PurposeWith conventional planar imaging, preoperative anatomic localization of a sentinel lymph node is possible in only two dimensions. To improve spatial localization of sentinel lymph nodes, a dual-head camera equipped with a transmission source was used to create combined transmission–emission SPECT images in a patient with a malignant melanoma of the left forearm.MethodsLymph node scintigraphy was performed after injection of Tc-99m-labeled nanocolloid around the tumor site 1 day before operation. SPECT was performed using a gamma camera equipped with a transmission collimator system originally designed to correct attenuation. Transmission and emission images were created simultaneously, matched, and displayed in three dimensions.ResultsIn the combined emission–transmission images, the sentinel lymph node was clearly located in the left axilla. The lymph nodes could be identified during operation at the same location as that detected by SPECT. Based on preoperative information, the sentinel lymph node was identified rapidly and the extent and duration of the operation were minimized.ConclusionsThis method provides better anatomic information, especially in deep structures such as the axilla or pelvis. With accurate three-dimensional preoperative information, intraoperative access is quicker and less invasive for the patient.