A generalized 4D image registration scheme for targeted radionuclide therapy dosimetry

An iterative, generalized four-dimensional (4D) method is presented in this paper that allows simultaneous registration of a series of single-photon emission computed tomography (SPECT) scans acquired in the course of a radionuclide therapy or pretherapy tracer study. The method combines temporal information with voxel-based similarity criteria to carry out simultaneous registration of the SPECT scans. A polynomial function was fitted to the maximum counts of each tumor site over the 4D study. Each tumor site was normalized to its maximum on the reference scan, and a template 4D dataset was generated, employing the polynomial fitting and the normalization map. Then, each 3D scan was registered to the corresponding simulated scan, using a 3D similarity criterion. The correlation coefficient (CC), the mutual information (MI), and the sum-of-absolute differences (SAD) similarity criteria were employed. Simulated data, based on a head-neck (131)I-MIBG study, were used to compare the proposed method for 4D registration with sequential 3D registration. Sequential 3D registration resulted in residual registration errors of 3.5 +/- 2.5, 3.2 +/- 2.0, and 7.0 +/- 3.5 mm for the CC, MI, and SAD criteria respectively, whereas the corresponding 4D method gave errors of 2.4 +/- 1.6, 1.9 +/- 1.1, and 5.3 +/- 2.9 mm for the CC, MI, and SAD criteria, respectively. The 4D method was applied to (186)Re HEDP SPECT patient studies and registration was verified by a dual-cursor display tool.