Our current understanding of how pancreatic beta cell mass fluctuates during the course of diabetes development is largely based on indirect evidence. Various approaches based on in vivo metabolic testing have been described, each reflecting specific aspects of beta cell function [1]. These measurements are correlated with actual beta cell mass only to a certain extent, and were developed to allow estimates of mass following surgery, therapy or transplantation. Direct visualisation of beta cell mass by means of novel imaging technologies is anticipated to provide more detailed insight into the true kinetics of key processes such as physiological beta cell turnover, islet graft loss and the pathophysiology of type 1 and type 2 diabetes. Likewise, a substantial part of what we know about the autoimmune component of type 1 diabetes has historically been derived from ex vivo, cross-sectional studies in rodents. Improved intravital microscopy techniques could also shed new light on the in situ behaviour of immune cells—after all, seeing is believing.

In this issue of Diabetologia, Holmberg and Ahlgren review recent progress in the area of optical imaging technologies that is specifically applicable to monitoring the pancreas [2]. Although most investigators may be familiar with conventional non-optical imaging modalities such as magnetic resonance imaging (MRI) and positron