http://pec.lib.wvu.edu/record/P165471972The Effect of film quality and other factors on the roentgenographic categorization of coal workers' pneumoconiosis.Journal article reprint from: <em>The American Journal of Reontgenology, Radium Therapy and Nuclear Medicine</em>, v.115:no.3 (1972:July). Kibelstis, John A.Reger, Robert B.Morgan, William Keith C.Smith, C. A.Coal miners--Diseases.Pneumoconiosis--Diagnosis.Lungs--Dust diseases--Diagnosis.14256