The traditional goal of radiology has been to provide images of the hi
ghest technical quality that permit the most accurate diagnoses possib
le. From a more global perspective, diagnostic radiology is part of a
larger system that has as its goal effective and efficient treatment o
f patients. A six-tiered hierarchical model of efficacy that includes
this more global view is presented. This model is intended to improve
understanding of the continuum that efficacy is and to conceptually re
late efficacy to technology assessment and outcome research. Better un
derstanding of efficacy/technology assessment and outcome research fos
tered by the model should encourage radiologists to participate active
ly in federally supported research in these areas. Those radiologists
who do so will come to understand better how radiology can help patien
ts and society as a whole. Use of the model's concepts should also aid
radiologists in becoming more effective consultants to their clinical
colleagues about optimal use of high-technology imaging from the pers
pectives of clinical efficacy, patient outcome, and societal efficacy.