基于Metropolis—SA算法的脑部磁共振血管造影图像分割

目的利用三维Markov随机场（MRF）模型分割脑部磁共振血管造影（MRA）。方法MRF的似然概率采用了瑞利分布和高斯混合分布函数,并利用最大期望（EM）算法精确估计出混合参数;先验概率采用Ising—MRF模型,并利用误差试探法估计出正则化参数。为避免利用迭代条件模式（ICM）进行图像分割时常陷入局部最优解,实验提出了基于Metropolis采样算法的模拟退火（SA）技术。结果实现了三维MRF的全局最优解,分割模型可分辨3个体素的细小血管。临床数据采用南方医院影像中心提供的患者TOF-MRA数据（1.5TGE MRI scanner）,空间分辨率0．43mm×0．43mm×0．50mm：原始数据的像素空间大小为512×512×128;实际采用的空间大小和分辨率分别为256×256×64和0．80mm×0．80mm×1．20mm。实验对每一套临床数据采用SA、ICM、MSA算法分别进行分割比较,分割结果存在有限差异,采用15步迭代计算的时间消耗分别为1029S、463S、560S。结论实验通过三维仿真数据分割结果表明,Metropolis—SA迭代求解算法能够实现更低的全局误差．并且实际脑部MRA数据的分割与最大密度投影相比较．反映出较好效果．     

An algorithm for the optimum combination of data from arbitrary magnetic resonance phased array probes

When summing the spectra acquired with phased array coils, signals with low signal-to-noise ratio or wrongly corrected phase may degrade the overall signal-to-noise ratio (SNR). Here we present a mathematical expression predicting the dependence of combined SNR on the signal-to-noise ratios and errors in phase correction of composite signals. Based on this equation, signals that do not lead to an overall increase in signal-to-noise ratio can be identified and excluded from the weighted sum of signals. This tool is particularly useful for the combination of large numbers of signals. Additionally, a simple and robust algorithm for calculating the complex weighting factors necessary for the signal-to-noise weighted combination of spectroscopic data is presented. Errors in the calculation and correction of relative phase differences between composite spectra are analysed. The errors have a negligible effect on the overall spectral SNR for typical clinical magnetic resonance spectroscopy (MRS). The signal combination routine developed here has been applied to the first in vivo MRS study of human rectal adenocarcinomas at 1.5 T (Dzik-Jurasz A S K, Murphy P S, George M, Prock T, Collins D J, Swift I and Leach M O 2001 Magn. Reson. Med. at press), showing improvements of combined spectral SNR of up to 34% over the maximum SNR from a single element.     

Effect of radial position on volume measurements using the conductance catheter

A finite-difference computer model has been used to determine the potential distributions arising from a dipole current source aligned parallel to the axis of bounding cylinders. The radial position of this source had large and nonlinear influence on the potentials along the dipole axis. The accuracy of the computer simulation was established from comparison with an analytic solution of a simple geometry. Measurements using a conductance catheter in saline-filled cylinders also demonstrated the dependence of the conductance on the radial position. The dependence of the potential distribution on the radial position of the dipole places limits on the ultimate accuracy of the conductance catheter technique when used for the measurement of ventricular volume. Radial movement of the catheter within the ventricular cavity, resulting in changes in the potential distribution, could explain some artefacts that appear on volume recordings from the conductance catheter.     

An image fusion algorithm based on multi-resolution decomposition for functional magnetic resonance images

This paper presents a new functional image fusion algorithm which is the combination of SPM and ICA using multi-resolution decomposition. Firstly, we designed the fMRI experiments and obtained the fMRI image data from different experimental conditions. The brain activated regions were extracted by the SPM and ICA methods respectively. Secondly, by constructing the Laplacian pyramids of the source image, a new fusion rule based on the salience and matching measure is proposed in various resolutions. Finally, the fused functional images are reconstructed by the inverse Laplacian pyramid transformation. The results show that the algorithm can retain the details of the source images and pinpoint exactly the brain functional area associated with the hand action, thus outperforming SPM or ICA for functional regions extraction.     

An image fusion algorithm based on multi-resolution decomposition for functional magnetic resonance images

Previous studies have shown that behavioral sensitization is modulated by drug-associated context, in which memory processes may be critically involved. Sleep has been suggested to play an important role in memory processes. However, the relationship between sleep and context-modulated effects on behavioral sensitization remains to be elucidated. In the present study, we designed three experiments to explore the effects of rapid eye movement sleep deprivation (RSD) on context-modulated effects on morphine locomotor sensitization in mice. Mice were subjected to 6 h RSD starting either immediately after morphine pairing training or 6 h later. The control mice were returned to their home cages immediately after pairing training and left undisturbed. In experiment 1, RSD from 0 to 6 h but not from 7 to 12 h disrupted paired context-modulated enhancement of locomotor activity. In experiment 2, RSD from 0 to 6 h but not from 7 to 12 h disrupted unpaired context-modulated suppression of locomotor activity. In experiment 3, RSD from either 0 to 6 h or 7 to 12 h had no effect on conditioned locomotor activity. Our findings suggest that sleep plays a critical role in memory processes underlying context-modulated effects on morphine locomotor sensitization.     

Functional mapping of neural pathways in rodent brain in vivo using manganese-enhanced three-dimensional magnetic resonance imaging

This work presents three-dimensional MRI studies of rodent brain in vivo after focal and systemic administration of MnCl2. Particular emphasis is paid to the morphology and dynamics of Mn2+-induced MRI signal enhancements, and the physiological mechanisms underlying cerebral Mn2+ uptake and distribution. It turns out that intravitreal and intrahippocampal injections of MnCl2 emerge as useful tools for a delineation of major axonal connections in the intact central nervous system. Subcutaneous administrations may be exploited to highlight regions involved in fundamental brain functions such as the olfactory bulb, inferior colliculus, cerebellum and hippocampal formation. Specific insights into the processes supporting cerebral Mn2+ accumulation may be obtained by intraventricular MnCl2 injection as well as by pharmacologic modulation of, for example, hippocampal function. Taken together, Mn2+-enhanced MRI opens new ways for mapping functioning pathways in animal brain in vivo with applications ranging from assessments of transgenic animals to follow-up studies of animal models of human brain disorders.     

An algorithm for stereotactic localization by computed tomography or magnetic resonance imaging

Stereotactic localization of an intracranial lesion by computed tomography or magnetic resonance imaging requires the use of a head frame that is fixed to the skull of the patient. To such head frames are attached either N-shaped or V-shaped localization rods. Because of patient positioning, the transverse imaging slices may not be parallel to the frame base; a coordinate transformation algorithm that takes this possibility into consideration is crucial. Here we propose such an algorithm for a head frame with V-shaped localization rods. Our algorithm determines the transformation matrix between the image coordinate system of a transverse image and the frame coordinate system. The determining procedure has three steps: (a) calculation of the oblique angles of a transverse image relative to the head frame and calculation of the image magnification factor; (b) determination of the coordinates of four central markers in both coordinate systems; and (c) determination of the 3 x 3 transformation matrix by using the coordinates of the four markers. This algorithm is robust in principle and is useful for improving the accuracy of localization.     

An algorithm for automatic segmentation and classification of magnetic resonance brain images

In this article, we describe the development and validation of an automatic algorithm to segment brain from extracranial tissues, and to classify intracranial tissues as cerebrospinal fluid (CSF), gray matter (GM), white matter (WM) or pathology. T1 weighted spin echo, dual echo fast spin echo (T2 weighted and proton density (PD) weighted images) and fast Fluid Attenuated Inversion Recovery (FLAIR) magentic resonance (MR) images were acquired ino 100 normal patients and 9 multiple sclerosis (MS) patients. One of the normal studies had synthesized MS-like lesions superimposed. This allowed precise measurement of the accuracy of the classification. The 9 MS patients were imaged twice in one week. The algorithm was applied to these data sets to measure reproducibility. The accuracy was measured based on the synthetic lesion images, where the true voxel class was known. Ninety-six percent of normal intradural tissue voxels (GM, WM, and CSF) were labeled correctly, and 94% of pathological tissues were labeled correctly. A low coefficient of variation (COV) was found (mean, 4.1%) for measurement of brain tissues and pathology when comparing MRI scans on the 9 patients. A totally automatic segmentation algorithm has been described which accurately and reproducibly segments and classifies intradural tissues based on both synthetic and actual images.     

Coronary magnetic resonance angiography for the detection of coronary stenoses.

BACKGROUND: An accurate, noninvasive technique for the diagnosis of coronary disease would be an important advance. We investigated the accuracy of coronary magnetic resonance angiography among patients with suspected coronary disease in a prospective, multicenter study. METHODS: Coronary magnetic resonance angiography was performed during free breathing in 109 patients before elective x-ray coronary angiography, and the results of the two diagnostic procedures were compared. RESULTS: A total of 636 of 759 proximal and middle segments of coronary arteries (84 percent) were interpretable on magnetic resonance angiography. In these segments, 78 (83 percent) of 94 clinically significant lesions (those with a > or = 50 percent reduction in diameter on x-ray angiography) were also detected by magnetic resonance angiography. Overall, coronary magnetic resonance angiography had an accuracy of 72 percent (95 percent confidence interval, 63 to 81 percent) in diagnosing coronary artery disease. The sensitivity, specificity, and accuracy for patients with disease of the left main coronary artery or three-vessel disease were 100 percent (95 percent confidence interval, 97 to 100 percent), 85 percent (95 percent confidence interval, 78 to 92 percent), and 87 percent (95 percent confidence interval, 81 to 93 percent), respectively. The negative predictive values for any coronary artery disease and for left main artery or three-vessel disease were 81 percent (95 percent confidence interval, 73 to 89 percent) and 100 percent (95 percent confidence interval, 97 to 100 percent), respectively. CONCLUSIONS: Among patients referred for their first x-ray coronary angiogram, three-dimensional coronary magnetic resonance angiography allows for the accurate detection of coronary artery disease of the proximal and middle segments. This noninvasive approach reliably identifies (or rules out) left main coronary artery or three-vessel disease.     

Pulse sequence design for volume selective excitation in magnetic resonance

The design of a pulse sequence for volume localization in magnetic resonance spectroscopy is described in detail. The sequence is based on the volume selective excitation technique (VSE) proposed by Aue et al. [J. Magn. Reson. 56, 350 (1984)] and overcomes the high rf power requirements of VSE. The implications of various design stages are demonstrated experimentally and by computer simulations.     

3.0T磁共振三维容积内插屏气序列在骨骼模型重建中的应用

目的利用3.0T磁共振三维容积内插屏气序列(3D-Vibe)数据进行骨重建并评价其精准性。方法借助计算机辅助设计及增材制造技术制备不同型号的中空树脂模型。预先在1 000.00 m L纯水中加入3.75 g NiSO46H2O、5.00 g Na Cl及10 m L碘普罗胺注射液制成灌注液,在扫描开始前注入中空模型中并密封,保证模型内部完全充盈,然后针对同一模型分别进行CT、常规磁共振序列(T1WI-TSE、T2WI-TIRM)、3D-Vibe各向同性序列及3D-Vibe各向异性序列扫描。利用Mimics对不同扫描参数所得的数据进行三维重建,得到对应的数字模型。将所有模型置于同一坐标原点,通过计算重建模型与原始模型间的匹配度评价重建模型的精准性,利用统计学方法进行比较。最后将筛选出的磁共振序列用于制备新西兰大白兔股骨干模型并参照实物对重建模型的外观进行主观及客观评价。结果树脂模型的重建结果提示CT组与T1WI-TSE及T2WI-TIRM组模型间匹配度比较,差异均有统计学意义(P0.01); 3D-Vibe各向同性组与3D-Vibe各向异性组重建模型间匹配度比较,差异有统计学意义(P0.05); CT组与3D-Vibe各向同性组模型间匹配度比较,差异无统计学意义(P0.05); T1WI-TSE与T2WI-TIRM组模型间匹配度比较,差异无统计学意义(P0.05)。股骨模型重建结果提示3D-Vibe各向同性组模型匹配度优于常规序列组,差异有统计学意义(P0.01)。结论 3D-Vibe各向同性磁共振数据可用于股骨3D打印模型的重建。     

An automated iterative algorithm for water and fat decomposition in three-point Dixon magnetic resonance imaging

An iterative, outlier exclusion, second-order surface fitting algorithm has been developed to solve the well-known phase wraparound problem associated with in vivo applications of the three-point Dixon magnetic resonance imaging method. The technique was optimized for speed by reducing the problem to a pair of planar fits. The spatial misalignment between water and fat components due to the chemical shift was handled on a subpixel level by invoking the shift theorem of Fourier transformation. From the chemical shift corrected water and fat images, high quality recombined MR images were generated. The algorithm was validated in both phantom and patient studies. In vivo breast images and pelvic images are provided as a demonstration of the method.     

Application of magnetic resonance imaging and magnetic resonance angiography as diagnostic measures for the first attack of suspected cerebrovascular diseases in Korea

Purpose

No precise data are available showing how magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) can be applied to diagnosis for the first attack of a suspected cerebrovascular disease in Korea. The purpose of this study was to evaluate the application level of MRI and MRA as diagnostic tools and the related factors to the use of these techniques.

Materials and Methods

This study used the health benefit claim data of 89,890 patients who were hospitalized for the first time due to suspected cerebrovascular disease in 2007 without having visited medical institutions as an outpatient or inpatient from 2003 to 2006.

Results

Of the 89,890 cases, 28.4% took both MRI and MRA, 10.7% took only MRI and 6.9% took only MRA. The related factors identified in the multivariate logistic regression analysis were gender, type of insurance, type of medical institution, type of department, duration of hospitalization, and type of disease.

Conclusion

This study showed that the application level of MRI and MRA as diagnostic measures for the first attack of a suspected cerebrovascular diseases varied depending on several factors. It is necessary to study more accurate levels of computerized tomography (CT), computerized tomography angiography (CTA), MRI or MRA as measures to diagnose a first attack of suspected cerebrovascular disease.     

Radiologist evaluation of a multispectral image compression algorithm for magnetic resonance images

With the advent of teleradiology and picture archiving and communication systems (PACS), the expense and time required for image transmission and long term image archiving become important. The use of validated image compression algorithms can greatly reduce these costs. A lossy, multispectral image compression scheme at compression ratios (CR) of 25∶1 and 32∶1 was used for a set of 26 different patient MR exams. The original and compressed/decompressed (CD) image sets were evaluated in a blinded fashion by four radiologists in two phases. The main objective was to determine whether radiologic interpretation would vary between the two types of CD image sets and the corresponding originals. In general, the compression algorithm caused a slight decrease in image quality; however, the interpretation of pathology did not change between the original and CD image sets. In only one case at the maximum CR=32 did one of four radiologists change the interpretation of pathology after CD. In this study, lossy multispectral image compression of MR images at CR=25 maintained diagnostic integrity. This could play a significant role in image storage and communications.     

On the use of electric and magnetic data to determine electric sources in a volume conductor

Methods of obtaining detailed information about electrical sources in semi-infinite and spherical volume conductors using electric and magnetic surface data are investigated. Surface data produced by various actual sources in the conductors are calculated. Using these data, a least-squares error (LSE) solution is then obtained for the dipoles in a multiple dipole assumed source and a comparison of the actual and assumed sources is made. Noise is simulated by the addition of random numbers to the data; modeling errors by the use of actual and assumed sources with different configurations. It is found that it is not possible to calculate a condition number (CN) which serves as a useful measure of the sensitivity of the LSE solutions to noise and modeling errors. It is also found that no useful information about the actual source can be obtained from LSE solutions when noise and modeling errors are present. No improvement is obtained when magnetic or a combination of electric and magnetic data are used. However, it is found that three additional solutions developed from the LSE solutions can provide some accurate information. These three solutions provide information about the general magnitude and orientation of the electrical activity of the actual source as well as the “flow” and “rotation” characteristics of the source. The most accurate flow information tends to be produced by electric or a combination of electric and magnetic data; the most accurate rotation information tends to be produced by magnetic or a combination of data. This indicates that electric and magnetic measurements can provide different information when noise and modeling errors are present. The results also show that information about the location of the actual source is provided by a comparison of differences between actual surface data and that produced by a series of LSE solutions. There are no improvements in the location information when a combination of data is used. Work supported by Public Health Service Research Fellowship (National Heart, Lung, and Blood Institute) No. 1 F32 HL05419.     

Visualization of the ophthalmic artery by phase-contrast magnetic resonance angiography: a pilot study

Objective

This study aimed at investigating whether phase-contrast (PC) magnetic resonance (MR) angiography is useful for visualizing the ophthalmic artery (OA).

Methods

This prospective study enrolled 196 consecutive outpatients who underwent three-dimensional PC MR angiography. The basal image parallel to the anteroposterior dimension of the OA was extracted for analysis from the imaging data.

Results

The 99 male and 97 female subjects were aged from 10?years to 80?years (mean 47.9?years). The OAs were supplied only by the external carotid system or in combination with the internal carotid artery (ICA) in 18 subjects (9.2?%). The bilateral OAs were symmetrical in 12?%, asymmetrical in 87?%, and unidentified in 1?%. The contour of the proximal segment of the OAs could be classified into straight, curved, and tortuous types. The ICA–OA angle defined by the angle between the approximate line of the proximal OA and the vertical line was also variable. The first bend of the OA corresponded to the anastomosis site with the external carotid system. The proximal medial bend was the origin of the posterior ethmoidal artery, and the distal medial bend was the origin of the anterior ethmoidal artery.

Conclusions

According to the results the OA not only possesses three characteristic bends, but also shows prominent individual variability and commonly shows bilateral asymmetry. The contour of the OA may be regulated by the anchor effect at the bend sites. PC MR Angiography is useful for visualizing the main trunk of the OA.     

大脑动脉环的解剖及在磁共振血管成像上的应用

目的探讨运用三维时间飞跃法(3D-TOF)磁共振血管成像显示大脑动脉环,为构建大脑基底动脉环三维可视化动脉图谱提供形态学资料。方法对10例尸体的大脑动脉环进行动脉间角度及距离的测量。同时,对30例正常人的头颅进行3D-TOF磁共振血管成像检查,图像经西门子Syngo B17工作站后处理,从影像学分析大脑动脉环。结果大脑前动脉显示率为100!,均表现为双支型。动脉环内的均值距离为(1.06±0.23)cm,其与颈内动脉间的均值夹角为(63.13±9.72)°,与前交通动脉的均值夹角为(107.95±57.70)°;颈内动脉环内段显示率为100!,其与大脑前动脉的均值夹角为(63.13±9.72)°,与后交通动脉的均值夹角为(123.20±10.37)°;大脑后动脉显示率为100!,动脉环内的均值距离为(0.56±0.12)cm,其与后交通动脉的均值夹角为(70.00±8.87)°,与基底动脉的均值夹角为(123.95±11.43)°;后交通动脉显示率为100%,动脉环内的均值距离(1.06±0.17)cm,其与颈内动脉的均值夹角为(123.20±10.37)°,与大脑后动脉的均值夹角为(70.00±8.87)°,与大脑中动脉的均值夹角为(131.15±15.21)°;前交通动脉的显示率为80%,动脉环内的均值距离为(0.23±0.16)cm,其与大脑前动脉的均值夹角为(107.95±57.70)°。结论明确了大脑动脉环的解剖组成,测量了动脉间的距离及动脉环内各动脉间的角度,3D-TOF法磁共振血管成像可清晰显示大脑动脉环的组成,三维重建技术可以从各个角度显示大脑动脉环。     

Rest period duration of the coronary arteries: implications for magnetic resonance coronary angiography

Magnetic resonance (MR) and computed tomography coronary imaging is susceptible to artifacts caused by motion of the heart. The presence of rest periods during the cardiac and respiratory cycles suggests that images free of motion artifacts could be acquired. In this paper, we studied the rest period (RP) duration of the coronary arteries during a cardiac contraction and a tidal respiratory cycle. We also studied whether three MR motion correction methods could be used to increase the respiratory RP duration. Free breathing x-ray coronary angiograms were acquired in ten patients. The three-dimensional (3D) structure of the coronary arteries was reconstructed from a biplane acquisition using stereo reconstruction methods. The 3D motion of the arterial model was then recovered using an automatic motion tracking algorithm. The motion field was then decomposed into separate cardiac and respiratory components using a cardiac respiratory parametric model. For the proximal-to-middle segments of the right coronary artery (RCA), a cardiac RP (<1 mm 3D displacement) of 76+/-34 ms was measured at end systole (ES), and 65+/-42 ms in mid-diastole (MD). The cardiac RP was 80+/-25 ms at ES and 112+/-42 ms at MD for the proximal 5 cm of the left coronary tree. At end expiration, the respiratory RP (in percent of the respiratory period) was 26+/-8% for the RCA and 27+/-17% for the left coronary tree. Left coronary respiratory RP (<0.5 mm 3D displacement) increased with translation (32% of the respiratory period), rigid body (51%), and affine (79%) motion correction. The RCA respiratory RP using translational (27%) and rigid body (33%) motion correction were not statistically different from each other. Measurements of the cardiac and respiratory rest periods will improve our understanding of the temporal and spatial resolution constraints for coronary imaging.