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Dose and detectability for a cone‐beam C‐arm CT system revisited
Author(s) -
Ganguly Arundhuti,
Yoon Sungwon,
Fahrig Rebecca
Publication year - 2010
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 - 10.1118/1.3397465
Subject(s) - noise (video) , resampling , mathematics , filter (signal processing) , range (aeronautics) , physics , optics , nuclear medicine , mathematical analysis , algorithm , image (mathematics) , computer science , artificial intelligence , materials science , computer vision , medicine , composite material
Purpose: The authors had previously published measurements of the detectability of disk‐shaped contrast objects in images obtained from a C‐arm CT system. A simple approach based on Rose's criterion was used to scale the date, assuming the threshold for the smallest diameter detected should be inversely proportional to( dose )1 / 2. A more detailed analysis based on recent theoretical modeling of C‐arm CT images is presented in this work. Methods: The signal and noise propagations in a C‐arm based CT system have been formulated by other authors using cascaded systems analysis. They established a relationship between detectability and the noise equivalent quanta. Based on this model, the authors obtained a relation between x‐ray dose and the diameter of the smallest disks detected. A closed form solution was established by assuming no rebinning and no resampling of data, with low additive noise and using a ramp filter. For the case when no such assumptions were made, a numerically calculated solution using previously reported imaging and reconstruction parameters was obtained. The detection probabilities for a range of dose and kVp values had been measured previously. These probabilities were normalized to a single dose of 56.6 mGy using the Rose‐criteria‐based relation to obtain a universal curve. Normalizations based on the new numerically calculated relationship were compared to the measured results. Results: The theoretical and numerical calculations have similar results and predict the detected diameter size to be inversely proportional to( dose )1 / 3and( dose )1 / 2.8, respectively. The normalized experimental curves and the associated universal plot using the new relation were not significantly different from those obtained using the Rose‐criterion‐based normalization. Conclusions: From numerical simulations, the authors found that the diameter of detected disks depends inversely on the cube root of the dose. For observer studies for disks larger than 4 mm, the cube root as well as square root relations appear to give similar results when used for normalization.