Phantoms
The relationships between Z-number and artifact length, width, intensity, and needle width are plotted below. All except artifact length are significantly associated with Z-number. In particular, the relationship between needle width and Z-number appears to be non-monotone and is fitted by a quadratic curve (a linear fit yields low \(R^2\) and non-significant \(p\)-values).
Swine model
In the swine model, artifact length, width, intensity, and needle width are compared between aluminum and stainless by kidney, liver, and lung below. The variables are summarized by median (IQR), with \(p\)-values computed by the Wilcoxon rank sum test.
| Aluminum | Stainless | p-value | |
|---|---|---|---|
| Artifact Length (mm) - Kidney | 2.8 (2.8, 2.8) | 81.6 (52, 96.3) | 0.004 |
| Artifact Length (mm) - Liver | 2.8 (2.8, 15.5) | 92.8 (89.5, 97.7) | 0.007 |
| Artifact Length (mm) - Lung | 28.8 (26.2, 47.8) | 116.4 (110.9, 131.3) | 0.065 |
| Artifact Width (mm) - Kidney | 0.7 (0, 2.3) | 9.8 (7, 10.8) | 0.008 |
| Artifact Width (mm) - Liver | 1.5 (0.4, 2.3) | 9.8 (8.2, 11.2) | 0.005 |
| Artifact Width (mm) - Lung | 3.4 (3.2, 4.3) | 8.9 (7.8, 10.6) | 0.065 |
| Artifact Intensity (HU) - Kidney | -126.2 (-215.9, -80.9) | -464.4 (-666.6, -405.6) | 0.002 |
| Artifact Intensity (HU) - Liver | -35.1 (-40.7, -19.6) | -698.7 (-806.3, -538) | 0.002 |
| Artifact Intensity (HU) - Lung | -88.3 (-110.8, -73.4) | -562 (-728.2, -496.1) | 0.002 |
| Needle Width (mm) - Kidney | 4.1 (2.4, 19.9) | 25.7 (23.3, 27.6) | 0.180 |
| Needle Width (mm) - Liver | 2.3 (1.8, 2.7) | 26.1 (24.8, 27.2) | 0.002 |
| Needle Width (mm) - Lung | 3.1 (3, 3.8) | 25.5 (25.2, 25.7) | 0.002 |
The following shows the bar charts comparing the means of aluminum and stainless by kidney, liver, and lung (with error bars indicating the standard error of the mean; * \(p<0.05\), ** \(p<0.01\)).
