Colloidal agents are used as these particles enter lymphatic channels and migrate to lymph nodes, where they are retained by macrophages. Commonly used agents vary worldwide due to regulatory approval status 1,2:
- Tc-99m sulfur colloid: United States
- Tc-99m nanocolloid human serum albumin: Europe
- Tc-99m antimony trisulfide colloid: Europe, Canada, Australia
To map drainage from cutaneous lesions such as melanoma, radiotracer is injected intradermally around the lesion. Fine (25- or 27-gauge) needles are inserted nearly tangential to the skin, 5 to 10 mm from the lesion margin 1. Typically, two to four sites are injected. About 0.1-0.2 mL of tracer is deposited at each injection site, with a total activity of 7.4-37 MBq (200-1000 μCi) 1.
To map drainage from the breast, multiple techniques are available, listed here in order of decreasing popularity 2:
- perilesional (intraparenchymal, peritumoral) injection: on the side of the lesion and generally around the lesion, whether superficial or deep; involving 3-4 mL containing 7.4-111 MBq (200-3000 μCi)
- cutaneous injection: intradermal or subcutaneous at the skin superficial to the lesion; involving 0.2-1 mL containing 5.55-74 MBq (150-2000 μCi)
- areolar region injection: injection at the areola rather than at or superficial to the lesion; involving similar volume and activity as the cutaneous injection method
- intralesional injection: palpation- or image-guided injection into the tumour
Images are usually acquired with a planar gamma camera consisting of a large field-of-view detector, parallel-hole collimator, and energy setting appropriate for Tc-99m (140 keV). Dynamic and/or static acquisitions are performed until 45 minutes to an hour after injection, with the use of a cobalt-57 flood source as needed to outline the body 1. Alternatively, in regions of more complex anatomy such as the head and neck, SPECT-CT can be used for cross-sectional delineation.
The patient is taken to surgery, during which the surgeon can use a handheld gamma probe to localise the nodes containing the highest activity.
- 1. Intenzo CM, Truluck CA, Kushen MC, Kim SM, Berger A, Kairys JC. Lymphoscintigraphy in cutaneous melanoma: an updated total body atlas of sentinel node mapping. (2009) Radiographics : a review publication of the Radiological Society of North America, Inc. 29 (4): 1125-35. doi:10.1148/rg.294085745 - Pubmed
- 2. Krynyckyi BR, Kim CK, Goyenechea MR, Chan PT, Zhang ZY, Machac J. Clinical breast lymphoscintigraphy: optimal techniques for performing studies, image atlas, and analysis of images. (2004) Radiographics : a review publication of the Radiological Society of North America, Inc. 24 (1): 121-45; discussion 139-45. doi:10.1148/rg.241025713 - Pubmed