Discussion

Tranquille CA, Breingan J, Collins SN, Dyson SJ, Bloomer S, Ellam S, Wimpenny DI, Hall J, Murray RC.

Introduction: 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 magnetic resonance (MR) images give excellent anatomical detail but presence of signal abnormalities in multiple structures may give a poor guide as to their relative clinical significance. It would be ideal to be able to determine the exact position of increased radiopharmaceutical uptake based on 3D registration with MR images of the same limb. Aims: To determine the feasibility of 3D co-registration of MR and scintigraphic data obtained from a foot model. Methods: A multi-compartment phantom of the equine foot was constructed by rapid manufacturing. Images were obtained by MR imaging (clinical scanning protocol) and scintigraphy. Different copper sulphate (MR) or radiopharmaceutical concentrations (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 copper sulphate or radiopharmaceutical into the appropriate compartment. 3D scintigraphic data was obtained by rotating the phantom through 360degrees (acquisition every 3degrees). The data were co-registered using 'state-of-the-art' techniques by Hermes Medical Solutions. Results: The MR image assessment showed good resolution of the respective compartments of the phantom and where simulated lesions were located. The anatomical resolution of the scintigraphic images was less clear. Accurate localisation of simulated lesions was best with co-registered images. Conclusions and practical significance: A method for 3D co-registration of volumetric scintigraphic and MR images using an equine foot phantom has been developed and optimised. In future, 3D co-registration of volumetric scintigraphic and MR images may prove clinically useful to enable differentiation between active and inactive injury. Acknowledgements: Pet Plan Charitable Trust for funding.