MR image segmentation using vector decomposition and probability techniques: A general model and its application to dual-echo images

A general model is developed for segmenting magnetic resonance images using vector decomposition and probabilfty techniques. Each voxel is assigned fractional volumes of q tissues from p differently weighted images (q ≤ p + 1) in the presence of partial-volume mixing, random noise, and other tissues. Compared wtth the eigenimage method, fewer differently weighted images are needed for segmenting the q tissues, and the contrast-to-noise ratio in the calculated fractional volumes is improved. The model can produce com-posrte tissue-type images similar to that of the probability methods, by comparing the fractional volumes assigned to different tissues on each voxel. A three-tissue (p = 2, q = 3) model is illustrated for segmenting three tissues from dual-echo images. M provides statistical analysis to the algebraic method. A three-compartment phantom is segmented for validation. Two clinical examples are presented.     

The Effect of Quisqualic Acid-Induced Lesions of the Nucleus Basalis Magnocellularis on Latent Inhibition

Latent inhibition (LI) is a reduction in the rate of acquisition of a Pavlovian conditioned response that results from prior nonreinforced preexposure to a conditioned stimulus (CS). LI has been suggested to reflect the operation of mechanisms involved in stimulus selection for subsequent cognitive processing. The present experiment was conducted to assess the effect of bilateral lesions of the nucleus basalis magnocellularis (NBM) on LI employing a conditioned emotional response paradigm. Bilateral lesions of the NBM were produced by administration of 0.12 M quisqualic acid and resulted in decreased cortical acetylcholinesterase staining, as well as a 40% reduction in cortical choline acetyltransferase activity. Following lever press training, preexposed animals received 40 presentations of a 60-s tone CS. Nonpreexposed animals received no tone presentations. Acquisition of conditioned suppression was then assessed over the course of 4 tone-shock (0.6 mA, 0.5 s) pairings. Control, preexposed animals displayed a retarded rate of acquisition in comparison to nonpreexposed controls, thereby demonstrating that the parameters used in the present experiment produced LI. In contrast, lesioned animals preexposed to the CS acquired conditioned suppression as readily as non-preexposed lesioned animals. However, the acquisition of conditioned suppression in both lesioned groups was found to be similar to that displayed in the preexposed control group. This pattern of results was interpreted as being attributable to a lesion-induced impairment in the ability to maintain stimulus processing, rather than a deficit in the ability to filter a stimulus. Copyright © 1996 Elsevier Science Inc.     

Advances in processing of surface myoelectric signals: Part 1

During sustained voluntary or electrically elicted muscle contractions the surface myoelectric signal is nonstationary and it undergoes progressive changes reflecting the modifications of the motor unit action potentials and their propagation velocity. In particular, during sustained electrical stimulation, the evoked signals show progressive amplitude, time scaling and shape modification. The quantitative evaluation of these changes is important for non-invasive muscle characterisation and may be performed in either the time or frequency domain using parametric and nonparametric spectral analysis as well as alternative methodologies. The paper introduces the detection techniques, reviews and compares the methods of spectral estimation based on FFT and autoregressive models, and discusses their applications and limitations in extracting information from the surface myoelectric signal with particular regard to myoelectric manifestations of localised muscle fatigue during sustained contractions.     

Pixel value modification using RVG-4 automatic exposure compensation for instant high-contrast images

The RVG-4 permits automatic exposure compensation (AEC). The purpose of this investigation was to determine the effects of AEC on image contrast. Images were made either with or without a dental QA jaw phantom using a fixed image projection geometry. Exposures were 6.3 through 27.3 μC/kg using an X-ray generator operated at 70 kVp. Region of interest pixel value distributions were measured at tissue thicknesses in this phantom, and the average pixel values and signal-to-noise ratios (SNR) were calculated. The use of AEC without an object in place resulted in a disproportionate relationship between pixel value and exposure with a marked reduction in SNR. The use of AEC on under- and over-exposed images of the phantom simultaneously enhanced image contrast and reduced SNR. Thus, AEC provides a convenient and quick method for achieving high-contrast images with sub-optimal exposures, however, this could lead to inappropriate patient dosages if the function is used for over-exposed images. AEC reduces the SNR and produces disproportionate pixel values relative to exposure.     

中药饮片加工炮炙在临床中的意义

本文简述了中药炮炙的根据、原理、方法以及各种不同辅料和炮炙方法对饮片药性与作用的影响。说明不同的炮炙方法可以直接影响和改变中药的药性和作用,影响到临床疗效,因此,必须重视中药饮片的炮炙工作。以确保临床安全有效的用药。     

中国食管癌高发区食管原发性腺癌组织病理学研究Ⅰ．食管原发性腺癌的临床病理学分析

中国食管癌高发区河南省近１５年（１９８０～１９９４）病理确诊的７３６４例食管癌中，其中食管原发性腺癌（ＰＥＡ）２３９例，占３．２５％。通过对２３９例ＰＥＡ手术标本（包括早期癌２０例，其余为中、晚期癌）切片系统观察，指出中国食管癌高发区ＰＥＡ主要起源于食管固有腺体的各级导管部分。ＰＥＡ的病理组织学可分６型：腺导管癌（１０９例）、腺鳞癌（５４例）、腺样囊性癌（２９例）、粘液表皮样癌（２０例）、基底细胞样癌（１５例）、胃型腺癌（１２例）。每型的组织图象及预后均各有特点，提示ＰＥＡ组织学再分型有意义。     

Is it time to reconsider initial antibiotic treatment strategies for severe urinary tract infections in Europe?

Until recently, most reported cases of bacteraemia caused by multidrug-resistant strains of Enterobacteriacae producing an extended-spectrum beta-lactamase (ESBL) in Europe have been nosocomial in origin. However, increasing numbers of reports of community-acquired bacteraemia and urinary tract infection caused by ESBL-producing microorganisms suggest that the geographical origin of patients should be taken into account as a risk-factor for possible ESBL production. Early identification of patients at high-risk of infection with ESBL-producing microorganisms, based on their geographical origin and travel history, should help to optimise initial antibiotic treatment strategies for severe urinary tract infections in Europe.     

Phase-derivative analysis in MR angiography: Reduced Venc dependency and improved vessel wall detection in laminar and disturbed flow

A problem of current MRA techniques is the inability to accurately depict the vascular anatomy, particularly in areas of disturbed flow. Various reasons, such as intravoxel phase dispersion, saturation, temporal variations, and maximum intensity projection (MIP) nonlinearity, cause a wrong delineation of vessel boundaries. A phase contrast (PC)-based postprocessing operation, the phase derivative (PhD), is introduced to detect phase fluctuations indicating flow. Two-dimensional and three-dimensional angiographic reconstruction algorithms are presented. Mathematical formulas are derived to predict the effect of sampling to flow profiles and the effect on the PhD of these profiles. Numerical, phantom, and preliminary in vivo experiments demonstrate that PhD images do not suffer from phase wraps and allow a velocity dynamic range extension only limited by a differential phase change. It is also shown that PhD MIPs produce higher signal-to-noise ratios than conventional PC angiograms and give a better impression of the anatomy of (stenotic) vessels and of their diameters for both laminar and disturbed flow.