Magnetic resonance (MR) undoubtedly constitutes a major technological advance, but as yet we do not know whether this invention also represents a breakthrough from the clinician's point of view.

Guyatt and Drummond suggest that the clinical value of MR is tested by means of a randomized clinical trial (RCT) in a well-defined and limited clinical area, and I fully agree with the authors that the use of such trials should not be confined to the testing of new treatments. In this particular field, however, I miss a discussion of alternative options. With few exceptions, new drugs can only be tested satisfactorily by means of an RCT, but the superiority of one imaging technique over another can sometimes be proved in other ways. Imagine, for instance, that the CT-scan is normal but that MR reveals a space-occupying lesion, the presence of which is confirmed by surgical operation or an autopsy. In that case the diagnostic superiority of MR has been proved in that particular patient. If such cases are seen frequently, and if it is known from controlled therapeutic trials that they are susceptible to treatment, then the value of MR has been proved without doing an RCT.