Finding-specific display presets for computed radiography soft-copy reading

The properties of the human visual system (HVS) relevant to the diagnostic process are described after a brief introduction on the general problems and advantages of using soft copy for primary radiology interpretations. At various spatial and temporal frequencies the contrast sensitivity defines the spatial resolution of the eye-brain system and the sensitivity to flicker. The adaptation to the displayed radiological scene and the ambient illumination determine the dynamic range for the operation of the HVS. Although image display devices are determined mainly by state-of-the-art technology, analysis of the HVS may suggest technical characteristics for electronic displays that will help to optimize the display to the operation of the HVS. These include display size, spatial resolution, contrast resolution, luminance range, and noise, from which further consequences for the technical components of a monitor follow. It is emphasized that routine monitor quality control must be available in clinical practice. These image quality measures must be simple enough to be applied as part of the daily routine. These test instructions might also serve as elements of technical acceptance and constancy tests.     

Cathode-ray tube displays for medical imaging

This paper will discuss the principles of cathode-ray tube displays in medical imaging and the parameters essential to the selection of displays for specific requirements. A discussion of cathode-ray tube fundamentals and medical requirements is included.     

Temporal response of medical liquid crystal displays

Displays based on liquid crystal technology suffer from slow temporal response due to the dynamics of the molecular rearrangement in response to a pixel voltage change. A slow display can affect the visualization by the human observer of subtle contrast in dynamic presentation of volumetric image datasets or real-time image sequences. In this paper, we describe a measurement method for the characterization of the temporal response of medical liquid crystal displays (LCDs). The ratio of luminance difference to noise at the gray levels of concern determines the reliability of measurements. Coefficients of variations are used to represent the measurement reliability. We optimized the repeatability of most response time measurements to less than 10%. However, poor repeatability is encountered for the response of adjacent gray levels. 256 X 255 inter-gray-level transition time matrices were measured for four medical displays and one high-definition TV LCD display. Response times range from below 20 ms to above 150 ms. For each display, response times are not uniformly distributed, with a faster response for large gray-level transitions. Transition times are smaller when the starting gray level is between 10 and 20 for a target between 25 and 150. The difference could be over 100 ms for different transitions within a display. For transitions with poor temporal response, the luminance after 1, 3, and 5 frames reaches only 12, 45, and 75% of the target value, respectively. We also found that LCD response time depends on temperature, with 1 h warm-up reducing the response time by a factor of 2.     

Viewing angle performance of medical liquid crystal displays

Cathode-ray tube (CRT) and liquid crystal display (LCD) are currently two main technologies for displaying medical images. LCDs possess a number of advantages, but their performance varies as a function of viewing angle. Our purpose in this study was to characterize the angular response performance of five medical-grade LCDs, and to substantiate their impact on their compliance with the DICOM gray scale display function (GSDF). Furthermore, the study aimed to test a framework to define an angular acceptance range for medical LCDs based on the recent AAPM TG18 guidelines. Measurements were made on five calibrated dual-domain LCDs, including two 3 megapixel monochrome LCDs, two 5 megapixel monochrome LCDs, and one 9 megapixel color LCD. The luminance performance of each display device was measured as a function of the viewing angle at 17 discrete levels using TG18-LN test patterns and a Fourier-optics-based luminance meter. The luminance data were analyzed according to the AAPM TG18 methodology. The displays showed notable variation in luminance and contrast performance as a function of the viewing angle, particularly in diagonal viewing orientations. Overall, the luminance ratio remained greater than 175 within +/-20 degrees and +/-33 degrees viewing angle cones (beta175 = 20 degrees-33 degrees). Aiming to maintain a maximum deviation from the GSDF contrast less than 0.3, i.e., kappa17 < or = 0.3, acceptable viewing angle cones of +/-22 degrees and +/-35 degrees were indicated (alpha 0.3= 22 degrees-35 degrees). The findings demonstrate the significant impact of angular response on image contrast, and the utility of alpha 0.3 and beta175 quantities for defining the viewing angle cones within which a medical LCD device can be effectively utilized.     

A comparative contrast-detail study of five medical displays

The objective of this study was to compare the contrast-detail performance of five different commercial liquid crystal displays (LCDs) to other LCD and cathode-ray tube (CRT) displays for medical applications. A contrast-detail phantom, supplemented with 5 in. of acrylic, was imaged on a commercial digital radiographic system using techniques comparable to chest radiography. The phantom design enabled observer evaluation by a four-alternative forced choice paradigm. The acquired images were independently scored by five observers on five medical display devices: a 5 megapixel monochrome LCD, a 3 megapixel monochrome LCD, a 9 megapixel color LCD, a 5 megapixel monochrome CRT, and a mammographic-grade monochrome CRT. The data were analyzed using the method suggested by the manufacturer based on a nearest neighbor correction technique. They were further analyzed using a logistic regression response model with a natural threshold using an overall chi-square test for display type followed by pairwise comparisons for individual display performance. The differences between the display devices were small. The standard analysis of the results based on the manufacturer-recommended method did not yield any statistically discernible trend among displays. The logistic regression analysis, however, indicated that the 5 megapixel monochrome LCD was statistically significantly (p <0.0001) superior to the others, followed by the 3 megapixel monochrome LCD (p<0.0001). The three other displays exhibited lower but generally similar performance characteristics. The findings suggest that 5 and 3 megapixel monochrome LCDs provide comparable but subtly superior contrast detectability than other tested displays, with the former performing slightly better in the detection of subtle and fine details.     

Quality standards for medical laboratories

In France, medical laboratories must engage a quality approach according to the standard guide de bonne exécution des analyses (GBEA) and, for hospital laboratories, according to the Agence nationale d'évaluation en santé (Anaes). Except the GBEA and the Anaes handbook, which are obligatory standards by regulations, the biologists can choose, for a complementary and voluntary quality process, between the standards ISO 9001, ISO 17025 or ISO 15189. Our aim is to shed light on the advantages of these five standards by realizing a comparative study of their requirements. This work enabled us to highlight a great number of similarities and to raise the characteristics of these five standards. According to their objectives, the biologists will choose a recognition of their quality management system with an ISO 9001 certification or a recognition extended to the technical skills with an ISO 17025 or ISO 15189 accreditation. The contents of these last two documents are rather close and both integrate requirements of the standard ISO 9001. The standard ISO 17025 is, at first sight, rather distant from the biological analysis, requiring many efforts of adaptation, just like the ISO 9001 standard. The standard ISO 15189 seems to be well adapted but more constraining seeing the details requirements level needed. It necessitates a perfect control of the preanalytical phase, which is difficult to acquire in a clinical framework where the biological fluids are not taken by the laboratory staff.     

Quality control of storage phosphor digital radiography systems

Quality control (QC) of storage phosphor devices is important in assuring that the image information entered into an Image management and communication (IMAC) system is sufficient for diagnosis. QC of storage phosphor digital radiography systems is complex because of the self-corrective nature of the image-processing software used in these machines. Currently, one must produce hard copy to perform adequate QC. Inspection of images with reject analysis and inspection of cassettes and imaging plates has helped us in our QC program. For those QC tests using control limits, the appropriate settings for these limits are unknown. Starting approximations are given. Recommended tests are described.     

Resolution and noise measurements of five CRT and LCD medical displays

The performance of soft-copy displays plays a significant role in the overall image quality of a digital radiographic system. In this work, we discuss methods to characterize the resolution and noise of both cathode ray tube (CRT) and liquid crystal display (LCD) devices. We measured the image quality of five different commercial display devices, representing both CRT and LCD technologies, using a high-quality charge-coupled device (CCD) camera. The modulation transfer function (MTF) was calculated using the line technique, correcting for the MTF of the CCD camera and the display pixel size. The normalized noise power spectrum (NPS) was computed from two-dimensional Fourier analysis of uniform images. To separate the effects of pixel structure from interpixel luminance variations, we created structure-free images by eliminating the pixel structures of the display device. The NPS was then computed from these structure-free images to isolate interpixel luminance variations. We found that the MTF of LCDs remained close to the theoretical limit dictated by their inherent pixel size (0.85 +/- 0.08 at Nyquist frequency), in contrast to the MTF for the two CRT displays, which dropped to 0.15 +/- 0.08 at the Nyquist frequency. However, the NPS of LCDs showed significant peaks due to the subpixel structure, while the NPS of CRT displays exhibited a nearly flat power spectrum. After removing the pixel structure, the structured noise peaks for LCDs were eliminated and the overall noise magnitude was significantly reduced. The average total noise-to-signal ratio for CRT displays was 6.55% +/- 0.59%, of which 6.03% +/- 0.24% was due to interpixel luminance variations, while LCD displays had total noise to signal ratios of 46.1% +/- 5.1% of which 1.50% +/- 0.41% were due to interpixel luminance variations. Depending on the extent of the blurring and prewhitening processes of the human visual system, the magnitude of the display noise (including pixel structure) potentially perceived by the observer was reduced to 0.43% +/- 0.01% (accounting for blurring only) and 0.40 +/- 0.01% (accounting for blurring and prewhitening) for CRTs, and 1.02% +/- 0.22% (accounting for blurring only) and 0.36% +/- 0.08% (accounting for blurring and prewhitening) for LCDs.     

Considerations regarding the application of capillary optics to medical radiography.

The generation of monoenergetic or quasimonoenergetic x-ray spectra has been accomplished by several methods including the use of K-edge filtration, characteristic radiation, crystal monochromators, and multilayer mirrors. In this paper some practical questions are discussed regarding the possibility of obtaining narrow-band spectra using x-ray reflection in glass capillary optics which have been reported recently in connection with the focusing and generation of parallel x-ray beams. Derivation of formulas for double and triple reflection with and without additional K-edge filtration imply that these methods are superior to the use of filtration alone. It is shown that the double reflection scheme is most sensitive to the angular divergence of the beam emanating from the capillary array used to generate the incident parallel beam. Simulations using three reflections predict output spectra which are relatively insensitive to blurring due to angular divergence. A small amount of K-edge filtration in combination with three reflections provides considerable sharpening of the x-ray spectrum. Aside from the spectral selectivity provided by the capillary array, the reduced divergence of the primary transmission may have advantages for scatter rejection in situations where the air gap between the patient and detector is increased by an amount consistent with the resolution requirements of the application. In parallel beam situations, the use of capillary arrays between the patient and detector may also be useful for the rejection of divergent scattered radiation.     

医疗机构医疗器械不良事件监测系统评价模型研究

目的设计医疗机构医疗器械不良事件监测系统评判模型,对医疗器械不良事件监测系统进行的全面、科学的评价,为国家管理部门实施对医疗机构的考核提供科学的方法。方法使用德尔菲法确立指标权重,使用系统分析法建立医疗器械不良事件监测系统的综合评价体系,使用模糊综合评判方法建立数学模型。结果本研究建立的评价模型适合作为评价工具,为国家管理部门在考核、评价医疗机构医疗器械不良事件监测系统方面提供科学的指导方法。结论综合评价体系中的评价指标、指标权重等数据应在实际应用中持续地改进和完善。     

Angular dependence of the luminance and contrast in medical monochrome liquid crystal displays

Active-matrix liquid crystal displays (AMLCDs) are light-modulating devices that generate images by differentially transmitting a nearly uniform luminous field provided by a backlight. While emissive displays exhibit a quasi-Lambertian emission with almost constant contrast at off-normal viewing, the anisotropy of the electro-optic effect that controls light transmission in AMLCDs causes a pixel luminance that varies, sometimes strongly, with viewing angle. These variations are not identical for all gray levels and can eventually cause grayscale inversions. In this paper, we measured the luminance emission of a monochrome medical AMLCD, a medical cathode-ray tube monitor, and a color desktop AMLCD, using a collimated photopic probe positioned on a manual rotation arm, and a research radiometer with automatic readout. The probe measures luminance with a small acceptance angle and provides optical shielding from emissions at other viewing directions that contaminate the readings. We obtained luminance response curves versus angle in the vertical, horizontal and at 45 degrees diagonal directions. The display systems were calibrated to reflect the DICOM Part 3.14 standard grayscale display function (GDF) when measured using the manufacturer's probe and software tools. We analyzed the measurements at different viewing directions with respect to their departure from the GDF by computing the normalized contrast (deltaL/L) as a function of the DICOM just-noticeable difference index. Although cathode-ray tubes are known to be quasi-Lambertian emitters, the luminance at normal viewing is higher than the luminance observed at large angles. This decrease in luminance is however proportionally similar for all gray levels, resulting in a relatively flat contrast response for all angles. In addition to being more pronounced, the angular variation in AMLCDs does not follow the same profile at different intensities with the subsequent variation in the achieved display contrast. The changes due to off-normal viewing are substantial at large angles in the horizontal and vertical directions, and much worse in the diagonal viewing directions.     

Dynamic dual-energy chest radiography: a potential tool for lung tissue motion monitoring and kinetic study

Dual-energy chest radiography has the potential to provide better diagnosis of lung disease by removing the bone signal from the image. Dynamic dual-energy radiography is now possible with the introduction of digital flat-panel detectors. The purpose of this study is to evaluate the feasibility of using dynamic dual-energy chest radiography for functional lung imaging and tumor motion assessment. The dual-energy system used in this study can acquire up to 15 frames of dual-energy images per second. A swine animal model was mechanically ventilated and imaged using the dual-energy system. Sequences of soft-tissue images were obtained using dual-energy subtraction. Time subtracted soft-tissue images were shown to be able to provide information on regional ventilation. Motion tracking of a lung anatomic feature (a branch of pulmonary artery) was performed based on an image cross-correlation algorithm. The tracking precision was found to be better than 1 mm. An adaptive correlation model was established between the above tracked motion and an external surrogate signal (temperature within the tracheal tube). This model is used to predict lung feature motion using the continuous surrogate signal and low frame rate dual-energy images (0.1-3.0 frames per second). The average RMS error of the prediction was (1.1 ± 0.3) mm. The dynamic dual energy was shown to be potentially useful for lung functional imaging such as regional ventilation and kinetic studies. It can also be used for lung tumor motion assessment and prediction during radiation therapy.     

Quality management of medical laboratory--a survey for National University Hospital

Since ISO (International Organization for Standardization) 15189 for medical laboratories was established in Japan in 2003, 60 medical laboratories had been certified until April 2011. Among them, 10 medical laboratories belong to national university hospitals. To investigate the current status for the development of a quality management system, we carried out a questionnaire survey targeting all national university hospitals. ISO and ISO 15189 have already been introduced in about 70% of all laboratories and 53% are ready to accept them. In medical laboratories that have already accepted ISO 15189, it was suggested that their quality management systems have been functioning effectively and a gradual decrease of the number of the incidents has been confirmed.     

Quality indicators: a tool for quality monitoring and improvement

Quality indicators are one of the quality management system (QMS) tools to monitor and control efficiency of the system key segments, while the results collected serve as a basis for implementation of corrective measures and continuous quality improvement. There are several classifications of quality indicators. According to the objectives of their establishment and utilization, they can be internal and external. In line with the tripartite quality model, quality indicators can be classified as structural indicators, process indicators and outcome indicators. Quality indicators should ideally possess a number of attributes. Besides objectivity (measurability), the most common requirements are as follows: importance and potential for use, reliability and validity. Quality indicators offer the possibility of fast and simple insight into the level of product and service quality and their pattern over time to the interested parties within and outside the institution. Although quality management has long been recognized as being of utmost importance in transfusion medicine, quality indicators as a QMS tool did not receive due attention until recently. Implementation of quality indicators is a complex process which requires scientific approach as well as testing and verification before routine usage. Quality indicators are defined on the basis of scientific concepts, own experiences, results of literature searches, discussion with experts within and outside the institution, etc. On setting quality indicators, the numerator and denominator should first be strictly defined. Quality indicators should be monitored continuously, including trend monitoring and detection of deviations. Whenever considered necessary, appropriate corrective measures have to be undertaken.