Improved time scale
The time scale of the last versions of IDEA is based on a full day scheme: In this scheme the retention functions refer to the body or organ activity at the end of the respective day, whereas the excretion functions refer to the integral urinary or fecal excretion from the beginning until the end of the respective day.
So, in this scheme the first value of any body or organ retention function refers to the body or organ content at the end of the first day. This may give rise for some problems with the interpretation of short-lived radionuclides, such as Tc-99m. In this case the first value of the whole-body retention function is 5 % of the intake and the second value only 0,2 % (see blue dots in the figure to the left). So, in the last version of IDEA the retention function starts when most of the activity already has decayed. Thus, the main information about the intake is not available for evaluation.
For solving this problem, the new version IDEAplus provides a time scale with a better time resolution. In this new time scale the retention functions starts already at 1 h or 0,042 d, respectively, after intake. The first day is covered now by 10 grid points on a quasi-logarithmic scale. The second day has 8 grid points, the third day 4 grid points, etc. Because of the increased number of grid points the measured values can be allocated much better to the retention function as in the last version.
Thus, the new time scale allows for a more precise definition of the time of intake, this being of importance especially for short-lived radionuclides such as Tc-99m and I-131.