For those patients in which focal lesion(s) can be visualized the clearance curves and half-lives will be determined from the images for both the I-131 and the I-124 studies. A manually drawn region-of interest (ROI) will be placed around each lesion as visualized on the diagnostic whole body scan performed at 48hrs post administration of the radioiodine. This ROI will then be positioned over the comparable area on each of the scans. A background ROI adjacent to the lesion will also be drawn. The total counts in the lesion after background correction will be determined for each time point. In the case of the PET scans first each PET study will be co-registered to the diagnostic scan using the Hermes image registration tool. The coronal slices will then be added to generate a whole body scan that is "equivalent" to that of I-131. Regions of interest will be defined in the same manner as discussed above. A least squares single exponential fit will be applied to each of the lesion clearance curves. The half-life of the exponential will then be computed and the values derived for I-131 compared with I-124 for each identified lesion.