Table 5.
Summary of speed of sound accuracy and uniformity measurements. The measurements were performed for five phantoms. The mean value is the average of three ROI measurements (n = 3) within each phantom. The SD values represent one standard deviation across all the number of pixels within an ROI. Uniformity is calculated as NAAD as described above and is essentially related to the percentage ratio of the standard deviation and mean values. Actual values are the reference speed of sound values for the phantoms as measured by the piston transducer setup. Bias values represent the speed measurement accuracy and are calculated as difference between the actual and the measured mean value. Percentage bias values are ratio of bias and actual speed of sound value. The coefficient of variation is a measure of speed of sound precision and is a ratio of SD (n = 3) and mean (n = 3)
| Phantom# | Mean (m/s) | SD (m/s) | Uniformity (%) | Actual (m/s) | Bias (m/s) | Bias (%) | Coefficient of variation (%) |
|---|---|---|---|---|---|---|---|
| 1 | 1515.5 | 6.4 | 99.58 | 1510 | −5.5 | 0.36 | 0.22 |
| 2 | 1518.5 | 6.8 | 99.55 | 1516 | −2.5 | 0.16 | 0.10 |
| 3 | 1432.0 | 5.1 | 99.64 | 1435 | 3.0 | 0.21 | 0.09 |
| 4 | 1493.5 | 7.8 | 99.48 | 1494 | 0.5 | 0.04 | 0.21 |
| 5 | 1449.2 | 5.9 | 99.59 | 1448 | −1.2 | 0.08 | 0.17 |
| Mean= | 99.57 | Mean= | 0.17 | 0.16 |