Usefulness of medium-energy collimator for sentinel node lymphoscintigraphy imaging in breast cancer patients

This study was performed to investigate the usefulness of a general-purpose medium-energy (ME) collimator for the accurate localization of the sentinel lymph node (SLN) in breast cancer patients.

We compared phantom images and lymphoscintigraphy images obtained under different conditions for a patient with breast cancer. Comparisons were performed between 2 cameras, between a low-energy high-resolution (LEHR) collimator and a general-purpose ME collimator, and between energy windows centered at 141 keV and at 146 keV. Profile curves and image contrast were evaluated along with the visual interpretation of images. The most suitable imaging time was selected from the relationship between contrast and the data acquisition time.

The images obtained with the general-purpose ME collimator and the energy window centered at 141 keV were of poorer quality than those obtained with the LEHR collimator and the same energy window. However, the quality of the images obtained with the general-purpose ME collimator improved when the energy window was centered at 146 keV. The method involving the general-purpose ME collimator and the energy window centered at 146 keV showed excellent image quality similar to that obtained with the LEHR collimator. The enhancement of contrast was confirmed at more than 3 cm away from the center of the injection site. Stable contrast was obtained with a data acquisition time of 5 min, with the general-purpose ME collimator, and with the energy window centered at 146 keV.

The method involving the general-purpose ME collimator and the energy window centered at 146 keV has the merit of the lymph node not being concealed by a lead shield. This new method is expected to improve the rate of detection of SLN and has the potential for shortening the acquisition time.