Objective measurements of image quality in synchrotron radiation phase-contrast imaging versus digital mammography

Purpose

Phase-contrast mammography with synchrotron radiation is an innovative X-ray imaging practice that improves the identification of breast lesions. Previous studies have proven the superiority of the mammography images taken in the phase-contrast modality using synchrotron radiation beams as compared with images taken in conventional mammography by subjective analyses. However, to our knowledge, no previous study has compared different acquisition systems in order to quantify this improvement by means of objective robust indicators. In this research, we intend to quantify the superiority of phase-contrast imaging by means of objective metrics of image quality.

Methods

Images from the American College of Radiology Mammographic Accreditation Phantom were obtained at hospitals, in two digital mammography equipment and at the Elettra synchrotron radiation facility (Trieste, Italy), using free space propagation phase-contrast modality. Regions of interest were selected to analyze image quality at the fibers (phase object) and masses (area object) simulated on the phantom by means of the signal-to-noise ratio, the figure of merit, the contrast and the edge visibility.

Results

The image contrast and edge visibility were significantly higher at the phase-contrast modality as compared with digital mammography equipment. The figure of merit using phase-contrast modality was higher for the fibers and comparable for the masses.

Conclusion

The results showed an improvement of the contrast and edge visibility in phase-contrast images. These improvements may be important in the detection of small lesions and details.

     

Objective measurements of static anterior and rotational knee laxity

Several devices allow to measure anterior and rotational static knee laxity. To date, the use of rotational laxity measurements in the daily clinical practice however remains to be improved. These measurements may be systematically integrated to the follow-up of knee injuries. Physiologic laxity measurements may particularly be of interest for the identification of risk factors in athletes. Furthermore, knee laxity measurements help to improve the diagnosis of knee soft tissue injuries and to follow up reconstructions. Further prospective follow-ups of knee laxity in the injured/reconstructed knees are however required to conclude on the best treatment strategy for knee soft tissue injuries.     

基于图像处理的眼屈光度客观测量系统

背景:目前的眼屈光度测量方法均采用红外LED发光二极管作光源,红外光通过人眼角膜、房水、晶状体、玻璃体以及视网膜,造成反射的眼底图像不均匀,边缘判别难免出现误差,影响测量结果.目的:为了解决人眼屈光度测量方法和精度问题,设计了一套基于图像处理的眼睛屈光度测量系统.方法:将六点红外光射入眼底,经光学系统接收成像在CCD上,首先利用自适应多阈值方法对图像进行二值化分割,然后用重心法求每个点的中心坐标,最后再用最小二乘拟合的方法计算眼睛屈光度.实验用标准模拟眼进行了测试,并同目本TPCON验光仪进行了比较.结果与结论:设计的眼睛屈光度测量系统测量精度能达到国家计量规定的±0.25m-1.避免了由于人眼系统结构造成CCD接受图像不均匀而导致的计算精度误差;系统结构简单,光源能量能满足需要,实验表明可以提高眼睛屈光度参数测量精度,利用该技术已经做出了样机.在医院临床快速检查、普查视力具有重要应用.不足之处在于结构简化,大屈光度测量容易造成误差,对光源同光学系统的同轴性要求高,这是以后设计和工艺需要改进的地方.     

Errors in ultrasound digital image distance measurements

Digital image distance measurements have two sources of error: they are the inherent image pixelation error and modality-specific registration errors. A theoretical analysis was performed to determine the pixelation error uncertainty in ultrasound (US) clinical and phantom digital image distance measurements. For horizontal or vertical phantom image distance measurements, the average absolute image pixelation error was found to be 0.5 pixel width. In the clinical horizontal case, the combined absolute distance measurement error due to pixel size and operator cursor placement errors was found to be 1.5 pixel widths (for a cursor placement error of 1 pixel width). For image clinical distance measurements, a formula is given for the dependence of the measurement error on the inclination of the measured structure in the pixel matrix. A protocol is recommended that minimizes all sources of error in clinical image distance measurements.     

Objective performance testing and quality assurance of medical ultrasound equipment

There is an urgent need for a measurement protocol and software analysis for objective testing of the imaging performance of medical ultrasound equipment from a user's point of view. Methods for testing of imaging performance were developed. Simple test objects were used, which have a long life expectancy. First, the elevational focus (slice thickness) of the transducer was estimated and the in-plane transmit focus was positioned at the same depth. Next, the postprocessing look-up-table (LUT) was measured and linearized. The tests performed were echo level dynamic range (dB), contrast resolution (i.e., gamma of display, number of gray levels/dB) and sensitivity, overall system sensitivity, lateral sensitivity profile, dead zone, spatial resolution and geometric conformity of display. The concept of a computational observer was used to define the lesion signal-to-noise ratio, SNR(L) (or Mahalanobis distance), as a measure for contrast sensitivity. All the measurements were made using digitized images and quantified by objective means, i.e., by image analysis. The whole performance measurement protocol, as well as the quantitative measurements, have been implemented in software. An extensive data-base browser was implemented from which analysis of the images can be started and reports generated. These reports contain all the information about the measurements, such as graphs, images and numbers. The approach of calibrating the gamma by using a linearized LUT was validated by processing simultaneously acquired rf data. The contrast resolution and echo level of the rf data had to be compressed by a factor of two and amplified by a gain factor corresponding to 12 dB. This resulted in contrast curves that were practically identical to those obtained from DICOM image data. The effects of changing the transducer center frequency on the spatial resolution and contrast sensitivity were estimated to illustrate the practical usefulness of the developed approach of quality assurance by measuring objective performance characteristics. The developed methods might be considered as a minimum set of objective quality assurance measures. This set might be used to predict clinical performance of medical ultrasound equipment, taking into account the performance at a unique point in space i.e., the coinciding depths of the elevation and in-plane (azimuth) foci. Furthermore, it should be investigated whether the approach might be used to compare objectively various brands of equipment and to evaluate the performance specifications given by the manufacturer. Last but not least, the developed approach can be used to monitor, in a hospital environment, the medical ultrasound equipment during its life cycle. The software package may be viewed and downloaded at the website http://www.qa4us.eu.     

Low-field magnetic resonance image enhancement via stochastic image quality transfer

Low-field ($<1$T) magnetic resonance imaging (MRI) scanners remain in widespread use in low- and middle-income countries (LMICs) and are commonly used for some applications in higher income countries e.g. for small child patients with obesity, claustrophobia, implants, or tattoos. However, low-field MR images commonly have lower resolution and poorer contrast than images from high field (1.5T, 3T, and above). Here, we present Image Quality Transfer (IQT) to enhance low-field structural MRI by estimating from a low-field image the image we would have obtained from the same subject at high field. Our approach uses (i) a stochastic low-field image simulator as the forward model to capture uncertainty and variation in the contrast of low-field images corresponding to a particular high-field image, and (ii) an anisotropic U-Net variant specifically designed for the IQT inverse problem. We evaluate the proposed algorithm both in simulation and using multi-contrast (T1-weighted, T2-weighted, and fluid attenuated inversion recovery (FLAIR)) clinical low-field MRI data from an LMIC hospital. We show the efficacy of IQT in improving contrast and resolution of low-field MR images. We demonstrate that IQT-enhanced images have potential for enhancing visualisation of anatomical structures and pathological lesions of clinical relevance from the perspective of radiologists. IQT is proved to have capability of boosting the diagnostic value of low-field MRI, especially in low-resource settings.     

The image quality of extraoral x-ray pictures

A check was made on 594 X-ray examinations of ambulant oral surgery patients (= 1378 single pictures in several radiographic techniques). A good quality had 72% of the pictures. A decreased quality had 23% of them. A diagnosis was still possible. 5% of pictures were useless. Radiographic techniques were used in 8% of the 594 X-ray examinations with not optimal methods for the intended aim. In these cases it were better to change to other methods (other focussing or other apparatus).     

Domain-invariant interpretable fundus image quality assessment

Objective and quantitative assessment of fundus image quality is essential for the diagnosis of retinal diseases. The major factors in fundus image quality assessment are image artifact, clarity, and field definition. Unfortunately, most of existing quality assessment methods focus on the quality of overall image, without interpretable quality feedback for real-time adjustment. Furthermore, these models are often sensitive to the specific imaging devices, and cannot generalize well under different imaging conditions. This paper presents a new multi-task domain adaptation framework to automatically assess fundus image quality. The proposed framework provides interpretable quality assessment with both quantitative scores and quality visualization for potential real-time image recapture with proper adjustment. In particular, the present approach can detect optic disc and fovea structures as landmarks, to assist the assessment through coarse-to-fine feature encoding. The framework also exploit semi-tied adversarial discriminative domain adaptation to make the model generalizable across different data sources. Experimental results demonstrated that the proposed algorithm outperforms different state-of-the-art approaches and achieves an area under the ROC curve of 0.9455 for the overall quality classification.     

Influence of iterative image reconstruction on CT-based calcium score measurements

Iterative reconstruction techniques for coronary CT angiography have been introduced as an alternative for traditional filter back projection (FBP) to reduce image noise, allowing improved image quality and a potential for dose reduction. However, the impact of iterative reconstruction on the coronary artery calcium score is not fully known. In 112 consecutive stable patients with suspected coronary artery disease, the coronary calcium scores were assessed. Comparisons were made between the Agatston, volume and mass scores obtained with traditional FBP, and by using adaptive statistical iterative reconstruction (ASIR). A significant reduction of the Agatston score, volume score and mass score was observed for ASIR when compared to FBP, with median differences of resp. 26, 5 mm³ and 1 mg. Using the ASIR reconstruction, the number of patients with a calcium score of zero increased by 13 %. Iterative CT reconstruction significantly reduces the Agatston, volume and mass scores. Since the calcium score is used as a prognostic tool for coronary artery disease, caution must be taken when using iterative reconstruction.     

Fixed and dynamic health-related quality of life measurements

Measuring population health is important to evaluate the impact of interventions, to monitor the changes in health status, and to predict the need for health care. A number of tools have been developed to measure quality of life and health-related quality of life. According with the current taxonomy, the questionnaires may be classified as generic or specific, multidimensional or global. Recently, advances in the field of health outcome assessment have resulted in a new generation of approaches and measures that are based on a novel approach called dynamic health assessment. Through this approach, subjects or patients answer only those questions relevant to their evaluation, in contrast to the fixed approach in which the number of questions is a priori determined. The dynamic headache impact test (HIT) that evaluates several dimensions such as ability to function on the job, at school, and in social situations, is presented and its value with respect to other fixed migraine-specific questionnaires is discussed.     

Objective and subjective cognitive dysfunction and quality of life in multiple sclerosis

We examined the effect of subjective cognitive dysfunction on the quality of life of 18 patients with MS and subjective cognitive dysfunction; 8 patients also showed objective cognitive impairment, but 10 did not. Using multiple methods to assess quality of life, we found quality of life in the total group seriously impaired. Comparing quality of life of the objectively intact with that of the objectively impaired subgroups, we found only few differences. Thus, subjective cognitive dysfunction appears to be important for quality of life. This suggests that cognitive rehabilitation programs for patients with MS may need to include patients with subjective cognitive dysfunction and treat this problem in its own right.     

能谱CT最佳单能量成像优化甲状腺结节图像质量的研究

目的探讨能谱CT最佳单能量成像优化甲状腺结节图像质量的价值。方法回顾性分析经病理证实的45例129个甲状腺结节的患者,术前均行颈部能谱CT双期增强扫描,得到动、静脉期的70 keV和最佳单能量(Opti keV)图像。分别对两组图像质量进行客观评价(测量图像的噪声和对比噪声比)和主观评价(5分量表),采用Wilcoxon配对秩和检验,比较两组间的差异。并采用配对卡方检验比较两组图像在甲状腺结节的边界、结节包膜完整强化环、包膜节段性缺损("残圈征")、微钙化四个征象显示率的差异。结果共检出129个结节,其中良性结节66个,恶性结节63个。动脉期Opti keV为61.16±5.07 keV,静脉期Opti keV为61.87±4.28 keV。动脉期Opti keV为61.16±5.07 keV,静脉期Opti keV为61.87±4.28 keV。动、静脉期中,Opti keV组的噪声、对比噪声比和主观评分均明显高于70 keV组(P均=0.00)。Opti keV组在甲状腺结节边界、微钙化、包膜完整强化环、包膜节段性缺损四个征象的显示率均明显高于70keV组(P均=0.00)。结论能谱CT最佳单能量成像显著提高甲状腺结节图像的主客观评价,优化图像质量,有利于甲状腺良恶性结节的鉴别。     

Objective and subjective measures of the quality of managed care in nursing homes

BACKGROUND: The number of nursing home (NH) residents enrolled in managed care plans (HMO) will increase, and there is concern that the quality of their medical care may be compromised by cost-containment pressures. In this study, we evaluated the medical care of residents enrolled in 3 health maintenance organizations (HMO) that developed specific long-term care programs. OBJECTIVES: To compare the medical care received by NH residents enrolled in HMO and Fee-for-Service (FFS) plans with both objective process of care and consumer perception (subjective) measures. To describe the relationship between the objective and subjective measures. MEASURES: Number of primary care visits per month; process of medical care for 2 geriatric tracer conditions (falls, fevers); family and residents' perceptions of the adequacy of sickness episode management; and the frequency of primary provider visits. DESIGN: Quasi-experimental. RESULTS: HMO residents received more timely and appropriate responses to falls and fevers than did FFS residents. HMO residents also received more frequent routine visits by a primary care provider team consisting of a physician and nurse practitioner. Consumer perceptions of quality did not differ between the HMO and FFS groups. Families within both groups were significantly more positive than were residents about the frequency of visits by both physicians and nurse practitioners. Within the HMO group, both families and residents were more positive about the frequency of nurse practitioner visits than were physician visits even when the frequency of visits by the 2 providers were similar. CONCLUSIONS: Although the medical care received by HMO residents was better on most objective process measures than that received by FFS residents, consumer perceptions of care did not detect those differences. NH residents and families have different perceptions about the adequacy of visits by physicians and nurse practitioners, and both families and residents appear to have different expectations concerning how often they want physicians to visit as compared with nurse practitioners.     

Objective and expert-independent validation of retinal image registration algorithms by a projective imaging distortion model

Fundus camera imaging of the retina is widely used to diagnose and manage ophthalmologic disorders including diabetic retinopathy, glaucoma, and age-related macular degeneration. Retinal images typically have a limited field of view, and multiple images can be joined together using an image registration technique to form a montage with a larger field of view. A variety of methods for retinal image registration have been proposed, but evaluating such methods objectively is difficult due to the lack of a reference standard for the true alignment of the individual images that make up the montage. A method of generating simulated retinal images by modeling the geometric distortions due to the eye geometry and the image acquisition process is described in this paper. We also present a validation process that can be used for any retinal image registration method by tracing through the distortion path and assessing the geometric misalignment in the coordinate system of the reference standard. The proposed method can be used to perform an accuracy evaluation over the whole image, so that distortion in the non-overlapping regions of the montage components can be easily assessed. We demonstrate the technique by generating test image sets with a variety of overlap conditions and compare the accuracy of several retinal image registration models.     

Comparative quality measurements part 1: run charts

Quality assessment may be based on data of quality indicators. There are two main approaches for comparative quality measurements: comparison of data of the same service at different points over time or comparison of data of different services at the same time. Risk adjustment and standardisation must be performed and random variation must be adequately taken into account. In Statistical Process Control (SPC) theory common cause and special cause variation are distinguished. Processes in statistical control are stable and predictable. If processes exhibit special cause variation the management should investigate the reasons for this and manage the causes. Run charts as simple tools to display and analyse data of processes and outcomes over time are discussed in this article. They can be used for self-comparison. The following two parts of this three-part series explain control charts and funnel plots.