71easily extended to procedures performed by single operators. In this circumstance, the single operator would be equivalent to the operator #2 referred to in our manuscript.Finally, you are correct to point out that mechanical injector devices have been used safely for coronary arteriography. Although the use of such a device would allow the operator to increase their distance from the x-ray source and further minimize exposure, there are circumstances where hand injections may be preferable. For reasons I have never completely understood, it has always been a tradition to "hand-inject" the coronary arteries in this country, and the use of mechanical injectors has never really "caught on".