Lymphoscintigraphy for the visualization of sentinel lymph nodes and body contour

It is important to create clear lymphoscintigraphic images when assessing the sentinel lymph nodes. This clarity needs to reach a level where the sentinel lymph nodes (SLNs) and the body contour are clearly visible. We have developed a simple image processing method using the division of primary and scattered photon counts.

Twenty patients with breast cancer were enrolled in this study. Manual injection of 150 MBq of Tc-99m tin colloid with small particle size into the peritumoral and subdermal regions was performed. Lymphoscintigraphy using a conventional gamma camera was performed three hours after the injection. Dual energy windows were set from 130 to 150 keV for the primary photons and 70 to 110 keV for the scattered photons. An anterior view of the chest and a lateral view from the affected side were obtained. Primary photon image counts were divided by the scattered photon image counts for each pixel after the addition of some constant counts to each pixel of the acquired image to improve the contrast of the scintigrams. We evaluated the ability to accurately visualize the body contour and the SLNs on the processed image.

Image processing time was 20 to 40 seconds for each patient. In every case, the processed image clearly identified the body contour. The processed images allowed the identification of the same number of SLNs as the original images.

This proposed method for image processing is a simple and useful means to clearly visualize both SLNs and body contours.