Comprehensive quantitative evaluations of reconstruction method using oil-gel-based phantom in ultrasound computed tomography

The performance of a reconstruction method in ultrasound computed tomography (CT) ideally should be evaluated using various kinds of phantoms at a wide range of speeds of sound when inclusions are made. However, generating real phantoms is more time consuming than generating simulated ones. In our previous study, we developed an oil-gel-based phantom by including water or salt water. In this study, we designed an evaluation method including various contrast conditions using the oil-gel-based phantom by changing the liquid and temperature. The phantom including water or salt water in 10-, 7-, 5-, or 3-mm holes was measured using our prototype ultrasound CT at temperatures of 15, 17.5, 20, 22.5, 25, 27.5, and 30 degrees C, making the number of measurements 14. For these conditions, the difference (= contrast) in the speed of sound between the inclusions and the oil gel was -37 to 92 [m/s]. The filtered back projection (FBP) and full waveform inversion (FWI) were evaluated. The mean error of the speeds of sound in inclusions with the FBP and FWI were 17.1 +/- 14.9 and 8.8 +/- 10.1 [m/s], respectively. The mean percentage error of the sizes of the phantom (51 mm) and inclusions with the FBP and FWI were 22.5 +/- 22.5% and 3.9 +/- 4.3%, respectively. A single oil-gel-based phantom provided various contrast conditions after the temperature and liquid were changed. This kind of phantom can be used for comprehensive quantitative evaluations of the reconstruction method.