基于正则化方法的加权最小模估计在脑磁源成像中的应用

脑磁图 ( m agnetoencephalography,MEG)逆问题的研究 ,根据点源和分布源两种源模型 ,可分为偶极子定位和磁源成像两大类求逆方法。采用非参数的分布源模型 ,MEG逆问题转化为一个病态的欠定方程组的求解。本文系统地阐述了结合 Tikhonov正则技术的加权最小模磁源重建方法 ,着重介绍了深度归一化算法、低分辨率脑电磁断层成像技术、局部欠定系统解法、选择性最小模方法 ,此外还从广义的加权最小模估计角度对最大熵重建方法 ,融合其它脑功能成像技术的方法以及最大后验概率估计方法加以解释和分析。不同的磁源成像方法目的都是通过引入合适的约束条件 ,从算法公式本身及神经细胞活动的特性中加以修正 ,减少逆问题的不适定程度 ,因此均可认为是使用正则方法来约束解空间 ,从而获得与测量磁场数据相拟合的并具有神经生理学和解剖学意义下的最合理的解。基于正则化技术的加权最小模估计是 MEG逆问题研究中最早开展、并已被广泛应用的磁源分布图像重建方法 ,本文给出了一个较为完整的理论发展框架     

Equivalent Charge Source Model Based Iterative Maximum Neighbor Weight for Sparse EEG Source Localization

How to localize the neural electric activities within brain effectively and precisely from the scalp electroencephalogram (EEG) recordings is a critical issue for current study in clinical neurology and cognitive neuroscience. In this paper, based on the charge source model and the iterative re-weighted strategy, proposed is a new maximum neighbor weight based iterative sparse source imaging method, termed as CMOSS (Charge source model based Maximum neighbOr weight Sparse Solution). Different from the weight used in focal underdetermined system solver (FOCUSS) where the weight for each point in the discrete solution space is independently updated in iterations, the new designed weight for each point in each iteration is determined by the source solution of the last iteration at both the point and its neighbors. Using such a new weight, the next iteration may have a bigger chance to rectify the local source location bias existed in the previous iteration solution. The simulation studies with comparison to FOCUSS and LORETA for various source configurations were conducted on a realistic 3-shell head model, and the results confirmed the validation of CMOSS for sparse EEG source localization. Finally, CMOSS was applied to localize sources elicited in a visual stimuli experiment, and the result was consistent with those source areas involved in visual processing reported in previous studies.     

Intracerebral dipole sources of EEG FFT power maps

Summary The described method opens a way to compute intracerebral source localizations of ongoing EEG activity. A sine-cosine diagram of the Fourier-transformed data is constructed for each frequency point, forming a "FFT constellation" of entries. Into the FFT constellation of each diagram, a straight line is fitted which produces the least squared deviation sum between the original entry positions and their orthogonal projections onto that line. The map landscape described by the voltages between the projected positions ("FFT approximation") is the least error compromise landscape of all possible landscapes during the paradigmatic cycle of the given FFT frequency. The map thus constructed can be used in the usual dipole source localization procedures. There is one for each FFT frequency point. The squared forward solution of the fitted dipole source and the squared FFT approximation map are "power maps" which are very similar to the original power map. For an average-reference power map with two peaks, the source tends to lie between the peaks; a power map with one peak might show closely neighboring maximal and minimal potential values in the FFT approximation, indicative of a tangential source close to the surface.Acknowledgement: The authors thank D. Brandeis and W. Karniski for helpful discussions. Support from the EMDO Foundation, the Hartmann-Muller-Foundation and the Sandoz-Foundation for Medical-Biological Research is gratefully acknowledged.     

Gaussian source model based iterative algorithm for EEG source imaging

Estimation of the neural active sources from the scalp electroencephalogram (EEG) is an ill-posed inverse problem. In this paper, we propose a new source model: Gaussian distributed Source Model (GSM), to model the activations in brain. GSM may imitate an Isolated Source Model (ISM) or a Distributed Source Model (DSM) by adopting different supporting range parameter of the Gaussian function. Using GSM, an iterative Gaussian source Imaging Algorithm (GIA) is developed to detect the EEG sources. As GIA dynamically reduces the solution space, the solution may gradually converge to a desired distribution. A comparative evaluation among LORETA, FOCUSS and GIA was conducted for both isolated point sources and distributed sources, the results demonstrate that GIA is more flexible and efficient for various actual sources configurations. Finally, GSM was applied to real recordings obtained from a visual spatial attention task; the corresponding source activation areas of the early component are localized in contralateral occipital cortices, consistent with the retinotopic organization of early visual spatial attention effects.     

Refinements to the geometry factor used in the AAPM Task Group Report No. 43 necessary for brachytherapy dosimetry calculations. American Association of Physicists in Medicine

Determination of the geometry factor is necessary for brachytherapy dosimetry calculations as recommended by the AAPM Task Group No. 43 (TG-43). The equivalence and errors associated with use of a point source approximation for an extended line segment source are examined. For all angles, the error using the point source approximation is less than 2% for distances in which the ratio of radius to active source length, (r/L), exceed about 3.6. A novel approach to determining the geometry factor using Monte Carlo methods is discussed in which the particle flux emanates from the active source and streams with no interactions occurring within the source or phantom. This method was performed for determining the geometry factor along the transverse axis for six brachytherapy sources. Differences in the geometry factor exceeding 2% between the point source approximation and that obtained using Monte Carlo methods occurred at distances ranging from 0.5 to 5 mm from the source center along the transverse plane. The merits of the Monte Carlo approach for solving the geometry factor are discussed in light of using a point or line source approximation for calculating additional brachytherapy dosimetry parameters.     

Psychopathology of acute paraphrenic syndrome, its typological forms and their relation to variants of paroxysm-like progredient schizophrenia

A total of 60 patients with different forms of paroxysm-like progredient schizophrenia were examined to clarify psychopathology of acute paraphrenic syndrome in different variants of the disease. Three typological variants were distinguished: with picturesque delirium, manifestations of Knadinsky-Clerambault syndrome, and confabulation disorders. It was shown that paroxysm-like progredient schizophrenia akin to recurrent one is characterized by acute paraphrenic syndrome with picturesque delirium; paroxysm-like progredient schizophrenia akin to juvenile malignant one is characterized by acute paraphrenic syndrome dominated by Knadinsky-Clerambault syndrome and picturesque delirium; paroxysm-like progredient schizophrenia akin to paranoid one is characterized by acute paraphrenic syndrome dominated by Knadinsky-Clerambault syndrome or acute paraphrenic syndrome with confabulation disorders. The study confirms specificity of acute paraphrenic syndrome for paroxysm-like progredient schizophrenia     

Applicability of the single equivalent point dipole model to represent a spatially distributed bio-electrical source

Although the single equivalent point dipole model has been used to represent well-localised bio-electrical sources, in realistic situations the source is distributed. Consequently, position estimates of point dipoles determined by inverse algorithms suffer from systematic error due to the non-exact applicability of the inverse model. In realistic situations, this systematic error cannot be avoided, a limitation that is independent of the complexity of the torso model used. This study quantitatively investigates the intrinsic limitations in the assignment of a location to the equivalent dipole due to distributed electrical source. To simulate arrhythmic activity in the heart, a model of a wave of depolarisation spreading from a focal source over the surface of a spherical shell is used. The activity is represented by a sequence of concentric belt sources (obtained by slicing the shell with a sequence of parallel plane pairs), with constant dipole moment per unit length (circumferentially) directed parallel to the propagation direction. The distributed source is represented by N dipoles at equal arc lengths along the belt. The sum of the dipole potentials is calculated at predefined electrode locations. The inverse problem involves finding a single equivalent point dipole that best reproduces the electrode potentials due to the distributed source. The inverse problem is implemented by minimising the χ² per degree of freedom. It is found that the trajectory traced by the equivalent dipole is sensitive to the location of the spherical shell relative to the fixed electrodes. It is shown that this trajectory does not coincide with the sequence of geometrical centres of the consecutive belt sources. For distributed sources within a bounded spherical medium, displaced from the sphere's centre by 40% of the sphere's radius, it is found that the error in the equivalent dipole location varies from 3 to 20% for sources with size between 5 and 50% of the sphere's radius. Finally, a method is devised to obtain the size of the distributed source during the cardiac cycle.     

A patch source model for treatment planning of ruthenium ophthalmic applicators

Beta-ray emitting Ru-106/Rh-106 ophthalmic applicators have been used for close to 4 decades in the treatment of choroidal melanoma. The form factor of these applicators is a spherically concave silver bowl with an inner radius of curvature between 12 and 14 mm, and a total shell thickness of 1 mm. The radioactive nuclide is deposited in a layer 0.1 mm below the concave surface of the applicator. Calculation of dose distributions for clinical treatment planning purposes is complicated by the concave nature of the distributed source, the asymmetric shape of the active region of some applicators, imperfections in the manufacturing process which can result in an inhomogeneous distribution of activity across the active surface, and absorption and scatter in the 0.1 mm layer of silver which seals and protects the radioactive layer. A semi-empirical method of calculating dose distributions for these applicators is described which is fundamentally compatible with treatment planning systems that use the AAPM TG43 brachytherapy formalism. Dose to water is estimated by summing a "patch source" dose function over a discrete number of overlapping patches uniformly distributed over the active surface of the applicator. The patch source dose function differs conceptually from a point source dose function in that it is intended to represent the macroscopic behavior of a small, disk-like region of the applicator. The patch source dose function includes an anisotropy term to account for angular variation in absorption and scatter as particles traverse the 0.1 mm silver window. It geometrically models the nearfield of a patch with properties akin to both a small disk and infinite plane, and models the farfield as if the patch were a point. This allows a manageable number of discrete patches (300 to 1000) to provide accuracy appropriate for clinical treatment planning. This approach has the advantages of using familiar concepts and data structures, it is computationally quick, and it readily adapts to asymmetric applicator shapes and inhomogeneities in the radionuclide distribution. A method for optimizing the patch source dose function parameters is presented, and the dosimetric calculations are compared with published Monte Carlo calculations and measurements.     

用于硼中子俘获治疗的加速器超热中子源靶的设计

提出适合硼中子俘获治疗加速器^7Li(p,n)^7Be反应中子源一 个金属锂靶的设计，并对中子产额进行了计算。用MonteCarlo的方法研究了中子在水中的慢化和反射层对中子能谱的影响。结果表明，在这种几何结构下^7Li(p,n)^7Be反应产生的中子经过5cm的水层慢化后可作为硼中子俘获治疗的超热中子源。     

Functional imaging and localization of electromagnetic brain activity

Functional imaging of electric brain activity requires specific models to transform the signals recorded at the surface of the human head into an image. Two categories of model are available: single-time-point and spatio-temporal methods. The instantaneous methods rely only on the few voltage differences measured at one sampling point. To create a spatial image from this limited information, they require strict assumptions that rarely conform with the underlying physiology. Spatio-temporal models create two kinds of images: first, a spatial image of discrete equivalent multiple dipoles or regional sources, and second, an image of source current waveforms that reflect the temporal dynamics of the brain activity in circumscribed areas. The accuracy of the spatial image is model dependent and limited, but it can be validated from the spatio-temporal data by the "regional source imaging" technique, introduced here. The source waveforms are linear combinations of the scalp waveforms, and thus, specific derivations which image local brain activities at a macroscopic level. Brain source imaging of somatosensory evoked potentials revealed temporally overlapping activities from the brainstem, thalamus and from multiple sources in the region of the contralateral somatosensory projection areas.     

Spatial- and frequency-domain ring source models for the single-muscle fibre action potential

In the paper, single-fibre models for the extracellular action potential are developed that will allow the potential to be evaluated at an arbitrary field point in the extracellular space. Fourier-domain models are restricted in that they evaluate potentials at equidistant points along a line parallel to the fibre axis. Consequently, they cannot easily evaluate the potential at the boundary nodes of a boundary-element electrode model. The Fourier-domain models employ axial-symmetric ring source models, and thereby provide higher accuracy than the line source model, where the source is lumped into a line source at the centre of the fibre. In the paper, new spatial models are developed based on elliptic integrals. These models employ axial-symmetric ring source models, and therefore are more accurate than the line source model. In the analysis, dual transform pairs are identified. Numerical examples including anisotropy show that the spatial models require extreme care in the integration procedure owing to the singularity in the weighting functions. With adequate sampling, the spatial models can evaluate extracellular potentials with high accuracy.     

Models of brain sources

Summary Two categories of models are available for the functional imaging of scalp recorded electric brain activity: single-time-point and spatio-temporal. Instantaneous models require strict assumptions that do not conform with the underlying physiology, because they rely on the few voltage differences measured at only one sampling point. Spatio-temporal models create a spatial image of discrete multiple sources and a temporal image of source current wave forms which reflect the time course of the local activity in circumscribed brain areas at a macroscopic level. The spatial image may be limited in accuracy because it depends both on model and data, but it can be validated by scanning the brain with regional dipole sources. In many cases of temporal lobe epilepsy, for example, interictal spikes can be described adequately by as few as two equivalent dipoles, which image the vertical source current arising from the medio-basal aspect of the temporal lobe and the horizontal source current from its lateral surface.     

Digital reconstruction of point sources imaged by a zone plate camera.

Zone plate cameras are used for high sensitivity imaging of X- and gamma-ray sources. The image thus obtained requires decoding and numerical techniques are devised for this purpose. The response function and the signal-to-noise ratio for a single point source have been evaluated for zone plates with varying numbers of zones. Autocorrelation is the best of the methods examined, and the results are in good aggreement with those obtained using Monte Carlo techniques. The autocorrelation method can give a gain of 50% in signal-to-noise for a single point source over the maximum obtainable with optical decoding. Criteria for the choice of number of zones are discussed.     

利用井型电离室测量后装放射源192Ir活度的方法及放射源活度的验证

目的:阐述井型电离室测量后装放射源活度的理论基础和具体测量方法,对所使用的192Ir放射源活度进行验证。方法:首先通过井型电离室系统校准因子计算得出电离室电流与192Ir活度之间的换算系数,然后制定计划寻找192Ir源测量活度的有效驻留点。再利用PTW Unidos E剂量计和PTW SOURCECHECK 4π井型电离室测量192Ir照射电离室后产生的电流并转换为放射源活度。连续测量7个月,测量值与计划系统计算值两组数据进行配对样本t检验,分析两组数据差异。结果:在总共14次的测量计算中,川北医学院附属医院新购进192Ir源活度的测量值与计划系统计算值相对误差均在±1%以内。其最大偏差为0.946%,符合国标WS 262-2017后装γ源近距离治疗质量控制检测规范中源活度稳定性检测±5%内的要求,达到了AAPM临床应用192Ir源活度标定小于±3%的标准。且两组数据配对样本t检验显示,差异无统计学意义（P=0.665>0.05）。结论:井型电离室能够准确测量192Ir源的活度,本院所使用的放射源按照理想的半衰期衰变,放射源杂质少、纯度高。     

生物人工肝中肝细胞来源及培养的新进展

肝细胞的活性是生物人工肝成功的关键 ,而良好的细胞来源及培养是肝细胞活性的保证。近年来 ,生物型人工肝中肝细胞来源及培养有了很大的进展。其中 ,肝细胞来源的研究主要表现在原代肝细胞、人肝癌细胞、传代及转化的肝细胞等方面。肝细胞培养的研究集中在培养方式、培养条件、培养时间及所需肝细胞数量等方面。这些研究解决了许多理论和实践上的问题 ,促进了生物人工肝的发展     

Congenital synspondylism

We present 3 patients with a specific pattern of congenital familial extensive vertebral anomalies (CFEVA) with vertebral and carpal coalition. It is proposed that these patients and two previously reported cases have a vertebral disorder akin to symphalangism in the fingers. The name synspondylism is proposed. Two instances of sib recurrence point to Mendelian segregation in some instances of synspondylism. The syndromes and associations encompassed by CEFVA are reviewed. The clinical and radiographic manifestations of congenital synspondylism are discussed in the perspective of the possible pathogenesis of segmentation disorders of the spine.     

Learned contextual cue potentiates eating in rats

Explicit cues associated with food consumption when hunger prevails will enhance eating when they are subsequently presented under conditions of satiety. Here we examined whether contextual conditioned stimuli (CSs) paired with consumption of food pellets while rats were food-deprived would enhance consumption of this food in rats that were not food-deprived. The conditioning context enhanced rats' consumption of the training food, but it did not change their consumption of the familiar, lab chow. These results show that the contextual CSs, like discrete cues, could modulate food consumption in a CS-potentiated eating paradigm. Furthermore, the data suggest that CS-potentiation of eating does not induce a general motivation to eat, akin to hunger, but instead more likely produces a more specific motivational state, akin to craving.     

固定型腔内后装施源器治疗宫颈癌的剂量分布特点

目的:研究固定型腔内后装施源器及标准腔内后装施源器的剂量分布特点,评价固定型腔内施源器是否符合临床剂量学要求。方法:比较固定型腔内后装施源器和标准型腔内施源器的等剂量曲线分布图,并根据腔内近距离放疗中剂量分布与距离平方成反比的剂量学特点,按照施源器材料中的指数衰减及吸收系数,计算出两种施源器x和y轴两个方向上的剂量比。结果:标准Ⅲ通腔内施源器和固定Ⅲ通腔内施源器等剂量曲线分布图通过TPS优化,图形基本一致:在冠状面上等剂量曲线呈扁梨行,宫颈、阴道剂量大于宫体剂量,在横断面上等剂量曲线呈扁椭圆形;且固定型扁平腔内施源器源中心到模表面距离为0.5 cm,而标准Ⅲ通腔内施源器从源中心到模表面距离为1 cm,通过计算可知当r=0.5 cm,l=1.0 cm时其剂量比大于l=1.5 cm时的剂量比,因此给予A点相同剂量所需要的时间较标准腔内后装施源器要短,由于治疗时间短,膀胱直肠所受剂量就小,通过优化,直肠剂量只有A点剂量的70%,而宫颈粘膜表面剂量比经典施源器剂量要高出45%。结论:固定型腔内后装施源器剂量分布符合临床剂量学要求,且优于标准施源器,同时由于使用简单方便,不用模拟机拍片,剂量计算模式也固定,更适合宫颈癌患者多的治疗中心使用。     

基于真实头模型的EEG参考电极标准化技术

目的 :研究基于真实头模型的参考电极标准化技术并验证它的有效性。方法 :基于真实头模型的等效源技术 ,建立了由以头表某点或平均电位为参考点的实际记录近似得到以无穷远点为参考的记录的方法。由于无穷远点的电位可假设为常数零 ,因此可称该方法为真实头模型的参考电极标准化技术 (REST)。对真实头模型全空间内任意位置的源的实际头表记录进行REST处理 ,然后计算经REST处理后的近似记录与以无穷远点为参考的记录之间的相对误差 ,以此检验该技术的有效性。结果 :对于真实头模型REST是有效的 ,尤其对重要的表层皮质区域更为有效 ,它的应用可以降低因非零的参考电位而引入头表记录的干扰。结论 :采用参考电极标准化技术能得到更真实的脑电 (EEG)记录 ,从而可能对脑电的应用产生重要的影响。     

基于红外技术的人体异常热源的探测研究

采用红外测温技术及改进蚁群算法求解导热反问题中的内热源强度及表面换热系数。通过建立含有内热源的二维稳态导热反问题实验模型,用红外热像仪测量试件的表面温度,并选用若干点温度作为求解反问题的补充条件,来反演热源强度及表面换热系数,并讨论了测点布置方式对反演结果的影响。计算结果表明：采用红外热像仪测温,结合改进蚁群算法可准确地对热源强度和表面换热系数进行反演识别。在整个边界上均匀布置测点的个数越多,则反演时计算步数越少,反演结果越精确;在测点个数相同时,在整个边界上均匀布置测点比在部分边界上均匀布置测点,更容易反演计算出准确的结果。