Study of inks used in biomedical optics phantoms: stability and ageing

Abstract

Inks are the most common absorbers added in phantoms for biomedical optics experiments. Due to the small quantities required, it is usual to prepare dilutions in distilled water and to store them for future use. However, they may degrade with time. This work investigates the stability, over a 60 day period, of various types of ink dilutions as a component used in tissue-mimicking phantoms. For this purpose, the optical properties, particularly the absorption coefficient, of a diffusive phantom fabricated with various pre-diluted inks have been determined by using time-resolved experiments, for the period of time under investigation. Two commercial India inks were studied, namely Rotring® and Higgins®, as well as a third type, a black ink-jet printer ink (Powertec®). Results suggest that all ink dilutions suffer from ageing, affecting the reproducibility of the optical properties of the phantoms. For the investigated period, this effect was more noticeable for the India inks, but almost negligible for the ink-jet printer ink.