生物力学影响的靶区位姿精度保持方法研究

目的:分析二次摆位中靶区位姿在生物力学影响下的器官肿瘤变形规律,控制机械臂位置来补偿此误差。方法:利用解剖学和生物力学相关知识,通过Mimics v17.0软件建立包含肿瘤的肺组织有限元模型,将建立的有限元模型导入ANSYS15.0,利用前人总结的生物力学特性参数仿真分析肺和肿瘤的变形误差。结果:得到在二次摆位中肺组织最大变形为21.24 mm,肿瘤最大变形为3.17 mm,并利用二次多项式拟合给出了误差模型,摆位验证后其误差变形均在此范围内,其中头脚方向变形最大。结论:基于自主设计的六自由度摆位医用机械臂提出一种通过前馈修正的位置控制方法,该方法在二次摆位过程中可以预先补偿肿瘤的位移误差,提高放疗精度和效率,减少对治疗靶区周围正常组织的损伤。 【关键词】靶区位姿;生物力学;变形误差;前馈修正     

反馈效症学说的源流、概念及鉴别

“反馈效症”一词主要脱胎于《伤寒杂病论》,为张仲景无形中建立的一种异常精确的反馈体系。中医在治疗疾病过程中,需要根据患者反应,对诊断和治疗的正确性作出判断,根据系统的反馈,为临床提供决策。本文整理了其源流、基本概念和分类,提出了具体应用方向,以期为正确治疗患者抢占先机。     

Subpopulations of GABAergic neurons containing parvalbumin, calbindin D28k, and cholecystokinin in the rat hippocampus.

The possible coexistence of calbindin D28k with parvalbumin and of calbindin D28k with cholecystokinin was studied in nonpyramidal cells of the rat dorsal hippocampal formation. Neighbouring Vibratome sections were immunostained either for calbindin D28k and parvalbumin or for calbindin D28k and cholecystokinin. The cells, halved during sectioning, were identified in both sections immunostained for different antigens. The coexistence of calbindin D28k and parvalbumin in the same neuron was rare throughout the hippocampal formation with the exception of stratum oriens of the CA1 region, where 9.6% of the parvalbumin-immunoreactive cells also contained calbindin D28k. In stratum radiatum of the CA3 region, calbindin D28k and cholecystokinin coexisted in 12.5% and 21.2% of the calbindin D28k and cholecystokinin-immunoreactive cells, respectively. In other regions of the hippocampal formation, the two markers coexisted in less than 5% of the cells of either type. The present results demonstrate that calbindin D28k-, parvalbumin- and cholecystokinin-containing nonpyramidal cells represent largely nonoverlapping cell populations and may thus be involved in different inhibitory circuits.     

Phase relations of hippocampal projection cells and interneurons to theta activity in the anesthetized rat

The correlation between cell firing and hippocampal theta activity was studied with the spike-triggered averaging method in rats anesthetized with urethane. Projection cells in the CA1 region and the dentate gyrus fired with highest probability on the negative phase of the theta waves recorded from the corresponding regions. CA1 interneurons discharged mainly on the positive phase. In the dentate gyrus about half of the interneurons fired on the negative phase, while the remaining half discharged preferentially on the positive phase of the locally derived theta waves. It was suggested that septal theta ‘pacemaker’ cells directly excite hippocampal interneurons which in turn rhythmically inhibit a large number of projection cells.     

Afferent and efferent synaptic connections of somatostatin-immunoreactive neurons in the rat fascia dentata

The aim of this study was to determine whether somatostatin (SS)-immunoreactive neurons of the rat fascia dentata are involved in specific excitatory circuitries that may result in their selective damage in models of epilepsy. Synaptic connections of SS-immunoreactive neurons were determined at the electron microscopic level by using normal and colchicine pretreated rats. Vibratome sections prepared from both fascia dentata of control animals and from rats that had received an ipsilateral lesion of the entorhinal cortex 30-36 hours before sacrifice were immunostained for SS by using a monoclonal antibody (SS8). Correlated light and electron microscopic analysis demonstrated that many SS-immunoreactive neurons in the hilus send dendritic processes into the outer molecular layer of the fascia dentata, and dendrites of the same neurons occupy broad areas in the dentate hilar area. The majority of SS-immunoreactive axon terminals form symmetric synapses with the granule cell dendrites in the outer molecular layer and also innervate deep hilar neurons. Via their dendrites in the outer molecular layer, the SS-immunoreactive neurons receive synaptic inputs from perforant pathway axons which were identified by their anterograde degeneration following entorhinal lesions. The axons from the entorhinal cortex are the first segment of the main hippocampal excitatory loop. The hilar dendrites of the same SS-immunoreactive cells establish synapses with the mossy axon collaterals which represent the second member in this excitatory neuronal chain. These observations suggest that SS-immunoreactive neurons in the dentate hilar area may be driven directly by their perforant path synapses and via the granule cells which are known to receive a dense innervation from the entorhinal cortex. These observations demonstrate that SS-immunoreactive neurons in the hilar region are integrated in the main excitatory impulse flow of the hippocampal formation.     

Morphology of identified interneurons in the CA1 regions of guinea pig hippocampus

Identified interneurons in the CA1 region of guinea pig hippocampus were examined using light and electron microscopic (EM) techniques. The HRP was intracellularly injected into cells, recorded in the in vitro slice preparation, which met physiological criteria for interneurons. These neurons were characterized at the light and electron microscopic level, and used as standards for identifying interneurons which had not been HRP-labeled. Pyramidal basket cell somata were found in stratum oriens and stratum pyramidale; they were easily identifiable by their convoluted nucleus, dense endoplasmic reticulum, and numerous organelles. Aspinous dendrites reached into stratum oriens, where they received profuse synaptic input (primarily asymmetric synapses). Many of the asymmetric synapses degenerated following commissural lesions, suggesting that much of the input to interneurons was from extrinsic afferents. Dendrites were characterized by their spindled appearance, especially at distal sites. They showed postsynaptic degenerative changes following commissural lesions. Interneuron axons were extremely fine, with regular enlargements or "beads" which made apparent synaptic contacts primarily on pyramidal cell somata. The axon of a single, HRP-injected interneuron made many apparent contacts on large numbers of pyramidal cells; axons arborized over distances of several hundred micra within stratum pyramidale. This study provides direct evidence that neurons, with an identified inhibitory interneuron function in hippocampus, can mediate feed-forward as well as feed-back (recurrent) inhibition. Interneuron output showed extreme divergence, with influence over large distances. The high density of intracellular organelles in these cells suggested high metabolic activity and demand, perhaps making these interneurons exceptionally vulnerable to trauma-induced damage.     

Model-wise and point-wise random sample consensus for robust regression and outlier detection

Popular regression techniques often suffer at the presence of data outliers. Most previous efforts to solve this problem have focused on using an estimation algorithm that minimizes a robust M-estimator based error criterion instead of the usual non-robust mean squared error. However the robustness gained from M-estimators is still low. This paper addresses robust regression and outlier detection in a random sample consensus (RANSAC) framework. It studies the classical RANSAC framework and highlights its model-wise nature for processing the data. Furthermore, it introduces for the first time a point-wise strategy of RANSAC. New estimation algorithms are developed following both the model-wise and point-wise RANSAC concepts. The proposed algorithms’ theoretical robustness and breakdown points are investigated in a novel probabilistic setting. While the proposed concepts and algorithms are generic and general enough to adopt many regression machineries, the paper focuses on multilayered feed-forward neural networks in solving regression problems. The algorithms are evaluated on synthetic and real data, contaminated with high degrees of outliers, and compared to existing neural network training algorithms. Furthermore, to improve the time performance, parallel implementations of the two algorithms are developed and assessed to utilize the multiple CPU cores available on nowadays computers.     

Neurovascular coupling in rat brain operates independent of hemoglobin deoxygenation

Recently, a universal, simple, and fail-safe mechanism has been proposed by which cerebral blood flow (CBF) might be coupled to oxygen metabolism during neuronal activation without the need for any tissue-based mechanism. According to this concept, vasodilation occurs by local erythrocytic release of nitric oxide or ATP wherever and whenever hemoglobin is deoxygenated, directly matching oxygen demand and supply in every tissue. For neurovascular coupling in the brain, we present experimental evidence challenging this view by applying an experimental regime operating without deoxy-hemoglobin. Hyperbaric hyperoxygenation (HBO) allowed us to prevent hemoglobin deoxygenation, as the oxygen that was physically dissolved in the tissue was sufficient to support oxidative metabolism. Regional CBF and regional cerebral blood oxygenation were measured using a cranial window preparation in anesthetized rats. Hemodynamic and neuronal responses to electrical forepaw stimulation or cortical spreading depression (CSD) were analyzed under normobaric normoxia and during HBO up to 4 ATA (standard atmospheres absolute). Inconsistent with the proposed mechanism, during HBO, CBF responses to functional activation or CSD were unchanged. Our results show that activation-induced CBF regulation in the brain does not operate through the release of vasoactive mediators on hemoglobin deoxygenation or through a tissue-based oxygen-sensing mechanism.     

Entorhinal cortical innervation of parvalbumin-containing neurons (basket and chandelier cells) in the rat ammon's horn

Physiological data suggest that in the CA1–CA3 hippocampal areas of rats, entorhinal cortical efferents directly influence the activity of interneurons, in addition to pyramidal cells. To verify this hypothesis, the following experiments were performed: 1) light microscopic double-immunostaining for parvalbumin and the anterograde tracer Phaseolus vulgaris-leucoagglutinin injected into the entorhinal cortex; 2) light and electron microscopic analysis of cleaved spectrin-immunostained (i.e., degenerating axons and boutons) hippocampal sections following entorhinal cortex lesion; and 3) an electron microscopic study of parvalbumin-immunostained hippocampal sections after entorhinal cortex lesion. The results demonstrate that in the stratum lacunosum-moleculare of the CA1 and CA3 regions, entorhinal cortical axons form asymmetric synaptic contacts on parvalbumin-containing dendritic shafts. In the stratum lacunosum-moleculare, parvalbumin-immunoreactive dendrites represent processes of GABAergic, inhibitory basket and chandelier cells; these interneurons innervate the perisomatic area and axon initial segments of pyramidal cells, respectively. A feed-forward activation of these neurons by the entorhinal input may explain the strong, short-latency inhibition of pyramidal cells. © 1996 Wiley-Liss, Inc.