Comparison of measurements of the transverse diameter and perimeter of the fetal thymus obtained by magnetic resonance and ultrasound imaging - De Leon-Luis, J; Ruiz, Y; Gamez, F; Pintado, P; Oyelese, Y; Pereda, A; Ortiz-Quintana, L; Santolaya-Forgas, J (J Magn Reson Imaging., 2011)