Preoperative fast MRI of brain tumors using three-dimensional segmented echo planar imaging compared to three-dimensional gradient echo technique

The purpose of this study was to compare the diagnostic efficacy of a newly developed T(1)-weighted three-dimensional segmented echo planar imaging (3D EPI) sequence versus a conventional T(1)-weighted three dimensional spoiled gradient echo (3D GRE) sequence in the evaluation of brain tumors. Forty-four patients with cerebral tumors and infections were examined on a 1.0 T MR unit with 23 mT/m gradient strength. The total scan time for the T(1) 3D EPI sequence was 2 min 12 s, and for a conventional 3D GRE sequence it was 4 min 59 s. Both sequences were performed after administration of a contrast agent. The images were analyzed by three radiologists. Image assessment criteria included lesion conspicuity, contrast between different types of normal tissue, and image artifacts. In addition, signal-to-noise and contrast-to-noise-ratio (C/N) were calculated. The gray-white differentiation and C/N ratio of 3D EPI were found to be inferior to conventional 3D GRE images, but the difference was not statistically significant. In the qualitative comparison, lesion detection and conspicuity of 3D EPI images and conventional 3D GRE images were similar, but a tow-fold reduction of the scanning time was obtained. With the 3D EPI technique, a 50% scan time reduction could be achieved with acceptable image quality compared to conventional 3D GRE. Thus, the 3D EPI technique could replace conventional 3D GRE in the preoperative imaging of brain.     

MR imaging of flow with locally high spatial resolution.

Locally focused magnetic resonance imaging (LF MRI) allows imaging with variable spatial resolution within the field of view (FOV). Because LF MRI uses a priori information to provide locally high resolution in regions with rapid spatial variations in intensity (e.g., blood/tissue interface), it allows accurate reproduction of intense sharp edges in the specimen without blurring and truncation artifacts. This study employs LF MRI for 3D imaging of stationary and pulsatile flow. In the implemented version of LF MRI analytically defined basis functions are used to determine image intensity in regions depicted with low or high resolution. It is demonstrated that LF MRI of flow allows a significant (i.e. 3-4 times) reduction in scan time as compared to conventional FT MRI. It is also shown that LF images of pulsatile flow have a decreased appearance of ghosting artifacts as compared to the images reconstructed by using the conventional method.     

High-definition,single-scan 2D MRI in inhomogeneous fields using spatial encoding methods

An approach has been recently introduced for acquiring two-dimensional (2D) nuclear magnetic resonance images in a single scan, based on the spatial encoding of the spin interactions. This article explores the potential of integrating this spatial encoding together with conventional temporal encoding principles, to produce 2D single-shot images with moderate field of views. The resulting “hybrid” imaging scheme is shown to be superior to traditional schemes in non-homogeneous magnetic field environments. An enhancement of previously discussed pulse sequences is also proposed, whereby distortions affecting the image along the spatially encoded axis are eliminated. This new variant is also characterized by a refocusing of T₂^* effects, leading to a restoration of high-definition images for regions which would otherwise be highly dephased and thus not visible. These single-scan 2D images are characterized by improved signal-to-noise ratios and a genuine T₂ contrast, albeit not free from inhomogeneity distortions. Simple postprocessing algorithms relying on inhomogeneity phase maps of the imaged object can successfully remove most of these residual distortions. Initial results suggest that this acquisition scheme has the potential to overcome strong field inhomogeneities acting over extended acquisition durations, exceeding 100 ms for a single-shot image.     

3D-snapshot flash NMR imaging of the human heart

SNAPSHOT-FLASH is a recently developed, ultrafast imaging technique, based on conventional FLASH imaging. The application of this new variant to 3D imaging allows the acquisition of a 128 x 128 x 32 data set in 12.5 seconds without triggering, or for cardiac imaging with gating within 32 heartbeats. Compared to standard 3D-FLASH this is 128 times faster, because triggering is only required when the 3D phase-encoding gradient is incremented. The method depicts for the first time fast three-dimensional views of the human heart without motional artifacts. The images are spin-density weighted. Using suitable prepulses any desired T1- or T2-contrast may be achieved. The generation of 3D movies is possible without an increase of the total scan time.     

Sensitive and automated detection of iron-oxide-labeled cells using phase image cross-correlation analysis

Superparamagnetic iron oxide (SPIO) nanoparticles are increasingly being used to noninvasively track cells, target specific molecules and monitor gene expression in vivo. Contrast changes that are subtle relative to intrinsic sources of contrast present a significant detection challenge. Here, we describe a postprocessing algorithm, called Phase map cross-correlation Detection and Quantification (PDQ), with the purpose of automating identification and quantification of localized accumulations of SPIO agents. The method is designed to sacrifice little flexibility - it works on previously acquired data and allows the use of conventional high-SNR pulse sequences with no extra scan time. We first investigated the theoretical detection limits of PDQ using a simulated dipole field. This method was then applied to three-dimensional (3D) MRI data sets of agarose gel containing isolated dipoles and ex vivo transplanted allogenic rat hearts infiltrated by numerous iron-oxide-labeled macrophages as a result of organ rejection. A simulated dipole field showed this method to be robust in very low signal-to-noise ratio images. Analysis of agarose gel and allogenic rat heart shows that this method can automatically identify and count dipoles while visualizing their biodistribution in 3D renderings. In the heart, this information was used to calculate a quantitative index that may indicate its degree of cellular infiltration.     

Quantitative 3D VUSE pulmonary MRA

The purposes of this study were to quantitatively evaluate a free-breathing three-dimensional (3D) variable angle uniform signal excitation (VUSE) magnetic resonance angiography (MRA) technique in normal volunteers, to demonstrate breathold 3D VUSE MRA in a normal volunteer, and to investigate the ability of the free-breathing 3D VUSE MRA technique to quantify differential flow in lung transplant patients. A free-breathing 3D VUSE MRA pulse sequence was run on the right lungs of 15 normal volunteers and both lungs of eight single or double lung transplant patients. A breathold scan was also used on one volunteer. No contrast agents were used. Normal lung MRA images were analyzed for maximum level of branching observed and minimum distance between distal vessels seen and the pleura. In patients, differential flow was determined with a program that counted the number of MRA pixels over a threshold signal level in each lung. These values were compared to radionuclide perfusion (Q) scan results. Average observed branching order in normal lung images was 5.9 +/- 0.7. Average distance between the most peripheral vessels seen and the pleura was 0.9 cm. Differential blood flow measured by pulmonary MRA was well correlated with that measured by Q scan (R2 = 0.84, p < 0.005). In addition to providing good visualization of normal pulmonary vessels, this technique was demonstrated to provide accurate estimates of differential blood flow in lung transplant patients free of serious lung scarring.     

Regeneration of elemental images in integral imaging for occluded objects using a plenoptic camera

In this Letter, we propose an elemental image regeneration method of three-dimensional(3D) integral imaging for occluded objects using a plenoptic camera. In conventional occlusion removal techniques, the information of the occlusion layers may be lost. Thus, elemental images have cracked parts, so the visual quality of the reconstructed 3D image is degraded. However, these cracked parts can be interpolated from adjacent elemental images. Therefore, in this Letter, we try to improve the visual quality of reconstructed 3D images by interpolating and regenerating virtual elemental images with adjacent elemental images after removing the occlusion layers. To prove our proposed method, we carry out optical experiments and calculate performance metrics such as the mean square error(MSE) and the peak signal-to-noise ratio(PSNR).     

Three-dimensional recognition of occluded objects by using computational integral imaging

We have proposed a method to recognize partially occluded three-dimensional (3D) objects by using 3D volumetric reconstruction integral imaging (II). An II system captures multiple perspectives of occluded objects by using a microlens array. The reconstruction of the occluded 3D scene and target recognition are done digitally to reduce the effects of the occlusion. To verify system performance, we have implemented an optimum filter for object recognition. Both two-dimensional (2D) images and 3D II volumetric reconstructed images are considered. The correlation results of occluded 3D images for volumetric reconstruction show substantial improvements compared with those for conventional 2D imaging of occluded images.     

Three-dimensional magnetic resonance imaging after ultrasonography for assessment of fetal gastroschisis

A 24-year-old woman (Gravida I, Para I) at estimated 32 weeks of pregnancy was referred to our department for evaluation of a suspected fetal gastroschisis. Ultrasound scan revealed multiple loops of dilated bowel outside the fetal abdomen and absence of membrane surrounding the herniated loops of the intestines. Three-dimensional (3D) magnetic resonance imaging was performed to obtain more information on the bowel both outside and inside the abdomen. Images were constructed with T1-weighted fat-suppressed 3D fast low-angle shot sequences using a maximum intensity projection algorithm. The 3D images made possible the realization of fetal bowel conditions with greater definition and accuracy.     

Encoding Textual Information in Magnetic Resonance Imaging

The data of magnetic resonance imaging (MRI) studies include not only grayscale images, but also textual information associated with them —personal data about the patient, parameters of scanning and data processing, etc. This information is stored separately from graphic images. Therefore, the possibility for its correction and loss cannot be excluded. In this paper, the method of generation of marker information on diagnostic images is described. The marker information, as a textual analogue, is entered on the image during an MRI scan and becomes an integral part of the diagnostic material along with the images of anatomical structures. The method is realized by using the selective radiofrequency presaturation of non-scanable slices oriented perpendicularly to the scanned slices. It leads to the formation of bands of reduced signal in the areas of intersections of these slices on images. In this case, the band thicknesses are equal to the thicknesses of non-scanable slices. Different combinations of these bands (marker lines) are formed directly on images and can contain information about MRI studies. This information is determined not only by positions and angle orientations of bands, but also by their thickness, total brightness and brightness distribution in the transverse direction of these bands. The examples of introducing and positioning the marker information in conventional MRI studies are presented.     

High-resolution,three-dimensional diffusion-weighted breast imaging using DESS

PurposeTo evaluate the use of the double-echo steady-state (DESS) sequence for acquiring high-resolution breast images with diffusion and T2 weighting.Materials and MethodsPhantom scans were used to verify the T2 and diffusion weighting of the DESS sequence. Image distortion was evaluated in volunteers by comparing DESS images and conventional diffusion-weighted images (DWI) to spoiled gradient-echo images. The DESS sequence was added to a standard clinical protocol, and the resulting patient images were used to evaluate overall image quality and image contrast in lesions.ResultsThe diffusion weighting of the DESS sequence can be easily modulated by changing the spoiler gradient area and flip angle. Radiologists rated DESS images as having higher resolution and less distortion than conventional DWI. Lesion-to-tissue contrast ratios are strongly correlated between DWI and DESS images (R = 0.83) and between T2-weighted fast spin-echo and DESS images (R = 0.80).ConclusionThe DESS sequence is able to acquire high-resolution 3D diffusion- and T2-weighted images in short scan times, with image quality that facilitates morphological assessment of lesions.     

Dynamic contrast-enhanced 3D breath hold MRA using a multiple variable orientation slab acquisition.

With the conventional 3D MR angiographic sequences, it is difficult to prescribe multiple phases in different orientations, though multiple phases may be prescribed in the same orientation as the initial scan. Magnetic resonance angiography (MRA) was performed in which three slabs were prescribed in different orientations and were acquired in a sequential measurement. A fixed delay of 8 s between the slabs was used to prepare patients to hold their breath for subsequent measurements. All subjects tolerated the entire breath hold examination. The results were easily reproducible and yielded high-resolution 3-dimensional images in various planes.     

3D卷积自动编码网络的高光谱异常检测

高光谱图像包含丰富的地物光谱信息,在遥感图像领域有着巨大的发展前景。高光谱图像异常检测无需任何先验光谱信息,便可检测出图像中的异常目标。因此,在国防军事和民用领域都有广泛的应用,是现阶段高光谱图像处理领域的研究热点。然而,高光谱图像存在数据复杂、冗余性强、未标记以及样本数量少等特点,这给高光谱图像异常检测带来了很大的挑战。尤其是在深度学习中,往往需要大量的图像数据作为训练样本,这对高光谱图像来说很难获得。针对现有大多数算法对高光谱图像自适应性不强和空间-光谱信息利用不足的问题,提出一种基于3D卷积自动编码网络的高光谱异常检测算法,可以在少量训练数据的前提下,有效利用高光谱图像信息,学习更加有判别性的特征表达,提高检测精度。首先,通过3D卷积、3D池化和3D归一化等步骤设计3D卷积网络,进而提取高光谱图像的空间-光谱结构特征。然后,将3D卷积网络和3D反卷积网络分别嵌入自动编码网络的编码器和解码器,通过最小化结合均方差和光谱角距离的重构误差进行背景重构。最后,利用原始高光谱图像待测像元与重构的背景图像之间的马氏距离进行异常检测。该算法可以在无先验信息的情况下,自动训练网络中的所有参数,以无监督的方式学习高光谱图像的有效特征并进行背景重构。为证明算法的有效性,利用截取来自三组真实高光谱数据集的九个图像进行异常检测,并与RX,SRX,CRD,UNRS和LRASR五种算法进行对比。结果表明,与现有的其他算法相比,该算法可以在复杂程度不同的高光谱图像背景下可以保持较高的检测效果和准确率。     

A new strategy for respiration compensation, applied toward 3D free-breathing cardiac MRI

In thorax and abdomen imaging, image quality may be affected by breathing motion. Cardiac MR images are typically obtained while the patient holds his or her breath, to avoid respiration-related artifacts. Although useful, breath-holding imposes constraints on scan duration, which in turn limits the achievable resolution and SNR. Longer scan times would be required to improve image quality, and effective strategies are needed to compensate for respiratory motion. A novel approach at respiratory compensation, targeted toward 3D free-breathing cardiac MRI, is presented here. The method aims at suppressing the negative effects of respiratory-induced cardiac motion while capturing the heart's beating motion. The method is designed so that the acquired data can be reconstructed in two different ways: First, a time series of images is reconstructed to quantify and correct for respiratory motion. Then, the corrected data are reconstructed a final time into a cardiac-phase series of images to capture the heart's beating motion. The method was implemented, and initial results are presented. A cardiac-phase series of 3D images, covering the entire heart, was obtained for two free-breathing volunteers. The present method may prove especially useful in situations where breath-holding is not an option, for example, for very sick, mentally impaired or infant patients.     

基于单摄像机的昆虫自由飞行参量三维重构

研究昆虫飞行的三维空间运动参量需要对二维图像进行重构,传统的重构方法是采用两个或者多个相机从不同角度拍摄以获得同时刻不同角度的图像。介绍了一种采用单一相机完成三维重构的方法。通过在单相机镜头前面附加四块两两平行的平面镜组来获得三维信息,该装置可以在同一照片上获得物体两个角度的观察图像,等效于用两个高速摄影仪对昆虫的飞行进行拍摄。分别标定出每个等效摄像机的参量,根据机器视觉原理进行三维重构。实现了用单个相机完成昆虫自由飞行状态的翅膀三维参量重构过程,避免采用多个相机的需要增加复杂同步电路以及引起的高额费用,同事也克服了过去基于单相机的三维重构需要增加某些假设所引起的与真实飞行的差异。     

3D MRI of non-Gaussian (3)He gas diffusion in the rat lung

In (3)He magnetic resonance images of pulmonary air spaces, the confining architecture of the parenchymal tissue results in a non-Gaussian distribution of signal phase that non-exponentially attenuates image intensity as diffusion weighting is increased. Here, two approaches previously used for the analysis of non-Gaussian effects in the lung are compared and related using diffusion-weighted (3)He MR images of mechanically ventilated rats. One approach is model-based and was presented by Yablonskiy et al., while the other approach utilizes the second order decay contribution that is predicted from the cumulant expansion theorem. Total lung coverage is achieved using a hybrid 3D pulse sequence that combines conventional phase encoding with sparse radial sampling for efficient gas usage. This enables the acquisition of nine 3D images using a total of only approximately 1 L of hyperpolarized (3)He gas. Diffusion weighting ranges from 0 s/cm(2) to 40 s/cm(2). Results show that the non-Gaussian effects of (3)He gas diffusion in healthy rat lungs are directly attributed to the anisotropic geometry of lung microstructure as predicted by the Yablonskiy model, and that quantitative analysis over the entire lung can be reliably repeated in time-course studies of the same animal.     

旋风分离器固体颗粒浓度三维电容层析成像分布

本文采用12电极电容传感器测量得到旋风分离器锥体部分的电容信号,利用线性逆反推算法得到断面固体颗粒的二维浓度分布。基于二维断面浓度分布,采用电容三维图像重建算法,得到锥体部分的三维颗粒浓度分布。图像重建结果与旋风分离器实际运行状况和数值计算结果吻合,说明电容层析成像及三维图像重建方法的准确性和可行性。     

MR image reconstruction of sparsely sampled 3D k-space data by projection-onto-convex sets

In many rapid three-dimensional (3D) magnetic resonance (MR) imaging applications, such as when following a contrast bolus in the vasculature using a moving table technique, the desired k-space data cannot be fully acquired due to scan time limitations. One solution to this problem is to sparsely sample the data space. Typically, the central zone of k-space is fully sampled, but the peripheral zone is partially sampled. We have experimentally evaluated the application of the projection-onto-convex sets (POCS) and zero-filling (ZF) algorithms for the reconstruction of sparsely sampled 3D k-space data. Both a subjective assessment (by direct image visualization) and an objective analysis [using standard image quality parameters such as global and local performance error and signal-to-noise ratio (SNR)] were employed. Compared to ZF, the POCS algorithm was found to be a powerful and robust method for reconstructing images from sparsely sampled 3D k-space data, a practical strategy for greatly reducing scan time. The POCS algorithm reconstructed a faithful representation of the true image and improved image quality with regard to global and local performance error, with respect to the ZF images. SNR, however, was superior to ZF only when more than 20% of the data were sparsely sampled. POCS-based methods show potential for reconstructing fast 3D MR images obtained by sparse sampling.     

基于主分量分析法的小波域三维目标序列图像隐藏技术

针对在一幅载体图像中隐藏三维目标序列图像的问题,本文利用主分量分析法获取三维目标的本征图像,将本征图像的小波域系数嵌入到载体图像的小波域系数中,利用分解系数和提取得到的本征图像重构出三维目标的系列图像.本文所提出的方法不是直接存储目标图像,而是存储能够反映三维目标特征的一组本征图像.研究结果表明,该方法有效地将三维目标的特征隐藏在了载体图像中,隐藏信息量大. 关键词： 信息隐藏 三维目标 主分量分析 小波变换     

Robust visual correspondence computation using monogenic curvature phase based mutual information

Visual correspondence has been a major research topic in the fields of image registration, 3D reconstruction, and object tracking for some decades. However, due to the radiometric variations of images, conventional approaches fail to produce robust matching results. The traditional method of intensity-based mutual information performs very good for global variations between images, however, its performance degrades in the case of local radiometric variations. Monogenic curvature phase information, as an important local feature of the image, has the advantage of being robust against brightness variation. Hence, in this Letter, we propose an approach to compute the visual correspondence by coupling the advantages of mutual information and monogenic curvature phase. Experimental results demonstrate that the proposed approach can work robustly under radiometric variations.