Images acquired with volumetric CT showing the definition of QA metrics used to analyze image quality. (a) Image of the CatPhan phantom. (b) Interface of the analysis software. (c) Verification of image scale. (d) Assessment of image uniformity.
Signal-to-noise ratio in the calibration flood field, measured on unit F over a period of 26 months. Over this period, the x-ray tube of this unit was replaced twice.
High contrast spatial resolution for seven volumetric imaging systems. (a) Representative slice through the high resolution module of the CatPhan 500 phantom for unit A. (b) MTFs for ten volumetric CBCT systems and (c) average MTF for the two vendors. (d) Dramatic improvements in MTF are produced when scattered radiation is decreased by reducing the x-ray field size.
Linearity of CT numbers for seven volumetric systems. (a) Representative slice through the sensitometric module of the CatPhan 500 phantom. (b) Comparison of expected and measured CT numbers for six of our units. (c) The measurement for units A, G, H, and I were repeated with the CatPhan phantom fitted within an asymmetric annulus to affect scatter conditions (dashed line), thereby showing a shift of the curve.
Recommended image quality QA for a kilovoltage imaging system mounted on an accelerator. Tolerances and frequency may change according to expectations, experience, and performance. Tests denoted with an asterisk indicate minimal tests required after replacing system components.
Discrepancies between measured and actual distances between objects 5 cm apart for six Elekta units. Data has been accrued over varying periods of time. No time trend was apparent in the plotted results.
Summary of the MTF measurement for our volumetric imaging systems. The frequencies at which the MTF are 0.5 and 0.1 are shown.
Axial reconstruction uniformity metrics for ten volumetric imaging systems. Numbers in parentheses indicate measurements with x-ray fields smaller than that used at acceptance, thereby reducing in-phantom scatter and improving the uniformity of axial reconstructions and reducing capping/cupping artifacts.
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