Monitoring skeletal changes by radiological techniques

The longitudinal sensitivity of a technique, i.e., its ability to monitor s keletal changes, is affected by two parameters: the long-term precision err or (PEIt) and the subject group-specific response rate (i.e., annual rates of change), Both need to be considered to avoid misinterpretation of measur ed changes. A new concept to aid clinical decision making for longitudinal measurements is proposed which is based on three types of measures: criteri a for detecting changes-the "least significant change" (LSC) is the smalles t change to be considered statistically significant, but for certain clinic al questions a smaller margin, the "trend assessment margin" (TAM), can be sufficient for decision making; follow-up time intervals-for follow-up exam s the patient should be called in at about the time interval specified by t he (population specific) "monitoring time interval" (MTI) or, about one-thi rd of the time earlier, after the "trend assessment interval" (TAI), depend ing on whether the decision can be based on the LSC or the TAM; and the sta ndard precision error (stdPE)-the smaller stdPE, the more sensitive the tec hnique to monitor skeletal changes. Together, these three measures yield a good characterization of a technique's ability to monitor skeletal changes. Compared with previous concepts, the proposed standardization by a respons e ratio instead of measures of spread or response rates makes the stdPE sub stantially less subject group dependent. It allows comparison of stdPE acro ss different studies and could replace the misleading concept of expressing precision as a coefficient of variation. Application of this concept shoul d facilitate the interpretation of measured skeletal changes.