Precise fusion of MRI and dual energy ¹¹¹InWBC/^99m Tc HDP SPECT/CT in the diabetic foot using companion CT: An example of SPECT/MRI imaging

Aim: The purpose of our study was to correctly fuse MRI and SPECT ¹¹¹In WBC and ^99m Tc HDP images using companion CT images. The fused images could be used to assess proper surgical approach in treatment of the diabetic foot. Methods: Nine patients who had dual energy ¹¹¹ In WBC/^99m Tc HDP SPECT/CT and MRI studies within a week were investigated in an ongoing project. A GE Infinia SPECT/CT camera and Siemens MAGNETOM 1.5T MR system were used in this study. First, the MRI and corresponding CT images were coregistrated using a transformation based on normalized mutual information. The transformation was saved and used for MRI and ¹¹¹In WBC/^99m Tc HDP SPECT fusion. A Jaszczak phantom study was also performed in order to estimate accuracy of MRI/SPECT fusion. Results: The Jaszczak phantom study with 3.7 MBq ¹¹¹In hot sphere showed that MRI/SPECT alignment using the approach described above produced registration with 0.7±0.4 mm accuracy in all three dimensions (3D). The nine clinical cases were visually evaluated and showed 1-2 mm 3D fusion accuracy. MRI provides almost perfect anatomy of soft tissue and bony structures but it may exaggerate the extent of infection, ¹¹¹In WBC/^99m Tc HDP SPECT imaging is more accurate for infection detection but lacks anatomical reference. Combination of these images proved an essential adjunct to diagnosis. A clinical utility of the approach is illustrated in two clinical examples. Conclusion: The CT in dual energy ¹¹¹In WBC/^99m Tc HDP SPECT/CT studies can be used to accurately fuse and compare ¹¹¹In WBC/^99m Tc HDP SPECT and MRI images of the diabetic foot. This can significantly help in conservative treatment planning and limb salvage procedures in treatment of diabetic foot infections.