## 4 Discussion
### Influence of Scanning Strategy on Porosity
This is simply due to the high number of spherical pores as opposed to the irregular pores, which is high in volume (and equation diameter), while low in numbers, as seen in Figure 10.  
[PERSON] et al. [16] investigated the porosities of laser powder-bed specimens using synchrotron based micro-tomography (uSXCT), resulting in scans with a spatial resolution of 1.5 um. They found that for laser powder-bed AM the larger porosities caused by lack-of-fusion defects and key-holing dominated the total volume of defects, making the gas porosities less significant, \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Specimen** & \multicolumn{3}{c}{**Vol.\% of Pores (\% of Total) (\%)**} & \multicolumn{3}{c}{**Avg. Spherical Equation Diameter (\(\mu\)m)**} \\ \cline{2-7}
**Designation** & **Total** & **Spherical** & **Irregular** & **Total** & **Spherical** & **Irregular** \\ \hline
**Line Scan–LFOV** & 0.37 & 0.35 (95) & 0.018 (5) & 21 & 21 & 47 \\
**Line Scan–4x** & 0.10 & 0.094 (94) & 0.0037 (4) & 10 & 10 & 19 \\
**Island Scan** & 1.4 & 0.41 (29) & 0.96 (69) & 22 & 20 & 78 \\
**Stripes–LFOV** & 1.2 & 0.29 (24) & 0.94 (78) & 11 & 10 & 30 \\
**Island Scan** & 0.77 & 0.69 (90) & 0.062 (8) & 21 & 21 & 64 \\
**Modeled–LFOV** & 0.80 & 0.58 (73) & 0.23 (29) & 10 & 10 & 19 \\
**Modeled–4x** & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Calculated volume percentage and average spherical equivalent diameter of pores detected in Avizo on reconstructed CT using LFOV and 4\(\times\) objectives, respectively, on SLM specimens scanned with different strategies. depending on the processing parameters (powder, velocity, and hatch spacing). The presence of irregular and spherical porosities depended strongly on the processing parameters, and for some specimens, the amount of spherical porosities was close to that of the irregular porosities, making them equally significant [16]. Similarly, the pore statistics of the line scan, island scan stripes, and modeled specimens clearly show that both the amount and type of pores can be highly dependent on scanning strategy. Smaller average equivalent pore diameters can be observed for all three specimens (Table 2) when investigated with 4\(\times\) objective compared to LFOV objective, which can be ascribed to the smaller voxel size, allowing for the detection of smaller pores, which is evident in Figure 10. Figure 10 also shows how both a smaller and a higher amount of especially spherical pores was detected with the 4\(\times\) objective in all samples. Although it does little to the total pore volume, due to the low influence of the small pores, is seems to affect the evaluation of spherical vs. irregular pores. For the island scan specimens, the irregular pores account for a higher percent of the total pore volume in the 4\(\times\) analysis than the LFOV analysis. For all three specimens, the average equation diameter of the irregular pores decreased, which is also reflected in Figure 10, where the irregular pores have higher frequencies at lower equation diameters for all three specimens. This can be explained by the smaller voxel size equaling higher surface resolution, allowing for a more correct description of both volume and area of the pores.