Over-exposures with gamma rays of a 192 Ir source performed on pig skin, have been followed by magnetic resonance imaging. A group of 3 minipigs was given single doses of 96, 32 and 64 Gy applied to the back skin (between 17 and L4) from bottom to neck respectively. NMR images were taken from a Siemens Magnetom 63 SP system operating at 1.5 tesla. T 2 -weighted spin echo images showed that signal intensities in the irradiated areas were significantly decreased during the three weeks following irradiation. The signal evolution was similar in skeletal striated muscle, subcutaneous adipose tissue and skin but with noticeably different amplitudes. The larger variation was observed on skin. This observation, which can be done in the early days after the exposure, suggests that the method could be an important aid to diagnose or to predict tissue necrosis and fibrosis.

Localized irradiation of the skin and subcutaneous tissues with large single doses of gamma rays can induce immediate effects characterized by erythema, desquamation, and necrosis. Correlations between the evolution of the lesions and dosimetry studies have to be established by biophysical methods. NMR studies of the effects of an irradiated Fricke solution might be a means of controlling the delivered irradiation doses. After exposition to ionizing radiations, ferrous ions are transformed into ferric ions. Both are paramagnetic ions, and proton spin-lattice relaxation is accelerated depending on the oxidation reaction. In this study, solution of ammonium ferrous sulfate in an acid environment was incorporated into a gelling substance made with agarose, so that T1 weighted image contrast could be used to detect ferric ion formation. Experiments with 192Ir and 60Co gamma rays with doses in the 0 to 100 Gy range were conducted with Fe2+ concentrations of 0.5, 1, 1.5, and 2 mM in a gelling substance containing 4% agarose. A relationship was established between the amount of Fe3+ created and the spin-lattice proton relaxation rate, which led to a straightforward dose-effect relation. The use of such high doses allowed us to reproduce realistic conditions of accidental overexposure. A linear relationship was obtained between the doses absorbed and the NMR parameters measured (T1 and relative image intensity).

Over-exposures with gamma rays of a 192 Ir source performed on pig skin, have been followed by magnetic resonance imaging. A group of 3 minipigs was given single doses of 96, 32 and 64 Gy applied to the back skin (between 17 and L4) from bottom to neck respectively. NMR images were taken from a Siemens Magnetom 63 SP system operating at 1.5 tesla. T 2 -weighted spin echo images showed that signal intensities in the irradiated areas were significantly decreased during the three weeks following irradiation. The signal evolution was similar in skeletal striated muscle, subcutaneous adipose tissue and skin but with noticeably different amplitudes. The larger variation was observed on skin. This observation, which can be done in the early days after the exposure, suggests that the method could be an important aid to diagnose or to predict tissue necrosis and fibrosis.