Improvement of Sentinel Lymph Node Detection after Radiopharmaceutical Injection of 99mTc Phytate Colloid

A sentinel lymph node (SLN) is defined as the lymph node to which it is most likely cancer cells will spread from a primary tumor. Although lymphoscintigraphy is a useful method of detecting malignancy in a sentinel node, conventional lympho-scintigraphy does not determine the exact anatomical location of that node. Breast cancer has the property of spreading to the whole body through the lymph nodes around the breast. If lymph node metastases are negative, a large lymphadenectomy is generally unnecessary. However, in lymphoscintigraphy with a radiopharmaceutical, the image may be less than ideal. We investigated three methods of image improvement for lympho-scintigraphy of breast cancer. Lymphoscintigraphy was performed 12 hours after injection of 37 MBq of 99mTc-phytate colloid into the peritumoral region. The particle size of 99mTc-phytate was 150-200 nm (labeling after 15 min). Images were obtained with dual-energy windows of 140±10 keV for the primary image and 90±20 keV for the scatter image. Image processing employed the Annular Background Subtraction (ABS) method and logarithmic analysis. In brief, first the dosage site was obliterated automatically, and then the background was removed. Next, the logarithm of each pixel value was taken to improve image contrast. Third, a binarization was employed for the pixels in the scatter image, and an outline was extracted. Three kinds of logarithmic processing were used in the three versions of image processing in attempting to improve the detection of the SLN. In addition, it was not necessary to cover the injection position with lead and metastasis of the injection position neighborhood was detected well.