Volume 33, Issue 3

Recent theoretical results on low-rank matrix reconstruction have inspired significant interest in low-rank modeling of MRI images. Existing approaches have focused on higher-dimensional scenarios with data available from multiple channels, timepoints, or image contrasts. The present work demonstrates that single-channel, single-contrast, single-timepoint $k$ -space data can also be mapped to low-rank matrices when the image has limited spatial support or slowly varying phase. Based on this, we develop a novel and flexible framework for constrained image reconstruction that uses low-rank matrix modeling of local $k$ -space neighborhoods (LORAKS). A new regularization penalty and corresponding algorithm for promoting low-rank are also introduced. The potential of LORAKS is demonstrated with simulated and experimental data for a range of denoising and sparse-sampling applications. LORAKS is also compared against state-of-the-art methods like homodyne reconstruction, $\ell_{1}$ -norm minimization, and total variation minimization, and is demonstrated to have distinct features and advantages. In addition, while calibration-based support and phase constraints are commonly used in existing methods, the LORAKS framework enables calibrationless use of these constraints.

近期关于低秩矩阵重建的理论成果激发了对MRI图像低秩建模的浓厚兴趣。现有方法主要关注多通道、多时间点或多图像对比度的高维数据。本研究表明，当图像具有有限空间支撑或缓慢变化的相位时，单通道、单对比度、单时间点的k空间数据也可以映射到低秩矩阵。基于此，我们开发了一种新颖且灵活的约束图像重建框架，该框架利用局部k空间邻域的低秩矩阵建模（LORAKS）。还引入了一种新的正则化惩罚项及相应的促进低秩的算法。通过一系列去噪和稀疏采样应用的仿真与实验数据，展示了LORAKS的潜力。此外，LORAKS与同态重建、ℓ1范数最小化和全变分最小化等最先进方法进行了比较，并显示出独特的特点和优势。同时，尽管现有方法通常使用基于校准的支持和相位约束，LORAKS框架实现了无需校准便可使用这些约束。

Images of electrical conductivity and permittivity of tissues may be used for diagnostic purposes as well as for estimating local specific absorption rate distributions. Magnetic resonance electrical properties tomography (MREPT) aims at noninvasively obtaining conductivity and permittivity images at radio-frequency frequencies of magnetic resonance imaging systems. MREPT algorithms are based on m...

组织的电导率和介电常数图像可用于诊断目的以及估计局部比吸收率分布。磁共振电阻抗断层成像（MREPT）旨在非侵入性地获得磁共振成像系统射频频率下的电导率和介电常数图像。MREPT算法基于...

Previous studies have shown that by minimizing the total variation (TV) of the to-be-estimated image with some data and/or other constraints, a piecewise-smooth X-ray computed tomography image can be reconstructed from sparse-view projection data. However, due to the piecewise constant assumption for the TV model, the reconstructed images are frequently reported to suffer from the blocky or patchy...

先前的研究表明，通过最小化待估计图像的全变分（TV）并结合一些数据和/或其他约束，可以从稀疏视角投影数据重建出分段光滑的X射线计算机断层扫描图像。然而，由于TV模型的分段常数假设，重建图像经常被报告出现块状或片状...

Positron emission tomography (PET) images usually suffer from poor signal-to-noise ratio (SNR) due to the high level of noise and low spatial resolution, which adversely affect its performance for lesion detection and quantification. The complementary information present in high-resolution anatomical images from multi-modality imaging systems could potentially be used to improve the ability to det...

正电子发射断层扫描（PET）图像通常由于高噪声水平和低空间分辨率而导致信噪比（SNR）较差，这不利于病灶检测和量化。来自多模态成像系统的高分辨率解剖图像中的互补信息可能用于提高检测能力。

Parallel transmission is a very promising candidate technology to mitigate the inevitable radio-frequency (RF) field inhomogeneity in magnetic resonance imaging at ultra-high field. For the first few years, pulse design utilizing this technique was expressed as a least squares problem with crude power regularizations aimed at controlling the specific absorption rate (SAR), hence the patient safety...

平行传输是一项非常有前景的候选技术，旨在减轻超高场磁共振成像中不可避免的射频场不均匀性。在最初几年，利用该技术的脉冲设计被表述为一个最小二乘问题，并采用粗略的功率正则化来控制特定吸收率（SAR），从而确保患者安全……

Cardiac electrical imaging from body surface potential measurements is increasingly being seen as a technology with the potential for use in the clinic, for example for pre-procedure planning or during-treatment guidance for ventricular arrhythmia ablation procedures. However several important impediments to widespread adoption of this technology remain to be effectively overcome. Here we address ...

来自体表电位测量的心脏电成像越来越被视为一种具有临床潜力的技术，例如用于室性心律失常消融手术的术前规划或术中指导。然而，该技术广泛采用仍有几个重要障碍需要有效克服。在此，我们解决...

Preoperative diagnostic magnetic resonance (MR) breast images can provide good contrast between different tissues and 3-D information about suspicious tissues. Aligning preoperative diagnostic MR images with a patient in the theatre during breast conserving surgery could assist surgeons in achieving the complete excision of cancer with sufficient margins. Typically, preoperative diagnostic MR brea...

术前诊断性磁共振（MR）乳腺图像能够提供不同组织之间的良好对比度以及可疑组织的三维信息。在保乳手术中，将术前诊断性MR图像与手术台上的患者对齐，可以帮助外科医生实现具有足够切缘的完全切除。通常，术前诊断性MR...

A new step-by-step comprehensive MR physics simulator (MRISIMUL) of the Bloch equations is presented. The aim was to develop a magnetic resonance imaging (MRI) simulator that makes no assumptions with respect to the underlying pulse sequence and also allows for complex large-scale analysis on a single computer without requiring simplifications of the MRI model. We hypothesized that such a simulati...

本文介绍了一种新的逐步全面的布洛赫方程MR物理模拟器（MRISIMUL）。目的是开发一种磁共振成像（MRI）模拟器，该模拟器对底层脉冲序列不作任何假设，并且允许在单个计算机上进行复杂的大规模分析，而无需简化MRI模型。我们假设这样的模拟...

Mutual information (MI) quantifies the information that is shared between two random variables and has been widely used as a similarity metric for multi-modal and uni-modal image registration. A drawback of MI is that it only takes into account the intensity values of corresponding pixels and not of neighborhoods. Therefore, it treats images as “bag of words” and the contextual information is lost...

互信息（MI）量化了两个随机变量之间共享的信息，并已广泛用作多模态和单模态图像配准的相似性度量。MI的一个缺点是它只考虑对应像素的强度值，而不考虑邻域信息。因此，它将图像视为“词袋”，丢失了上下文信息...

In this paper, we propose a novel method to detect glandular structures in microscopic images of human tissue. We first convert the image from Cartesian space to polar space and then introduce a novel random field model to locate the possible boundary of a gland. Next, we develop a visual feature-based support vector regressor to verify if the detected contour corresponds to a true gland. And fina...

本文提出了一种在人体组织显微图像中检测腺体结构的新方法。我们首先将图像从笛卡尔空间转换到极坐标空间，然后引入一种新的随机场模型来定位腺体的可能边界。接下来，我们开发了一种基于视觉特征的支持向量回归器，以验证检测到的轮廓是否对应于真正的腺体。最后...

We propose a new method for deformable registration of pre-operative and post-recurrence brain MR scans of glioma patients. Performing this type of intra-subject registration is challenging as tumor, resection, recurrence, and edema cause large deformations, missing correspondences, and inconsistent intensity profiles between the scans. To address this challenging task, our method, called PORTR, e...

我们提出了一种针对胶质瘤患者术前与复发后脑部MR扫描的形变配准新方法。进行此类受试者内配准具有挑战性，因为肿瘤、切除、复发和水肿会导致扫描之间出现大的形变、缺失对应关系以及不一致的强度分布。为了解决这一挑战，我们的方法称为PORTR，...

It is known that a reduction of the field-of-view in 3-D X-ray imaging is proportional to a reduction in radiation dose. The resulting truncation, however, is incompatible with conventional reconstruction algorithms. Recently, a novel method for region of interest reconstruction that uses neither prior knowledge nor extrapolation has been published, named approximated truncation robust algorithm f...

已知在三维X射线成像中，视野的减少与辐射剂量的减少成正比。然而，由此产生的截断与传统的重建算法不兼容。最近，一种既不使用先验知识也不使用外推法的感兴趣区域重建新方法被发表，称为近似截断鲁棒算法...

System designs in single photon emission tomography (SPECT) can be evaluated based on the fundamental trade-off between bias and variance that can be achieved in the reconstruction of emission tomograms. This trade off can be derived analytically using the Cramer-Rao type bounds, which imply the calculation and the inversion of the Fisher information matrix (FIM). The inverse of the FIM expresses ...

在单光子发射断层成像（SPECT）中，可以根据重建发射断层图像时所能实现的偏差与方差之间的基本权衡来评估系统设计。这种权衡可以通过克拉美-罗型界进行解析推导，这需要计算和求逆Fisher信息矩阵（FIM）。FIM的逆表达了...

We have previously implemented the direct reconstruction of dense kinetic model parameter images (“parametric images”) from sinogram data, and compared it to conventional image domain kinetic parameter estimation methods . Although it has been shown that the direct reconstruction algorithm estimates the kinetic model parameters with lower root mean squared error than the conventional image domain ...

我们此前已经实现了从正弦图数据直接重建密集动力学模型参数图像（"参数图像"），并将其与传统的图像域动力学参数估计方法进行了比较。虽然已表明直接重建算法估计动力学模型参数的均方根误差低于传统图像域方法...

In the above paper (ibid., vol. 33, no. 1, pp. 85-98, Jan. 2014), the title appeared incorrectly as "SCoRS—A Method Based on Stability for Feature Selection and Apping in Neoroimaging." The title should have appeared as "SCoRS—A Method Based on Stability for Feature Selection and Mapping in Neuroimaging."

在上述论文（同上，第33卷，第1期，第85-98页，2014年1月）中，标题错误地显示为“SCoRS—一种基于稳定性的特征选择与神经影像映射方法”。正确的标题应为“SCoRS—一种基于稳定性的神经影像特征选择与映射方法”。

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