基于小波的医学超声图像斑点噪声抑制方法

斑点噪声是超声图像中固有的噪声。本文提出了一种新的去除斑点噪声的方法，这种方法结合中值滤波和多尺度非线性小波软阈值的优点，首先把原网像进行对数转换，然后把对数转换后的图像进行中值滤波处理，从而把转换后的图像分成两部分，对每一部分进行小波分析，假设小波系数服从广义高斯分布（GGD），利用小波系数的统计特性估计出各个部分各个尺度的阈值，最后用软阈值方法对上述两部分分别去噪。实验结果表明，本文提出的方法在有效去除斑点噪声方面，优于中值滤波，维纳滤波和多尺度非线性阈值算法（MSSNT-A）。     

Biased cell migration of fibroblasts exhibiting contact guidance in oriented collagen gels

We present here the first quantitative correlation for cell contact guidance in an oriented fibrillar network in terms of biased cell migration. The correlation is between the anisotropic cell diffusion parameter,D _A=D_x/D_y, and the collagen gel birefringence, Δn, a measure of axially biased collagen fibril orientation in thex-direction. The cell diffusion coefficients,D _x andD _y, measure the dispersal of cells in the directions coincident with and normal to the axis of fibril orientation, respectively. Three essential methodological components are involved: (i) exploiting the orienting effect of a magnetic field on collagen fibrils during fibrillogenesis to systematically prepare uniform axially oriented collagen gels; (ii) using a microscope/image analysis workstation with precise, computer-controlled rotating and translating stages to automate birefringence measurement and, along with rapid “coarse optical sectioning” via digital image processing, to enable 3-D cell tracking of many cells in multiple samples simultaneously; and (iii) employing a rigorous statistical analysis of the cell tracks to estimate the magnitude and precision of the direction-dependent cell diffusion coefficients,D _x andD _y, that defineD _A. We find that this measure of biased migration in contact guidance (D _A) increases with increasing collagen fibril orientation (Δn) due mainly to a rapid enhancement of migration along the axis of fibril orientation at low levels of fibril orientation, and to a continued suppression of migration normal to the axis of fibril orientation at high levels of fibril orientation.     

Real-time extraction of tissue impedance model parameters for electrical impedance spectrometer

This paper presents a new algorithm for real-time extraction of tissue electrical impedance model parameters from in vivo electrical impedance spectroscopic measurements. This algorithm was developed as a part of a system for muscle tissue ischemia measurements using electrical impedance spectroscopy. An iterative least square fitting method, biased with a priori knowledge of the impedance model was developed. It simultaneously uses both the real and imaginary impedance spectra to calculate tissue parameters R₀, R_∞, α and τ. The algorithm was tested with simulated data, and during real-time in vivo ischemia experiments. Experimental results were achieved with standard deviations of , σ_α=0.72%, and σ_τ=1.26%. On a Pentium II based PC, the algorithm converges to within 0.1% of the results in 17 ms. The results show that the algorithm possesses excellent parameter extraction capabilities, repeatability, speed and noise rejection.     

Effect of intracellular anisotropy on electrical source determination in a muscle fibre

Expressions are available for describing, quantitatively, the source associated with an action potential propagating along an excitatble fibre. For a nerve fibre one such expression defines an equivalent volume dipole density function τ(x) = − ∂/∂x (σ_i φ_i(x) − σ_e φ_e(x))a_x (where x is the axial co-ordinate, i is the intracellular and e the extracellular region, σ_i and σ_e are isotropic conductivities, ϕ the potential at the membrane, while axial symmetry is assumed), and this source fills the intracellular region. This source, as distinct from transmembrane current formulations, lies in a uniform, isotropic, extracellular, medium. Consequently, for a fibre bundle a simple superposition of sources, all lying in a uniform, isotropic, extracellular space, can be accomplished. However, for muscle fibres the presence of non-conducting myofibrils causes the intracellular space to be anisotropic. The paper describes the modification in the aforementioned expressions for the case of longitudinal and transverse propagation and extrapolation to an arbitrary angle of propagation. The resultant source continues to be expressed relative to a uniform, isotropic, extracellular medium.     

On the Mechanism of Antifibrillatory Effect of Afobazole

Effect of afobazole on the threshold of electrical fibrillation of the heart was studied on anesthetized rats with intact myocardium. It was shown that the drug considerably increased the threshold of electrical fi brillation of the heart, being not inferior to reference class I antiarrhythmic drugs (lidocaine and procainamide) according to V. Williamse classification. Against the background of preliminary injection of σ-receptor antagonist haloperidol, afobazole exhibited no antifibrillatory activity. These findings and analysis of published reports suggest that antifibrillatory activity of afobazole is determined by its antagonistic influence on σ₁-receptors localized in cardiomyocyte cytosol.     

Cardiac assessment mechanics: 1 Left ventricular mechanomyocardiography,a new approach to the detection of diseased myocardial elements and states

The inadequacies of currently employed methods for assessment of cardiac mechanics are discussed, and the need for development of more intrinsic assessment parameters is emphasised. To this end, a new technique is presented to enable determination of regional mechanical constitutive properties of the myocardium during diastole; this technique has been originally named left-ventricular mechanomyocardiography (or l.v.-m.m.c.g.). The data required for implementation of the techniques consist of left-ventricular sequential dynamic geometry and associated recorded chamber pressure. The method entails matching of the inner-boundary deformations of the instantaneous finite-element model of the left ventricle (which is loaded by the recorded instantaneous incremental pressure) with the actual instantaneous endocardial deformations (as derived from either cineangiocardiography or 2-dimensional echocardiography), to determine the regional distribution of the Young's modulus E_ne and the incremental stresses Δσ_ne (and hence the total stress σ_ne=∑_nΔσ_ne) of the myocardial elements. The mechanical constitutive properties of the myocardial elements can be then characterised by the constitutive relation E_ne=a+bσ. The constitutive parameters a and b have typical ranges for normal and pathological (ischaemic and infarcted) myocardial elements and hence can be employed to distinguish diseased elements. The values of a and b are calculated for normal and pathological subjects and their normal and pathological ranges are presented.     

Ex vivo biomechanical behavior of abdominal aortic aneurysm: Assessment using a new mathematical model

Knowledge of the biomechanical behavior of abdominal aortic aneurysm (AAA) as compared to nonaneurysmal aorta may provide information on the natural history of this disease. We have performed uniaxial tensile testing of excised human aneurysmal and nonaneurysmal abdominal aortic specimens. A new mathematical model that conforms to the fibrous structure of the vascular tissue was used to quantify the measured elastic response. We determined for each specimen the yield σ_y and ultimate σ_u strengths, the separate contribution to total tissue stiffness by elastin (E _E) and collagen (E _C) fibers, and a collagen recruitment parameter (A), which is a measure of the tortuosity of the collagen fibers. There was no significant difference in any of these mechanical properties between longitudinal and circumferential AAA specimens, nor inE _E andE _C between longitudinally oriented aneurysmal and normal specimens.A, σ_y, and σ_u were all significantly higher for the normal than for the aneurysmal group:A=0.223±0.046versus A=0.091±0.009 (mean ± SEM;p<0.0005), σ_y versus σ_y (p<0.05), and σ_u versus σ_u (p<0.0005), respectively. Our findings suggest that the AAA tissue is isotropic with respect to these mechanical properties. The observed difference inA between aneurysmal and normal aorta may be due to the complete recruitment and loading of collagen fibers at lower extensions in the former. Our data indicate that AAA rupture may be related to a reduction in tensile strength and that the biomechanical properties of AAA should be considered in assessing the severity of an individual aneurysm.     

Non-invasive imaging of optical parameters of biological tissues

The normalised back-scattered intensity (NBI) profiles at various locations on the forearms of ten human subjects were obtained by moving the multi-probe of a laser reflectometer. The statistical analysis of the NBI data showed that the variation in the NBI was significantly higher at the ulnar region compared with that at other regions. For determination of the scattering (μ _s ) and absorption (μ _a ) coefficients and the anisotropy parameter g at each location on the forearm, these profiles were matched with the NBI profiles simulated by a Monte Carlo procedure (χ _0.99 ² ). For the reconstruction of images of variation of these parameters, the averaged values ofμ _a ,μ _s and g at all locations on the forearms of the subjects were determined. The absorption coefficient had a minimum (1.92 cm⁻¹) and maximum (2.21 cm⁻¹) at the wrist and the lateral region of the forearm, respectively. The scattering coefficient had a maximum (194 cm⁻¹) at the medial side and near the elbow, and a minimum (186 cm⁻¹) at the lateral side of the forearm. Similar changes in the anisotropy parameter were also observed. By interpolation of the data of each parameter on a 100×100 image matrix and after median filtering, colour-coded images of the variation in the optical parameters were constructed. These images could be useful for diagnostic and therapeutic applications of lasers.     

Model of electrical conductivity of skeletal muscle based on tissue structure

Recent experiments carried out in our laboratory with the four-electrode method showed that the electrical conductivity of skeletal muscle tissue depends on the frequency of the injected current and the distance between the current electrodes. A model is proposed in order to study these effects. The model takes into account the structure of the tissue on the scale of individual fibres. It discerns three main components with respect to electrical properties: (a) extracellular medium with electrical conductivity σ_e; (b) intracellular medium with electrical conductivity σ_i; (c) muscle fibre membrane with impedance Z_m. The model results show an apparent frequency dependence of the electrical conductivity of skeletal muscle tissue, as well as the way the conductivity is affected by the length the current is conducted.     

Quaternion-based strap-down integration method for applications of inertial sensing to gait analysis

The proposed strap-down integration method exploits the cyclical nature of human gait: during the gait swing phase, the quaternion-based attitude representation is integrated using a gyroscope from initial conditions that are determined during stance by an accelerometer. Positioning requires double time integration of the gravity-compensated accelerometer signals during swing. An interpolation technique applied to attitude quaternions was developed to improve the accuracy of orientation and positioning estimates by accounting for the effect of sensor bias and scale factor drifts. A simulation environment was developed for the analysis and testing of the proposed algorithm on a synthetic movement trajectory. The aim was to define the true attitude and positioning used in the computation of estimation errors. By thermal modelling, the changes of bias and scale factor of the inertial sensors, calibrated at a single reference temperature, were analysed over a range of ±10°C, for measurement noise standard deviations up to σ_g = 2.5° s⁻¹ (gyroscope) and σ_a = 0.05 m s⁻¹ (accelerometer). The compensation technique reduced the maximum root mean square errors (RMSEs) to: RMSE_θ=14.6° (orientation) and RMSE_d=17.7 cm (positioning) for an integration interval of one gait cycle (an improvement of 3° and 7 cm); RMSE_θ=14.8° and RMSE_d=30.0 cm for an integration interval of two gait cycles (an improvement of 11° and 262 cm).     

Sorption of ethylene oxide by medical polymers

Conclusions 1. Sorption capacities have been measured for some polymer materials used in medical components in relation to E0 as sterilizing gas. 2. Effective sorption coefficients for E0 have been calculated for these materials. 3. The values of σ_ef lead to the recommendation that polyethylene and silicone rubbers should be used preferentially for components of apparatus that is to be gas sterilized. These rubbers have a fairly high sorption (close to that for natural rubber), but they differ from other rubbers in having very high diffusion coefficients [2], so they are degassed rapidly. 4. The effective sorption coefficients enable one to calculate the equilibrium E0 sorption by a polymer for various E0 concentrations and temperatures within the range examined. All-Union Disinfection and Sterilization Research Institute, Ministry of Health of the USSR, Moscow. Translated from Meditsinskaya Tekhnika, No. 6, pp. 46–48, November–December, 1982.     

The effect of physical conditioning on antipyrine clearance

The effects of physical conditioning on antipyrine clearance were studied in two groups of subjects. Healthy men not engaged in the systematic practice of any sport were compared with endurance runners (defined as men running >80 km/week). Studies were carried out at three different periods of the annual plan training at 4-month intervals. Antipyrine was administered orally and pharmacokinetic parameters were obtained from saliva samples by the multiple-sample method. Endurance performance, expressed in terms of the maximal oxygen uptake (V˙O_{2 max}), the ventilatory threshold and the 4-mM · l⁻¹ lactate threshold (OBLA), was higher in trained than in control subjects at each of the three periods. Antipyrine clearance was also significantly elevated and antipyrine half-life reduced in runners during all periods. No significant difference in V˙O_{2 max} or antipyrine clearance was found between the various periods in either trained or control subjects. Both ventilatory threshold and OBLA increased significantly along the training period in conditioned subjects. Significant correlations were found between antipyrine clearance and V˙O_{2 max}, ventilatory threshold and OBLA. In summary, these results indicate an association between aerobic conditioning and increased hepatic oxidative metabolism of low-clearance drugs. Accepted: 15 July 1997     

Dynamic model of the short-term regulation of arterial pressure in the cat

The purpose of this study was to characterise the dynamics of the short-term control of arterial pressure in the cat with the aid of a model consisting of a nonlinear negative-feedback control system. The arterial system was described by a three element windkessel model (peripheral resistance, R, aortic characteristic impedance, R_c, and total arterial compliance, C). The resistance regulation was represented by a second-order system with static gain G_R, a damping factor σ and an undamped natural frequency ω_n. The resistance gain, G_R, and the windkessel parameters were obtained from measurements of aortic and venous pressures and cardiac output in two steady states. The parameters σ and ω_n were estimated from mean pressure and mean flow during the transient from control to the new steady state. Pressure reductions averaged 10 per cent and resistance changes averaged 12 per cent. Average windkessel model parameters in the control condition were: C=(25·9±6·1) 10⁻⁶ g⁻¹ cm⁴ s², R_c=(2·51±0·53) 10³ g cm⁻⁴ s⁻¹, R=(40·9±9·8) 10³ g cm⁻⁴ s⁻¹. Average estimates of parameters of the resistance regulator were: G_R=(4·14±2·38) 10⁻³ min ml⁻¹, ω_n = 1·0 ± 1·0 rad s⁻¹, σ=0·41±0·19. A satisfactory fit was found between model predicted and measured pressure. The results suggest that the dynamic short-term control of pressure is underdamped and oscillatory. The amplitude of these oscillations is affected by arterial compliance, suggesting an interaction between the arterial system and short-term resistance regulation.     

Estimation of the retainer height biomechanical contribution in posterior resin-bonded fixed partial dentures: a structural-thermal coupled finite element analysis

This study determines the RBFPD (resin-bonded fixed partial dentures) biomechanical aspects to retainer height using structural-thermal coupled finite element (FE) analysis under normal (37°C) and high (51°C) oral temperatures. Three RBFPD FE models with different retainer heights (100, 75, and 50% of the distance from 2 mm above the CE (cementum-enamel) junction to the occlusal surface) were created using image processing, contour stacking, and mapping mesh procedures. After FE model validation, the maximum first principal and von Mises stresses in the remaining tooth (σ_T) and prosthesis (σ_P), were recorded for all models under structural-thermal coupled analyses. The simulation results showed that the σ_T and σ_p values decreased with greater retainer height as a result of the increasing prosthesis stiffness and maximizing bonding area between the enamel and retainer at normal oral temperature (37°C). However, no significant stress differences were found according to the retainer height varying dimensions at high (51°C) temperatures. The RBFPD retainer height biomechanical response is dominated by the structural analysis result (at 37°C) and it is recommended that the prosthesis retainer have as great a height as possible to decrease the stress values.     

Information Entropy Measure for Evaluation of Image Quality

This paper presents a simple and straightforward method for synthetically evaluating digital radiographic images by a single parameter in terms of transmitted information (TI). The features of our proposed method are (1) simplicity of computation, (2) simplicity of experimentation, and (3) combined assessment of image noise and resolution (blur). Two acrylic step wedges with 0–1–2–3–4–5 and 0–2–4–6–8–10 mm in thickness were used as phantoms for experiments. In the present study, three experiments were conducted. First, to investigate the relation between the value of TI and image noise, various radiation doses by changing exposure time were employed. Second, we examined the relation between the value of TI and image blurring by shifting the phantoms away from the center of the X-ray beam area toward the cathode end when imaging was performed. Third, we analyzed the combined effect of deteriorated blur and noise on the images by employing three smoothing filters. Experimental results show that the amount of TI is closely related to both image noise and image blurring. The results demonstrate the usefulness of our method for evaluation of physical image quality in medical imaging.     

Experimental approach for testing the uncoupling between cardiovascular variability series

In cardiovascular variability analysis, the significance of the coupling between two series is commonly assessed by defining a zero level on the magnitude-squared coherence (MSC). Although the use of the conventional value of 0.5 does not consider the dependence of MSC estimates on the analysis parameters, a theoretical threshold T_t is available only for the weighted covariance (WC) estimator. In this study, an experimental threshold for zero coherence T_e was derived by a statistical test from the sampling distribution of MSC estimated on completely uncoupled time series. MSC was estimated by the WC method (Parzen window, spectral bandwidth B=0.015, 0.02, 0.025, 0.03 Hz) and by the parametric autoregressive (AR) method (model order M=4, 8, 12, 16), on time series with length L=180, 300, 420, 540s. T_e decreased with increasing B and L and with decreasing M (range: 3.11–0.54 for WC estimator, 0.06–0.46 for AR estimator). Values for the typical parameter settings of WC and AR estimation (B=0.025Hz; M=8; L=300s) were, respectively, 0.24 and 0.17. Moreover, T_t was always higher (range: 0.12–0.65) and the results were less dependable than those for T_e in defining the zero level of MSC. Thus, with the proposed method, the hypothesis of uncoupling is rejected by accounting for the parameters that affect the confidence of spectral and cross-spectral estimates. The broad applicability of this approach should favour its introduction for assessing the significance of the coupling between cardiovascular variability series.     

An improved matched filter for blood vessel detection of digital retinal images

The matched filter has been widely used in the detection of blood vessels of the human retina digital image. In this paper, the matched filter response to the detection of blood vessels is increased by proposing better filter parameters. These filter parameters are found by using an optimization procedure on 20 retina images of the DRIVE database. Comparisons with other approaches show that the matched filter that uses the newly found parameters outperforms the matched filter that uses the classical filter parameters as well as some vessel detection techniques. A technique is also discussed to find the best threshold value for the continuous matched filter output image and hence the best segmented vessel image.     

Detail-enhanced multimodality medical image fusion based on gradient minimization smoothing filter and shearing filter

In this paper, a detail-enhanced multimodality medical image fusion algorithm is proposed by using proposed multi-scale joint decomposition framework (MJDF) and shearing filter (SF). The MJDF constructed with gradient minimization smoothing filter (GMSF) and Gaussian low-pass filter (GLF) is used to decompose source images into low-pass layers, edge layers, and detail layers at multiple scales. In order to highlight the detail information in the fused image, the edge layer and the detail layer in each scale are weighted combined into a detail-enhanced layer. As directional filter is effective in capturing salient information, so SF is applied to the detail-enhanced layer to extract geometrical features and obtain directional coefficients. Visual saliency map-based fusion rule is designed for fusing low-pass layers, and the sum of standard deviation is used as activity level measurement for directional coefficients fusion. The final fusion result is obtained by synthesizing the fused low-pass layers and directional coefficients. Experimental results show that the proposed method with shift-invariance, directional selectivity, and detail-enhanced property is efficient in preserving and enhancing detail information of multimodality medical images.

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Graphical abstract The detailed implementation of the proposed medical image fusion algorithm.

     

Conductivity and geometrical factors affecting volume measurements with an impedancimetric catheter

With a model based on Poisson’s equation, computations employing published data and measurements made in glass cylinders filled with saline, the influence of conductivity and geometry on the determination of volume was analysed with an impedancimetric catheter. Two distal electrodes inject a constant current while a set of central electrodes sense by sections the potential along the cylindrical chamber. It was concluded that each section ought to be independently calibrated, the distribution of the electrodes along the catheter and its relationship to the chamber radius being of paramount importance for a linear calibration. The ratio σ _r , of the external medium conductivity σ _e to the internal conductivity σ _i influences drastically both the linearity and the calibration of each section. If a section volume is linearly related to the total chamber volume, that section admittance is a total volume estimator.     

Speckle reduction in ultrasound medical images using adaptive filter based on second order statistics

This article discusses an adaptive filtering technique for reducing speckle using second order statistics of the speckle pattern in ultrasound medical images. Several region-based adaptive filter techniques have been developed for speckle noise suppression, but there are no specific criteria for selecting the region growing size in the post processing of the filter. The size appropriate for one local region may not be appropriate for other regions. Selection of the correct region size involves a trade-off between speckle reduction and edge preservation. Generally, a large region size is used to smooth speckle and a small size to preserve the edges into an image. In this paper, a smoothing procedure combines the first order statistics of speckle for the homogeneity test and second order statistics for selection of filters and desired region growth. Grey level co-occurrence matrix (GLCM) is calculated for every region during the region contraction and region growing for second order statistics. Further, these GLCM features determine the appropriate filter for the region smoothing. The performance of this approach is compared with the aggressive region-growing filter (ARGF) using edge preservation and speckle reduction tests. The processed image results show that the proposed method effectively reduces speckle noise and preserves edge details.