Usefulness of sentinel lymph-node SPECT/CT using multi unsharp masking method (MUSM): A novel technique for improving sentinel lymph-node detection

Objectives Sentinel lymph-node (SLN) scintigraphy is useful method in determining operative procedure. However, it is not always easy to detect SLN located close to primary tumor owing to higher radioactivity of injected tracer. To overcome the limitation, we developed a new technique of SLN SPECT/CT using Multi Unsharp Masking Method (MUSM) for compressing the dynamic range (DRC). The current study was done to validate the effectiveness of MUSM treated SPECT/CT in detecting SLN.

Methods 43 examinations with various cancers (17 head and neck cancer, 16 cutaneous malignant tumors and 10 breast cancer) just before surgical operations were analyzed. Three hours after subcutaneous Tc-99m-phytate (37 MBq) injection, SLN SPECT/CT was done. Just after the scintigraphy, X-ray CT was done for making software image fusion. We made modified SPECT/CT image using MUSM in addition to the conventional SLN SPECT/CT. We compared the number of SLN visualized by conventional methods with those by SPECT/CT treated with MUSM technique.

Results In comparison with conventional method, SPECT/CT with MUSM improved the detectability of SLN (head and neck cancer 26 vs. 24 cutaneous malignant tumors 31 vs. 26 breast cancer 13 vs. 11) by discovering ‘hidden’ SLN located close to the RI injection site.

Conclusions Using SPECT/CT with MUSM, we could detect more numerical SLN in comparison with conventional SLN SPECT/CT. MUSM is feasible for improving the sensitivity of detecting SLN.