Medical/biological study (experimental study)

Effects of in utero exposure to 4.7 T MR imaging conditions on fetal growth and testicular development in the mouse med./bio.

By: Carnes KI, Magin RL

Published in: Magn Reson Imaging 1996; 14 (3): 263-274

To study the effects of exposure in utero to high field (4.7 Tesla) magnetic resonance imaging conditions on fetal growth, adult growth, and testicular development in the mouse.

Exposures of 8 h duration were made on day 9 and/or day 12 of gestation. Effects of a combined treatment regime using continuous wave, ultrasound (1 MHz unfocused, without MRI) on day 9 and MRI on day 12 were also investigated. Fetal data were taken on day 18 of gestation. Data from adult animals that were exposed in utero were taken on day 50 postpartum.

Exposure	Parameters
Exposure 1: 200 MHz Modulation type: pulsed Exposure duration: continuous for 8 h on day 9 and/or day 12 of gestation	magnetic flux density: 4.7 T SAR: 1.5 mW/kg spatial average (whole body)
Exposure 2: 1 MHz Modulation type: CW Exposure duration: 30 s	power density: 5 W/cm²

animals were treated in seven groups: i) sham ii) MRI exposure on day 9 of gestation iii) MRI exposure on day 12 of gestation iv) MRI exposure on day 9 and day 12 of gestation v) ultrasound exposure on day 9 and MRI exposure on day 12 vi) sham exposure on day 9 and MRI exposure on day 12 vii) ultrasound exposure on day 9 and sham exposure on day 12

Frequency	200 MHz
Type	electromagnetic field
Exposure duration	continuous for 8 h on day 9 and/or day 12 of gestation
Additional info	200 MHz RF field + Gradient DC field. Reference article: P.Mansfield, P.G Morris. NMR imaging in biomedicine. New York: Academic Press; 1982: pp. 297-332.

Modulation type	pulsed
Pulse width	5 ms
Additional info	Spin echo sequence with standard characteristics (TR/TE 2000/30 ms) was applied.

Exposure source	SISCO 4.7 T/33 cm bore imaging spectrometer
Setup	animals in cylindrical plastic exposure chambers (14 cm in diameter, 20 cm long) which were placed inside the imaging coil; coil positioned at the center of the superconducting magnet
Sham exposure	A sham exposure was conducted.

Measurand	Value	Type	Method	Mass	Remarks
magnetic flux density	4.7 T	-	-	-	-
SAR	1.5 mW/kg	spatial average	calculated	whole body	-

Modulation type	CW

Exposure source	unfocused ultrasound transductor
Sham exposure	A sham exposure was conducted.

Measurand	Value	Type	Method	Mass	Remarks
power density	5 W/cm²	-	-	-	-

Exposed system:

effects on embryo/fetus: fetal weight; crown-rump length; embryonic death; number of fetuses, of resorptions and of stillborn fetuses
effects on the reproductive system: daily sperm production; testis weight and volume; ovary weight; number of spermatids per testis
postpartum death rate; body weight at day 50; sex ratio; body weight of pups; spleen weight; seminal vesicle weight

Investigated system:

Investigated organ system:

Time of investigation:

Significant differences in biological endpoints following in utero exposure to complex MRI field conditions were revealed.
Fetal weights of the irradiated groups ranged from 11% (day 9 MRI) to 17% (day 9 ultrasound, day 12 MRI) lower than those of the cage control and sham-exposed fetuses. Crown-rump length of exposed animals was reduced by 8%. The postpartum death rate increased significantly and was as high as 38% following MRI exposure on day 9 and day 12 of gestation. Daily sperm production was reduced by 44% in adults exposed to MRI on day 12 of gestation. A reduction in testis weight and volume in the adult males was also found, but the difference was not statistically significant.
No effect was revealed on embryonic deaths, sex ratio, body weight at day 50, spleen weight, or seminal vesicle weight.
The data show that in utero exposure of mice to high field, long duration MRI conditions alone or in combination with ultrasound exposure reduces fetal growth, neonatal survival, and male reproductive development when it occurs during sensitive times of the developmental cycle (day 9 and/or day 12), and that some of these effects are permanent.

Study character: