Interleaved EPI based fMRI improved by multiplexed sensitivity encoding (MUSE) and simultaneous multi-band imaging

© 2014 Chang et al. Functional magnetic resonance imaging (fMRI) is a non-invasive and powerful imaging tool for detecting brain activities. The majority of fMRI studies are performed with single-shot echo-planar imaging (EPI) due to its high temporal resolution. Recent studies have demonstrated that, by increasing the spatial-resolution of fMRI, previously unidentified neuronal networks can be measured. However, it is challenging to improve the spatial resolution of conventional single-shot EPI based fMRI. Although multi-shot interleaved EPI is superior to single-shot EPI in terms of the improved spatial-resolution, reduced geometric distortions, and sharper point spread function (PSF), interleaved EPI based fMRI has two main limitations: 1) the imaging throughput is lower in interleaved EPI; 2) the magnitude and phase signal variations among EPI segments (due to physiological noise, subject motion, and B0 drift) are translated to significant in-plane aliasing artifact across the field of view (FOV). Here we report a method that integrates multiple approaches to address the technical limitations of interleaved EPI-based fMRI. Firstly, the multiplexed sensitivity-encoding (MUSE) post-processing algorithm is used to suppress in-plane aliasing artifacts resulting from time-domain signal instabilities during dynamic scans. Secondly, a simultaneous multi-band interleaved EPI pulse sequence, with a controlled aliasing scheme incorporated, is implemented to increase the imaging throughput. Thirdly, the MUSE algorithm is then generalized to accommodate fMRI data obtained with our multi-band interleaved EPI pulse sequence, suppressing both in-plane and through-plane aliasing artifacts. The blood-oxygenation-level-dependent (BOLD) signal detectability and the scan throughput can be significantly improved for interleaved EPI-based fMRI. Our human fMRI data obtained from 3 Tesla systems demonstrate the effectiveness of the developed methods. It is expected that future fMRI studies requiring high spatial-resolvability and fidelity will largely benefit from the reported techniques.published_or_final_versio

Free-breathing black-blood CINE fast-spin echo imaging for measuring abdominal aortic wall distensibility: a feasibility study.

The paper reports a free-breathing black-blood CINE fast-spin echo (FSE) technique for measuring abdominal aortic wall motion. The free-breathing CINE FSE includes the following MR techniques: (1) variable-density sampling with fast iterative reconstruction; (2) inner-volume imaging; and (3) a blood-suppression preparation pulse. The proposed technique was evaluated in eight healthy subjects. The inner-volume imaging significantly reduced the intraluminal artifacts of respiratory motion (p  =  0.015). The quantitative measurements were a diameter of 16.3  ±  2.8 mm and wall distensibility of 2.0  ±  0.4 mm (12.5  ±  3.4%) and 0.7  ±  0.3 mm (4.1  ±  1.0%) for the anterior and posterior walls, respectively. The cyclic cross-sectional distensibility was 35  ±  15% greater in the systolic phase than in the diastolic phase. In conclusion, we developed a feasible CINE FSE method to measure the motion of the abdominal aortic wall, which will enable clinical scientists to study the elasticity of the abdominal aorta

Improved Image Quality for Static BLADE Magnetic Resonance Imaging Using the Total-Variation Regularized Least Absolute Deviation Solver.

In order to improve the image quality of BLADE magnetic resonance imaging (MRI) using the index tensor solvers and to evaluate MRI image quality in a clinical setting, we implemented BLADE MRI reconstructions using two tensor solvers (the least-squares solver and the L1 total-variation regularized least absolute deviation (L1TV-LAD) solver) on a graphics processing unit (GPU). The BLADE raw data were prospectively acquired and presented in random order before being assessed by two independent radiologists. Evaluation scores were examined for consistency and then by repeated measures analysis of variance (ANOVA) to identify the superior algorithm. The simulation showed the structural similarity index (SSIM) of various tensor solvers ranged between 0.995 and 0.999. Inter-reader reliability was high (Intraclass correlation coefficient (ICC) = 0.845, 95% confidence interval: 0.817, 0.87). The image score of L1TV-LAD was significantly higher than that of vendor-provided image and the least-squares method. The image score of the least-squares method was significantly lower than that of the vendor-provided image. No significance was identified in L1TV-LAD with a regularization strength of λ= 0.4-1.0. The L1TV-LAD with a regularization strength of λ= 0.4-0.7 was found consistently better than least-squares and vendor-provided reconstruction in BLADE MRI with a SENSitivity Encoding (SENSE) factor of 2. This warrants further development of the integrated computing system with the scanner

The impact of video gaming on cognitive functioning of people with schizophrenia (GAME-S): study protocol of a randomised controlled trial

Background: Video gaming is a promising intervention for cognitive and social impairment in patients with schizophrenia. A number of gaming interventions have been evaluated in small-scale studies with various patient groups, but studies on patients with schizophrenia remain scarce and rarely include the evaluation of both clinical and neurocognitive outcomes. In this study, we will test the effectiveness of two interventions with gaming elements to improve cognitive and clinical outcomes among persons with schizophrenia.Methods: The participants will be recruited from different outpatient units (e.g., outpatient psychiatric units, day hospitals, residential care homes). The controlled clinical trial will follow a three-arm parallel-group design: 1) cognitive training (experimental group, CogniFit), 2) entertainment gaming (active control group, SIMS 4), and 3) treatment as usual. The primary outcomes are working memory function at 3-month and 6-month follow-ups. The secondary outcomes are patients' other cognitive and social functioning, the ability to experience pleasure, self-efficacy, and negative symptoms at 3-month and 6-month follow-ups. We will also test the effectiveness of gaming interventions on neurocognitive outcomes (EEG and 3 T MRI plus rs-fMRI) at a 3-month follow-up as an additional secondary outcome. Data will be collected in outpatient psychiatric services in Hong Kong. Participants will have a formal diagnosis of schizophrenia and be between 18 and 60 years old. We aim to have a total of 234 participants, randomly allocated to the three arms. A sub-sample of patients (N = 150) will be recruited to undergo an EEG. For neuroimaging assessment, patients will be randomly allocated to a subset of patients (N=126). We will estimate the efficacy of the interventions on the primary and secondary outcomes based on the intention-to-treat principle. Behavioural and EEG data will be analysed separately.Discussion: The study will characterise benefits of gaming on patients' health and well-being, and contribute towards the development of new treatment approaches for patients with schizophrenia.</p

Genome-Wide Association Study in Asian Populations Identifies Variants in ETS1 and WDFY4 Associated with Systemic Lupus Erythematosus

Systemic lupus erythematosus is a complex and potentially fatal autoimmune disease, characterized by autoantibody production and multi-organ damage. By a genome-wide association study (320 patients and 1,500 controls) and subsequent replication altogether involving a total of 3,300 Asian SLE patients from Hong Kong, Mainland China, and Thailand, as well as 4,200 ethnically and geographically matched controls, genetic variants in ETS1 and WDFY4 were found to be associated with SLE (ETS1: rs1128334, P = 2.33×10−11, OR = 1.29; WDFY4: rs7097397, P = 8.15×10−12, OR = 1.30). ETS1 encodes for a transcription factor known to be involved in a wide range of immune functions, including Th17 cell development and terminal differentiation of B lymphocytes. SNP rs1128334 is located in the 3′-UTR of ETS1, and allelic expression analysis from peripheral blood mononuclear cells showed significantly lower expression level from the risk allele. WDFY4 is a conserved protein with unknown function, but is predominantly expressed in primary and secondary immune tissues, and rs7097397 in WDFY4 changes an arginine residue to glutamine (R1816Q) in this protein. Our study also confirmed association of the HLA locus, STAT4, TNFSF4, BLK, BANK1, IRF5, and TNFAIP3 with SLE in Asians. These new genetic findings may help us to gain a better understanding of the disease and the functions of the genes involved

Geometrical Distortion Correction in Echo Planar Imaging using A Modify Reversed Gradient Method: Techniques & Applications

本論文展示一種平面回訊影像幾何扭曲的修正方法。這個方法是建基於反向梯度磁場方法，它是利用兩張影像在極性相反的相位編碼梯度磁場下，幾何扭曲在影像上的剛好呈現相反的表現，最後利用幾何扭曲在兩張影像上相反的特性所提供的資訊，來修正影像。但是，這個修正方法在修正一些低信號部份時，由於缺乏幾何扭曲的資訊，因此導致在這些低信號部份產生修正上的錯誤。在實行反向梯度磁場方法時，加入了位移表示圖像 (displacement map) 的概念去減低在低信號部份的修正錯誤。這個位移表示圖像的概念包括了除去位移表示圖像上錯誤的資訊、進行表面近似和濾波。在3T高磁場下實驗的結果顯示，相對於本來的反向梯度磁場方法，改良反向梯度磁場反法修正的影像展示出減低影像的幾何扭曲以及在低信號部份錯誤的修正。把改良反向梯度磁場法應用在螺旋槳式磁振平面回訊影像上，對每一個葉片資料作額外的修正，在高解析度擴散張量影像上有一定的優勢，可以提高影像的品質以及在臨床的應用。A technique suitable for echo planar imaging (EPI) geometrical distortion correction is presented in this thesis. The method is based on reversed gradient method (RG) using phase-encoding gradient with reversed polarity that produces distortion in opposite direction, from which the information on the difference in spatial displacements is then used to correct for distortion. However, this method is problematic in regions with low signals because of a lack of information on distortions which leads an error correction in regions with low signals. The implementation of reversed gradient method induced a displacement map concept to reduce the error correction in regions with low signals. The displacement map concept consists of eliminating error displacement map, surface fitting and filtering. Experimental results on a 3.0 Tesla MR system showed that the modified reversed gradient method corrected images exhibit substantially reduced geometric distortions and correction error in regions with low signals compared with original reversed gradient method. Applied reversed gradient method in high-resolution DTI using PROPELLER EPI to extra correct each blade, shows benefits from the modified reversed gradient method. It can increase the image quality for routine diffusion tensor imaging applications in clinical practice.Abstract 1 中文摘要 2 1. INTRODUCTION 3 1.1 Echo Planner Imaging (EPI) and sequence 3 1.2 EPI geometrical distortion 6 1.3 Motivation 8 2. THEORY 10 2.1 Reversed gradient method 10 2.2 Modified reversed gradient method with displacement map concept 16 3. MATERIALS AND METHODS 19 3.1 Phantom and subjects 19 3.2 Data processing 20 4. RESULTS 25 4.1 Correction of phantom and brain EPI image at 3.0T MRI scanner 25 4.2 Correction of diffusion tensor imaging at 1.5T MRI scanner 28 5. APPLICATION: PROPELLER EPI diffusion weighted imaging 32 5.1 Introduction of PROPELLER EPI 32 5.2 PROPELLER EPI with reversed gradient method 36 5.3 Result: high resolution diffusion tensor imaging at 3.0T MRI scanner 39 5.4 Discussion 46 6. DISCUSSION AND CONCLUSION 48 6.1 Discussion of modified reversed gradient method 48 6.2 SNR in reversed gradient method 48 6.3 Conclusion 51 7. REFERENCE 52 8. APPENDIX I 54 2D polynomial surface fitting 5

Applying N/2 ghost artifact correction methods prior to PROPELLER-EPI reconstruction

在這篇論文中，提出了兩個改良型的二維相位修正方法，能夠提升它們抑制面迴訊影像N/2鬼影假影的效能；並克服當物體存在大範圍無信號時無效的修正問題。N/2 鬼影假影是面迴訊影像值得注意的問題。因此，在每個螺旋槳式面迴訊影像的葉片資料影像，抑制N/2鬼影假影是一個必須的處理步驟。螺旋槳式面迴訊影像透過採集一系列的k空間葉片資料，且每一葉片資料均實行不同的旋轉角度的相位編碼方向，最後由所以葉片資料組合成完整的k空間資料。幾乎所有轉動葉片都是傾斜的採集方式，並使用面迴訊影像技術讀取訊號。這個傾斜的採集方式會造成傾斜 N/2 鬼影假影，它同時包含迴波位移與交錯的取樣方式。相較於一維相位修正方法，無論是基於參考掃描的改良型二維相位修正方法，或者是無參考掃描的改良型二維相位修正方法，均能夠幫助減低殘餘的傾斜N/2鬼影；因此，能夠在進行螺旋槳式面迴訊影像重建前，提高每個葉片資料影像的影像品質。此提出的改良型二維相位修正方法，同時展現了具有良好的運動免疫能力。三個初步的螺旋槳式面迴訊擴散影像臨床應用測試結果，包括測量腮腺的擴散系數、腦部擴散權重影像結合運動校正、以及自然呼吸肝臟擴散權重影像。螺旋槳式面迴訊擴散影像臨床測試結果展現了兩個改良型二維相位修正法的應用。此外，無參考掃描二維相位修正方法，能夠排除每個葉片影像額外的參考描掃時間，可能擴展螺旋槳式面迴訊擴散影像的應用。Two improved 2D phase correction methods were proposed in this thesis to increase the effectiveness of ghost reductions of low-resolution blade images, and to solve the issue of ghost reduction within large signal-free regions. N/2 ghost artifact is a significant issue of EPI readout techniques. Thus, ghost reduction of each blade data is an essential processing step prior to PROPELLER-EPI reconstruction. PROPELLER-EPI acquires a set of rotating blades with different rotating angles to fill out the entire k-space. Most of rotating blades are oblique acquisition with EPI readout, which result in oblique ghost with echo shift and interlaced sampling. Either the improved reference-based 2D phase correction or the improved reference-free 2D phase correction can help to reduce the residual oblique ghost when using 1D phase correction, thus increase the image quality of each blade data before applying PROPELLER-EPI reconstruction. The proposed improved 2D phase correction methods were demonstrated, both of which exhibit good immunity to motion. Three preliminary clinical results, ADC measurement in parotid glands, brain DWI with motion correction, and free-breathing liver DWI, showed the possible application of PROPELLER-DW-EPI with the two improved 2D phase correction methods. In addition, the reference-free 2D phase correction method can eliminate the need of reference scan time of each blade, and thus may broaden the clinical use of PROPELLER-DW-EPI

A robust multi-shot scan strategy for high-resolution diffusion weighted MRI enabled by multiplexed sensitivity-encoding (MUSE)

Diffusion weighted magnetic resonance imaging (DWI) data have been mostly acquired with single-shot echo-planar imaging (EPI) to minimize motion induced artifacts. The spatial resolution, however, is inherently limited in single-shot EPI, even when the parallel imaging (usually at an acceleration factor of 2) is incorporated. Multi-shot acquisition strategies could potentially achieve higher spatial resolution and fidelity, but they are generally susceptible to motion-induced phase errors among excitations that are exacerbated by diffusion sensitizing gradients, rendering the reconstructed images unusable. It has been shown that shot-to-shot phase variations may be corrected using navigator echoes, but at the cost of imaging throughput. To address these challenges, a novel and robust multi-shot DWI technique, termed multiplexed sensitivity-encoding (MUSE), is developed here to reliably and inherently correct nonlinear shot-to-shot phase variations without the use of navigator echoes. The performance of the MUSE technique is confirmed experimentally in healthy adult volunteers on 3. Tesla MRI systems. This newly developed technique should prove highly valuable for mapping brain structures and connectivities at high spatial resolution for neuroscience studies. © 2013 Elsevier Inc.Link_to_subscribed_fulltex

Susceptibility-weighted imaging in diagnosing brain capillary telangiectasia: A case report

A 65-year-old lung cancer patient was screened for intracranial metastases. Post-gadolinium-enhanced T1-weighted imaging revealed a small enhancing pontine lesion slightly hypointense on T2*-weighted gradient echo, invisible on T1-/T2-weighted imaging. Susceptibility-weighted imaging (SWI) showed marked hypointensity; a small linear hypointensity extension suggested a draining vein. Capillary telangiectasia or transitional capillary-venous malformation was diagnosed. To the best of our knowledge, brain capillary telangiectasia rarely has been previously reported by SWI.Link_to_subscribed_fulltex