Preliminary reference levels in interventional cardiology

This article describes the European DIMOND approach to defining reference levels (RLs) for radiation doses delivered to patients during two types of invasive cardiology procedures, namely coronary angiography (CA) and percutaneous transluminal coronary angioplasty (PTCA). Representative centres of six European countries recorded patients' doses in terms of dose-area product (DAP), fluoroscopy time and number of radiographic exposures, using X-ray equipment that has been subject to constancy testing. In addition, a DAP trigger level for cardiac procedures which should alert the operator to possible skin injury, was set to 300 Gyxcm2. The estimation of maximum skin dose was recommended in the event that a DAP trigger level was likely to be exceeded. The proposed RLs for CA and PTCA were for DAP 45 Gyxcm2 and 75 Gyxcm2, for fluoroscopy time 7.5 min and 17 min and for number of frames 1250 and 1300, respectively. The proposed RLs should be considered as a first approach to help in the optimisation of these procedures. More studies are required to establish certain "tolerances" from the proposed levels taking into account the complexity of the procedure and the patient's size.     

A review of image quality and dose issues in digital fluorography and digital subtraction angiography

This paper addresses image quality and dose issues in Digital Fluorography (DF) and Digital Subtraction Angiography (DSA), commencing with a brief review of methods and protocols for image quality assessment in DF and DSA. The relative scarcity of standards and test protocols for unsubtracted DF is highlighted. Pooled results from a large number of quality assurance tests are then used to illustrate trends in the choice of radiation dose per image currently employed in typical DF and DSA work. It is concluded that, although relatively high doses per image may be justified in terms of image quality improvement for DSA, there is little justification for the large range of exposures used in DF for nominally identical examinations. It is argued that the use of high doses per image in DF would not be expected to offer an advantage in terms of image signal-to-noise ratio.     

Image processing in the fight against breast cancer

The detection of breast cancer at an early stage is of vital importance if the high mortality rate from this disease is to be reduced. The national breast-screening programme aims to use regular X-ray examinations amongst the age group most at risk to increase the early detection rate. A result of this is that over 1 million pairs of X-ray images per year will need to be reviewed by radiologists. Over 90% of these images will show no abnormality. Potentially, the successful application of image processing techniques to this task could greatly ease the burden of the very large numbers of examinations performed, and improve detection accuracy by directing the human expert's attention only to those results suspected of being abnormal. The problem is, however, for both technical and ethical reasons, formidable     

Reference levels in PTCA as a function of procedure complexity

The multicentre assessment of a procedure complexity index (CI) for the introduction of reference levels (RLs) in percutaneous transluminal coronary angioplasties (PTCA) is presented here. PTCAs were investigated based on methodology proposed by Bernardi et al. Multiple linear stepwise regression analysis, including clinical, anatomical and technical factors, was performed to obtain fluoroscopy time predictors. Based on these regression coefficients, a scoring system was defined and CI obtained. CI was used to classify dose values into three groups: low, medium and high complexity procedures, since there was good correlation (r = 0.41; P < 0.001) between dose-area product (DAP) and CI. CI groups were determined by an ANOVA test, and the resulting DAP and fluoroscopy time third quartiles suggested as preliminary RLs in PTCA, as a function of procedure complexity. PTCA preliminary RLs for DAP are 54, 76 and 127 Gy cm2, and 12, 20 and 27 min for fluoroscopy time, for the three CI groups.     

Experiments as parables.

Comments on G. S. Howard's (see record 1991-17124-001) article on narrative in which K. Gergen remarked on the paucity of important experiments in narrative psychology. In social psychology, however, these few have become classics. The 1963 experiment for which S. Milgram is remembered had all of the elements of a parable: vivid imagery, conceptual simplicity, a story line, and an outcome that few expected. Such narratives can be told as parables and are the mythical underpinnings of social psychology; they form the culture that tells social psychologists who they are. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development and application of programs to measure modulation transfer function, noise power spectrum and detective quantum efficiency

This project aimed to produce programs to calculate the modulation transfer function (MTF), noise power spectrum (NPS) and detective quantum efficiency (DQE) of digital X-ray systems, given a suitable digital image. The MTF was calculated using the edge technique and the NPS was calculated from a flat field image. Both programs require a suitably edited DICOM image as input. The DQE was then calculated from the output of MTF and NPS programs. This required data external to the DQE program to estimate the number of quanta per mm2 in the beam which formed the NPS image. All three programs run independent of each other on a PC and require no special software to be installed. Results for MTF, NPS and DQE for a Philips AC3 CR system are presented. In addition, the results for MTF from a Siemens Duo CT scanner with a specially designed PTFE edge are also shown.     

The influence of patient size on patient doses in cardiology

In cardiology and interventional radiology, areas that contribute large components to medical radiation exposure, a major source of variation in patient dose is the variation in complexity between cases for nominally identical procedures. In patient dose surveys, this variation tends to mask that due to patient size. The effect of applying a previously defined size correction to cardiology patient dose-area product (DAP) records was investigated. The correction method uses the experimentally determined relationship between patient diameter and DAP to derive a factor to convert DAP to that which would be expected had the patient been similar in size to ICRP Reference Man. The size correction was found to greatly reduce the residual correlation of DAP with patient weight. An implication of this finding is that data collection for the setting of diagnostic reference levels in cardiology can be performed for all patients rather than just 'standard-sized' patients.     

Quantification of motion unsharpness in digital fluoroscopy

The objectives of this work were first to develop a convenient method to quantify persistence in digital fluoroscopy systems, then to quantify the effect of variable temporal averaging on the detection of moving low-contrast test details within digital fluoroscopic and pulsed fluoroscopic images. The results were analysed to clarify the relationship between the optimum persistence required to see the lowest contrast for circular test details for a range of diameters and their speed of movement. The optimum persistence values obtained are compared with the limited data available on speeds of movement of patient organs during fluoroscopy. It is tentatively concluded that for imaging the abdomen, the optimum imaging system persistence time constant is approximately 0.15 s. For the much greater speeds associated with cardiac motion, no additional frame averaging is necessary, i.e. just the persistence provided by the observer's visual system appears to be optimal for small objects.     

Pilot study into optimisation of viewing conditions for electronically displayed images

The increased use of soft-copy reporting introduces new concerns over the effect of viewing conditions on the observer's ability to report images. Owing to their lower luminance, electronic display screens may be more susceptible to poor viewing conditions than conventional viewing boxes and there is the potential for images to be displayed in locations not optimised for viewing radiographs. In the present work, the effects of sub-optimal viewing conditions on the observer's performance for images on an electronic display device are investigated. A test object was used to produce a computed radiography image containing a wide range of grey levels. The image was scored under quasi-ideal and sub-optimal conditions and the effect of changing the viewing conditions on the observer's performance determined. Basic photometric quantities were used to characterise the viewing conditions and the degradation in observer performance related to these quantities. The presence of structured reflection had a significant effect on the observer's ability to discern low-contrast objects. The study demonstrates the need for adequate viewing conditions especially when images are displayed on low luminance devices in sub-optimal conditions.     

The use of dynamic phantoms in interventional radiology

The authors have constructed a 2D motor-controlled test object phantom holder to simulate clinical situations in which patient movement could be a cause of image degradation. The PAtient MOvement SImulation Test Object (PAMOSITO) has been constructed with modular parts to use different mobile test objects and static structures. The system allows the programming of different cycles of movement along two axes. PAMOSITO has been used in X ray equipment dedicated to interventional radiology. Those systems usually allow for different values for frame rate, pulse width or weighted frame averaging methods. The influence of selecting different values of the parameters, patient movement and its relation to patient dose and image quality has been studied. Image blurring due to motion has been evaluated with Leeds test objects TO.10 and 18FG. Spatial resolution limits and the threshold contrast detail detectability performance have been studied.