A system for high-speed NIR transmission imaging of drug delivery in tissue

The development and characterisation of new drug delivery techniques often requires visualising the location of delivered fluid in tissue samples. The opacity of tissue means that this can typically only be done with destructive post-processing techniques, or with the use of ionising radiation (eg. X-ray). In this work we present a novel approach to imaging fluid during delivery into port-mortem tissue samples using transmission imaging at near-infrared (NIR) wavelengths. The system makes use of wavelengths just above the visible range (765 nm), at which tissue is relatively transparent, and to which visible light cameras remain sensitive. Thus, this system utilised a low-cost high-speed (1000 fps) camera and optical components designed for use with visible light. We demonstrate that this NIR imaging system is capable of measuring the location of delivered fluid and an 18G needle in 12 mm thick samples of muscle and fat tissue at 1000 fps. Predictions of needle depth using the imaging system compared well to the known needle position in the tissue: the standard deviation of the depth measurements was approximately 0.7 mm in muscle and 1.2 mm in fat. NIR images captured during and after delivery compare favourably with observations made using 2D X-ray and by sectioning the tissue post-injection. This system can support studies of fluid dispersion and penetration into tissue by new drug delivery systems, thus assist the development of new drug delivery techniques.