This is a single-institution study seeking to evaluate if mobile gamma camera imaging can be used independent of standard fixed gamma camera imaging in patients undergoing sentinel node biopsy for melanoma.

Patients who are scheduled to undergo sentinel node biopsy as part of recommended clinical care will be offered participation in this study.

Patients enrolled in this study will receive standard lymphoscintigraphy in nuclear medicine; however, these images will not be reviewed by the investigator until the preoperative mobile gamma camera(MGC)images have been obtained. Upon completion of the preoperative MGC imaging, the investigator will define the location of SLNs and the plan for the surgical approach. The investigator will then review the FGC images and assess the agreement of these two imaging methodologies. The hand-held gamma probe will be used to further evaluate the patient at this time and a final determination of true hot spots will be made based on the information and the clinical judgment of the operating surgeon. The final surgical plan will be decided. The primary data to be obtained from this cohort will be confirmation of the use of MGC imaging as a screening device to identify all nodal basins containing SLNs.

An additional goal of this study will be to identify techniques that may improve the use of the MGC and opportunities for optimizing the MGC device and imaging system. To the extent possible, improvements to the system will be made incrementally. A goal is to have a more optimized system before the next trial.

In addition to the preoperative imaging data discussed above, the participants will be reevaluated intraoperatively with a MGC and the hand-held probe at the following time points:

1. after removal of each sentinel node
2. after completion of the sentinel node biopsy procedure In each of these assessments, the following will be recorded: the number and location of sentinel nodes, the correspondence with preoperative hot spots determined by the clinical gamma detection devices (fixed camera, MGC and hand-held probe), the time required for imaging, and technical features of use, advantages, and limitations of the MGC imaging system. The individual sentinel nodes will be imaged ex vivo and counted with the hand-held probe.

Inclusion Criteria:

• Patients with a diagnosis of melanoma for whom a sentinel node biopsy is planned as part of standard surgical management of the melanoma. Patients may have more than one primary lesion.
• Patients with other malignancies may be included in this study, but the primary focus of this study is on melanoma, and data analysis of the melanoma patients will be independent of patients for whom sentinel node biopsy is done for other malignancies. It may also include patients for whom the diagnosis of melanoma is not certain but sentinel node biopsy is planned as part of the standard management (e.g.: severely atypical melanocytic neoplasms of uncertain malignant potential).
• All patients must have the ability and willingness to give informed consent.
• Age 18 years or older at the time of study entry. (Younger patients are excluded for simplicity since this avoids the requirement for separate consent documents, this is just a pilot study, and patients under age 18 are uncommon enough that they would not be likely to be enrolled in this small pilot study)

Exclusion Criteria:

• Participants in whom there is a medical contraindication or potential problem in complying with the requirements of the protocol in the opinion of the investigator
• Patients receiving there technetium injection more than 12 hours prior to their scheduled surgery

Patients with melanoma scheduled to undergo sentinel node biopsy as part of recommended clinical care, age 18 years or older.