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Comparison of entrance exposure and signal‐to‐noise ratio between an SBDX prototype and a wide‐beam cardiac angiographic system
Author(s) -
Speidel Michael A.,
Wilfley Brian P.,
StarLack Josh M.,
Heanue Joseph A.,
Betts Timothy D.,
Van Lysel Michael S.
Publication year - 2006
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2198198
Subject(s) - isocenter , kerma , detective quantum efficiency , imaging phantom , physics , automatic exposure control , nuclear medicine , optics , computed radiography , signal to noise ratio (imaging) , image intensifier , beam (structure) , materials science , dosimetry , image quality , medicine , artificial intelligence , computer science , image (mathematics)
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 ∕ cm 2iodine 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 ( ⩾ 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 ( 1.7 × – 2.3 × , 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.