Finding an optimal method for imaging lymphatic vessels of the upper limb

Lymphoscintigraphy involves interstitial injection of radiolabelled particulate materials or radioproteins. Although several variations in the technique have been described, their place in clinical practice remains controversial. Traditional diagnostic criteria are based primarily on lymph node appearances but in situations such as breast cancer, where lymph nodes may have been excised, these criteria are of limited use. In these circumstances, lymphatic vessel morphology takes on greater importance as a clinical endpoint, so a method that gives good definition of lymphatic vessels would be useful. In patients with breast cancer, for example, such a method, used before and after lymph node resection, may assist in predicting the development of breast cancer-related lymphoedema. The aim of this study was to optimise a method for the visualisation of lymphatic vessels. Subcutaneous (sc) and intradermal (id) injection sites were compared, and technetium-99m nanocolloid, a particulate material, was compared with ^99mTc-human immunoglobulin (HIG), which is a soluble macromolecule. Twelve normal volunteers were each studied on two occasions. In three subjects, id ^99mTc-HIG was compared with sc ^99mTc-HIG, in three id ^99mTc-nanocolloid was compared with sc ^99mTc-nanocolloid, in three id ^99mTc-HIG was compared with id ^99mTc-nanocolloid and in three sc ^99mTc-HIG was compared with sc ^99mTc-nanocolloid. Endpoints were quality of lymphatic vessel definition, the time after injection at which vessels were most clearly visualised, the rate constant of depot disappearance (k) and the systemic blood accumulation rate as measured by gamma camera imaging over the liver or cardiac blood pool. Excellent definition of lymphatic vessels was obtained following id injection of either radiopharmaceutical, an injection route that was clearly superior to sc. Differences between radiopharmaceuticals were less clear, although after id injection, ^99mTc-HIG gave images that were marginally but significantly better than those given by ^99mTc-nanocolloid. Image quality correlated inversely with time after injection at which the best image was obtained, consistent with the notion that good vessel definition was dependent on a narrow bolus width. k was approximately three times higher after id injection than after sc injection but it was not significantly different between radiopharmaceuticals for either injection route. Intradermal ^99mTc-HIG gave a cardiac blood pool signal that, over the first 60 min, increased about five times faster than that with sc ^99mTc-HIG, but no clear difference was observed in the rate of increase in hepatic activity between id ^99mTc-nanocolloid and sc ^99mTc-nanocolloid. We conclude that id injection provides rapid access of radiotracers to lymphatic vessels, which is ideal for imaging lymphatic vessel morphology. ^99mTc-HIG is marginally superior to nanocolloid for this purpose and, in drainage basins from which lymph nodes have been excised, is not handicapped by a potentially inferior ability, compared with radiocolloid, to image lymph nodes.