The role of fluoroscopic imaging is critical for diagnostic and image guided therapy. However, fluoroscopic imaging
can require significant radiation leading to increased cancer risk and non-stochastic effects such as radiation burns.
Our purpose is to reduce the exposure and dose to the patient by an order of magnitude in these procedures by use of
the region of interest method. Method and Materials: Region of interest fluoroscopy (ROIF) uses a partial attenuator.
The central region of the image has full exposure while the image periphery, there to provide context only, has a
reduced exposure rate. ROIF using a static partial attenuator has been shown in our previous studies to reduce the
dose area product (DAP) to the patient by at least 2.5 times. Significantly greater reductions in DAP would require
improvements in flat panel detectors performance at low x-ray exposures or a different x-ray attenuation strategy.
Thus we have investigated a second, dynamic, approach. We have constructed an x-ray shutter system allowing a
normal x-ray exposure in the region of interest while reducing the number of x-ray exposures in the periphery
through the rapid introduction, positioning and removal of an x-ray attenuating shutter to block radiation only for
selected frames. This dynamic approach eliminates the DQE(0) loss associated with the use of static partial
attenuator applied to every frame thus permitting a greater reduction in DAP. Results: We have compared the two
methods by modeling and determined their fundamental limits.
Visual assessment of arterial lesions from angiograms is subject to considerable inter- and intra-observer variability. To overcome these limitations, we are developing a method to perform reconstruction of vascular cross-sectional images from a limited number of x-ray angiographic cone-beam projections. The projection data are simplified by identifying blood vessels in each angiogram and removing signals due to other structures. The reconstruction is performed using the method of simulated annealing. An application of this approach to projections of cerebral vessels obtained from segmented CT slices of a cadaver injected with contrast agent are shown. We have also reconstructed an excised animal heart in order to test our method under more realistic image acquisition conditions including scatter, beam hardening, and variations in background signal.