The scanning-beam digital x-ray (SBDX) system uses an inverse geometry, narrow x-ray beam, and a 2-mm thick 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, max). Phantoms were acrylic with an iohexol-equivalent disk placed at midthickness ( iodine radiographic density). Imaging was performed at , with the disk at mechanical isocenter and an 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 (, ), the SBDX SNR was 107%–69% of the II/CCD SNR, depending on phantom thickness, and the SBDX entrance exposure rate was ( air kerma). For phantoms where an equal-kVp imaging comparison was possible , 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 detectordetective quantum efficiency (66%–73%, measured from 70 to ), and large entrance field area (, 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.
The authors wish to give thanks to Bill Peterson, Bruce Floyd, Augustus Lowell, Jerry Pretti, Tom Case, Ed Solomon, Marc Whyte, and former associates of NexRay Inc. and Cardiac Mariners Inc. for their technical support and advice during this project. The authors also thank Larry Whitesell and Jennifer Buck for their assistance in constructing the phantoms used in this study. Partial financial support for this work was provided by the National Heart, Lung, and Blood Institute, Grant No. R01 HL55409, and by the National Cancer Institute Grant No. 5 T32 CA09206.
II.A. Large-area signal-to-noise ratio
II.B. Relative entrance dose
II.C. SBDX design tradeoffs
III.A. Phantoms and imaging conditions
III.B. SBDX prototype
III.B.1. Large-area SNR
III.B.3. Noise equivalent quanta
III.B.4. Phantom entrance exposure
III.B.5. Scatter fraction
III.B.6. Detection efficiency
III.C. Conventional II/CCD system
III.C.2. Signal linearization
III.C.3. Large-area SNR
III.C.4. Entrance exposure
III.D. X-ray spectrum modeling
IV.A. Measured SNR and entrance exposure
IV.B. Relative entrance exposure at equal kVp
IV.C. Detection efficiency and scatter fraction
IV.D. Comparison with model
IV.D.1. Relative entrance exposure
IV.D.2. Relative SNR
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