How to count toothbrush bristles

CT microtomography makes it possible to obtain information about the external and internal, optically inaccessible geometry as well as the structure of the sample material. This fact opens up a very wide application field for this method.
As one of a number of applications, microtomography can be used to determine the number of difficult-to-count (number, visibility) objects (particles, elements).
To illustrate such an example, we decided to determine the number of fibers in a toothbrush. Here we will be interested in whether the number of bristles declared by the manufacturer is close to the value stated on the package (5460) and the diameter of the fibers (0,1mm).

After the acquisition (at a resolution of 18 μm), we performed a reconstruction in the XAct program and then determined the surface. We used the Wall thickness module to determine the fiber thickness in the VGSTUDIO MAX program. The measured mean value was 0,095 mm, which corresponds to 0,1 mm stated by the manufacturer.

To accurately determine the number of fibers, we used a single slice image that we analyzed in FIJI.

It can be seen from the images that the detection of individual fibers was quite accurate. The resulting number of threads was determined as 5772, but the real number will be even higher, because sometimes 2-3 threads merged into one cell and were counted as one thread.
VGSTUDIO MAX performs quantization of course as well. After we detect the monitored structure in the relevant module and have it analyzed with the given parameters of the selected module, we have a number of statistical analyzes at our disposal, i.e. the number of detected objects. In this case, however, we found the method chosen above to be simpler.

RX Solutions (Destom, XAct), Volume Graphics (VGSTUDIO MAX), FIJI.