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Radiation dose is particularly a concern in pediatric cardiac fluoroscopy procedures, which account for 7% of
all cardiac procedures performed. The Scanning-Beam Digital X-ray (SBDX) fluoroscopy system has already
demonstrated reduced dose in adult patients owing to its high-DQE photon-counting detector, reduced detected
scatter, and the elimination of the anti-scatter grid. Here we show that the unique flexible illumination platform
of the SBDX system will enable further dose area product reduction, which we are currently developing for
pediatric patients, but which will ultimately benefit all patients. The SBDX system has a small-area detector
array and a large-area X-ray source with up to 9,000 individually-controlled X-ray focal spots. Each focal spot
illuminates a small fraction of the full field of view. To acquire a frame, each focal spot is activated for a fixed
number of 1-microsecond periods. Dose reduction is made possible by reducing the number of activations of
some of the X-ray focal spots during each frame time. This can be done dynamically to reduce the exposure
in areas of low patient attenuation, such as the lung field. This spatially-adaptive illumination also reduces the
dynamic range in the full image, which is visually pleasing. Dose can also be reduced by the user selecting a
region of interest (ROI) where full image quality is to be maintained. Outside the ROI, the number of activations
of each X-ray focal spot is reduced and the image gain is correspondingly increased to maintain consistent image
brightness. Dose reduction is dependent on the size of the ROI and the desired image quality outside the ROI.
We have developed simulation software that is based on real data and can simulate the performance of the
equalization and ROI filtration. This software represents a first step toward real-time implementation of these
dose-reduction methods. Our simulations have shown that dose area product reductions of 40% are possible
using equalization, and dose savings as high as 74% are possible with the ROI approach. The dose reduction
achieved in clinical use will depend on patient anatomy.
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