Investigating a multi modality imaging technique
Accurate determination of reason for pain is the primary objective in assessment of lameness. However this can be challenging when evaluating palmar foot pain because of the complex anatomy. Scintigraphic imaging provides information on lesion activity but has poor anatomic detail while MRI give excellent anatomical detail but presence of signal abnormalities in multiple structures may give a poor guide to their relative significance. It would be ideal to be able to determine the exact position of increased radiopharmaceutical uptake based on registration with MR images of the same limb. Our study, in collaboration with Hermes Medical Solutions and De Montfort University in Leicester, aimed to determine the feasibility of 3-dimensional (3D) co-registration of MR and scintigraphic data obtained from a foot model. A multi-compartment phantom of the equine digit was constructed by rapid manufacturing. Images were obtained by MR imaging (using clinical scanning protocol) and by scintigraphy. Different copper sulphate concentrations (CuSO4) (for MRI) or radiopharmaceutical concentrations (for scintigraphy) were introduced into the respective compartments, to mimic the normal limb appearance for each image modality. Lesions at specific locations were simulated by introducing increased concentrations of CuSO4 or radiopharmaceutical into the appropriate compartment. 3D scintigraphic data was obtained by rotating the phantom through 360° (acquisition every 3°). The data was co-registered using state-of-the-art techniques carried out by Hermes Medical Solutions. MR image assessment showed the individual compartments of the phantom, and whether or not there was a simulated lesion. The anatomical resolution of the scintigraphic images was less clear. Accurate localisation of simulated lesions was best with co-registered images. A method for volumetric scintigraphic and MR image co-registration using an equine distal limb phantom has been developed and optimised. In the future, co-registration of volumetric scintigraphic and MR images may prove clinically useful to differentiate between active and inactive injury.