The O-arm is a cone beam imaging system designed primarily to support orthopedic surgery and is also used for image-guided and
vascular surgery. Using a gantry that can be opened or closed, the O-arm can function as a 2-dimensional (2D) fluoroscopy device or
collect 3-dimensional (3D) volumetric imaging data like a CT system. Clinical applications of the O-arm in spine surgical procedures,
assessment of pedicle screw position, and kyphoplasty procedures show that the O-arm 3D mode provides enhanced imaging
information compared to radiographs or fluoroscopy alone. In this study, the image quality of an O-arm system was quantitatively
evaluated. A 20 cm diameter CATPHAN 424 phantom was scanned using the pre-programmed head protocols: small/medium (120
kVp, 100 mAs), large (120 kVp, 128 mAs), and extra-large (120 kVp, 160 mAs) in 3D mode. High resolution reconstruction mode
(512×512×0.83 mm) was used to reconstruct images for the analysis of low and high contrast resolution, and noise power spectrum.
MTF was measured using the point spread function. The results show that the O-arm image is uniform but with a noise pattern which
cannot be removed by simply increasing the mAs. The high contrast resolution of the O-arm system was approximately 9 lp/cm. The
system has a 10% MTF at 0.45 mm. The low-contrast resolution cannot be decided due to the noise pattern. For surgery where
locations of a structure are emphasized over a survey of all image details, the image quality of the O-arm is well accepted clinically.
The radiant quantum efficiency (RQE) of x-ray phosphors is defined as the ratio of the emitted luminescent power and
the power absorbed by the material. For a given x-ray imaging technique, a high RQE phosphor means a lower x-ray
exposure to patients and a better image quality. To improve RQE, phosphors such as LiF and BaFX:Eu ( X = Br, Cl, I)
host lattices, which are commonly used in medical dosimetry and imaging system, are always doped with Cu, Ti, or Tb.
Experimental observations showed that these dopants can increase phosphor RQE significantly. In this study, we
theoretically investigated the effect of additional dopants on the RQE of LiF:Mg and BaFX:Eu host lattices using
Density Functional Theory (DFT) in the Local Density Approximation (LDA). Self-consistent charge density
calculations were performed. The energy loss function L(w) was obtained and used to calculate the RQE for different
phosphors. The results showed that additional dopants produced changes in the optical properties of the phosphors,
particularly the energy loss function L(w). Doping with more substitutional impurities increased the RQE of all host
lattices except the BaFI lattice where the RQE decreased.
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