Usefulness of medium-Energy Collimator for Sentinel Node Lymphoscintigraphy Imaging in Breast Cancer Patients

金沢大学大学院医学系研究科小野口, 昌久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. Methods: 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. Results: 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. Conclusion: 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

Advantages of upright position imaging with medium-energy collimator for sentinel node lymphoscintigraphy in breast cancer patients

金沢大学大学院医学系研究科先端医療技術学Objective: To evaluate the advantage of upright position imaging with a medium-energy collimator for the detection of sentinel lymph node (SLN). Methods: Thirty-four patients with operable breast cancer underwent sentinel node lymphoscintigraphy with 99mTc-tin colloid. Images were obtained in 5 different positions and paired images from the same patient were compared using side-by-side interpretation. Images were compared in 3 groups: group 1 (anterior view); supine (SAV) vs. upright (UAV), group 2 (oblique view); supine (SOV) vs. upright (UOV), and group 3 (oblique view); modified supine (MOV) vs. UOV. Image quality was evaluated using a 3-grade scale of clear, faint, and equivocal depiction, and correlated to 3 parameters: distance from injection site to lymph node (hot node), counts in hot node, and image contrast. Parameters in group 1 were compared by classifying the primary tumor site into 4 subregions. Results: Image quality in all 3 groups was more enhanced on the image obtained in the upright position than that in the supine position. Obtaining images in an upright position increased the mean distances by 1.5-3.2 cm, and mean contrasts were significantly increased by 0.13-0.31 (p < 0.05). It was shown that image quality was more greatly affected by image contrast than by counts in the hot node. Image contrast of 0.5 seemed an appropriate threshold level for detection of the hot node. On comparison of tumor sites, the upper outer quadrant (C) region of the 4 subregions demonstrated greater contrast enhancement on upright position images. Conclusion: Clinical images obtained in an upright position with a medium-energy collimator were superior to those obtained in a supine position. Use of this procedure is recommended to enhance lymph node detection on sentinel node lymphoscintigraphy