Hybrid integration of real-time US and freehand SPECT: proof of concept in patients with thyroid diseases.

Purpose: To report an initial experience regarding the feasibility and applicability of quasi-integrated freehand single photon emission computed tomography (SPECT)/ultrasonography (US) fusion imaging in patients with thyroid disease. Materials and Methods: Local ethics committee approval was obtained, and 34 patients were examined after giving written informed consent. After intravenous application of 75 MBq of technetium 99m pertechnetate, freehand three-dimensional SPECT was performed. Data were reconstructed and transferred to a US system. The combination of two independent positioning systems enabled real-time fusion of metabolic and morphologic information during US examination. Quality of automatic coregistration was evaluated visually, and deviation was determined by measuring the distance between the center of tracer distribution and the center of the US correlate. Results: All examinations were technically successful. For 18 of 34 examinations, the automatic coregistration and image fusion exhibited very good agreement, with no deviation. Only minor limitations in fusion offset occurred in 16 patients (mean offset +/- standard deviation, 0.67 cm +/- 0.3; range, 0.2-1.0 cm). SPECT artifacts occurred even in situations of clear thyroid findings (eg, unifocal autonomy). Conclusion: The freehand SPECT/US fusion concept proved feasible and applicable; however, technical improvements are necessary.