP was significantly lower than in T(2)-prep bSSFP (P < 0.05), and the M(0) effect in cine bSSFP was significantly higher than in T(2)-prep bSSFP (P < 0.05). Hence the acquisition strategies that wish to maximize myocardial edema contrast in cine bSSFP imaging should take both relaxation and M(0) effects into account.
Full-text · Article · Jul 2011 · Magnetic Resonance in Medicine