The scanning-beam digital x-ray (SBDX) system is designed for x-ray dose reduction in cardiac angiographic applications. Scatter reduction, efficient detection of primary x-rays, and an inverse beam geometry are the main components of the entrance dose reduction strategy. This paper reports the construction of an SBDX prototype, image reconstruction techniques, and measurements of spatial resolution and x-ray output. The x-ray source has a focal spot that is electronically scanned across a large-area transmission target. A multihole collimator beyond the target defines a series of x-ray beams directed at a distant small-area detector array. The prototype has a 23 cm X 23 cm target, 100 X 100 focal spot positions, and a 5 cm X 5 cm CdTe detector positioned 150 cm from the target. With this nonmechanical method of beam scanning, patient images with low detected scatter are generated at up to 30 frame/s. SBDX data acquisition is tomosynthetic. The prototype simultaneously reconstructs 16 planes spaced throughout the cardiac volume using shift-and-add backprojection. Image frames analogous to conventional projection images are generated with a multiplane compositing algorithm. Single-plane versus multiplane reconstruction of contrast-filled coronary arteries is demonstrated with images of the porcine heart. Phantom and porcine imaging studies show multiplane reconstruction is practicable under clinically realistic levels of patient attenuation and cardiac motion. The modulation transfer function for an in-plane slit at mechanical isocenter measured 0.41-0.56 at 1 cycle/mm, depending on the detector element to image pixel interpolation technique. Modeling indicates that desired gains in spatial resolution are achievable by halving the detector element width. The x-ray exposure rate 15 cm below isocenter, without table or patient in the beam, measured 11.5 R/min at 120 kVp, 24.3 kWp and 3.42 R/min at 70 kVp, 14.2 kWp.

The scanning-beam digital x-ray (SBDX) system uses an inverse geometry, narrow x-ray beam, and a 2-mm thick CdTe detector to improve the dose efficiency of the coronary angiographic procedure. Entrance exposure and large-area iodine signal-to-noise ratio (SNR) were measured with the SBDX prototype and compared to that of a clinical cardiac interventional system with image intensifier (II) and charge coupled device (CCD) camera (Philips H5000, MRC-200 x-ray tube, 72 kWp max). Phantoms were 18.6-35.0 cm acrylic with an iohexol-equivalent disk placed at midthickness (35 mg/cm2 iodine radiographic density). Imaging was performed at 15 frame/s, with the disk at mechanical isocenter and an 11-cm object-plane field width. The II/CCD system was operated in cine mode with automatic exposure control. With the SBDX prototype at maximum x-ray output (120 kVp, 24.3 kWp), the SBDX SNR was 107%-69% of the II/CCD SNR, depending on phantom thickness, and the SBDX entrance exposure rate was 10.7-9.3 R/min (9.4-8.2 cGy/min air kerma). For phantoms where an equal-kVp imaging comparison was possible (> or = 23.3 cm), the SBDX SNR ranged from 47% to 69% of the II/CCD SNR while delivering 6% to 9% of the II/CCD entrance exposure rate. From these measurements it was determined that the relative SBDX entrance exposure at equal SNR would be 31%-16%. Results were consistent with a model for relative entrance exposure at equal SNR, which predicted a 3-7 times reduction in entrance exposure due to SBDX's comparatively low scatter fraction (5.5%-8.1% measured, including off-focus radiation), high detector detective quantum efficiency (66%-73%, measured from 70 to 120 kVp), and large entrance field area (1.7x - 2.3x, for the same object-plane field width). With improvements to the system geometry, detector, and x-ray source, SBDX technology is projected to achieve conventional cine-quality SNR over a full range of patient thicknesses, with 5-10 times lower skin dose.

No abstract

IGCT with stationary source arrays could be an imaging platform potentially capable of imaging a complete 16-cm thick volume within a tenth of a second.

This study demonstrated that conformal treatments of deep-seated targets were achievable with kilovoltage x-rays with dose distributions comparable to MV beams. However, due to the larger volumes irradiated to clinically tolerated low doses, KVAT x-ray source usage for deep-seated lesions will be further evaluated to determine optimal target size.