Three methods for determining anteversion and retroversion of a total hip prosthesis.

Three new methods to assess the degree of anteversion or retroversion of the femoral component of a total hip prosthesis are described. Compared with previously described methods, the new methods make few physical demands on the recently operated patient. The only requirement is that the affected femur be held in a neutral position parallel to the x-ray table. The methods are relatively easy to perform and are accurate and objective.     

Implications of bulk motion for diffusion-weighted imaging experiments: effects, mechanisms, and solutions

This review article describes the effect of bulk motion on diffusion-weighted imaging experiments, and examines methods for correcting the resulting artifacts. The emphasis throughout the article is on two-dimensional imaging of the brain. The effects of translational and rotational motion on the MR signal are described, and the literature concerning pulsatile brain motion is examined. Methods for ameliorating motion effects are divided into three generic categories. The first is methods that should be intrinsically insensitive to macroscopic motion. These include motion-compensated diffusion-weighting schemes, single-shot EPI, projection reconstruction, and line scanning. Of these, only single-shot EPI and projection reconstruction methods can obtain high-quality images without compromising on sensitivity. The second category of methods is those that can be made insensitive to bulk motion. The methods examined here are FLASH and RARE. It is shown that for both sequences motion insensitivity is in general attained only at the cost of a 50% reduction in sensitivity. The final set of methods examined are those that correct for motion, primarily navigator echoes. The properties and limitations of the navigator echo approach are presented, as are those of methods which attempt to correct the acquired data by minimizing image artifacts. The review concludes with a short summary in which the current status of diffusion imaging in the presence of bulk motion is examined.     

Similar Acts or Facts as Evidence

The correct determination of time since death is an important goal in medico legal investigation. Recent advances in the methods for estimating time since death have enabled us to determine post-mortem interval more precisely. Since the 1850s, scientists have been working on different methods to determine post-mortem interval. Earlier methods were based on body cooling, rigor mortis, changes in the eye, putrefaction, supravital reactions, and contents of stomach. These methods were relatively crude and only an approximate time could be estimated. Due to the lack of precision the focus has now been shifted to biochemical methods. The biochemical methods are based on systematic pathophysiological changes and are found to be more accurate since the effect of external conditions is less. This review describes the various methods used for estimating time since death.     

New approaches to receiver operating characteristic methods in functional magnetic resonance imaging with real data using repeated trials.

Receiver operating characteristic (ROC) methods are useful tools for evaluating the sensitivity and specificity of various postprocessing algorithms used in fMRI data analysis. New ROC methods using real fMRI data are proposed that improve a previously introduced method by Le and Hu (Le and Hu, NMR Biomed 1997;10:160-164). The proposed methods provide more accurate means of estimating the true ROC curve from real data and thereby aid in the comparative evaluation of a wide range of postprocessing tools in fMRI. The mathematical relationships between different ROC curves are explored for a comparison of different ROC methods. Examples using real and simulated data are provided to illustrate the ideas involved.     

Principles of cerebral perfusion imaging by bolus tracking

The principles of cerebral perfusion imaging by the method of dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI) (bolus tracking) are described. The MRI signals underlying DSC-MRI are discussed. Tracer kinetics procedures are defined to calculate images of cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT). Two general categories of numerical procedures are reviewed for deriving CBF from the residue function. Procedures that involve deconvolution, such as Fourier deconvolution or singular value decomposition (SVD), are classified as model-independent methods because they do not require a model of the microvascular hemodynamics. Those methods in principle also yield a measure of the tissue impulse response function and the residue function, from which microvascular hemodynamics can be characterized. The second category of methods is the model-dependent methods, which use models of tracer transport and retention in the microvasculature. These methods do not yield independent measures of the residue function and may introduce bias when the physiology does not follow the model. Statistical methods are sometimes used, which involve treating the residue function as a deconvolution kernel and optimizing (fitting) the kernel from the experimental data using procedures such as maximum likelihood. Finally, other hemodynamic indices that can be measured from DSC-MRI data are described.     

Comparison between computer tomography and ultrasound in abdominal and renal growing and displacing processes (author's transl)

The advantages and limitations of both methods are analyzed and compared. The comparison is effected on the basis of the present standard of equipment. The results obtained with both methods are demonstrated by means of the example of frequent epigastric diseases. Despite the still limited number of patients examined simultaneously both by ultrasound and computer tomography, it seems that the sensitivity of both methods in case of growing and displacing processes in the epigastric or renal regions, does not differ greatly. A comparison of the specificity of both methods will be effected only after a large number of patients has been examined by both methods at the same time.     

Bayesian parallel imaging with edge-preserving priors.

Existing parallel MRI methods are limited by a fundamental trade-off in that suppressing noise introduces aliasing artifacts. Bayesian methods with an appropriately chosen image prior offer a promising alternative; however, previous methods with spatial priors assume that intensities vary smoothly over the entire image, resulting in blurred edges. Here we introduce an edge-preserving prior (EPP) that instead assumes that intensities are piecewise smooth, and propose a new approach to efficiently compute its Bayesian estimate. The estimation task is formulated as an optimization problem that requires a nonconvex objective function to be minimized in a space with thousands of dimensions. As a result, traditional continuous minimization methods cannot be applied. This optimization task is closely related to some problems in the field of computer vision for which discrete optimization methods have been developed in the last few years. We adapt these algorithms, which are based on graph cuts, to address our optimization problem. The results of several parallel imaging experiments on brain and torso regions performed under challenging conditions with high acceleration factors are shown and compared with the results of conventional sensitivity encoding (SENSE) methods. An empirical analysis indicates that the proposed method visually improves overall quality compared to conventional methods.     

Further considerations on the basis of the Ellis-formula and its application (author's transl)]

Computational methods for the determination of normal tissue tolerance under various modes of dose fractionation are applied at many radiation therapy installations. The methods differ in details, but most are based on the Ellis-formula. A survey of the relevant quantities and relations is given in order to facilitate comparison of the various methods. The established equations which are applicable to regular fractionation are related to the generalization of the Ellis-formula which is also applicable to irregular fractionation modes.     

The application of phase shifts in NMR for flow measurement

A brief overview of the history of the application of phase shifts in NMR, and in particular NMR imaging, is presented. The imaging methods include direct phase mapping, Fourier flow imaging (where the flow data are Fourier transformed into one dimension of an image), and alternative methods, where flow-related phase shifts are utilized for flow measurement from the magnitude of the signal. A discussion then follows of the principal errors that can affect the accuracy of the various flow imaging techniques, with particular reference to the phase mapping methods that have been used extensively in our institution. The results from a number of experiments are included to illustrate the extent of the errors and methods of removing or minimizing these effects are suggested.     

More effective devices for teaching undergraduate radiology.

Two effective methods of teaching radiology to medical students are described. The Rotating Exhibit and Matching Displays methods allow students to master film facts by themselves and provide contact with the teaching radiologist for discussion of the film findings. Elements of participation, entertainment, variety, and discovery are features of these teaching techniques which supplement self-instructional methods.     

Review of methods for functional brain connectivity detection using fMRI

Since the mid of 1990s, functional connectivity study using fMRI (fcMRI) has drawn increasing attention of neuroscientists and computer scientists, since it opens a new window to explore functional network of human brain with relatively high resolution. A variety of methods for fcMRI study have been proposed. This paper intends to provide a technical review on computational methodologies developed for fcMRI analysis. From our perspective, these computational methods are classified into two general categories: model-driven methods and data-driven methods. Data-driven methods are a large family, and thus are further sub-classified into decomposition-based methods and clustering analysis methods. For each type of methods, principles, main contributors, and their advantages and drawbacks are discussed. Finally, potential applications of fcMRI are overviewed.     

基于Laplace方程的脑电逆问题求解方法

目的 针对近似于球形的脑生物医学电磁逆问题求解,以实现对脑电活动的源定位。方法 本文基于拉普拉斯方程给出由头皮测量脑电逆推皮层电位分布的两种方法,方法建立在无源似稳电场的基础上,可以逐层递推头皮下各层组织结构上的电位分布。结果 我们针对人头接近于球形或椭球形的特点,由给出的两种方法进行了仿真推演。结论仿真计算初步证明了方法的可行性。     

Critical remarks on gross alpha/beta activity analysis in drinking waters: Conclusions from a European interlaboratory comparison

The most common gross alpha/beta standard methods used for drinking water analysis are discussed, and sources of interferences are reviewed from a metrological point of view. Our study reveals serious drawbacks of gross methods on the basis of an interlaboratory comparison analyzing commercial mineral water samples with the participation of 71 laboratories. A proposal is made to obtain comparable measurement results using true standardized methods.     

Current diagnosis of dissecting aortic aneurysm

The prerequisites for proper treatment of a dissecting aneurysm are for the diagnosis to be established quickly and for the location and extent to be identified precisely. For this purpose, various partially complementary methods of examination in addition to the history and clinical findings are at our disposal: plain chest roentgenography, abdominal sonography, transthoracic and transesophageal echocardiography, computed tomography, magnetic resonance imaging and angiography. Thirty-one of our patients have been studied to assess the reliability of the different methods. The advantages, diagnostic criteria and limitations of the methods are discussed.     

Methodologic considerations in comparing imaging methods

Current methods for evaluating and comparing imaging methods may be inadequate in several important aspects. Prospective investigations often fail to provide uniform conditions for data collection due to variable physician skills in performing the studies being evaluated. The double-blind format, although seemingly objective, is inherently unable to prevent the effects of examiner or observer prejudice when imaging methods are being compared. Commonly used statistical terms are limited in their ability to characterize the clinical efficacy of imaging methods, and are easily misused. Reference examinations, or "gold standards," may be used in a manner preordaining an inferior result for the diagnostic method under evaluation. These problems are discussed and examples of their effects are presented. Suggestions are presented for minimizing existing methodologic limitations.     

A comparison of three established age estimation methods on an adult Spanish sample

Most current methods for adult skeletal age-at-death estimation are based on American samples comprising individuals of European and African ancestry. Our limited understanding of population variability hampers our efforts to apply these techniques to various skeletal populations around the world, especially in global forensic contexts. Further, documented skeletal samples are rare, limiting our ability to test our techniques. The objective of this paper is to test three pelvic macroscopic methods [(1) Suchey-Brooks; (2) Lovejoy; and (3) Buckberry and Chamberlain] on a documented modern Spanish sample. These methods were selected because they are popular among Spanish anthropologists and because they never have been tested in a Spanish sample. The study sample consists of 80 individuals (55 males and 25 females) of known sex and age from the Valladolid collection. Results indicate that in all three methods, levels of bias and inaccuracy increase with age. The Lovejoy method performs poorly (27%) compared with Suchey-Brooks (71%) and Buckberry and Chamberlain (86%). However, the levels of correlation between phases and chronological ages are low and comparable in the three methods (<0.395). The apparent accuracy of the Suchey-Brooks and Buckberry and Chamberlain methods is largely based on the broad width of the methods’ estimated intervals. This study suggests that before systematic application of these three methodologies in Spanish populations, further statistical modeling and research into the covariance of chronological age with morphological change are necessary. Future methods should be developed specific to various world populations and should allow for both precision and flexibility in age estimation.     

A proposed method for the automatic interpretation of images obtained by computer tomography]

A preliminary study is described relative to the possibility of using methods of automatic image interpretation in the field of biomedical images. These general methods are capable of recognizing characteristic shapes inside the image. In this paper the structures are described and interpreted. These methods are capable of outlining shapes which are important from a clinical point of view--e.g., spine, vertebrae. They can also evaluate the shapes by plausible methods, to explain the meaning of the whole image. A feasibility study is described concerning the automatic recognition of vertebral contour in axial CT images. The results suggest that the employed techniques can be used in real diagnostic applications.     

Magnetic resonance temperature imaging for guidance of thermotherapy

Continuous thermometry during a hyperthermic procedure may help to correct for local differences in heat conduction and energy absorption, and thus allow optimization of the thermal therapy. Noninvasive, three-dimensional mapping of temperature changes is feasible with magnetic resonance (MR) and may be based on the relaxation time T(1), the diffusion coefficient (D), or proton resonance frequency (PRF) of tissue water. The use of temperature-sensitive contrast agents and proton spectroscopic imaging can provide absolute temperature measurements. The principles and performance of these methods are reviewed in this paper. The excellent linearity and near-independence with respect to tissue type, together with good temperature sensitivity, make PRF-based temperature MRI the preferred choice for many applications at mid to high field strength (>/= 1 T). The PRF methods employ radiofrequency spoiled gradient-echo imaging methods. A standard deviation of less than 1 degrees C, for a temporal resolution below 1 second and a spatial resolution of about 2 mm, is feasible for a single slice for immobile tissues. Corrections should be made for temperature-induced susceptibility effects in the PRF method. If spin-echo methods are preferred, for example when field homogeneity is poor due to small ferromagnetic parts in the needle, the D- and T(1)-based methods may give better results. The sensitivity of the D method is higher that that of the T(1) methods provided that motion artifacts are avoided and the trace of D is evaluated. Fat suppression is necessary for most tissues when T(1), D, or PRF methods are employed. The latter three methods require excellent registration to correct for displacements between scans.     

Comparison of three radiochemical purity control methods of (99m)Tc-macroaggregated albumin

(99m)Tc-macroaggregated albumin is widely used to diagnose pulmonary embolism. To control the radiochemical purity of this radiopharmaceutical, three rapid control methods using filter, thin layer chromatography or centrifugation, are described in the academic literature. In this paper, the interactions between impurities and (99m)Tc-macroaggregated albumin were presented. For each control method, the influence of these interactions on the determination of the radiochemical purity of labeled macroaggregated albumin was evaluated. Then, a comparison of radiochemical purity obtained by these three methods was performed in normal condition and with different addition of pertechnetate. Finally, a correlation between these three methods was investigated. The results show a specificity difference between these three control methods. However in practice, this difference has no impact on the evaluation of the radiochemical purity of (99m)Tc-macroaggregated albumin by these three methods. In additions, methods are still correlated with pertechnetate additions in (99m)Tc-macroaggregated albumin suspension. Thus, this study demonstrates that these three control methods are exchangeable in radiopharmacy.