  The tumour microenvironment (TME) strongly influences tumorigenesis and
metastasis. Two of the most characterized properties of the TME are acidosis
and hypoxia, both of which are considered hallmarks of tumours as well as
critical factors in response to anticancer treatments. Currently, various
imaging approaches exist to measure acidosis and hypoxia in the TME, including
magnetic resonance imaging (MRI), positron emission tomography and optical
imaging. In this review, we will focus on the latest fluorescent-based methods
for optical sensing of cell metabolism and MRI as diagnostic imaging tools
applied both in vitro and in vivo. The primary emphasis will be on describing
the current and future uses of systems that can measure intra- and
extra-cellular pH and oxygen changes at high spatial and temporal resolution.
In addition, the suitability of these approaches for mapping tumour
heterogeneity, and assessing response or failure to therapeutics will also be
covered.
