Distribution of Radiation in Synovectomy of the Knee with 166Ho-FHMA Using Image Fusion

Abstract

Radiation synovectomy is an effective technique for the treatment of chronic synovitis in patients with rheumatoid arthritis (RA), and is an alternative for surgical synovectomy. Holmium ferric hydroxide macroaggregates (166Ho-FHMA) is suitable for radiation synovectomy, especially because it emits high-energy beta particles and a smaller proportion of low-energy photons that are suitable for gamma-camera imaging. The aim of this study was to develop a method to fuse 166Ho-FHMA single photon emission computed tomography (SPECT) and magnetic resonance (MRI) images, to show the distribution of 166Ho-FHMA inside the joint with images that localize synovitis. The knees of 6 patients with RA were treated with 166Ho-FHMA. (99m)Tc-human immunoglobulin ((99m)Tc-HIG) SPECT images and MRI images were taken before 166Ho-FHMA injections. 166Ho-FHMA SPECT images were taken 4, 28, and 40 hours after injections. SPECT and MRI images were merged using a specific image fusion method, called mutual information algorithm, to study associations between anatomical and metabolic information from these images. Fusion of SPECT and MRI images indicated that intensity of radioactivity was associated with the amount of synovitis. Activity distribution of 166Ho-FHMA could be registered using anatometabolic images. A new method to fuse the distribution of radiation in the synovectomy of the knee was developed using SPECT/MRI image registration. Image registration of SPECT and MRI can be used to determine the activity distribution of radioisotopes in relation to synovitis.