First experience with real-time hybrid ultrasound/freehand SPECT system

Objectives Evaluate the clinical applicability and feasibility of a mobile hybrid SPECT/Ultrasound system for fused image analysis in thyroid and sentinel lymph node diagnostics.

Methods Navigated Ultrasound with capability of loading SPECT/CT and PET/CT (GE’s Logiq E9, Milwaukee, USA) was extended to load and display freehand SPECT images (SurgicEye’s declipseSPECT, Munich, Germany) without need of registration. Thus, SPECT imaging and ultrasound examination are performed in the same treatment room within one session. 53 patients (38 Tc-99m-TcO4 thyroid scintigraphy, 13 breast lymphoscintigraphy and 2 melanoma lymphoscintigraphy scintigraphy) underwent freehand SPECT imaging after planar scintigraphy (fig.1, top) followed by fused ultrasound / freehand SPECT imaging (fig.1, bottom) by an expert Nuclear Medicine physician.

Results The fused images show good match with the interpretation of the conventional images. The mean scan time for the SPECT imaging was three minutes, the mean examination time for the ultrasound fusion was 11 minutes. Handling was very easy. The estimated overlay accuracy varies from perfect to 1.5 cm offset. Source of this moderate misregistration in some cases are soft tissue deformation caused by applying ultrasound transducer as well as slight patient movement between freehand SPECT and Navigated Fusion Ultrasound scan.

Conclusions This initial experience provides a successful proof of principle of real-time fusion imaging of ultrasound with freehand SPECT, and has potential to be established as hybrid imaging modality like PET/CT, SPECT/CT and PET/MR. There is a wide range of applications for the facilitation of clinical benefits beyond the reported indications.