The homeotic skeletal shift test as an indication of teratogenic risk of x-ray or MRI exposure

The authors examined the teratogenic risk of midgestation exposure to X-rays or Magnetic Resonance Imaging (MRI) in BALB/c in mice using the homeotic shift test of skeletal features. This test measures teratogenic injury to cartilaginous and osseous tissues as shifts in the number of costosternal junctions, sternebrae, thoracic ribs, and axial vertebrate. The X-ray exposures were performed to evaluate the sensitivity of this test. Pregnant mice were exposed to 0, 25, 50, or 100 rads X-rays on gestational day 9 1/4. At term, fetuses were processed and scored for skeletal shifts. Additional ribs, costosternal junctions, thoracic vertebrae and presacral vertebrae resulted from exposure to 50 or 100 rads X-rays. Fetuses exposed to MRI (0.35 Tesla, pulsed gradients 2.3 x 10/sup -4/ T/cm for 2.5-10m sec; 15 MHz RF at 61 mW for 15H) demonstrated no significant skeletalshifts. This approach should be valuable for evaluating the safety of MRI and of fetal exposures to other radiation sources