A system and method for determining at least one geometric property of a particle in a sample. A sample is irradiated to thereby generate Raman scattered photons. These photons are collected to generate a Raman chemical image. A first threshold is applied wherein the first threshold is such that all particles in the sample are detected. A particle in the sample is selected and a second threshold is applied so that at least one geometric property of the selected particle can be determined. At least one spectrum representative of the selected particle is analyzed to determine whether or not it is a particle of interest. The step of determining a second threshold may be iterative and automated via software so that candidate second thresholds are applied until a satisfactory result is achieved.