Isotherm mapping in hyperthermia using subtraction X-ray computed tomography.

The prospects for the use of X-ray computed tomography (CT) for isotherm mapping were investigated. The spatial distribution of CT changes was obtained by digital subtraction of images taken before and during heating of a 200 mm diameter cylindrical 4% agar phantom. Due to a rather unfavourable signal-to-noise ratio, the noise level in the resulting image had to be reduced by low-pass filtering using the 2-dimensional Fast Fourier Transform followed by spatial averaging. The resulting isotherms showed a resolution of 0.5 degree C at a spatial resolution of 4.2 mm. Isotherms so obtained are presented and the possibility of using the method in clinical hyperthermia is discussed.