Iterative decomposition of water and fat with echo asymmetry and least‐squares estimation (IDEAL) of the wrist and finger at 3T: Comparison with chemical shift selective fat suppression images

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.     

Practical Application of Iterative Decomposition of Water and Fat with Echo Asymmetry and Least-Squares Estimation (IDEAL) Imaging in Minimizing Metallic Artifacts

Iterative decomposition of water and fat with echo asymmetry and the least-squares estimation (IDEAL) is a recently developed method for robust separation of fat and water with very high signal-to-noise-ratio (SNR) efficiency. In contrast to conventional fat-saturation methods, IDEAL is insensitive to magnetic field (B0 and B1) inhomogeneity. The aim of this study was to illustrate the practical application of the IDEAL technique in reducing metallic artifacts in postoperative patients with metallic hardware. The IDEAL technique can help musculoskeletal radiologists make an accurate diagnosis particularly in musculoskeletal imaging by reducing metallic artifacts, enabling the use of contrast enhancement, improving SNR performance, and providing various modes of MR images with one scan parameter.     

Iterative decomposition of water and fat with echo asymmetry and least‐squares estimation (IDEAL): Application with fast spin‐echo imaging

Chemical shift based methods are often used to achieve uniform water–fat separation that is insensitive to B_o inhomogeneities. Many spin‐echo (SE) or fast SE (FSE) approaches acquire three echoes shifted symmetrically about the SE, creating time‐dependent phase shifts caused by water–fat chemical shift. This work demonstrates that symmetrically acquired echoes cause artifacts that degrade image quality. According to theory, the noise performance of any water–fat separation method is dependent on the proportion of water and fat within a voxel, and the position of echoes relative to the SE. To address this problem, we propose a method termed “iterative decomposition of water and fat with echo asymmetric and least‐squares estimation” (IDEAL). This technique combines asymmetrically acquired echoes with an iterative least‐squares decomposition algorithm to maximize noise performance. Theoretical calculations predict that the optimal echo combination occurs when the relative phase of the echoes is separated by 2π/3, with the middle echo centered at π/2+πk (k = any integer), i.e., (–π/6+πk, π/2+πk, 7π/6+πk). Only with these echo combinations can noise performance reach the maximum possible and be independent of the proportion of water and fat. Close agreement between theoretical and experimental results obtained from an oil–water phantom was observed, demonstrating that the iterative least‐squares decomposition method is an efficient estimator. Magn Reson Med, 2005. © 2005 Wiley‐Liss, Inc.     

两种场强磁共振IDEAL-IQ序列对质子密度脂肪分数和铁含量定量分析的初步对比研究

目的 比较3.0 T和1.5 T MR最小二乘法估计和不对称回波迭代分解水和脂肪成像（IDEAL-IQ）序列质子密度脂肪分数（PDFF）和铁含量（R2*）测量值的异同。 方法 于2019年12月选取佛山市第一人民医院健康志愿者20名[其中男性13名、女性7名,年龄（23.7±2.5）岁]并用不同脂肪含量的塑料试管模型进行前瞻性研究,分别在3.0 T（A组）和1.5 T（B组）2台 MRI设备上应用IDEAL-IQ序列进行扫描。在自动生成的FatFrac图和R2*图上自动勾画感兴趣区（ROI）,分别测量模型、健康志愿者的肝脏和皮下脂肪的PDFF、R2*值。符合正态分布的计量资料采用配对样本t检验（方差齐）和Mann-Whitney U检验（方差不齐）进行比较。 结果 模型A1组和B1组PDFF的测量平均值分别为（20.59±14.39）%和（21.89±14.95）%,差异无统计学意义（Z=−1.550,P=0.121）;A1组和B1组R2*的测量平均值分别为（84.86±116.43） Hz和（43.61±54.59） Hz,差异有统计学意义（Z=−3.448,P=0.001）。健康志愿者3.0 T和1.5 T MRI肝脏、皮下脂肪PDFF测量平均值分别为（3.33±2.95） %和（4.39±2.80） %、（81.78±6.33） %和（81.54±5.53） %,差异均无统计学意义（Z=−1.867、t=−0.301,均P>0.05）;A组肝脏、皮下脂肪的R2*测量平均值为（52.42±12.22） Hz、（50.88±10.32） Hz,分别高于对应的B组[（32.73±5.62） Hz、（39.41±9.11） Hz],且差异均有统计学意义（Z=−3.920、t=4.372,均P<0.001）。 结论 基于IDEAL-IQ序列的3.0 T和1.5 T MR模型、健康志愿者肝脏和皮下脂肪的PDFF测量值的差异无统计学意义,但3.0 T MRI的PDFF测量值可能比1.5 T MRI更接近临床实际情况;2种场强获得的R2*值的差异有统计学意义,其影响因素需进一步研究。     

Non-physiological Aortic Flow and Aortopathy in Adult Patients with Transposition of the Great Arteries after the Jatene Procedure: A Pilot Study Using Echo Planar 4D Flow MRI

PurposeDilated aortic root and ascending aorta (AAO) with progressive aortic regurgitation is a well-known sequela after arterial switch operation (ASO) in adults with transposition of the great arteries (TGA). We aimed to quantitatively assess aortic flow profiles in adults with TGA after ASO (Jatene procedure with LeCompte maneuver) using echo planar imaging (EPI) 4D flow MRI.MethodsProspectively, 9 consecutive adults (30.2 ± 6.6 years) after ASO (Jatene operation with LeCompte technique), 13 consecutive adults (34.3 ± 7.2 years) after the atrial switch operation with Senning procedure, and 8 age-matched control patients, who underwent turbo field echo (TFE) EPI 4D flow MRI (average scan time of approximately 4 min), were enrolled.ResultsTGA after ASO showed a markedly dilated sinus of Valsalva, compared to TGA after atrial switch operation (26.6. ± 4.9 vs. 18.6. ± 1.5 mm/cm²). Vorticity, helicity, wall share stress (WSS), and energy loss (EL) in the aortic root and the AAO in TGA were greater than in the controls. Vorticity, helicity, WSS, and EL in the aortic root and the AAO were also greater in TGA after ASO than after atrial switch operation. More acute aortic arch angle correlated with greater vorticity of the aortic root, and the significant diameter ratio of the sinus of Valsalva and the AAO was relevant to greater vorticity, helicity, and EL in TGA after ASO.ConclusionA non-physiological blood flow pattern of the aortic root was identified in TGA adults after the ASO (Jatene procedure with LeCompte maneuver). Missing spiral looping of the great arteries and the unique structure after the Jatene procedure may play an adjunctive role in promoting aortopathy. The evaluation of aortic flow profile using EPI 4D flow MRI may be useful for risk stratification for aortopathy in this population.