^Bigongiari LR, Patel SK, Appelman H, Thornbury JR. Medullary rays. Visualization during excretory urography. The American Journal of Roentgenology, Radium Therapy, and Nuclear Medicine. December 1975, 125 (4): 795–803. PMID 1211509. doi:10.2214/ajr.125.4.795.