Because according to the image below, in the format change stage, there is an option to change the format for each CT- section and finally an extracted file for each, and it is not a single file.
To extract a single 3D file from a set of CT sections, you can use a medical image conversion software such as 3D Slicer or ITK-SNAP. Here is a general outline of the process:
Open the medical image conversion software and load the CT sections. This can usually be done by selecting "File > Open" and selecting the CT images from your computer.
Convert the CT sections to a 3D volume. This can usually be done by selecting "Volume > Create Volume" or a similar option in the software.
Save the 3D volume in the desired format. This can usually be done by selecting "File > Save As" and choosing the desired format (e.g. mha, nii, etc.) from the drop-down menu.
Very good. I have experience working with 3D slicer. It is a time-consuming process because is necessary to select slice by slice of images to create a single volume file.
Is the process you described related to ITK-SNAP or another software? It doesn't seem like the time-consuming process of 3D Slicer.