Technical performance evaluation of mobile x-ray systems for chest imaging

To present both quantitative and test object-based imaging performance measurements for the latest mobile digital radiography (DR) x-ray systems for bedside imaging.

Seven mobile DR systems with CsI-based detectors were assessed. The modulation transfer function (MTF) and detective quantum efficiency (DQE) were measured using the RQA8 beam quality at three detector incident air kerma levels (K_B). A weighted polynomial model applied to the variance was used to estimate electronic, quantum and structure noise fractions versus K_B. Technical image quality was assessed by imaging the Leeds TO12 contrast-detail phantom with 10 cm, 15 cm and 20 cm PMMA, using the x-ray technique factors specified by the applications specialists for the adult Chest AP examination.

Electronic noise dominated below a mean value of 0.14 µGy, while quantum noise comprised 91.6% ,on average, of total image noise at 2.5 µGy. The spatial frequency for an MTF of 0.1 ranged from 3.2 mm^-1 to 4.7 mm^-1, with a mean of 3.8 mm^-1. DQE at 0.5 mm^-1, measured at the RQA8 quality and a target K_B value of 2.5 µGy, ranged from 0.46 to 0.64 with a mean of 0.55. Mean nominal threshold contrast for the 2 mm diameter disc (±1 standard deviation) was 1.72% ± 0.23%, 3.66% ± 0.68% and 8.05% ± 2.78%, for 10 cm, 15 cm and 20 cm PMMA, respectively.

Despite some variation between detectors, overall imaging performance for the systems was good. These data could act as reference values for medical physicists assessing x-ray devices for bedside imaging.