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1.
Ananth J. Madhuranthakam PhD Huanzhou Yu PhD Ann Shimakawa MS Reed F. Busse PhD Martin P. Smith MD Scott B. Reeder MD PhD Neil M. Rofsky MD Jean H. Brittain PhD Charles A. McKenzie PhD 《Journal of magnetic resonance imaging : JMRI》2010,32(3):745-751
Purpose:
To develop a robust 3D fast spin echo (FSE) T2‐weighted imaging method with uniform water and fat separation in a single acquisition, amenable to high‐quality multiplanar reformations.Materials and Methods:
The Iterative Decomposition of water and fat with Echo Asymmetry and Least squares estimation (IDEAL) method was integrated with modulated refocusing flip angle 3D‐FSE. Echoes required for IDEAL processing were acquired by shifting the readout gradient with respect to the Carr‐Purcell‐Meiboom‐Gill echo. To reduce the scan time, an alternative data acquisition using two gradient echoes per repetition was implemented. Using the latter approach, a total of four gradient echoes were acquired in two repetitions and used in the modified IDEAL reconstruction.Results:
3D‐FSE T2‐weighted images with uniform water–fat separation were successfully acquired in various anatomies including breast, abdomen, knee, and ankle in clinically feasible scan times, ranging from 5:30–8:30 minutes. Using water‐only and fat‐only images, in‐phase and out‐of‐phase images were reconstructed.Conclusion:
3D‐FSE‐IDEAL provides volumetric T2‐weighted images with uniform water and fat separation in a single acquisition. High‐resolution images with multiple contrasts can be reformatted to any orientation from a single acquisition. This could potentially replace 2D‐FSE acquisitions with and without fat suppression and in multiple planes, thus improving overall imaging efficiency. J. Magn. Reson. Imaging 2010;32:745–751. © 2010 Wiley‐Liss, Inc. 相似文献2.
McMahon CJ Madhuranthakam AJ Wu JS Yablon CM Wei JL Rofsky NM Hochman MG 《Journal of magnetic resonance imaging : JMRI》2012,35(2):361-369
Purpose:
To assess the feasibility of combining three‐dimensional fast spin echo (3D‐FSE) and Iterative‐decomposition‐of water‐and‐fat‐with‐echo asymmetry‐and‐least‐squares‐estimation (IDEAL) at 1.5 Tesla (T), generating a high‐resolution 3D isotropic proton density‐weighted image set with and without “fat‐suppression” (FS) in a single acquisition, and to compare with 2D‐FSE and 3D‐FSE (without IDEAL).Materials and Methods:
Ten asymptomatic volunteers prospectively underwent sagittal 3D‐FSE‐IDEAL, 3D‐FSE, and 2D‐FSE sequences at 1.5T (slice thickness [ST]: 0.8 mm, 0.8 mm, and 3.5 mm, respectively). 3D‐FSE and 2D‐FSE were repeated with frequency‐selective FS. Fluid, cartilage, and muscle signal‐to‐noise ratio (SNR) and fluid‐cartilage contrast‐to‐noise ratio (CNR) were compared among sequences. Three blinded reviewers independently scored quality of menisci/cartilage depiction for all sequences. “Fat‐suppression” was qualitatively scored and compared among sequences.Results:
3D‐FSE‐IDEAL fluid‐cartilage CNR was higher than in 2D‐FSE (P < 0.05), not different from 3D‐FSE (P = 0.31). There was no significant difference in fluid SNR among sequences. 2D‐FSE cartilage SNR was higher than in 3D FSE‐IDEAL (P < 0.05), not different to 3D‐FSE (P = 0.059). 2D‐FSE muscle SNR was higher than in 3D‐FSE‐IDEAL (P < 0.05) and 3D‐FSE (P < 0.05). Good or excellent depiction of menisci/cartilage was achieved using 3D‐FSE‐IDEAL in the acquired sagittal and reformatted planes. Excellent, homogeneous “fat‐suppression” was achieved using 3D‐FSE‐IDEAL, superior to FS‐3D‐FSE and FS‐2D‐FSE (P < 0.05).Conclusion:
3D FSE‐IDEAL is a feasible approach to acquire multiplanar images of diagnostic quality, both with and without homogeneous “fat‐suppression” from a single acquisition. J. Magn. Reson. Imaging 2012;361‐369. © 2011 Wiley Periodicals, Inc. 相似文献3.
Kang Wang MS Huanzhou Yu PhD Jean H. Brittain PhD Scott B. Reeder MD PhD Jiang Du PhD 《Journal of magnetic resonance imaging : JMRI》2010,31(4):1027-1034
Purpose:
To demonstrate the feasibility of combining a chemical shift‐based water‐fat separation method (IDEAL) with a 2D ultrashort echo time (UTE) sequence for imaging and quantification of the short T2 tissues with robust fat suppression.Materials and Methods:
A 2D multislice UTE data acquisition scheme was combined with IDEAL processing, including T2* estimation, chemical shift artifacts correction, and multifrequency modeling of the fat spectrum to image short T2 tissues such as the Achilles tendon and meniscus both in vitro and in vivo. The integration of an advanced field map estimation technique into this combined method, such as region growing (RG), is also investigated.Results:
The combination of IDEAL with UTE imaging is feasible and excellent water‐fat separation can be achieved for the Achilles tendon and meniscus with simultaneous T2* estimation and chemical shift artifact correction. Multifrequency modeling of the fat spectrum yields more complete water‐fat separation with more accurate correction for chemical shift artifacts. The RG scheme helps to avoid water‐fat swapping.Conclusion:
The combination of UTE data acquisition with IDEAL has potential applications in imaging and quantifying short T2 tissues, eliminating the necessity for fat suppression pulses that may directly suppress the short T2 signals. J. Magn. Reson. Imaging 2010;31:1027–1034. ©2010 Wiley‐Liss, Inc. 相似文献4.
Basak E. Dogan MD Jingfei Ma PhD Ken Hwang PhD Ping Liu PhD Wei Tse Yang MD 《Journal of magnetic resonance imaging : JMRI》2011,34(4):842-851
Purpose:
To evaluate a single‐pass fast spoiled gradient echo (FSPGR) two‐point Dixon sequence and a gradient echo sequence with spectral fat suppression in their performance at 3 T for fat suppressed contrast‐enhanced bilateral breast imaging.Materials and Methods:
Twenty patients were prospectively enrolled in an imaging protocol that included axial Dixon and 3D FSPGR with spectrally selective fat saturation sequences as part of patient care in this study. Qualitative analysis was performed retrospectively by two readers who scored the images for homogeneity and degree of fat saturation, severity of artifacts, and quality of normal anatomical structures. Enhancing lesions were scored according to the confidence with which American College of Radiology (ACR) BI‐RADS magnetic resonance imaging (MRI) features were identified.Results:
The Dixon sequence showed superior fat saturation homogeneity, quality of posterior anatomical structures, and decreased artifact severity that were statistically significant (P < 0.0001). The degree of fat saturation was scored higher in the Dixon sequence, although the difference did not reach statistical significance. There were no significant differences between the 3D T1‐weighted FSPGR and Dixon groups for assessing lesion features.Conclusion:
Our findings suggest that the Dixon technique is an effective fat suppression method for contrast‐enhanced breast MRI. The Dixon technique also seemed to provide better anatomical definition of posterior structures and improvement in severity of artifacts. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc. 相似文献5.
Reeder SB McKenzie CA Pineda AR Yu H Shimakawa A Brau AC Hargreaves BA Gold GE Brittain JH 《Journal of magnetic resonance imaging : JMRI》2007,25(3):644-652
Purpose
To combine gradient‐echo (GRE) imaging with a multipoint water–fat separation method known as “iterative decomposition of water and fat with echo asymmetry and least squares estimation” (IDEAL) for uniform water–fat separation. Robust fat suppression is necessary for many GRE imaging applications; unfortunately, uniform fat suppression is challenging in the presence of B0 inhomogeneities. These challenges are addressed with the IDEAL technique.Materials and Methods
Echo shifts for three‐point IDEAL were chosen to optimize noise performance of the water–fat estimation, which is dependent on the relative proportion of water and fat within a voxel. Phantom experiments were performed to validate theoretical SNR predictions. Theoretical echo combinations that maximize noise performance are discussed, and examples of clinical applications at 1.5T and 3.0T are shown.Results
The measured SNR performance validated theoretical predictions and demonstrated improved image quality compared to unoptimized echo combinations. Clinical examples of the liver, breast, heart, knee, and ankle are shown, including the combination of IDEAL with parallel imaging. Excellent water–fat separation was achieved in all cases. The utility of recombining water and fat images into “in‐phase,” “out‐of‐phase,” and “fat signal fraction” images is also discussed.Conclusion
IDEAL‐SPGR provides robust water–fat separation with optimized SNR performance at both 1.5T and 3.0T with multicoil acquisitions and parallel imaging in multiple regions of the body. J. Magn. Reson. Imaging 2007;25:644–652. © 2007 Wiley‐Liss, Inc. 相似文献6.
Zhang L Zhong X Wang L Chen H Wang YA Yeh J Yang L Mao H 《Journal of magnetic resonance imaging : JMRI》2011,33(1):194-202
Purpose
To obtain positive contrast based on T1 weighting from magnetic iron oxide nanoparticle (IONP) using ultrashort echo time (UTE) imaging and investigate quantitative relationship between positive contrast and the core size and concentration of IONPs.Materials and Methods
Solutions of IONPs with different core sizes and concentrations were prepared. T1 and T2 relaxation times of IONPs were measured using the inversion recovery turbo spin echo (TSE) and multi‐echo spin echo sequences at 3 Tesla. T1‐weighted UTE gradient echo and T2‐weighted TSE sequences were used to image IONP samples. U87MG glioblastoma cells bound with arginine‐glycine‐aspartic acid (RGD) peptide and IONP conjugates were scanned using UTE, T1 and T2‐weighted sequences.Results
Positive contrast was obtained by UTE imaging from IONPs with different core sizes and concentrations. The relative‐contrast‐to‐water ratio of UTE images was three to four times higher than those of T2‐weighted TSE images. The signal intensity increases as the function of the core size and concentration. Positive contrast was also evident in cell samples bound with RGD‐IONPs.Conclusion
UTE imaging allows for imaging of IONPs and IONP bound tumor cells with positive contrast and provides contrast enhancement and potential quantification of IONPs in molecular imaging applications. J. Magn. Reson. Imaging 2011;33:194–202. © 2010 Wiley‐Liss, Inc. 相似文献7.
Lukas Havla MS Tamer Basha PhD Hussein Rayatzadeh MD Jaime L. Shaw BS Warren J. Manning MD Scott B. Reeder MD PhD Sebastian Kozerke PhD Reza Nezafat PhD 《Journal of magnetic resonance imaging : JMRI》2013,37(2):484-490
Purpose:
To develop an improved chemical shift‐based water‐fat separation sequence using a water‐selective inversion pulse for inversion recovery 3D contrast‐enhanced cardiac magnetic resonance imaging (MRI).Materials and Methods:
In inversion recovery sequences the fat signal is substantially reduced due to the application of a nonselective inversion pulse. Therefore, for simultaneous visualization of water, fat, and myocardial enhancement in inversion recovery‐based sequences such as late gadolinium enhancement imaging, two separate scans are used. To overcome this, the nonselective inversion pulse is replaced with a water‐selective inversion pulse. Imaging was performed in phantoms, nine healthy subjects, and nine patients with suspected arrhythmogenic right ventricular cardiomyopathy plus one patient for tumor/mass imaging. In patients, images with conventional turbo‐spin echo (TSE) with and without fat saturation were acquired prior to contrast injection for fat assessment. Subjective image scores (1 = poor, 4 = excellent) were used for image assessment.Results:
Phantom experiments showed a fat signal‐to‐noise ratio (SNR) increase between 1.7 to 5.9 times for inversion times of 150 and 300 msec, respectively. The water‐selective inversion pulse retains the fat signal in contrast‐enhanced cardiac MR, allowing improved visualization of fat in the water‐fat separated images of healthy subjects with a score of 3.7 ± 0.6. Patient images acquired with the proposed sequence were scored higher when compared with a TSE sequence (3.5 ± 0.7 vs. 2.2 ± 0.5, P < 0.05).Conclusion:
The water‐selective inversion pulse retains the fat signal in inversion recovery‐based contrast‐enhanced cardiac MR, allowing simultaneous visualization of water and fat. J. Magn. Reson. Imaging 2013;37:484–490. © 2012 Wiley Periodicals, Inc. 相似文献8.
Koji Tanabe DDS PhD Keiichi Nishikawa PhD Tsukasa Sano DDS PhD Osamu Sakai MD PhD Hernán Jara PhD 《Journal of magnetic resonance imaging : JMRI》2010,31(5):1277-1281
Purpose:
To test a newly developed fat suppression magnetic resonance imaging (MRI) prepulse that synergistically uses the principles of fat suppression via inversion recovery (STIR) and spectral fat saturation (CHESS), relative to pure CHESS and STIR. This new technique is termed dual fat suppression (Dual‐FS).Materials and Methods:
To determine if Dual‐FS could be chemically specific for fat, the phantom consisted of the fat‐mimicking NiCl2 aqueous solution, porcine fat, porcine muscle, and water was imaged with the three fat‐suppression techniques. For Dual‐FS and STIR, several inversion times were used. Signal intensities of each image obtained with each technique were compared. To determine if Dual‐FS could be robust to magnetic field inhomogeneities, the phantom consisting of different NiCl2 aqueous solutions, porcine fat, porcine muscle, and water was imaged with Dual‐FS and CHESS at the several off‐resonance frequencies. To compare fat suppression efficiency in vivo, 10 volunteer subjects were also imaged with the three fat‐suppression techniques.Results:
Dual‐FS could suppress fat sufficiently within the inversion time of 110–140 msec, thus enabling differentiation between fat and fat‐mimicking aqueous structures. Dual‐FS was as robust to magnetic field inhomogeneities as STIR and less vulnerable than CHESS. The same results for fat suppression were obtained in volunteers.Conclusion:
The Dual‐FS‐STIR‐CHESS is an alternative and promising fat suppression technique for turbo spin echo MRI. J. Magn. Reson. Imaging 2010;31:1277–1281. ©2010 Wiley‐Liss, Inc. 相似文献9.
Madhuranthakam AJ Smith MP Yu H Shimakawa A Reeder SB Rofsky NM McKenzie CA Brittain JH 《Journal of magnetic resonance imaging : JMRI》2012,35(5):1216-1221
Purpose:
To develop a robust T2‐weighted volumetric imaging technique with uniform water‐silicone separation and simultaneous fat suppression for rapid assessment of breast implants in a single acquisition.Materials and Methods:
A three‐dimensional (3D) fast spin echo sequence that uses variable refocusing flip angles was combined with a three‐point chemical‐shift technique (IDEAL) and short tau inversion recovery (STIR). Phase shifts of ?π/6, +π/2, and +7π/6 between water and silicone were used for IDEAL processing. For comparison, two‐dimensional images using 2D‐FSE‐IDEAL with STIR were also acquired in axial, coronal, and sagittal orientations.Results:
Near‐isotropic (true spatial resolution—0.9 × 1.3 × 2.0 mm3) volumetric breast images with uniform water‐silicone separation and simultaneous fat suppression were acquired successfully in clinically feasible scan times (7:00–10:00 min). The 2D images were acquired with the same in‐plane resolution (0.9 × 1.3 mm2), but the slice thickness was increased to 6 mm with a slice gap of 1 mm for complete coverage of the implants in a reasonable scan time, which varied between 18:00 and 22:30 min.Conclusion:
The single volumetric acquisition with uniform water and silicone separation enables images to be reformatted into any orientation. This allows comprehensive assessment of breast implant integrity in less than 10 min of total examination time. J. Magn. Reson. Imaging 2012;35:1216‐1221. © 2012 Wiley Periodicals, Inc.10.
Purpose
To evaluate a prototype fast spin‐echo (FSE) triple‐echo Dixon (FTED) technique for T2‐weighted spine imaging with and without fat suppression compared to conventional T2‐weighted fast recovery (FR) FSE and short‐tau inversion recovery (STIR) imaging.Materials and Methods
Sixty‐one patients were referred for spine magnetic resonance imaging (MRI) including sagittal FTED (time 2:26), STIR (time 2:42), and T2 FRFSE (time 2:55). Two observers compared STIR and FTED water images and T2 FRFSE and FTED T2 images for overall image quality, fat suppression, anatomic sharpness, motion, cerebrospinal fluid (CSF) flow artifact, susceptibility, and disease depiction.Results
On FTED images water and fat separation was perfect in 58 (.95) patients. Compared to STIR, the FTED water images demonstrated less motion in 57 (.93) of 61 patients (P < 0.05), better anatomic sharpness in 51 (.84) and patients (P < 0.05), and less CSF flow artifact in 7 (.11) P < 0.05) patients. There was no difference in fat suppression or chemical shift artifact. T2 FRFSE and FTED T2 images showed equivalent motion, CSF flow, and chemical shift artifact. Lesion depiction was equivalent on FTED water and STIR images and FTED T2 and T2 FRFSE images.Conclusion
FTED efficiently provides both fat‐suppressed and nonfat‐suppressed T2‐weighted spine images with excellent image quality, equal disease depiction, and 56% reduction in scan time compared to conventional STIR and T2 FRFSE. J. Magn. Reson. Imaging 2011;33:390–400. © 2011 Wiley‐Liss, Inc. 相似文献11.
Mürtz P Kaschner M Träber F Kukuk G Skowasch D Gieseke J Schild HH Willinek WA 《Journal of magnetic resonance imaging : JMRI》2012,35(2):456-461
Purpose:
To improve image quality of diffusion‐weighted body magnetic resonance imaging (MRI) with background body signal suppression (DWIBS) at 3.0 T.Materials and Methods:
In 30 patients and eight volunteers, a diffusion‐weighted spin‐echo echo‐planar imaging sequence with short TI inversion recovery (STIR) fat suppression was applied and repeated using slice‐selective gradient reversal (SSGR) and/or dual‐source parallel radiofrequency (RF) transmission (TX). The quality of diffusion‐weighted images and gray scale inverted maximum intensity projections (MIP) were visually assessed by intraindividual comparison with respect to the level of fat suppression and signal homogeneity. Moreover, the contrast between lesions/lymph nodes and background (Clb) was analyzed in the MIP reconstructions.Results:
By combining STIR with SSGR, fat suppression was significantly improved (P < 0.001) and Clb was increased two times. The use of TX allowed the reduction of acquisition time and improved image quality with regard to signal homogeneity (P < 0.001) and fat suppression (P = 0.005).Conclusion:
DWIBS at 3.0 T can be improved by using SSGR and TX. J. Magn. Reson. Imaging 2012;456‐461. © 2011 Wiley Periodicals, Inc. 相似文献12.
Chia‐Ying Liu PhD Thorsten A. Bley MD Oliver Wieben PhD Jean H. Brittain PhD Scott B. Reeder MD PhD 《Journal of magnetic resonance imaging : JMRI》2010,31(1):248-254
Purpose:
To develop a magnetization preparation method to achieve robust, flow‐independent blood suppression for cardiac and vascular magnetic resonance imaging (MRI).Materials and Methods:
T2Prep‐IR sequence consists of a T2 preparation followed by a nonselective adiabatic inversion pulse. T2Prep separates the initial longitudinal magnetization of arterial wall from lumen blood. After the inversion recovery pulse the imaging acquisition is then delayed for a period that allows the blood signal to approach the zero‐crossing point. Compared to the conventional double inversion recovery (DIR) preparation, T2Prep‐IR prepares all the spins regardless of their velocity and direction. T2Prep‐IR was incorporated into the fast spin echo and fast gradient echo acquisition sequences and images in various planes were acquired in the carotid arteries, thoracic aorta, and heart of normal volunteers. Blood suppression and image quality were compared qualitatively between two different preparations.Results:
For in‐plane flow carotid images, persistent flow‐related artifacts on the DIR images were removed with T2Prep‐IR. For cardiac applications, T2Prep‐IR provided robust blood suppression regardless of the flow direction and velocity, including the cardiac long‐axis views and the aorta that are often problematic with DIR.Conclusion:
T2Prep‐IR may overcome the flow dependence of DIR by providing robust flow‐independent black‐blood images. J. Magn. Reson. Imaging 2010;31:248–254. © 2009 Wiley‐Liss, Inc 相似文献13.
Allison Grayev MD Ann Shimakawa PhD Joseph Cousins MD PhD Patrick Turski MD Jean Brittain PhD Scott Reeder MD PhD 《Journal of magnetic resonance imaging : JMRI》2009,29(6):1367-1374
Purpose
To implement IDEAL (iterative decomposition of water and fat using echo asymmetry and least squares estimation) water‐fat separation with 3D time‐of‐flight (TOF) magnetic resonance angiography (MRA) of intracranial vessels for improved background suppression by providing uniform and robust separation of fat signal that appears bright on conventional TOF‐MRA.Materials and Methods
IDEAL TOF‐MRA and conventional TOF‐MRA were performed in volunteers and patients undergoing routine brain MRI/MRA on a 3T magnet. Images were reviewed by two radiologists and graded based on vessel visibility and image quality.Results
IDEAL TOF‐MRA demonstrated statistically significant improvement in vessel visibility when compared to conventional TOF‐MRA in both volunteer and clinical patients using an image quality grading system. Overall image quality was 3.87 (out of 4) for IDEAL versus 3.55 for conventional TOF imaging (P = 0.02). Visualization of the ophthalmic artery was 3.53 for IDEAL versus 1.97 for conventional TOF imaging (P < 0.00005) and visualization of the superficial temporal artery was 3.92 for IDEAL imaging versus 1.97 for conventional TOF imaging (P < 0.00005).Conclusion
By providing uniform suppression of fat, IDEAL TOF‐MRA provides improved background suppression with improved image quality when compared to conventional TOF‐MRA methods. J. Magn. Reson. Imaging 2009;29:1367–1374. © 2009 Wiley‐Liss, Inc. 相似文献14.
Takatoshi Aoki MD Yoshiko Yamashita MD Hodaka Oki MD Hiroyuki Takahashi MD Yoshiko Hayashida MD Kazuyoshi Saito MD Yoshiya Tanaka MD Yukunori Korogi MD 《Journal of magnetic resonance imaging : JMRI》2013,37(3):733-738
Purpose:
To compare fat‐suppressed magnetic resonance imaging (MRI) quality using iterative decomposition of water and fat with echo asymmetry and least‐squares estimation (IDEAL) with that using chemical shift selective fat‐suppressed T1‐weighted spin‐echo (CHESS) images for evaluating rheumatoid arthritis (RA) lesions of the hand and finger at 3T.Materials and Methods:
MRI was performed in eight healthy volunteers and eight RA patients with a 3.0T MR system (Signa HDxt GE healthcare) using an eight‐channel knee coil. FS‐CHESS‐T1‐SE and IDEAL imaging were acquired in the coronal planes covering the entire structure of the bilateral hands with a slice thickness of 2 mm. In the RA patients both images were obtained after intravenous gadolinium administration. Image quality was evaluated on a five‐point scale (1 = excellent to 5 = very poor). Synovitis and bone marrow contrast uptake on MR images were reviewed by two musculoskeletal radiologists using the Rheumatoid Arthritis MRI Scoring System (RAMRIS) of the Outcome Measures in Rheumatoid Arthritis Clinical Trials (OMERACT) group.Results:
IDEAL showed uniform FS unaffected by magnetic field inhomogeneity and challenging geometry of hand and fingers, while CHESS‐T1‐SE often showed FS failure within the first metacarpal joint, tip of the finger, and ulnar aspect of the wrist joint. Overall image quality was significantly better with IDEAL than CHESS‐T1‐SE images (4.43 vs. 3.43, P < 0.01). Interobserver agreement (κ value) for synovitis and bone marrow contrast uptake was good to excellent with IDEAL (0.74–0.91, 0.62–0.89, respectively).Conclusion:
IDEAL could compensate for the effects of field inhomogeneities, providing uniform FS of the hand and finger than did the CHESS‐T1‐SE sequence. J. Magn. Reson. Imaging 2013;37:733–738. © 2012 Wiley Periodicals, Inc. 相似文献15.
Shreyas S. Vasanawala Huanzhou Yu Ann Shimakawa Michael Jeng Jean H. Brittain 《Magnetic resonance in medicine》2012,67(1):183-190
MRI imaging of hepatic iron overload can be achieved by estimating T2* values using multiple‐echo sequences. The purpose of this work is to develop and clinically evaluate a weighted least squares algorithm based on T2* Iterative Decomposition of water and fat with Echo Asymmetry and Least‐squares estimation (IDEAL) technique for volumetric estimation of hepatic T2* in the setting of iron overload. The weighted least squares T2* IDEAL technique improves T2* estimation by automatically decreasing the impact of later, noise‐dominated echoes. The technique was evaluated in 37 patients with iron overload. Each patient underwent (i) a standard 2D multiple‐echo gradient echo sequence for T2* assessment with nonlinear exponential fitting, and (ii) a 3D T2* IDEAL technique, with and without a weighted least squares fit. Regression and Bland–Altman analysis demonstrated strong correlation between conventional 2D and T2* IDEAL estimation. In cases of severe iron overload, T2* IDEAL without weighted least squares reconstruction resulted in a relative overestimation of T2* compared with weighted least squares. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc. 相似文献
16.
Jiang Du Juan C. Hermida Eric Diaz Jacqueline Corbeil Richard Znamirowski Darryl D. D'Lima Graeme M. Bydder 《Magnetic resonance in medicine》2013,70(3):697-704
We describe the use of ultrashort echo time (UTE) sequences and fast spin echo sequences to assess cortical bone using a clinical 3T scanner. Regular two‐ and three‐dimensional UTE sequences were used to image both bound and free water in cortical bone. Adiabatic inversion recovery prepared UTE sequences were used to image water bound to the organic matrix. Two‐dimensional fast spin echo sequences were used to image free water. Regular UTE sequences were used together with bicomponent analysis to measure T*2s and relative fractions of bound and free water components in cortical bone. Inversion recovery prepared UTE sequences were used to measure the T*2 of bound water. Saturation recovery UTE sequences were used to measure the T1 of bone water. Eight cadaveric human cortical bone samples and a lower leg specimen were studied. Preliminary results show two distinct components in UTE detected signal decay, a single component in inversion recovery prepared UTE detected signal decay, and a single component in saturation recovery UTE detected signal recovery. Regular UTE sequences appear to depict both bound and free water in cortical bone. Inversion recovery prepared UTE sequences appear to depict water bound to the organic matrix. Two‐dimensional fast spin echo sequences appear to depict bone structure corresponding to free water in large pores. Magn Reson Med 70:697–704, 2013. © 2012 Wiley Periodicals, Inc. 相似文献
17.
Catherine D.G. Hines MS Huanzhou Yu PhD Ann Shimakawa MSE Charles A. McKenzie PhD Jean H. Brittain PhD Scott B. Reeder MD PhD 《Journal of magnetic resonance imaging : JMRI》2009,30(5):1215-1222
Purpose:
To validate a T1‐independent, T2*‐corrected fat quantification technique that uses accurate spectral modeling of fat using a homogeneous fat‐water‐SPIO phantom over physiologically expected ranges of fat percentage and T2* decay in the presence of iron overload.Materials and Methods:
A homogeneous gel phantom consisting of vials with known fat‐fractions and iron concentrations is described. Fat‐fraction imaging was performed using a multiecho chemical shift‐based fat‐water separation method (IDEAL), and various reconstructions were performed to determine the impact of T2* correction and accurate spectral modeling. Conventional two‐point Dixon (in‐phase/out‐of‐phase) imaging and MR spectroscopy were performed for comparison with known fat‐fractions.Results:
The best agreement with known fat‐fractions over the full range of iron concentrations was found when T2* correction and accurate spectral modeling were used. Conventional two‐point Dixon imaging grossly underestimated fat‐fraction for all T2* values, but particularly at higher iron concentrations.Conclusion:
This work demonstrates the necessity of T2* correction and accurate spectral modeling of fat to accurately quantify fat using MRI. J. Magn. Reson. Imaging 2009;30:1215–1222. © 2009 Wiley‐Liss, Inc. 相似文献18.
Brian A. Hargreaves PhD Weitian Chen PhD Wenmiao Lu PhD Marcus T. Alley PhD Garry E. Gold MD Anja C.S. Brau PhD John M. Pauly PhD Kim Butts Pauly PhD 《Journal of magnetic resonance imaging : JMRI》2010,31(4):987-996
Purpose:
To demonstrate accelerated imaging with both artifact reduction and different contrast mechanisms near metallic implants.Materials and Methods:
Slice‐encoding for metal artifact correction (SEMAC) is a modified spin echo sequence that uses view‐angle tilting and slice‐direction phase encoding to correct both in‐plane and through‐plane artifacts. Standard spin echo trains and short‐TI inversion recovery (STIR) allow efficient PD‐weighted imaging with optional fat suppression. A completely linear reconstruction allows incorporation of parallel imaging and partial Fourier imaging. The signal‐to‐noise ratio (SNR) effects of all reconstructions were quantified in one subject. Ten subjects with different metallic implants were scanned using SEMAC protocols, all with scan times below 11 minutes, as well as with standard spin echo methods.Results:
The SNR using standard acceleration techniques is unaffected by the linear SEMAC reconstruction. In all cases with implants, accelerated SEMAC significantly reduced artifacts compared with standard imaging techniques, with no additional artifacts from acceleration techniques. The use of different contrast mechanisms allowed differentiation of fluid from other structures in several subjects.Conclusion:
SEMAC imaging can be combined with standard echo‐train imaging, parallel imaging, partial‐Fourier imaging, and inversion recovery techniques to offer flexible image contrast with a dramatic reduction of metal‐induced artifacts in scan times under 11 minutes. J. Magn. Reson. Imaging 2010;31:987–996. ©2010 Wiley‐Liss, Inc. 相似文献19.
Cukur T Shimakawa A Yu H Hargreaves BA Hu BS Nishimura DG Brittain JH 《Journal of magnetic resonance imaging : JMRI》2011,33(4):931-939
Purpose:
To propose a new noncontrast‐enhanced flow‐independent angiography sequence based on balanced steady‐state free precession (bSSFP) that produces reliable vessel contrast despite the reduced blood flow in the extremities.Materials and Methods:
The proposed technique addresses a variety of factors that can compromise the exam success including insufficient background suppression, field inhomogeneity, and large volumetric coverage requirements. A bSSFP sequence yields reduced signal from venous blood when long repetition times are used. Complex‐sum bSSFP acquisitions decrease the sensitivity to field inhomogeneity but retain phase information, so that data can be processed with the Iterative Decomposition of Water and Fat with Echo Asymmetry and Least‐Squares Estimation (IDEAL) method for robust fat suppression. Meanwhile, frequent magnetization preparation coupled with parallel imaging reduces the muscle and long‐T1 fluid signals without compromising scan efficiency.Results:
In vivo flow‐independent peripheral angiograms with reliable background suppression and high spatial resolution are produced. Comparisons with phase‐sensitive bSSFP angiograms (that yield out‐of‐phase fat and water signals, and exploit this phase difference to suppress fat) demonstrate enhanced vessel depiction with the proposed technique due to reduced partial‐volume effects and improved venous suppression.Conclusion:
Magnetization‐prepared complex‐sum bSSFP with IDEAL fat/water separation can create reliable flow‐independent angiographic contrast in the lower extremities. J. Magn. Reson. Imaging 2011;33:931–939. © 2011 Wiley‐Liss, Inc. 相似文献20.
Zhou Y Kumaravel M Patel VS Sheikh KA Narayana PA 《Journal of magnetic resonance imaging : JMRI》2012,36(4):920-927