General imaging methods..

-> Whole body/tissue fluorescence (fluorescence reflectance imaging):
• Principle: animal or tissue is illuminated and the emitted fluorescence is captured
using a camera.
• Advantages: non-invasive, multiple colours or probes and spectral analysis can
provide additional information, can detect a few hundred cells, can image day after
day. It can provide information about populations of cells.
• Disadvantages: limited resolution, not all anatomical sites image equally well, often
requires the introduction of exogenous fluorophores, autofluorescence.

-> Whole body/tissue bioluminescence:
• Principle: tumour is engineered to express a protein that catalyses a luminescence
reaction, substrate is injected and the emitted light is captured using a camera.
• Advantages: non-invasive, can detect a few hundred cells, can image day after day.
• Disadvantages: limited resolution, not all anatomical sites image equally well, threedimensional
reconstruction is difficult, requires the introduction of exogenous
luminescent enzymes and substrates.


-> Invasive confocal/epifluorescence:
• Principle: similar to fluorescence reflectance imaging except that a much smaller
region is imaged, usually after some surgical manipulation or implantation of a
‘window chamber’.
• Advantages: high spatial and temporal resolution — subcellular structures can be
visualized, multiple colours or probes, confocal techniques provide threedimensional
information.
• Disadvantages: imaging depth currently limited to ~500 ìm even with multiphoton
microscopy, usually requires some surgical manipulation.

-> Raman spectroscopy:
• Principle: light shifted in wavelength from the illuminating source is analysed, the
shifting is influenced by the chemical composition of the tissue being analysed
(changes in the type of C–C bond and amide and CH2 groups can be
identified).
• Advantages: no need for imaging probes, can provide useful chemical information,
can be combined with confocal techniques to improve spatial resolution. Coherence
methods offer much greater sensitivity.
• Disadvantages: sensitivity, still difficult to obtain high resolution images in a useful
time frame.