REGISTRATION AND DISPLAY OF BRAIN SPECT AND MRI USING EXTERNAL MARKERS

Accurate anatomical localisation of abnormalities observed in brain pe rfusion single-photon emission computed tomography (SPECT) is difficul t, but can be improved by correlating data from SPECT and other tomogr aphic imaging modalities. For this purpose we have developed software to register, analyse and display Tc-99m-hexamethylpropyleneamine oxime SPECT and 1.0 T MRI of the brain. For registration of SPECT and MRI d ata external skin markers containing Tc-99m (220 kBq) in 50 mu l of co conut butter were used. The software is coded in the C programming lan guage, and the X Window system and the OSF/Motif standards are used fo r graphics and definition of the user interface. The registration algo rithm follows a noniterative least-squares method using singular value decomposition of a 3 x 3 covariance matrix. After registration, the i mage slices of both data sets are shown at identical tomographic level s. The registration error in phantom studies was on average 4 mm. In t he two-dimensional display mode the orthogonal cross-sections of the d ata sets are displayed side by side. In the three-dimensional mode MRI data are displayed as a surface-shaded 3D reconstruction and SPECT da ta as cut planes. The usefulness of this method is demonstrated in pat ients with cerebral infarcts, brain tumour, herpes simplex encephaliti s and epilepsy.