The effect of time delay for magnetic resonance contrast-enhanced scan on imaging for small-volume brain metastases

To study the effect of different enhancement timings of magnetic resonance (MR) on small-volume brain metastases (BM) visualisation and provide a basis for the contour of tumour targets. We prospectively enrolled 101 patients with BM who received radiotherapy. All patients underwent computed tomography (CT) and MR simulations. MR contrast-enhanced (CE) scans at 1, 3, 5, 10, 18, and 20 min after injection of contrast medium were performed. The tumour target was determined on MR images at different enhancement times, and the differences of tumour target volume, maximum diameter, and MR signal intensity were compared. (1) Of the 453 metastatic lesions, 24 (5.2%) were not detected at 1 min and 8 (1.8%) were not detected at 3 min; however, all metastases were detected after 5 min. The volume and maximum diameter of the 28 (6.2%) metastases were stable at any time. (2) The average volume of metastatic lesions at 1, 3, 5, 10, 18, and 20 min was 0.09 cm3, 0.10 cm3, 0.12 cm3, 0.12 cm3, 0.13 cm3, and 0.13 cm3, respectively. Compared to 1 min, BM volume at other times increased by 13.1%, 21.5%, 31.6%, 39.6%, and 41.7%, and the difference between the maximum and minimum volumes was statistically significant (p<0.05). (3) The distribution of the maximum ratio of tumours to white matter mean signal intensity at different times were 39.6%, 20%, 14.6%, 8.0%, 10.4%, and 10%, respectively. The visualisation of small-volume BM was significantly different at different enhancement times. Our results suggest that multi-timing enhancement scans for small-volume BM should be implemented and that scanning at >10 min is essential.