Comparison of statistical methods in MR imaging

The problem of recovering the true underlying scene from a noisy image is considered. Several methods are compared empirically by applying them to magnetic resonance (MR) images. It turns out that a simple method, the Gaussian window filter, gives good results. This method requires only “instantaneous” processing.     

Comparison of imaging methods used for dental implant osseous integration assessment

Two different imaging techniques used to determine bone tissue response to dental implants were compared. Dental implants were implanted into the maxillae of 18 pigs, which were sacrificed after 4, 8 and 12 weeks. Implants with surrounding bone tissue were retrieved for methyl methacrylate histology and contact radiography. On identical sections peri-implant bone density and bone implant contact (BIC) ratio were assessed with two different imaging methods. Evaluation of Giemsa eosin stained and contact radiographed sections showed direct osseous integration for all implants and both methods showed a strong correlation with correlation coefficient r = 0.930 (P < 0.0001) for peri-implant bone density and r = 0.817 (P < 0.0001) for bone implant contact ratio. While the two imaging methods showed moderate differences for peri-implant bone density there were significant differences between the BIC values determined. In general, contact radiography tends to underestimate BIC for approximately 4.5 % (P = 0.00003).     

Small-kernel superresolution methods for microscanning imaging systems

Two computationally efficient methods for superresolution reconstruction and restoration of microscanning imaging systems are presented. Microscanning creates multiple low-resolution images with slightly different sample-scene phase shifts. The digital processing methods developed here combine the low-resolution images to produce an image with higher pixel resolution (i.e., superresolution) and higher fidelity. The methods implement reconstruction to increase resolution and restoration to improve fidelity in one-pass convolution with a small kernel. One method uses a small-kernel Wiener filter and the other method uses a parametric cubic convolution filter. Both methods are based on an end-to-end, continuous-discrete-continuous microscanning imaging system model. Because the filters are constrained to small spatial kernels they can be efficiently applied by convolution and are amenable to adaptive processing and to parallel processing. Experimental results with simulated imaging and with real microscanned images indicate that the small-kernel methods efficiently and effectively increase resolution and fidelity.     

Calculated microdosimetric characteristics of 125I and 103Pd brachytherapy seeds at different depths in water

Both (125)I and (103)Pd sources have been widely used in the permanent prostate implant. An important consideration for the choice of brachytherapy sources is the relative biological effectiveness (RBE) for the source/seed used in the implantation. As RBE is closely related to the microdosimetric parameter, it is desirable to calculate the dose mean lineal energies for both (125)I and (103)Pd at various radial distances to the seed surface. Monte Carlo simulation was performed for photons emitted from (125)I and (103)Pd. Energy depositions from photons and all their secondary electrons were tracked. Dose distributions of lineal energy, d(y), were calculated for spheres of 1 microm in diameter and at various radial distances to the seed surface. From the dose distribution of lineal energy, the dose mean lineal energy, y(D), was derived. The results showed that the radiation qualities are constant in the distance range from 0.5 to 5 cm. In this distance range, the quality factor, relative to gamma rays from (60)Co, is 2.2 for (125)I and 2.5 for (103)Pd.     

Comparison of distributed methods for resource allocation

Resource allocation problems aim to achieve certain goals or objectives by allocating resources. Traditionally, centralized methods are applied to such problems. However, the inherent, decentralized nature of many corporates/companies/factories drives the investigation on decentralized or distributed methods. This paper provides an overview of research activities in the field of distributed methods for resource allocation problems. We concentrate on classifying the resource allocation problems, comparing different methods and discussing how these different methods can be applied to the problems. Finally, a range of open issues and future challenges are highlighted.     

超疏水表面制备方法的比较

超疏水性是一种特殊的润湿性,它是指水滴与表面的静态接触角大于150°或者滑动角小于10°,其最初来源于"荷叶效应".本文对近几年关于超疏水理论和自然界中超疏水现象研究进行介绍,并对超疏水表面的制备方法及其应用进行综述.分别总结了基于模板法、涂覆法、刻蚀法的超疏水表面制备方案的优缺点及其改进措施,重点阐述超疏水表面在金属...     

Terahertz imaging: materials and methods

Terahertz (THz) imaging is rapidly developing. We present two new methods, based respectively on (a) a broadband thermal source (globar) and (b) a coherent, monochromatic source (optically-pumped THz laser). A room-temperature detector (Golay cell) is employed. Image quality is similar to that reported by others using more complex sources (quantum cascade lasers) and detectors (superconducting tunneling junctions).     

Comparison of stress field forming methods for vibro-acoustography

Vibro-acoustography is a method that produces images of the acoustic response of a material to a localized harmonic motion generated by ultrasound radiation force. The low-frequency, oscillatory radiation force (e.g., 10 kHz) is produced by amplitude modulating a single ultrasound beam, or by interfering two beams of slightly different frequencies. Proper beam forming for the stress field of the probing ultrasound is very important because it determines the resolution of the imaging system. Three beam-forming geometries are studied: amplitude modulation, confocal, and x-focal. The amplitude of radiation force on a unit point target is calculated from the ultrasound energy density averaged over a short period of time. The profiles of radiation stress amplitude on the focal plane and on the beam axis are derived. The theory is validated by experiments using a small sphere as a point target. A laser vibrometer is used to measure the velocity of the sphere, which is proportional to the radiation stress exerted on the target as the transducer is scanned over the focal plane or along the beam axis. The measured velocity profiles match the theory. The theory and experimental technique may be useful in future transducer design for vibro-acoustography.     

Comparison of neural networks and regression-based methods for temperature retrievals

Two methods for performing clear-air temperature retrievals from simulated radiances for the Atmospheric Infrared Sounder are investigated. Neural networks are compared with a well-known linear method in which regression is performed after a change of bases. With large channel sets, both methods can rapidly perform clear-air retrievals over a variety of climactic conditions with an overall RMS error of less than 1 K. The Jacobian of the neural network is compared with the Jacobian (the regression coefficients) of the linear method, revealing a more fine-scale variation than expected from the underlying physics, particularly for the neural net. Some pragmatic information concerning the application ofneural nets to retrieval problems is also included.     

Comparison of passive ranging integral imaging and active imaging digital holography for three-dimensional object recognition

We present an overview of three-dimensional (3D) object recognition techniques that use active sensing by interferometric imaging (digital holography) and passive sensing by integral imaging. We describe how each technique can be used to retrieve the depth information of a 3D scene and how this information can then be used for 3D object recognition. We explore various algorithms for 3D recognition such as nonlinear correlation and target distortion tolerance. We also provide a comparison of the advantages and disadvantages of the two techniques.     

In vivo optical imaging and dynamic contrast methods for biomedical research

This paper provides an overview of optical imaging methods commonly applied to basic research applications. Optical imaging is well suited for non-clinical use, since it can exploit an enormous range of endogenous and exogenous forms of contrast that provide information about the structure and function of tissues ranging from single cells to entire organisms. An additional benefit of optical imaging that is often under-exploited is its ability to acquire data at high speeds; a feature that enables it to not only observe static distributions of contrast, but to probe and characterize dynamic events related to physiology, disease progression and acute interventions in real time. The benefits and limitations of in vivo optical imaging for biomedical research applications are described, followed by a perspective on future applications of optical imaging for basic research centred on a recently introduced real-time imaging technique called dynamic contrast-enhanced small animal molecular imaging (DyCE).     

Comparison of methods for auto-coding causation of injury narratives

Manually reading free-text narratives in large databases to identify the cause of an injury can be very time consuming and recently, there has been much work in automating this process. In particular, the variations of the naïve Bayes model have been used to successfully auto-code free text narratives describing the event/exposure leading to the injury of a workers’ compensation claim. This paper compares the naïve Bayes model with an alternative logistic model and found that this new model outperformed the naïve Bayesian model. Further modest improvements were found through the addition of sequences of keywords in the models as opposed to consideration of only single keywords. The programs and weights used in this paper are available upon request to researchers without a training set wishing to automatically assign event codes to large data-sets of text narratives. The utility of sharing this program was tested on an outside set of injury narratives provided by the Bureau of Labor Statistics with promising results.     

Standardized methods for assessing the imaging quality of intraocular lenses

The relative merits of three standardized methods for assessing the imaging quality of intraocular lenses are discussed based on theoretical modulation-transfer-function calculations. The standards are ANSI Z80.7 1984 from the American National Standards Institute, now superseded by ANSI Z80.7 1994, and the proposed ISO 11979-2 from the International Organization for Standardization. They entail different test configurations and approval limits, respectively: 60% resolution efficiency in air, 70% resolution efficiency in aqueous humor, and 0.43 modulation at 100 line pairs/mm in a model eye. The ISO working group found that the latter corresponds to 60% resolution efficiency in air in a ring test among eight laboratories on a sample of 39 poly(methyl) methacrylate lenses and four silicone lenses spanning the power (in aqueous humor) range of 10-30 D. In both ANSI Z80.7 1994 and ISO 11979-2, a 60% resolution efficiency in air remains an optional approval limit. It is concluded that the ISO configuration is preferred, because it puts the intraocular lens into the context of the optics of the eye. Note that the ISO standard is tentative and is currently being voted on.     

网络系统可靠性近似估算方法的对比研究

在讨论了网络系统可靠性计算难题的基础上，以满足工程实际的精度需要并减少分析计算工作量为目标，对现有的4种近似估算网络系统可靠性的方法进行了分析，指出了各种方法产生误差的原因，定性分析了有关方法为减少误差所采取措施的合理性。针时2种不同复杂程度的典型网络系统，通过数值算例，给出了单元可靠度不同情形下的系统可靠度计算值；与精确算法时比之后，得到了量化的误差．基于对各方法的工作量和误差的综合分析，给出了具有工程指导意义的建议．     

Comparison of three flaw-location methods for automated ultrasonic testing

Two well-known methods for locating flaws by measurement of the transit time of ultrasonic pulses are examined theoretically. It is shown that neither is sufficiently reliable for use in automated ultrasonic testing. A third method, which takes into account the shape of the sound field from the probe and the uncertainty in measurement of probe-flaw distance and probe position, is introduced. An experimental comparison of the three methods indicates that use of the advanced method results in more accurate location of flaws.     

Comparison of direct blind deconvolution methods for motion-blurred images

Direct methods for restoration of images blurred by motion are analyzed and compared. The term direct means that the considered methods are performed in a one-step fashion without any iterative technique. The blurring point-spread function is assumed to be unknown, and therefore the image restoration process is called blind deconvolution. What is believed to be a new direct method, here called the whitening method, was recently developed. This method and other existing direct methods such as the homomorphic and the cepstral techniques are studied and compared for a variety of motion types. Various criteria such as quality of restoration, sensitivity to noise, and computation requirements are considered. It appears that the recently developed method shows some improvements over other older methods. The research presented here clarifies the differences among the direct methods and offers an experimental basis for choosing which blind deconvolution method to use. In addition, some improvements on the methods are suggested.     

Comparison of multivariate statistical methods for dynamic systems modeling

In this paper two multivariate statistical methodologies are compared in order to estimate a multi‐input multi‐output transfer function model in an industrial polymerization process. In these contexts, process variables are usually autocorrelated (i.e. there is time‐dependence between observations), posing some problems to classical linear regression models. The two methodologies to be compared are both related to the analyses of multivariate time series: Box‐Jenkins methodology and partial least squares time series. Both methodologies are compared keeping in mind different issues, such as the simplicity of the process modeling (i.e. the steps of the identification, estimation and validation of the model), the usefulness of the graphical tools, the goodness of fit, and the parsimony of the estimated models. Real data from a polymerization process are used to illustrate the performance of the methodologies under study. Copyright © 2010 John Wiley & Sons, Ltd.