# Comparison of Bone Segmentation Software over Different Anatomical Parts
## 4 Discussion  
For the first time, the main features of five commercial software packages (Mimics(r), Amira(tm), D2 PTM, SimplewareTM, and Segment 3D PrintTM) for the generation of STL bone models were investigated. Relevant performance in bone model reconstruction was analyzed by the same operator, using a single computer workstation, and compared accurately in fifteen different CT scans, from five anatomical areas with distinct morphological complexity, by the same operator and using the same computer hardware to avoid possible bias. Amongst the scope, there was also the quantitative comparison of specific features with those from four freeware software packages (3 DSlicer, ITK-SNAP, InVesalius, and VuePACS3D--the latter being accessible free-of-charge in our radiological unit), analyzed recently by the same authors [25]. To our knowledge, these nine software packages are amongst the most popular for medical imaging segmentation of the musculo-skeletal system [22; 27; 28; 35]. To make rational and objective comparisons, both the CT scans and the operator were the same in the two studies, and manual intervention was limited as much as possible also in the present analysis. Additionally, all software packages were used on the same computer to avoid the situation wherein segmentation performance is affected by the hardware specifications. The present work did not seek to investigate either the segmentation algorithms, tools, and features of these commercial software packages, clearly very different from one another, or the degree of automation in 3D model reconstruction, but rather to assess only the main quantitative features and the gross results for comparison. Therefore, apart from a few basic final refinements, only the standard segmentation tools, such as thresholding, were used in each software package for bone shape reconstruction. The present work obviously has limitations. To limit the cost of the present exercise, access to these commercial software packages was sought in the geographical area of the authors; five amongst the most popular were found and tested with no additional charges. Clearly, many other software packages are available on the market, but it was not possible to further enlarge this exercise, also because the condition of a single operator and a single computer was pursued. In this respect, the operator could not become very familiar with each software package in a short time; therefore, local users, already familiar with these, provided some support, only that necessary to obtain the final results. Threshold values for optimal mask visualization in bone segmentation were set by the operator in each software program, according to the specific density of each bone under analysis but generally in the range of 130-226 Hounsfield unit values, as in the previous work [25]. Of course, these commercial software packages feature many additional tools for manual editing and refinements, particularly with regard to the final number and the density of mesh triangles, but these were not exploited, to maintain the comparison of the initial basic performance. Finally, given the scope of this work, there was no need to distinguish between the different bones within a model, so all bones in each scan were segmented as a single object. Our findings compare well with recent similar studies in the literature in terms of tested scan resolution, threshold, and accuracy of 3D bone model reconstruction [23; 36]. With respect to similar previous studies where features and reconstruction techniques from different software packages are investigated and compared [22; 27; 28; 35], the present work offers quantitative objective outcomes also in terms of the number of triangles, file size, and relevant ratio. In addition, the present analysis was not biased by single anatomical areas or limited scans, but involved full morphological reconstructions from five different anatomical areas with different complexity, overall from fifteen different subjects.