In a 2:1 randomization , subjects either underwent MRIat 1.5-T of the chest , cervical , and head regions to maximize radiofrequency exposure up to 2 W/kg specific absorption rate and gradient field exposure to 200 T/m/s per axis ( MRI group , n = 175 ) , or they underwent a 1-h waiting period without MRI ( control group , n = 88 ) .