SPECT/CT Image Generation and Criteria for Sentinel Lymph Node Mapping

Abstract

Following a display similar as conventional CT, SPECT/CT has been incorporated in the sentinel lymph node procedure. Multiplanar reconstruction (MPR) enables two-dimensional display of fusion images in relation to CT and SPECT. The use of cross-reference lines, allowing the navigation between axial, coronal and sagittal views, leads to correlation of radioactive sentinel lymph nodes depicted on fused SPECT/CT with lymph nodes seen on CT. This may be helpful for the intraoperative procedure and the post-excision control using portable gamma cameras or probes. Fused SPECT/CT images may also be displayed using maximum intensity projection (MIP) enabling 3D display by addition of various slices improving anatomical sentinel node localization and recognition. When using volume rendering for 3D display, different colours are assigned to anatomical structures such as muscle, bone and skin. This leads to depiction of sentinel lymph nodes in their anatomical environment using specific references to blood vessels and muscles. A comprehensive interpretation of SPECT/CT imaging combined with planar lymphoscintigraphy facilitating the use of criteria to identify radioactive lymph nodes as sentinel lymph nodes and to differentiate them from second-tier lymph nodes is necessary. All these aspects need to be incorporated in the generation of the imaging report, which will be used as a roadmap by the surgeon in the operating room.