QUANTITATIVE IMAGING OF I-124 WITH PET

PET is potentially very useful for the accurate in vivo quantitation o f time-varying biological distributions of radiolabeled antibodies ove r several days. The short half-lives of most commonly used positron-em itting nuclides make them unsuitable for this purpose. Iodine-124 is a positron emitter with a half-life of 4.2 days and appropriate chemica l properties. It has not been widely used because of a complex decay s cheme including several high energy gamma rays. However, measurements made under realistic conditions on several different PET scanners have shown that satisfactory imaging and quantitation can be achieved. Met hods: Whole-body and head-optimized scanners with different detectors (discrete BGO, block BGO and BaF2 time-of-flight), different septa and different correction schemes were used. Measurements of resolution, q uantitative linearity and the ability to quantitatively image spheres of different sizes and activities in different background activities w ere made using phantoms. Results: Compared with conventional PET nucli des, resolution and quantitation were only slightly degraded. Sphere d etectability was also only slightly worse if imaging time was increase d to compensate for the lower positron abundance. Conclusion: Quantita tive imaging with I-124 appears to be possible under realistic conditi ons with various PET scanners.