Dynamic and static tomographic renal coincidence imaging with a gamma camera using Rb-82: a feasibility study

Rb-82, a positron emitter with a half-life of /spl sim/75 s, is a promising radionuclide that can potentially turn the concept of sequential dynamic tomographic renal imaging into reality. In this preliminary investigation, we explored several aspects of renal imaging with Rb-82 on a hybrid single photon emission computed tomography (SPECT)-positron emission tomography (PET) system, which relate to the feasibility of such imaging. First, the resolution of Rb-82 was approximated using the Deluxe ECT phantom with solid spheres (0.95 to 3.18 cm in diameter) and compared with Tc-99m. In addition, the impact of spatial resolution was assessed in-vivo in terms of the visualization of wax objects placed in the kidneys. Furthermore, the possibility of performing dynamic and static tomographic Rb-82 renal imaging was explored. A single 3-mCi Rb-82 bolus and limited angle tomography were used for dynamic imaging, while multiple bolus infusions in combination with either single- or multiple-step acquisitions were used for static imaging. Renal acquisitions were done using New Zealand White Rabbits weighing between 4 and 7 kg. Similar visualization of the cold spheres was noted in the phantom, and better visualization of the wax inserts was noted in the in vivo study for Rb-82 compared to Tc-99m. With decay and resolving time loss correction, the limited-angle dynamic tomographic studies showed the kidneys to have the highest uptake of any organ by 20-30 s. The renal uptake continued to increase up to 120-150 s when it became approximately constant. This significant and relatively constant renal uptake of Rb-82 allowed full tomographic imaging of the kidneys to be performed with multiple bolus infusions. In conclusion, we showed that it is possible to do dynamic renal imaging and due to the short half-life, acquisitions can be repeated every 7 min. This gives the clinician a powerful tool to track changes in the kidney over short intervals.