Usefulness of Temporal Subtraction Images for Identification of Interval Changes in Successive Whole-Body Bone Scans: JAFROC Analysis of Radiologists’ Performance1

Rationale and Objectives

We evaluated the usefulness of temporal subtraction images obtained from two successive whole-body bone scans, in terms of improvement in radiologists’ diagnostic accuracy in detecting interval changes and of a reduction in reading time, by use of a jackknife free-response receiver operating characteristic (JAFROC) analysis method.

Materials and Methods

Twenty pairs of successive whole-body bone scans (72 consented interval changes) and their temporal subtraction images were used for an observer performance study. Our institutional review board approved the use of this database and the participation of radiologists in this study. In the first session of the observer study, without temporal subtraction images, the previous and current images were shown to five radiologists independently for their marking of the locations on current images and confidence ratings on potential interval changes from previous images. In the second session, temporal subtraction images were shown together with the modified previous and current images. JAFROC analysis was used for assessing the statistical significance of differences between radiologists’ performance without and with temporal subtraction images.

Results

The average sensitivity for detecting interval changes was improved from 58.6% to 73.2% at a false-positive rate of two per case by use of temporal subtraction images, and the difference was statistically significant by use of JAFROC analysis (P = .035). In addition, the mean reading time per case was reduced considerably from 134 seconds to 91 seconds (P < .01).

Conclusions

Temporal subtraction imaging for successive whole-body bone scans has the potential greatly to assist radiologists by increasing both their accuracy and productivity.

Key Words: Temporal subtraction, whole-body scan, observer study, jacknife free-response receiver operating characteristic (JAFROC) analysis