Suggested revision of NEMA standards

The purpose of the NEMA Standards is to "eliminate misunderstandings between the manufacturer and the purchaser and to assist the purchaser in selecting the proper product for its particular need" (NEMA Bylaw Art. V, Sec. 1). The sections on count-rate performance, however, have caused considerable misunderstanding of NEMA specifications by salespersons and users, many of whom fail to distinguish between input and observed count rates and between intrinsic and system (extrinsic) performance. The "maximum count rate" is shown to be an unreliable index of camera performance at useful count rates, and is misconstrued by some users to mean the maximum clinically useful count rate. The sections on count-rate performance can be made more meaningful to users by substituting "observed count rate" for "input count rate," by deleting the section on "maximum count rate," and by adding a section on system count-rate performance.