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Figure 1 Early and late static images of a 43-year-old man with a melanoma in the right parasternal region. The early images (a, b) show the lymphatic channel running from the primary lesion site to the sentinel node in the right axilla. On the late images (c, d), the radioactivity has largely cleared the lymphatic duct. The sentinel node and remaining radioactivity at the injection site are depicted. The lateral views (b, d) also depict a second-tier node.

contour can be displayed by moving a radioactive point source along the outline of the body during data acquisition (Fig. 2). This will outline anatomic landmarks on the images. A more elegant technique to visualize the body contour involves placement of a cobalt-57 flood source behind the patient during data acquisition [40,43]. A flood source is a large radioactive disk with the size of the gamma camera head. Imaging with the flood source behind the patient is comparable to photography with backlighting: The patient attenuates radioactivity from the flood source and the body contour is outlined. Simultaneous transmission imaging

Figure 2 Anterior lymphoscintigraphy of a 47-year-old man with a melanoma on the back. Indication of the body contour greatly facilitates orientation: (a) image without contour;(b) body contour outlined with radioactive marking pen;(c) contour outlined with flood source backlighting.

with the flood source yields images with both the lymph nodes depicted and the body contour outlined (Fig. 2). Orientation is greatly facilitated in this manner.

The location of a sentinel node can also be indicated on the patient. The nuclear medicine physician can mark the course of the lymphatic duct and the exact location of a sentinel node on the overlying skin. The marking procedure is performed with the patient in the same position as during the operation. With the gamma camera in the real-time view mode and the sentinel node within the field of view, a radioactive marker is moved over the skin. Its hot spot coincides with the hot spot representing the sentinel node when the marker is directly over the node. The location of a sentinel node can also be established with a gamma-ray detection probe. This technique works particularly well in the axilla. A skin mark is applied with an indelible ink in that exact location. The sentinel node location can also be indicated by an intradermal tattoo [41]. The skin mark provides the surgeon with valuable information about where to pick up the lymphatic duct and where to expect the sentinel node. The marking procedure requires careful attention to detail and should be done by a dedicated nuclear medicine physician with special expertise. Each patient should be assessed with regard to his or her individual requirements.

The nuclear medicine report should indicate the type of tracer used, its volume, the amount of radioactivity, and the injection site. Both the dynamic and static study should be described. The report should state the lymphatic field(s) of drainage and the number of sentinel nodes. It should mention whether second-tier nodes were visualized and explain which nodes should be considered as such. The skin marks applied by the nuclear medicine physician should be described. Uncertainty with regard to the true number of sentinel nodes should be admitted. It is of crucial importance for the nuclear medicine physician and the surgeon to review the images together. It is equally important for the surgeon to report the operative findings back to the nuclear medicine physician. It is even better for the nuclear medicine physician to come to the operating room to see for himself.

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