The perfect qMR machine: Measurement variance much less than biological variance

Implementing quantitative MR (qMR) methodology can be a time-consuming task, sometimes seemingly without an end. The concept of the Perfect qMR Machine offers the possibility that the implementation is complete and that no further improvements are needed. This is achieved by making the measurement repeatability variance much less than the biological variance. Thus the proposal is: A Perfect Quantitative MR machine is one that, in making a measurement, contributes no significant extra variation to that which already exists from biological variation. A medal system (platinum, gold, silver and bronze) recognises different sources of biological variance, depending on the type of measurement being carried out (whether a serial study or a group comparison), and different kinds of measurement variance (single machine or multi-centre). A perfect machine can in principle be demonstrated for each quantitative measure (T₁, ADC etc).