EFFECTS OF IN-UTERO EXPOSURE TO 4.7-T MR-IMAGING CONDITIONS ON FETAL GROWTH AND TESTICULAR DEVELOPMENT IN THE MOUSE

The effects of exposure in utero to high field (4.7 T) magnetic resona nce imaging (MRI) conditions on fetal growth, adult growth, and testic ular development in the mouse were investigated, Exposures of 8-h dura tion were made on day 9 and/or day 12 of gestation, Also investigated were effects of a combined treatment regime using continuous wave, unf ocussed 1 MHz ultrasound on day 9 and MRI on day 12, Treatment groups consisted of 8 to 10 pregnant darns, Fetal data were taken on day 18 o f gestation and data from adult animals that were exposed in utero wer e taken on day 50 postpartum, Significant differences in sensitive bio logical end points following in utero exposure to complex MRI held con ditions were found. Fetal weights of the exposed groups ranged from 11 % (day 9 MRI) to 17% (day 9 ultrasound/day 12 MRI) lower (p less than or equal to .05) than those of the cage control and sham-exposed fetus es and crown-rump length of exposed animals was reduced by 8% (p less than or equal to .05). The postpartum death rate was as high as 38% (s ignificant atp p less than or equal to .05 level) following MRI exposu re on day 9 and day 12 of gestation, Daily sperm production was reduce d by as much as 44% (p less than or equal to .05) in adults exposed to MRI on day 12 of gestation, A reduction in testis weight and volume i n the adult males was also seen, but the difference was not statistica lly signifcant at the p less than or equal to .05 level, No effect was seen on embryonic deaths, sex ration, body weight at day 50, spleen w eight, or seminal vesicle weight, The mechanism responsible for these results could involve one or more of the applied fields interacting wi th a sensitive stage of fetal development, Further studies are planned to isolate the individual held components and to elucidate biochemica l and/or hormonal changes that may follow in utero exposure.