Human observer

In the human observer experiment, three medical physicists took part in four alternative forced choice (4-AFC) experiments in order to yield a percentage of correct responses (PC) indicating how well they managed to detect the signals. The 4-AFC experiment consisted in selecting the signal-present image in a batch of three signal-absent images and one signal-present image, which were presented together in a randomised order. All observers were blinded to the CT acquisition and reconstruction conditions and began their test with a training session that was made of images acquired at high dose level. They were then asked to make decisions for all 32 categories acquired. The previously made acquisitions provided 100 signal-present ROIs and 1000 signal-absent ROIs for each category. ROIs among those data were selected randomly and used for the 4-AFC tests. For each observer and category, every answer to the 100 trials was stored and compared with the correct response, allowing the computation of the PC.