Registration of small-animal SPECT/MRI studies for tracking human mesenchymal stem cells

Single-photon emission computed tomography (SPECT) offers the possibility to study the biodistribution of 111In-labeled human mesenchymal stem cells (hMSCs). This functional information can be complemented by magnetic resonance imaging (MRI) that provides the anatomical context to the SPECT image. However, acquiring such studies with separate SPECT/MRI systems requires a multimodality registration in order to fuse both images. In this work, a special bed was designed based on three non-coplanar glass capillary tubes filled with a mixture of 99mTc and CuSO4, visible in both modalities. Moreover, it was necessary to design a semi-automated rigid registration procedure based on matching these rods by minimizing the distance between corresponding lines. The maximum target registration error achieved was 0.9 mm, in the range of SPECT resolution.