quantity of a material to a region of a patient 39 s body to be imaged 5 when the region to be imaged is reached by the probe 1 the material is required to form a layer 3 on the surface of the region to be imaged 5 to this end the material is chosen so as to be fairly stiff at temperatures slightly below the normal temperature of the region of the body being imaged but to soften to an extend sufficient to take up the shape of the region 5 on being brought into contact with the region 5 and raised to its temperature in addition the material is required to be biologically compatible with the body containing the region to be imaged the material is thus suitably a lipid formulated to have the required degree of change of viscosity with temperature in addition to carrying the lipid material to the region to be imaged the probe 1 produces light signals which can be processed to produce an image representation of the region 5 to this end the lipid material carried by the probe 1 includes a small quantity of a fluorescent dye which in response to incidence thereon of light of one wavelength emits light of a different wavelength the probe 1 carries light guide means 2 e g an optical fibre for directing light of the one wavelength from a laser external to the body containing the region to be imaged 5 onto the layer 3 formed on the region 5 and means for.