Thin-layer MR enhancement scans of patients with brain metastases should be routinely used in approximately 40% of patients in whom an increased number of metastases is detected on gamma knife-localized thin-layer image scans, according to a study in the Journal of Clinical Neurosurgery. METHODS: The number of metastases was determined by 2 physicians on each of the two scanned images before and during treatment, and the two MR images analyzed for the study were separated by up to 4 weeks. Routine enhanced MR scans were layer thickness of 6 mm spaced at 2 mm intervals, and gamma knife localized enhanced MR scans were taken on rigid fixed frames with 3.0 mm thin layers without intervals. RESULTS: An increase in the number of metastases at gamma knife localization was detected in 41.2% of 1336 patients compared to 58.8% with the same number, and an increase from single to multiple metastases was detected in 13.8%. In colorectal and esophageal cancer cases, the percentage of single metastases was 66.2%, which was higher than that of patients with other malignant tumors.