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IMAGE INTERPRETATION · LYMPHOSCINTIGRAPHY

Filtered Tc-99m Sulfur Colloid for Breast Lymphoscintigraphy

Breast lymphoscintigraphy — anterior and oblique views showing injection site and sentinel lymph node in the axilla; labeled '400 UCI TC99M SC FILTERED'
Breast lymphoscintigraphy — anterior and oblique views showing injection site and sentinel lymph node in the axilla; labeled '400 UCI TC99M SC FILTERED'

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Question

The image label reads '400 UCI TC99M SC FILTERED.' Why is FILTERED Tc-99m sulfur colloid used for breast lymphoscintigraphy rather than unfiltered sulfur colloid?

  1. AFiltering removes free pertechnetate that would otherwise migrate too quickly through the lymphatics and produce excessive background activity throughout the chest
  2. BFiltered sulfur colloid has a longer shelf life and remains stable for up to 8 hours after preparation, making it more practical for procedure scheduling
  3. CFiltering increases particle size so the tracer stays at the injection site longer, giving the surgeon more time to locate the sentinel node intraoperatively
  4. DFiltering produces smaller particles (0.1–0.2 micron) that travel more efficiently through the lymphatic channels to reach the sentinel lymph node
Show the answer and explanation

D. Filtering produces smaller particles (0.1–0.2 micron) that travel more efficiently through the lymphatic channels to reach the sentinel lymph node

Unfiltered Tc-99m sulfur colloid has a wide range of particle sizes (up to 1 micron), and larger particles tend to remain at the injection site rather than migrating through lymphatics. Filtering through a 0.1–0.22 micron membrane produces a uniform smaller-particle preparation that moves more readily through the lymphatic system to the sentinel node, improving image quality and sentinel node identification. This is why filtered sulfur colloid is the standard radiopharmaceutical for lymphoscintigraphy in the United States.

More lymphoscintigraphy images

Breast lymphoscintigraphy — anterior and oblique projections of the axilla acquired to map the sentinel lymph nodeBreast Lymphoscintigraphy: Why Oblique Views Melanoma lymphoscintigraphy — anterior immediate image (left) and anterior 45-minute delayed image (right) showing the injection site and sentinel lymph nodesMelanoma Lymphoscintigraphy: The Immediate Image Melanoma lymphoscintigraphy — 45-minute delayed image showing sentinel lymph nodes appearing in more than one draining basin from a truncal melanomaMelanoma Lymphoscintigraphy: Multiple Draining Basins
← Melanoma Lymphoscintigraphy: Multiple Draining BasinsBreast Lymphoscintigraphy: Why Oblique Views →

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