The influence of 241-Am and DTPA on morphometric parameters of the rat femur.

Microradiographically detectable alterations of the bone structure in the femur of young rats induced by monomeric 241-Am(III) (i.v., 30 muCi/kg) were studied. The morphometric and dosimetric measurements were carried out by means of an electronic image analyzer. 8 weeks after injection of 241-Am a characteristic alteration of the frequency distribution of the chord lengths over the trabeculae in the epiphysis and over the metaphyseal marrow spaces was found. The structure of the spongiosa is irregular with both large, coarse and small fragmented trabeculae. The complexity of the bone architecture and the area of the endosteal surfaces is reduced. The surface/volume ratio in control animals varies between 36 mm-1 in the epiphysis and 64 mm-1 in the region of the epiphyseal cartilage plate. From the specific surface burden (pCi/mm2) the average dose rates were determined. There is no significant difference between the calcified tissue fraction in controls and animals with 241-Am, with the exception of the metaphyseal band where the locally high dose rates cause a devitalization of the tissue with inhibition of bone resorption as well as an abnormal trabeculation in the metaphysis. Treatment by Ca-DTPA reduces the 241-Am deposition nonuniformly and the pathological manifestations are markedly less pronounced. The mean trabecular width is about 100 mum in the epiphysis and has a minimum of 40 mum in the central part of the epiphyseal plate. The mean chord length over the marrow spaces varies between 90 and 210 mum.