## 2 Materials and Methods
### Procedure to Obtain a Digital Pelvic Model  
The Digital Imaging and Communications in Medicine (DICOM) data of the patients were obtained from the GE-MS Revolution CT multidetector tomograph--Discovery750 HD (GE Medical Systems, Buckinghamshire, UK) at St. Jadwiga Queen Clinical Regional Hospital No. 2 in Rzeszow. The traditional scanning protocol for the hip joint area was used, with the following parameters: helical mode; Tube voltage: 120 kV; Tube current-time product: 90 mAs; Total Collimation width: 40 mm; Convolution Kernel: Soft; Matrix size: 512 \(\times\) 512; Pixel size: 0.5 mm \(\times\) 0.5 mm; Slice thickness: 0.625 mm. Due to some limitations in the obtained DICOM data, a patented procedure for numerical processing was implemented in Amira 5.4 software, as detailed in the publication [25]. This procedure also involved removing noise created by metal artifacts using a noise reduction minimum filter, increasing the spatial resolution of the DICOM data by applying the Lanczos interpolation method, and sharpening the boundary between bone structure and soft tissue using an unsharpening filter. Furthermore, the segmentation process was improved by dividing the pelvic region into three sub-areas based on local thresholding in the numerical segmentation process. The entire process is illustrated in Figure 2.  
This procedure aimed to improve the accuracy of segmenting the extracted bone structure by selecting an individual threshold expressed in the Hounsfield [HU] unit scale in the desired area. This was determined based on information about the average grey shade values of the pixels assigned to the bone structure. By developing local segmentation thresholds, three separate areas of the pelvis were segmented, i.e., Ilium, Acetabulum,  
Figure 2: Procedure for increasing the accuracy of numerical model development within the part of a pelvic bone area.  
Pubis, and Ischium. During the segmentation process for patients no.1 and no.3, the implant was separated from the bone structures. This process was enhanced by adjusting the pixel visibility thresholds in the 2D image. The iso-surface method was used to create the 3D model. It is an indirect surface method based on the marching cube algorithm. This algorithm divides the space into a series of cubes, each encompassing one or more voxels. The values at the nodes of each designated cube are then evaluated against a specified iso-value. Based on whether a node's value is higher or lower than the iso-value, polygons representing the iso-surface that intersects between these points are generated within the cube. There are 256 possible cube orientations relative to the surface; however, only 15 unique canonical orientations can be recognized. Considering the whole algorithm, the following main steps can be distinguished:  
* Cell selection (iso-voxel);
* Classification of the position of each vertex (internal/external);
* Creation of an index i;
* Finding the edges intersected by the contour surface according to the case table for the index i of the cell;
* Determination of intersection points, linear interpolation;
* Attaching the determined points (triangles) to the contour surface;
* Transfer to the next cell.  
The final models obtained during reconstruction were saved in a StereoLitography (STL) file. The research process involved testing two options. The first option focused on selecting measurement procedures to assess geometric accuracy and surface roughness in the pelvic part's three distinct areas (ilium, acetabulum, pubis, and ischium). The second option aimed to verify and measure the geometry of a pelvic part model created as a single piece.