The Maximum Feret Diameter is expressed in microns and represents the longest dimension of the particle independent of its angular rotation at the time the image was captured. The Maximum Feret Diameter is determined by isolating the corner pixels of the object’s perimeter and taking the maximum distance between each corner pixel to all other corner pixels.
A graphical representation of this algorithm can be seen in the figure. Once the longest dimension (in pixels) has been determined, this value is converted to microns using proprietary conversion techniques to avoid the error inherent with performing direct calculations based on field of view dimensions.
The conversion techniques are based on a mapping of the entire instrument size range using NIST traceable polystyrene beads. Although the conversion is based on polystyrene beads, the unique operation of the MFI product platform will guarantee the results obtained from the instrument are insensitive to the particle material properties. Therefore, the instrument does not require calibration against specific sample types for proper operation.
