A new quality of bone ultrasound research

Quantitative ultrasound (QUS) methods have strong power to predict osteoporotic fractures, but they are also very relevant for the assessment of bone quality. A representative sample of recent studies addressing these topics can be found in this special issue. Further pursuit of these methods will establish micro-QUS imaging methods as tools for measuring specific aspects of bone quality. Once this is achieved, we will be able to link such data to the clinical QUS methods used in vivo to determine which aspects of bone quality cause QUS to be a predictor of fracture risk that is independent of bone mineral density (BMD). Potentially this could lead to the development of a new generation of QUS devices for improved and expanded clinical assessment. Good quality of basic science work will thus lead to good quality of clinical patient examinations on the basis of a more detailed assessment of bone quality.     

Review of relationships between physical measurements and user evaluation of image quality

Some of the findings of a review of the relationship between physical measurements and clinical image quality have been summarised. Mixed results were found: some studies had no relationship at presently typical dose levels, whereas others had a clear correlation between them. It is concluded that the various image quality evaluation tasks in an X-ray department are best done by different methods. Presently, exact physical measurements cannot supersede subjective evaluation in judging the acceptability of clinical images, whereas they are indispensable in specification and testing of technical performance.     

Subjective and objective measures of image quality in digital fluoroscopy

There are numerous methods for assessing image quality in diagnostic X ray. In our study we assessed how imaging quality assurance methods perform in practice. Physics assessments were based on IPEM protocols using Leeds test objects. Clinical assessment was based on a questionnaire. A total of 15 systems in three European locations were assessed, covering a range of image intensifier-TV digital fluoroscopy units. Analysis of 274 clinical questionnaires showed that clinical and physics assessments did not place systems in the same order, based on a given image quality parameter. In almost all the comparisons, low level correlation was measured for statistical comparison of rank order (rs < 0.3). However, broad agreement was observed between physics and clinical assessments for image quality associated with contrast and noise. This study emphasises the importance of maintaining links with clinical assessment, when developing quality assurance metrics, and measuring the mutual performance of clinical and physical assessments of image quality.     

Analysis of Approximate Inverses in Tomography I. Resolution Analysis of Common Inverses

The process of using physical data to produce images of important physical parameters is an inversion problem, and these are often called tomographic inverse problems when the arrangement of sources and receivers makes an analogy to x-ray tomographic methods used in medical imaging possible. Examples of these methods in geophysics include seismic tomography, ocean acoustic tomography, electrical resistance tomography, etc., and many other examples could be given in nondestructive evaluation and other applications. All these imaging methods have two stages: First, the data are operated upon in some fashion to produce the image of the desired physical quantity. Second, the resulting image must be evaluated in essentially the same timeframe as the image is being used as a diagnostic tool. If the resolution provided by the image is good enough, then a reliable diagnosis may ensue. If the resolution is not good enough, then a reliable diagnosis is probably not possible. But the first question in this second stage is always &;#x201C;How good is the resolution?&;#x201D; The concept of resolution operators and resolution matrices has permeated the geophysics literature since the work of Backus and Gilbert in the late 1960s. But measures of resolution have not always been computed as often as they should be because, for very data rich problems, these computations can actually be significantly more difficult/expensive than computing the image itself. It is the purpose of this paper and its companion (Part II) to show how resolution operators/matrices can be computed economically in almost all cases, and to provide a means of comparing the resolution characteristics of many of the common approximate inverse methods. Part I will introduce the main ideas and analyze the behavior of standard methods such as damped least-squares, truncated singular value decomposition, the adjoint method, backprojection formulas, etc. Part II will treat many of the standard iterative inversion methods including conjugate gradients, Lanczos, LSQR, etc.     

Derivation of the Lorentzian probability model for use in constrained image restoration

The Lorentzian nonlinear restoration algorithm is based on the empirical observation that the gradients in a general image have a Lorentzian probability density. In this paper an attempt is made to justify this observation by modelling the scene as a series of random sized features each with a random change in intensity across them. The high spatial frequency content of an image exists largely at edges and sharp features and is often lost due to aberrations in the optics of imaging systems. Nonlinear image restoration may be used to recover these frequencies, the most effective methods being constrained. In many nonlinear restoration techniques the amount of high spatial frequency content introduced into the restored image is uncontrolled. This problem has been overcome through the use of the Lorentzian algorithm, which imposes a statistical constraint on the distribution of gradients within the restored image. Images are presented to demonstrate the effectiveness of this method.     

Three-dimensional unconstrained and constrained image-reconstruction techniques applied to fluorescence, frequency-domain photon migration

The development of near-infrared (NIR) optical imaging for biomedical optical imaging is hampered by the computational intensiveness of large-scale three-dimensional (3-D) image reconstruction and the potential lack of endogenous contrast for detection of relevant tissue features. In this contribution the inverse optical imaging problem is formulated in three dimensions in a noncompressive geometry as a simple-bound constrained minimization problem in order to recover the interior fluorescence properties of exogenous contrast agent from frequency-domain photon migration measurements at the boundary. The solution of the forward optical diffusion problem for the frustum shape containing fluorescence inclusions of 10:1 contrast is accomplished by use of the Galerkin finite-element formulation. The inverse approach employs the truncated Newton method with trust region and a modification of automatic reverse differentiation to speed the computation of the optimization problem. The image-reconstruction results confirm that the constrained minimization may offer a more logical approach for the 3-D optical imaging problem than unconstrained optimization.     

Methods and materials for the measurement of subjective and objective measurements of image quality

The evaluation of medical imaging systems may be performed using both subjective (e.g. high contrast limiting resolution, and low contrast detail detectability), and objective/physical (e.g. characteristic curve, signal-to-noise ratio, modulation transfer function, and Wiener spectra) indices of image quality. For the purposes of Quality Assurance subjective measurements currently have a wider usage in the clinical environment due to the inherent simplicity of the measurements; however, more rigorous objective approaches are gaining acceptability, and represent a paradigm for possible future QA measurements. Both approaches have their advantages and disadvantages. There is currently wide debate as to the interpretation of these measurements. However, there appears to be a lack of standardisation among scientists in the various approaches to making these measurements, and especially so in the case of objective indices; furthermore, the measurement protocol used must have a bearing on the interpretation of subsequent results. The purpose of this paper is to (i) present the most fundamental indices in the characterisation of 'image quality', and (ii) recommend approaches to the measurement of these indices.     

Using categorisations of citations when assessing the outcomes from health research

Summary This paper describes an attempt to explore how far a categorisation of citations could be used as part of an assessment of the outcomes from health research. A large-scale project to assess the outcomes from basic, or early clinical, research is being planned, but before proceeding with such a project it was thought important to test and refine the developing methods in a preliminary study. Here we describe the development, and initial application, of one element of the planned methods: an approach to categorising citations with the aim of tracing the impact made by a body of research through several generations of papers. The results from this study contribute to methodological development for the large-scale project by indicating that: only for a small minority of citing papers is the cited paper of considerable importance; the number of times a paper is cited can not be used to indicate the importance of that paper to the articles that cite it; and self-citations could play an important role in facilitating the eventual outcomes achieved from a body of research.     

某光测设备上消像旋的设计

地平式光电成像跟踪测量设备进行目标观测时,由于物像空间旋转而产生像旋,使目标提取和测量出错。为消除像旋,先建立了以球面三角和坐标变换为基础的像旋模型,对像旋模型中各个变量的关系进行了分析,并简介了目前几种常用的消像旋的方法,提出一种采用 CCD相机旋转消像旋的设计思路,详细地描述了消像旋指标、单元结构和控制流程的设计过程,并在某光测设备上实现应用。厂内检测数据和在外场运行试验结果证明,采用 CCD相机旋转消像旋的设计达到设计指标,满足设计要求,保证了光电跟踪测量设备对目标的准确提取和稳定跟踪。     

Quality control measurements for fluoroscopy systems in eight countries participating in the SENTINEL EU coordination action

Quality control (QC) is becoming increasingly important in relation to the introduction of digital medical imaging systems using X rays. It was, therefore, decided to organise and perform a trial on image quality and physical measurements. The SENTINEL toolkit for QC measurements of fluoroscopy systems containing equipment and instructions for their use in the assessment of dose and image quality circulated among participants in the trial. The participants reported on their results. In the present contribution, the impact of the trial on the selected protocols is presented. The Medical Physics and Bioengineering protocol appeared to be useful for QC, and also for digital systems. The protocol needs an additional section, or an addition to each section, to state compliance with the requirements. The circular cross-sections of the Leeds test objects need adaptation for rectangular flat panel detector (FPD) systems. Only one participant was able to perform the monitor test using MoniQA. This is due to the fact that assistance is required from the suppliers of the X-ray systems. This problem needs to be solved to apply MoniQA in practice.     

Code aperture optimization for spectrally agile compressive imaging

Coded aperture snapshot spectral imaging (CASSI) provides a mechanism for capturing a 3D spectral cube with a single shot 2D measurement. In many applications selective spectral imaging is sought since relevant information often lies within a subset of spectral bands. Capturing and reconstructing all the spectral bands in the observed image cube, to then throw away a large portion of this data, is inefficient. To this end, this paper extends the concept of CASSI to a system admitting multiple shot measurements, which leads not only to higher quality of reconstruction but also to spectrally selective imaging when the sequence of code aperture patterns is optimized. The aperture code optimization problem is shown to be analogous to the optimization of a constrained multichannel filter bank. The optimal code apertures allow the decomposition of the CASSI measurement into several subsets, each having information from only a few selected spectral bands. The rich theory of compressive sensing is used to effectively reconstruct the spectral bands of interest from the measurements. A number of simulations are developed to illustrate the spectral imaging characteristics attained by optimal aperture codes.     

An efficient approach to converting three-dimensional image data into highly accurate computational models

Image-based meshing is opening up exciting new possibilities for the application of computational continuum mechanics methods (finite-element and computational fluid dynamics) to a wide range of biomechanical and biomedical problems that were previously intractable owing to the difficulty in obtaining suitably realistic models. Innovative surface and volume mesh generation techniques have recently been developed, which convert three-dimensional imaging data, as obtained from magnetic resonance imaging, computed tomography, micro-CT and ultrasound, for example, directly into meshes suitable for use in physics-based simulations. These techniques have several key advantages, including the ability to robustly generate meshes for topologies of arbitrary complexity (such as bioscaffolds or composite micro-architectures) and with any number of constituent materials (multi-part modelling), providing meshes in which the geometric accuracy of mesh domains is only dependent on the image accuracy (image-based accuracy) and the ability for certain problems to model material inhomogeneity by assigning the properties based on image signal strength. Commonly used mesh generation techniques will be compared with the proposed enhanced volumetric marching cubes (EVoMaCs) approach and some issues specific to simulations based on three-dimensional image data will be discussed. A number of case studies will be presented to illustrate how these techniques can be used effectively across a wide range of problems from characterization of micro-scaffolds through to head impact modelling.     

数字影像分辨率的均衡匹配

分辨率的匹配与均衡是数字影像高质量表现的关键。均衡匹配的方法是根据应用需要倒推获取加工该采用的分辨率以及辅之以必要的插值处理。确认输出设备是连续色调的还是非连续色调的，对分辨率的均衡至关重要。     

Major issues in quality assessment and improvement of clinical hyperbaric services: an international perspective.

The continued rapid worldwide diffusion of clinical hyperbaric facilities has substantially increased interest in clinical quality assessment and service improvement. This paper examines major issues, perspectives, and methods integral to the measurement and improvement of the quality of care provided to hyperbaric patients and their relevance and applicability across different societies. Special focus is directed toward the importance of quality assessment and improvement of clinical hyperbaric care, multiple stakeholder perspectives on improved clinical quality, measurement of clinical outcomes of hyperbaric care, importance of facility accreditation, process improvement methods, and the future importance of quality management in clinical hyperbaric facilities.     

Microarray image enhancement by denoising using stationary wavelet transform

Microarray imaging is considered an important tool for large scale analysis of gene expression. The accuracy of the gene expression depends on the experiment itself and further image processing. It's well known that the noises introduced during the experiment will greatly affect the accuracy of the gene expression. How to eliminate the effect of the noise constitutes a challenging problem in microarray analysis. Traditionally, statistical methods are used to estimate the noises while the microarray images are being processed. In this paper, we present a new approach to deal with the noise inherent in the microarray image processing procedure. That is, to denoise the image noises before further image processing using stationary wavelet transform (SWT). The time invariant characteristic of SWT is particularly useful in image denoising. The testing result on sample microarray images has shown an enhanced image quality. The results also show that it has a superior performance than conventional discrete wavelet transform and widely used adaptive Wiener filter in this procedure.     

Comparative study of image quality for MSCT and CBCT scanners for dentomaxillofacial radiology applications

The image quality of four cone-beam computed tomography (CBCT) scanners dedicated for dentomaxillofacial imaging and one multi-slice computed tomgoraphy (MSCT) scanner was compared. For the MSCT scanner, a clinical and a low-dose protocol for oral indications were evaluated. The image quality was assessed by dedicated software that allows an automated analysis of accuracy measurements and evaluation of metal artefacts on two image quality phantoms. Bone was segmented with sub-millimetre accuracyin all scanners.     

Implementing CQI projects in hospitals

BACKGROUND: Quality improvement approaches such as continuous quality improvement (CQI) and total quality management are widely used, but little is known about how much it costs to use the principles and techniques required to implement CQI processes. In the Robert Wood Johnson Foundation's Improving the Quality of Hospital Care (IQHC) program, four consortia of hospitals were funded in the early 1990s. Interviews with quality managers at 38 of the consortia hospitals were conducted in 1995 to determine the costs of conducting CQI projects to allow an estimation of the marginal cost of using CQI processes (particularly cross-disciplinary teams) to improve quality of care. CQI PROJECTS: Quality managers described 69% of project outcomes as critical to clinical services. Team members identified the issues their teams addressed and selected the project 64% of the time, the methods of analysis 87% of the time, and the approaches to resolving the problem or issue 97% of the time. Most of the respondents agreed that the team members had the authority to resolve the problem without appealing to higher levels of management. Costs for hospitals' most recently completed projects varied widely, from $148 for the entire project to $18,590. The length or duration of the projects also varied widely, from 1 month to 66 months. DISCUSSION: In the hospitals included in this sample, all of which were highly self-selected (evidenced by their participation in a voluntary consortium of hospitals focused on quality of care), knowledge of CQI processes appeared to be fairly thorough. Teams appeared to have a reasonable amount of autonomy. New CQI projects should be subjected to scrutiny in terms of their likely contribution to quality of care, as distinct from other positive outcomes.     

Assessment and optimisation of the image quality of chest-radiography systems

A complete evaluation strategy had been developed for thoracic X-ray imaging. It has been validated by investigating five chest-radiography systems, two of these systems after optimising image processing. The systems were a screen-film combination, a selenium drum, a conventional and a transparent imaging plate and a Cs/I-based flat panel detector (the two latter ones have been optimised using different post processing). At first all detectors have been characterised using physical parameters like DQE and MTF. After that all systems have been evaluated by human observer studies using anatomy in clinical images (VGA, ICS) and added pathological structures in thoracic phantom images (ROC). The ranking of the image quality of the systems was nearly the same in all studies. There was a similar assessment of main image quality parameters like spatial resolution, dynamic range and MTF. The modification of image post processing changed the visibility of pathological structures more than the visualisation of the anatomical criteria. The assessment of the clinical image quality has to be done for anatomical structures, and the recognition of pathological structures has to be evaluated.     

Miniaturized three-dimensional endoscopic imaging system based on active stereovision

A miniaturized three-dimensional endoscopic imaging system is presented. The system consists of two imaging in channels that can be used to obtain an image from an object of interest and to project as tructured light onto the imaged object to measure the surface topology. The structured light was generated with a collimated monochromatic light source and a holographic binary phase grating. The imaging and projection channels were calibrated by use of a modified pinhole camera. The surface profile was extracted by use of triangulation between the projected feature points and the two channel ofthe endoscope. The imaging system was evaluated in three-dimensional measurements of several objects with known geometries. The results show that surface profiles of the objects with different surfaces and dimensions can be obtained at high accuracy. The in vivo measurements at tissue sites of human skin and an oral cavity demonstrated the potential of the technique for clinical applications.