Accuracy evaluation of fusion of CT, MR, and SPECT images using commercially available software packages (SRS PLATO and IFS)

Purpose: A problem for clinicians is to mentally integrate information from multiple diagnostic sources, such as computed tomography (CT), magnetic re sonance (MR), and single photon emission computed tomography (SPECT), whose images give anatomic and metabolic information. Methods and Materials: To combine this different imaging procedure informat ion, and to overlay correspondent slices, we used commercially available so ftware packages (SRS PLATO and IFS). The algorithms utilize a fiducial-base d coordinate system (or frame) with 3 N-shaped markers, which allows coordi nate transformation of a clinical examination data set (9 spots for each tr ansaxial section) to a stereotactic coordinate system. The N-shaped markers were filled with fluids visible in each modality (gadolinium for MR, calci um chloride for CT, and Tc-99m for SPECT), The frame is relocatable, in the different acquisition modalities, by means of a head holder to which a fac e mask is fixed so as to immobilize the patient, Position errors due to the algorithms were obtained by evaluating the stereotactic coordinates of fiv e sources detectable in each modality. Results: SPECT and MR position errors due to the algorithms were evaluated with respect to CT: Delta x was less than or equal to 0.9 mm for MR and les s than or equal to 1.4 mm for SPECT, by was less than or equal to 1 mm and less than or equal to 3 mm for MR and SPECT, respectively. Maximal differen ces in distance between estimated and actual fiducial centers (geometric mi smatch) were in the order of the pixel size (0.8 mm for CT, 1.4 mm for MR, and 1.8 mm for SPECT), In an attempt to distinguish necrosis from residual disease, the image fusion protocol was studied in 35 primary or metastatic brain tumor patients. Conclusions: The image fusion technique has a good degree of accuracy as we ll as the potential to improve the specificity of tissue identification and the precision of the subsequent treatment planning, (C) 1998 Elsevier Scie nce Inc.