Importance of Image Registration for Quantitative SPECT Imaging

Quantitative SPECT imaging is useful for many clinical applications including I-131 radioimmunotherapy. CT image is usually acquired before SPECT acquisition and is used multiple times for attenuation correction, ROI delineation, and side information for filtering or reconstruction. Thus, accurate alignment between SPECT and CT images is crucial for quantitative SPECT. We investigated the effect of misaligned CT image on SPECT quantitation and the usefulness of standard multimodal image registration for correcting misalignment. We observed up to 9% degradation of recovery coefficient (RC) due to 4mm misregistration. Multimodal registration yielded erroneous rigid motion estimation even for small 1-voxel shift, so that RC values became worse after registration. These simple simulation results suggest that developing accurate image registration method between SPECT and CT is important for more accurate quantitative SPECT