Scatter correction in digital radiography using interpolated local sampling of aperture signals.

A scatter correction scheme for radiographic images which is based on two-dimensional interpolation of local scatter measurements is described. Local scatter measurements are obtained using an aperture array. The effect of the scheme on physical imaging performance is evaluated by examining the broad-area contrast, edge sharpness, square wave response function and signal-to-noise ratio of images from a digital fluoroscopy system. It is found that the scheme generates substantial improvement in broad-area contrast and densitometric linearity, has no direct effect on sharpness and limiting spatial resolution, and considerably reduces the signal-to-noise ratio. This latter result is the sole deleterious feature of the correction scheme.

The implementation of an integrated on-line health education system at RMIT.

The Faculty of Biomedical and Health Sciences at RMIT has been developing an on-line health education system using a systems thinking approach, to create a learning environment whose basis is supported by Information Technology (IT). The centre-piece of this system is the Faculty Learning Centre, which has been created, both in space and layout, to promote collaborative learning between the students, so that the educator is physically assimilated with the student body. This facility is supplemented by the Faculty WWW server, which has been the main vehicle for course material dissemination to students. To ensure an effective on-line teaching environment, the position of an on-line facilitator has been created, whose responsibilities include both the continual evaluation of the system and the implementation of appropriate system changes. Aspects have included the production of a staff development training program and extensive user documentation. This paper discusses the systems thinking approach used to implement this integrated on-line system, and the establishment of explicit educational rationales in the use of IT to support learning strategies. Some examples of the on-line educational programs are also presented.

Examination of aperture signals in digital radiography.

Lead discs have been widely used to measure scattered radiation in radiographic imaging. An alternative approach, which offers advantages in terms of practical simplicity and radiation dose efficiency, is based on measurements obtained using a narrow aperture. The use of such an aperture for scatter measurement is examined from an experimental perspective in this paper. The examination is based on analysing features in images of apertures of 0.5 mm to 10 mm in diameter using a digital fluoroscopy system. Clinical imaging conditions were simulated using a 15 cm thickness of scattering material and a kilovoltage of 80 kVp. It was found that images of broad apertures consist of a transmitted signal, with primary and scatter components, which is surrounded by a skirt resulting from scatter. Furthermore, it was found that the skirt and the scatter component of the transmitted signal become negligible for narrow apertures. It was also found that a 1.5 mm aperture generates a scatter-free primary signal within the limits of accuracy of the detection system employed. This outcome was confirmed on the basis of accurate densitometric measurements and aperture signals which were independent of air gap. It is concluded that the signal measured using a 1.5 mm aperture can be related to the open field signal to determine the scatter signal and that this is an accurate method for such measurement with this experimental arrangement.

A contrast-detail study of interpolated scatter and glare correction of digital fluoroscopic images.

A scheme to correct for the effects of scattered radiation and veiling glare on the contrast of digital fluoroscopic images was investigated. The correction scheme is based on using spatial interpolation of signals generated in the shadows of a lead disk array, placed in the radiation beam. Contrast-detail plots obtained using the Leeds TO.10 test object, for corrected images were compared with those for unprocessed images, for images processed using digital contrast enhancement and for images acquired using a grid. It was found that substantial improvements in image contrast were obtained using the correction scheme.

Evaluation of the processing functions of a digital subtraction angiography image processor.

A large number of imaging systems for digital subtraction angiography (DSA) are now commercially available. Numerous evaluations of the performance of these systems have been reported in the literature. However systematic evaluations of the processing functions of DSA image processors have not been widely reported. Such an evaluation for one commercial system is presented in this paper. Functions evaluated include linear transformation, logarithmic transformation, integration, subtraction and temporal filtration. The observations indicate that image processing results are frequently achieved by indirect routes which compromise the fidelity of the image data.

Experimental examination of videodensitometry of large opacifications in digital subtraction angiography.

With the recent introduction of digital radiography the possibility of extracting clinically useful quantitative indices of function has emerged. In digital subtraction angiography (DSA), videodensitometric analysis has been widely applied. An experimental investigation of the usefulness of logarithmically transformed pixel values in DSA images for quantitative densitometry is performed. Dependence on image uniformity, transmittance, scattered radiation and video offset voltages is examined. Results indicate independence of both uniformity and transmittance and dependence on both scattered radiation and offset voltages. The possible use of lead absorbers to derive corrections for contributions from scattered radiation and similar aberrations in each image used for subtraction is also examined. Observations indicate that such corrections can allow accurate videodensitometry.